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Case Study A: Report of the Panel on Sewage Sludge William A. Garber, Bureau of Sanitation, Los Angeles, Chairman John F. Andrews, Rice University David G. Davis, Environmental Protection Agency James J. Gift, Ecological Analysts, Inc. Thomas D. Hinesly, University of Illinois, Urbana Ronald L. Kolpack, West Covina, California Cecil Lue-Hing, Metropolitan Sanitation District, Chicago Thomas Walton, City of Philadelphia Water Department Laurent McReynolds, City of Los Angeles Albert L. Page, University of California, Riverside 5.1 INTRODUCTION 5.1.1 Why Must Wastewater Sludges Be Studied? For every 1000 cubic meters of wastewater received in a wastewater treatment plant there will be of the order of 60 to 320 kilograms dry weight of solids that must be disposed of. The amount depends on factors such as wastewater strength, use of anaerobic stabilization, and the presence or absence of combined sewers. Since this residual is usally produced as a slurry of from 2.5 to 10 percent solids it is termed sludge. The sludge can be further processed by dewatering and drying prior to final disposal. However, because of its possible content of toxic contaminants, sludge whether wet or dry has had constraints placed on its use or disposal. These constraints apply to ultimate land, air, or water placement and have made the problem of sludge solids disposal a major one for almost all municipalities and industries. The magnitude of the problem can be illustrated by the treatment facilities of the City of Los Angeles, where a 113,550 m3 per day secondary treatment plant must dispose of 18,000 dry kilograms per 146
147 day and a 1,589,700 m3 per day facility must dispose of 180,000 dry kilograms per day. For cities such as Chicago, Illinois, or Atlanta, Georgia, only land or air disposal seems feasible. For coastal communities, sea disposal would appear to be a logical alternative. However, as pointed out in the report The Role of the Ocean in a Waste Management Strategy by the National Advisory Committee on the Oceans and Atmosphere (1981) current legislation or its interpretation, or both does not allow a full evaluation of alternatives. Decisions regarding the disposal of industrial and domestic sludges are now being made at the political, regulatory, project design, and operational levels. In many if not most cases, these decisions involve the commitment of large amounts of funds for capital expen- ditures, operations, and maintenance. Once such commitments are made, it becomes difficult, if not impossible, to make changes that take new environmental, financial, or scientific-technical developments into account. Given this fact, a basic question arises: Is the scientific-technical information now available about sludge disposal sufficient for making decisions within some reasonable risk factor? Similarly, the data a decision maker must deal with in regard to sludge disposal must include public perceptions of what is safe and suitable. Wastewater sludge from the city of Los Angeles, for example, could have been pumped to solar drying beds in the desert and then utilized for agricultural purposes or disposed of in a hazardous-waste landfill near the drying beds. Although this idea had considerable merit (see Chapter 4, Table 4.3), it was never a realistic possibility because of intense oppo- sition from desert residents and environmental organiza- tions. If this plan had included some type of benefit for desert residents, such as a park or a camping area or swimming pools, their opposition might have been defused, thereby allowing the environmental soundness of the plan to be objectively reviewed. Court-mandated time schedules prevented this, however, and an incineration scheme in an air-quality nonattainment area was adopted. At present the commitment of construction funds to the incineration alternative prevents further consideration of any other option. A decision maker considering waste disposal alternatives must take into account environmental conditions, current scientific-technical knowledge, public perception, mandated time schedules, and capital investment already made. The scientist cannot be truly
149 5.1.3 Approach to the Problem Sewage sludge is the residue that results from treatment of domestic and industrial wastewater. During the treatment process, a percentage of the impurities in the wastewater are concentrated by gravity settling (with or without f~occulant use), dissolved air flotation, or various mechanical methods and converted into a liquid slurry called sludge. ~ Being an aggregate of settleable fats, carbohydrates, and proteins with wastewater con- taminants a sludge may contain all the constituent elements found in domestic and industrial wastewaters. Because of the differences in the characteristics of communities, the composition of sludge can vary con- siderably from city to city. For example City of Los Angeles wastewaters receive 12 percent industrial- commercial waste, while Los Angeles County Sanitation Districts wastewaters have a 30-35 percent industrial flow. Other factors include the degree of wastewater pretreatment required of industry, the diversity of the processes utilized in treating wastewater, and the Presence of combined or separate sewers. It is therefore essential that the physical, chemical, and biological characteristics of each specific sludge be taken into consideration in deciding on a disposal method. Cur- rently, a variety of disposal/reuse options with differing potential impacts on land, air, and water resources are practiced. However, no option will ever have zero risk to society or the environment. Therefore, a comparative cross-media impact assessment incorporating uniform risk-analysis procedures applicable to all disposal media must be performed, and the results of this assessment must be used as a basis for selection. It is particularly important that the assessment be realistic, balancing risks, benefits, and costs. Some of the materials in waste sewage sludge are bio- dearadeable. others are not. . . · . . ~ ~ The end products of aerobic biodegradation are chiefly carbon dioxide and water. A major end product of anaerobic biodegradation is methane. These processes are time dependent and may produce a number of intermediate products that could potentially be more harmful than the parent material. Additionally, some organic compounds are persistent and require long periods of time (perhaps decades) to decompose. Inorganic elements, for the most part, are not biodegradeable. The choice of an option for sludge disposal/utilization will depend on physical, chemical, and biological character
150 istics of the sludge, the availability of suitable disposal sites, and local considerations. Local considerations include environmental factors (hydro- geology, climate, soils, water quality and quantity, and topography, for example), sociopolitical factors (governmental structure, socioeconomic Factors, ana public attitudes, for example), and technological factors (scale, transport, and available energy sources, for example). These factors, among others, determine not only the suitability of land, air, and ocean receptors but also the specific type of land, air, or ocean option best suited for disposal/reuse. Specific land-based options include landfill, dedicated land disposal, agri cultural reuse, land reclamation, and land maintenance (landscaping, for example). Ocean disposal options include transporting the sludge through pipes into deep or shallow water or dumping it from barges. Obviously, sewage sludges cannot be directly disposed of in air, but the products of thermal processing (incineration, pyrolysis) are disposed in the atmosphere, as well as on land (ash and fallout). Other disposal techniques include chemical or thermal fixation plus disposal in the ocean or on land. The remainder of this chapter is divided into four sections. Section 5.2 describes the source in terms of a multimedia disposal evaluation of the quantity and quality of a sludge. Section 5.3 outlines available sludge disposal/reuse options. Section 5.4 presents a discussion of site-specific and local considerations that must be recognized in a multimedia assessment. Section S.5 discusses elements of the evaluation process for a specific sludge and a specific site. Finally, a summary of salient points is given. A, , _, - ~ . 2 THE MATERIAL The starting point in a multimedia assessment is a knowledge of sewage sludge quantity and quality, both currently and in the future. This section describes sludge characteristics and the various processes that influence those characteristics.
154 background levels of trace contaminants from nonpoint sources are such that the use of digested sludge in horticulture and agriculture is viable, a considerable amount of toxicity testing and evaluation of risk must be performed. The risk evaluation model, now used in EPA water-quality criteria (U.S. Environmental Protection Agency, 1979b) may be so conservative that its results in specific cases preclude what may actually be viable uses of sludge. 5.2.3 Sludge Conversion In the past few years, most major cities have experienced considerable difficulty in obtaining new sites for sewage sludge disposal. Consequently, a variety of methods for stabilizing sludge or converting it to other products have been explored. One of the older techniques for sludge conversion is that of drying. In this process, heat is applied to reduce the moisture content of sludge to approximately 10 percent. The temperatures attained during this process are high enough to sterilize the sludge. The resulting product is a low-grade soil amendment-fertilizer. Sludge drying has been used successfully by several major cities, including Milwaukee, Houston, Los Angeles, and Chicago. Sludge drying is expensive, however, since it requires substantial amounts of energy. Furthermore, marketing of the product can sometimes be difficult, and there is now greater concern over trace contaminants, such as cadmium. It seems clear that cities cannot totally rely on this method of disposal. Another conversion process is comporting. This is an aerobic-facultative organism process in which partially dry sludge is mixed with composted sludge or other materials. The resulting combination is dry enough so that oxygen can reach the microbiological organisms. Forced ventilation is used in static pile procedures, while windrow agitation often relies on natural ventila tion. Stirring can be accomplished by the regular turning of windrows of the sludge or in mechanical units similar to furnaces used for cement production or multiple-hearth incineration. Composting provides further exothermic biological breakdown of the organic material, with the principal breakdown products being carbon dioxide and water. Temperatures high enough to inactivate bacterial, viral, and parasitic contaminants
155 can be achieved. The final compost is a stabilized material well suited for application on land. Several major population centers, including Philadelphia, Washington, D.C., and Los Angeles County have used comporting to dispose of part of their sludge. Composting can be an expensive operation, however, and marketing of the product can sometimes be difficult. Obtaining public acceptance of the process can also be difficult. Other sludge treatment techniques include chemical stabilization and irradiation. Chemical stabilization is usually used as a temporary expedient prior to landfilling or other land disposal. Only limited experience is available on the use of irradiation. A variety of thermal conversion processes is also available. These processes, which result in the con- version of sludge to gases and a residual ash, will be considered in a separate section, since air emissions and land disposal of an ash with concentrated trace con- taminants introduce other disposal problems. 5.2.4 Pathogens Domestic wastewater contains pathogenic microorganisms, such as bacteria, viruses, parasites, and fungi). These organisms are concentrated in sludge and must be inacti- vated to levels satisfactory to regulatory agencies prior to disposal. Reductions in pathogen levels can be accomplished in secondary wastewater treatment and sludge processing operations (anaerobic and aerobic digestion). Further reductions take place in sludge storage systems and after discharge to the ultimate disposal medium. suggested that ocean disposal causes increases in pathogen levels, but further work is required to provide or dis- prove this thesis (O'Malley et al., 1982; Sawyer et al., 1982). The best evidence of the limited degree of micro- biological hazard is the fact that digested sludge has been applied to land for many years with no known outbreaks of disease. Some agencies (State of California, 1956), as an extra precaution, recommend that root crops that can be eaten raw not be grown on land to which digested sludge is applied. This precaution may not be necessary for thermophi~ic digested sludge processed at 49-65°C. It has been
156 Anaerobic or aerobic digestion, as well as composting and sludge pasteurization, probably lead to minimal hazard. Table 5.1 presents the results of bacteriological analyses conducted by the Municipal Environmental Research Laboratory (MERL), Environmental Protection Agency, Cincinnati, Ohio, on samples of raw mesophilic (36°C) and thermophilic (50°C) sludges from the Hyperion plant in Los Angeles (Gerber, 1982b; Berg and Berman, 1980). The results indicate that both mesophilic and thermophilic digestion bring about substantial reductions in the num- bers of the indicator organisms as well as Salmonellae. In fact, Salmonellae populations were reduced below detectable limits by thermophilic digestion. Twelve animal enteric virus analyses were also conducted, and the results are presented in Table 5.2. Mesophilic and thermophilic anaerobic digestion substantially reduced virus concentrations. At 37°C, parasitic eggs are more resistant to destruc- tion under mesophilic digestion than are viruses and bacteria. For this reason thermophilic digestion (50°C) is the process used to treat sewage in Moscow, USSR. Poppua and Bolotina (1963) state: "The most essential advantage of this process is the sanitary quality of the TABLE 5.1 Reduction in Bacterial Densities in Mesophili and Thermophilic Anaerobic Digestion (20-Day Detention)a c Bacterial Densities (number/100 mLlb Raw Mesophilic Thermophilic Sludge Digestion Digestion Bacteria Feed (36°C) (50°C) Fecal streptococcus Fecal coliform Total coliform 2.7 x 107 2.0 x 106 3.7 x 104 3.6 x 108 5.5 x 106 2.9 x 104 5.2 x 109 7.0 x 107 6.4 x 104 Salmonella 7530 62 BDL~ ~From Garber, 1982. verage of measurements taken over 2-year period. ~BDE, Below detection limits (~3/100 mL).
161 The problem of cadmium toxicity in human foods grown on sludge-treated soils has already been considered. As for animals, it has frequently been observed that elevated concentrations of cadmium in feed obtained from soils treated with sewage sludge have not adversely affected animal health. However, soils vary in acidity- alkalinity. Studies did not necessarily take this into account. In acid soil, cadmium is picked up in leafy plants and ingested. Additional observations are needed to determine whether cadmium has any effect on animals under various soil conditions. Excessive dietary Co can cause toxicity in ruminant animals, but nonruminant animals are hardier. Diets containing more than 10 ug of Co g~1 have injured cattle and sheep. Crop plants used as animal feed have been shown to accumulate Co in excess of 10 fig g~1 when cobalt was present in the soil and other soil conditions were favorable (A. Page, University of California, Riverside, personal communication). It is considered improbable that ruminant animals would be at risk when foraging on sludge-treated soils, however, since only a few plant species accumulate Co and the concentration of Co in sludge is low. Copper fluoride toxicity has been reported where excessive amounts of this compound occurred in the diets of sheep, cattle, and swine. AS with Co, however, the probability that this element would accumulate to harmful levels in forage crops grown on sludge-treated soils is remote. S.2.5.2 Phytotoxic Elements in Sludge Studies have shown that repeated applications of sewage sludge to land may result in the accumulation of B. Cd, Cu. Ni, and Zn to levels that are phytotoxic. While B is quite mobile in soil and can be leached to nontoxic levels, Cd, Cu. Ni, and Zn are quite immobile and tend to accumulate at or near the depth of incorporation. Plant species vary substantially in their ability to tolerate B. Cd, Cu. Ni, and Zn in soils. Even varieties of the same Plant species frequently show marked differ ences in tolerance. The phytotoxic effects of Cd, Cu. Ni, and Zn are far more prevalent and acute on plants grown in acid soil than on plants grown in neutral or calcareous soils. Except for cadmium, EPA does not currently regulate the amounts of these elements that may
162 enter cropland soils through sludge applications. However, a number of the states have developed land disposal guidelines that specify limits for Cu. Ni, and Zn. Limits vary somewhat among the various states. The limits most commonly cited call for the affected soils to be maintained at a pH of 6.5 or greater and require cumulative loadings of Cu. Ni, and Zn not to exceed 250, 500, and 1,000 kg ha~l, respectively. The upper limits of metal loading are based in general on the cation exchange capacity (CEC) of the soil; as the CEC increases, the quantity of metal may increase accordingly. These limits are designed to protect the productivity of soils and apply only to soils used for the production of crops. Phytotoxicity is also considered in Chapter 3, Section 3.2, and Chapter 4, Section 4.2.9. Specific concerns are possible long-term biological effects and possible long-term removal from the soil to the groundwaters. This chapter considers the effects of inorganic con- taminants on societal health and sensitive ecosystems since the panel had available to it information regarding inorganic materials arising from actual sludge applica- tions. The effect of undesirable concentrations of xenobiotic contaminants is considered in Chapter 4 on biological concerns since much of the ongoing work has been carried on by biological scientists. 18.104.22.168 Selection of Disposal/Utilization Sites The same hydrological and geological considerations that apply to land disposal of other contaminant containing wastes must be taken into account in selecting a site for sludge disposal. Except for B. Mo, and Se, trace elements are chemically more active (i.e., more soluble and mobile) in acidic than in neutral and alkaline soil. Therefore, the chemical characteristics of the soil receiving the sludge are also important. Also of importance is the extent to which these trace contaminants will remobilize and therefore how long the sludge-treated soil will present a hazard. The relative permanency of disposal into any medium should be an important part of any environmental evaluation. Sludge deposition on soil may result in a relatively permanent potential hazard. Although it has often been assumed that these contaminants could be better controlled through land disposal than through air or water disposal because of the relatively inert nature of trace elements in the
163 soil, it is not believed that this postulate has been adequately proven. Certainly, a review of the pollutants to which EPA gives highest priority (U.S. Environmental Protection Agency, 1979b) would indicate that there are many chemicals whose mobility in soil and plants is poorly understood. It would therefore always appear to be necessary to make a careful review of all media for each specific disposal problem, since changes in soil and groundwater caused by sludge disposal may be long lived. 5.3 AVAILABLE DISPOSAL AND/OR REUSE OPTIONS Available technologies for sewage sludge management are discussed in the following subsections. 5.3.1 Thermal Processes Thermal processing accomplishes volume reduction of sludges and partial disposal to the atmosphere. All processes produce a residual that generally requires land disposal. 22.214.171.124 Incineration Wastewater and other organic sludges can be disposed of or reduced in volume by incineration processes. The temperature of the incinerator must be on the order of 705°C to prevent smoke and odors and as much as 1650-2200°C to ensure that the bulk of the organic matter is converted to heat and carbon dioxide. Approximately 30-50 percent of incinerated wastewater sludge is left as nonvolatile ash, depending on such factors as the sources of the solids (i.e., separate or combined sewers and percentage and types of industrial-commercial flow). Such ash may contain concentrated amounts of toxic metals that are also likely to be more soluble/mobile because they are no longer tied to organic material and that may consequently result in its being classified as a haz- ardous waste that must be disposed of at specifically permitted sites. If on land, these disposal sites must be designed to minimize the possibility of groundwater contamination. Because incineration processes produce gaseous and particulate effluents, a careful review of their use in
164 air-quality nonattainment areas is quite necessary. Cleanup trains, which partially remove particulates NOx, SOx, and residual hydrocarbons are available and must be evaluated. Heat and carbon dioxide produced by incineration may also be serious pollutants in enclosed basins, such as those at Salt Lake City and Los Angeles (G. Csanady, Woods Hole Oceanographic Institution, personal communication). Such materials as arsenic, mercury, cadmium, and lead may pass through the cleanup trains and enter the air, with eventual impacts on public health and land and water resources. A special caveat is that for some percentage of the time there will be operational problems, and the likeli- hood of such problems increases with process complexity. Any overall evaluation of a sludge disposal operation must therefore include an estimation of the reliability of the disposal process. With respect to incineration, representative operating data that make it possible to estimate rates of volatilization of metals and other constituents at various operating temperatures is important information. The operational and maintenance costs of incineration are usually high because capital, energy, maintenance, and personnel costs are high. Including interest on capital, operating costs range up to $300-400 per dry ton of sludge combusted. 126.96.36.199 Pyrolysis Pyrolysis is a starved air (oxygen) combustion process that is used to burn sludges at between 500 and 900°C, producing either fuel oil or combustible gas and an ash. The fuel oil or gas is then used as an energy source for boilers, gas turbines, internal combustion engines, or similar units that produce electrical current or directly drive other equipment. The earlier comments about ash disposal and air emission problems caused by incineration also apply to pyrolysis through the gas-oil combustion step. Because pyrolysis is an incineration process, gaseous and particulate effluents from its separation and from use of its products must be reviewed in terms of air- quality requirements and land disposal of its ash. Organic contaminants are broken down, but trace metals will concentrate in the ash. Costs are as high. A difficult-to-treat liquid side stream, as from ash quenching or air-pollution control processes, may occur and have to be treated in wastewater treatment facilities.
165 Pyrolysis generally requires sludges that are 25-35 percent solids (cake). This is necessary to permit the combustion process to be self-sustaining. Cake is fed into the combustion chamber at a maximum rate of 8-12 pounds wet weight per square foot of hearth area per hour. Multiple-hearth and rotary-hearth furnaces may have differing requirements, but the oil or gas produced is essentially similar in composition. When a pyrolytic combustor is used to make an oil, the fuel value of the composite liquid residue is approxi- mately 69,300 BTU s per gallon at 500°C, and 87,800 BTU s per gallon at 900 °C. By comparison, heavy petroleum has a fuel value of 120,000 BTU S per gallon. 188.8.131.52 Wet Combustion This process consists of feeding a ground-homogenized liquid-sludge slurry of approximately 3 percent dry solids into an enclosed reactor operated at about 315°C and 1800 psi at a rate of about 2 tons per hour. The reactor may or may not be operated at controlled oxygen levels. At this temperature and pressure the system is capable of converting organic matter to C°k, which is vented to the atmosphere, and water. The system is not self-sustaining; fuel requirements range from 900 to 1,000 BTU s per gallon of sludge. The gases generated by the reactor must be treated by an afterburner operated at between 345 and 400 °C to control odorous emissions. The combusted material is sent to a liquid/solid separator, from which a liquid, high in organic content, is returned to the wastewater treatment plant for additional treatment prior to discharge. The solids/ash are disposed of in a landfill. Construction costs are reported to be about $130,000 per dry ton per day of capacity, while operation and maintenance costs range from $35 to $90/dry ton. 5.3.2 Land-Based Alternatives Land disposal of sludges has been considered in detail in Chapter 3. However, certain features common to all the available land-based options for wastewater sludges should be emphasized. These include the need to protect surface waters from contaminants in runoff and to protect potable groundwater from contaminants in leachates. In
166 situations where commercial crops that enter the food chain are grown on sludge-treated soils, the productivity of the soil must be maintained or improved and potentially harmful elements must not accumulate in the crops. In situations where sewage sludge is used to produce crops used as feed for farm animals, which in turn are used as food for human beings, it is necessary to ensure that the food does not contain contaminants at concentrations that may be harmful to man. Where sewage sludge is used to reclaim marginal or drastically disturbed lands, surface water and groundwater must be protected as well as the health of the livestock. Current federal regulations address all the above ssues (U.S. Environmental Protection Agency, 1978) and are more than adequate to provide the margin of safety required. Landfills have been increasingly used to isolate wastewater sludges containing trace contaminants at levels high enough to be of regulatory concern. The assumption 1 nas been that remobilization of such con- taminants is minimized by using landfills and that release of contaminants to the environment is unlikely. The panel believes that the data supporting such a conclusion are scant and that remobilization of con- taminants in surface and groundwaters as well as to the atmosphere is possible. __ _ _ The finding of substantial vinyl chloride in landfill gases (Los Angeles Times, 1983), as w-11 as the mobilization of metals because of the generation of carbon dioxide and conversion to carbonic acid with lowered overall pH, are well known. The effects and risks of using landfills for sludge disposal, however, are still largely unknown. Suitable land disposal sites are also becoming increasingly scarce, particularly in urban areas, and an assumption that such sites will always be available may no longer be valid. S.3.3 Ocean-Based Alternatives A considerable amount of effort has been devoted to measuring the constituent elements in domestic and industrial wastes, analyzing concentration and dispersion in the marine environment, and assessing the effects of disposal on marine organisms that have direct or indirect contact with wastes. An inherent problem in attempts to analyze and synthesize the available information is the substantial effort required to locate material published
167 in a wide variety of disciplinary journals and symposium volumes, as well as numerous unpublished reports and data files. The problem is further complicated by the diffi- culty of assessing the quality of this information, since critical details about analytical techniques and accuracy are often not readily available. Some previous attempts to assess the problem of waste disposal (for example, National Research Council, 1976) have concluded that the problem is basically intractable from the standpoint of existing knowledge and that a long term and large-scale examination is needed to obtain a sufficient base of information about the marine environment. The implication is that the marine system is so complex and so poorly understood at present that there is no reasonable hope of evaluating the problem of safely disposing of waste including sludge. The present state of knowledge does not appear to support this conclusion. Enough information now exists about the New York and southern California Bights to allow a reasonable evaluation of the environ- mental impacts of specific discharges. This in turn allows a comparison with land or air disposal options to determine the disposal procedure most likely to cause the least net negative environmental impact. Further studies in areas such as pathogen persistence may well be desir- able, but much of the work now going on can best be categorized as a perpetuation of data gathering rather than attempts to synthesize and interpret information so as to achieve more rational decisions. The panel believes it is important to redirect some of the funds now being used for monitoring toward filling gaps in present knowledge. Chapter 2 discusses these gaps. 5.3.4 Other Processes 184.108.40.206 Chemical Fixation Wastewater sludges and sludges arising from certain chemical manufacturing operations now disposed at certain ocean dumping sites (chemical sludges) can be fixed or solidified by the addition of chemical materials. Limestone, cement, fly ash, polymers, clay products, sand, gravel, and plastics are mixed with sludges to produce a product with high solids content that will reduce leaching of pollutants when finally disposed of (e.g., in a landfill or ocean dumping site)
169 ence, energy consumption, emissions, product character- istics and marketability, and costs will be assessed annually. Current estimates are for a net unit cost of $155 per dry ton of sludge. Another example of this technology is a project developed by the Washington Suburban Sanitary Commission (WSSC) in cooperation with the University of Maryland for converting sewage sludge to brick. Sewage sludge of various types is dewatered to about 20 percent solids (cake) and mixed volumetrically with clay and shale as follows: sludge cake = 30%, clay = 46.66%, and shale = 23.34%. The mixture is molded in regular brick molds, after which it is extracted and air dried for about 24 h. The material is then further dried by the hot gases from a brick kiln (200 to 300°F) for another 24 h. The material then travels through the brick kiln at an initial temper- ature of about 200 °F and progresses through a maximum temperature of 2000°F down to a temperature of about 200°F at exit from the kiln. The total firing time ranges from 30 to 40 h. The finished brick is said to be of construction quality and is currently priced at 12¢ to 14¢ per brick. The technology is said to be ready for full-scale produc- tion, with between a half million and a million bricks already produced. 5.4 LOCAL CONSIDERATIONS Any environmental legislation or regulations to control the disposal of sewage sludge must allow decision makers sufficient flexibility to take local considerations into account. Current regulations for air, land, and ocean disposal have been developed separately and do not necessrily provide equal levels of protection for a specific location. The physical and sociopolitical characteristics of the locality where the sludge is generated, as well as those of the locality where it is to be disposed of or utilized, will so strongly affect acceptability or implementation that they may have to be given precedence over questions of cost-effectiveness and optimal technology. They include:
175 regulations appear to prevent. This may allow them to work toward necessary changes in the laws, regulations, and standards for the receiving medium to make a previously prohibited procedure possible. To be considered truly available, a sludge disposal process must have been either in operation for a number of years or must have recently gone through a procedure of laboratory evaluations, pilot plant operation, and expansion to a full-scale operational unit from which operational data suitable for design decisions are available. Sludge management or disposal systems are substantial public works projects with high capital costs that are designed to operate from 20 to 50 years. Consequently, local policy makers would be well advised to evaluate carefully the state of the true availability of a tech- nology before committing themselves to its implementation. Failing this, they may have to seek substantial funds to rebuild the system. Both proprietary and nonproprietary systems should be considered. Imported and sole-source systems should be studied with special care, since maintenance costs can become a serious problem. System reliability is important. This means that a system should have a good performance and maintenance record over an extended period of time. This approach, however, can be criticized as discriminating against emerging technology. Local policy makers should there- fore decide whether to purchase a well-established system or a new system with little experience but strong advocates. The case of operation and maintenance is another important factor that is sometimes overlooked or given inadequate attention during the evaluation process. This may be addressed in the following ways: . Assure that the control funding agency and the designers have full recognition of startup and continuing costs. Such costs should be an important part of the evaluation of competing systems for handling sludge processing and disposal. · Funding agency and designers should recognize the impacts on the community and the workers of upgrading the plant staff to handle the new system. · The funding agency and local decision makers should make sure that an adequate engineering staff is available to design the system and aid in startup. A
176 premium should be included in financing plans to cover projected engineering costs. An environmental assessment should include examination of ecological effects, human health effects, and cultural effects. Such an evaluation would include a balancing of the environmental effects of sludge disposal options, utilizing a matrix approach that compares the potential effects of each option in each medium. Some of the comparisons will be quantitative, while others will be semiquantitative or qualitative. The panel believes that enough data are currently available or are readily obtainable to make well-reasoned, technically supported decisions about sludge disposal. Where the data are not so well developed as may be desired, ongoing multimedia assessments can be used to identify further research needs. The starting point in an environmental evaluation is a comprehensive characterization of the wastewater sludge itself. Such a characterization should include estimates of sludge quantity, solids content, nutrient content, biological oxygen demand (BOD), heavy metals, persistent organics, and pathogens. It is also important to under- stand how quantity and quality are expected to change over the next 5, 10, or 20 years in response to service- area changes, pretreatment programs, or general regulatory actions, such as bans on DOT and PCB manufacture and use. After the present and future characteristics of the sludge are determined, technological and local agency operational preferences are used to select the most feasible disposal option for further evaluation. For each of the disposal technologies identified in this process, the affected media (air, land, water) are then specified. Most of the potential effects of disposal in the ocean will be contained there, although it is theo- retically possible that some of the effects will reach human being through the consumption of seafood or exposure in recreational beaches. Disposal in the air will cause increased air emissions, as well as deposits of incin- erator ash or pryolysis residues on land. A portion of the air emissions ultimately come back to the land or oceans in precipitation or by particulate settling. Disposal on land will mean direct depositing of the sludge in landfills or in other soils. Constituents of the sludge will eventually move into soils and may potentially move into ground or surface waters.
177 After the affected media are identified, it is necessary to develop estimates of the dispersion of the constituents of concern in each medium. It is important to estimate both short-term dispersion (to address poten- tial acute toxicity effects) and longer-term dispersion (to address potential chronic effects). Models of the physical transport relationships are fairly well developed for the ocean and air and to a lesser extent for soil- groundwater movement. Where possible, an additional element signifying the chemical fate of the constituents should be added to the model. Analysis should focus on those materials that may affect the ecosystem or human health. In developing an understanding of trace-contaminant movements in a medium to be used by a sludge disposal project, it is important to contrast proposed contaminant loading from the sludge with the contaminant loading already in the medium at the proposed disposal point. That is, it is important to put into perspective whether the contribution by the wastes will represent a large or small percentage of the amount of contaminant that will be present after a project is in service. While ecosystem effects are addressed in detail in Chapter 4, a brief reiteration is appropriate here. It is important to collect background ecosystem information for each medium. In designing programs to collect this information, it is important to have adequate control areas--as similar as possible to the discharge area but distant from proposed discharge points. This should help to identify effects that may be the results of more widespread environmental factors. The background data that should be collected should include hydrological or meteorological data; sediment or soil quality data; fisheries or terrestrial population data and associated diseases; benthic or soil community data; and information on plant, animal, and human uptake of constituents of concern. Enough information on uptake has been collected to make reasonable multimedia assess- ments of potential effects on ecosystems or areas of particular interest such as public beaches. In addition, bioassay data should be assembled or developed on the acute toxicity of constituents to aquatic or terrestrial organisms. Further analysis should include laboratory studies that address bio- accumulation potential and its possible effects on growth or other sublethal responses. Such test methodology is
178 well developed. Short-term tests can be used in conjunction with dispersion models to assess potential acute effects, while long-term tests, such as bioaccumu- lation evaluations, can identify potential chronic effects that require further evaluation. Using the various kinds of data mentioned above, com- parative assessments can be made to determine whether disposal will lead to unreasonable short-term effects, unreasonable chronic effects, or the destruction of unique habitats. Another ecosystem issue that should be addressed is whether changes in the media that are caused by sludge disposal will be temporary or permanent. Ecosystem data can be compared to determine the relative effects of different disposal options. Some of these will be quantitative comparisons, but many will be semiquantitative or qualitative. As more data become available, such multimedia comparisons will become more quantitative in nature. 5.5.2 Human Health Risk A multimedia environmental evaluation should also include comparisons of the human health risks of a proposed disposal option. These comparisons should focus on the potential health risks associated with metals, persistent organics, and pathogens. Many of the required elements needed for these comparisons are available, having been developed in the process of establishing regulatory criteria for the individual media. integration of the individual media assessments into a multimedia, multichemical analysis. Such an analysis is currently possible. It is necessary to identify human populations at risk, estimate average population exposures to the pollutant, and determine the probability of a health effect for each pollutant in each medium. At this point a multimedia comparison should have been developed for each individual constituent of concern to human health. The next step is to normalize the data on a wide variety of constituents and their associated health effects into a common index that permits overall relative health risk comparisons. Methods have been developed to rank the severity of various health problems (e.g., nasal cancer, lung cancer, What is needed is an
179 kidney disease, dermatitis) and to use such rankings to normalize individual health effects into a common denominator. It is also important that the assessment address the "added," or "delta," risk to human beings rather than the absolute risk. Such risk indices are useful in making disposal decisions by showing how risk can be minimized. Although multimedia risk assessment is a relatively new concept, much of the necessary methodology already exists. The sophistication of these multimedia assess- ment techniques will improve in the future, but valid assessments are possible today. The last element of a multimedia environmental assessment includes cultural considerations (aesthetic, recreational, and historical resources, for example). These judgments are qualitative in nature and include direct comparisons of whether any unique cultural resources exist in each medium and how such resources will be affected by constituent loading. 5.5.3 Conclusions A combination of quantitative, semiquantitative, and qualitative assessments will make it possible to address the issues raised by sludge disposal in each medium. These evaluations will be based on sludge characteristics, local physical characteristics, and the characteristics of local or regional media. The simplistic approach to the problem of sludge disposal suggested by a single national standard is inappropriate and could result in decisions that are environmentally and financially irresponsible. Scientists can always argue that more definitive data would be helpful or that better models should be used. To some degree this is always true. However, enough data are available within the many technical disciplines to allow adequate multimedia analyses. What is required now is open, effective communication among the scientists working on these problems so that the best information can be integrated into the analyses. Table 5.4 is a simplified version of a multimedia matrix as used by environmental consultants to assess the barge disposal of sludge in the New York Bight by New York City (Hinesly, 1971).
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