key: cord-0935865-vcx0r4xm authors: Dharmaraj, Selvakumar; Ashokkumar, Veeramuthu; Pandiyan, Rajesh; Halimatul Munawaroh, Heli Siti; Chew, Kit Wayne; Chen, Wei-Hsin; Ngamcharussrivichai, Chawalit title: Pyrolysis: An effective technique for degradation of COVID-19 medical wastes date: 2021-02-23 journal: Chemosphere DOI: 10.1016/j.chemosphere.2021.130092 sha: 61d0cc90946731e7e4c2bdc53053ca8ff530348e doc_id: 935865 cord_uid: vcx0r4xm COVID-19 has led to the enormous rise of medical wastes throughout the world, and these have mainly been generated from hospitals, clinics, and other healthcare establishments. This creates an additional challenge in medical waste management, particularly in developing countries. Improper managing of medical waste may have serious public health issues and a significant impact on the environment. There are currently three disinfection technologies, namely incineration, chemical, and physical, that are available to treat COVID-19 medical waste (CMW). This study focuses on thermochemical process, particularly the pyrolysis process to treat medical waste. Pyrolysis is a process that utilizes the instability of organic components in medical waste to convert it into valuable products. Besides, the technique is environmentally friendly, more efficient, requires less landfill capacity, causes lower pollution, and cost-effective. The current pandemic situation generates a high amount of plastic medical waste, which has components like polyethylene (PE), polypropylene (PP), polystyrene (PS), polyethylene terephthalate (PET) and nylon (N). These plastic wastes can be converted into valuable energy products like oil, gas and char through the pyrolysis process. This study provides detailed information about CMW handling, treatments, valuable product generations (biofuels), and proper discharge into the open environment. developing countries for the handlers engaged in COVID-19 waste management because they are 242 not properly equipped with PPE. Other people who are more prone to get infected from virus-243 laden waste in developing countries would be the rag and casual waste collectors. The crucial 244 steps that have to be followed to overcome the pandemic situation will be the appropriate 245 treatment facility and safe disposal of CMW, which would control as well as prevent the 246 spreading (Cutler, 2020) . (Table 1) . Due to the outbreak of COVID-19, some places have 295 caused recycling operations to be temporarily stopped, which has caused an enormous amount of 296 plastic packaging waste, including the CW that gets accumulated in garbage collecting bins, 297 dumping sites, and even sometimes on roadsides (WHO, 2020f). Pharmaceutical industries that 298 aim to supply medical commodities worldwide and their high demand during COVID-19 have 299 also caused increased plastic packaging waste. Many countries exhibited a sudden increase in 300 online shopping during the COVID-19 pandemic due to high safety and hygiene concerns. The 301 packing plastic usage was mostly confined to food and groceries and these were either in the 302 form of thin films, Styrofoam, or thick plastic materials. The main concerns for an 303 environmentalist now are about the recyclability of these huge piles of packing plastics emerging 304 during the COVID-19 pandemic (Hyun, 2020; Jribi et al., 2020). 305 In some countries, the public's implementation of single-use plastic bags was forced due 306 to health concerns during COVID-19. Often the usage of single-use plastic bags is beneficial, but 307 it generates lots of waste and this adds up challenges to the already stressed waste management 308 system prevailing in any country. This temporary usage of single-use plastic bags would change 309 consumers' behavioral patterns, preferring to use them as a guard against contamination. subsequently, single-use plastic bags will increase and will get retained in average circulation 312 even after the pandemic (Sharma et al., 2020). 313 It has been estimated that during COVID-19, plastic waste has increased a lot, accounting 314 for nearly 44.8% from the packaging and 13.2 % from others (medical). This rise is mainly due 315 to online shopping as well as certain consumables like hand sanitizer, disinfectant spray, 316 cleaning agents, disposable wipes, facemask, gloves, etc. It all reflects that the production of 317 plastics for packaging and other purposes has got increased. Even the governments have 318 increased their output due to the demand (WHO, 2020g). Meanwhile, most of the packing 319 material, as well as the medical accessories (Facemask, gloves, shield, gowns, syringe), are made 320 from plastics, which is in wide demand during the COVID-19 pandemic situation. The plastics 321 consumption will further increase and the condition will worsen upon online ordering of food 322 and groceries. The COVID-19 pandemic will pose a significant danger to the environment as 323 enormous amounts of plastics are used, which will create major health problems for humans and 324 animals (Sharma et al., 2020). Recycling plastic waste -Naturally, there are four ways to degrade plastics from the 326 environment: photodegradation, thermo-oxidative degradation, hydrolytic degradation, and 327 biodegradation using microorganisms. In which some process like photodegradation followed by 328 thermo-oxidation may lead to the breaking of the plastic materials. Later the carbon in the 329 polymer on microbial action is changed to carbon-dioxide or utilized for biomolecule synthesis, 330 but it takes many years to proceed. So, recycling of plastics would be the best solution to be 331 adopted (Grigore, 2017). There are four ways of the recycling process of plastics or plastic waste, which include 1) 333 Primary recycling, 2) Mechanical recycling, 3) Chemical recycling and 4) Energy recovery 334 (Francis, 2016) . In the primary recycling process, the reuse or recycle of the native products as 335 such but it carries certain demerits like limited recycles for that recycled products though they 336 are cost-effective. Mechanical recycling is otherwise called secondary recycling in which 337 thermoplastics are remelted and processed to their respective end products. It is the physical 338 method in which the plastic waste polymers are either shredded or granulated or made into 339 pellets and melted to regenerate new products. Sometimes they are mixed with virgin plastics to 340 look like new ones. The major demerits in these products' usage include their heterogenicity and 341 quick declining properties in each recycle. Comparatively, this process is less expensive, but it 342 needs considerable investment initially. In the chemical recycling process, the plastic waste Thermal treatments of the CMW are much safer when compared with other techniques. One would be the complete destruction of the pathogenic agents and its meltdown, which may 363 lead to excellent energy recovery from the plastic waste polymers. Generally, reusable facemask, 364 which are mostly made of polypropylene, has several layers and they are recyclable using the 365 thermochemical process or mechanical recycling. It has to be assured that complete destruction 366 of residual pathogens carried by the hospital waste and health care centers because if they are not 367 properly disposed of, it may lead to contamination and can be a source of infections (Nzediegwu 368 and Chang, 2020). Recycling of waste during COVID-19 is a huge challenge because most recycling 370 facilities are shut down because the authorities might be at the risk of spreading the infections in 371 management system will be got saddled with piling up of the waste materials and it would be a 378 risk of whole recycling system failure (Plastics Today, 2020). Landfilling process: Landfilling is considered an efficient way of disposal of the plastic waste Landfilling is considered exclusively for waste management rather;, incineration is applied for 383 energy recovery from the plastic waste. It has been identified that less carbon-dioxide emission Furthermore, the WHO has recommended that underdeveloped might not advance waste 402 COVID-19 has enormously affected the world, infecting millions of people and leaving 403 numerous dead. The world has been facing unexpected disasters now, and each government aims 404 to protect the people's lives. It has been a great challenge for the government to handle the 405 pandemic situation with the prevailing infrastructure facilities and inadequate safety equipment. The accomplishment of multiple testing centers, sudden changes and improvisation in medical 407 standards and public policy alterations have been adopted to face the current public health crises 408 (UNEP, 2020). Imparting complete lockdown, social distancing among individuals in public places, self- The sudden appearance of COVID-19 and the spread among people has led to the 439 tremendous use of some items essential accessories such as facemasks, gloves, hand sanitizers, 440 disinfectant sprays to reduce virus transmission (Barcelo, 2020) . Hospitals or health centers 441 alone should not be regarded as the sources of infectious waste, but the carriers of the viruses can 442 also be asymptomatic people or those with moderate symptoms and masks, gloves, tissues 443 discarded by them. Moreover, the virus can survive for extended periods of time, sometimes up 444 to days in plastics, metals and cardboard. Dumping of these items will affect sanitary workers 445 who are involved in the collection of these wastes. In some underdeveloped or developing countries, the condition will still be worse for the sanitary works because either they are not 447 properly equipped or not wearing any type of PPE while handling CW. It has become difficult 448 even for the waste treatment facility centers to handle the unusual quantum of waste generated 449 during COVID-19 (Singh et al., 2020) . In developing countries, management of CW has been a 450 great challenge from the collection, transportation, treatment and disposal without being affected. available ranges from 0.5 to 3 tonnes/hour. Those designated as toxic or hazardous wastes like 522 CW has to be operated separately and to be located in an isolated environment. It is an adequate 523 technology for handling infectious wastes, cytotoxic wastes, chemical and pharmaceutical wastes 524 but not adequate for radioactive wastes (treatment does not affect its properties and may get 525 dispersed its radiations), pressurized containers (gets exploded during the process and may cause 526 damage to the incinerator) and high heavy metal content wastes (emission of toxic heavy metals 527 into the atmosphere on incineration process). Exhaust gases and ashes are produced upon 528 incineration of CW, which may still carry some toxic substances and has to be treated again. Generally, the equipment and operation costs are high due to its excess energy consumption, and 530 the by-products so formed are highly corrosive, which causes the kiln to get often repaired or Alternative disinfection technology that can be adopted for the treatment of CMW would be 1) 540 High-heat Pyrolysis, 2) Medium-heat Microwave and 3) Low-heat autoclave techniques. Table 2 . Considering the advantageous nature of pyrolysis techniques and its capacity in effective 612 dealing of municipal wastes, the same can be enforced for the treatment of COVID-19 waste. The technology utilizes high-temperature combustion, which can be applied for complete as well as lesser residence time. In the carbonization process, the feeding stock or CW upon 682 slow pyrolysis gets converted to highly stable carbonaceous products, namely charcoal or char 683 and non-condensable gases, which are excellent sources of fuels. In the metallurgical industry, 684 charcoal has been widely used as a reductant in the smelting and sintering processes. Char is 685 formed during slow pyrolysis, which on further processing forms the activated carbon as a 686 product and they have the property of good absorbent. Torrefaction is a thermal process that 687 converts the feeding stock or CW to coal-like substances and they are highly brittle, less energy-688 intensive and can also be used as fuels (Das and Tiwari, 2018). Table 4 . Pyrolysis occurring in a fixed-bed reactor makes it easier to build and easier to run, but since the 859 plastic waste has low thermal conductivity, which can produce a wide temperature gradient in a 860 batch method as well as in the continuous but due to the irregular feedstock shapes, they face 861 feeding problems. So, these types of reactors are not to be fit for industrial purposes. Residence time can be regulated by changing the feeding rate or product discharge rate. More Furthermore, a lower percentage of oil in the product and a higher percentage of char result in polymers do not melt; rather than start cracking, they release useful energy-bearing products 899 such as liquid oil, gases (syngas, hydrogen gas), hydrocarbons (HCs) and charcoal (Gao, 2010) . 900 The most common methods adopted in refining and upgrading the liquid fuels or bio-oils recover other valuable byproducts compared with another factional condensation system after the 920 pyrolysis process (Papari and Hawboldt, 2018). Therefore, similar techniques or technology can be adopted for processing the CW or CMW to get converted into useful products like liquid fuels 922 or bio-oils, which can act as a better replacement for fossil fuels (Klemes et al., 2020) . In order to lower reaction temperatures and improve product delivery, catalysts have been 931 studied for the CFP of waste polymers. In the resulting oil, HZSM-5 catalyzed PP pyrolysis will 932 reduce BTX formation temperature from 700 °C for pure PP to 300 °C with three main 933 compounds, i.e., alkenes, dienes, and aromatics. This is an essential influence on the pyrolysis 934 processes of both the polymer microstructure and the feed mixture. Pyrolysis of pure HDPE 935 using HZSM-5 has, on the other hand, significantly increased the production of gaseous 936 products, particularly C10-C16 hydrocarbons. In the pyrolysis furnace, the solid product obtained by pyrolysis of medical plastic waste 938 was mainly the solid residue remaining and the carbon black produced. A gas chromatography-939 mass spectrometry was used to assess the chemical compositions of liquid products. Gas Also, the COVID-19 pandemic has led to an increase in the enormous amount of plastic wastes. These non-renewable polymers upon pyrolysis result in the formation of syngas, HCs and H 2 969 gas. Pyrolysis may also be an environmentally benign and process-efficient way of handling 970 plastic waste from COVID-19, producing value-added products simultaneously. Pyrolysis makes 971 it a simpler and cleaner way to turn waste into energy products, such as ready-to-use fuels. Other 972 technology like incineration of plastic waste may lead to the emission of toxic pollutants such as 973 dioxins and furans, which needs additional flue-gas treatment facilities. As we look forward to a 974 post-COVID-19 future, it will be of primary concern to counter fear-driven prejudices toward Table Table 1 : List of some common materials of COVID-19 Medical Waste (CMW) and their associated plastic wastes Table 2 : Different types of reactors used in pyrolysis process for the treatment of CW The feedstock is mounted in the stainless-steel reactor, which is externally heated by an electric furnace. It is flushed by inert gas such as nitrogen or argon until the reactor becomes usable and this gas flow is retained throughout the entire process to provide an anaerobic atmosphere. During pyrolysis, the obtained gases and vapours are discharged from the reactor, but char is normally extracted after the process. Low heating rate is defined for the fixed bed reactor. 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The reactor provides the solids with excellent movement, leading to high transfer rates of heat between phases, making them ideal for flash pyrolysis. In addition, the conical sputter bed reactor is ideal for continuous operation, which is particularly important for the largerscale implementation of biomass pyrolysis. Spouted beds have been successfully implemented for pyrolysis of a number of polymers including polystyrene, polyethylene, polypropylene and polyethylene terephthalate. In this type of reactor, waste plastics melt as they are fed into the reactor and, due to their cyclic movement, provide a J o u r n a l P r e -p r o o f 65 uniform coating around the sand particles. It also provides high heat transfer with sticky solids from plastics between phases and smaller defluidization problems.broadly dispersed particles. 3. In addition, with respect to gas flow, the device has great flexibility, allowing operation with short residence times for gas. 4. The pattern of solid flow and the spout's action reduces the agglomerate formation. In the slow pyrolysis of MSW, rotary kiln reactors were used and normally performed at temperatures of around 500 C with a residence time of around 1 h. It is vital that solid waste of different shapes, sizes and heating values can be fed either in batches or continuously into a rotating kiln; this feature makes it possible to use this type of reactor extensively. Rotary kilns provide improved heat transfer to the feedstock than fixed beds and are less difficult to run than fluidized beds at the same time.In the pyrolysis process, the residence time of the feedstock in the reactor is a very significant parameter since it defines the energy obtained at a given heating rate by the charge. Residence time is usually a function of the mean volumetric flow and the rotational speed of the kiln in rotary kilns.1. This is the only type of reactor that has so far been successfully implemented on different scales as a practical industrial solution. 2. The slow rotation of an inclined kiln causes the waste to be blended well more uniform pyrolytic products can therefore be obtained. 3. The versatile residence time change will make the pyrolysis reaction easy to conduct under optimum circumstances. Microwave energy is derived from electrical energy and most of the domestic microwave ovens use the frequency of 2.45 GHz. The transfer of energy occurs as a result of interaction between the molecules and atoms using microwave. The whole process of drying and pyrolysis are carried out in a microwave oven chamber connected to electricity source. The carrier gas is inert and is also used to create oxygen-free chamber. The reactor has proven to be highly effective in chemical recovery from biomass. Plasma is a gaseous mixture of negatively charged electrons and positively charged ions produced by intensively heating a gas or by exposing a gas to a powerful electromagnetic field. Two major plasma classes exsist, namely plasma fusion and gas discharges. A direct current or alternating current electrical discharge or radio frequency induction or microwave discharge may be used to produce thermal plasma. To generate plasma, also a 2.45 GHz magnetron available from a commercial microwave oven can be used. As carbonaceous wastederived particles are pumped into a plasma, they are heated very quickly, releasing and cracking the volatile matter, resulting in hydrogen and light hydrocarbons such as methane and acetylene. Only two streams are formed by thermal plasma pyrolysis of organic waste: a combustible gas and a solid residue, all of which are useful products and simple to handle. Gas yields range between 50 and 98 percent by weight. In this reactor the feedstock is conveyed into the vacuum chamber with a high temperature with the aid of a conveyor metal belt with periodical stirring by mechanical agitation. The heat carrier normally consists of a burner while the feedstock is melted using molten salts by heating inductively. It has the potential to process feedstock of larger particle size, but needs special solids feeds to specialised discharge devices to provide an efficient seal all the time. Under very low pressures, which can be around 5 kPa, vacuum pyrolysis is performed. This is a slow pyrolysis reactor with a very low rate of heat transfer. This usually results in lower bio-oil yields in the range of 35 to 50 percent by weight.