5 Hazardous Wastes “Any useless, unwanted and discarded material that may pose a threat to human health andlor environment is called hazardous waste”. Introduction: As per the abbreviated definition by the United States Environmental Protection Agency (US EPA), hazardous waste means “a waste or combination of wastes which because of the quantity, concen- tration or physical, chemical or infectious characteristics may cause, or Significantly contribute to increase in mortality or an increase in serious irreversible, or incapacitating reversible illness, or pose a substantial present or potential hazard to human health or the environment when improperly treated, stored, transported or disposed off, or otherwise managed. The hazardous wastes include wastewater treatment sludges from electroplating, spent halogenated solvents used for degassing (e.g., trichloroethylene, methylene chloride, etc.), spent unhalogenated solvents such as xylene, acetone, ethylbénzene, ethyl ether, etc.), sludges from petroleum refineries, dewa- tered aif pollution control scrubber sludges from coke ovens and blast furnace sludges, radioactive materials and medical wastes. In this chapter, we mainly concentrate on the management of the following three types of wastes: (i) Radioactive wastes (ii) Bio-medical wastes and (iii) Non-radioactive industrial liquid wastes. (i) Radioactive Wastes Nuclear power’ production is the ro ot cause of radioactive waste problem. The environmental effects of nuclear Power generation mainly arise from (a) the nuclear fuel cycle (b) low-level dose radiations from nuciear-power-planteffluents, and 133134 A Text Book of Environmental Chemistry (©) low-and high-level dose radiations from radio-active wastes. All nuclear reactors rely on uranium as fuel. the natural uranium contains 99.2% of U-238 and 0.72% of U-235. It can be used as such in heavy water reactors. For use in light water reactors, it should be enriched to about 3 to 3.6% with respect to U-235 content in an isotope enrichment plant, The enriched uranium is fabricated into fuel rods and are inserted in nuclear reactors. During operation of the reactor (for 1 or 2 years), the fuel rods become intensely radioactive due to the generation of fission products and trans-uranium elements such as plutonium americium and curium, After the fuel rods are removed from the reactor, they should be cooled in water-filled pools (known as spent-fuel storage bay) to remove the heat liberated due to radioactive decay. The fucl cycle is then completed by disposing of the fuel in an underground repository or separating the residual plutonium from uranium and fission products in a chemical reprocessing plant. The fission products are then immobilized by incor- porating into ceramic or glass matrix and disposed off into an underground repository. The enriched uranium fuel cycle involving light-water reactor is shown in Flow chart No.1, given below. Low-level radioactive wastes arise from a broad spectrum of radio- isotopes produced by mining facilities, and by medical and research activities ¢.g., Fadio-isotopes used for cancer treatment, contaminated glass, clothes, filter paper and other laboratory appliances. High-level radioactive wastes are generated in nuclear reactor fuel cores as spent fuel and also from nuclear fuel reprocessing. jon on living cells __ The particulate and electromagnetic radiations emanating from radioactive materials inflict deleterious effects on the living cells. These effects are Classified as “somatic” and “genetic”. “Somatic effects” are caused on the exposed individuals and the cell damage caused may manifest in malig- nancies such as leukemia or cancer. “Genetic effects” are transmitted to the descendants of exposed individuals and thus can affect unexposed generation too. The radiation-induced changes in the genes may manifest themselves in (a) gene mutations, (b) chromosome aberrations and (c) changes in the number of chromosomes. Such changes can result in abnormalities in the offsprings which may be mild or lethal. The extent of damage from radioactive materials depends on (a) physical properties such as half-life of the radioisotope involved and the type and energy of the radiations emanating. (b) their ability to enter the food-chain, and (©) their tendency to become concentrated in the living’ tissues.» 135 [any poyouud orimbox yoy sOrDEaI xOTEM-1YBE J0J BDA YONA “1 “ON UEYD MOLL Teung JOIN SOISEA\ [OAT] MOT Tepuoww0D, JomMod, woneouqed "an poyouuy Sura quaur Burssoooidoy jong wods { Sussesoideu SIEM PHOS Tao UST woruesn porajdop -youus °4n, - Jo d8ei0g Hoxardous Wastes ‘Kiousoday, Axons136 A Text Book of Environmental Chemistry The extent of damage is maximum in the reproductive organs, block forming tissues, the digestive tract and developing embryos which are called radiosensitive organs. Environmental Problems & Management of Nuclear Wastes Wastes from uranium mining and milling Uranium is present in the earth’s crust in a concentration of about 3 parts per million (ppm) by weight. However, economic recovery is possible only if the urafiium content of host rock is about 300 to 3000 ppm. Canada, USA and South Africa are the three largest uranium-producing countri inthe world. Uranium mining operations in Canada are located in the vicinity of the granitic precambrian shield. The locations are also characterised by the presence of large number of muskegs, rivers and lakes, and precipitation rates far exceeding those of evaporation. Hence, on the basis of climatic considerations, more emphasis is put on gurading against:the leaching of radioactive isotopes (¢.g., Rs-226) into surface waters. In contrast to this, most of the uranium mining in USA is carried out in sand-stone deposits. The milling operations associated are conducted in semi-arid regions of the midwest and southwest, where evaporation rates far exceed the rates of precipitation. Thus, water seepage from the surface is not a significant problem. The serious problem in these areas is the dispersion of tailings by wind-storms or flash floods. Thus, in view of these climatic features, greater emphasis is naturally placed on ensuring that the tailings are disposed of in such a way as to prevent erosion by wind or flood water. The standard proposed by the United States Environmental Protection Agency (EPA) in Jan 1981 for the radon emission flux from the tailing piles was < 2 pci/m’s (2 pico curies per square meter per second), which was nearly equivalent to the natural background in many parts of that country. However, the standard was increased 2 years later to $ 20 pci/m?s to be maintained for at least 2 centuries. In South Africa, most of the uranium is recovered as a by-product from gold mining operations, The uranium concentrations are generally below 300 ppm and hence the radioactive hazard is far less than that from the richer North American ores. ‘The uranium recovery from the ore involves crushing and grinding “the ore to a finely divided state, followed by dissolution of the uranium- containing minerals in an acid or alkali. The solution is filtered to separate it from the bulk of the inert ore and is then treated further to recover the * uranium, The large mass of the residual solids is then piped as a slury to the tailing pond for disposal. The tailings pose problems due to the presence of chemical, mineral and radioactive contaminants. For instance, if the ore contains pyrites (Fe S,), the fine particles of pyrites formed during crushing and grinding ofHazardous Wastes 137 the ore go with the tailings. These particles of pyrite are most susceptible for the attack by oxygen, water and bacteria than the original massive form of the ore underground. Thus, sulphuric acid is formed which can percolate slowly into the rivers and lakes nearby which is undesirable. Further, the tailings also contain toxic metals such as As, Cd, Hg, Fe, V, Zn and molybdenum and large quantities of ammonium, chloride and sulfate ions which may pose a threat to the nearby environment. However, the radioactive isotopes present in the tailings include Ra-226, Th-230 and Rn-222 (and its radioactive daughters) which are of greater environmental concern. The Ra-226 found in freshly discharged tailings can undergo slow dissolution by the water percolating through the deposit and contaminate the surface waters. When ingested by humans, the Ra-226, which is similar to Ca, gets deposited into the bone structure, Even when 1 microgram of Ra- 226 is retained in the body, it can cause serious bone damage. The radio concentration above the tailing piles can be several hundred times higher than thenormal background level butitquickly gets diluted by thesurrounding air mass and does not pose any threat beyond 1 km distance from the tailings piles. Th-230 has a long half-life of 7.7 x 10* years and hence has a relatively low specific activity. But, it is the continuous generation of its daughter element! viz., Ra-226 (with a half-life of 1600 years and having higher chemical mobility) which poses a low-level radioactive hazard over thousands of years after disposal. ‘~The methods for storage and disposal of the tailings are site-specific f depend upon parameters such as the local climatic features, topography, geology, the nature of mining operation (i.e., open pit or underground) and the proximity of populated areas. In the arid regions of the south western regions of U.S., the tailings are disposed in a depression below the ground level and covered with 1 to 3 meters thick layer of soil, sand gravel or crushed rock. In areas where precipitation (i.e., rainfall) is higher such as at Alliot Lake in Canada, the design of the tailings disposal facility is based ‘on ensuring minimum dissolution of Ra-226, toxic metal ions and other contaminants such as chlorides and sulphates. Wastes from refinery and fuel fabrication In the refineries where uranium concentrates from mines are purified, small quantities of uranium bearing wastes are generated. These wastes are usually accepted back into the milling circuit at mine-mill sites at no charge because those wastes are equivalent to high-grade ore from many mines. In fuel fabrications such as pressing, sintering and grinding, small amount of uranium oxide waste is produced. Since uranium is so valuable, this waste is recycled through the fabrication process by dissolving it in138 A Text Book of Environmental Chemistry nitric acid, precipitating as ammonium diuranate and converting to uranium dioxide powder, ‘Thus uranium refining and fuel fabrication processes are closed circuit operations and no significant uranium wastes escape into the environment, High-level wastes from spent nuclear fuel When spent fuel is discharged from light-water reactors, it consists of a mixture of uranium, plutonium and fission products. Since the heat flux from the decaying fission products is too high during the first one or two years, underwater storage is the most desirable option. However, as the time passes, interim dry storage in concrete canisters seems to be a more economical option, even for longer storage times. The ultimate waste disposal process envisages the use of multiple- barrier system. The spent fuel bundles are loaded into containers made up of corrosion-resistant material such as titanium-, nickel- or copper-based alloys. The interstices between the fuel bundles and the container are filled with a particulate support (¢.g., glass beads) or by a lead-antimony alloy. The sealed containers would then be placed in cavers drilled in a geologically- stable granite rock repository, around the container to separate it from the rock, After filling of the repository, all rooms, boreholes and shafts would - be backfilled and plugged so that no further supervision is required. ‘The possibility of disposal into underground salt domes has also been studied in USA. Another possibility that is being explored is the disposal of radioactive waste into the deep sea bed, where tectonic movement would slowly propel the wastes downwards into the earth’s crust. , Technology is also available for incorporating highlevel radioactive wastes into borosilicate glass or ceramic matrix or polycrystalline “synrock”. ‘Thus, the radioactive waste is fixed or immobilized into the solid matrices of proven stability so that it can then be safely disposed in suitably designed and constructed underground repositories that remain free from any disruptive seismic or tectonic activity for millions of years. ‘The general public still seems to believe that there are serious unresolved environmental problems associated with the nuclear fuel cycle. This view is fostered because of incomplete, incorrect and exaggerated information. But, despite the perceived problems, the fact remains that technical solutions are now available for the safe, long-term management of uranium mine and mill tailings and of high-level wastes from nuclear power reactors. (i) Biomedical Wastes Biomedical wastes originate from hospitals, clinics, research and testing laboratories and: drug companies, These include pathological and surgical wastes : experimental animals and cadavers, drug and chemicalHazardous Wastes 139 residues and their containers ; discarded bandages, linens and other infectious wastes ; disposable syringes, needles and surgical instruments ; contaminated equipment, food and other waste materials. Chemical and chemotherapy wastes, organic solvent wastes and radioactive wastes are not included in the biomedical wastes because they are governed by different regulations. In countries like USA and Canada, biomedical wastes are controlled as per USEPA’S 1985 guidelines for Infectious Waste Management and the Ontario Ministry of the Environment’s Guidelines for the Handling and Disposal of Biomedical Wastes respectively. On-site handling of wastes and their off-site disposal are considered as the responsibility of the waste generators themselves, The normal practice for handling hospital wastes is the on-site incineration of the combustible solids in a specially designed high temperature incinerator provided with after-bumers to heat the gases leaving the chamber to 700°C for controlling odours. The ash thus produced is disposed in a sanitary landfill. Wastes from such hospitals which do not have facilities for incineration or sterilization are segregated, packed in specially coded and labelled containers, and transported to a place where such facilities exist. Chemical Wastes Modern civilization hasresulted in large scale-manufacture of products suchas TV sets, aerosol cans, pesticides, plastics; preservatives, automobiles, etc. These industries generate a multitude of hazardous industrial wastes, toxic substances such as heavy metals. Proper management of these hazardous industrial wastes is mandatory from the point of view of public health and environmental protection. Incidents like “ Love Canal Episode’*, which “Love Canal Eplsode : Hooker Chemical company (Niagara, New York) disposed its hazardous wastes for several years until 1952 by burying them in 55-gallon drums in a ditch known as the Love Canal. After the ditch was filled, it was capped with clay. Later the land was sold for a throw- away price to the Board of Education of Niagara Falls. A school and some residences were built on the site.The clay cap was cracked due to construction, water got infiltrated into the trenches containing the waste, Afler 25 years, the wastes began to leach out. The leachate enetrated the basement walls in the area, surfaced in back-yards and volatalizéd in the air. Several people fell ll. Over 300 different chemicals, including some carcinogens, were identified {in the ambient alr. The President of USA had to declare in August 1978 that Love Canal was 4 Federal Emergency Disaster area. Several families were evacuated from the area. The clean-up of the canal and stabilization of the area (by claycapping and drainage ditches) costed over 40 million dollars. Hooker Chemical Company was sued for claims amounting 10 about 2 billion dollars, ‘The disaster obviously was the result of improper disposal of hazardous waste. In 1985, it was found that Love Canal Experience is only the tip of an ice-berg and several other waste disposal sites in USA need federal cleanup assistance over the next 50 Years at a cost of about 100 billion dollars.140 A Text Book of Environmental Chemistry festered for 30 years before its dangers to humans were exposed, emphatically demonstrated the consequences of improper disposal of hazardous wastes, Environmental Effects All chemicals are toxic to humans beyond some concentration. From the environmental protection point of view, the important points to be considered are (a) at what concentration a particular substance becomes toxic, and in what form ? (b) What are its environmental pathways ? That is, what are the entry routes for these hazardous chemicals and wastes into the environment ? (c) With what persistence and at what biological concentrations that toxicity is manifested in the environment ? The various entry routes for hazardous chemicals and wastes (for dumps and industries) into the environment include (a) leaching into adjacent land, (b) leaching into streams, * (©) leaching down into the water table, (d)_ evaporation, To : (©) incineration, and . (f) spillage during transit. Toxic chemicals The inorganic chemicals of concer are heavy metals such as Hg, Cd, Pb and As which act as biological poisons even at parts per billion (ppb) levels, These toxic elements accumulate in organic matter in soil and sediments and are taken up by growing plants, thus entering the food chain. Since these chemicals are poorly excreted by humans, they accumulate in organs and tissues to toxic levels in the body. Toxic metals enter the atmosphere by burning of fossil fuels (e.g., coal and leaded gasolene), reach receiving waters through atmospheric fall-out and leaching from mines and landfills, and contaminate land as a result of sewage sludge application. Low pH caused by acid rain or the generation of carbon dioxide increases the transportability and hence availability of these metals by rendering them more soluble, . ‘The organic chemicals of concem are those that persist (i.e., those that degrade slowly) in the environment and are fat soluble, since they an accumulate in the food chain. Polychlorinated biphenyls (PCB's) andHazardous Wastes 141 pesticides fall under this category which cause inimediate toxicity as well as long term effects such as carcinogenicity and mutagenicity. Many of these persistent pollutants are generated from the degradation of primary substances or from burning of chlorine compounds. Also, incineration of municipal solid wastes, and burning of organic materials and fossil fucls also release toxic chlorinated organics into the atmosphere, Some of these polluting organics are also adsorbed on dust and fly ash, thus enabling wide spread distribution in the atmosphere. Other important organic pollutants include pesticides (e.g., DDT), biocides (e.g., Dioxin), insecticides (e.g., Fenitrothion and Mirex), CHC, and trihalomethanes. Identification of Hazardous wastes A simple approach to identify hazardous wastes is to consider these under general categories, such as toxic, inflammable, radioactive etc. Such a Classification system helps the Fire Service to properly deal with the hazardous wastes under emergencies. Many countries (¢.g., UK, Germany, France and Netherlands) supply a supplementary classification system for hazardous substances along with the general classification system and some countries also set maximum concentration limits for different contaminants. However, in Japan, the following four types of wastes viz., sludges, slags, acidic wastes and alkaline ‘wastes; which contain any of the 9 toxic materials (viz., As, Cd, Cr(VI), ~Pb, Hg, CN, PCB’s and organic phosphates) beyond permissible limits, are considered to be hazardous. It is best to identify the hazardous wastes on the basis of algorithms that consider toxicity, reactivity, persistence, corrosivity, inflammability, quantity of waste involved, the extent of hazard to the environment and the ultimate effects on living organisms. The hazardous wastes are identified in the U.S. as per the Federal Register of May 19, 1980. The US EPA (United States Environmental Protection Agency) considers the following five basic criteria for identifying a hazardous waste : (i) Whether the material falls under the category of solid wastes as defined by the Resource Conservation and Recovery Act (RCRA) of 1976 ? As per this definition, the term “solid waste” included not only just solids, but liquids, semi-liquids and contained gaseous materials as well. (i) Whether the waste has been legally discarded ? This stipulation is applicable to the wastes that are stored or treated prior to disposal but not to those to be recycled.12 A Text Book of Environmental Chemistry (iii) Whether the waste is specifically excluded by the regulations? 'Forinstance, agricultural wastes, municipal solid wastes, animal manures, ctc., are excluded. (iv) Whether the waste has toxic or hazardous characteristics ? That is, whether it has the potential to increase the mortality or illness or whether it poses a substantial threat to human health or environment on the basis of hazardous characteristics such as flammability, corrosivity, toxicity or explosiveness ? As regards the human toxicity, in the absence of adequate toxicity data, a waste is considered to be hazardous if (a) it has an oral LDSO toxicity equal to or greater than 50 mg/ kg (i.e., LD5O is the lethal dose of the toxic waste at which 50% of the experimental animals die as a result of oral ingestion or dermal penctration), or (b) thas an inhalation LC50 toxicity of 2 mg/kg (LCS0 is the lethal ambient concentration of the toxic material in mg/L of air causing 50% mortality to test rats during 4 hour-inhalation). As regards the hazard to health or the environment, the following, standard tests which have been quantified by EPA, are considered:., (i) Ignitability (:., whether the waste causes or enhances fires) (ii) Corrosivity (i.e., whether the waste destroys the tissues or metal), (ii) Reactivity (i.e., whether the substance reacts violently or causes explosion, and (iv) Toxicity (j.e., whether: the substance pollutes water supplics and threatens the health). As far as the toxicity to the groundwater is concemed, limits for 14 common contaminants have been considered as the basis for determining human toxicity. These 14 toxic substances include 8 metals (viz., Hg, Cd,Cr, As,Pb, Ba, Se and Ag), 4 Pesticides (viz., Endrin, Lindane, Methoxychlor and Toxaphene and 2 herbicides (viz., 2, 4-D and 2,4,5-TP). When the concentration of these contaminants exceeds 100 times their respective permissible concentration in drinking water, the waste is designated aS hazardous.This toxicity of the waste is determined by the “Extraction Procedure (EP) Toxicity Test” which consists of agitating not less than 100 grams of the “solid waste” in 16 times its weight of de-ionised water at a controlled pH of 5 for 24 hours. The leachate is then analyzed for the 14 toxic substances listed above. If their concentrations exceed 100Hazardous Wastes 143 times those allowed in drinking water, the waste is designated as “hazardous”, Tests for radioactivity, phytotoxicity, mutagenicity, infectiousness, etc. are also being developed. (v) Whether the waste is listed as hazardous ? Wastes which are known to be hazardous (carcinogenic, mutagenic, etc.) but not amenable to the EP Toxicity Test described above are listed in the following three categories : (a) spent solvents used for degreasing etc., (b) specific sources such as process waste from wood preservation or manufacture of materials such as halo- genated hydrocarbons, and (c) discarded products such as mercury compounds, toluene, xylene, etc. and their containers, Management of Hazardous: Wastes ‘The primary objective of a hazardous waste management plan, is to eliminate or reduce the hazardous waste through processing changes or resource recovery. Having accomplished this objective, the remaining hazardous wastes must be accounted for from its origin to ultimate disposal. This “cradle-to-grave” concept is followed by countries like USA and Canada. The important components of a hazardous waste management plant are as follows : “ (1) Inventory : All the industries producing more than 100 kg of hazardous wastes per month should be registered. An inventory of such waste generating agencies and the quantity of the waste produced per month should be prepared. (2) Storage: The hazardous waste generating industries should equip themselves with special on-site tanks or basins for storage of large quantities of hazardous wastes. Chemically resistant drums should be used for temporarily storing small quantities of corrosive materials. (3) Transport : The wastes stored as above must be collected at regular intervals by licensed haulers and transported by suitable tanker trucks or flat-bed trucks (for the drums) or rail cars (for large volume of waste) to the approved disposal sites. (4) Spillage : A well-publicized emergency plan should be prepared todeal with unexpected spillage or accidental release of contaminants during transport to prevent environmental damage or public health hazard. (5) Disposal : The wastes collected as above should be transported toa physical and chemical treatment plant (PCT) for processing or concentration; or directly hauled to an approved hazardous waste treatment facility for final disposal,oo A Text Book of Environmental Chemin 2 Where onsite recycling of recorvery f ty of waste exchange shoul h Transferring wastes from big industries to amnaller ones w/ reuse low-purity oils, acids, alkalis, solvents, catalysts, valuable metals and other materials from concentrated wz be comsidered. Treatment and Disposal of Hazardous Chemical Wastes (A) Treatment and Disposal by Industry Where recovery or reuse of the waste is mA coon ideal underground conditions occur. In North America and Caz Centof the leasthazardous wastes are dispored on-site, in az) ponds and landfills, However,in France, West Germany, Denmark, 73 to 80 per cent of the hazardous wastes is centralized hazardous waste treatment and disposal fai ‘When wastes are unsuitable for disposal, a suitable meshed ox of methods described below, for pretreatment of the waste before sale disposal must be selected. (A) Physical methods : A number of physical processes are avai for pretreatment of hazardous wastes before safe disposzt. Solid-l separation can be achieved by centrifugation, sedimentation, fi flotation, Adsorption of toxic organic components can be accom with activated carbon. Removal of specific components can be Ss by stripping, distillation or membrane processes such 2s dialysis, elec dialysis and reverse osmosis. . (B) Chemical methods : Chemical processes play 2n important pat in hazardous waste treatment operations. Some of the important examples are given below. (i) Oxidation of cyanides to cyanates or to CO, and N,by alkaline chlorination, (ii) Reduction of hexavalent chromium to less toxic trivalent chromic compounds using suitable reducing agents such as SO.. (iii) Precipitation of toxic heavy metal salts as sulfides. (iv) Ton-exchange for removing dissolved metallic or nonmetallic inorganic compounds.Hazardous Wastes 4s (v) pH-adjustment of lime slurries with acidic pictkle liquor. (vi) Immobilization or Stabilization or chemical fixation of toxic inorganic sludges using ceramic, glass, cement or lime based inert matrices. (©) Biological Processes The various biological processes used in wastewater treatment have been discussed in the chapter on Water Pollution. Some toxic organic materials e.g., phenols, oils, refinery wastes, etc., can be successfully treated and over 60% removal of many heavy metals (e.g., Cd, Pb, etc.) can be achieved if the concentration of these toxic materials isnot high and the biological process can be acclimatized to these materials. ‘These results are usually accomplished in municipal wastewater treatment _ plants in combination with sanitary wastes which provide dilution and buffering capacity along with organics and nutrients required for the growth of micro-organisms. Aerobic biological processes where rapid microbial growth occurs are less sensitive to toxic materials as compared to the anaerobic processes which have slower microbial growth. Further, other factors which improve the ability of conventional biological treatment plants to accept toxic wastes are high active solids concentration, long sludge retention time and a high organic concentration (i.e., a strong sewage). However, if sufficient sewage is not available for combining with the industrial wastes, degradation’ of toxic organics or removal of metals by the conventional biological processes may not be feasible. In such cases, use of other biological methods may be explored. For instance, land farming jily wastes offers an efficient and economic treatment method if thin layers of waste are spread over longer intervals of time. Another interesting but distinct Possibility seems to be the use of bacteria for removing more concentrated metals from wastes. It has been reported that 15 to 20% of the copper production in USA is by bacterial leaching. A uranium mine in Canada is reported to rely totally on bacterial leaching for its uranium production. (B) Off-site hazardous waste disposal Whenan industrial establishmentis not able to dispose of its hazardous waste in an on-site facility or into municipal sewers, the following three alternatives for offsite disposal are considered. (i) Hazardous ‘waste treatment facility : In a hazardous waste treatment facility, organic wastes are either incinerated or treated (physically and/or biologically) to produce an acceptable liquid effluent and a concentrated sludge that can be landfilled. Inorganic wastes are detoxified, neutralized and concentrated to produce an acceptable liquid effluent and a sludge which can be further concentrated and solidified by chemical fixation for146 A Text Book of Environmental Chemisir landiill disposal. Gencrally, a combination of these or other processes may be required for treatment and disposal of hazardous waste products and by- products, (ii) Co-disposal : The hazardous waste may sometimes be codisposed with municipal refuse. In such a case, the relatively small quantitics of hazardous inorganic liquid wastes and some organics will be absorbed by large quantities of the refuse so that the contaminants are attenuated by the waste and the surrounding soil. (iii) Secure landfill : The practice of disposing some detoxified hazardous wastes under carefully controlled conditions was followed in Japan, but, however, most of the hazardous waste systems rely on land disposal at some stage or the other. In places like California, New York and Illinois, landfills have been the usual repository for untreated or inadequately treatéd industrial wastes. In contrast, European countries used security landfills only for the residues from physical and chemical treatment (PCT) facilities, incineration and solidification, thereby reducing the waste and Ieachate volumes to be stored, treated and monitored indefinitely. In Denmark, 20% of the hazardous wastes are landfilled with an option for heavy metal recovery from them in future. Secure landfills are meant to accept and retain concentrated inorganic and organic hazardous wastes for indefinite period, perhaps, in perpetuity. Ifnecessary, leachate can be periodically removed for treatment and disposal. The secure landfill is the ultimate repository for all hazardous wake, residues and it should be considered as the last resort when all other eff@fts, tocliminate the waste problem fail. In designing a security landfill, protec! of groundwater from pollution is the main concern, apart from subsidence, fires, explosion, erosion and migration of organics. In the absence of adequate data regarding the migration, degradation and synergistic effects of hazardous pollutants in the soil, the North American practice is to design secure landfills for total containment. In contrast to this, the approach in the UK considers in its design the attenuation of the contaminants in the soil. A secure landfill must be located in a land of marginal agricultural potential in a rural area, at ledst 8 km from populated areas and 750 m from the nearest neighbour. It should have 1 to 5 % surface slopes overlying deep impermeable clay and the maximum ground water table should be at least 1.5 m below the bottom of the landfill. Other hydrogeological parameters, surface drainage, wild life, flooding potential, access to vehicles to the area and connection to major water resources and community water _ Supplies are the other important considerations in selecting the land for security landfills.Hazardous Wastes . 147 Although many designs are possible for a secure landfill, a typical one used in Niagara Falls, New York is described here to illustrate an example. An area of about 10 hectares and located in heavy clay, partly above and partly below the original ground, to provide an overall depth of over 10 meters. Three lifts were allowed for several cells, with each lift and cell being separated by a clay or absorbent barrier. The clay bottom is excavated and sloped to instal an underdrain monitoring system below the landfill for future surveillance. A synthetic membrane liner (made up of PVC, Hyapalon or High Density Polyethylene) sandwiched between protecting clay layers, was then placed over the sloped bottom. Sump pipes of about 900 mm dia were installed vertically as the filling progressed for leachate monitoring. If there is a probability of burial of organic wastes, provision for gas venting is also made. Finally, when the filling was completed, a sloping clay cap with a synthetic membrane was placed and finished with Jop soil and grass cover. Some of the features of a Secure landfill are shown in Fig 14. Internal Monitoring & Leachate Collection wells. soil cover External [ma WLS Cloy cover Top-soll & gross \ = Menibfone Liner Historically high woier table Fig. 14, Some special features of a secure land-fll. A secure landfill should not be considered as the sole means to hazardous waste disposal. It should be a part of an overall system which minimizes the volume and hazard of the waste by physical and chemical ueatment (PCT), incineration and solidification. Since the leachate characteristics are mostly site-specific and waste- specific and vary considerably, the type of the leachate treatment, disposal, recycling or interim storage have to be decided accordingly. So far, no148 A Text Book of Environmental Chemistry standardized approach to leachate treatment could be made. However, recent researches on the use of upflow anaerobic filter and anacrobic fluidised bed systems for treating organics present in leachate seem to be very promising. To sum up, a secure landfill is an essential component of a hazardous waste management plan. It should not be used as a receptacle for untreated hazardous wastes. It should serve only as the ultimate resting place for the unrecyclable, detoxified and solidified hazardous waste residues. Even then, the leachate formed should be collected and treated to specified requirements before disposal. Questions 1, ‘What are hazardous wastes and how are they classified ? 2. Discuss the environmental problems associated with nuclear wastes? How can they be managed ? 3, Write informative notes on biomedical waste management. 4, What are the major types of chemical wastes that we are generally confronted with ? What are the various entry routes for them to escape into the environment ? 5. Discuss the important factors that should be considered for a hazardous waste management plant ? 6. Discuss the various methods used for the treatment and disposal of hazardous chemical wastes from industrial processes ? 7. Describe with the help of a diagram the essential features of a secure land-fill. 8 Write informative notes on any two of the following : (a) Considerations in the design of a security land-fill (b) Co-disposal (©) Biological processes used in treatment of wastewaters contain- ing hazardous chemicals (d) Basis for the identification of hazardous wastes.