Showing papers in "Journal of Water Pollution Control Federation in 1990"

Physicochemical treatment processes

Abstract: This article discussed work done and accomplishments made in various methods and processes for physicochemical wastewater treatment. Processes discussed include general, precipitation, coagulation/flocculation, sedimentation/flotation, filtration, adsorption, ion exchange, membrane processes, mass transfer processes, phtotlytic processes, and oxidation/reduction processes.

A sensitivity analysis of nine diversity and seven similarity indices

Abstract: Indices summarizing community structure are used to evaluate fundamental community ecology, species interaction, biogeo graphical factors, and environmental stress. Some of these indices are insensitive to gross community changes induced by contaminants of pollution. Sixteen indices commonly used to assess the status of aquatic com munities in water quality studies were evaluated using computer simu lation techniques to determine specific index responses. Three com munities of different initial structure (19 species, 38 species, and 83 species) were generated using the lognormal equation. Each community was then perturbed in three ways: common species disproportionally reduced, all species proportionally reduced, and rare species dispropor tionally reduced. The behavior of the indices was analyzed graphically and differential response due to initial community structure and type of community change was documented. Some recommendations of poten tial sources of error using community level indices were developed. Res. J. Water Pollut. Control Fed., 62, 749 ( 1990).

Kinetics of chlorinated hydrocarbon degradation by suspended cultures of methane-oxidizing bacteria

Abstract: The kinetics of methane utilization and the biod?gra dation of trichloroethylene (TCE) and 1,1,1-trichloroethane (TCA) by a mixed, methanotrophic bacterial culture were studied in a closed-system reactor. Methane oxidation followed Michaelis-Menten kinetics. TCE and TCA degradation followed first-order kinetics with rate constants of 3.7 X 10-4 and 8.8 X 10"5 L/mg VSS-h, respectively, for concen trations less than 3000 fig/L. Oxidative activity of the methanotrophic culture ceased at a dissolved TCE concentration of 7770 ?tg/L. TCA, but not TCE, biod?gradation was inhibited by dissolved methane con centrations in excess of 0.25 mg/L. In the absence of methane, the culture continued to degrade TCE and TCA, but degradation ceased after 104 hours. Lower biod?gradation rates were observed when treating a mixture of TCE and TCA. Res. J. Water Pollut. Control Fed, 62, 124 ( 1990). solvents by methanotrophs is initiated by the methane mono oxygenase enzyme that is also responsible for the first step of methane oxidation. In this way the solvent competes with meth ane for access to the oxidation site, the methane monooxygenase enzyme. The competition between the toxic organic compound and methane for the nonspecific monooxygenase enzyme has been termed substrate competitive inhibition. The chlorinated compound degradation has also been referred to as cometabo lism, in that the bacteria can degrade the toxic compound without deriving any energy for growth with the same enzyme that de grades its growth substrate, methane. The products of chlorinated solvent detoxification are carbon dioxide and chloride, and in some cases low levels of chlorinated aliphatic acids briefly ap pear.413 The rational development of treatment processes that use methanotrophic bacteria requires an understanding of the bio degradation rates of methane and the toxic compound(s) of interest and the factors that affect these rates. Of particular im portance is the influence of competitive inhibition on degra dation. Previous studies were of limited value for estimation of kinetic parameters since mixing was not sufficiently controlled4 or an insufficient number of rate measurements were made.5 The purpose of this research was to determine the stoichiometry and kinetics of methane utilization and of biod?gradation of TCE and TCA for a mixed culture of methanotrophs. In addi tion, the inhibitory effects of methane and of the chlorinated solvents on the degradation of each other were studied.

Low-level alkaline solubilization for enhanced anaerobic digestion.

Abstract: A low-level, ambient temperature alkaline solu bilization process has been investigated for its ability to enhance the anaerobic digestion of waste activated sludge. The pretreatment process consists of adding 20 meq of alkali/L, followed by anoxic mixing for 24 hours. Both lime and sodium hydroxide were eval uated. Pretreatment using either chemical improves anaerobic digestion, however sodium hydroxide provides better perfor mance. Pretreatment using sodium hydroxide improves VS re movals in the range of 25 to 35% over no pretreatment and in creases gas production from 29 to 112% over the control sludge. Volatile solids and COD removals for sodium hydroxide pre treated sludge at a 7.5-day retention time were similar to the VS and COD removals without pretreatment at a 20-day retention time. Res. J. Water Pollut. Control Fed., 62, 81 (1990).

Monterey wastewater reclamation study for agriculture.

Abstract: Results from a five-year study indicate that the use of reclaimed water for food crop irrigation is safe and acceptable. No soil or groundwater quality degradation occurred. Conventional farming practices were adequate, excellent crop yields were obtained, and there were no obstacles to the marketability of the produce. There was no accumulation of heavy metals in the crops or soil; chlorine residuals had no observable effect on crops, and dechlorination was not necessary. Res. J Water Pollut. Control Fed., 62, 216 (1990).

Biological fixed-film systems

Abstract: Proceedings of three conferences contained a number of papers on fixed-film processing wastewater and hazardous waste treatment. Eckenfelder et al. described a rational method for the selection of biological fixed-film treatment for specific industrial wastewaters. Also, Rittman and Huck discussed the application of immobilized biofilm treatment to produce safe water that meets EPA drinking water regulations.

Effects of chemicals on microorganisms

Abstract: 55. Ferminella, J. W., et al, "Periphyton Responses to Invertebrate Grazing and Riparian Canopy in Three Northern Californian Coastal Streams." Freshwater Biol, 22, 445 (1989). 56. McCormick, P. V., and Stevenson, R. J., "Effects of Snail Graz ing in Benthic Algal Community Structure in Different Nutrient Environments." J. N. Am. Benthol. Soc, 8, 162 (1989). 57. Marks, J. C., and Lowe, R. L., "The Independent and Interactive Effects of Snail Grazing and Nutrient Enrichment on Structuring Periphyton Communities." Hydrobiologia (Den.), 185, 9 (1989). 58. Fairchild, G. W., et al, "Effects of Nutrient (N, P, C) Enrich ment, Grazing, and Depth upon Littoral Periphyton of a Softwater Lake." Hydrobiologia (Den.), 173, 69 (1989). 59. Steinman, A. D., et al, "Effects of Irradiance and Grazing on Lotie Assemblages." J. PhycoL, 25, 478 (1989). 60. Lamberti, G. A., et al, "Productive Capacity of Periphyton as a Determinant of Plant-herbivore Interactions in Streams." Ecol ogy, 70, 1840 (1989). 61. Swamikannu, X., and Hoagland, K. D., "Effects of Snail Graz ing on the Diversity and Structure of a Periphyton Community in a Eutrophic Pond." Can. J. Fish. Aquat. Scl, 46, 1698 (1989). 62. Power, M. E., et al, "Grazing, Catfish, Fishing Birds, and At tached Algae in a Panamanian Stream." Environ. Biol. Fish., 26, 285 (1989). 63. Carrick, H. J., and Lowe, R. L., "Benthic Algal Response to N and P Enrichment Along a pH Gradient." Hydrobiologia (Den.), 179, 119(1989). 64. Bushong, S. J., and Bachmann, R. W., "//i situ Nutrient En richment Experiments with Periphyton in Agricultural Streams." Hydrobiologia (Den.), 178, 1 (1989). 65. Munn, M. D., et al, "Factors Influencing Periphyton Growth in Agricultural Streams of Central Illinois." Hydrobiologia (Den.), 174, 89 (1989). 66. Robinson, C. T., "Diatom Flora of Mink Creek, Idaho, USA." Great Basin Nat., 49, 155 (1989). 67. Bothwell, M. L., et al, "Evidence of Dark Avoidance by Pho totrophic Periphytic Diatoms in Lotie Systems." J. PhycoL, 25, 85 (1985).

Control of anaerobic GAC reactors treating inhibitory wastewaters.

Abstract: Operational techniques for reducing the cost of treating a coal gasification wastewater using expanded bed an aerobic granular activated carbon (GAC) bioreactors were inves tigated. The wastewater toxicity was overcome by periodic partial replacement of the reactor medium with virgin GAC. The first phase of this study was devoted to determining the minimum mass of GAC that needs to be replaced. The second phase inves tigated the dependence of system performance on hydraulic re tention time and volumetric COD loading rate. Finally, the impact of waste strength on treatability was assessed through the operation of three anaerobic reactors with 30, 60, and 100% wastewater. Res. J. Water Pollut. Control Fed., 62, 65 (1990).

Nitrification and phosphorus precipitation with biological aerated filters.

Abstract: The biological aerated filter is an innovative technology that combines aerobic degradation of pollutants and physical retention of suspended matter in one reactor. A high concentration of active bio mass can be achieved in the packed bed reactor, and nitrifying bacteria can be retained on the filter media, allowing ammonia oxidation inde pendently of sludge age. The options of phosphorus and nitrogen removal with biological aerated filters were explored with semi-industrial pilot plants. Examples of full-scale plants, designed according to collected data, are given. Phosphorus was precipitated with iron salts in lamella settlers before aerated biofilter treatment. The efficiency of settling and biological treatment was related to hydraulic and operational parameters. Nitrification can be achieved by reducing the carbonaceous load on the biofilter. The limits of loading were verified to obtain a final effluent quality of around 1 mg/L each of phosphate-P and ammonia-N, and 10 mg/L each of BOD and SS. The results of a full-scale nitrifying biofilter and of a highly loaded aerated biofilter plant with seasonal pollution variations are presented. Res. J. Water Pollut. Control Fed., 62, 169 (1990).

Denitrification in a batch wastewater treatment system using sequestered organic substances.

Abstract: A process incorporating sequencing batch reactors for organic removal and denitrification and a fixed-film device for nitrification was investigated in a bench-scale study. Emphasis was placed on the phenomena of sequestering of organic material and its later use as an electron donor for denitrification. Parameters varied to optimize system performance included the nature of the carbon source, the operating scheme during organic removal, and the nature of the nitrified feed stream to the denitrification stage. It was concluded that aeration for organic removal should be provided only until TOC and oxygen respiration sta bilize, providing a residual source of electron donor for later denitrifi cation. Further, a small amount of nitrite in the denitrification feed stream resulted in a robust population of organisms capable of reducing nitrite faster than nitrate, resulting in a 30% increase in the denitrification rate over systems fed only nitrate as an electron acceptor. Res. J. Water Pollut. Control Fed., 62, 259 (1990).

Simplified design of biofilm processes using normalized loading curves

Abstract: The design of biofilm processes can be based on the mechanistically rigorous steady-state biofilm model and can also be simple to do when normalized loading curves are employed. A family of nor malized loading curves is developed from principles of biofilm kinetics. The significance of the three dimensionless design parameters?S^ltl, L*, and J/JR?is discussed. Finally, the design approach is illustrated by an example for completely mixed and segmented reactors removing soluble BOD in a biofilm reactor. Res. J. Water Pollut. Control Fed., 62, 185(1990).

Economic considerations in wastewater treatment with duckweed for effluent and nitrogen renovation.

Abstract: Duckweed is one of the floating aquatic macrophytes with a preference for ammonia uptake. The ammonia is assimilated into valuable nitrogen compounds that can subsequently be used for animal feed or agricultural fertilization. Outdoor experiments were conducted in shallow miniponds (20 and 30 cm deep) to evaluate the performance of the duckweed species, Lemna gibba, as a stripper for domestic waste water. The results indicate that under adequate operational conditions the quality of accepted secondary effluents meets irrigation reuse criteria. The annual yield (dry matter) of duckweed, which is harvested two to three times a week, is anticipated to be about 55 ton/ha, with a protein content close to 30%. The benefit of the additional byproduct means a reduction in wastewater expenses in the range of $0,020 to $0.050/m3. Res. J. Water Pollut. Control Fed., 62, 692 (1990).

Giardia in wastewater?effect of treatment

Abstract: Giardiasis is one of the most commonly identified wa terborne intestinal diseases in the U. S. A person infected with Giardia lamblia may shed on the order of 108 cysts /day, which may be collected in wastewater. The objective of this research was to study the removal of Giardia cysts by selected unit processes during wastewater treatment at three wastewater treatment plants in the U. S. Background data were obtained during a nationwide study of cyst concentrations in raw and treated wastewaters. These data suggest seasonal and geographic differences in Giardia cyst concentrations in raw waste water. More intensive sampling indicated that cysts are removed with varying effectiveness during primary clarification and almost completely removed in the biological treatment processes. However, a direct com parison of cyst removal efficiencies showed that cyst concentrations in the trickling filter effluent were higher than in the activated sludge process effluent. These data also suggest that cysts are concentrated in the mixed liquor suspended solids and, thus, in the sludges. Res. J. Water Pollut. Control Fed., 62, 670 (1990).

Operation of a three-stage SBR system for nitrogen removal from wastewater

Abstract: Bench- and pilot-scale experiments were conducted to investigate the feasibility of a three-stage sequencing batch reactor (SBR) process for carbon and nitrogen removal. Carbon removal was carried out in SBR operated under high loading conditions (Stage 1 ). Nitrification was accomplished in a fixed-film reactor (Stage 2), the effluent from which was returned to the SBR for denitrification ( Stage 3 ). Under both laboratory and field conditions, it was shown that sequestered substances remaining after completion of the Stage 1 process may increase the de nitrification rates by as much as an order of magnitude over true en dogenous rates. To ameliorate the development of a nitrite peak during denitrification, selection methods should be used that promote the growth of true denitrifiers. The overall nitrogen removal capacity of the system is limited to about 75%, not as a result of kinetic limitations but because of the necessity of retaining influent nitrogen in the settled sludge from the first stage. Res. J. Water Pollut. Control Fed., 62, 268 (1990). Biological nitrification and denitrification can be carried out in a variety of process configurations. Among these are proprie tary configurations such as the Bardenpho, Carrousel, Orbal, and Biodenitro processes1_5 as well as the sequencing batch re actor (SBR).6 Operation of these alternative systems requires very low loading rates and a long solids retention time (SRT). As a result, nitrogen removal via these processes is expensive in terms of both capital and operational costs,7 although some sav ings may be realized through reduced sludge management re sulting from lower yields at longer SRTs. Sequencing batch reactors have a distinct advantage over continuous flow processes in that reaction and aeration times are directly and separately controllable. Carbon removal, nitri fication, and denitrification can each be optimized individually, accounting for varying flow conditions and wastewater strengths through manipulation of the reaction periods. Further, with the advent of microprocessor technology, these processes can be controlled automatically at minimal expense. The SBR operates by separating in time, in a single tank, those processes that are separated spatially in a conventional continuous-flow process. A typical operation sequence consists of five steps: fill, react (with or without aeration), settle, decant, and idle. The sequence begins with the introduction of waste water to a partially filled reactor containing settled sludge from a previous cycle. The contents may remain unmixed during fill, a procedure that saves energy and aids in control of filamentous organisms.8-10 Aeration is provided for a length of time sufficient to produce an effluent of the desired quality. Aeration and mixing are then shut off, the microbial floes are allowed to settle under quiescent conditions, and the supernatant is finally drained from the reactor. During low-flow periods, a decanted reactor may undergo an idle period. Sequencing batch reactor systems have been successfully ap plied throughout the world for carbon removal, nitrification, and denitrification. As in continuous-flow systems, the problem with denitrification is an imbalance between availability and demand of electron donors. Often the denitrification rate as well as the quantity of oxidized nitrogen that can be reduced is limited. The purpose of this paper is to discuss the feasibility, advantages, and disadvantages of a method that has been proposed to increase the availability of electron donors without addition of supple mentary substances.

Biodegradation of 2-chlorophenol using immobilized activated sludge.

Abstract: Biodegradation of 2-chlorophenol was studied using immobilized activated sludge System response to variation in temperature and concentration of 2-chlorophenol was studied in an air-sparged reactor A recirculation reactor, run in a batch mode, was used to study kinetic parameters The system response was examined following changes in 2-chlorophenol concentration, flow rate, and biomass loadings Stoichiometric amounts of free chloride detected at the end of the experiments confirmed min eralization of 2-chlorophenol A nonlinear regression model was developed to verify and evaluate the kinetic parameters for the removal of 2-chlorophenol The model was modified to accom modate the removal of 2-chlorophenol by stripping Res J Water Pollut Control Fed, 62, 73 (1990)

Parachlorophenol degradation using bioaugmentation.

Abstract: Chemostats containing unacclimated biomass were sub jected to spiked inputs of parachlorophenol (4-CP) and supplemented with varying amounts of 4-CP degrading culture. Without bioaugmen tation, 4-CP degradation was negligible. Accelerated 4-CP removal rates were observed in reactors supplemented with 4-CP degrading biomass. Bioaugmentation test results were used to verify a kinetic model incor porating the Haldane equation for microbial growth and separate met abolic requirements for supplemental and indigenous microbial popu lations. Accurate short-term predictions of reactor performance were achieved using the model. For simulations longer than 10 hours, model predictions deviated from experimental results. Res. J. Water Pollut. Control Fed., 62,227 (1990).

Performance of four full-scale nitrifying wastewater treatment plants incorporating selectors

Abstract: The effect of installing selectors to control filamentous bulking at four full-scale nitrifying wastewater treatment plants was eval uated. The results indicate that a selector can be effective in controlling filamentous sludge bulking. Little difference in effectiveness was observed for aerobic, anaerobic, or anoxic selectors. Long-term operating data indicate that selectors, coupled with an appropriate aeration basin con figuration, are capable of producing a nonbulking activated sludge (SVI less than 150 mL/g). Average S Vis in the 60 to 90 mL/g range can be expected, with values as low as 20 to 30 mL/g observed on occasion. An aerobic selector was not effective in controlling bulking in a complete mix nitrifying system using surface mechanical aerators. Res. J. Water Pollut. Control Fed., 62, 676 (1990).

Factors governing methane fluctuations following shock loading of digesters.

Abstract: A non-steady-state energetic/kinetic model was developed to predict methane production, organic substrate and product concentrations, hydrogen partial pressure, and bacterial mass concentrations in a methanogenic continuously stirred tank reactor (CSTR) receiving ethanol and propionate as organic sub strates for growth. The model was used to simulate a shock-load perturbation of the steady-state CSTR by sudden addition of a large quantity of ethanol and propionate. A cyclic pattern in methane production, corresponding to sequential utilization of substrates and intermediates, was predicted by the model. Ex perimentally measured methane production showed a similar cyclic pattern, but was more erratic due to reduced product for mation which shifted methane production to latter stages in the transient. Res. J. Water Pollut. Control Fed., 62, 58 (1990).

Dissolved organic carbon in the unsaturated zone under land irrigated by wastewater effluent.

Abstract: Field evidence indicates that high concentrations of dis solved organic carbon (DOC > 20 mg/L) are found throughout the 30 m thick unsaturated zone of a phreatic aquifer under land irrigated with wastewater effluent. The DOC is not correlated with the sedimentary organic carbon and therefore is related to the liquid phase. The latter is divided into two fractions: one is associated with clay and has a constant ratio to the sediment surface area (1 X 10~3 mg/m2) and the second is suggested to be paniculate organic matter found in the sands. The source of DOC can be either the irrigation water or a result of biochemical interactions in the sediments. The DOC is mobile through the unsaturated zone and is oxidized when it reaches the water table. Field data showing DOC persistance under unsaturated conditions and laboratory BOD tests of sediments from the unsaturated zone suggest that moisture content may be a major controlling factor in biod?gradation. The findings ques tion the suitability of irrigation with water containing a high DOC on the replenishment area of phreatic aquifers. Res. J. Water Pollut. Control Fed., 62, 861(1990).

Chemostat studies of a mixed culture growing on phenolics.

Abstract: The growth of a mixed culture was studied in a two stage chemostat with growth limited by phenolics. The first stage provided a fully viable, adapted population that was fed at a constant rate to the second stage, where the concentration of phenolics could be varied. The population exhibited inhibition kinetics at high concentrations of phe nolics. The viability of the culture decreased with increasing dilution rate, or with increasing phenolic concentration. The nonviable population did not utilize significant amounts of substrate, but ignoring viability can lead to a significant underestimate of the growth rate. The mainte nance requirements were insignificant at noninhibitory levels of phenolics, but rose to 0.15 g/g*h at inhibitory levels, possibly due to the need to repair damaged cell membranes. Res. J. Water Pollut. Control Fed., 62, 684(1990).

Characteristics of Nostocoida limicola and its activity in activated sludge suspension.

Abstract: The filamentous microorganism, Nostocoida limicola, was investigated in pure culture and full-scale studies to determine nu tritional requirements and growth factors. In pure culture, N. limicola reproduced very well in aerobic and anaerobic conditions on a variety of carbohydrates if peptone was present in the media. In activated sludge its occurrence was associated with the conditions of low organic loading and extended MCRT. Growth of N. limicola can be controlled success fully in activated sludge systems by means of an anoxic selector or reduced sludge age. Res. J. Water Pollut. Control Fed., 62, 137 (1990).

Biologically enhanced oxygen transfer in the activated sludge process.

Abstract: Biologically enhanced oxygen transfer has been a hy pothesis to explain observed oxygen transfer rates in activated sludge systems that were well above that predicted from aerator clean-water testing. The enhanced oxygen transfer rates were based on tests using BOD bottle oxygen uptake rates (OURs) on samples removed from the activated sludge system. Benchand full-scale plant studies were per formed to compare results of in situ OUR measurement techniques to BOD bottle OUR measurements. The studies showed that the condition of low dissolved oxygen (DO) and high OUR for which the greatest enhanced oxygen transfer was reported resulted in OURs in the BOD bottle tests well above the actual in situ OURs. For high DO and high OUR activated sludge operating conditions, the BOD bottle OURs were below the actual in situ OURs. The BOD bottle OUR values accurately described in situ OURs for endogenous respiration conditions with non limiting DO concentrations. These results suggest that previously observed biologically enhanced oxygen transfer was not actually occurring but was the result of the BOD bottle test method and activated sludge op erating condition. Res. J. Water Pollut. Control Fed., 62, 193 (1990).

Denitrification in a moving bed upflow sand filter.

Abstract: The denitrification performance of a moving bed upflow sand filter with methanol added as a carbon source was evaluated. Hy draulic loading rates were varied between 3.4 and 11.0 m/d and influent N02 + N03-N concentrations of up to 22 g/m3 were tested. The turnover rate of the sand bed ranged between 0.4 and 3.8 bed volumes/d. It was found that complete denitrification (effluent N02 + NO3-N < 1.0 g/m3) was obtained at daily loadings of up to 2.7 kg/m3 total equivalent nitrate nitrogen (N03-N?,). The minimum methanol dosage required for com plete denitrification was in the range of 3.3 to 3.5 g CH3OH/g N03-Neq. Methanol leakage, as evidenced by an increase of BOD5 across the filter, was negligible at dosages of 3.5 g/g NOa-Ngq or less. Res J. Water Pollut. Control Fed., 62,239 (1990).

Comparison of activated sludge stabilization under aerobic or anoxic conditions.

Abstract: The feasibility of anoxic sludge digestion, along with controlled aerobic digestion is evaluated in this study In the endogenous nitrate respiration system, nitrate instead of oxygen is utilized as the terminal electron acceptor for the microorganisms involved in biomass destruction under anoxic conditions The results indicated that the anoxic cell decay rate was a first-order reaction with respect to volatile suspended solids (VSS), but with a decreasing rate The nitrate requirement was approximately 054 mg N03"-N/mg VSS destruction The digester pH was almost three units higher than that of the aerobic digester (pH 85 versus 55) After 10 days of anoxic digestion, the VSS destruction, al kalinity production, and ammonium generation was 2000 mg/L, 18 mg CaC03/mg VSS destroyed, and 012 mg NH4+-N/mg VSS destroyed, respectively The digester supernatant contains a large quantity of colloidal particles (between 045 and 12 ^m) which cause poor sludge dewater ability These fine particles also contain high concentrations of organic nitrogen resulting in a high amount of organic matter recycling back to the plant The practical application of the use of the anoxic sludge is discussed Res J Water Pollut Control Fed, 62, 160 ( 1990)

Batch biodegradation of industrial organic compounds using mixed liquor from different POTWs.

Abstract: This study compared the levels at which organic com pounds could be biologically treated by the mixed liquor from different publicly owned treatment works (POTWs). Experiments conducted using several 5-L batch reactors involved degradation of single compounds and mixtures of compounds with two different mixed liquors. One mixed liquor came from a municipal treatment plant with a throughput of 9.5 ML/d (2.5 mil gal/day) of domestic waste; the other came from a plant that treats 9.5 ML/d (250 mil gal/day) of waste that is 55% industrial on a BOD basis, including about 227 kg/d (500 lb/day) phenol (0.25 ppm). Microorganisms from the domestic treatment plant degraded chlori nated hydrocarbons (2-chlorophenol, 2,6-dichlorophenol, and 2,4-D) at rates that were virtually the same as those for the plant handling industrial waste. The phenol degradation rates were the same, even though the latter plant had experienced significant prior exposure. The dominant microbial populations were also similar, both before and after phenolic exposure. Microbial adaption to the compounds was quite rapid, resulting in a twoto five-fold increase in the average degradation rates after only the second exposure in a batch reactor. When multiple substrates were tested, the individual compound degradation rates in the mixture were very similar to the degradation rates as sole carbon source. The amount of throughput and the magnitude of the degradation rates indicate the potential of the plant handling industrial waste to treat significant quantities of the compounds tested. Res. J. Water Pollut. Control Fed., 62, 803 (1990).

Effect of selected RCRA compounds on activated sludge activity.

Abstract: Thirty-three RCRA-listed compounds were studied to determine their impacts on the activity of biomass over a broad range of biogenic substrate concentrations. Eleven of them were insufficiently inhibitory to justify further testing and eight had responses that varied over time, making it impossible to quantify their efforts. The kinetic impacts of the remaining 14 were quantified by measuring the Monod kinetic parameters for butyric acid degradation in the presence of several inhibitor concentrations using a respirometric-based assay. Attempts to model the effects of inhibitor concentration on the Monod kinetic pa rameters with classical linear, reversible inhibition models were unsuc cessful, but it was possible to model them with a general inhibition model proposed by Han and Levenspiel. Res. J. Water Pollut. Control Fed., 62,654(1990).