T D 7* i REESE LIBRARY OF THK UNIVERSITY OF CALIFORNIA. , igo . ? Accession No. 90251 * THI<: Bacterial treatment of Sewage. A HANDBOOK FOR COUNCILLORS, ENGINEERS, AND SURVEYORS. BY GEORGE THUDICHUM, F.C.S, LONDON: "The Councillor and Guardian" Offices, 29, Old Queen Street, S.W. Price, 1/3 post free. Six or more Copies, I/- each post free, SHONE PNEUMATIC AUTOMATIC EJECTORS. COMPRESSED 7UR lalFTS. FOR RAISING SEWAGE, WATER, SLUDGE, &c. For all information apply to HUGHES & LANCASTER, 47, Victoria Street, Westminster, S.W. the standard Work on Sewage Purification. Now ready. Second Edition. Revised and Enlarged, with with numerous Illustrations and Diagrams. ifl Price 21 net. .The Purification of Sewage and Water By W. J. DIBDIN., F.I.C., F.C.S., Late Chemist to the London County Council. INDISPENSIBLE TO LOCAL HEALTH AUTHORITIES BECAUSE In its pages the Bacterial Treatment of Sewage is fully described and illustrated, This work has had a larger sale than any work previously published dealing with sewage disposal, and is in increasing demand. The following are brief selections from an exhaustive list of appreciative Press Opinions. " A work of great interest, and considerable value, especially to those who are called upon to advise as to the disposal of sewage." The Engineer. "An accurate and valuable gauge of the present position of matters relating to the more pressing questions of modern hygiene." The Lancet. " Every health officer should possess it." British Medical Journal. " A most interesting and welcome contribution to our information upon a problem of world- wide importance." The Chemical Trade Journal. " For those who wish to obtain, in clear and concise form, an account of certain of the bacteriological processes involved in sewage puri6cation, and who wish to have a summary of the chemical changes and results obtained, no better book is at present published." Nature. The Sanitary PublishingCompany, Limited, 5, Fetter Lane, London, E.G. BACTERIAL . SEWAGE TREATMENT ON THE NEW SYSTEM OF Polaritc Oxidising Beds. Construction cost 75 per cent, less than any other system and no expenditure for subsequent maintenance required. EFFICIENCY GREATER. No Sludge, Chemicals, or Large Tanks. No Royalties or Expert Fees. Highest Award Sanitary Institute Great Britain, Particulars, Reports, and Analyses on application to The International Purification Syndicate, (FRANK CANDY, General Manager), 109, VICTORIA STREET, LONDON, S.W. THE "Councillor & Guardian" ZTbe OLeaMno rgan of Xocal (Government ant) tbe poor %aw. Editor and Proprietor = = THOMAS FARROW. Id. Weekly. Subscription, 6/6 per Annum, post free. THE BEST AND CHEAPEST MEDIUM FOR OFFICIAL ADVERTISEMENTS. STRIKING TESTIMONY. A Borough Engineer Writes: "I have used the paper as an advertising medium with satisfactory results." A Clerk to R.D.C. says : " I advertised for tenders for granite and other materials solely in THE COUNCILLOR AND GUARDIAN, and received upwards of seventy replies." A Surveyor to U.D.C.: "No sooner had my advertisement appeared than I received sixty-one replies asking for particulars." See Advertisement on Inside Back Cover. Supplied Free by Post to Engineers and Surveyors for 12 months from the date of receipt of Official Advertisement. EDITORIAL & PUBLISHING OFFICES: 29, Old Queen Street, Westminster, S.W. SEND FOR FREE SPECIMEN COPY. BACTERIAL FILTERS. ADAMS' PATENT Automatic filling, Emptying^ Discharging Apparatus, Regardless of volume, and wholly without movement or attention. Equally useful for the "Holding Up" or the "Continuous" Systems. Mr C CHAMBERS SMITH, Sutton, says of it : 'A most ingenious and admirable apparatus, which does all that is claimed fo it." AS AT SUTTON, SURREY. Adams' Patent Sewage Lift Co., HYDRAULIC ENGINEERS, WORKS: YORK. London Offices: 7, OLD QUEEN STREET, WESTMINSTER, S.W. Makers of Alternating, Simultaneous Discharge, and Coupled and Controlled Syphons, Automatic Sewage Lift, Penstocks, Valves, &c. For Domestic Sanitary Appliances, write : ADAMS & CO., Park Lane, Leeds; and Old Queen Street, Westminster, S.W. THE BACTERIAL TREATMENT OF SEWAGE. A HANDBOOK FOR COUNCILLORS < ENGINEERS, AND SURVEYORS. GEORGE THUDICHUM, F.C.S., LONDON: " THE COUNCILLOR AND GUARDIAN " OFFICES, 29, OLD QUEEN STREI-.T, S.W. V CHAPTER I, INTRODUCTORY AND HISTORICAL. The fact that no work at present exists which deals solely with the modern bacteriological methods of purification must be my excuse for adding yet another to the already long list of books on sewage treatment. Up to the present chemical treatment of some sort has occupied a prominent place in all books dealing with this subject ; and chapters have been devoted to the various methods of disposing of the sludge which necessarily resulted. Innumerable schemes have been propounded by means of which the patentees of a particular process and the local authorities availing themselves of the same but more especially the former were to make fabulous fortunes by recovering the manurial -constituents of the sewage. But times and opinions change, and precipitation, sludge production, and profitable utilisation of the waste matters of the population are no longer seriously considered, although, perhaps, the knowledge acquired during the past few years may render the last-mentioned in some degree attainable. A local authority, brought face to face with the sewage problem, should first of all accept without 90251 hesitation the dictum of the Royal Commission on Rivers Pollution, that sewage is not to be looked upon as a source of profit, but as a nuisance, and therefore something to be got rid of in the cheapest possible way, consistently with efficiency. Such a resolve will at once remove from consideration all schemes suggesting the production of a valuable manure, or of various paying bye-products. Since the Local Government Board insists on a final purification (?) by passage through land, that part of the process to be adopted is settled, in the case of most inland towns, without further debate. Then all chemical precipitation schemes whatever, as pre- liminary to land treatment, should be regarded as taboo and be left quite without consideration, unless in the case of a town, the sewage of which is so> influenced by discharges from the local industries as to be hostile to microbial life or heavily charged with matters which, soluble in the crude sewage, would become insoluble in the course of treatment,. and so choke the bacteria beds. All precipitation processes produce sludge ; sludge is an abomination,, and can be avoided ; therefore, except as stated above, no precipitation need be thought of, and this holds good in the vast majority of cases. Irrigation without previous treatment also* invariably ends in failure, unless the land be of exceptional nature, and of very large area compared with the population to be served. The sewage of London, for example, to be properly treated on a farm without previous removal of the solids, would require, if the soil were of a most favourable nature, one hundred square miles of irrigation area ; and even then any question of crops would have to be subservient to the real object of the farm, viz., the disposal of the sew r age. Setting aside, then, precipita- tion and direct irrigation, there remains bacterial .action in specially prepared areas, which may be called the purely natural method worked under conditions which are readily controllable. In my opinion, there are only two adaptations of this principle which have as yet shown themselves capable of being carried out on working lines on a large scale ; and, in saying this, I intend no hostile criticism of the many ingenious schemes which .are now being exploited. All, save the Sutton system and the Septic tank, are dependent on some special method of construction, of distribution, of heating, or of the preservation of some special condition by means which are artificial, which may fail unless constantly attended, and which in any case cost money. But by either of the two methods mentioned, a constantly good result can be obtained without any difficulties in first construction, without .any mechanical heating or aerating, without any special watching and at a low cost. Which of these two a local authority should adopt is a matter of, to some extent, personal predilection and of local conditions, for the latter will often determine in favour of the one as against the other on purely economic grounds, which it is of course the duty of all Town and District Councils to study, when equal efficiency can be obtained by either method. I need not here discuss the merits of these two systems, as they are considered at length later ; but I would point out to all authorities concerned that in the adoption of a bacterial method of disposal lies their only hope of making sewage treatment yield any reasonable return. The working expenses are extremely low ; the effluent contains phosphates, alkalies, and nitrogen in the form most readily available as plant food, viz., nitrates ; there are no- suspended solids to clog the ground ; and, most important of all, the effluent is fit to discharge into- any stream, however small, whenever the land and the crops are better without it. The economy in working expenses effected by the use of either of the systems named is also a striking feature. The chemicals bill is a heavy one in most precipitation schemes ; and sludge disposal is very expensive, whatever means may be adopted. The cheapest method of sludge disposal is probably that used by the London County Council, viz., the taking it away in specially constructed vessels and discharging it into the sea. The chemicals bill for the Barking and Crossness outfalls is some ^"20,000 per annum ; the ship charges for sludge removal are about 4^d. per ton, or say ^"40,000 per annum, the two items thus amounting to 60,000 per annum, or the interest on two millions of money. Taking the water capacity of a coarse bed at 25 per cent, of its total cubic contents, and supposing each bed to be worked twice daily ; allowing also ^"3,000 per acre (4-ft. deep) for cost of construction ; then London, by the capital expenditure of one million sterling, would effect a clear saving of ^"30,000 a year. I am supposing here, for the sake of argument, that the wages bill would remain as at present, whereas, of course, it would be very largely reduced. The articles written by me for the Councillor and Guardian some twelve months ago, and re-published by the proprietor of that paper in pamphlet form, have had a very wide circulation, and this little book is intended as an enlargement on them and for the same class of readers. I therefore deal with my subject in a similar manner, avoiding points which are at present controversial between scientists, and giving only practical information which may be understood by those who are not professional chemists or bacteriologists. The writing of a correct historical account of the various discoveries and advances which have led up to the present position in our knowledge of sewage purification offers many difficulties. Some observers, intent on particular questions, have noted facts the general application of which escaped them ; others, again, have adapted the knowledge so obtained to the questions they were studying as a whole. The historian therefore has to consider the rival claims of, say, the discoverers of the nitrifying organisms and experimentalists who made practical use of such discovery. This difficulty of correctly estimating the relative value of the work of each individual, and the many claims for priority which have been put forward, will perhaps best be over- come by omitting many dates, giving only those of discoveries or adaptations to which the term epoch- making may be properly applied. Such chapters in the history of sewage treatment are opened by the discoveries or work of Schloesing and Miintz, when they demonstrated the fact of the nitrifying ferment being a living organism ; by the Massachusetts experiments on the nitration of sewage ; by the Barking experiments in continuation of these ; by Scott -Moncrieff, when he proposed the peptonising of the organic matters by one set of organisms, followed by nitrification through the agency of another set ; by Cameron, on the introduction of the so-called Septic Tank; and by Dibdin, when he brought out the now well-known Sutton system. During the years which elapsed between the first and last named (1877 J 896), many observers have come to recognise the great part that was played by organisms in the destruction of waste matters ; and their views are placed on record in writings, too numerous to be more than merely referred to in a work of such limited scope as the present one. The writer will therefore pass at once to a more detailed consideration of the experiments already mentioned as specially marking the various phases in the history of bacterial treatment. Pasteur, many years ago, expressed the opinion that nitrification was due to the action of an organised ferment, i.e., that it was probably a func- tion of a low form of vegetable life. In 1877 Schloesing and Miintz demonstrated that the nitro- genous matters in sewage could be oxidised and nitric acid produced by the slow passage of sewage through a filter composed of quartz sand and powdered limestone, it being evident, from the time that elapsed before nitrification became apparent, that a seeding and growing of germs was necessary before the filter became active. They also showed that the vapour of chloroform prevented the nitrify- ing action. This experiment clearly proved (i) That sewage itself contained a ferment capable of pro- ducing nitric acid from the nitrogen contained in the dissolved organic matter and (2) That this ferment was a living organism. To Messrs. Schloesing and Miintz, therefore, belongs the credit of having con- structed and worked the first bacterial sewage filter. In the year 1889, the State Board of Health of Massachusetts commenced its striking series of experiments on the purification of sewage by filtration. The fact was clearly established that such purification was obtained by the agency of bacteria, and the conclusion arrived at that the necessary conditions were the presence of air and the slow movement of thin films of water in contact with the surface of the bed material. This work of the Massachusetts Board constituted a very great advance in the study of the sewage problem, but it unfortunately did not go far enough, in that the quantity which could be dealt with per unit area of filter was so small as to render the process imprac- ticable, unless under most favourable natural conditions. Acting on the advice of their Chemist, the London County Council took up the work at the point at which the Massachusetts authority had left 10 off, and from 1892 to 1896 continuous experiments were made at the Barking Creek outfall on the bacterial filtration of sewage effluent, with results as set forth in the official reports to the Main Drainage Committee, and fully discussed in a paper by the then Chemist to the Council, read before the Society of Chemical Industry ; and in one read by the present writer before the Society of Engineers, in December, 1896. Briefly put, it was found that sewage effluent, containing in suspension some 7 grains of solid matter per gallon, could be treated on a pan breeze filter bed, 3-ft. in depth, at the rate of about one million gallons per acre per diem, and that the purification effected was far in advance of that obtained by any* method except a well-managed sewage farm under most favourable conditions. Mr. Scott-MoncriefF was the first, as far as the writer is aware, to show that there are two necessary stages in the bacterial purification of sewage, namely, the rendering soluble or peptonising of the organic solids, and their preparation for final oxidation ; and that final oxidation, which in the case of the nitrogen is called nitrification. The plant with which he worked consisted of a filter bed of flint, coke, and gravel, used anaerobically, the sewage passing through from bottom to top ; and of half-channel pipes filled with coke, through which the effluent flowed continuously. This apparatus has since been modified in many essential particulars. Following this were evolved the two principal methods of biological sewage treatment which are now generally before the public, namely, the Septic II Tank and Sutton systems. As both of these will be dealt with at length in subsequent chapters it is only necessary to say here that in each two stages are recognised ; but in the case of the Septic system anaerobic organisms are relied on to perform the first part of the work, whereas at Sutton this is effected, anyhow to the greatest extent, by aerobes ; whilst the final process is identical in the two cases,, being that evolved from the Barking experiments. All other so-called bacteriological methods may be considered as developments of these two. The principle in all is practically the same, the differences- being those of special construction, bed material, methods of distribution, and so on. A host of inventors, each claiming some improvement over the original, was a necessary corollary of the publication of the Sutton and Exeter results. All of these, with which the writer has acquaintance, will be discussed later on. Any historical sketch of the growth of know- ledge in this regard would be incomplete without some mention of the so-called intermittent downward filtration, as suggested to the Rivers Pollution Commission by the late Sir Edward Frankland, and put into active and successful operation at Merthyr- Tydvil by the late Mr. Bailey Denton. This method is practically that of the modern bacteria bed, and its failure to make a permanent stand as the true system of purification is due almost entirely to the fact that its promoters, whilst recognising its powers, failed to realise the true causes of its action, and therefore did not take care to supply the conditions 12 which are now known to be essential. If the land be porous enough and not too deep, and the drains can be locked so as to retain the sewage in contact with the soil for a definite period, an area prepared for intermittent downward filtration is the exact counterpart of the Barking or Sutton bacteria bed. In Massachusetts, at the present time, many acres are being so laid out, the soil being a coarse, clean sand, which lends itself admirably to the purpose. CHAPTER II. THE SU.TTON SYSTEM. The Sutton or aerobic system of sewage purifi- cation is the natural outcome of the experiments on sewage treatment made by the Metropolitan Board of Works and the London County Council between the years 1884 and 1896. When the writer first entered the municipal service, in February of the former year, the then Chemist, Mr. W. J. Dibdin, had already grasped the fundamental truth that any process of sewage purification must be designed rather to foster- the organisms, by which the purifi- cation was completed, than to hinder or destroy them. Dr. Dupre, who acted as consultee during the first three or four years of the experiments, holding similar views regarding the powers of microbial action, the whole of the work was carried out with that object in view. Chloride of lime, at first used as a deodorant, was abandoned in favour of manganate of soda, principally because the latter killed the smell without killing the organisms, whereas the former acted as a regmicide. Pro- longed experiments were made on aeration, with a view to assisting the aerobes in performing their functions. The quantity of chemicals employed for precipitation was reduced to the lowest possible, not merely from economical considerations, but also to prevent any antiseptic action which might arise from a free use of lime. Seen in the light of present knowledge, it is clear that all these things were done with a definite purpose, namely, the preservation of the micro-organisms, and the ascertaining of the conditions necessary for their well being. But in 1887 public opinion was not on the side of the biologists. When, in that year, in the course of a paper read before the Institution of Civil Engineers, Mr. Dibdin suggested that the proper way of treating sewage would probably be found to consist in the addition of a cultivation of the proper organism, whatever it might be, and quoted Dr. Dupre in support of his contention, the whole audience and the theatre was well filled laughed heartily. Dr. Angell alone, amongst those taking part in the discussion, saw the possibilities of such a method, and characterised the conception as "philosophical, scientific, and reasonable." It is true that the actual method suggested, viz., adding a charge of the proper organisms to the sewage, has not proved itself the correct one ; but adding the sewage to the proper organisms, carefully cultivated under fitting conditions, can hardly be said to differ in principle ; it is merely another method of application. Recognising the great value of the experiments of the Massachusetts State Board of Health, the Main Drainage Committee of the London County 15 Council in 1892 decided to make further investiga- tions in the same direction, with a view to ascer- taining if the results, which till then had only a purely academic value, could be so far extended as to be capable of being applied practically and on a large scale. With this object several small filter beds were built and filled with various materials, to determine in the first instance which was best for the purpose ; and finally, a bed covering exactly one acre was prepared and filled to a depth of 3 -ft. with pan breeze, the latter being weighted with a few inches of pebbles. The results obtained from the use of this filter are now well known over the whole world, and need not be repeated here. In 1894 Sutton laid out a sewage farm and works at a cost of 66,000. The system adopted was one of chemical precipitation, followed by arti- ficial filtration through a patent material, the sludge being pressed into cake. In 1895, however, the Sutton Local Board found itself quite unable to meet the requirements of the Thames Conservancy, owing to the failure of the filters to deal with anything like the quantity of tank effluent which they were intended to take. Under these circumstances Mr. Dibdin, then a member of the Board, was consulted, and proposed the supplementing of the existing patent filters by others made on the Barking model with coke breeze, and later with burnt ballast. The immediate result was a marked improvement in the quality of the final effluent. The sludge trouble, however, remained. In 1896, therefore, Mr. Dibdin, having already counselled the London County i6 Council to make experiments on a large scale with crude sewage, suggested to the Sutton authority the advisability of trying whether such a bed, of coarse material, could not be made to take the place of chemical precipitation and sludge pressing, by des- troying in its interstices the whole of the suspended solids. The suggestion was at once adopted, and the first coarse grain bacteria bed received its first charge of crude sewage in October, 1896. The experiment proved eminently successful. This original bed, having an area of 186 square yards, and a depth of 3|-ft. (altered during some time to 5-ft.) has up to now dealt with 22,000,000 gallons ot crude sewage, which had undergone no previous treatment beyond straining; has destroyed 185 tons of dry solid matter, equal to one-half its own total cubic contents; has been filled 2,000 times, or an average of 2^ times each day, including all rest periods ; and still treats 20,000 gallons of crude sewage daily. The Sutton Authority, quick to grasp the importance of this revolution in sewage treatment, at once proceeded to prepare other beds similar to the first, paying for the work out of revenue. As each enlargement only confirmed the results obtained in the first instance, the Urban District Council finally decided to apply to the Local Government Board for sanction to obtain a loan and finish the conversion of the works without further delay ; but the Board censured the Sutton Council for having taught the world how to treat sewage and refused the sanction asked for. No obstruction, however, I? can prevent advance based on scientific truths, though it may for a brief period delay it ; the Sutton Council is continuing the alterations, paying for them, as before, out of revenue ; and the aerobic biological process is replacing the cruder and out of date precipitation methods all over the world. In the Sutton method, the sewage passes first of all through a grid, or sieve, to remove large pieces of floating matter, which otherwise, being retained on the top of the bed instead of penetrating its interstices, would tend to clog the surface. In the case of a town sewered on the " combined " principle i.e., where the s^ame channels convey sewage proper and also surface and storm water provision must be made for intercepting the road grit, which would otherwise enter the beds and steadily diminish their water capacity, besides preventing free aeration. Unless the particular sewage contain some specific germicidal ingredient in large quantities, or some other manufacturing refuse of the kind alluded to in the introduction, no other preliminary treatment whatever is necessary. The screened sewage is then passed into a coarse-grained bacteria bed. This consists of a tank, either built or formed merely by excavating the ground when conditions are favourable, filled with coke, burnt ballast, broken brick or clinker or other suitable material of a size which will all pass, say, a 3-in. ring, and from which all the finer part has been removed by riddling. In the latest experi- ments of the London County Council walnut-sized material was chosen. The bed is provided with B i8 some means for preventing the sewage from always- entering on the same spot, although elaborate sprinklers or other special means of distribution are quite unnecessary ; it is also underdrained in the simplest manner with agricultural drain pipes laid open-jointed, and leading to the discharge point ; and is provided with inlet and outlet valves of some kind. It can thus be seen that the con- struction of bacteria beds is a very simple operation ; but their size, number, depth, nature and grade of material and working capacities must be deter- mined in each case by the expert, after full con- sideration of all the local circumstances. The sewage flows into such a bed until the water level has nearly reached that of the bed material ; the inlet valve is then closed, and the bed allowed to stand full during about two hours. If much longer time is allowed there is danger of anaerobic action replacing the aerobic ; if much less, insufficient time is given to the organisms in the bed to perform their proper function. During these two hours the suspended matters are deposited in the interstices of the bed and are partly solu- tionised ; whilst the organic matter in solution is also attacked and oxidised to the extent of about one half. The bed is then emptied on to another similar in construction, but filled with finer-grained material, and a resting period of equal duration is allowed. In this fine-grain bed any small quantity of sus- pended solids that may have escaped the coarse bed is finally arrested, rendered soluble and oxidised ; and the purification of the dissolved matters is 19 continued. In cases where a very high degree of purity is essential, as, for example, when the volume of the effluent is relatively large when compared with that of the stream into which it flows, and the latter serves as the source of a town water supply a short distance below the point of discharge, a third treatment on another similar bed may be given, the bed material in this case being again finer than before, say coarse sand. Such a third treatment has been adapted at Hampton, Middlesex, on the advice of Mr. Dibdin and the writer ; and the effluent produced, from a very foul and highly polluted sewage, is probably the best that has up to now been discharged from any sewage works as a matter of daily routine. The work of a bacteria bed has not finished when the effluent has been discharged. There re- mains in the bed the sludge, of which only a portion will have been dissolved and oxidised whilst the bed was full. The interstices of the bed being now filled with air, which replaces the water as the latter flows away, the se'robic organisms are provided with the conditions necessary for their well being and rapid reproduction; they have food, moisture, ox)gen, darkness, and an even temperature. Under these circumstances the deposited organic matters are rapidly attacked, and in the course of a few hours the bed is ready for another charge. The quantity of sewage with which a bacteria bed can deal daily is a point regarding which at present no universal rule can be laid down. The Local Government Board at present insist that a 20 bed shall be used once daily only, and fixes the water capacity arbitrarily at one quarter of the gross con- tents. On these lines, therefore, a bacteria bed can only treat one quarter of its volume each day ; in other words, for each cubic foot of dry weather flow there must be provided four cubic feet of bed material. The apparent object of the Board in demanding this capacity is to enable a certain volume of storm-water to be dealt with in exactly the same way as ordinary sewage, and this poiM will be fully discussed in Chapter VI. It is quite clear from practical experience that bacteria beds may with advantage work twice daily ; in fact in many cases better work will be done than if they are only filled once. The original bed at Sutton has been filled, as already pointed out, more than twice a day on an average taken over three years. There is, however, a disadvantage in too frequent working", in that the water capacity becomes diminished and less sewage can be treated at each charge. Twice a day would seem the best for regular working. Setting aside, then, any considerations due to the exceptional strength or degree of dilution of the sewage to be purified, or to its containing ingredients requiring particular treatment ; accepting also the 25 per cent, water capacity fixed by the Local Government Board ; then one million gallons of sewage, the beds being filled twice daily, will require 320,000 cubic feet of coarse beds, and practically the same of fine, or a total area for the double treatment, if 4-ft. deep, of 3f acres. It will of course be understood that in 21 times of storm this area could deal with an enormously increased volume, in the manner shown later. Fine-grained beds can be worked constantly at a higher rate, but in order to ensure regularity in the times of filling, emptying, and aerating it is advisable to have them correspond exactly in number and in water contents with the coarse-grain beds, and to work the whole system in pairs. A feed culvert common to all the fine beds may be provided in case it is required to throw one of them o-.t of action, but it is not needed for regular work. It has already been observed that no special distributing apparatus is required. Many such have recently been invented and patented, but their use is confined to filter beds which are intended to work continuously, as otherwise there is a danger of the sewage finding its way from inlet to outlet by too direct a passage. There is, of course, no such danger in the case of a bed worked on the Sutton principle. I shall deal later with some of these special distributors, but with Sutton beds they need not be further considered. Heating apparatus, I think, should be entirely condemned. In the first place, it is not needed when bacteria beds are used, since the temperature is kept constantly elevated naturally, as in a hot bed. Secondly, the expense of warming any considerable volume of sewage is quite prohibitive. This, of course, can be readily demonstrated by a simple calculation. A first-class steam coal yields 15,000 heat units per pound, i.e., one pound of coaL = -SMeBQsing the whole heat of 22 combustion could be utilised, will raise i5,ooo-lbs. of water i degree Fahrenheit. To raise the tem- perature of i million gallons of sewage 10 degrees would require a coal value equal theoretically to about 3 tons. But in actual practice only a portion of this could be really used, say 25 per cent ; the daily coal consumption would therefore be 12 tons. Let us imagine this applied to London : 200 million gallons a day at 12 tons of coal per million gives a yearly coal requirement of 876,000 tons. A similar calculation applied to the city of Leeds shows that to raise the temperature of the sewage 10 degrees Fahrenheit would require 96,360 tons of coal per annum, which at 10 shillings per ton would cost, in round figures, ^"50,000. Supposing the heating process to be applied only during four winter months, the ridiculous nature of the proposition is still sufficiently apparent. But in addition to the cost being prohibitive, it has been proved over and over again that no such assistance is really needed. The Barking filter, during the great frost of February-March, 1895, was covered for weeks with a sheet of ice, with openings only in the immediate neighbourhood of the outlets from the distributing trough ; yet the bed was worked throughout this period with perfect success. In the Massachusetts experiments it was shown that even the American winter did not prevent the bacterial filters from doing their work ; the only result of prolonged severe frost was a decrease in nitrification, involving storage of nitrogen in the beds, and a consequent loss of water 2 3 capacity. In the spring nitrification was resumed with renewed vigour, and by early summer the whole of the stored material had been oxidised and got rid of. In the Leeds experiments, where a careful record of temperature was kept, it was found that the body of the bed was always warm ; and in an experiment now proceeding in the north of Scotland on the purification of distillery refuse, the tempera- ture of the beds is frequently 30-40 degrees Fahrenheit higher than that of the external air. Therefore, as they are both needless and expensive, no local authority need consider the question of heating arrangements. The only mechanical appliances which can with profit be applied to bacteria beds are those for automatically controlling the operations of screening, filling/ standing full and emptying. Messrs. Smith and Co., of Carshalton, Surrey, have patented a very ingenious arrangement for performing the first named operation. It consists of a water-wheel driven by the sewage itself, which causes an endless band of wire-net to revolve slowly, thus catching and lifting out all suspended matters beyond a certain size ; a brush revolving in an opposite direction cleans the net as its passes, and the solid matters are automatically cleared to one side, ready for final disposal by burying or otherwise. Of filling and emptying apparatus, there are two that claim special notice Cameron's, which works by an arrangement of tipping buckets, which open and close valves, .and which is the property of the Septic Tank Syndicate ; and Adams', which 24 depends on syphon action. A great advantage of the last-named lies in the fact that the syphon can be set to discharge at any fixed time after the water level in a bed has reached a certain height, and consequently each bed is perfectly independent of the others. 27 -DESCRIPTION OF ADAMS' PATENT AUTOMATIC /FEED AND TIMED WITHDRAWING SYPHON FOR SEWAGE FILTRATION. The Automatic Feed consists of a simple cast iron trap. This draws its supply from the sewage channel, the sewage passing through to the filter bed only when the air pipe con- nected has a free outlet, i.e., when it is not immersed in liquid. Sewage rises in the filter bed, surrounds the dome attached to the air pipe, and forces the air from within to enter the feed, preventing (by pressure of air) the further passage of sewage through it. The dome may be placed in any desired bed, and may shut off a supply to that in which it is placed or to another. Thus the discharge of one bed will unlock the feed to another, -whilst the filling of a bed will shut off the supply to another. The operations are absolutely automatic and without movement. The use of the controlled syphons makes it possible for a filter bed to stand full for any desired interval of time, and then discharge automatically These syphons depend for their action upon the escape of air from within. A ball float, attached to a plain through way valve on the escape pipe, allows of this, the float being set to lift at top water level. An outer dome, called the air dome, is placed over the syphon and float, to which entry of water can take place only as the air contained therein is displaced. The escape of air thus displaced is through a small stop cock. The interval occupied in this escape, and the consequent entry of liquid within the dome (until the level of float is reached), is the time during which the syphons will stand with sewage around them. The moment the float is moved the syphon starts and discharges the contents of the bed. The syphons may be set to stand for any period from a quarter to four hours. Thus, without manual labour, and without moving sluices or valves, &c., the automatic filling, standing, emptying, aerating, and re-filling of sewage filter beds, is brought about in the simplest possible manner, regardless of the volume dealt with. CHAPTER III. SUTTON PROCESS (CONTINUED). It is held by many that anaerobic action is not only useful but is actually essential in preparing the organic matters in sewage for their final oxidation ; . and the Sutton coarse grain bacteria bed method has been described as an attempt at performing anaerobic work under aerobic conditions. Whilst fully alive to the powers of the anaerobic organisms, I do not by any means regard them as essential, and a close study of a bacteria bed certainly leads to the belief that the action is really aerobic, only a very small part of the work being otherwise per- formed. This is borne out by the undoubted fact that the powers of such a bed decrease if the aeration decreases, as by surface clogging. In the scheme recently adopted for the treatment of the sewage of Manchester, the experts advising the City Council have evidently acted in the belief that preliminary anaerobic action is at any rate of great advantage ; and it certainly does possess a very equalising effect upon the flow, inasmuch as the 2 9 sewage, which varies continually in strength as it arrives at the works, becomes blended into one whole in the septic tank. In this connection I feel that attention should be called to the fact that the Manchester system of " double contact beds " is actually nothing more than the Sutton bacteria beds preceded by a Septic Tank. Palmam qni meruit ferat : and it is at least remarkable that no acknowledgment whatever has been made regarding the source from which the knowledge utilised at Davyhulme was obtained. This source was the works of the Sutton Urban District Council, sup- ported by the published work of Mr. Dibdin and the present writer ; and the Manchester authorities have learned, at doubtless no small expense, that which had been experimentally demonstrated before they commenced their investigations. The system is not patented or protected in any way, and any person has a right to take it up and use it ; but it is certainly unfair to take the product of other men's brains and years of work and, by giving the method another name, deny to those men the credit that undoubtedly belongs by right to them. But some general good may be found to arise even from the action of the Manchester experts, in that they have declared in evidence that after numerous experiments and most careful investigation, they have arrived at the conclusion that this system is the proper and the only one, not alone for Manchester but for the whole world. I have so far dealt with the Sutton System in its relation to the treatment of the sewage of towns; 30 but it is also particularly applicable to the purifica- tion of waste matters from small communities and individual houses. At Radley College, for example, the sewage difficulty has been completely overcome by allowing the overflow from a large cesspool to pass into coarse grain coke bacteria beds, which are used on alternate days, each bed being of sufficient capacity to take a whole day's flow. When the sewage is diverted to the empty coarse grain bed, the contents of the full one are passed into a fine grain coke bed, where they remain for two hours, and are then finally discharged. When last I inspected this effluent, it was water-white and absolutely inodorous and tasteless, and it proved on analysis to be of exceptional purity. A very similar installation has recently been put up in the grounds of a large country house in Sussex ; and, in this case, the effluent passes through an ornamental channel into a small fish pond. The method has also been successfully adopted at lunatic asylums and isolation hospitals. It possesses the great advantage of being workable on any scale, a bed dealing with a pint of sewage at a time giving results quite com- parable with those obtained on an acre. In order to make the erection of very small plants simpler, Messrs. Adams & Co., of York, have devised a self-contained set consisting of two coarse beds and one fine one, with automatic feed and timed-discharge syphons. Such sets are readily transported and fixed, and should prove of great benefit to the owners of small country houses. I do not propose to burden my readers with many tables showing analytical results ; but some may be usefully studied as showing of what the method is capable in typical instances. At Sutton, for example, the sewage is purely domestic, contain- ing no factory refuse whatever. It is, however, collected on the separate system and is very concen- trated and foul. The following short table gives the average of the analyses made for the Sutton Council during the twelve months ending on March 3ist, 1899. Here, and throughout the book, the analyses are given in parts per 100,000. Ammonia. Oxygen Absorbed. Nitrogen. T3 T3 o5 c/i c a3 8 '5 s BS and all these effluents were perfectly amenable to treatment on fine beds. A very interesting point in connection with beds filled with these materials is that relating to their water capacity as compared with coke or ballast. The coarse bed effluent pro- duced by these last mentioned materials is distinctly superior in quality to that obtained from chalk, granite, or slate ; but whereas the water capacity of the ballast bed cannot be taken at more than 20-25 per cent, if constantly worked, the water capacity of a granite or slate bed remains at 48-50 per cent. If, then, continued experience shows that the fine grain beds can deal with the granite or slate effluent equally with that from coke or ballast and my 34 experience of the Barking filter would certainly lead me to that opinion it may easily be possible to reduce the area of coarse bed required by one half. This of course is only applicable where fine beds are to be provided ; in the case of a town dis- charging into a tidal river or the sea, one treatment only would be necessary, but it must not be with slate or granite. CHAPTER IV. THE SEPTIC TANK SYSTEM. In 1895 Mr. Donald Cameron, City Surveyor of Exeter, having become convinced as a result of experiment that the solid matters in sewage were capable of being dissolved and destroyed by the action of anaerobic micro-organisms, erected an installation intended to treat sewage in that way, .the first portion of the work being performed anae- lobically in a closed tank and the final purifica- tion aerobically in clinker filters made after the Barking pattern. Immediate success attended Mr. Cameron's efforts and the principle of the Septic Tank was at once established. The main difference between this method and that adopted at Sutton lies in the fact that in the former case anaerobes and in the latter aerobes are chiefly relied on to effect the solution of the sus- pended solids and-the preliminary breaking down of 36 complex organic substances. I say chiefly advisedly,, since theie is no doubt that a certain amount of anaerobic action takes place in a Sutton bacteria bed, anyhow when full ; and it has been shown experimentally that the aerobes in sewage multiply in a greater proportion than the anaerobes during the passage through the Septic Tank. But judging from the chemical results the action of the Tank is- mainly anaerobic and that of the Sutton bacteria bed aerobic. The installation at Belleisle, Exeter, with which the experiments were principally made, and! which was used as a model for the larger works to- deal with the whole sewage of Exeter, consists essentially of a grit chamber, a Septic Tank, and five filter beds, of which four are constantly at work and one held in reserve. The tank has a capacity of about 54,000 gallons, which represents roughly 1 8 to 20 hours' flow of the sewage of the district with which it deals. The grit chamber is an integral part of the tank, and is formed by building a wall across the tank, about y-ft. from the inlet end and i foot below the surface of the liquid in the tank; and is divided into two portions by a wall along the median line. In the chambers thus formed,. the velocity of passage of the sewage being only some 2-ft. per hour, the whole of the grit and road detritus carried down the sewer is deposited, and the sewage which passes on into the tank proper contains only traces of mineral suspended matter. In the tank, which has a total length (including the grit chamber) of 64-ft. io-in., the sewage sojourns 37 for 1 8 to 24 hours, according to the volume of water supplied by the sewer ; and during this time the organic matters in suspension are dissolved, and .both they and those in solution are broken down .and simplified by microbial action, so that the ^effluent which finally leaves the tank is already oxidised to the extent of some 50 per cent., whilst the whole is in a condition to be readily purified in the oxidising aerobic beds. The tank is constructed of cemented bricks and is covered with an arch -of similar material. From the tank the effluent flows, by means of a pipe, the inlet of which is below the water level in the tank, into an open chamber, the outlet from which is provided with a V-shaped notch for the purpose of gauging the quantity passing at any given time. It then enters a trough closed at both ends and fixed carefully in a horizontal position, so that the water escapes over the sides in a very thin layer, and is thereby aerated ; and from thence on to the aerobic beds. These are filled with furnace clinker, excepting one, which is made with coke breeze, and have each an area of 80 square yards and a depth of 5-ft. By means of a most ingenious apparatus, designed and patented by Mr. Cameron, the filling, standing full, emptying, and resting empty for aeration are regulated automatically. One filter is filled at a time ; it stands full whilst the next is filling, and is then discharged, standing empty whilst the third and fourth are filling. It will be seen that the method adopted is not that of filtration in the ordinary sense, but is a 38 replica of that which had been found at Barking to- yield the best results, viz., locking the bed so as to compel the contact of the tank effluent with the bed material for a certain period of time. In this regard the Belleisle installation was defective, in that the time of contact depended on the rate of flow of the incoming sewage and consequently varied greatly ; but this has been modified in the larger scheme so as to ensure a more nearly constant period of resting full. The effluent produced by this double process is an admirable one. It is clear, colourless, and inodorous ; does not putrefy on keeping, and always contains appreciable quantities of nitrates. It is fit to discharge into any stream and contains nothing injurious to fish life. It would also appear, from evidence given by Dr. Pickard at the Local Govern- ment Board Inquiry at Exeter, in November, 1897,. that the system constitutes a great protection against the dissemination of disease, more particu- larly of typhoid. Experiments showed that by the passage through a tank from 70 to 90 per cent, of typhoid organisms originally added were destroyed ;. 88J- per cent, of the remainder were killed in the filter beds ; and the few that survived were so greatly enfeebled that there was practically no> chance of their becoming dangerous. The process that takes place within the Septic Tank is two-fold mechanical and biological. It was found by experiment at the Barking Creek, outfall works that sedimentation was practically effected if the rate of flow of the sewage in the 39 settling channels did not exceed three feet per minute ; and since the rate of flow in a Septic Tank is very much less than this at Belleisle, the average is about two feet per hour it follows that the whole of the suspended solids must be pre- cipitated before travelling far from the inlet end of the tank. These solids falling to the floor of the tank, remain subject to the attack of the micro- organisms, and are partly rendered soluble. In time the particles become buoyant, owing to the entangling of gas bubbles generated during the process, and rise to the top of the tank, forming a thick, leathery-looking scum. This scum is in a very high state of bacterial activity, the process of liquefaction progressing freely ; and the matter which finally falls back to the bottom of the tank is a black, powdery humus, quite inoffensive and of very small bulk when compared with the original suspended solids from which it is derived. In the case of the Belleisle plant, for example, the whole deposit after fifteen months' working was only 80 cubic yards ol sludge of 87 per cent, moisture ; whilst the original bulk of the suspended matters would represent, as sludge, over 600 cubic yards. And even this small deposit no doubt still contained matters upon which the bacteria were capable of acting further, and it must therefore not be taken as representing the final results of the tank's operations. The leathery scum above alluded to forms with great freedom and makes an almost impervious covering, beneath and on the under surface of which 4 the micro-organisms appear to thrive under anaerobic conditions, even when the tank is not roofed. The experiment has been tried at Sutton as a temporary expedient to avoid the making of sludge whilst converting precipitation tanks into coarse grain bacteria beds ; and it is now under observation at Manchester, where it seems to be viewed with favour by the experts who are advising the Town Council of that city. Should experience prove that sufficient anaerobic action can be ensured by using the scum as a protection against the admission of atmospheric oxygen, the Septic process will be in an even more favourable position than at present, since the construction of a roof which it was supposed must be practically air- tight over a large tank, or series of tanks, is necessarily a somewhat costly operation. There is, however, the possibility of nuisance to be con- sidered, since an open Septic Tank would have a most powerful and foetid odour, which would be very pronounced in the event of an accidental disturbance of the scum ; and this alone would make it desirable to cover the tank, unless far removed from houses. It is also possible that variations in temperature would take place more readily and so militate against the complete success of the open tank. A great virtue of the septic method lies in the fact that only one loss of head is required in the great majority of cases, instead of there being necessarily two as with the Sutton system. Where fall is slight, this is a great consideration. The 4 1 sewage leaves the Septic Tank at the same level as that at which it enters, and the oxidising bed need not necessarily exceed 2-ft. in depth ; therefore the whole process can be accomplished with a fall of about 3-ft. In other cases also, in which the fall is sufficient as a whole but very gradual, aerobic beds must be made shallow and therefore cover a very large area of land, whereas a Septic Tank can be made any depth and can replace the coarse bed area by a very small one, leaving such freed area available for irrigation or other purposes-. Occasions will arise, with the Septic as with the aerobic method, where a peculiarly obstinate sewage is met with, which will not .yield sufficiently good results with the ordinary plant. In such cases a second set of fine grain bacteria beds must be provided. This has been done in the trial installation at Yeovil, where the Septic System is in course of adoption. The sewage of Yeovil is of a particularly foul nature, the principal industry of the town being felt- mongering and glove leather making ; and the effluent from the first set of beds was not quite satisfactory. When, however, a second set was added, a good effluent was produced, and the instal- lation to deal with the whole sewage of the town will be on these lines. The effluents at Belleisle have been analysed by many chemists, the results being almost uniformly good. The following table gives the analysis of various samples of tank and of final effluent, with the name of the observer. 4 2 Ammonia. Qxygen Nitrogen as Free ausoroea in Nitrus Observer. and Saline. Organic. 4 hours. and Nitrates. Tank effluent 4*03 0-69 2' traces. f Pearmain {and Moor. ,, 3'94 0-25 2 ! o- J Dibdin and ( Thudichum ,, 4'9 0-64 4^2 0-04 Rideal. ,, II-2 2-66 273 0-022 n ,, 5'6 243 0-05 Dupre. Final effluent i-6 5 0-15 0-47 i'4 j Pearmain |and Moor. ,, 2-43 O'll 0'55 0-864 f Dibdin and ( Thudichum ,, 2-48 078 03 Rideal. M 6-05 I-I3 i -06 M 2-91 ~ 078 1-16 Dupre. By the courtesy of Messrs. Cameron, Commin, and Martin I am enabled to give a sketch of the Septic Tank installation recently erected to deal with the sewage of Barrhead. The works .are designed to serve a population of 10,000, and to purify a maximum flow of sewage and storm-water of 400,000 gallons per diem. There are two grit chambers, four Septic Tanks, and eight fine grain bacteria beds, all constructed in concrete. Each of the tanks is loo-ft. long by iS-ft. wide by y-ft. deep at low water, the capacity of the four to this level being about 312,500 gallons. Above this there is storage for about 70,000 gallons of storm- water, the quantity flowing to the filters being kept constant by means of two controlling modules. Each filter- bed is 55-ft. long by 54-ft. wide, and is filled to a 43 depth of 4-ft. with broken furnace clinker. Six of these beds form the ordinary working set, the other two being held in reserve. The total nitration area is about 2,540 square yards. <* CHAPTER V. OTHER BACTERIAL METHODS. I propose in this chapter to sketch briefly the special characteristics of some of the more promi- nent of the many variations of the bacterial process, viz., those associated with names of Scott Moncrieff, Lowcock, Adeney, Waring, Garfield, Ducat, and Whitaker. Mr. Scott Moncrieff, as already pointed out, was without doubt amongst the first of investigators who recognised the two stages in the bacteriolysis of sewage, viz., preliminary solutionising and simplifying followed by oxidation. In accordance with these views he erected a filter bed to deal with the sewage of a private house. The grease was, as far as possible, kept back by a grease-trap, and the sewage, entering at the bottom of the filter bed, passed upwards through a false bottom and then through successive layers of flint, coke and gravel. In this filter, worked under anaerobic conditions, it was found that the solid organic matters were broken down and dissolved, and an effluent was produced comparable to that obtained from a septic 4 6 tank. The effluent from this filter passed into what Mr. Moncrieff terms nitrifying channels, these originally consisting of half channel pipes jointed with cement and filled with coke. These are now replaced by trays, through which the effluent passes successively, and judging from some analytical data laid before the Sanitary Institute Congress at Southampton in September of the present year, a remarkably high degree of nitrification is attained, the loss of nitrogen during the process being only about 25 per cent., and the final effluent containing 9-0 parts of nitric nitrogen per 100,000. For the details in the first portion of this sketch I am indebted to a report by Dr. Houston, pub- lished in 1893, whilst the nitrification figures are taken from the paper already mentioned as having been read at the Sanitary Congress at Southampton. Lowcock's patent filter, as shown in a pamphlet dated 1894, was constructed of the following materials, in order from below upwards: 12 inches pebbles, 6 inches bean gravel, 2 feet 6 inches pea gravel, 12 inches pebbles (with air pipes), 4^- inches bean gravel, 4$- inches pea gravel, and 9 inches sand. In the upper layer of pebbles .are embedded perforated pipes, or pipes laid with open joints, by means of which air is forced into the body of the filter by a blower or other arrangement. In this process the filter is supposed to work continuously, the necessity for .emptying the bed for aeration being assumed to be obviated by the constant pumping of air. It has been claimed of this filter that the area required is 47 far less than is the case with other methods, but a modern bacteria bed will deal with a million gallons per acre per day of "tank effluent" such as was used by Lowcock in 1893 5 an( ^ Lowcock's filter then treated on an average 353,800 gallons per day ; or, in other words, the powers of this patent filter were only half those of a coarse grain bed dealing with- crude sewage, or one third those of a fine grain bed dealing with clarified effluent. All the necessary air can be supplied by working the beds inter- mittently, instead of having to pump ; and the construction of the bed is wrong in principle, inasmuch as the upper layer should admit the solids and not prevent their entrance into the body of the bed material. Adeney's process differs from all the others mentioned in this chapter in that no filters of any kind are employed, and the oxygen necessary for the well-being of the organisms is supplied by chemical and not by mechanical means. The sewage first undergoes a process of subsidence, by which some 90 per cent, of the suspended solids are removed (see pamphlet of The Oxygen Sewage Purification Company, Limited, 1895) ; on passage into another tank the settled sewage is treated with crude manganese compounds, which, it is claimed, can be profitably recovered ; then direct chemical oxidation is accomplished by the use of manganate of soda ; and finally the effluent is treated with nitrate of soda. I believe that the intermediate treatment with manganate of soda has been abandoned, and no doubt it would be found very 4 8 costly ; in a paper read before the Sanitary Institute Congress at Leeds, in 1897, b y Mr - Kaye Parry, Adeney's method is summarised as follows : " (i) Clarification under the best conditions by the " use of a precipitant, at once the most effective " and economical at present obtainable ; (2) purifi- " cation of the clarified liquid in the simplest "possible way by supplying it with a sufficient " quantity of oxygen through the agency of nitrate "of soda; (3) the production of the minimum of "sludge, inodorous and incapable of creating a " nuisance." It appears strange nowadays to find any practical person advocating the manufacture of sludge, a product which has been the main cause of trouble in most sewage works, and this alone would appear to condemn the process advocated by Mr. Adeney. The addition of nitrate of soda also appears to be a very expensive method of furnishing oxygen, and can, in addition, not be looked upon as a safeguard against after-putrefaction should the previous purification of the effluent not have been carried sufficiently far. The presence of nitrate produced from the nitrogen originally existing in organic matter in the sewage may be safely thus regarded, since it shows that the mass of putrescible substances has been broken up and oxidised ; but experiments made ten years ago convinced me that with a bad initial effluent, such as that from the precipitation tanks at Barking Creek, the addition of nitrate was of little or no value. The next process we have to consider is that suggested by Waring, and it is sufficiently striking 49 in that it may almost be looked upon as a parent of the Sutton method. Waring proposed to allow crude sewage to pass continuously through a coarse grain filter until it became choked by suspended matter, and the oxidise this last by forcing air through. There can be no reasonsable doubt that such a method could be successfully worked, but it could not compete with a process in which no machinery is employed, as the pumping of air is necessarily wasteful and costly, and difficult to apply on a very large scale. It was suggested that four such straining filters should be employed, allowing to each a period for aeration three times as long as the period of use. Purification was to be completed in nitrifying filters worked continuously and supplied with an air blast constantly in use. Garfield has arranged a filter constructed of coal, graded in various sizes, for which great success is claimed. I have, however, been unable to find any special virtue in coal, as compared with say coke or cinder. In or about the year 1895, whilst in charge of chemical operations at the Barking outfall, I carried out a series of comparative experiments with two small filters, filled the one with coal and the other with coke ; and the results failed to indicate that any special advantage was held by one material over the other. This also appeared to be the general consensus of opinion when the matter was discussed at the Southampton Congress during the present year (1899). Garfield's filter is worked on what may be termed the intermittently-continuous system ; the sewage effluent is passed through 50 continuously for 12 hours, and then a like period is allowed for rest and aeration. Ducat's patent self-aerating filter is constructed on a novel plan. The walls are built of drain pipes with the inner ends at a slightly lower level than the outer, and there are layers of aerating pipes passing quite through the bed material. It is intended to purify sewage in one operation only. It is supposed that owing to its construction there is free circulation of air throughout the substance of the filter ; special means of distribution are provided, also a roof, walls, or other arrangements to yield shelter from wind and cold, and a heating apparatus of some kind. With regard to this latter I have already written ; in the case ot the ordinary Sutton bed or Septic Tank, it is not required, and it must be in any case very expensive. Distributing gear is also something to be avoided where possible, and the necessity for its employment must always militate against a process ; and roofs and walls must also add considerably to the initial cost of the installation. Whitaker also has a patent sprinkling gear and heating apparatus, which are, of course, open to the same objections. When large quantities of sewage are to be dealt with, all alterations and improvements in works should tend towards simplicity. Distributing troughs that must be set level to within a hundredth of an inch are sure to give trouble; whereas with a Sutton bed, the roughest bit of plank troughing will suffice. The same applies to sprinklers and heating 5 1 apparatus, and neither the Sutton nor the Septic system needs a great coat in the winter time. The principle on which the majority of the latest patent processes are supposed to work is the aerobic bacterial, but all appear to me to be greatly inferior to the original in that without producing better results, they one and all depart from simplicity and travel in the direction of complexity, and therefore of increased original cost and trouble of working. CHAPTER VI. THE TREATMENT OF STORM WATER. The question as to what degree of dilation should be attained by sewage during storm periods, before it may be safely discharged into a stream with- out treatment has been much discussed recently, but whatever may be the views of individuals regarding the subject, an Authority preparing a sewage disposal scheme has no option but to follow the rule laid down hy the advisers of the Local Govern- ment Board. This rule which, generally speaking, is a fair and reasonable one is shortly as follows : there must be treated exactly as ordinary sewage a mixed volume of sewage and storm water equal to three times the normal daily dry w r eather flow;, an additional volume equal also to three times the normal dry weather flow must be treated by passage through a special separate storm filter of proper extent or on an area of land used for this purpose only ; and any excess may then be permitted to dis- charge directly into the stream. The maximum rate at which storm water may pass through a special storm filter is 500 gallons daily per square yard. It will be seen that before a storm overflow 53 can come into operation under these rules the sewage must have been diluted by the addition of five times its bulk of water. Without entering into any discussion as to whether this requirement is excessive or not, it may safely be agreed that it is anyhow sufficient. The first rush of storm water is frequently, as is well known, much fouler than the ordinary sewage, owing to the washing down of matters accumulated in the sewers, and from the surface of roads and yards ; and this of course more particularly after any continued spell of dry weather. But after a short time this flush will have done its work and what arrives at the outfall will only be normal sewage plus clean rain water. There can be no doubt that this point will be fully attained by the time the three volumes of mixed sewage and storm water have been treated as required by the Local Government Board. At this stage, if the sewage flow proper be at its maximum, the dilution will of course be not nearly so great as i vol. to 2 vols. ; and when this is the case the treatment of a further quantity is certainly necessary. When, on the other hand, it happens that the actual sewage is small in amount, as for instance during the early hours of the morning, the degree of dilution will be high and further treatment unnecessary. It is, how- ever, impossible to fix these points with any exact- ness, and the uniform treatment up to six volumes ensures that, at the worst, the sewage will be diluted two or three times before it is discharged direct and without filtration. But whilst fully recog- nising this, it must be borne in mind that a great TUB OF THB UNIVERSITY 54 additional burden is thrown upon Local Authorities, In the case of a pumping scheme, for instance., power must be provided to lift six .times the normal flow and, in addition, the plant must be duplicated to avoid any danger from breakdowns. A town, therefore, with a daily sewage output of ioo,ooO' gallons, must have power to lift 1,200,000 gallons in 24 hours, one half of such power always standing idle and only one twelfth being employed during dry weather. So far I have considered this question solely on the hypothesis that the undiluted sewage of the town is of normal quality, say equal to 20-30- gallons per head of the population. If, however, special cases be considered, the circumstances will be found widely different, and the difficulty of apply- ing any fixed rule to sewage treatment will be at once apparent. There are towns where, owing to the in-leakage of subsoil water or other causes, the quantity of sewage in dry weather is equal to 60 or more gallons per head of the inhabitants without any increase whatever in the amount of pollutive matter. Such a town w r ould discharge, in storm periods as in droughts, a sewage very much less foul than that from a town in which the normal flow equalled only 30 gallons per head. Calling the town with 30 gallons per head A and that with 60 gallons B : in dry weather B sewage is half the strength of A; when diluted to three volumes A sewage is as foul as B sewage diluted to only i; and B sewage diluted to 6 volumes would have a strength only equal to that of A sewage diluted to 12 volumes. It would therefore seem as if, in 55 deciding upon a limit of dilution, the original volume of sewage per head of the population should be taken into account, always supposing, of course, that the volume is not increased by factory refuse but only by clean, or relatively clean water. The argument would not apply, for instance, to Burton- on-Trent, where the normal sewage is equal to about 200 gallons for each inhabitant ; but in this case the large increase is occasioned by the enormous quantity of water used and fouled by the breweries and the resulting sewage has been found a very difficult one to treat. If the relative volume of domestic sewage be not considered we arrive at the anomalous result, pointed out by Mr. A. J. Martin in a very able paper read before the Sanitary Congress at Southampton, that "the diluted sewage "which one public body may discharge without "treatment, will be considerably stronger than that "which another authority will be called upon to " purify. " Whatever may be the degree of dilution insisted upon, it is evident that in almost all cases a volume of sewage several times greater than the normal will have to be dealt with during storm periods, and the question arises, how can this best be accom- plished? Here again the bacterial systems possess an enormous advantage over any precipitation method, by reason of their elasticity and more automatic manner of working. If an installation on the Sutton principle be erected according to the present requirements of the Local Government Board, three times the normal volume of sewage can 56 be perfectly dealt with by merely filling the bacteria beds three times instead of once daily. But the beds can be made to perform several times this duty, if desired, provided that such special effort is not of very long continuance. If the water be allowed to stream through the beds that is, if it escape as fast as it enters, the bed being kept full all the while, storm water up to more than ten times the normal volume can be satisfactorily purified. This method has been tried at Sutton and at the Cheam and Cuddington Sewage works at Worcester Park, with perfect success. An effluent is produced which answers requirements and the activity of the beds is hardly at all impaired, perfect recovery being very rapid; whilst the method possesses ~ one very great advantage over that of supplying a special storm filter, in that the organisms in the latter will never become properly developed, whilst in the former the extra duty is demanded when the bed is in its best possible working condition. Hence the storm effluent produced by streaming through the bacteria beds used in daily work is likely to be far purer than that obtained by treatment on a filter which only comes into occasional operation. This practice has not yet been sanctioned by the Local Government Board, but I have little doubt that as experience of its value increases it will receive the seal of official recognition. The septic tank also lends jtself admirably to the treatment of volumes of storm water largely in excess of the normal dry weather flow. This is well illustrated in the case of the installation re- 57 cently completed at Barrhead, the following par- ticulars being taken from the paper already men- tioned, read by Mr. A. J. Martin before the South- ampton Congress in September last. The overflow weir is placed in the grit chambers, its crest being 1 8 inches above the ordinary working level of the sewage in the tanks. The intermediate space amounts to 10,800 cubic feet, or 67,500 gallons, and no overflow can take place until this is filled up. This means that sewage can arrive at the works at the rate of six times the average flow for a period of two hours before any overflow whatever occurs; and in cases in which the storm flow is of short duration, as in a thunder shower, there would be no overflow. And this is manifestly a great advantage, since (i) the whole first rush of a storm is treated in the tank, and (2) the number of times at which untreated storm-water is discharged is greatly diminished. CHAPTER VII. THE TREATMENT OF TRADE REFUSE LIQUORS. The problem of how sewage may best be puri- fied is frequently rendered more complicated, especially in the Midlands and the North, by the admission into the sewers of waste waters from manufactories. Not only is the actual bulk of sewage to be dealt with largely augmented thereby in some cases the water due to factories is several times greater than the sewage proper but an element of difficulty is introduced, inasmuch as many trade effluents are highly resistant to all processes of purification, whilst some are actually hostile to microbial growth or even direct germicides. This difficulty is largely to the fore in the neighbour- hood of Birmingham, in the manufacturing districts of Yorkshire and Lancashire, and in certain parts of the Scottish Highlands, where the distillery refuse even threatens to render barren some of the hitherto most prolific salmon rivers. The question is a very large one, and not easy of solution, but an extended experience leads me to the belief that there are very few waste factory liquors which cannot be 59 finally dealt with by microbial means, although in certain cases preliminary or preparatory treatment of some kind is undoubtedly necessary. Sewages containing considerable quantities of the following have come under my personal obser- vation : Effluents from breweries, distilleries, fell- mongers, tanneries, dye-works, galvanizing-works, glove-leather dressers, gas-works, soap-works, paper mills, margarine- works, copper- works (wet process), woollen trades ; and I have also had the opportunity of observing the behaviour of many of the above effluents in their undiluted and untreated states, and have made numerous experiments upon their purification. Brewery waste consists principally of the washing of barrels and vats, and is of a highly putrescent nature. This very fact, however, as I have recently pointed out in an article contributed to the Brewing Trade Review, indicates that the organic matters contained in the waste liquor are readily amenable to bacterial purification, of which putrefaction is one of the initial forms. It is recommended by many that precipitating agents, such as lime or some form of sulphate of alumina, should be employed to remove the solids, but in practice it will be found that mere natural subsidence is quite sufficient ; and beyond this, and cooling all liquors to a temperature not exceed- ing ioo-i2o F., the brewer need not be asked to take any steps, but may be permitted to discharge the clarified and cooled effluent into the sewers, where such exist. In cases where 6o such effluents have to be discharged directly into a stream, further measures of purification must of course be adopted, and it will be found that aerobic bacterial treament wil) give highly success- ful results. The principal points to observe in the microbial purification of brewery waste are, firstly, that it should be treated as fresh as possible ; and secondly, that extra care must be taken to ensure the fullest measure of aeration, the anaerobic organisms in this case taking a very long time to effect their purpose, whilst at the same time they produce a highly offensive condition of the liquid, and leave it in a state in which it is not readily purified by the aerobes. When brewery waste is mixed, even in very large quantities, with ordinary domestic sewage, treatment by the Sutton bacterial process on the ordinary lines proves quite efficacious. This is, I am aware, contrary to the opinion expressed by Dr. Maclean Wilson, Chief Inspector of the West Riding of Yorkshire Rivers Board, in a paper read by him at the Leeds Congress of the Sanitary Institute in 1897; but Ms objection that the ready putrescibility of the brewery waste renders the whole more offensive and less amen- able to treatment does not hold good according to my experience. At Alton, in Hampshire, for example, brewery refuse forms one- third of the whole bulk of the sewage, yet works constructed on the Sutton method have been successfully deal- ing with this sewage for some considerable time, and the effluent produced is in all regards satisfactory, conforming to any of the generally recognised 6i standards. At Worcester Park, again, where the sewage of Cheam and Cuddington is treated accord- ing to aerobic bacterial principles, brewery waste forms a very large proportion of the whole ; but the effluent is of such a quality that it is readily passed as satisfactory by the Thames Conservancy, and has actually during many months of the past dry season formed the only source of water in the upper portion of the Beverley Brook, without any suggestion of nuisance having arisen. Neither of these two effluents exhibits the least tendency towards secondary putrefactive decomposition. The necessity for the avoidance* of anaerobic conditions, and for promoting the fullest access of air to the beds has, however, been noticed, though only in slight degree as compared with a case in which brewery waste is treated by itself. Another case in which sewage containing large proportions of refuse liquor from breweries has proved itself amenable to bacterial treatment is that of Maidstone, where an experimental plant on the lines of the Sutton system has been successfully worked for some time.. Distillery effluent is far n ore obstinate in its resistance to treatment than is that derived from breweries, owing principally to the presence in the former of " burnt ale," which is the residue from the first distillation. Its nature may be partly gauged from an analysis of a sample from a High- land distillery, which yielded 60 parts of free and saline and 43 parts of albuminoid ammonia, and absorbed 667 parts of oxygen from permanganate in four hours per 100,000 parts of ale. It is this 62 burnt ale which is principally responsible for the pollution, already referred to, of the Scotch salmon rivers, notably the Spey and its tributaries, and a considerable amount of litigation over the question has already taken place. In one well-known case, it was laid down that the distiller was bound to -effectually purify the waste liquors before permitting their discharge into the river ; and in another, the distiller succeeded in establishing the position, subject to appeal not yet decided, that he had the right to turn his effluents into the town sewers, provided he first' settled and cooled them, and with sundry other minor provisions. Burnt ale possesses a very high manurial value, and has been and is applied with the greatest benefit to certain crops, as for instance swedes and turnips, no doubt owing to the large amounts of alkalies and phosphoric acid which it contains. The problem which confronts us, however, in all attempts to dispose of sewage by land irrigation only is met with here also neither the land nor the crops can take it at all times and seasons, whereas it is produced and must be got rid of continuously, excepting during the hottest period of summer. A further difficulty lies in the taking the ale from the distillery to the land, a process which in many cases is only practicable by means of carts and slung casks. All precipitation methods, without exception, have failed to produce any satisfactory results with this material. Acting, however, on the principle already enunciated, that whatever is liable to putrefaction can be treated bacterially, if only the paiticular conditions 63 necessary can be established, a series of experiments on biological lines was undertaken, with the result that it was clearly shown that, anyhow in the laboratory, burnt ale could be completely purified by adapting the aerobic process to its special requirements. The ale must be cooled and settled, when a large amount of suspended solids separates out and can be employed as manure, for which it is very suitable. The cooled and clarified liquid may then be mixed with the other effluents, viz., the steep water, spent lees, &c., and the whole treated on a series of aerobic bacteria beds, about three times in number those required by an equal quantity of sewage and, anyhow the first five of the series, very open grained, it being even more necessary in this case than in that of breweries to provide for the fullest possible aeration and to avoid anything like septic action. The ale should also be treated whilst quite fresh, as much lactic acid is formed on keeping. A mixture of sewage and burnt ale, treated on a series of such beds, yielded on analysis the following results : PARTS PER 100,000. Free and saline ammonia Albuminoid ammonia . . Oxygen absorbed, 4 hrs. Raw liquor. Final effluent. Raw liquor. Final effluent. I 5 -0 15-6 310-0 O'l 0-045 0-48 9-0 66 137-0 0-47 v 5 0-48 Using an effluent produced in this way as the sole source of water supply I succeeded in January 6 4 and February, 1898, in hatching almost the whole of a batch of salmon ova, kindly supplied for the purpose of this experiment by the Solway Fishery Company, at the request of Mr. R. B. Marston, the editor of the Fishing Gazette. The specific fungus, Apomya lactea, so well known to all those acquainted with the streams in the neighbourhood of large distilleries, absolutely refuses to grow in this effiuent, which is water- white, perfectly clear, taste- less and inodorous, and incapable of putrefactive change. Experiments on a large scale are now proceeding at a well-known Highland distillery, with a view to ascertaining whether results com- parable with those obtained in the laboratory and at the distillery on a smaller scale can be re- produced. Fellmongers' and leather-dressers' refuse forms a large part of the sewage at Yeovil, which is of a particularly obnoxious character. This has now been treated experimentally, on a large scale, for some considerable period of time by the Septic Tank process, and with perfect success. Owing to the nature of the sewage it has been found advis- able to subject the tank effluent to treatment in two- sets of beds instead of one, as is usual in this process, and the results are in every way satis- factory. Sewage of this nature can also be effectually purified by employing the aerobic method throughout. Tannery refuse, where it exists in considerable but not in preponderating amount, as for instance at Leeds and Maidstone,, offers little difficulty beyond that met with in 65 ordinary mixed sewage ; but a quite different problem has to be faced in certain cases, in which the tannery waste exceeds in bulk the whole normal sewage of the town or district. In such cases the manufacturers should probably be called upon to mix the lime and tan-pit liquors, and collect the sludge formed by settlement ; and it is also at present a question as to whether the extreme alkalinity ought not to be somewhat reduced before the effluent is admitted into the sewers. Such liquids are highly resistant to microbial influences, but have yielded, on experimental lines, to aerobic bacterial treatment. The beds, however, must be of greater capacity than would be required for an equal volume of ordinary sewage, since they cannot be worked so frequently ; the number of series must be increased to admit of several treatments ; and aeration must be carefully attended to. Dyeworks refuse and similar matters can also be dealt with by the aid of microbes. At Hyde, near Manchester, for example, the sewage contains large quantities of this refuse, together with that from many other trades ; yet during the past six months a portion has been regularly and success- fully treated, passing first through an open septic tank having a capacity equal to one day's flow, and thence on to a Whitaker-Bryant filter, which is a continuous aerobic bacterial filter provided with special heating and distributing apparatus. The results obtained, though not equal to those pro- duced with a purely domestic sewage, are nevertheless far in advance of anything attained by 66 any of the precipitation and mechanical filtration methods, the effluent being fairly clear, with a slight earthy smell, and, what is most important, not liable to further putrefactive change, so that it may safely be discharged into a stream. The acid pickle liquor from galvanising works is very troublesome to deal with. It is in itself not capable of being attacked by bacteria, and if present in relatively large amounts, renders sewage difficult to treat. Depending, of course, on the quantity, this trouble may frequently be met by arranging with manufacturers for the continuous small dis- charge of such matters, thereby ensuring a constant dilution. At West Bromwich an experimental Sutton plant has been working very successfully for some time ; and at Leeds, where the pickle liquor is strongly in evidence, good results have also been obtained. The iron in solution, however, is readily separated, and must necessarily tend to clog the beds and to give a rusty appearance and an inky flavour to the final effluent. It is readily precipi- tated by being rendered alkaline with lime, and the clarified liquor then has no deleterious effects upon a bacteria bed. The waste liquor derived from the wet copper process is of a similar nature. The remainder of the trades mentioned have been principally investigated in conjunction with one another or with others, although experiments have been specially made with the waste waters from gas works and margarine works ; and the general result has been to establish the fact that there are very few trade refuse liquors which 6 7 cannot be successfully purified by bacterial agencies, although in some cases a preliminary treatment must be resorted to. This is well shown in the case of the sewage of Manchester, which contains very large quantities of factory waste of most varied description ; it is proved again at Leeds, where the Button method produces a constantly good effluent, .but the water capacity of the coarse beds is greatly lowered by the deposition in them of fine particles of resistant solid matter. There can be no doubt that the solution of the problem of the final dis- posal of such matters will be found to lie in this direction. CHAPTER VIII. LAND TREATMENT. Until the introduction of water-borne sewage the land was the natural recipient of all the eftete matters of a community. Quite apart from any question of manurial value, it was the simplest and easiest method of disposal. But with the gather- ing together of large numbers of people in towns and cities arose two difficulties ; firstly, that such matter when collected in quantity is extremely offensive and in many cases actually dangerous to health, and cannot easily be carried through the streets of a town without creating a nuisance ; and secondly, that a large area of land was required in the immediate vicinity of the town, whereon the filth might be deposited. On the introduction of water carriages for sewage, both difficulties were removed, and the nearest water-course offered the readiest means of final disposal. But from this course arose other evils pollution of the rivers, killing of fish, fouling of water supplies ; at the same time a great outcry was raised as to the wanton waste of so much supposedly valuable 6 9 manure, and the Royal Commission, appointed in 1857, reported that "The right way to dispose of '" town sewage is to apply it continuously to land, " and it is only by such application that the pollution "of rivers can be avoided." Another Royal Com- mission declared that in the case of sewage, preci- pitants did not precipitate and niters did not effect filtration, and in the first report of the Rivers Pol- lution Commission, issued in 1866, and dealing with the question of the river Thames, accord is expressed with the opinion of the 1857 Commission, and many examples of land treatment are given. Then sewage farms began to spring up all over the country and worked for a time with a fair measure of success. But it was gradually found that these dicta of the Royal Commissioners had by no means finally solved the problem, and constant complaints were made in many places of the ineffective working of the farms, and of nuisance arising from them. The Local Government Board, however, acting on the report the Committee appointed by it in 1875, has insisted, and does now insist, upon the final purifica- tion of all effluents in inland places by passage through land. That this action was a wise one in the case of all effluents from chemical treatment and mechan- ical filters there can be no doubt, and the wisdom of applying it also to bacterial effluents need not be discussed here. But nevertheless the majority of sewage farms failed to produce the results antici- pated from their use, and many of them became in the course of time simply stinking quagmires. Is it the system that is wrong, or does the fault lie in 70 its application ? Some authorities, as Col. Jones, V.C., formerly of Finchhampstead and now of Aldershot, maintain that the whole fault lies in the management, and that the application of a certain amount of ordinary intelligence and knowledge is as necessary in this as in other business undertakings. From the latter opinion no one can dissent for a moment, and Col. Jones has certainly done a great deal towards proving the correctness of his own views by his admirable management of the works under his care. But the whole case cannot be met in this way. If the quantity of sewage be too unwieldly, the land unsuitable, or the climate unpropitious, the best management in the world cannot make a success of a sewage farm, although it may lessen some of the evils. It would appear, therefore, that the causes of failure are two principally : the one to do with the management, in cases where all the conditions are favourable ; the other, the impossibility of pro- ducing these conditions, excepting in small degree, where they do not naturally exist. No manage- ment can effect the purification of sewage on a solid clay ; in winter, when wet, it becomes water- logged and much of the sewage simply flows over instead of through the land, and when frozen, it accumulates on the surface until the occurrence of a thaw, and then flows off directly into the stream ; in summer, if the weather be hot and dry, cracks are formed through which the sewage finds its way ' unchanged. Some benefit may, of course, be derived by burning, but the amount of this which would be of the greatest use to the ordinary farmer is quite insufficient in the case of a sewage farm, and a heavy expense is consequently incurred. But supposing the land and other conditions to be suitable, what is the proper procedure ? In the first place, and most important of all, the land must be regarded not as a farm from which a profit can be extracted, but merely as a machine whereby to purify the sewage. If this principle be departed from the certain result is failure. Then the area of land should be very much greater than that usually allowed ; the acre for 2,000 persons (in the case of a fair effluent) sanctioned generally by the Local Government Board means that the daily supply of water, if collected on the surface, would cover it to a depth of nearly i\ inches ; equivalent, supposing it to be only clean water, to a rainfall of over 900 inches in a year. It is quite clear that farming under these conditions becomes practically impossible ; and not only can no crops be successfully grown, but the soil is unable to deal with so great a quantity of water, unless the upper stratum be coarse sand or some- thing similar, such as is largely found in Massachu- setts. Then as to the arrangement of the farm, and the method of application of the efHuent. An area of sufficient size should be provided, on which no crops whatever are to be grown, to take the efHuent at such times when its application to the farm land proper would be unnecessary or injurious, owing either to the quantity already applied within a given time, the state of the weather, or the nature or 7 2 condition of the crop. The remainder of the land should be laid out in broad flat ridges, and narrow, deep furrows ; the ridges may be from 1 2 to 20 feet across, and on these the crops should be raised, the effluent soaking in from the furrows and never touching the actual plant. By these means the roots will be in soil which will always be kept damp, owing to capillary attraction, but will never stand in water, whilst the surface of the land can be kept porous and open to the air. If under-drains be necessary, they should be placed under the middle of the ridge, at whatever depth the nature of the soil and the amount of fall available render necessary or desirable. By such a combination of farming with downward intermittent filtration, applying the effluent to the crops only when such application will do good, either from its manurial value or simply as supplying moisture, land treatment under favourable conditions of soil may be very successfully carried out. Only in the case of grass should the effluent be permitted to flow over the actual surface of the land. Another point to be observed is that many soils requires to be limed at intervals. One reason for this is ^that a base is required for the acid formed during the nitrifying process, as otherwise the organisms are unable to continue their work and the nitrogen is never converted to that form in which it can be assimilated by the crops. Also a general condition of feeble alkalinity is most favourable to the growth and well-being of the microbes engaged in the whole process of purification, 73 and a sewage farm is nothing but a big bacteria bed. Regarding the actual manurial value of sewage when applied to land, opinions are as many as various. Letheby (The Sewage Question, 1872, pp. 140 et seq) says : " As regards the commercial and agricultural " value of sewage, the discrepancies are still more " remarkable. In the evidence before the Select " Committee of the House of Commons in 1862, " the value of it was variously stated at from -|d. to " gd. per ton. The Earl of Essex thought it should " be supplied to the farmer at rather less than id. " per ton ; but Messrs. Lawes, Way & Morton " valued it at id. ; Leibig & Voelcker at i|d. ; " Mechi, Hoffmann & Witt at 2d. In reality, how- " ever, no one will buy it at any price, unless he has " the opportunity of using it when he pleases,and then "he will pay at the rate of from 55. to 6s. per " acre for it, provided the local authority will deliver " it upon his land in the quantity required, and " whenever required. A farmer would be glad to " take water at this price. . . ." And again, "If ' ' sewage had possessed but half the value which some " loud-talking people are ever proclaiming, it would "long since have been the subject of successful " speculation, and have formed the basis of many a " flourishing stock-joint company." These opinions appear really to epitomise all the facts of the case. Sewage has some manurial value, but it is small ; what there is cannot always be employed, but the manufacture must continue con- stantly, and in very many cases the benefit attributed 74 to the manure is really derived simply from the appli- cation of water when the land is dry and needs it. And herein lies the great advantage of the bacterial processes. On all occasions when the land is sufficiently moist, the filtrate may be permitted to discharge directly into a stream ; it is already as pure as the land could make it, and, indeed, in many cases purer, as for example at Hampton, where the excellent bacteria bed effluent is actually fouled to a slight extent by passage through the land. But when the crops require water it may be freely given to them, to their very great advantage, and since the manufial constituents are to a great extent retained in the bacterial effluent, the plants can still derive whatever benefit is possible ; and, in addition, the burden of purification and oxidation is not thrown upon the land, and the available nitrogen is presented in the form of nitrate, to which it must be brought in most cases before the plant can use it. To sum up, the actual manurial value of sewage is very small, whatever may be said by those who base their calculations on the constituents as determined by analysis ; it can only be usefully applied at those times when simple water would be useful ; if so employed in conjunction with a bacterial system of purification, farming operations can be carried out with advantage. CHAPTER IX. STANDARDS METHODS OF ANALYSIS. The question of how much impurity may be permitted to remain in an effluent discharging into a stream has been very much debated, and the standards are as various as the authorities controll- ing them. That laid down in the Report of the Royal Commission on the pollution of rivers is as follows : " The following liquids should be deemed " polluting and inadmissible into any stream: " (a) Any liquid containing, in suspension, " more than three parts by weight of dry mineral " matter, or one part by weight of dry organic " matter in 100,000 parts by weight of the liquid. " (b) Any liquid containing, in solution, more " than two parts by weight of organic carbon, or " 0-3 parts by weight of organic nitrogen in 100,000 " parts by weight. " (c) Any liquid which shall exhibit by day- " light a distinct colour when a stratum of it, one " inch deep, is placed in a white porcelain or earthen - " ware vessel. 7 6 " (d) Any liquid which contains, in solution, " in 100,000 parts by weight more than two parts " by weight of any metal except calcium, magnesium, " potassium, and sodium. " (e) Any liquid which in 100,000 parts by " weight contains, ivhethev in solution or suspension, " in chemical combination or otherwise, more than " 0-05 parts by weight of metallic arsenic. " (/) Any liquid which, after acidification 11 with sulphuric acid, contains in 100,000 parts by " weight more than one part by weight of free " chlorine. " (g) Any liquid which contains in 100,000 " parts by weight more than one part by weight of " sulphur, in the condition either of sulphuretted " hydrogen or of a soluble sulphuret. " (h) Any liquid possessing an acidity greater " than that which is produced by adding two parts " by weight of real muriatic acid to 1,000 parts by weight of distilled water. " (i) Any liquid possessing an alkalinity " greater than that produced by adding one part by "weight of dry caustic soda to 1,000 parts by " weight of distilled water. " (k) Any liquid exhibiting a film of petroleum " or hydro-carbon oil upon its surface, or containing ''in suspension in 100,000 parts, more than 0-05 " part of such oil. This standard has not been generally adopted, owing no doubt to the fact that the determination of organic carbon and nitrogen, valuable as it is, is tedious and costly, whilst the albuminoid ammonia 77 and oxygen processes are cheap and speedy, and if not quite so absolute, give a sufficient indication, besides being fairly reliable, even when used by other than the most practised hands. It will be found accordingly, that the majority of the standards at present in vogue depend upon these two simpler processes, which will be dealt with at length later on. The Thames Conservancy does not, so far as I am aware, insist upon any published standard ; but generally speaking, an effluent which yields les than o'2 parts of albuminoid ammonia per 100,000 parts will not be objected to by that body. Accord- ing to Mr. Nayler, Chief Inspector of the Kibble Joint Committee, this albuminoid ammonia figure very nearly approximates to the 03 part of organic nitrogen suggested by the Rivers Pollution Com- mission, and is accordingly fixed by the Ribble Committee as a standard. The Mersey and Irwell Joint Committee have taken as a standard an effluent yielding o-i grain per gallon of albuminoid ammonia and absorbing i-o grain of oxygen in four hours from permanganate. This body also very properly Jays great stress upon the putrescibility of the effluent, determining this factor by an estimation of the oxygen absorbed in three minutes when first taken, as compared with that absorbed after keeping five days in an incubator ; and by the amount of oxygen taken up from fully aerated water. It will readily be seen that the fixing of a universal standard is a matter of the utmost difficulty, 78 if not actually impossible. It appears also to be unnecessary, since so many factors have to be taken into account in judging the pollutive power of an effluent. The relative size of the stream, for example, should always be considered, as should also the possibility or otherwise of the water at a lower point being used as a source of domestic supply. But the greatest difficulty in fixing a limit of 'Organic impurity lies in the fact that a mere determination of the amount of organic matter, unless supplemenced by a knowledge of its condition, is more or less useless. An effluent which has passed a coarse grain bacteria bed, for example, will yield more albuminoid ammonia than is considered admissible by any of the authorities quoted ; yet the processes of simplification and of nitrification have been so far advanced that such an effluent will only on the rarest occasions show signs of secondary putrefaction under natural conditions of tempera- ture, and will continue to purify itself without giving rise to any nuisance. I have never known an effluent from a fine grain bacteria bed, in proper condition, to yield any putrefactive symptons ; yet such an effluent may frequently show more than 0-2 part per 100,000 of albuminoid ammonia. It follows, therefore, that to condemn an effluent on the albuminoid ammonia factor alone, or on that coupled with the oxygen absorbed, is clearly wrong. Two other points should be determined, viz.. the relative amount of oxidised nitrogen, whether as nitrites or nitrates, and the liability to secondary putrefactive decomposition at ordinary temperatures. 79 And here I mnst call attention to the fact, to which I alluded at the Southampton Congress, that it is necessary that such oxidised nitrogen should be derived from organic nitrogen originally present in the sewage and not from added nitrate. It has been abundantly shown by experiment in the laboratory of the London County Council at Barking Creek, that the putrefaction of sewage effluent is not inhibited by the addition even of large quantities of nitrate. But since nitrate cannot exist as such until a certain stage in the decomposition of the organic matter has been reached, the presence of any quantity of naturally derived nitric acid may be taken, generally, as an indication of the fitness of an effluent for discharge. In order, then, to determine whether an effluent may be safely discharged into a stream of relatively small volume, I would suggest that it should fulfil the following conditions : (a) It should contain practically no suspended matter ; the amount allowed by the Rivers Pollution Commission is unnecessarily high. (b) It should fulfil the Commissioners' require- ments as regards poisonous metals, free chlorine, acidity, and alkalinity, and should contain no appreciable quantity of any germicide whatever. (c) It should, when first taken, yield not more than 0-2 to 0-25 part of albunimoid ammonia per 100,000 parts, and should absorb not more than i-o to 1-5 part of oxygen from permanganate in 4 hours at 80 F. 8o (d) It should show, when first taken, distinct indications of nitrification. (e) After 14 days' keeping in the laboratory, the albuminoid ammonia should be considerably reduced and the nitric nitrogen proportionately increased. (/) It should not, at any time during the 14 days, develop any unpleasant odour. It will be seen that some of these conditions are interdependent ; for example, the presence of any quantity of germicide would prevent the success- ful application of test (e). An effluent that would answer all these requirements could not at any time cause any nuisance in the stream into which it was discharged, and yet is, in the majority of cases, fairly easy to produce, being such as would be con- stantly derived from the Sutton system pf treatment properly applied. In the case of tidal streams far less purification need be insisted upon, the mere removal of suspended matters being in most cases quite sufficient ; and here all danger of nuisance would be removed by a single treatment of coarse grain bacteria beds. Of analytical processes I propose dealing only with those generally employed for ascertaining the free and saline and albuminoid ammonia, the oxygen absorbed from permanganate, the nitrous and nitric nitrogen, and the chlorine, the latter being of great value, as by its means the fact of samples of crude sewage and effluent being comparable with one another may be readily determined. The organic carbon and nitrogen process, valuable as it un- doubtedly is, is at the same time, as already stated, 8i costly and cumbersome, and can only be worked in highly skilled hands. At the present time Kjehldahl's process has practically superseded it as a method for determining the nitrogen ; but I do not propose to describe this, as in most cases it will be found unnecessary to do more than that mentioned above, coupled with the factors of appearance, odour and reaction, and the estimation of suspended solids, should such be present in appreciable quantity. The free and saiine ammonia is that which is driven off by boiling, without the addition of any re-agent beyond a small quantity of pure carbonate of soda if necessary, in order to render the sample operated upon slightly alkaline. In performing this operation it is always advisable, in the case of sewage and sewage effluents, to dilute very largely with distilled water that has been recently boiled to expel any traces of ammonia which it may contain. A quantity of the sample varying, according to its strength, from 10 t 50 cubic centimetres, is made up to 500 or 700 c.c., and placed in a glass retort of sufficient capacity ; and a small quantity of car- bonate of soda is added as above. Heat is then applied and the distillate collected, either 50 c.c. at a time, until the application of the Nessler test yields no reaction ; or 250 c.c. may be collected at once and then successive amounts of 50 c.c. tested until it is shown that no more ammonia is coming over. The quantity of ammonia contained in the distillates is determined by preparing solutions of known strength until the depth of colour pro- duced on addition of the Nessler test is equal to 82 that produced in the distillates. If the first method of collection be adopted, the whole ammonia present will be the sum of that contained in the various portions of the distillate ; if the second method be used, an aliquot portion of the 250 c.c. is tested, the result multiplied by the proper factor, and the product added to the sum of the quantities found in its remaining small portions. To the residual contents of the retort, after the expulsion of the free and saline ammonia, are added 50 c.c. of a strong solution of permanganate of potash and caustic soda, which has been boiled for a considerable period of time. Heat is again applied and the distillates collected and Nesslerized as before. The ammonia so obtained is known as " albuminoid," from the iact of the authors of the process having conducted their first experiments with albuminous substances. The free and saline ammonia may be taken roughly as an index of the amount of nitrogenous organic matter that has already undergone the first processes of purification by simplification of complex substances; the albuminoid ammonia similarly represents the amount of such matter that remains to be split up, and is, of course, infinitely the more important of the two. The free ammonia, in fact, is a sort of half-way house between the original organic nitrogen and the resultant nitric acid, and shows past dangers only, whilst the albuminoid ammonia is a gauge to a present danger, the liability to putrefaction. 83 The amount of oxygen absorbed from per- manganate of potash is determined by adding to the diluted sample an excess of a standard solution of permanganate and some dilute sulphuric acid, and determining the amount of unchanged per- manganate after the expiration of a certain period of time. This has been fixed by the Society of Public Analysts at four hours, the temperature being maintained at 80 F. In the case of sewage effiuents it is also advisable to determine the quantity absorbed at once, as a measure of the more readily oxidisable and therefore easily putrescible substances ; and also, in the case of a sewage highly charged with, say, proto- salts of iron, to admit of this factor being determined and applied ns a correction to the result of the four hours test. The modus operandi is as follows : A quantity of the sample to be tested, largely diluted with pure distilled water, is placed in a closely stoppered bottle in a chamber which is kept at a temperature of 80 F. When a sufficient time has elapsed for the contents of the bottle to attain this temperature, a known quantity of a standard solution of permanganate in excess of that estimated as being required is added, together with a small quantity of water containing 10 per cent, of pure sulphuric acid. The bottle is then replaced in the warm chamber, and is inspected occasionally to see whether the permanganate remains in excess, which can be readily determined from the colour ; should the amount already taken prove insufficient, a further measured quantity must be added. After 8 4 the expiration of four hours from the time of first adding permanganate, the bottle is removed from the warm chamber and a crystal of pure iodide of potassium is added, when iodine will be liberated in exact proportion to the amount of permanganate remaining unchanged, and can be determined by a solution of thiosulphate of sodium (hyposulphite or hypo) of known value, the end of the reaction being shown by the discharge of the blue colour produced by the addition of a small quantity of starch solution after the yellow of the iodine has nearly disappeared. The difference between the oxygen in the permanganate added and in that found unaltered represents the quantity absorbed by the sample under examination. The oxygen absorbed at once is determined in a precisely similar way, excepting that for the four hours' interval is substituted one of about a minute. In effiuents containing nitrites, a proportionate amount must be deducted from the oxygen absorbed found. A valuable application of this test is made by Mr. F. Scudder, in the laboratory of the Mersey and Irwell Joint Committee. The oxygen absorbed at once or in five minutes is determined, and a portion of the sample is then kept in a chamber at a slightly raised temperature for a certain number of days, when the same factor is again estimated. In all cases in which putrescible organic matter is present in dangerous amount, the oxygen absorbed at once increases with the incubation ; where such increase does not occur, or on the contrary a decrease 85 is noted, there is no danger of after putrescence, the organic matters remaining having arrived at a more or less stable condition. Another very valuable test for an effluent, originally introduced by Dr. Dupre, consists in determining the amount of oxygen taken up by the sample from fully aerated water after contact for some hours or days. Mr. Scudder has observed lately that, generally speaking, an effluent which does not absorb more than imparts of oxygen from permanganate in four hours (i-o grain per gallon) will not appreciably diminish the oxygen in fully aerated water in two or three days. It is clear that such an effluent is fit to discharge into any stream. The nitrous acid is best estimated by adding to the sample in a Nessler glass a small quantity of a o ( 5 per cent, solution of meta-phenylene-diamine and diluted sulphuric acid, and exactly reproducing the tint obtained by known quantities of pure nitrite of potassium in similar glasses. The process is analogous to Nesslerizing and is readily carried out. There are many methods of ascertaining the nitric acid, but where considerable quantities are present, as in a good effluent, the best and certainly the easiest process is the modified indigo method. This consists essentially in liberating the nitric acid by the addition of a large excess of sulphuric acid and determining the amount of indigo solution which can be decolourized thereby, the indigo being standardised against pure nitrate of potassium. This method gives both nitrous and nitric nitrogen, and the amount of the former found by the 86 meta-phenylene-diamine test must be deducted, the remainder being the nitric acid. Both of these are generally expressed in the form of " nitrogen as nitrous (or nitric) acid." The presence of any considerable quantity of nitric acid in an effluent has a two-fold value ; in the first place it indicates that the oxidation of some of the organic nitrogen has been carried to its highest point ; and in the second place it proves that what remains has progressed far on the road to complete purification. So important is the latter question that it has even been suggested that any effluent may be passed in which the available oxygen of the nitric acid equals or exceeds the amount of oxygen absorbed in four hours from permanganate. On the other hand, the effluents obtained from some trade refuse liquors, as the " burnt ale " from whisky distilleries, contain practically no nitrates, although they can be produced so as to be in all ways satisfactory, so that this test must be applied with caution, and with a knowledge of the source of the particular effluent which is under consideration. The estimation of the amount of chlorine present is principally of value, as already stated, as showing whether samples of sewage and effluent are comparable one with another. This factor is not appreciably altered by treatment, and therefore can be employed as showing that a particular sewage and effluent correspond, which is of the utmost importance in estimating the percentage purification effected. The determination is made by adding to a known quantity of the sample a 87 standard solution of nitrate of silver. A little pure chromate of potassium is first added, and the silver is then dropped in until a permanent red colour is produced, due to the formation of chromate of silver, which only takes place after the whole of the chloride has been precipitated. In the case of over- worked bacteria-beds the chlorine, will occasionally exhibit an apparent increase. This is due to anaerobic action having taken place, the sulphates present being reduced to sulphides. The proper treatment is rest with full aeration. It should be observed, that although the analyses indicated above are readily made after a little practice, the correct reading of the results is only attained after years of work. The manager of a sewage purification may soon learn how to obtain the results and apply them to the particular sewage, but in the case of another sewage, with which he was not so intimately acquainted, he would find great difficulty in arriving as correct conclusions. That can only be successfully done by an expert who has studied the question in all its bearings. CHAPTER X. GENERAL CONCLUSIONS. The present time is perhaps not a very favour- able one for the expression of very decided opinions upon the sewage question, since the report of the Royal Commission which is now sitting will prob- ably be issued shortly and, right or wrong, will command a respect which would never be given to the views of an individual, however much know- ledge and experience of the subject he might possess. Even at the risk, however, of disagreeing with the opinion of a Royal Commission, I must state my conviction that bacterial processes are the the only methods so far adduced which are right in principle, and which can be brought to a success- ful issue in practice ; and, further, that to insist upon subsequent land treatment is in most cases unnecessary and in many cases actually wrong. To attempt to forecast the report ot the Commissioners is of course dangerous, since all the meetings have been held with closed doors, and there therefore exist no means of knowing with any degree of accuracy what is the exact nature of the evidence 8 9 laid before them ; but it is certain that all promi- nent exponents of bacterial theories, and many who have had much experience in their working or prac- tical lines, have been called as witnesses, and it is reasonable to assume that such an amount of evidence, similar as regards the principles ex- pounded and differing only as to the method of application, should have very great influence upon the decision arrived at. It is impossible for the Commissioners to close their eyes to the results obtained at Sutton, Worcester Park, Leeds, West Bromwich, Manchester, Oswestry, Hampton, Alton, Harrow, Haywards Heath, Maidstone, Woodford, St. Albans, Aylesbury, Barking Creek, Crossness, Blackburn, Carlisle, and elsewhere, by the Sutton or aerobic system ; at Exeter, Yeovil, and Barr- head, by the Septic Tank or anaerobic, followed by aerobic method ; and at numerous public institu- tions and private establishments by either system. Looked at from this point of view, it appears in the highest degree improbable that the long looked for report can be otherwise than favourable to the views expressed in this little book. Of the anxiety with which the decision is awaited there can be no doubt. Many towns are postponing alterations or re-construction of existing works, or delaying to arrive at a decision regarding a plan of action until the issue of what is hopefully regarded as an authoritative statement which will indicate the real solution of their several problems. Some of these towns, although actually under injunction to remedy an existing nuisance, make no attempt at progress pending the publication of the report. It is to be hoped that it will not be too long delayed. Speaking generally, the sewage question has never engaged more of the public attention than at present. This is in great part owing to the formation within recent years of bodies specially constituted to deal with the pollution of rivers in their particular districts, as the Mersey and Irwell Joint Committee, the Ribble Committee, and the West Riding of Yorkshire Rivers Board ; to the action taken by County Councils ; and to the greatly increased activity of the Thames Conservators since their acquirement of the additional powers conferred upon them by their Act of 1894. The jurisdiction of the last mentioned body, for example, previous to this date, extended only two miles up the tributary rivers from their point of confluence with the Thames ; now it covers practically the whole watershed except the valley of the Lea, which has a Conservancy Board of its own. It will be readily seen how greatly such an alteration increased the powers and efficacy of the Conservators, and how numerous are the places which before discharged what they liked into the stream, but which are now called upon to take the steps necessary to prevent pollution. Within the area under the jurisdiction of the Mersey and Irwell Committee there are 413 factories discharging their refuse directly into the streams, and a population of two and a quarter million persons whose sewage is ultimately disposed of in the same rivers. Consideration of these and similar cases shows how alive the authorities now are to the necessity for preventing the water-courses from becoming foul, and what a state of activity must prevail amongst those who cause the fouling. But there is no need for these to wait or to experiment, unless in the case of single factories or of towns where the sewage is of an exception kind owing to the nature and quantity of the trade refuse mixed with it. Wherever the sewage is purely domestic, or the latter kind greatly predominates, either the aerobic or the anaerobic method of purification can be adopted with absolute confidence. Every village, every large country house, every isolated public institution can have its own installation, purifying its" waste and preventing contamination of the streams in its neighbourhood for a reasonable initial outlay and a nominal annual cost of upkeep. The question of using sewage as manure and thereby seeking to get some return for the expense incurred in its purification has been fully discussed in the last chapter, but it cannot be too often reiterated and impressed upon the minds of Local Authorities that sewage is something to be got rid of, and that any question of pecuniary return must be absolutely subsidiary to this main point. The talk about waste is also merely talk ; seeking to utilise the nitrogen, for example, in sewage is much like seeking to extract the silver from sea water, as has been ably said by Dr. Dupre. The total quantity there is no doubt great, but the expense of making it available is so much in excess 92 of its market value that it must of necessity be commercially unprofitable. Those who have calculated the theoretical value of the nitrogen have also either not known or have overlooked the fact that a large proportion m'ust always escape as nitrogen itself or as one of its oxides during the process of oxidation and nitrification, whilst the very nitrates which are found in the effluent water, from sewage farms, and which are relied upon as indicating the degree of purity and as showing the value of the product, only prove in reality that a considerable quantity of nitrogen has escaped and is running to waste into the river. In writing this little book I have endeavoured, as far as possible, to distinguish facts from opinions, and to support the latter by arguments which will be readily understood by Councillors and Surveyors of Local Authorities, for whom the work is mainly intended. If I have departed from this plan and made occasional ex-parte statements, I trust to be excused on the ground that within the intended limits it was impossible to fully discuss all the points of such a large question. H. R. GRUBB, PRINTER, NORTH END, CROYDON. THE THE LEADING ORGAN OF LOCAL GOVERNMENT AND THE POOR LAW. Editor and Proprietor, THOMAS FARROW. Id. Weekly. 1d. Weekly. }J[\mlc\pal xi$ THE COUNCILLOR AND GUARDIAN is acknowledged by Councillors, Medical Officers of Health. Municipal Engineers, Surveyors, and Sanitary Inspectors to be of immense assistance to them in the performance of their official duties. 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