United States Environmental Protection Agency Risk Reduction Engineering Laboratory Cincinnati OH 45268 Research and Development EPA/600/S2-88/064 Feb. 1990 &EPA Project Summary Treatment of Hazardous Landfill Leachates and Contaminated Groundwater Robert C. Ahlert and David S. Kosson The objective of this study was to assess pilot- and field-scale application of separate or combined biological and physical/chemical treatment to high-strength hazardous dump site or landfill leachates, extracted sludges and wastes, and land-spilled hazardous substances. Four types of real-world toxic, concentrated, complex wastes served as prototype waste streams: industrial landfill leachate, leachate from an industrial sludge Impound- ment, forced extract from impounded industrial sludge, and groundwater contaminated with a chlorinated solvent Techniques evaluated during bench- and laboratory-scale experi- ments were: dispersed and fixed-film aerobic and anaerobic mixed mlcroblal systems, flocculation/pre- cipitation, ultrafiltratlon (UF), and reverse osmosis (RO). In general, some physical/chemical pretreatment (liming, floe/settle) was required to obtain high efficiency biodegrada- tion. The biodegradation effluent could be "polished- by UF, RO, or ion exchange when required to meet National Pollutant Discharge Elimina- tion System (NPDES) standards. Soil- based field pilot plants were constructed and operated to dem- onstrate sequential aerobic/an- aerobic mlcrobial treatment for leachates from two CERCLA-NPL sites and for groundwater contam- inated with 1,1,1-trichloroethane (TCA) at a third site. Even in the presence of high concentrations of inorganic salts, organic carbon reductions of 95% to 99% were achieved. The levels of chlorinated solvents extracted In subsurface waters were reduced from 5 mg/L to less than 20 pg/L (greater than 99.6%). The contaminant reductions attained are not the maximum that could be achieved but reflect pragmatic, cost effective treatment levels. This Project Summary was devel- oped by EPA's Risk Reduction Engineering Laboratory, Cincinnati, OH, to announce key findings of the research project that Is fully documented In a separate report of the same title (see Project Report ordering information at back). Introduction The major objective of this study was to demonstrate pilot- and field-scale treatability of high-strength dump or landfill leachates, extracted sludges or wastes, and land-spilled hazardous substances. Two specific treatment types were examined: biological treatment and physical/chemical treatment. Biological investigations involved dispersed and fixed-film mixed and indigenous cultures for treating representative concentrated hazardous aqueous wastes that could contain both organic and inorganic compounds. The need for sequential process steps was recognized. At the outset, only bench- scale methodologies were undertaken. ------- Various sources of microbial seed were used, and evidence for long-term adaptations and responses were considered of primary importance. Experiments were designed to fill a gap in existing literature that focuses on degradation of single hazardous species and binary or very simple multiple solutes in solution with water. Studies of complex—mixed organic and inorganic- solute systems have not been reported. Physical/chemical treatment of influent to and effluent from bioreactors was identified as important, but was given a lower priority since it is less novel. Potential physical/chemical treatments included: RO, UF, flocculation/sedi- mentation, membrane separations, and adsorption. As with biological treatment, feed streams were mixed solutions of multiple organic species and heavy metals in water. Emphasis was placed on high-strength and complex solutions and on the need to inactivate or detoxify toxic metal species, as well as biogenic, biodegradable, and refractory organic compounds. Investigations of biological treatment techniques were marked by two concerns: (1) product water quality suitable for discharge to the environment, and (2) minimum volume and maximum strength of concentrated residues for ease of handling and/or recovery. During the program, microbial treatment for four types of high-strength, complex aqueous wastewaters was investigated. These included: industrial landfill leachate, leachate from an industrial sludge impoundment, forced extract from impounded industrial sludge, and groundwater contaminated with chlorinated solvent. Pretreatment by physical/chemical methods was soon shown to be essential to remove colloids and fouling agents. Ultimately, total organic carbon (TOC) reductions of 95% to 99% were achieved, even in the presence of high concentrations of inorganic salts. Acclimated, mixed microbial populations were employed in all cases; no genetically engineered or specifically cultured organisms were used. Aerobic and anaerobic regimes were developed, in sequence, in packed- bed (soil-based) bioreactors. Biological treatment was evaluated in bench-scale experiments with laboratory column reactors. Much common ground was discovered with respect to organic carbon loading rates, nutrient require- ments, buffering, and co-substrates for co-metabolism. Design criteria for scaled- up investigations were derived. The laboratory column work pro- gressed so well that resources were available to treat three additional hazardous waste liquors treated in pilot plants designed specifically for the purpose. Out-of-door, pilot-scale treat- ment of landfill leachate was first demonstrated in a pilot unit at the University. Subsequently, sludge extract solution and chlorinated solvent solution were treated in field-site pilot plants built and operated at the actual sites of contamination. In these cases, field performance matched or exceeded bioreactor performance in the laboratory. In conjunction with Enviresponse, Inc., a conceptual design for a transportable, mixed microbial, hazardous organic solute treatment system was developed. In short, the ability to treat complex, organic waste solutions has been demonstrated in the field and is available for application to numerous CERCLA sites. Physical/chemical treatment is gener- ally necessary for pre- and post- biological reactor processing. Unit processes of this type are required for separation of dispersed oil and particulate matter and for quantitative reductions in heavy metal and inorganic salt concentrations. Through membrane separations and selective adsorption, it is possible to reduce solute concentrations to levels compatible with direct discharge of treated effluent. Several process tech- nologies in this category were demonstrated to function very effectively in conjunction with biological treatment. Methods, Discussion, and Results Leachate Characteristics For the initial phases of this work, leachate was obtained from a large commercial landfill receiving substantial quantities of industrial wastes. Leachate emanating from this landfill is collected in open basins or lagoons and allowed to settle by gravity. A floating oily layer is removed and stored in drums. The underflow from the collection basin is pumped to API separators for further oil removal. Bulk oil separated by gravity has been found to contain high concentrations of PCBs. The bulk aqueous phase has high residual turbidity consisting of colloids, stable emulsions, and fine particles coated with oil, which must be removed by pretreatment. After pretreatment, the clarified aqueous phase has the following range of properties: dissolved organic carbon (DOC) 8,000 - 12,000 mg/L chemical oxygen demand (COD) 23,000 - 30,000 mg total dissolved solids (TDS @ 103c C) 15,000 -17,000 mg Other typical values include TK ammonia-N, and sulfate at 1,450, 1,0t and 3,400 mg/L, respectively. A lari number of heavy metals, i.e., nickel, lee chromium, copper, etc., are present concentrations above 0.1 mg/L. Later, effluent was obtained fro natural leaching and by forced extracti of an industrial sludge disposal lagoc Primary and secondary sludges frc diverse chemical manufacturing opei tions had been impounded in the lago for several decades. The natural leache has the following properties: TOC TDS @ 103°C TKN 170-5,000 mg 2,700 4,300 mg 25 - 820 mg Extraction of the sludges with sodiu hydroxide solution, at pH 10 to 1 increases these values by factors of 3 5. Trace metal concentrations a increased also: aluminum and zinc at 1 10 mg/L, and, numerous others at 0.1 1 mg/L. During the period of investigation, problem of groundwater contaminati with chlorinated solvent was suggest for study. Concentrations of I to 15 mg of TCA had been encountered otherwise high-quality groundwate Lesser concentrations of byprodu species were also observed. Based ' environmental impacts and groundwal quality criteria, this situation could I defined as involving a high-streng wastewater. A microbial remediatii process comparable to the renovatii processes for the very high-streng leachates described above w, developed, tested in the laboratory, ai operated at pilot scale in the field. Pretreatment Physical/chemical pretreatment of hig strength leachates with coag lating/flocculating agents produces minimal decrease in DOC, while reduci turbidity and the level of heavy met! present in the wastewater. Lime gave t best results with the leachate samp involved in this study. Utilizing lime to a solution equilibria pH of 12 produced greater than 98 reduction in turbidity. Reductions dissolved TOC and COD averaged le than 5%. Polyelectrolytes were found ------- ncrease the rate but not the final level of urbidity reduction. A pretreatment Drotocol was developed; it included iddition of lime in sufficient quantity, ipproximately 6 g/L, to achieve a pH of 12 with subsequent floe settlement. The upernatant was decanted and sparged with C02 until the pH was reduced to 9 or ess. At this point, the supernatant was Jecanted and a second recarbonation tep was used to decrease final pH to 7.5. icrobial Treatment Biochemical Process Aerobic biological studies revealed that i dispersed mixed microbial population, icclimated to landfill leachate, degraded 30% to 90% of the organic species Dresent in the hazardous industrial waste iquor, with or without the addition of glucose or other nutrients. The decrease n DOC was not due to stripping, evaporation, and/or sorption; it was due to Diological oxidation. Biostabilization was rapid. Mixed microbial cultures exhibited a two-rate (diauxic) growth pattern (Figure 1). As signaled by the increase in pH during the first exponential growth phase, it is likely that the mixed culture utilizes the fatty acid fraction of the organic ;olutes in this first phase. Further, it is probable that at least two groups of organisms participate in the biooxidation process. Fatty acid metabolizing organisms have a higher specific growth rate than the other organisms that contribute to the second, lower rate portion of the growth pattern. Good agreement in carbon balances provides clear evidence for biodegradation of the organic species present in the leachate. Low sludge yield was observed in this study; this implies a reduced sludge problem associated with aerobic treatment. Oxygen uptake rates, as reflected in the volumetric flow of air-per- reactor volume, were quite nominal. If it is assumed that microbial maintenance requirements are negligible, as has been reported frequently for wastewater systems, it is possible to quantify the role of co-metabolism in the biological oxidation of anthropogenic compounds. The possibility of oxidative assimilation (nonproliferation) is ruled out because of the quantitative evolution of carbon dioxide; increase in cell mass and protein content were not measured. The ability of the acclimated population to utilize organic carbon and other nutrients solely 'rom the leachate further improves .jrocess prospects. It was possible to treat highly concentrated waste liquor, i.e., up to 10,000 mg/L of organic carbon. The absence of highly fluctuating DOCs indicates a stable and well-acclimated microbial population. Anaerobic biological studies demon- strated a DOC reduction of 64% for a culture grown on leachate and a reduction of 69% for a culture selected for the degradation of acetate, propionate, and butyrate. Specific DOC utilization rates of 0.15 and 0.21 day1 were observed for the leachate and these volatile fatty acid digesting cultures, respectively. Cell growth was not observed, to any significant extent, during these batch experiments. Leachate effects on the cultures were studied through examination of individual volatile fatty acids in the course of the exper- iments (Figure 2). Large concentrations of acetate were accumulated before overall removal was observed. The butyrate profile demonstrated responses similar to that of acetate removal. Propionate and isobutyrate were more difficult to remove, as both left an appreciable amount of unmetabohzed acid. However, their concentrations were small relative to acetate and butyrate. Acetate and butyrate are the major fatty acids contributing to methanogenesis. Also, the fraction of the nonvolatile fatty acid contaminants in the leachate that were converted to volatile fatty acids by the acid formers ended up primarily as acetate, with a small fraction converted to butyrate, propionate, and isobutyrate. Reactor failures were encountered in studies with 20 volume-% leachate. These failures were probably the result of overloading the system with volatile fatty acids. At leachate concentrations of 5% and 10%, no toxicity problems due to nonvolatile fatty acids were observed. Methane was produced at levels of 0.95 to 0.99 L/g (m3/kg) DOC removed. The data from this study clearly indicated that aerobic and anaerobic biological treatment can be used in conjunction to stabilize organic compounds found in high-strength hazardous waste residues. Microbiology of Chlorinated Hydrocarbons This phase examined mixed anaerobic population degradation of the haloorganic compounds dichloromethane (DCM), l,l- dichloroethane (DCA), and TCA. Half-kill doses, determined from batch experiments, defined a relative degree of toxicity for each of the compounds. The microorganisms exhibited great tolerance for DCA; there was no apparent inhibition at concentrations up to 35 mg/L. Acclimation studies with TCA demonstrated that continued periods of zero gas production do not necessarily reflect the death of the organisms. Reactors dosed with 2 and 4 mg/L recovered after 20 days of zero gas production. After this lag period, daily gas production was greater than or equal to control reactors. The overall acclimation period was 33 days, less than half the acclimation period of 10 wk cited in reports of previous work. However, acclimation periods tend to vary greatly for anaerobic seed cultures. Studies with separate anaerobic popu- lations indicated that the methanogens were most likely responsible for degra- dation of the chlorinated compounds considered. Microbial Reactor Design Soil-based sequential aerobic/an- aerobic microbial degradation was investigated as a potential onsite or in- situ treatment process. Laboratory soil column experiments were carried out for initial evaluation of the proposed process using three different contaminant streams and several soil types. Treatment of landfill leachates achieved reductions in DOC in excess of 90% (Figure 3). Influent leachate-derived organic carbon (LOC) concentration, organic carbon removal, effluent pH, and long-term system permeability are interrelated. Microbial acclimation periods increased in length with increased influent leachate concentration. In- creasing influent LOC concentration resulted in greater overall removal efficiency for DOC. In addition, increased influent LOC concentration is associated with reduced incidence of plugging, allowing the system to operate more closely to target volumetric flux. Treatment of TCA using the soil-based microbial system, operated under anaerobic conditions, resulted in quantitative removal of solvent. Influent concentrations of 20 mg/L corresponded to effluent concentrations of less than 20 p,g/L. Failure to observe any breakthrough phenomena, over long periods of operation, confirmed that sorption onto soil constituents was not controlling TCA removal. Gas evolution rates and gas analyses indicated that methanogenesis was the most probable rate-controlling step. ------- .o I 2400 2000 1600 7200 800 400 Cell Mass DOC 2.0 1.0 0.6 IB 0.4 * 12 16 20 Time.h Figun 1. Fate of organic carbon and microbial responses observed during a study with 20% leachate (with pH control @ 7.5 ±0.1). Microbial Process Demonstration Positive results from laboratory soil column experiments were followed by the design, construction, and operation of three field pilot plants to demonstrate the process feasibility for large-scale applications. One of the pilot plants was located at Rutgers and the other two at the actual sites of differing contamination problems. The first pilot plant in the series consisted of six self-contained lysimeters (bioreactor columns packed with soil), 2 ft in diameter and 6 ft in depth. These units were implanted in the ground, at a location on campus, and operated in simulation of site conditions. Pretreated leachate from a CERCLA-NPL industrial landfill was treated. TOO mineralization to CO2 and CH4 was obtained with a single- pass efficiency of 90% to 97%. Operation was carried out for two consecutive spring-through-fall operating periods of approximately 160 days each. Laboratory results were readily transferable to field operation. The second pilot plant was designed to demonstrate in situ sludge extraction coupled with soil-based microbial treatment of recovered extract; it was constructed and operated at the sludge disposal site for 140 days. The cleanup process consisted of two steps in sequence (Figure 4). The first step was removal of contaminants from mixed primary and secondary industrial sludges through in situ extraction with aqueous sodium hydroxide. Extractant solution was injected into the sludges throu well-points or applied to the surfa through a perforated pipe distribut network. Extract was recovered by mee of two wells screened near the bottom the sludge deposits. The results system operation indicated that as mi as a 15-fold increase in removal ra relative to natural processes driven infiltrating rainfall, could be obtain through controlled alkaline extraction. additional 4-fold increase in the rate site renovation can be obtained throi increased hydraulic flux through I sludges. In this second pilot plant, extr; recovered from the sludges was trea to remove TOG with a soil-bas< sequential aerobic/anaerobic microt reactor. Treatment occurred onsi ------- - 250 5% Leachate Leachate Culture 450 500 Figure 2. Acetate and propionate concentrations as functions of batch reaction time. immediately adjacent to the extraction unit. A diverse, mixed microbial population was developed in the soil system. Neutralized extract was applied to the surface of the treatment bed and allowed to percolate through the soil column. Aerobic and anaerobic microbial populations metabolized organic con- taminants to C02 and CH4. Treatment efficiencies in excess of 95% were observed. A third pilot plant, designed to demonstrate the treatment of groundwater contaminated with TCA, was operated at the site of a solvent spill. This pilot plant consisted of two self-contained lysimeters, 3 ft in diameter and 6 ft in depth. The soil packing employed was excavated from the site. Influent to the two lysimeters was contaminated ground- water, recovered from a monitor well, with TCA concentrations of 5 to 20 mg/L. Reactors were operated under entirely anaerobic conditions. At steady state, effluent TCA concentrations were less than 20 u.g/L. Sorption and Extraction Sorption and extraction are processes that influence the distribution of solutes between separate phases. The absolute performance of these processes is dictated by thermodynamic equilibria. Thus, the ultimate distribution of a solute between otherwise homogeneous phases (steady state in batch contact circumstances) is that at which the chemical potential of the solute is the same in the several phases. As used in this study, sorption is the exchange of dissolved organic solutes between aqueous solutions and a variety of solid substances. The direction of exchange is dictated by thermodynamic considera- tions, and the rate is influenced by physical transport and the strength of binding forces. Extraction is the removal of constituents from a solid phase by contact with solvent. Distribution and rate are controlled by thermodynamic equilibria and, also, by physical barriers to exchange. Granular Activated Carbon The time required to approach thermodynamic equilibrium must be determined experimentally for each carbon (GAC) and organic solute system combination. In general, greater than 95% of equilibrium sorptive capacity is attained in several days. However, it may take much longer periods to reach final equilibrium because of slow diffusion in carbon particle pores and/or slow changes in surface binding states. Pretreatment with lime to remove oily phases from otherwise aqueous leachate was necessary before the determination of carbon sorption isotherms. Interactions of GAC with leachate were independent of the primary pretreatment process. Control of pH through recarbonation with C02, air stripping, or sulfuric acid addition had little or no detectable effect on subsequent sorption of organic solutes onto GAC. The treatability of two leachate samples (EPA #01 and EPA #02) with GAC was identical. The relationship between equilibrium organic sorbate loading and equilibrium solute concentrations, in multiple solute systems, is dependent on initial conditions. Type A isotherms were obtained for full-strength leachate and varying masses of GAC. Type Bn isotherms were constructed with a constant mass of GAC; the subscript "n" represents the ratio of carbon-m ass-to- volume of full-strength leachate. Finally, ------- 4500 4000 3500- 3000- 2500. O 0 2000 7500- 7000- 500. Influent fffluent I 20 720 740 SO 700 Time, days Figure 3. Typical influent and effluent responses for sequential aerobic/anaerobic soil-based microbial treatment. 160 180 Type C isotherms used data for a fixed mass of GAC and varying leachate dilutions. With this conceptual separation of driving forces for sorption, it was possible to construct a mechanistic description for the process within classes (types). Plots of equilibrium loading versus equilibrium concentrations of TOC for these three types of isotherms can be used for leachate sample character- ization. There is a weak pH effect on sorptive capacities of GAC for TOC in leachate. It appears desirable to carry out measure- ments and treatment at near-neutral pH rather than at higher pH levels. Soil Soil is an active sorbent because of organic matter (humic) and clay fractions. These fractions interact with organic solutes in groundwater and infiltrating surface water to exchange organic substances and dissolved inorganic species. Thus, the presence of organic contaminants in groundwater and soil water infers the distribution of these substances in stable or transient equilibria. As an example of the role of the organic carbon fraction, the mass of 2,4-dichlorophenol sorbed onto a loam containing 4.7% organic matter has been observed to be approximately 5 times greater than the mass sorbed onto a sandy loam containing 0.84% organic matter. The sorption of a series of phenolic compounds onto a loam increases in the order: phenol < o-chlorophenol < 2,4- dichlorophenol. This order is preserved for the sorption of these solutes onto cupric and calcium salts of commercially available humic acid, which is a primary component of soil organic matter. The mass of TCA sorbed onto a loam containing 4.7% organic matter was observed to be 2.5 times greater than tli mass sorbed onto a sandy clay loai containing l.4% organic matter. In th presence of a mixed solvent (10 volum % ethanol), the mass of TCA sorbed onl a loam decreased by 40%, as compare to the single solute in aqueous solution. Solvent Extractions The presence of components of landfill leachate solute matrix altered th distribution of phenol and o-chlorophem between a bulk organic phase and th aqueous wastewater phase. Th alteration was more pronounced i experiments involving phenol than i experiments in which o-chlorophenol wa the distributed solute. Since phen< favors the aqueous phase, it i reasonable to expect solute-sa interactions in the aqueous phase t produce a larger change in th distribution of phenol than in th distribution of o-chlorophenol, whic favors the organic phase. Th ------- To NaOH Prep. pH 10-13 (Tank 1) Extract Ballast Tank (Tank 2) //// Extraction Bed Effluent Ballast Tank (Tank 4) Discharge Figure 4. Pilot plant process flow diagram. Soil Treatment Bed flQJt Hflft Nutrients COi Mixing Tank (Tank 3) components of a leachate solute matrix that contribute most to the salting-out of phenol appear to be the larger inorganic anions, i.e., C03-2 and S04-2. High concentrations of acetic, propionic, and butyric acids in leachate also contribute to observed changes in phenol as a result of solute-salt interactions in the aqueous or bulk organic phases. Membrane Separations Thin semi-permeable films become important in the separation of dissolved species, especially from aqueous solution. Membranes have been used for the production of process water and/or drinking water from sea water and natural brines. In addition, membranes have been adopted for commercial separations and concentration of products and valuable process constituents such as catalysts and recyclable intermediates. Membrane techniques have a role to play high-strength wastewater renovation. Reverse Osmosis Several hazardous wastewaters, e.g., industrial landfill leachates, lagoon wastes, pesticide wastewaters, and synthetic organic manufacturing effluent were successfully renovated with an RO system Moderate and high-strength industrial landfill leachates, pretreated by physical and chemical methods and treated biologically, were separated and concentrated in semi-batch, steady-state, and unsteady modes of operation. Physical/chemical pretreatment with lime was found necessary to remove suspended and colloidal matter, heavy metals, and dispersed oil phases in the raw leachate; these constituents can cause membrane fouling and rapid flux loss. All physically, chemically, and biologically treated leachates were separated to produce clear, turbidity-free permeates. Eight landfill leachate experiments were conducted over extensive periods of time. For example, high-strength, pretreated leachate EPA #07 with conductivity of 30,000 micromho/cm, IDS of 27,000 mg/L, and TOG of 6,700 mg/L was separated and concentrated in a semi-batch, unsteady experiment. At room temperature and moderate feed pressure (approximately 400 psig), inorganic solute rejection exceeded 95%. During feed concentration in the retentate (concen- trate) recycle mode, operation was limited to feed IDS concentrations of less than 30,000 mg/L. Flux became unacceptably low and pressure had to be increased to overcome the high osmotic pressure of the feed. In addition, concentration polarization appeared to occur at high recoveries accompanied by high-feed IDS concentrations. When feed was too concentrated, solutes may have exceeded solubility limits and caused additional deposition of mem- brane surfaces. ------- Moderate-strength leachates were renovated to a greater extent. In a study with a recovery of 75% at 170 hr of operation, initial and final rejections for inorganic species were in excess of 99%. Initial TOC rejection was low but increased, with time, to over 70%. This phenomenon of increasing TOC rejection is explained by the fact that the more permeable solutes were purged from the system early in the process, thus leaving the feed with organic species that were rejected continually at higher efficiencies as time/recovery advanced. No fouling was observed in any of the moderate- strength leachate studies. Biologically-treated landfill leachate was renovated successfully. TDS and conductivity rejection were in excess of 98%; maximum TOC rejection was 94%. Bulk permeate TDS and TOC con- centrations of 47 and 14 mg/L respectively, were obtained at recoveries of over 60%. No fouling was observed in this study; flux averaged 0.29 m3/m2d. Lagoon sludge extracts, resembling industrial landfill leachate, were also treated with an RO process. In a steady- state experiment, conductivity and TDS rejections averaged 97% and 99%, respectively; TOC rejection was 79%. A slight increase in rejection and decrease in flux appeared evident, possibly because of the formation of a nonfouling gel layer. Ultrafiltration Results of UF experiments indicated that a high proportion of the organic matter in leachate samples had a molecular weight below about 500. This agrees well with results in the literature from similar experiments. For raw leachate and lime-treated leachate, approximately 80% and 85% of the organic solutes had a molecular weight below 500, respectively. These results suggest that leachate samples contain primarily synthetic organic compounds and lesser amounts of biogenic matter, such as proteins and humic and fulvic substances. These observations were expected, since the leachate was generally of an industrial rather than a biochemical origin. Since most organic solutes in leachates studies do not pass the 500 MW membrane, the utility of UF for efficient removal of organic contaminants is subject to question. At best, UF can be used as a pretreatment process to remove high molecular weight compounds that interfere with other treatment technologies, i.e., RO. This UF study confirmed the pretreatment study results; lime treatment did not remove a significant mass of the organic solutes from industrial landfill leachate samples. The UF investigation suggested that lime treatment may remove organic species with molecular weights greater than 10,000; these represent a relatively small fraction of the total organic matter present in solution. Although membrane UF may not be effective for removing organic matter of low molecular weight from leachate, it is a valuable tool for evaluating the nature of a leachate sample and the effectiveness of other pretreatment processes. UF is not an effective treatment technique, since it does not eliminate any of the low molecular weight organic matter that is destroyed efficiently by biological renovation. Conclusions Several important conclusions can be drawn based on the study results. These are summarized in the same order as the sections of this summary. Pretreatment - Treatment of aqueous wastes with significant concentrations of dispersed or suspended phases — high levels of turbidity—by mem- brane or biological techniques either was not possible or inefficient without pretreatment to produce a homogeneous aqueous phase. - Lime addition to pH 12, followed by floe separation and recarbonation to pH 7 (addition of CO2), was an effective pretreatment process that resulted in greater than 98% reduction in turbidity. Microbial Treatment - Aerobic mixed microbial populations degraded a significant fraction of the dissolved organic solutes present in some leachates (80% to 90%), while being inherently limited in degrading dissolved organic solutes in other leachates (< 50%). - Aerobic mixed microbial populations may require a readily biodegradable co-substrate to mineralize anthropogenic compounds (co- metabolism) and may exhibit two distinctive growth regimes. -Anaerobic mixed microbial populations degraded a significant fraction of the dissolved organic solutes present in some leachc (60% to 70%). - Anaerobic mixed microb populations degraded sevc chlorinated hydrocarbons presen aqueous solution from ini concentrations up to 20 mg/L to I concentrations below the detec limit of 20 pg/L. Half-kill doses toxicity inhibition levels w determined. - Methanogens were most likely group of organisms responsible degradation of the chlorina compounds considered. - Soil-based sequential aerobic/ aerobic microbial degradat mineralized between 90% and 9 of the dissolved organic solt present in all leachates test Carbon dioxide and methane w principal end products. - Soil-based anaerobic microbial C radation reduced TCA contaminated groundwater from mg/L to less than 20 pg/L. ( production rates and c composition indicated tl methanogenesis was the control process. - Three pilot plants were design constructed, and operated in the f to demonstrate process feasibility the following wastes: (a) An industrial landfill leachate ' treated using a soil-bas sequential aerobic/anaero microbial process with sim pass organic destruct efficiencies between 90% , 97% . (b) In-situ sludge extraction \ coupled with soil-bas microbial treatment of the covered extract to demonsti controlled, rapid removal ; mineralization of extracta organic species, with treatrr efficiencies greater than 95% (c) TCA in groundwater v reduced from 5 to 20 mg/L less than 20 pg/L, utiliz anaerobic soil-based micro treatment. Pilot plants (a) and (b) treated waj from CERCLA-NPL sites. Pilot studies and (c) were conducted on site. ------- Sorption and Extraction - Activated carbon adsorption was inefficient when dispersed oily phases were present in the aqueous waste. - Relationships between equilibrium organic loading and equilibrium concentrations were dependent on initial conditions. - The mass fraction of organic matter strongly influenced the sorptive capacity of a soil. - A landfill leachate solute matrix can significantly alter aqueous/organic phase solute partitioning. Membrane Separations - RO was effective for removing inorganic species after biological treatment. - UF was an effective tool for characterizing leachates, but was of limited value for treatment because a majority of the solutes present had a molecular weight less than 500. ------- Robert C. Ahlert and David S. Kosson are with the Department of Chemical and Biochemical Engineering, Rutgers University, Piscataway, NJ 08855-0909. John E. Brugger is the EPA Project Officer (see below). The complete report, entitled "Treatment of Hazardous Landfill Leachates and Contaminated Groundwater," (Order No. PB 89-124 6481 AS; Cost: $28.95, subject to change) will be available only from: National Technical Information Service 5285 Port Royal Road Springfield, VA 22161 Telephone: 703-487-4650 The EPA Project Officer can be contacted at: Releases Control Branch Risk Reduction Engineering Laboratory U.S. Environmental Protection Agency Edison, NJ 08837 United States Environmental Protection Agency Center for Environmental Research Information Cincinnati OH 45268 BULK RATE POSTAGE & FEES PAK EPA PERMIT No. G-35 Official Business Penalty for Private Use $300 EPA/600/S2-88/064 000085836 HHERL USEPA REGI01I ¥ LIBRARI 230 S DEA880BM ST CHICAGO IL 6060H ------- |