STRAND'S SCIEftl ,' -E SERIES ^ . / r A- (^ jV V ^ , " x ' c. M :.'-.';, ! -IT rii'/. the ^Journal of the Society of A*. ." NE\V Yv/RK: I XObTiiAND, PT BLISHEK, I 'i ; 37 S'/AxiitEN STREETS. 1 8 v 7 . THE VAN NOSTRAND SCIEN 1 18mo, Grceen Boards. Price 50 Cents Each. lustrated when, the Subject Demands. r 'LACES A^ mg, C. E. X ^g2 / 'c*i/j t*~t+fjs ~ f nj . Chimneys, C * 3 erah '\ -n- <^ i ING- v />" > H S" BR.DG Q^ X W. F. Buth O>K ^^ ireenleaf. ^H p T | S AUCTION d (V kH " ^ ir Jacob, A *~j T ^ RMS OF R ^^ -*~" ^.S s^ }, C. E. QX <^ X ^ ^ SNGINE. 1 O ^ C^ r ith Additio; V-H ss r "\^ j., to which [ T ^ (^\V v i CIAL FUE1 o O >\ ^Sj ,y John We W . J ^ I ated from tl of America co JIT *csi w fc 3 lition. Allan. W 55 J ^ By Prof. V o; cc 1 ^ ES. By J. W ; To which rSTS. By E< ^ N . J. Atkinsc H7 | le, C. E. X^ *G CERTAI ID ^ Prof. Geo. 1 I V , >s ! r Prof. W. 1 v /C* 3\ / 5AT1ON. I Prof. W. H. Corfield. No. 19. STRENGTH OF BEAMS UNDER TRANSVERS LOADS. By Prof. W. Allan. No. 20. BRIDGE AND TUNNEL CENTRES. McMasters, C. E. No. 21. SAFETY VALVES. By Richard H. ] THE TREATMENT SEWAGE. Dr. C. MEYMOTT TIDY. \Abridged from the "Journal of the Society of Arts: NEW YORK: I). VAN NOSTRAND, PUBLISHER, 23 MURRAY AND 27 WARREN STREETS. 1887. THE TREATMENT OF SEWAGE. LIQUID EXCRETA. Every adult male person voids on an average 60 ozs. (= three pints) of urine daily. The 60 ozs. contains an average of 2.53 ozs. of dry solid matter, consist- ing of Urea 512 . 4 grains. Extractives (pigment, mucus, uric acid) 169.5 " Salts (chiefly chlorides of sodium and potassium) , 425 .0 " 1106.9 =2.53 ozs. The urine, therefore, of a population of 10,000 adults may be taken as 600,000 fluid ozs., or 3,750 gallons per day. Urine rapidly decomposes, the urea be- coming the volatile body carbonate of ammonia, and the urine thereby losing a valuable manurial constituent. After a time, but at a later stage, certain foul smelling gaseous products of decomposi- tion are evolved. To collect and preserve urine, therefore, presents practical diffi- culties. The ammonia from stale urine was formerly distilled and converted into a sulphate, at Courbeville, near Paris. SOLID EXCRETA. Every adult male person voids about 1,750 grains (or 4 ozs.) of faeces daily, of which 75 per cent, is moisture. The dry faecal matter passed daily is therefore about 1 oz. per adult head of the popu- lation. Of this dry faecal matter, about 88 per cent, is organic matter (of which 6 parts are nitrogen) and 12 per cent, in- organic, of which 4 parts are phosphoric acid. Of this dry faecal matter 11 per cent, is soluble in water. Taking a population of 10,000 adults, it follows that the moist faecal matter passed daily is equal to 2,500 Ibs. (=1 ton, 2 cwt., 8 Ibs.) or 1.116 ton, whilst the dry faecal matter is equal to 625 Ibs. (5 cwtl, 2 qrs., 9 Ibs.). The facts, therefore, respecting the ex- creta of a population of 10,000 adults may be thus tabulated : TABLE I. F^CAL MATTER PASSED PER 10,000 OF ADULT POPULATION PER DIEM. Pounds. Moist faecal matter excreted 2,500 Dry " " " (calculating 75 per cent, as moisture) 625 Soluble in water=68.55 Ibs | _ Insoluble in water=556.45 Ibs. . . . j" = TABLE II. URINE AND FAECES PASSED PER DAY BY 10,000 ADULTS. Total Solids Solids Solids Water. insol- solids. dry. soluble. uble. Moist Ibs. Gallons. Ibs. Ibs. Ibs. Faeces 2500 187.5 625.0 68.55 556.45 Urine. 3750.0 1581.21 1581.21 3937.5 2206.21 1649.76 556.45 The following table has been adapted from Letheby. The quantities given are somewhat below the normal. The facts o> P3,SS i co oo o: o as z> co JO 00 T* C* 0* TH I!5-a ^TJ ^G* 8 gts 3 i spipss Id 1O O CO O i I> I>- T-I 1C Ci CC Ci ^ic - ^ H g,So|o q CO CD C<1 OJ CO CO !> 1> CO CD O !> TH rfH H S"Ua f*l> 1 ||J|S8SS gSgS-~ t.O CO iO OO CO CO CO O5 CO Tt* sls~ J's'sl r^ fe s ||SSS^ gas r-H-S^O P rl Oi O5 (M t> CO t>. CO .g,aCco- -S'Crt -* S"S.2 SSI 02 OJ B |S|ggSS |8saa* SFoS&fe eg O* CO 1O TH O CD TH IflCOCOOOO'* 8,52,0 so" l> M 1 Sp'^8^^ THgglC^^TH 0) ~ . OC 1C J.-- CO i>- C^ COrH t>O50O NTfTHl>TtTfOO lglgll 2 SB' 2S 5 *- w | ^ 06 c CD OJ ^ O? 0- CD^ CO TH ^ & O5 d d d d d d cooooooo Constituents. UBINE. e tuents lie matter ning nitrogen al matter ning phosphoric acid, potash FAECES. es Ltuents vie matter ning nitrogen al matter ning phosphoric acid, potash iff lull? were collected from a Dumber of sources, the ratio of children to adults being that adopted by Boderer and Eichhorn. My own experiments would lead me to give one pint as an average quantity of urine passed by children daily up to the age of ten years, the quantity gradually increasing up to three pints in the adult. The solid constituents of the urine which, at the age of ten, are on an average 0.8 oz. daily, increase, according to my ob- servation, up to 2.5 ozs. in the adult. The quantity passed by girls and women is rather less than that passed by boys and men. The faeces passed by girls and women are considerably less than that passed by boys and men. The calculations in the table state the amount as less than one- third. My own observations, however, scarcely support these numbers. It would, I think, be more accurate to regard the faecal matters passed by female children and adults as about one half that passed by male children and adults. 8 VALUE OF NIGHT SOIL (HUMAN EXCRETA). Urine, in its natural condition, has a theoretical value of between 15s. and 16s. per ton. The dry solid matters of the urine have a theoretical value of about 18 16s. per ton. The quantity of ammonia per year voided by the average individual in the urine has been stated as from 10 Ibs. to 11.32 Ibs., having a value on the lower quantity of 6s. 8d., and on the higher of 7s. 3d. Faecal matter, in its moist and natural condition, has a theoretical value of 1 7s. 6d per ton. The dry solid matters of faeces have a theoretical value of 5 17s. 7d. per ton. The quantity of ammonia voided per year in the faeces, by an average individual, is estimated at 1.64 Ibs., having a value of about Is. 3d. The estimates given above are based on the agricultural values of the nitrogen calculated as ammonia, together with the phosphoric acid and potassium salts, these being materials of sparing occurrence in 9 land, but entering largely into the com- position of every variety of agricultural produce. Lime, magnesia, and iron, equally essential to plant development, occur largely in most soils. The details are stated in the second table. Respecting the value of the nitrogen, however, of sewage, Voelcker regards it as at least of 10 per cent, less value than the nitrogen of ammoniacal salts ready formed. Authorities differ between 6s. 6d. and 1 in estimating the annual value of the excreta of one adult. Thudichum gives it at 1; Hofmann and Witt at 11s. 9|d.; Voelcker at 9s. ; Lawes and Way at 8s. 5|d. ; Anderson, of Glasgow, at 8s. In the table we have estimated the mixed excreta of the population as worth 15s. 8d. per ton in their natural condition, and the solid matter of such mixed ex- creta as worth 14 16s. 4d. per ton. In this table, moreover, no corrections are made in stating the value of the solid constituents, either for the loss of am- monia that would occur during evapora- 10 -, ^OCO GO rH *> -HH (M rHCOTH rH CD 3 g S . j^j . i?*. ^ Z>CO CO ^* CO rH O s t> CD 00 rH rH rH rH rH rH rH H a 03O i S o c II 11 CO rH s^s iO COrH r$ ,=! c rH O3 p o ti i o |^2 . ^ O j o 1 i> gi> os 1 "* GO CS O O rH CO PH ^ W 03 O5 GO O3 CO ^03 CO COg S f" a cS "3 o b TH to co T*< > 1-1 O rH*>COrH OO GO g i I u H 2 CO 1O CO 11 O^CO 03 CO JO -^ i> iO rH rH rH ^THGO 1 1 ^ ::: $> a] d d d ' 1 @ _>. . o o.2 d | Q 2s "-3 ^* "cS ^ o C3 n> M QQ ft ^ ft< g 4 02 ft ,n ^ h-1 | 2 ^ ^ ^ ^rrj 53 fl g fj 1 Q ^ O X! 1 |J So 03 _, rj t^J C3 o3 S A bC i a 1 ( 3 N ! ; ^ !'! 111! sS"^ ill co I .0 ti cu A ^ 52 Solids, rine. rogen. Water closet town .sew-) age (50 samples from 17 > 50. 54 . 7.46 . 5.41 towns) ) Matters in Suspension. Total. Organic. Water closet town sew-) age (50 samples from- 31.29 .. 14.36 17 towns ) On this,, one question suggests itself how is it that the suspended matter in the sewage of midden towns is almost identical with that from water closet towns, seeing that Dr. Frankland states that an average of 25,561 tons of solid matter per annum is annually kept out of the sewers at the several midden towns mentioned. 16 The pail system may consist either in the use of a little disinfectant or of some absorbent material. Adopting Mr. Gilbert R. Redgrave's classification of the pan, pail and midden systems of disposing of sewage, we shall discuss the subject under the following three heads : I. Pails without absorb- ents. II. Pails with absorbents. III. Pails used for the joint collection of ashes and excreta. I. PAILS WITHOUT ABSOKBENTS. Of these the Rochdale system may be regarded as principal. In support of the non-use of any absorbent, it is urged that to keep out " the profligate as- sociate" is a main object; concentration, not increase of bulk, being the point to be aimed at. The execreta and dry house refuse should be collected at intervals in separate tubs of special construction, the excreta tub being fitted with an air-tight lid, so that transport may be effected without causing a nuisance. The cost 17 per pail per annum is about 5s. 8d. The ashes are carefully screened and sorted. From the experience of many towns (Rochdale, Salford, etc.) it would appear that two men and one horse (say at a working cost of 3 per week) can remove 600 tubs or pails per week, each pail con- taining an average of 84 Ibs. of excre- mental matter. This equals 22-J- tons per week at a working cost of 2s. 9d. per ton. At Rochdale 10,112 pails were in use in 1882, the weight of excreta collected be- ing 8,518 tons and of refuse ashes 18,396 tons, from 15,289 houses and 237 rnilJs and workshops, with an estimated popu- lation of 65,500. In 1881, 552 tons of manure was manufactured. It is calcu- lated that each tub is used by 9.2 per- sons living in 2.2 houses, the yield being 2.07 cwts. of excreta per head per annum. At Halifax it was calculated that each tub is used by 10.9 persons living in 2.6 houses, the yield being 3.26 cwt. of ex- creta per head per annum. At Birming- ham the returns give from 9.6 to 11.5 Ibs. per week per head. 18 II. PAILS WITH ABSORBENTS. In many places the use of boxes, pails, or tubs, charged with various absorbent materials (ashes, etc.) has been adopted. Numerous substances have been suggest- ed as absorbents. Of these Liebig re- commended coarsely powdered bog turf, and Stanford charred seaweed Stanford claims that seaweed is three times, weight for weight, as effective as dry earth (1 cwt. being sufficient for one month for a closet daily used by six persons). He claims, moreover, that it is easily reburnt, and that the ammonia and fixed salts have been recovered, the charcoal remains as effective as before. Various forms of refuse too have been suggested as ab- sorbents, of which may be noted, refuse wool or shoddy, dry horse dung, spent dye stuffs, etc. At certain towns spent dye wood (such as fustic), in the manner suggested by Goux, viz., ramming into a tub by a central core, so as to give a uni- form lining to the tub, has been employed. Thus splashing is prevented. This method necessitates the frequent removal of the 19 excreta (otherwise the absorbent lining would break down and a semi-liquid mass result), and it is also necessary that the re- ceptacle should be tightly secured before removal, to prevent escape of offensive effluvia during transit. III. PAILS USED FOR THE JOINT COLLEC- TION OF ASHES AND EXCRETA. Of this method the system adopted at Nottingham is a case in point. Here the tub takes the place of the midden pit. It is to be noted that the ashes are of less quantity in summertime, when the chance of nuisance is greatest. With respect to the mechanical appli- ances suggested for sifting the ashes, so as to apply only the smaller breeze to the excreta, practice proves them somewhat unsuccessful. The compost is removed every two or three months and conveyed to the manure wharf, where it is emptied into barges and sold at a price that covers two-thirds of the cost of scavenging. 20 At Birmingham, where galvanized pails are used to the extent of some 40,000 (representing a population of 250,000), the contents are collected weekly. These are emplied into a vat at the place of de- posit, and some sulphuric acid added to fix the ammonia. The contents are passed into a drying machine, consist- ing of a steam jacketed cylinder with- in which are revolving arms, the neces- sary heat being obtained by burning the cylinders and garbage collected in the town. The clinkers are utilized for vari- ous purposes. The process adopted at Manchester, devised by Mr. Leigh and carried out by Mr. Whiley, was described in detail by Mr. Alliott, of Nottingham, at the Society of Arts Conference, 1877. The objects are (1) the disinfection of the pail con- tents by the use of charcoal, produced by charring street sweepings . and (2) the reduction in bulk of the matters so col- lected. For the purpose of reducing bulk the liquid in the pails is drained off, and concentrated by a low heat to the con- 21 sistency of treacle (about one-tenth the original bulk.) I do not propose discussing the pneu- matic system of collecting excreta. In certain places on the Continent (Paris, Milan, &c.), the sewage is collected in water-tight cesspools. These are emptied by atmospheric pressure, the contents being forced into movable exhausted iron tanks, through flexible tubes lowered into the cesspool for the purpose. By this means the escape of noxious effluvia is supposed to be prevented. The cost of removing the excreta at Paris is about 5 per house per annum. The material is converted at Yillette in- to poudrette, great nuisance resulting. The arrangements of Liernur (which have been adopted in Amsterdam, and to a cer- tain extent in Prague), are, in many re- spects, similar. Liernur suggests cess- pool tanks being placed in the middle of a street, each tank communicating with from fifteen to twenty houses. The systems of Berlier, partly in use in Paris since 1881, and of Shone, a 22 method of pumping sewage by small pneumatic pumping engines, the power being generated at a central station, need only be mentioned. As general rules we consider : 1. That the removal of the pails should be under the control of the local authority. 2. That on an average they should be renewed once a week, a clean, well- washed pail being substituted for the full one. 3. That air- tight covers should be fit- ted to the pails before removal, and that they should be conveyed in air-tight vans to the depot. The utilization of the excreta collected in pails is a matter of great difficulty. At best a low class of manure results, unless some form of concentration be adopted. Voelcker states that having examined every form of night-soil manure, he never found one having a theoretical value greater than 1 per ton, unless the manure had been specially fortified with guano, or superphosphate, or sulphate of 23 ammonia, etc. The better varieties he valued at from 15s. to 17s. 6d. per ton, whilst those less carefully prepared were not worth more than from 7s. 6d. to 12s. 6d. THE EARTH CLOSET. The disinfecting power of earth has been known from remote antiquity. In China, the formation of a manure by mix- ing earth with the excreta is of ancient date. In this country Kosser in 1837 pro- posed the admixture of urine and faecal matter with earth, lime, etc. The sug- gestion took no practical shape until 1858, when the Kev. Henry Moule, the vicar of Fordington, investigated the dis- infecting and deodorizing power of earth on privy soil. As the result he invented his earth closet. At his own vicarage, where the cesspool proved to be danger- ously near the well, he abolished the cess- pool, and placed buckets beneath the pans. Their contents were, in the first instance, mixed with dry sifted earth, earth after- 24 wards being placed in the bucket itself, and the compost left to consolidate in a shed. After five or six weeks he found that the material had entirely lost its offensive odor, and was sufficiently dry to be used again. Thus eventually he not only dis- infected his sewage, but produced a ma- nure containing one- third its weight of dry excrement. The next point was the mere mechanical construction of a closet, worked by a handle, with contrivances to secure the application of a proper pro- portion of dry earth. The earth may, however, be thrown into the closet in one application daily, a method adopted in the latrines at Lancaster, which are under the control of the local authority. As regards the earth best adapted for the purpose, a well-dried clayey earth, that is, a heavy soil loaded with clay, holds the first place ; peaty earth comes next, although for efficiency a long way behind a clayey earth. The peaty earth used at the Wimbledon Camp in 1867 was not satisfactory, as it produced a wet and sour compost. Sand and clay are found 25 to have very little deodorizing power, and are therefore ill suited for the earth closet. The clay soil must be well dried artificially (for in a damp condition its absorbent power is inferior), and after drying, powdered and sifted. About 4 Ibs. of dry earth per head per day (i.e., 1^ Ibs. for each visit, three visits being allowed for each person) is required to obtain a consolidated and un- offensive compost. This quantity was ultimately used at the Dorset County Jail, the 3 Ibs. per head of earth, used in the first instance, being found insuf- ficient. A village of 1,000 persons would need, therefore, about 2 tons of dry earth per day. The dry earth system was used at the Dorset County School, at the vil- lages of Halton and Aston Clinton near Windover, in Lancaster, and at the Wim- bledon Camp. In this latter case Dr. Buchanan closely investigated the work- ing of the process. After the removal of the earth it may be dried and returned to the closet until its manurial value justifies its sale. 26 As regards composition and value of the product, much will depend on the demand, and on the method adopted in working (i.e., how many times the mate- rial had been used). At Lancaster the compost fetched 7s. 6d. to 10s. per cubic yard. At Dorset County Jail it reached 1 per ton, and at the Dorset County School 2 to 3 per ton. Perhaps 10s. per head of the population annually might be taken as an approximate value. The dry earth system has certain defi- nite advantages over the water closet. The first cost is less. It reduces the quantity of water required by each house- hold. The closet is less liable to go wrong, to suffer injury from frost, or to be damaged by improper substances be- ing thrown into it. No doubt an intelli- gent person can manage it, but if it be used in villages it should be managed by the local authority, easy access to the closets by the scavengers being in such case indispensable. Of course a dry earth system does not supersede the necessity 27 for some independent means of removing slops, rain, and subsoil water. A still further advantage claimed for the earth closet is the manurial value of the compost, and the ease with which it may be stored until required. No doubt the earth closet has its ob- jections. Of these a certain filthiness (real or imaginary), and the difficulties of supplying the necessary quantity of dry earth and of removing the compost, are those chiefly urged. No doubt the col- lection of material that may be more or less foul as the closet has or has not been attended to by the scavengers, and the after distribution of the compost, com- pare, at first thought, unfavorably with the cleanliness of water, and the ease with which it serves to convey the filth from the closet to the field. But this as- sumes (1st) no misadventure of the water- carried sewage between closet and field ; (2d) a farm and a crop ready at all times and seasons wet or dry, summer or winter to receive and to appropriate it; and (3d) no escape of noxious effluvia 28 and miasms, no spread of disease, and no pollution of water courses. How far such assumptions are realized, I shall consider presently. Earth closets have been largely used, and their use is rapidly extending, in In- dia, where the drying of the earth is a comparatively easy process. The author- ities in India, in 1867, reported to the Secretary of State that Moule's system, which was then generally employed in the barracks, jails, hospitals, and public institutions of the three presidencies, had been found to be a great public benefit. I can, myself, bear testimony to the ex- cellent results of the dry earth system where the closets are properly attended to proper earth used and the materials properly dried. SEWAGE. We now turn to water-carried sewage its composition, value and treatment. By the phrase " the sewage of a town" is implied : (1.) The excreta (solid and liquid) of the population. 29 (2.) The refuse from kitchens, Sun- dries, etc. (3.) The drainings from stables, slaugh- ter-houses, etc. (4.) The liquid impurities resulting from various trade operations (brewer- ies, dyehouses, fellmongeries, etc.) (5.) The washings of public thorough- fares, etc. (6.) Domestic and subsoil water. To speak broadly, we may define sew- age as u the refuse of communities their habitations, streets and factories." It is manifest, therefore, that it is not possible to define broadly what consti- tutes " average sewage." The quantity and quality of the sewage of a town will be influenced by the following amongst other conditions: (1.) The number and nature of the manufactures and trade operations pecu- liar to the place, and which are drained into the sewers. (2.) The existence of an excessive number of stables (such as result from the presence of barracks). 30 (3.) The volume of water supplied to the inhabitants. (4.) The proportion of rain or surface water admitted into the sewers. (5.) The quantity of subsoil water that leaks into the sewers. (6.) The density and general habits of the people. (7.) The season of the year. (8.) The time of day. Sewage may be subdivided into 1. Domestic sewage. 2. Manufacturing refuse. 3. Bain and storm water. We shall find, when we come to discuss the treatment of sewage, the first great difficulty is the large quantity to be dealt with. It has been suggested to meet this difficulty of quantity by adopting a duplicate set of sewers, the one for sew- age proper (domestic and manufacturing), and the other for storm and rain water, or at any rate for the larger part of the rain water. For irrigation purposes, no 31 doubt, it is desirable to have the domes- tic sewage as little diluted as possible^ but for chemical treatment dilution within certain limits is not an evil. A separate system must be more expensive, besides which it robs the sewers of one means of natural and effective flushing, such as occurs after heavy rains. It also excludes from the sewage to be treated many ma- terials (e.g., road washings), that certainly need treatment as much as, if not more than, any sewage proper. To limit the water for removal of filth to its smallest quantity is a sound principle, but there is a danger in over-reduction. The most earnest advocates of the separate system scarcely see their way to exclude from the public sewers the rain falling on pri- vate property, as this would for the most part necessitate two sets of house drains. It may be admitted that both the separ- ate and combined systems have their merits and defects, and that certain local conditions may determine the choice of the system. 32 The arguments used in favor of a sep- arate system are : (1.) Greater uniformity in the quantity of sewage conveyed. (2.) The prevention of deposits, the di- mensions of the pipes being capable of more accurate adjustment, permitting them to be daily filled to their maximum at the hour of maximum flow. (3.) If the sewage has to be pumped, expense will be saved by the limitation of quantity. (4.) Prevention of floodings from the capacity of the sewers being overtaxed, or from obstruction taking place in the surface channels during times of heavy rain, or on the occurrence of a rapid thaw after a long period of snow. Dan- ger arising from the gases in the sewers being forced by the rush of water thus filling the sewer, being driven through the nearest outlet, and possibly through house connections, will be avoided. (5.) Prevention of precipitation, and so of deposit in the sewers, from earthy matter (such as building lime) being car- 33 ried in at storm time, together with road detritus, leaves, etc., and which, under ordinary conditions, might not be removed until the next heavy rain. (6.) If obstruction occurs, a compara- tively small volume of water will be suf- ficient to flush the sewers effectively on account of the relative smallness of pipe. (7.) That with small pipes, good venti- lation of the sewers may be more easily effected. (8.) That the nuisance arising from or- ganic matters being carried into the pipes at the time of storm, and putrefying on the upper portions of the sewer pipe, where, under normal conditions of flow, it forms a slimy coating and develops swarms of organisms, will be prevented, the sewers being filled daily to their max- imum working capacity. (9.) That the quantity of sewage to be dealt with would be greatly decreased. On the other side it is urged that, however sound it may appear in theory to urge "the rainfall to the river, the 34 ' sewage to the soil," there are manifest objections to the separate system : 1. That it is practically impossible thus to separate rain water and sewage, things that ought not to be in the rain water pipes being certain to get there. 2. That the road washings and rilth, making the first wash of a heavy storm, is most often far more filthy than the very worst sewage, and, therefore special- ly requires treatment. 3. That storm water is the natural flush water for the sewers. It may be said that the third objection may be met by automatic flush tanks ; the second, by effective scavenging ; the first by educating the people. We have not yet attained the ideal of sanitary work. A separate system would, I fear, mean the intermittent pollution of our water-courses. There are legal difficul- ties, too, in carrying it out, which I will not discuss. I do not deal with the question of cost, except to say that the mere size of pipe is not the only, nor is it the main ques- 35 tion to be considered in laying pipes, the excavation, paving, etc., being practically the same, whether pipes be large or small. COMPOSITION OF SEWAGE. Sewage, we have said, is a complex fluid ; no absolute average analysis can therefore be stated. It will, however, be a good starting point to regard the aver- age sewage of London as a standard, and to speak of sewage of greater polluting power as a strong sewage, and of less polluting power, as a weak sewage. A large number of samples of London sewage were examined by Dr. Frankland and myself between 1883 and 1884. The following are certain average details worthy of record. The results are stated in grains per gallon of 70,000 grains : Maximum. Minimum. Average. Matters in solution ... 49 . 77 28 . 42 45 . 213 Matters in suspension. 163 .9 21 . 4 48 . 65 Ammonia 6.527 2.515 3.012 Chlorine 8.33 5.67 7.21 Organic carbon 3 . 847 2.118 3 . 069 Organic nitrogen 2 . 676 . 964 1 . 738 Average ratio of N to C 1 : 1.77. 36 These results, however, take no note of true storm sewage. Whilst an assistant of Dr. Letheby, I made, jointly with him, a very large series of analyses of sewage from ten of the large city sewers, the rate of flow being, on an average, 3,500 gallons per minute. The following are average details : Day Sew- age. Night Sew- age. Storm Sew- age. SOLUBLE MATTERS 55.74 65.09 70.26 ( ) Organic 15.08 7.42 14.75 Containing nitrogen. (b. ) Mineral 5.44 40.66 5.19 57.67 7.26 55.71 Containing phosphor- ic acid 0.85 0.69 1.03 Containing potash . . . 1.21 1.15 1.61 SUSPENDED MATTERS .... (#.) Organic 38.15 16 11 13.99 7.48 31.88 17 55 Containing nitrogen. . (#.) Mineral 0.78 22 04 0.29 6.51 0.67 14.33 Containing phosphor- ic acid 0.89 64 98 Containing potash . . . 0.08 0.04 0.16 It may be of importance to record that at the time the samples were collected for analysis, 37.5 gallons (6 cubic feet) was contributed per head of the popula- tion. Of this, 80 per cent, was repre- sented by the water supply. The follow- ing table exhibits, therefore, the weight in pounds of the chief constituents fof 375,000 gallons of sewage (mid-day sew- age being taken for comparison) fur- nished daily by 10,000 people, and its subdivision into excretal and non-excretal refuse : Constituents of 375,000 gallons. From excreta. From refuse other than excreta. Total. SOLUBLE MATTERS . . Ibs. 957 Ibs. 2029 Ibs. 2986 (#.) Organic 733 75 808 Containing nitrogen . (b. ) Mineral 200 224 1954 291 2178 Containing phosphor- ic acid 30 16 46 Containing potash . . . 34 ,31 65 SUSPENDED MATTERS (a. ) Organic . . 316 356 1628 507 2044 863 Containing nitrogen . (5) Mineral 23 60 19 1121 42 1181 Containing phosphor- ic acid. ... .... Containing potash . . . 21 8 27 48 8 38 Putting these results in a few words, we may say every 10,000 persons in Lon- don contribute, on an average, 375,000 gallons of sewage daily, and that this in- cludes about 1,671 Ibs. of organic matter, containing 333 Ibs. of nitrogen, and 335 Ibs. of mineral matter, containing 94 Ibs. of phosphoric acid and 69 Ibs. of potash. Of course the total quantity* in any given town will depend on a variety of causes. It is certain to be as much as the water supply, but it may be a great deal more. In London, as we have said, it may be taken that 80 per cent, of the sewage is represented by the water sup- piy-- Hofmann & Witt (1857) examined the sewage from the Savoy street sewer, an average sample beiog obtained by the admixture of samples taken hourly dur- ing the twenty-four hours. The results were as follows, stated in grains per gal- lon: (a.) Organic 80.70 Containing nitrogen 6.76 (.) Mineral (?) Containing phosphoric acid 1 . 85 " ' potash 1.03 39 A large number of sludge deposits (to which no precipitant was added) have been examined for the purpose of deter- mining the ratio of organic nitrogen to organic carbon. The results are marked by a great want of uniformity, ranging from a ratio of 1 to 3.4, to a ratio of 1 to 9.1.' Major Scott, after a review of a large number of analyses, says : " We may as- sume that with each [one] part of the three fertilizers, nitrogen, phosphoric acid, and potash, there will be associated in the sewage sludge of London 20 parts, 25 parts, and 56 parts respectively, of organic matter." Nitrogen to organic matter 1 : 20 Phosphoric acid to organic matter. . 1 : 25 Potash to organic matter 1 : 56 It will be impossible for us to discuss the pollution from sources other than excreta, which, together, make up the complex fluid we designate sewage. With respect, however, to stable drainage, I would note that an average horse excretes 40 thirteen times as much fsecal matter by weight, and about fifteen times as much urine, as an adult man. It may be noted further, that both horses and cows pro- duce by respiration about thirteen or fourteen times as much carbonic acid as an adult man, and as a consequence viti- ate the air in the same ratio. (Taking 1,200 cubic inches as the quantity of CO 3 produced per hour by a man, 14,750 inches is produced by a cow or horse.) There is, however, a not unimportant consideration which occurs in consider- ing the character of a town sewage, viz., the feeding of horses. The difficulty of dealing with the stable refuse where the horses have been fed upon maize, is far greater than where the animals have been fed on ordinary corn. In my own ex- perience as a health officer I have had abundant evidence of the peculiarly of- fensive character of the manure in such cases. In all inquiries respecting tho sewage of a town, the nature and amount of the liquid refuse from manufacturing works 41 (if admitted into the sewers) needs most careful consideration. Of these I may specially mention brewery refuse, the waste being of a singularly offensive na- ture. To add to the difficulty, a consid- erable quantity of yeast is discharged with the /waste liquor, whilst the high temperature of the refuse intensifies the trouble of treatment. The refuse from certain dye works, etc., are also difficult to deal with. As regards street washings, the follow- ing details may be worth noting : Granite roads were found at the time of a heavy shower to discharge water into the gul- leys containing 800 grains of solid matter per gallon, of which 219 grains were in solution and 520 in suspension. The precise composition of the washings, will, however, depend on many conditions, such as extent of traffic, previous period of drought, etc. The water from wood paving, taken about the same time as the above, was found to contain 50 grains of solid matter per gallon, of which 40 was in solution and 10 in suspension. Some 42 20 samples of road washings taken from all kinds of roads, under circumstances as nearly as possible similar to the condi- tions named above, were mixed together. The water contained 280 grains of solid matter per gallon, of which 120 were in solution and 160 in suspension. It would be outside my province to discuss the engineering details of a sew- age scheme. Yet let me note that sani- tary medicine must take cognizance of sewage in its progress through a town. There must be sufficient velocity, as well as an economy of scouring power, in or- der to prevent the solid matters from collecting. The ventilation of the sewers is again a question of importance upon which authorities differ, and no wonder, seeing how formidable are the difficulties. DISCHARGE or CRUDE SEWAGE INTO RIVERS. Nothing is more certain than that the discharge of crude sewage into a river is unadvisable. It is, in fact, a method of shifting a nuisance from the nuisance- producer to his immediate neighbor. The 43 evils arising from such discharge depend mainly upon the suspended matter in the sewage. This, first of all, floats about near the outfall, certain portions of the organic matter combining with aluminous compounds from alluvial mud raised by tides and steamers. In time, deposition takes place. In the course of flow the various ingredients are found to deposit more or less in the order of their specific gravity. The first deposits are mainly mineral, with small quantities of organic matter carried down at the same time. The later deposits are mostly finely di- vided organic matter, along with a small quantity of mineral matter. Thus there occurs, as the result of flow, a natural sorting of the matters in suspension. The organic imparities of the sewage in this manner collect in the bed of the river and ultimately putrefy. The gases developed and bottled up in time render the solids sufficiently buoyant to rise to the surface, where the gases of putrefac- tion (sulphur and phosphorus compounds for the most part) are given off, the solid 44 matter again sinking to undergo fresh putrefactive changes. Thus the nuisance from the discharge of sewage into the river may be far more offensive at a short distance from the outfall, -than at the outfall itself. Fur- ther, at a point of slack water, the nuis- ance arising from these solids in suspen- sion may be greatly aggravated. As regards the matters in solution, provided the sewage be sufficiently di- luted and allowed a certain flow, complete purification will be effected by oxidation. This fact is now-a-days admitted by nearly all chemists, and need not detain us further. The self-purification of run- ning water is, however, not to be regard- ed as an argument in support of allowing crude sewage to be discharged into a river. In 1875, a committee of the Local Government Board was appointed to make special inquiry into the practical efficiency of the chief systems of sewage disposals then in operation, and for which loans had been sanctioned by the 45 Board. It reported in 1876 (Sewage Disposal, Eeport of a Committee, 1876): " 4. That most rivers and streams are polluted by a discharge into them of crude sewage, which practice is highly objectionable." " 5. That, as far as we have been able to ascertain, none of the existing modes of treating town sewage by deposition and by chemicals in tanks appear to effect much change beyond the separation of the solids, and the clarification of the liquid. That the treatment of sewage in this manner, however, effects a consider- able improvement, and when carried to its greatest perfection, may in some cases be accepted." U 6. That, so far as our examinations extend, none of the manufactured ma- nures made by manipulating town's re- fuse, with or without chemicals, pay the contingent costs of such modes of treat- ment ; neither has any mode of dealing separately with excreta, so as to defray the cost of collection and preparation by a sale of the manure, been brought under our notice." 46 " 7. That town sewage can best and most cheaply be disposed of and purified by the process of land irrigation for agricultural purposes, where local con- ditions are favorable to its application, but that the chemical value of sewage is greatly reduced to the farmer by the fact that it must be disposed of day by day throughout the entire year, and that its volume is generally greatest when it is of the least service to the land." " 8. That land irrigation is not practi- cable in all cases ; and, therefore, other modes of dealing with sewage must be allowed." This being the sewage with which we have to deal, our object is twofold : (1.) To make use of any valuable con- stituents that it may contain ; and (2.) To purify it. Sanitary requirements, however, de- mand that no nuisance should result in the course of the operation of treatment. THE VALUE OF SEWAGE. The basis on which the theoretical 47 calculation of the value of sewage may be determined, is, authorities suggest, simplicity itself. It may be conceded that the animal excreta are, practically, the only constitu- ents of manurial value. Having determined the value of the excreta of a mixed population, it is only necessary to know (1) the population of any given town, and (2) the quantity of sewage produced during the twenty-four hours, to estimate the manurial value of the sewage. It may appear strange, however, the question being one, we are told, of such simplicity, that authorities before the Select Committee of the House of Commons (1862) should have stated it so variously as from |d. to 9d. per ton. Certain details upon which these money estimates were founded may be noticed. The Rivers Pollution Commissioners, who fix its value at about 2d. per ton, say : " The money value of these con- stituents (combined nitrogen, phosphoric acid and salts of potash), dissolved in 48 100 tons of average sewage, is about 15s., whilst that of the suspended matters is about 2s. That is to say that 100 tons of average sewage are worth 17s., or about 2d. per ton." Hofmann and Witt arrived at a similar conclusion. Six- sevenths, they say, of the valuable matters in sewage are in so- lution. Keckon that 700 tons of sewage contains one ton of solid matter, having a total money value of 6 Os. 3d. (5 5s. for dissolved matters, and 15s. 3d. for suspended matters), it follows that the one ton of sewage is worth about 2d. Lawes and Gilbert arrive at a similar conclusion. Beckoning the dry weather sewage of London as 24 gallons daily per head ( 40 tons per head per annum), and the ammonia as 10 Ibs. per head per annum, the money value would be 2d. per ton, whilst if the ammonia be taken at 12^ Ibs. per head per annum, it would be 2^d. per ton. Take it, says another authority (Mr. Bailey Denton), that the fertilizing ele- ments of one person (worth, let us say, 49 8s. 4d. per year) are diluted with 61 tons of water (an average quantity contributed by each individual to the outflow from towns), the value of sewage is 8s. 4d. divided by 61, or Ifd. per ton. Such are some of the estimates. But there were those who desired to be still more precise in their calculations. Authorities who desired to be cautious valued the London sewage, when the population was 3,000,000, at 1,000,000 sterling, that is at the low estimate (ridiculous to many people) of 6s. 8d. as the annual value of each person's excreta. The two chairmen of parliamentary com- mittees (Mr. Brady and Lord Robert Montagu), after a long inquiry, came to the conclusion that London sewage is equal in manurial value to 212,842 tons of Peruvian guano, with a market price of 2,890,000. Hofmann and Frankland considered that 1,250 tons of London sewage contained the fertilizing matters of one ton of Peruvian guano, whilst a very great authority indeed, one before whom the chemical world justly bows in 50 admiration, would listen to nothing less as the annual value of the metropolitan sewage than 4,081,430. Such being the teachings of science as to the value of sewage, nothing was more natural than to urge upon authorities its application to land. And here let me say at once, that I distinguish between utili- zation of the sewage and its purification. I consider them together, but they are totally different questions. Science had its story to tell. The land acts, first, as a mechanical filter, and, secondly, as a chemical laboratory. As a filter, the larger insoluble particles are arrested on its surface, whilst the smaller are entrapped a few inches down. The water is absorbed, i. e., each earth particle becomes covered with a liquid coating. Now follows the work of the chemical laboratory. The enormous surface of liquid thus formed is favorable to coerc- ing the combination of oxygen with the organic impurities of this subdivided sewage water, carbonic acid and water together with nitric acid, oxidation being 51 assisted possibly by the presence of certain micro -organisms resulting. The organic matters on the surface soon un- dergo slow burning. The nitric acid is your plant feeder. The process of slow burning is the work of oxygen, whilst that of nitrifica- tion, as the researches of Pasteur and Warrington have shown, is due to the combined work of oxygen and of certain lower forms of life. Hence, to purify, you need not only a flow of sewage, but a flow of air, that is, constant movement regulated in its order. As regards the lower organisms, they may be already in the soil or be provided by the sewage. The purifying power of a soil, however, is peculiar to itself. You cannot com- pletely control aeration, although drain- age and loosening of soil will promote it, and an excess of irrigation stop it. In fact, the soil, as a purifying agent, is, to say the least, capricious. Purification, the action of the soil, is greatly assisted by the action of vegeta- tion. In winter time, when there is no 52 vegetation, the soil only must do the work. Enthusiasts fall of faith were found to embark in private sewage farms, whilst local authorities, anxious to save the rates, offered the sewage to farmers in their neighborhood for a corresponding return. It was not long, however, before a certain unpleasant awakening occurred, owing to the farmers declining even to accept the sewage. Reasons for this were sought. Was it due, as was suggested, to the ignorance of farmers, and their blind attachment to old-fashioned ways? This contention was scarcely feasible, seeing how keenly they appreciate newly invented manures (e. oto THOCO O^ O ft 03 S 1 1O to O TH ^ CO 05 Oi> 05 .S 02 TH OCOOOO S "S 13 tO to O O O rf ^ 00 CO CO CO " !*l O5 O O TH iO O 1 S5 | "+3 i ssssaa 1 p d 1 OOtO O to TH > O Ci O5 CO to I TH TH TH TH IO O3 ol M ~2 co c8FQ O5 O CO O5 CO O ^ ^ CO 05 S 05 05 CO 05 CO ,. GO ^ d s- &- 1 ' O) O) fcO bO I II II ' 0) a r - oc c3 2 ^ "S x^ a c3 S *-( 03 2 ^JJ Q CO CD - CO S 03 QQ ^4 OO O O O GQ g ^"s cc S w to od r2 1- 129 The chloride of lime, although only one third of a grain per gallon, not only disinfected the sewage, but prevented the growth of the sewage fungus. My experience enables me to speak favorably of the employment of chloride of lime with lime, especially in hot wea- ther. About 56 Ibs. per 1,000,000 gal- lons will be found, as a rule, fully sufficient for a sewage represented by thirty gallons per head of the population. LIME AND SULPHATE OF SODA. Fuldds Process. This process was tried on a small scale at Pratt's cloth mills (Yeadon, near Leeds), and at Barnsley Union Workhouse in 1873. The process was abandoned, the effluent not proving satisfactory. SALTS or MAGNESIUM WITH TAR AND LIME. fritz Hilles Process. The process of Fritz Hille (patented 1870) was to be used as follows: A mixture of lime (100 Ibs.), gas tat- (3 Ibs.), chemical salts, viz., chloride of magnesium (17 lbs.),were 130 made into a paste with 180 Ibs. of water. Hille, however, does not bind himself to these exact quantities, varying them ac- cording to the composition, strength, and quality of the sewage to be treated. From the decomposition of the magne- sium chloride by the lime, a bulky pre- cipitate is formed, which carries down the suspended matter. The exact quantity of paste to be added must also be a matter of experiment. It will vary from Ib. to 1 Ib per 100 gallons, or from 10,000 Ibs. (=4 tons, 9 cwt., 1 qr., 4 Ibs.) to 2,500 Ibs. (= 1 ton, 2 cwt., 1 qr., 8 Ibs.) per million gallons. This quantity, however, supposes subse- quent nitration. Hille suggests that the sludge may be advantageously used again as a precipi- tant for fresh sewage, employing for this purpose a mixture of from two to five parts of sludge with one part of the paste. Further, he considers that depositing tanks are not essential, but that the sewage after treatment may with advan- tage be applied directly to the land. 131 If tanks be employed, they should not be used for more than three days at a time. SALTS OF ALUMINA. Numberless patents have been taken out for treating sewage by means of compounds of alumina. If sulphate of alumina only be used, the ammonia of the sewage would in time effect its decomposition, resulting in the precipitation of alumina. The action of alumina thus set free is to com- bine with the soluble organic matter, with which it forms an insoluble com- pound. Thus it is used as a mordant or fixing agent for colors when applied to fabrics, and to precipitate coloring mat- ters from their solutions, forming insolu- ble compounds called 4k lakes.'' Ammonia and phosphoric acid are also fixed by aluminous compounds. titothert (1852) patented a mixture of sulphate of alumina (or sulphate of zinc) r caustic lime and charcoal (obtained from sewage or night soil), as a precipitant for 132 sewage. The quantities suggested were 73.5 grains respectively of sulphate of al umina and charcoal, 3.5 grains of sulphate of zinc, and 22 grains of slaked lime per gallon. The lime was to be added first, and then the mixture of charcoal with sulphate of alumina. Hofmann and Witt report (1857) the following results pro- duced with 5 ozs. of lime and 10 ozs. of the alumina mixture to 40 gallons of London sewages . Matters in Solution. Total solids. Organic. Mineral. Raw sewage.. 107. 6 .. 52.36 .. 55.24 Effluent.. . 87.73 37.56 50 17 -Matters in Suspension. - Total solids. Organic. Mineral. Raw sewage.. 52.49 .. 36.4 .. 16.09 Effluent none. . . They record that the addition of the alumina caused a marked increase of sus- pended matter, as well as a largely in- creased flocculation and rapidity of sub- sidence. Stothert claims that a ton of the ma- terials, costing 30s., will make two tons 133 of manure worth 2 2s. per ton, contain- ing, when dried, 1.44 per cent, of am- monia, 8.6 per cent, of phosphate of lime, and 34 per cent, of organic matter. I do not know of this process having been employed on a large scale. Lenk's deodorizing liquid (patent, 1865), wasja solution of alum cake (crude sul- phate of alumina) containing 12 per cent, of alumina. In the case of London sew- age, 25 grs. by weight of the solution sufficed to defecate a gallon efficiently, a very flocculent precipitate forming, which required about 30 minutes to subside. This process \Y as tried at Tottenham in 1858 for about one week, one ton of solution (value 6 10s.) being used to treat 4,900,000 gallons (700,000 daily). The following results were obtained : ( Matters in Solution. -p Phosphoric Total solids. Ammonia. Organic, acid. Raw sewage.. 91. 10 .. 9.76 .. 42.30 .. 3.77 Effluent 63.39 .. 4.23 .. 9.70 ..trace i Matters in Suspension. N Total solids. Organic. Mineral. Raw sewage.. 367. 7 ..225.6 ..142.1 Effluent.. 3.01 0.77 2.24 134 The precipitation was very successful. Voelcker reported that " the effluent might be poured into any watercourse without causing a nuisance." He valued the dry deposit at from 25s. to 30s. per ton. A curious history is here presented of a local authority, guardians of the public health, and moreover, under an injunc- tion not to pollute the Lea, trying a process for one week, which they admit- ted gave " fair results," and which others know to have been more than fair, and then abandoning it, whether from care- lessness or parsimony I do not know. Manning (1853) suggested as a sew- age precipitant, a mixture of animal charcoal, alum carbonate of soda, and gypsum, some caustic lime in addition being also advised. The use of alum, on account of its expense, was afterwards dispensed with (patent, 1854), by the employment of a waste obtained in the course of the alum manufacture from the rough liquors (called soft sludge, con- sisting of sulphates of iron and alumina), 135 and afterwards (patent, 1855), by the use of various aluminous minerals and earths (alum slate, &c.), treated much in the same way as that adopted in the prepara- tion of alum. The sewage was to be treated as fol- lows : The aluminous preparation wa's to be added to the sewage, and the whole agitated, the unslaked lime with animal charcoal being introduced during the mixing. The treated sewage was then to be allowed to subside in proper tanks. This process was favorably spoken of by Penny, of Glascow, who gives the two following analyses of the sludge : Per cent. Per cent. Ammonia 2.22 .. 0.884 Phosphate of lime. . 2 . 05 . . 13.57 Organic matter 43 . 72 . . 31 . 74 The former he regards as of the esti- mated value of 1 16s. 5^d., and the latter of 1 15s. per ton. COMPOUNDS OF IKON AND ALUMINA (SULPHATED CLAY). Birds Process. Six cwt. of powdered 136 clay is treated with 120 Ibs. of sulphuric acid, and the mixture allowed to stand for a week. The following are places where the process has been used : Stroud (Gloucester shire). This solution of sulphate of alumina and iron is used in quantity equal to 28 to 37 grs. of mixed sulphates per gallon, at Stroud (population 8,000) in Gloucestershire, to defecate 200,000 gallons of sewage. The treated sewage is allowed to run into settling tanks passing from one to another through straw niters, and finally filtered through coke filters. The sludge is dried, and made into a manure by ad- mixture with sulphate of ammonia and phosphate of lime. The Stroud sewage was examined and reported on by the Kivers Pollution Commissioners in 1868, when a solution containing 6 cwt- of pulverized clay acted on by 120 Ibs. of sulphuric acid was added to 200,000 gallons of sewage. They record the effluent as inodorous, 137 but not of a high degree of purity. (See 1st Keport, 1868, p. 58.) Cheltenham. Bird's process was adopt- ed at Cheltenham in 1868. It was said not to be a success. Northampton. In 1872, Northampton sewage, which was then 1,000,000 gallons a day, was defecated with crude sulphate of alumina and iron, made by the action of sulphuric acid on a ferruginous clay. Three cwt. of chamber sulphuric acid were added to 2 tons of clay in a wooden trough, and allowed to remain in contact for a week. The solution was generally found to contain about 15 cwt. of a sul- phated ferruginous compound. There were six of these troughs in use the entire soluble contents of one trough being used daily. The flocculation was imperfect from the want of an efficient stirring apparatus. Moreover, the acid of the chemicals caused effervescence with the carbonates present, a scum being formed from the rise of the suspended matters. This, however, was kept back in the firdt tank by cross-bars. The sew- 138 age then flowed into a second tank, and finally over a weir into a channel a mile in length, when it was discharged into the river. The river itself was clean, the aquatic vegetation healthy, and fish abundant. The samples given below are averages of many samples taken over 24 hours. The effluents generally were clear and inoffensive. / Matters in Solution. ^ Oxygen required Total solids, to oxidize. Ammonia. Raw sewage 73.60 .. 2.265 .. 4.98 Effluent, 1st tank. 70.16 .. 1.980 .. 4.19 Effluent, 2d tank. 70.65 .. 1.243 ..3.247 * Matters in Suspension. > Total solids. Organic. Mineral. RawseWage 13.83 .. 8.48 .. 5.37 Effluent, 1st tank. 4.97 .. 2.91 .. 2.06 Effluent, 2d tank. 1.74 .. 1.11 .. 0.63 About 400 tons of sludge were removed per week. This was mixed with sifted ashes (48 tons) and burnt refuse (20 tons), and found a market at 3s. per ton. In 1875, the proprietors of Bird's pro- cess brought an action against the pro- prietors of the Coventry process for 139 infringement, in which they were unsuc- cessful. A process ( Cobleys patent) similar to the one just described (the precipitants being said to consist of iron, alumina and carbon) is in use at Crewkerne, the precipi- tant being placed in a box with perforated sides, the sewage being allowed to How through the box by which contact with the precipitant was secured. There is no stirrer, but sufficient mixing is said to be effected by the means described. The patentee states that the precipitant can be supplied (exclusive of a small royalty) at 2 per ton. A good effluent, which does not undergo putrefactive change by keeping, is stated to be produced. At Hertford (population 9,000) the sewage is treated with a solution of sul- phate of iron (1 part), lime (2 parts), and sulphate of alumina (2 parts). It flows into subsidence tanks (7 in all, 5 being used continuously ), and finally through a coke filter. 140 , LIME AND SALTS or ALUMINA (COVENTRY PROCESS). Anderson, of Coventry, suggested the use of lime and an aluminous compound, prepared by adding 1 part of common sulphuric acid, mixed with its own^'bulk of water, to 2 parts of clay (shale having also been used). The mixture is to be set aside in a warm place until it appears white on the surface. One pound of this mixture is to be well agitated with 100 gallons of sewage, and a J Ib. of lime (as cream of lime) after- wards added. He advises that the defe- cated sewage be allowed absolute rest for twenty-four hours, the clear effluent being then drawn off, and the sludge removed. Odling gives the following results by this process : f Matters in Solution. , Total solids. Organic matter. Ammonia. Raw sewage.. 42.77 .. 8.33 .. 0.77 Effluent 56.28 .. 6.30 .. 0.84 Matters in Suspension. , Total solids. Organic. Mineral. Raw sewage.. 89.74 .. 51.66 .. 38.08 Effluent 1.61 .. 0.91 .. 0.70 141 Both Odling and Voelcker reported highly of this effluent, as thoroughly deprived of noxious qualities. The sludge is valued by Voelcker at 30s. a ton. He gives the following anal- yses : Moisture 12.01 .. 15. tO Organic matter 26 . 89 . . 31 . 86 Phosphate of lime. . 2.60 . . 2.55 Mineral salt 6.61 .. 10.33 Silica, etc 51.89 .. 39.56 100.00 .. 100.00 Ammonia = 1.39 .. 1.22 At Coventry the use of this process was commenced in 1874. It has been ably supervised for many years by Mr. Melliss, C. E. There are, at the present time, four precipitating tanks worked on the continuous principle. The effluent flows through filter beds occupying 9 acres, used intermittently, and is ulti- mately discharged into the River Sher- bourne. The sewage of Coventry is about 2,000,000 gallons daily, very foul, and much colored with dye refuse, etc. It 142 needs far more chemicals than average sewage. The sludge produced is about 25 tons per day (90 per cent, moisture). About 2 tons of crude sulphate of alumina (but of which 2-5ths, being in- soluble in water, is not put into the sew- age), and 10 cwt. of lime are used daily. The cost for chemicals is said to be 1 14s. per 1,000,000 gallons, and the entire cost (including rent, capital on works, management, etc.) about 4 14s. per 1,0.00,000 (= 1.8-J- per head). Formerly, one portion of the sludge was got rid of in a semi-dry condition at 7s. per ton, whilst another portion, dried and reduced to a portable condition, fetched 2 per ton. Some of the sludge was also " fortified '' by added chemicals, and fetched from 5 to 6 per ton. A similar process was also in use at Nuneaton from 1872 to 1876, when the arrangements between the Local Board and the General Sewage and Manure Company fell through, from some mis- understanding respecting the average daily flow. Nuneaton sewage is offensive, 143 owing to the presence of manufacturing refuse. From 400,000 to 500,000 gallons were treated daily. The effluent was filtered through 2 acres of land. The yield of manure was about 1 ton daily. The cost was as nearly as possible the same as at Coventry. THE ABC PROCESS THE NATIVE GUANO COMPANY. The patent of the Messrs. Sillars and Wigner (1868) claim the use of alum, blood, and clay (hence termed the ABC process), with other agents, viz., com- pounds of manganese and magnesium, chloride of sodium, animal and vegetable charcoal, with the object (1.) Of deodorizing and purifying sew- age by means of these chemical sub- tances, and so obtaining a sediment which may be used as manure. (2.) The deodorizing and purifying sewage by means of the mud already precipitated from sewage as above de- scribed. 144 (3.) The addition of an acid to the mud in order to retain ammonia, and so fit it for use as a manure. The precise composition of the pre- cipitating material has been changed from time to time. When first used at Leicester, in 1868, the precipitating mix. ture consisted of : Parts. Alum 600 Blood 1 Clay ,...1,900 Magnesia 5 Manganate of potash 10 Burnt clay 25 Chloride of sodium 10 Animal charcoal 15 Vegetable charcoal 20 Magnesian limestone 2 These were mixed with water, and added to the sewage, until no further precipitate resulted. About 4 Ibs. of the mixture were required to every 1,000 gallons of sewage (= 28 grs. per gallon). The treated sewage then flowed into sub- sidence tanks, where the sediment was allowed to deposit. This sediment was 145 used five or six times over as a precipi- tant, until its power in this respect was exhausted. After the sludge had been dried, a small quantity of acid (preferably sulphuric acid) was added to fix the am- monia, in which state it was claimed to be a valuable manure. In 1869, the process was worked at Leamington, the composition of the pre- cipitating mixture being: Parts. Alum 259 Clay 896 Charcoal 56 Clay blood 40 Carbonates of soda and potash . . 6 Previous precipitate 14 Perchloride of iron solution 1 pint. This mixture was added in the pro- portion of about 51 grs. per gallon, at a cost of 15 18s. per million gallons of sewage. The mixture used at Leamington in 1870 was as follows : Parts. Ammonia alum 336 Clay 672 Animal charcoal 15 Vegetable charcoal 20 Sulphate of magnesium 20 Clay blood 4 146 Of this composition 56 grains per gallon was found to be necessary. 1873, the process was used for a short time at Crossness for the treatment of 500,000 gallons daily of the sewage at the Southern Metropolitan Outfall. The mixture used had the following com- position : Parts. Sulphate of alumina 5 Charcoal 29 Clay 26 Mixed with a little blood. This was added in the proportion of 224 grains per gallon, and yielded 12.33 tons of manure per million gallons of sewage (5.25 tons from sewage, and 7.08 tons from the added chemicals), the in- gredients costing 24 9s. 8d. Tottenham, Hastings, Bolton (1872), Southampton, and Leeds afterwards adopted the process, but in all it was abandoned on the ground of cost. At Southampton a contract to deal with the sewage was canceled after 10,000 had been spent on works, owing to some 147 erroneous expectations respecting profits. At Bolton, 1872-1873, the chemicals used were as follows : Parts. Sulphate of alumina 71 Clay 132 Carbon (waste from prussiate of potash factory) 81 Blood, small quantity. This mixture was added at the rate of about 90 grains per gallon. The quantity of sewage treated was 2,500,000 gallons daily. The process was abandoned on the ground of expense. At Leeds in 1870 (sewage 9,000,000 gallons daily, of which the ABC Company were to deal with 2,000,000) the pre- cipitating mixture employed was : Parts. Alum 5,964 Carbon (refuse from prussiate of potash factory) 4,480 Clay 7,460 Blood mixture 56 Lime .. . 186 About 120 grains per gallon of this mixture was employed. The cost for 148 chemicals per million gallons was 7 5s. The Company abandoned the works on June 1st, 1873. In June, 1875, however, they again treated the Leeds sewage for one week with the following precipitating mixture : Parts. Lime 15,990 Animal carbon 13,556 Alum 8,076 Clay 16,848 Carbolic acid 28 About forty grains of this mixture was used per gallon of sewage, at a cost of 2 8s. lOd. per 1,000,000 gallons. Another trial was made for one week in January, 1876, when the cost of chemi- cals was found to be 3 5s. 9d. per million gallons. The process, as carried out at Leam- ington (population 20,000, sewage 600,- 000 gallons daily in dry weather), was successful. The ABC mixture was stirred into the sewage in a circular tank, from which it passed into two settling tanks, each set being used for one week, 149 there being three sets of tanks for alter- nate working. The effluent then flowed into a channel 850 feet in length, 10 feet wide, 4 feet deep, the last third of which was converted into a filter of sand and animal charcoal, having a superficial area of 3,000 square feet. The sludge was converted into paste by centrifugal ma- chines, revolving 1,500 times per minute, and afterwards further dried by exposure to air. It was then sprinkled with dilute sulphuric acid (1 of acid to 6 water), the acid being used in the proportion of one per cent, of the manure. It was after- wards heaped for a fortnight, during which time it heated considerably, form- ing a rotten compost, which was further dried and sold for manure. About 28 grains per gallon of the A B C mixture was employed, whilst the dried precipitate, containing 20 per cent, of moisture, weighed about 80 grains. Analyses of the effluent at Leamington, as reported on by Dr. Letheby, are as follows : 150 'd ff Sc&Wi-iTtioojT-iofrJoaooioo i i_ S3 'O I / 52 Q i - 1 "* *o * s^ TO <* ^ r gi^ I flo?cooooooir;i-^ioc?pc >^ ^^s^s^ 05 ^ 1 ^^ 00 ^ 00 i 5 o s "18 S i ar if s I !| ww Q. r^"D, ^ P. 1 " p ^ ^ ^^ 151 It will be noted in these analyses that the chloride of sodium in the effluent is less than that of the original sewage. This may be partly explained by its di- lution with subsoil water, and also by the fact shown by Voelcker and Way that marly soils possess the power of re- moving alkaline chlorides from their solutions. At Hastings the works were situate on the seashore. The ABC material was agitated by a machine mixer with the sewage, and after flowing through sub- siding tanks, was discharged into the sea. The ABC process depends in great measure on the alumina as a precipitating agent. It is doubtful whether the blood is of any service, as it can scarcely be urged that in the quantity in which it is added, the fibrin can be of much value as an agent for entangling suspended matter. The clay is mainly a weighting agent, to assist the rapid (subsidence of the suspended impurities. Of course the quality of the manure 152 must depend on the quality of the sewage. Hence, as we should expect, its composi- tion is not absolutely constant. Against the valuations of authorities we have the indisputable fact that it is being sold continuously for about 3 10s. per ton. PHOSPHORIC ACID, MAGNESIA AND LIME. HerapatWs Process .Bly the 1 s Process. The object of this mixture as a sewage precipitant is to fix the ammonia (as an insoluble ammonio-phosphate of magne- sia) which in the employment of lime, or iron and alumina salts, remains in solu- tion in the effluent, and consequently is lost. The lime, however (in common with iron and alumina salts) precipitates the phosphoric acid in the sewage. The use of sulphate or chloride of magnesium as a precipitant, in order to form the in- soluble ammonio-phosphate of magnesia, was first suggested by Sir James Murray. Herapath, in 1853, patented a process for the use of magnesia or one of its compounds, in order to precipitate the 153 ammonia and phosphoric acid " at or about the same time as the deodorization of the same sewage is effected by the addition of some chemical agent which will not decompose ammonia or its salts." With this object he employed a mix- ture of 1 part of sulphate of iron, and 4 parts of burnt magnesian limestone. The process was tried at the sewage Works of St. Thomas, near Exeter, but* proving unremunerative, was abandoned. Murray and Her apat fa's process did nofc meet with the approval of Hofmann and Witt, on the ground that 1 part of the ammonio-phosphate of magnesia is soluble in 45,000 parts of water contain- ing free ammonia and in 15,000 parts of pure water, whilst in a water containing a salt of ammonia, it was soluble to the extent of 1 in 7,000 parts. In 1858, Blythe (Consulting Chemist of the Board of Health) patented the use of a solution of phosphate of magnesia in combination with lime or other pre- cipitating agent. The following is his description of the process : 154 " Superphosphate of magnesia is first to be prepared by the mutual decomposi- tion of superphosphate of lime and a salt of magnesia, the superphosphate of lime being obtained from bones, bone-ash, apatite, phosphorite, coprolite, phosphate of alumina, phosphate of iron, phosphate of copper, or any other substance con- taining phosphoric acid, by the aid of sulphuric or muriatic acid, or other apid, the proportions being, in the case of phosphate of lime, one ton of phosphate to half a ton of sulphuric acid of com- merce, previously mixed with three times its weight of water, or three quarters of a ton of hydrochloric acid of commerce diluted with twice its weight of water. These are allowed to stand together for two or three days, being frequently stirred, and then they are mixed with a ton of sulphate of magnesia, dissolved in a small quantity of water, say a little more than its own weight. Powdered charcoal is then added in sufficient quan- tity (about one ton) to bring the mixture into a solid and convenient form for 155 transport. When used for the purifica- tion of sewage, it is to be dissolved in water, and added to the sewage in the proportion of five parts of the phosphate to every 100 parts of solid matter in a gallon of the sewage. The whole is then to be well mixed and thoroughly incor- porated by means of an agitator. If the sewage does nob contain enough free ammonia or other alkali to neutralize and precipitate all the superphosphate of magnesia, lime is to be added, in the form of milk of lime, until the sewage is faintly alkaline to test paper. By this means the ammonia-phosphate of magnesia is thrown down as a flocculent precipitate, which carries with it, after the manner of a clarifier, any insoluble impurities sus- pended in the liquid. In like manner, instead of lime, he claims the use of any other alkali or alkaline earth, as potash, soda, magnesia or magnesian limestone, or alumina. He thus produces a valu- able manure, containing, as he supposed, the ammonia, as well as the nitrogenous organic matter of the sewage, and the 156 phosphoric acid employed ; i while the supernatant liquor being freed from am- monia and nitrogenous matter, liable to undergo putrefaction, becomes deodor- ized, and may be either applied to the irrigation of land, or run off into the ordinary channels of drainage without fear of creating any nuisance or offense.' " Way, in 1861, in the second report of the Commission to inquire into the best mode of distributing the sewage of towns, condemned the process as the most costly of all the plans that have been proposed, but on grounds that scarcely commend themselves to our judgment. lam ready to admit that the process may fail in re- moving the ammonia to the extent indi- cated by the patentee, but how it can possibly fail in removing the phosphoric acid (I am arguing now on chemical grounds), as Way's analyses show is be- yond comprehension. The only explana- tion can be that Mr. Way did not use sufficient lime. Many experiments were made with Blythe's mixture, of which the following 157 are illustrations. Superphosphate of mag- nesia was added, in the proportion of 10.3 grains of phosphoric acid per gallon, and :hen an excess of lime until the sewage was faintly alkaline. , Matter in Solution. Total Phosphoric Am- Oxygen solids. acid. monia. required. Metropolitan. Raw sewage. 68.33 .. .64 .. 6.33 .. 2.54 Effluent 90.02 .. .60 .. 6.24 .. 1.41 Coventry. Raw sewage. 46.61 .. .53 .. 1.16 .. .78 Effluent 68 07 . . .05 . . 1 .06 . . .43 Matters in Suspension. Total solids. Organic. Mineral. Metropolitan. Raw sewage . . Effluent 47.42 . . 27.51 . . 19.91 Coventry. Raw sewage . . Effluent . . 21.11 . . 8.87 . . 12.24 The dried precipitates had the following percentage composition : Organic matter 28.06 . . 12.16 Phosphate of lime 27.11 . . 32.65 Earthy matters 35.30 . . 45. 60 Sand, etc 9.53 . . 9.59 100.00 100.00 Nitrogen equal to ammonia.. 1.61 0.99 158 The process purified the sewage suc- cessfully. One ton 3 cwt. of the super- phosphate compound and 4 cwt. of lime was found on an average to be required for 1,000,000 gallons. This produces 3 tons 1 cwt. of a manure valued at 3 14s. per ton, the chemicals and labor to pro- duce which cost 1 15s., leaving a net profit of 1 19s. Blythe's later experiments showed that the magnesian compound might be omitted, and that the precipitated phos- phate of lime was as valuable for plants as the original superphosphate. Arrangements had been made to try the process at Southampton and Leicester, but fell through, owing to the death of the patentee. PHOSPHORIC ACID, LIME, AND ALUMINA. PHOSPHATE SEWAGE PROCESS. The patent of Mr. David Forbes, F. E. S., and of Dr. Astley Paston Price was taken out in 1870. It consisted in the use of an acid solution (sulphuric acid being generally, employed) of natural phosphate of alumina, with or without 159 lime or carbonate of lime. The object was to employ a precipitant of manurial value, in order to obtain a compost of high fertilizing power. The phosphate of alumina was obtained from the West Indies, where it occurs in such enormous quantities that on one island alone the deposit is estimated at 9,000,000 tons. It contains about 38 per cent, of phosphoric acid and 25 per cent, of alumina, with about 2.5 per cent, of peroxide of iron. It was formerly supposed to be phosphate of lime, but analysis shows that the material does not contain more than 2 per cent, of lime. Experiments with London and Coven- try sewage, in which was added 33 grains per gallon of the phosphatic material (= 10.38 grains of phosphoric acid) dissolved in its own weight of commercial sulphuric acid, gave results as follows : -Matters in Solution. Total Phosphoric Am- Oxygen solids. acid. monia. required. London. Raw sewage. 68.33 .. 0.64 .. 6.33 .. 2.54 Effluent 100.07 .. 0.68 .. 5.70 .. 1.44 Coventry. Raw sewage. 46.61 .. 0.53 .. 1.16 .. 0.78 Effluent.. . 82.59 .. 0.60 .. 1.04 .. 0.47 160 / Matters in Suspension. > Phosphoric Total solids. Organic. Mineral, acid. London". Kaw sewage. 47. 42 .. 27.51 .. 19.33 .. 0.68 Effluent .. ,' . ..0 Coventry. Raw sewage. 21. 11 .. 8.87 .. 11.96 .. 0.28 Effluent .. .. ..0 The dried precipitate gave as follows: London Covent'y sewage, sewage. Organic matter 24.80 . 10.40 Phosphate of lime 16.82 . 22.11 Carbonate of lime and magnesia 49.39 . 58.14 Silica, etc 8 99 . 9.34 100.00 100.00 Nitrogen equal to ammonia. ... 1.41 . 0.91 The effluent was clear and without smell, much soluble organic matter being removed. The process, however, is pe- culiar in this respect, that if no lime be added after the precipitating material, much soluble phosphate will remain in solution. The effluent may then be used for irrigation, no nuisance being likely to result from the use of the clarified water, the manurial value of which will be con- 161 siderable. In other words, we strengthen (the patentees would say) the manurial value of the sewage, and purify it by the same operation. If lime be used, the deposit may be made to contain any proportion of phos- phate of lime (indeed it may be rendered almost pure bone earth), necessary to pay its cost of carriage to a distance. Thus to effect a good sanitary result a small quantity only of precipitating mat- ter is required, whilst a commercial suc- cess may be effected by the use of a large quantity of the precipitant. Thus, if two tons of the phosphate be added to every 1,000,000 gallons of London sewage, it would yield four or five tons of manure, containing 15 to 18 per cent, of phos- phoric acid, whilst if three tons be added per million, a manure would be obtained worth, according to Voelcker, 7 7s. per ton, and having a composition as follows : Per cent. Moisture 3.98 Organic matters . . 20 . 11 Phosphoric acid.. 28.52=62.26 tribasic phos- phoric of lime. 162 Per cent. Lime 13.09 Alumina, etc 29.95 Sand, etc 4.35 100.00 Nitrogen 0.57=to ammonia 0.69. The only place where the process was worked to which we need refer is Hertford, where the process was in operation for two years (1876-1877). The results were good, but no details are given as to cost. The company paid 100 per year rent for the works, and received 300 per year as a subsidy from the corporation, i.e., at the rate of 7d. per head of the population. W/ntthreacTs Process (1872). The patentee employs superphosphate with a little milk of lime, the object being to re- cover the phosphoric acid in the sludge. Dugald Campbell's Process. (1872). ' The patentee employs superphosphate and some lime. It was tried at Totten- ham in 1872 for six days on 3,500,000 gallons, at a cost for chemicals of 16 6s. 5d. per million gallons, yielding 6.3 tons 163 of manure per million, valued at 5 per ton. It was also tried experimentally (1873 to 1875) on the metropolitan sewage, when the chemicals required to produce a good effluent were found to cost at the rate of 22 6s. per million gallons. The dry manure was valued at from 3 15s. to 4 15s. per ton. SALTS OF IRON. Brown (Feb. 1847) patented the use of the sulphates and chlorides of iron as sewage disinfectants, and JEJllerman(Oci. 1847) the use of the chlorides and pyroly- nates (acetates) of iron. Ellerman's fluid (price Is. 6d. a quart retail, 9d. wholesale), contained from 24 to 43 per cent, of the iron salts named, and had a specific gravity of from 1336 to 1443. Dales fluid (sp. gr. 1450, price 6d. per gallon) was a strong solution of per- chloride of iron, and was proposed by Hofmann, Frankland, and Miller, for de- odorizing the Thames during the hot summers of 1857 and 1860, on the ground 164 that it compared favorably, as regards cost, with lime or chloride of lime. Thus they said 1,000,000 gallons of London sewage required for deodorization the following quantities of the several ingre- dients named : Cost. s. d. 86 gallons of Dale's fluid.... 113 400 Ibs. of chloride of lime.. 2 2 10 132 bushels of lime 3 6 6 They remark that the sewage treated with lime became offensive after three days with chloride of lime after four days-whilst that treated with perchloride of iron did not become offensive even after nine days. The use, however, of the iron was objected to by Odling and Lethe- by, both urging that a black mud would form in the river, which, after a time, would undergo putrefactive changes, and be more unsightly than even the sewage. Letheby also urged the quantity of arsenic in tJae perchloride as an unanswerable ob- jection to its employment as a precipitant where the sludge is not removed before the treated sewage is allowed to escape into the river. 165 Dale's liquid (130 gallons to 1,000,000) was used at Croydon in 1852 and 1860. The results were not satisfactory, because the suspended matter was imperfectly re- moved, the iron sulphide giving the ef- fluent a black and polluted appearance. Dover 's patent (1851) claims the use of acids with iron filings or oxide of iron and protosulphate of iron, the defecated sewage being afterwards filtered through charcoal, peat, etc. Mudies disinfectant, a preparation of dry copperas, is valuable for the deodori- zation of drains, etc., owing to its prop- erty of absorbing ammonia and sulphur- etted hydrogen. It is hardly suited for the defecation of sewage, although it acts well as a general disinfectant, for which purpose it is largely used in the French slaughter-houses. LIME, SULPHATE or IRON, AND COAL DUST. HOLDEN'S PROCESS. This mixture, as a sewage precipitant, was patented by Jules Houzeau and Devedeix (1866), and was used at Brad- 166 ford by Mr. Holden (hence known as Holdens Process). The sulphate of iron was to be added first, and afterwards milk of lime mixed with coal dust. The use of clay is also mentioned in Holden's patent. The treated sewage then flows into subsiding tanks. A clear and inodor- ous effluent can be obtained, about one- half of the dissolved organic matter being precipitated. The manure is of little value. Bradford. The process was tried in 1868 on 130,000 gallons daily. It was reported against by the Kivers Pollution Commissioners, as giving a clear effluent, but of a quality worse than the original sewage, founding their opinion on the quantity of organic nitrogen present. They supposed that the putrescible or- ganic matters in suspension passed into solution by this treatment. Further, they considered the hardness of the effluent an objection to its being allowed to pass into water-courses. Marsden and Collins Process consists in the use of lime, carbon waste from the 167 prussiate manufacture, house ashes, soda, and perchloride of iron. This process was used in 1874 at Boltoti, in dealing with one sixth of the sewage (population, 93,000). The cost of chemicals was given at 1 7s. 3d. per million gallons of sewage, the total cost being 7 14s. 5d. per million. Hansons Process (1875) employs lime, black ash (tank waste, or refuse from alkali works, containing sulphides of cal- cium and sodium), and red haematite treated with sulphuric acid. This process was tried at Leeds, the chemicals used being in the proportion of: Tons. Cwts. Lime 20 Black ash 4 Red haematite and oil of vitriol. . 1 6 Two tons 16 cwt. and 1 qr. were added to every 1,000,000 gallons, at a cost of 2 5s. 8d. per million. The effluent was said to be good. Its use was discon- tinued in April, 1876. A modification of this process is now 168 in use at Leyton. The process was adopt- ed in 1882 by the Golcar Local Board. G-oodaWs Process (1875) employs lime, animal charcoal, ashes, and iron liquor (solution of sulphate of iron). LIME AND AN IRON SALT. At Ealing the lime (20 cwt. per week to 3,000,000 gallons) is added to the sew- age in the course of its transit to the subsidence tanks. These tanks, each measuring 64 ft. X 10 ft. X 10 ft. deep, are divided into five compartments by cross planks, where the lime precipitate subsides. In the last subdivision of the tanks, the defecated sewage is treated with an iron solution (crude sulphate 15 cwt. to 3,000,000 weekly). The sewage then flows upwards through two filter beds (No 1, gravel, 30 ft. X 10 ft. X 2 ft. thick ; No. 2, sand, 60 ft. X 10 ft. x 2ft. thick), the effluent being clear and in- offensive when discharged. At Northampton, in 1862, lime (as milk of lime) and chloride of iron (in solution) 169 were usedjas sewage precipitants. The constituents were mixed together, and so decomposed, before they were added to the sewage [60 Ibs. of solid chloride of iron, 12 bushels of lime to 400,000 gallons of sewage daily]. There was no mechanical contrivance to mix the sew- age with the chemicals. The sewage after treatment passed into two subsid- ing tanks (40 ft. X 30 ft. and 60 ft. X 30 ft., each 5 ft. deep), from the second of which it flowed over a weir into an out- fall channel a mile in length, being ulti- mately discharged into the River Nene. The tanks were worked for a fortnight, when the sludge was conveyed into pits, and mixed with the town refuse, the manure realizing Is. 9d. per load. Letheby recommended adding the iron salt to the sewage first and the lime after- wards, and that some mechanical contri- vance for stirring the treated sewage both after the addition of the iron and the lime should be adopted. He considered 4.5 grains of chloride of iron and 15 grains of lime per gallon was needed. These 170 details were adopted, and the results obtained were excellent. Some difficulty having occurred in procuring the chloride of iron, a solution was prepared on the works of 9.400 grains per gallon. A fit of economy then led the authorities to reduce the quantity to 0.006 grain of chloride of iron and 5.88 grains of lime per gallon, quantities manifestly insufficient, under which treat- ment it was seen and reported on by the Rivers Pollution Commissioners. For a short period combinations of lime and salts of iron were used both at Clifton and Cheltenham. Having now dealt with the various precipitants suggested, to throw down the suspended matter and coagulate a part of the dissolved slimy organic mat- ter of sewage, let me note that these precipitants, for practical purposes, are lime, chloride of magnesium, sulphate and phosphate of alumina, and salts of iron, alone or in conjunction with each other. In addition to these, clay and other 171 weighting bodies, together with charcoal and other absorbent substances, have been added under various patents. In selecting a chemical precipitant, five main points present themselves to us : 1. That, consistently with purity of effluent, the chemicals used should be cheap. 2. That the precipitant should act as a deodorizer and disinfectant as well as a precipitant. 3. That the precipitated matters should subside rapidly. 4 That the maximum purity should be obtained with the minimum of deposit, in other words, with the smallest quantity possible of chemicals. 5. That the sludge should part with its water readily. I now approach the really practical question, asked all over the country, from every sanitary authority, often in tones of painful despair, viz., How shall toe deal with our sewage ? And here let me say there is no one answer that can be given to this ques- 172 tion. The adviser, to advise fairly, must be prepared to sink his hobby, be it the hobby of precipitation or the hobby of irrigation, remembering that whilst con- ditions favorable to his hobby may exist at one place, conditions abso- lutely unfavorable may exist at another. Further, it is of no use telling how some pet plan, say, of irrigation or of precipitation,- has succeeded at some one place or another, persuading local authorities to undertake a pilgrimage of inspection (although they are usually ready enough to do so), and arguing that because such and such plan has succeeded at A, therefore it will succeed at B. There is no universal remedy for the sewage difficulty, and no one plan of treatment to be laid down. When people say, " The whole thing is easy enough, only do this or do that," be certain they have not grasped the diffi- culties of the subject, and, I fear, know little about it. Let me attempt, however, to suggest certain fundamental propositions that 173 may serve as a starting point in advising local authorities : 1. Towns must be prepared to pay to be clean. You will never be able to make your sewage pay your rates ; on the contrary, experience shows that you must purify your sewage at the expense of the rates. 2. That health demands that your sewage should be got rid of, and purified at any cost. Minimize the cost, but pay you must for purification. Hence you must be prepared not only to borrow money to erect works, but for an annual expenditure after the works have been erected. 3. That no matter how perfect your works, your sewage will require constant attention, Sunday as well as week-day, night as well as day. 4. That to let unpurified sewage pass into a stream means passing your filth on to your neighbors. Sewage ought to be treated where the sewage is pro- duced, as far as it is possible. And considering this aspect of the subject, let 174 me add, litigation is a more expensive luxury than sewage treatment, and breeds, if possible (although on this I admit a doubt), more ill-will. 5. That although our duty is to do our work well, at as small a cost as possible, we neither require (qua the effluent) to produce a drinking water, nor (qua the sludge) to produce Peruvian guano. Our sewage has to be treated. We shall necessarily inquire how much sew- age there is to treat, and what kind of sewage it is. Let me suppose that our first thought is the possibility of an irrigation scheme. Far be it from me to say that irriga- tion may not prove successful. But it is fair to note that, to attain the end of a sanitary authority, experience has shown that the sanitary authority must itself be the proprietor of the land. If you give the sewage to the farmers (supposing they would accept your gift) the interests of the local authority and of the farmers are opposite. For it is manifest that the 175 interest of the farmer is his crops, whilst the interest of the local authority is the purification of their sewage. The local authority, as a sanitary authority, must demand a pure effluent at all times, in winter and in wet seasons as well as in summer and in dry seasons. Between these divided interests of farmer and sanitary authority, the question of purity of effluent may, and in our experience usually does, fall to the ground. Hence, if irrigation is to be adopted, the local authority must provide its own land for the purpose. Sundry questions at once arise : 1. Is it practicable to obtain sufficient land, and land properly constituted as re- gards general character, level, etc., for irrigation purposes'? Let me note that the word " sufficient " is not capable of precise definition. What is sufficient in the case of one kind of land is in- sufficient in the case of another. What is sufficient land with one kind of engi- neering treatment, and with one kind of sewage, would prove insufficient with 176 another kind of engineering treatment and another kind of sewage. 2. Is this properly constituted land reasonably near to the town, so that the cost of conveying the sewage to the land will not be excessive, but at the same time reasonably distant, so that the town may not derive injury from the nuisance likely (we might almost say certain) at times to result? 3. Is the land of such a level as to necessitate pumping ? Is it near a water- course, canal, railway, etc. ? Let me suppose these questions an- swered satisfactorily. A very serious further question has now to be con- sidered, viz., where is the effluent to be discharged ? The importance of the question is this. In all irrigation schemes, of whatever nature, we are dependent for effective purification, on effective land, in effective order. The action of land may become ineffective from circumstances over which we have no control, viz., frost, where the ground may become absolutely impene- 177 trable, and water -logging, in times of heavy rains, when the sewage is in far greater quantity than normal, and for a time at least more foul than normal, from flushing of the sewers. Hence, if the outfall is into a river where considerable purity, and unfailing continuity of purity, is demanded, an irrigation scheme is, to say the least, un- safe. If, however, the discharge be into the sea, or into a tidal estuary, or into a stream where the occasional discharge of a little doubtful water is unimportant, an irrigation scheme, pure and simple, may pass muster. To secure land for a sewage farm (even after the proper land has been found) is not an easy matter. It often means a fancy price. It means, too, a mass of opposition from adjoining property hold- ers, who suddenly discover that all the fields in the vicinity of the land selected are building ground. I do not mean this as an objection peculiar to land required for irrigation purposes. 178 Another matter has to be considered. If land be taken on lease for a sewage farm, its renewal may prove difficult. - The lease of the Croydon farm expires in 1892. I will at once admit that my own ex- perience has led me to the opinion that greater advantages result from a com- bined process of precipitation and irriga- tion than can be obtained by either method independently, admitting as I do to the full, that a good effluent may be obtained by a precipitation process alone, nearly as good, in fact, as any effluent that can be obtained by irrigation. A precipitation scheme by itself has these two enormous advantages over irriga- tion, viz. (1) its efficient working is totally independent of weather, and (2) that, if sufficiently large works be erected, any emergency of quantity can be met. Pre- cipitation has had its greatest enemies in its most earnest advocates. Extravagant advantages have been claimed for it. The sludge has been advertised as of enor- mous manurial value. Patents by the 179 hundred have been taken out. Precipi- tation advocates have been for the most part advocates of a system in which they are interested. And there is no wonder that distrust in precipitation schemes have arisen, when the claims put forth by enthusiasts and patent-mongers have been weighed in the balance against the facts, and found wanting. Supposing, then, we determine on a precipitation process, there arises the first freat question, what precipitant shall be used f Here two points must be considered. At any rate it will not be disputed : 1. That, consistently with efficiency and purity of effluent, the chemicals should be cheap. 2. That the smallest quantity of chemi- cals that experience proves is capable of doing the work properly should be added to the sewage, so as to minimize the quantity of sludge formed. I am anxious to be in no sense the advocate of any one system of precipita- 180 tion. I will admit, however the process now is not a patent, and if it were I should speak with greater caution that the ABC turns out the best effluent with which I am acquainted. My own experience leads me to speak very highly indeed of the combined use of lime and sulphate of alumina. The quantity of lime which is to be added first should be such as to render the sewage faintly alkaline. Probably at the rate of from five to seven grains per gallon will be needed for this purpose. It should be added as milk of lime, and should be thoroughly stirred in by means of a paddle-wheel, or other efficient mixer. A flow of a few yards should now be allowed, to permit the aggregation of the precipi- tate. This having taken place, a solution of crude sulphate of alumina, in the proportion of about five grains of sul- phate of alumnia, is to be added, and the sewage again actively stirred. In the alkaline condition of the sewage, the alumina will be precipitated, and will then combine with a portion of the 181 organic matter, forming together an in- 'soluble precipitate. Thus treated, the sewage should be allowed to flow into tanks for the precipitated matters to col- lect. Let me attempt to indicate the effects of. such treatment. A portion of the lime will be at once converted into car- bonate of lime, by combining with the carbonic acid present in the sewage, and serve as a weighting material to aid in the deposition of the lighter flocculent materials. This mechanical action of the lime carbonate is of great importance. The flocculent suspended matter is no doubt one of the most important materi- als to remove, because it is that ingredi- ent of the sewage which readily putrefies, and in this way causes a nuisance. It is, moreover, so light that, unless weighted, it is difficult to precipitate. A second portion of the lime combines with some of the organic matter in solution, pro- ducing an insoluble precipitate (of un- certain composition) of a compound of lime an$ organic matter, the subsidence 182 of which is again assisted by the forma- tion of the carbonate of lime previously described. A third portion of the lirne renders the sewage slightly alkaline. The alumina salt is now to be added. The alumina is precipitated, owing to the alkalinity effected by the slight excess of lime. This alumina combines with some of the organic matter in solution, not precipitated by the action of the lime. The power of alumina in combining with dissolved organic matter, and so remov- ing it from solution, is taken advantage of in many commercial processes. Respecting the iron salts, one strong objection to their use is, that if the effluent be discharged into a river, the stream is liable to be blackened from the formation of a sulphide of iron, a condi- tion likely to be mistaken by the general public for a sewage deposit. I have, therefore, of late, admitting the value of iron compounds as precipitants, hesi- tated to recommend their use, save under very .exceptional circumstances. As re- gards the use of phosphates as precipi- 183 tants, the effluent is almost certain to contain some phosphoric acid, which greatly aids the growth of low forms of fungoid growths, amongst which may be included the so-called sewage fungus. It is advisable that the effluent, before its discharge into a stream, be at least neutral and preferably slightly acid. This condition is easily brought about by the addition of a small quantity of acid to the effluent before its escape. The effluent, after treatment, will no doubt have a slight odor. This is not, however, a sewage smell. If in this con- dition of comparative purity indicated by absence of color and freedom from suspended matter it be allowed to flow over and through a small area of land (a loamy sand or gravel by preference) to serve as a chemical filter, high degree of purity may be obtained, and the finer finishing touches of purification effected. The evils of irrigation under such cir- cumstances do not arise. Such a filtra- tion of the effluent (1) cannot produce a nuisance, because it contains no foul sus- 184 pended matters to collect on the surface and putrefy ; (2) it cannot clog the ground because the gelatinous and papier mac/ie matters in solution have been re- moved ; whilst (3) it has a certain manu- rial value, the quantity of ammonia in solution being not much less than that of the original sewage. Again I may quote from Dr. Monro's paper, who, it will be remembered, doubts the advisability of ordinary irrigation as a general process, on account of imper- vious deposits choking the pores of the land. He says, "The removal of the suspended matter, however, from the sewage, renders irrigation much more practicable. With a clear effluent and a porous soil, the nitrifying power brought into play is enormous, and a moderate area of soil, whether of grass land or arable, can deal with large and almost continuous doses of sewage water.'' Dr. Monro points out that the presence of objectionable organic matter is as destruc- tive to nitrification as the clogging of the pores of the soil, or a great lowering of temperature. 185 The following table will give some idea of the cost of chemical treatment of water-carried sewage. I may be asked what quantity of land is needed where sewage has been effi- ciently precipitated. Again the answer will depend on the nature of the land. But if I say an acre to every 5,000 to 7,000 people. I am well within the results of my experience. Sewage works of the kind I have men- tioned can be carried out without the slightest nuisance. The mixing should be done in closed wells. The mixture, as it flows into the tanks, should, if suffi- cient chemicals have been used, be as free from odor, at the distance of a few feet from the mixer, as common water. The land cannot possibly produce noxious effluvia or poisonous vapors, because the sewage has already been treated with antiseptic precipitants. Of course all depends on the treatment having been efficient. Success in the treatment of sewage obeys the same laws in this respect as success in any- thing else. 186 0?a 'saiAUd Sai -A^dxua pxre STIJO -ixuaxp aoj 'xre aad pisau; uad !}soo -^ox g dS X S From the above table it will be seen that if the proportion of water closets at Bradford and Leeds was larger, the cost of chemicals at the outfall must be considerably increased. If on the other hand the proportion of water closets at Cov- entry was as low as it is at Bradford and Leeds, the cost of chemicals could be considerably reduced, and would probably not exceed 8s. or 9s. per million gallons. From this it will be seen that alumina treatment, such as that employed at Cov- entry, is cheaper than lime treatment ; and it has already been shown by official investigations, that lime treatment and its modiflcations are not as efficient as, or equal in sanitary results to, alumina treatment. It is, moreover, still more expensive than is shown in this table, because of the fact that it produces twice the quantity of sludge as alumina treat* ment does, the dealing with and disposal of which is a very costly matter, particularly as it is practically useless as a manure, and not so readily saleable as that produced by alumina treatment. o^a 'saiAUd Sm -Adxua aoj xunuxTB J8(d puau; ,iad IJSOQ ^ ^ TJco o ^ S^ spjoiraaxp aoj } uinuuia aad he rfv -K pi?axj ,iad ;SOQ | sreoixuaxjQ aoj suoip3) uoiiUK -rad ^SOQ CO 05 T3*H tS S ^ S o^a 'suappiui 'saiAUd SuiAdraa jo isoo p3hxiuy TH" ^ Qtf Of o;a 'snappiui 'satALid mojj ^jBai; paAOiuaa asnj -aa jo ^!ji!juBn5 n so DO cc i> t>T 10 g" asn xn '-o^a 'snap -puu jo satAud jo aaquin^j ^i s s 1 i ft CO " asu ui siasop aa^-BM jo jaqranNi i * i s i ?? uoi^indOcC ^ ^ s 1 pasn ajaqM ^ b "2 s "8 <2 1 ! 1 J 00 Name of Process. Alumina, iron, etc. . . Alumina, iron, etc.^| sewagre if dye > were absent. . ) Precipitation by 1 Lime and Coke V Filtration J Lime process 187 I am desirous here of pointing out certain details of treatment essential for the success of a precipitation process : 1. It is necessary that the sewage treated should be fresh by which I mean sewage in which active putrefactive changes have not taken place. Perhaps, speaking generally, the sewage should not be more than 48 hours old for effect- ive precipitation. But it is certain that, with a sewage of not more than 24 hours old, a far better result, with a smaller amount of chemicals, can be obtained. In fixing, however, the time, a certain elasticity must be allowed, an elasticity by way of extension in winter and of compression in summer. I have said the 'treatment should be effected before active putrefaction commences. In sewage, the decomposition of the different constituents takes place at different times, in some cases the periods of active change being separated by periods of practical rest. Thus a certain alteration in sewage takes place almost immediately. This results (amongst 188 other changes) in the breaking up of the urea, and the formation from it of carbonate of ammonia. It is a rare thing indeed for any sewage, when it reaches the sewage works, to contain more than a trace of urea. No nuisance results from this change of the urea. A con- siderable interval occurs before any other putrefactive stage occurs, and it is during this interval when the precipitation should be effected. If this period be allowed to pass, increased difficulty in working re- sults. 2. The straining of the sewage before treatment, in order to remove rags, corks, and the various et ceteras, such as dead rats, walking sticks, etc., that come down along with the sewage, is advisable but not essential, in order to prevent accumu- lations on the surface of the tanks. Fixed wire gratings are objectionable, on the ground of their becoming so easily choked. Baldwin Latham's extractor is employed in several places with success. 3. It is essential that sufficient chemi- cals be employed to effect complete pre- 189 cipitation, disinfection, and deodorization of the sewage. No greater mistake can be committed than to starve the chemicals. To this must be attributed many cases where a precipitation process has proved a failure. A local authority will spend a large sum in erecting works, perfect in architectural detail, excellent for sewage treatment, whilst they shirk a small annual payment for the necessary chemicals. I need scarcely point out that efficient works will not purify sewage. They are but the means to an end. It is better to calculate the amount of chemicals to be used on the population than on the quantity of sewage. 4. It is essential that after the chemi- cals are added, the mixture should be well stirred. The chemist understands the value of the stirring rod in order to effect perfect chemical contact. My own experience is that the chemicals added to sewage are often wasted from insufficient stirring. Not only is it the case that they do not precipitate so much as they 190 might, but the process of flocculation is imperfect, and the difficulty of obtaining a clear effluent correspondingly great. 5. It is essential that there should be sufficient tank accommodation. Let me note sufficiency of tank accommodation is necessary for two reasons (1) That the precipitate may subside perfectly, and leave a clear colorless effluent. Shallow tanks, with considerable velocity of sew- age through them, or insufficient tank accommodation, means imperfect subsi- dence. Imperfect subsidence means the discharge of a certain quantity of floccu- lent organic matter in the effluent (the mineral matter being more likely to be deposited from its greater specific gravity), and which flocculent matter is likely to occasion nuisance from its decomposi- tion. The treated sewage should flow through at least two subsiding tanks in series, the first being capable of holding one hour's flow, and the second not less than four hours' flow. The tanks should be at least four feet deep, and the over- flow of the defecated sewage should be 191 over a weir, not more than an inch below the surface. There should be a double set of tanks for successful working. (2) Sufficiency of tank accommodation is also important, so that the sludge may be frequently removed, otherwise the freshly precipitated sewage may be con- taminated by the decomposing materials of a previous precipitation, or a nuisance result from a collection of decomposing matter. Many a good effluent is spoilt by foul materials being allowed to collect in the subsiding tanks. These materials undergo putrefaction, the gases given off contaminating the effluent. The solid matters, becoming specifically lighter than the liquid by the gases of putrefac- tion developed in and amongst them, rise to the surface, the floating black masses presenting an objectionable appearance, and discharging offensive products into the air. After a time these black masses sink, and thus, by constant commotion of the precipitated matters, a turbid effluent, with a more or less foul smell, results. 192 6. That the defecated water should flow through a shallow open conduit of not less than a quarter of a mile before being discharged into the stream. 7. The stream into which the effluent is discharged should have a free run, and in volume be not less than eight times the volume of the defecated sewage. 8. That the tanks themselves should not only be emptied of the sludge, but thoroughly cleansed before being re- filled. The extent of tank accommodation needful will depend a good deal on the dilution of the sewage to be dealt with, either by subsoil or surface waters, or by both, and whether the treatment em- ployed be intermittent or continuous. The following gives the tank capacity provided at certain successful works : 193 g o PH ;3 I O CQ 'd - 2 50 O jg o" ic" i^r cT ft o ^ ^ o Pk 02 p o 1 1 a -4-i a 8 ) OJ | Is 09 03 1 OD "3 s 02 o oi *s 1 a u S p HH a fl 1 1 1 ^ s S 1 1 5 o w J 194 The most suitable depth for tanks is from 5 to 6 feet. It may be worth noting the rate at which the precipitated matters deposit when the treatment with lime and sul- phate of alumina is efficient, and the sewage collected in tanks of 5 feet 6 inches. The water begins to clear a few minutes after the cessation of agitation. In thirty minutes it clears to a depth of 3 feet, with 8 inches precipitate, while after two hours the precipitate will measure 4| inches only. All this accomplished, two questions remain: (1.) Have you produced such an effluent that it will not pollute the watercourses'? (2.) Is not the sludge certain to cause a nuisance 1 ?' That a clear, colorless, non- fro thing effluent can be produced by mere chemi- cal precipitation, is not a matter of opin- ion, but of fact. That an effluent abso- lutely without smell can be produced, I doubt. The smell, however, of the efflu- ent from properly treated sewage is not the odor of sewage. I have never, I can- 195 didly confess, found an effluent without a certain smell. I have heard a well- known authority ascribe it to the pres- ence of minute traces of essential oils or strong smelling bodies (e.g., onions), dif- ficult of removal by precipitants. If the effluent is to be discharged into the sea, or into a tidal or large river (say 200 or 300 times the volume of the effluent), this odor is absolutely immaterial ; but where great purity is required, e.g., when the effluent has to be discharged into a small stream or into a river employed at a short distance from the outfall for drinking purposes, some further treat- ment is called for. Such further treatment consists either (1) in the use of artificially prepared fil- ter beds, such as are used for the filtra- tion of water, or (2) by filtration through a small area of land. Of these two methods, I prefer the latter. After careful consideration, I con- sider that for this purpose an acre to every 5,000 to 7,000 people (as I have before noted) is abundant. I shall not 196 discuss any question of manurial value, although I may point out that the am- monia of sewage is not appreciably af- fected by ordinary chemical precipitants. (2.) Is not the sludge an inevitable cause of nuisance? I confess it may be, and often has been. Allowing the sludge to accumulate week after week in the de- positing tanks, is not only an evil (as I have pointed out) so far as our endeav- ors to procure a good effluent is con- cerned, but an unmitigated nuisance, so far as relates to the sludge. Further, the old method of emptying the sludge into open sludge pits, where the liquid portion was allowed to drain away and to evaporate, has proved a constant cause of just complaint, more especially in warm weather. I am not sure whether the sludge, under these conditions, was not sometimes a greater nuisance after being taken out of the sewage than when left in it. Until lately the difficulty of the disposal of the sludge was one inherent to all precipitation works. Until lately I said because now the difficulty is over- come. 197 It is essential, both in the interests of the effluent and of the sludge, that it should be frequently removed from the tanks I mean that the sludge should be removed before putrefactive decomposi- tion sets in. This frequent removal is necessary (1) so that the effluent may not be polluted, and (2) so that no nuisance may result during the removal of the sludge and the cleansing of the tank. For here I must express a strong opinion that it is not enough merely to empty the tank of sludge, but it is imperative that, after being emptied, and before being refilled, the tank should be well cleansed in other words, that the mat- ters which stick to the sides of the tank should be completely and efficiently re- moved to prevent nuisance or fouling by subsequent decomposition. It would be outside my province to deal with the methods of raising the sludge out of the tanks. This is a purely mechanical question. The sludge is a thick black liquid, which may be pumped out of the tanks or lifted out by bucket 198 pumps into troughs, which serve to con- vey it wherever it may be wanted. I am indebted for the table on page 199 to the manager of a sewage works in a residential neighborhood of a population of 18,000. The process used is lime and sulphate of alumina. The sewage is pressed in one of Johnson's presses : The record of sludge begins on Feb- ruary 16, 1885, and ends on February 16, 1886. The wet sludge is got by a series of eighty different actual measurements on various days throughout the year. The pressed sludge is got by keeping a record of the number of times the presses were emptied on every day in the year. A cubic yard of wet sludge is taken as weighing .98 of a ton, and a cubic yard of pressed sludge as weighing .75 of a ton (actual determinations). The following details are taken from Mr. Lacey's report to the Brentford Local Board, on " The Disposal of Sew- age Sludge." (See page 200.) 199 t> O 3 O co bD d : d c8 g 3S o {S *5 1 s* ^ a ss O - &S *5 H^O at 201 It will be convenient at this point to consider the amount of sludge pro- duced, its value as a manurial agent, and the method suggested for its dis- posal. I. AMOUNT OF SLUDGE. The quantity of sludge varies enor- mously, according to the amount of sewage, and the precipitants employed. Thus, at Coventry the sludge from 1,000,000 gallons is about 12.5 tons, whereas at Birmingham it varies from 25 to 33 tons. The quantity of sludge produced from a given quantity of sewage will vary ac- cording to local circumstances and con- ditions ; such for instance as the charac- ter of the soil, the condition of the streets and roads, whether surface water be wholly or in part admitted to or excluded from the sewers, whether manufacturing refuse is included in the sewage to be treated, whether or no the w. c. be in general use, and whether the process of precipitation be complete and efficient or only partial. 202 In a town where w.c.'s are in general use, where the soil is of gravel and sand, where surface water is partially admitted into the sewers, where there are no manufactories, and where precipitation is well and efficiently done with chemicals of modern bulk, the proportion of pressed sludge containing 50 per cent, of moist- ure, may be taken at .6 (six tenths) of a pound per head per day, or about 2 tons, 14 cwt, daily per 10,000 of the population. The principle is right: Consistent with efficiency, produce as little sludge as practicable ; and this for two reasons (1) that if it has any value, you secure its maximum value ; whilst (2) if it has no value, you have the less to get rid of. Thus with some precipitants you get a large volume of valueless sludge. With sulphate of alumina you get comparatively little sludge, but a material of greater value. Of course it may be argued that the more sludge you obtain, the more perfect has been the removal of the im- purities of the sewage. This may or may not be true. 203 II. COMPOSITION AND VALUE OF SLUDGE. I am anxious at once to say that I place no intrinsic value on the sludge whatsoever. An estimate of the value of sludge from different places has been given on high authority, but it is better to regard the sludge as a thing to be got rid of, and as a thing which, to be got rid of, must cost money and may not bring money. The following table of the analyses of sludge from various places, and by various methods of precipitation, have been given by Dr. Wallace as fol- lows: 204 os ic co 1 ^ .as 34 e- ri w i O O? TH OJ TH TH f> OJ O CO CO r)J Oi i-l Tt< CO CO CO O CD s g 8lOOTtT o PQ $ 5 6 to 8 4 5 4 to 8 12. Halifax manure by Goux's process 17 7 5 10 to 8 9 * Calculated on the supposition that phosphate of lime is worth Id. per lb.; potash, 2d., and nitrogen (as ammonia) at 8d. f By this is implied its value as compared with good farmyard manure, which has a theoretical value of 15s. 7d., its market value being from 5s. to 7s. 6d. per ton. 206 The old system consisted in merely placing the sludge in pits, and allowing it to air-dry. In this condition it was sold or given to the farmers. I may mention here that a sludge containing 90 per cent, of moisture can be reduced to 80 per cent, by forty-eight hours' draining, to 75 per cent, by three days' draining, and to 71 per cent, after a week's draining. After this, air drying is comparatively slow, although no doubt the admixture of porous substances would render drying more rapid and more com- plete. III. DISPOSAL or THE SLUDGE. 1. Johnson's Process. By this pro- cess the liquid portion of the sludge is extracted by pressure in a series of com- partments. Each compartment is pro- vided with a canvas cloth, which acts as a strainer, and retains the solids as the liquid passes through. The sludge is driven into the compartments by com- pressed air, 100 to 120 Ibs. per square inch, until they can hold no more. On 207 opening the press, a solid cake of com- pressed sludge is found in each compart- ment. The cake is compact, easily handled, and practically has no smell. II has a certain manurial value. It is worth while to consider a few details of pressing. The sludge, as pre- cipitated, contains on an average 90 per cent, of water, whilst the pressed sludge cake contains 50 per cent. By simple air drying, the 50 per cent, of moisture may be reduced to less than 20 per cent. Thus in every ton (2,240 Ibs.) of un- pressed sludge, 2,016 Ibs. is moisture, and 224 Ibs. solid matter. After pressure, the 224 Ibs. of solid matter holds about 224 Ibs. of moisture, the removal of 1,792 Ibs., or about 179 gallons, of water hav- ing been effected. The time occupied in the compression of 5 tons is about one hour. The sludge cake, according to Monro, contains from 0.6 to 0.9 per cent, of nitrogen, and over 1 per cent, of phosphoric acid. It has been the prac- tice to run back the liquid expressed from the sludge into the sewer, to be re- 208 treated. Professor Dewar and myself have pointed out that this course is un- advisable. The liquid thus expressed is exceedingly foul, although perfectly clear, and does not readily lend itself to ordi- nary chemical precipitation. I will merely note that it requires separate treatment, and that our experiments indicate that chloride of lime or perchloride of iron in larger amount than is required for ordi- nary sewage may be rendered effective for the purpose. The manurial value of the pressed sludge cake from Coventry, Leyton and West Ham, has been the subject of care- ful investigation by Dr. Monro, from whom I have abstracted the percentage details of experiments on the dried sludge given in the following table : 209 PERCENTAGE DETAILS OF EXPERIMENTS ON THE DRIED SLUDGE. -332 QJ C C gfi 8|g **q c *5 aj w 3 c ? " ^a^-5 'O ^'5^5 |^| 8? "S * s^og " B ^^ ^I'fr I&S2 tll^ 02 Q.4J Bi| 0^3-^ 1^ |g |^S cc'C^ fl r a 02 cs Organic matter 26 14 26 08 40 32 Containing nitrogen 1 36 1 35 1 82 Potash 30 34 22 Total P-iO & 2 43 2 04 2 57 Soluble PaO 6 1.37 1 69 1.24 The phosphoric acid in sewage sludge is chiefly in combination with alumina. Dr. Monro notes that whilst Coventry sewage contains much manufacturing refuse from dye works, and West Ham sewage the refuse from industries of a most varied and polluting character, Leyton is a rural and suburban district, having no manufactures of any kind con- tributing to the sewage. 210 Dr. Monro has practically tested the agricultural value of these pressed sludge cakes, for the details of which the reader is referred to his original paper. Good crops of swedes were obtained. The three sludges gave almost identical re- sults as regards yield. The following were the results obtained by him with different dressings for comparison : RESULTS PER ACRE. Tons. Cwt. 1. 10 tons farmyard manure 13 11^ 2. 4 cwt. superphosphate 11 2J 3. 5 tons Leyton sludge 10 4 4. 5 tons farmyard manure 10 1| 5. 5 tons West Ham sludge 9 8J 6. 5 tons Coventry sludge 9 6^ 7. 2 cwt. superphosphate with 2 cwt. of nitrate 9 5J 8. 2 cwt. superphosphate 9 4 9. 2 cwt. coprolite 8 15 10. 4 cwt. coprolite 7 10 11. Unmanured 5 18 From these details it is evident that the air-dried filter- pressed cake has a certain manurial value at any rate, about equal 211 to farmyard manure which possibly, considering how easily it may be stored without causing a nuisance, may be worthy of being considered more fully than it has at present. It is worth noting that although the newly pressed cake is richer in nitrogen than farmyard manure, and contains more than double the amount of phosphoric acid, still that the manurial value is not greater, weight for weight. This Dr. Monro explains by differences of physical condition, viz., the loose texture of farmyard manure compared with the compact condition of the sludge cake ; the physical state of the one being as favorable to rapid oxidation and disintegration as that of the other is unfavorable. To overcome this difficulty, Dr. Monro suggests the reduction of the cake to a fine state of subdivision. The cost of procuring the sludge is stated by Mr. Hutchinson (to whose ex- cellent paper I must refer) as from 2s. to 2s. 6d. per ton at Coventry. I have no records as to what the further cost of grinding would involve. 212 The Johnson process is at work at Croyden Rural, High Wycombe, Cov- entry, Ley ton, Blackburn, and Ayles- bury. (2.) Major- General Scott's ^Process. This is adopted at Burnley. The lime precipitated sludge (i. e., lime and or- ganic matter) is drained until it contains about 65 per cent, of moisture. The sludge at this stage is tested as to the amount of lime present, more being added if necessary. The mass is now dried by heat, and finally burnt in kilns. The residual clinker is ground, and used as an hydraulic cement (Portland cement). The cement is said to have a tensile strength of 350 Ibs. per square inch after immersion in water for seven days, and to be worth 35s. per ton. It is evident that the composition of sewage sludge varies not only in differ- ent towns, but in the same town at different times. It is not quite clear how far this process can be worked so as to secure that which engineers know to be so important, viz., a cement of con- 213 stant character. (See paper by Granville Cole, Ph.D., Society of Arts Conference, 1879, p. 137.) The cost of drying is 7s. per ton. The coke employed for burning averages Is. 4d. per ton, and the labor, etc., 15s. per ton. Major Scott has suggested that in the case of the London sewage both a manure and a cement might be pre- pared. In the Journal of the Society of Arts, November 28, 1879, he suggests, in the treatment of sewage, that the primary separation of the coarser mineral sus- pended matter should be effected in a first tank, a sufficient period of rest being afterwards allowed for the subsidence (not the artificial precipitation) of the lighter suspended matters in a second tank. The sludge of this second tank (i. e., after the watery portion has been drawn off) is to be treated with about two-thirds its weight of milk of lime, sufficient superphosphate being after- wards added nearly to neutralize the 214 lime. (The superphosphate is to be pre- pared by mixing 20 cwt. of Cambridge coprolites with 17 cwt. of brown sul- phuric acid, sufficient water being added to render the mixture almost fluid). By this treatment the mixture (he states) becomes surprisingly inodorous, and dries with rapidity. The cost of chemi- cals he values at 16s. 6d. per ton of pre- pared manure, its removal from the tanks and subsequent drying being 3s. 6d. He considers it worth 3 10s. per ton. The sewage or liquid portion of the second tank, from which the organic matter has been recovered, is then to be treated with lime, and the precipitate thus obtained made into a cement. Major Scott seems to have overlooked the difficulty of effecting precipitation of the suspended matters of sewage (such as he is desirous of obtaining in the second tank) without the use of precipi- tants. Further, a limed sludge, when dried, is certain to lose ammonia, in other words, is certain to lose manurial value. 215 The deposit in the first tank Major Scott proposed should be burnt in a de- structor with waste cinders, and be used to reclaim a portion of the marshes. At any rate (he justly considers) it ought not to be allowed to pass into the river. (3.) Destructor. The destructor has been carried to its greatest state of per- fection at Baling, under the ingenious and careful management of Mr. Charles Jones. In this case, however, the ashes of the district are mixed with the sludge. The chemicals used for precipitation are 11.5 grains of clay and about 10 grains of lime per gallon, a little iron and alumina being also used. The sewage treated comes from a population of about 18,000, and is equal to 600,000 gallons daily. About 157 cubic yards of sludge are obtained per week. This is mixed with about 100 cubic yards of ashes and house refuse. Before the mass is burnt in the destructor, about 25 per cent, of the liquid portion is allowed to drain away. It may be advisable here to note the 216 difficulties that have been met with gen- erally in the use of destructors : 1. An escape of vapors that prove more or less offensive at a considerable dis- tance from the shaft. This depends on the materials having undergone incom- plete burning, in other words, that the materials in the destructor have been subjected to destructive distillation (in which case the products, consisting of various empyreumatic vapors, are offens- ive), rather than combustion, in which case the products would be simply water and carbonic acid, and inoffensive. No doubt, until lately, the escape of unburnt and partially burnt vapors, a very small quantity of which sufficed to cause a nuisance, have proved a serious objection to the use of destructors. 2. The escape from the shaft of un- burnt or partially charred paper, fine sand, etc., at certain stages of the pro- cess. I do not hesitate to say that both of these difficulties are met in Jones' de- structor. This has been done by mixing 217 the sludge with the house ashes, thus assisting effective combustion. Mr. Jones lays down that every town supplies suffi- cient house refuse to burn its sludge. The main point, however, on which he relies, is the construction of a muffle furnace (a fume destroyer, as he calls it) between the furnace and the main shaft. As a result, not only is a greatly increased draught secured, but the combustion of unburnt vapors discharged from' the fur- nace in which the sludge is placed is secured. I may add that Mr. Jones in- forms me that the muffle furnace is kept going at a cost of Is. 6d. per day, but that this, in addition, gives 10 Ibs. of steam for engine purposes. He obtains, as a residuum from the furnace, 25 per cent, of hard clinker, which is utilized in various ways, viz., for artificial stone, road-making, etc. Various suggestions for what may be called fortifying the sludge have been suggested. Thus, Colonel Jones, of Wrexham, after drying the sludge to 20 per cent, of moisture, adds to every 12 218 parts 7 parts of raw bone meal and one part of sulphate of ammonia. I do not propose discussing other sug- gestions for the disposal of sludge, such as the separation of the water by centrifu- gal machines converting the sludge into a fuel by admixture with other waste products its conversion into a combus- tible gas making it into bricks, etc. (Monson). These suggestions are scarcely practical. The question of cost must be consid- ered in conjunction with (1) the quantity of the sewage, (2) the quality of the sewage (that is, the nature of the sewage other than mere excreta), (3) the flow per head, and (4) the standard of excellence required. As regards quantity, I wish to say that you cannot apply the cost of treating small volumes of sewage to the cost of treating large volumes, the treatment of the former being more easily effected than the latter. 219 PRICES OF CHEMICALS. Green copperas or proto-sulphate of iron can be obtained for about 20s. per ton. Lime can be obtained from 10s. to 15s. per ton. Sulphate of alumina can be obtained from 46s. 6d. per ton, as per following analysis : Moisture 5.94 Crystallized sulphate of alumina. 77.44 " sulphate of iron 4.00 Sulphates of alkalies and sulphuric acid. 6.82 Insoluble iron and alumina 5.80 100.00 The annual cost of thoroughly and efficiently treating the sewage of Coven try, pressing the whole of the sludge etc., exclusive of interest on plant, land, and depreciation the population con- tributing being 45,000 persons, and the sewage containing large quantities of dye and manufacturing refuse is 2,800 per annum, an amount equal to Is. 3d. per head. 220 The cost at Hertford, where the sludge is not pressed, and manufacturing refuse is absent, with a population of 7,747, is 570 per annum, equal to Is. 5d. per head. A few words only on the analysis of sewage. No single analysis of a sewage effluent is satisfactory as proof of good or of inefficient working. Knowing as we do that sewage varies from hour to hour, no accurate conclusion can be drawn as to the composition of the raw sewage or of the effluent, except by col- lecting half hourly, or at least hourly, samples during one entire period of twenty-four hours, and the various sam- ples mixed in the proportion of the fluid. The analysis of a sample of raw sewage and of an effluent taken about the same time are not comparable, because the passage of the sewage through the tanks is commonly the work of some hours. Supposing, for example, I collect a sam- ple of twelve o'clock sewage and a sample 221 of effluent at the same time, the twelve o'clock sewage may be the very strongest sewage of the day; whilst the effluent sample is the effluent of the very weakest sewage. Precisely the opposite condi- tion may occur, viz., that I may compare the effluent of the strongest sewage with the weakest raw sewage delivered. Further, in all cases where analyses are made for test purposes, the weather should be noted, the rainfall and the flow being compared with the average flow. For accurate purposes a normal condi- tion of flow should be selected, and com- parison made between the average of twenty-four hours' sewage and twenty- four hours' effluent. As regards the analysis of sewage, it is advisable to estimate the quantity of the matters in suspension, and in these the amount of mineral and organic (with volatile) matters. In addition to this, I have of late adopted the system of esti- mating the organic carbon and nitrogen, and the oxygen required to oxidize the 222 organic matter in the effluent without removing the suspended matter. Seeing that the real issue is the condition of the effluent, I consider this method preferable to an analysis of the clear effluent after the removal of the suspended matter. I propose the following form as one which conveys the best information that chemistry can afford as to the chemical composition of a sewage and of an effluent : The results are stated in grains per imperial gal- lon of 70,000 grains. Matters in Suspension Total .... (a) Organic and volatile. . . . 09) Mineral The following details have been obtained from the effluent without the removal of the suspended matters: Total solids (suspended and dissolved) Ammonia Chlorine =Chloride of sodium Nitrogen (as nitrites and nitrates). . . . Oxygen required to oxidize organic matter Organic carbon Organic nitrogen 223 To get rid of execretal filth with the least possible delay is no doubt the teaching of sanitary science. The advo- cates of the water closet urge that water as a vehicle to carry the refuse commends itself to us on 'the ground of conven- ience, cleanliness and cheapness. They would compare, with plausible argument, the natural power of gravitation (such as is made use of in the water closet) with an organization of men and carts (such as is required by the dry earth system). The advantages, at first sight, seem all on one side. Facts, however, point in an opposite direction. Dilution with water is the best known method of rendering practically useless whatever is valuable in sewage indeed, worse than useless, an ungovernable nuisance. The excreta of animals are no doubt intended for the food of plants, and for our use through their intervention. Of course, do what we will, nature will assert herself and her plans. But nature is embarrassed by our meddlesomeness. The nutritive food of the plant we drown in water, our in- 224 genuity failing when we attempt to deal with the filthy mixture. We cannot utilize it, unless we abandon all sanitary precautions ; it pollutes our air, renders our ground a stinking morass, and defiles our watercourses. Thirty gallons of water daily per head is brought to us who live in London, from pure sources, at great cost, and with great engineering skill ; filtered, often refiltered, with ex- traordinary care ; stored with scrupulous anxiety; analyzed by one chemist after another. It is, however, a striking fact that only l-90th part of the entire water supply is used for drinking purposes, a large quantity being destined to become the diluent of our sewage, to perplex us by its quantity, to bother us by its use- lessness, and to steal our health by the perpetual nuisance it occasions. ** Any book in this Catalogue sent free by mail on receipt of price. VALUABLE SCIENTIFIC BOOKS PUBLISHED BY D. VAN NOSTRAND, 23 MURRAY STREET AND 27 WARREN STREET, N. Y. ADAMS (J. W.) Sewers and Drains for Populous Districts. Embracing Rules and Formulas lor the dimensions and construction of works of Sanitary Engineers. Second edi- tion. 8vo, cloth $2 50 ALEXANDER (J. H.) 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