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The expanded-bed anaerobic GAC reactor, operating with GAC replacement has been demonstrated to treat toxic wastes effectively. The concentration of adsorbable toxic compounds, the hydraulic detention time within the treatment system, and the GAC replacement rate represent three parameters that are strongly related and effectively control process performance. This study investigates the impact of the aforementioned process variables on treatment efficiency. A steady-state model that includes representations of the various phenomena that occur within the anaerobic reactors such as biodegradation, inhibition, competitive adsorption, and attached biomass shearing is presented. Using independently determined adsorption parameters, measured shear loss coefficients, and literature values for biodegradation kinetic parameters, the model predictions are found to be in good agreement with the experimental data.

Rotating drum biofilters (RDBs) are cost-effective for control of emissions of volatile organic compounds (VOCs) from waste gas streams. In this paper, a dynamic mathematical model is presented which simulates and predicts the variation in performance of a multi-layer ROB with time on the basis of the two-film theory. The model takes into account factors including biofilm growth and biomass loss, and a changing biofilm surface area and thickness assuming quasi-steady-state conditions in the two-phase system and uniform bacterial population. Toluene was assumed to be the only rate-limiting substrate. The model equations for the gas-phase mass balance and biofilm growth were solved using MATLAB based on the fourth-fifth-order Runge-Kutta technique, and the concentration profiles in the biofilms were obtained using the method of orthogonal collocation. Simulation results showed that the toluene removal efficiency decreased with increased toluene loading or increased duration of operation of the biofilter. Calculation results were compared to the experimental results, which demonstrated that the dynamic model provided a good simulation of the performance of the biofilter. [ABSTRACT FROM AUTHOR]

Thermo-oxidative treatment, applied at moderate temperatures below the boiling point of water and using hydrogen peroxide as oxidant, has been shown to enhance anaerobic digestion of excess municipal sludge, Due to the high economic impact of chemical addition on the process, a balance between process performance and economic cost has to be established. The effect of three low hydrogen peroxide dosages (0.1, 0.25 and 0.5 gH2O2/gVSSinfluent) applied at 90°C was evaluated. Increases in solids destruction of 13.9, 18.9 and 25.6% with respect to a control were observed when the thermo-oxidative co-treatment was operated at 0.1, 0.25 and 0.5 gH2O2/gVSSinfluent, respectively. [ABSTRACT FROM AUTHOR]

The effect of oxidative and thermo-oxidative co-treatment of excess municipal sludge was investigated. A mixture of primary and waste activated sludge was anaerobically treated using two different configurations: i) two stages and ii) a single stage with recycling. Oxidative or thermo-oxidative co-treatment placed in between the reactor or in the recycle line was studied. A two-stage configuration with no co-treatment served as a control and resulted in 50.1% overall solids removal. Compared to the control, an increase in solids removal of 10.8 and 2.7% was observed when oxidative co-treatment was placed between reactors and in the recycle line respectively. When thermo-oxidative co-treatment was placed between the two stages or in the recycle line an increase in solids removal of 25.1 and 26.9% respectively was observed. The performances of the different configurations were also evaluated with parameters such as COD, TKN, ammonia, and fecal coliform concentration. [ABSTRACT FROM AUTHOR]

A rotating drum biofilter (RDB) with multi-layered foam media was developed for the improvement of current biofiltration technology. The biofilter was used to investigate the effects of organic loadings and influent volatile organic compound (VOC) concentrations on VOC removal efficiency and biomass accumulation. These effects were evaluated using diethyl ether and toluene separately as model VOCs at an empty bed contact time (EBCT) of 30 s. When the toluene loading increased from 2.0 to 4.0 and 8.0 kgCOD m-3 day-1, toluene removal efficiency of the biofilter decreased from over 99% to 78% and 74%, respectively. The biomass distribution was found to be more even within the medium when removing toluene than when removing diethyl ether. Higher organic loading also resulted in the more even distribution of the biomass. The ratios of biomass accumulation rates in the medium of the outermost, middle and innermost layers ranged from 1:0.11:0.02 when removing diethyl ether at 2.0 kgCOD m-3 day-1 to1:0.69:0.51 when removing toluene at 8.0 kgCOD m-3 day-1. Review of these ratios revealed three biomass accumulation patterns: surface pattern, in-depth pattern and shallow pattern. Different patterns represent different removal mechanisms in the biofiltration process. Improved biofilter design and operation should be based on the biomass accumulation pattern. [ABSTRACT FROM AUTHOR]

Initial degradation of highly chlorinated compounds and nitroaromatic compounds found in munition waste streams is accelerated under anaerobic conditions followed by aerobic treatment of the degradation products. The establishment of anaerobic environment in a vadose zone can be accomplished by feeding appropriate anaerobic gas mixture, i.e.,'anaerobic bioventing'. The gas mixture contains an electron donor for the reduction of these compounds. Lab scale study was conducted toevaluate potential of anaerobic bioventing for the treatment of an unsaturated zone contaminated with 1,1,1-trichloro -2,2-bis(p-chlorophenyl)ethane (DDT) and 2,4-dinitrotoluene (DNT). Hydrogen was used as the electron donor. Using the soil columns innoculate with anaerobic microorganisms, it was observed that by feeding a gas mixture of 1% hydrogen, 1% carbon dioxide and nitrogen, methanogenic conditions wereestablished and DDT was reductively dechlorinated. 1,1-dichloro-2,2-bis(p-chlorophenyl)ethane (DDD) accumulated as the intermediate product. The half life of DDT was calculated to be 8.5 months. DNT completely disappeared after six months of operation and no intermediates could be detected. [ABSTRACT FROM AUTHOR]

MTBE degradation was investigated using a continuously stirred tank reactor (CSTR) with biomass retention (porous pot reactor) operated under aerobic conditions. MTBE was fed to the reactor at an influent concentration of 150 mg/l (1.70 mmol/l). A second identical reactor was operated as a control under the same conditions with the addition of 2.66 g/l of sodium azide, to kill any biological activity. Results from these experiments suggest that biomass retention is critical to the degradation of MTBE. The rate of MTBE removal was shown to be related to the VSS concentration. MTBE removal exceeded 99.99% when the VSS concentration in the reactor was over 600 mg/l. Results obtained from batch experiments conducted on mixed liquor samples from the porous pot reactor indicate that the individual rates of biodegradation of MTBE and TBA were higher for initial concentrations of 15 mg/l than for concentrations of 5 mg/l. The presence of TBA at lower concentrations did not effect the rate of MTBE degradation, however higher concentrations of TBA did reduce the rate of biodegradation of MTBE. Denaturing Gradient Gel Electrophoresis (DGGE) analysis reveals that the culture consisted of a community of bacterial organisms of about 6 species. [ABSTRACT FROM AUTHOR]

Mass transport phenomena occurring in the biofilms of gas phase trickle-bed biofilters are investigated in this study. The effect of biofilm structure on mass transfer mechanisms is examined using experimental observation from the operating of biofilters, microelectrode techniques and microscopic examination. Since the biofilms of biofilters used for waste gas treatment are not completely saturated with water,there is not a distinguishable liquid layer outside the biofilm. Results suggest that due to this characteristic, gas phase substrates (such as oxygen or volatile organic compounds) may not be limited by the aqueous phase because transport of the compound into the biofilm can occur directly through non-wetted areas. On the other hand, for substrates that are present only in the liquid phase, such as nitrate, the mass transfer limitation is more serious because of the limited liquid supply. Microscopic observations show that a layered structure with void spaces exists within the biofilm. Oxygenconcentration distributions along the depth of the biofilms are examined using an oxygen microelectrode. Results indicate that there are some high dissolved oxygen zones inside the biofilm, which suggests the existence of passages for oxygen transfer into the deeper sections of the biofilm in a gas phase trickle-bed biofilter. Both the low gas-liquid mass transfer resistance and the resulting internal structure contribute to the high oxygen penetration within the biofilms in gas phase trickle-bed biofilters. [ABSTRACT FROM AUTHOR]

In this study, an anaerobic fluidized bed reactor (AFBR) was used totreat a synthetically produced pink water waste stream containing trinitrotoluene (TNT). The synthesized waste consisted of 95 mg/l-TNT, the main contaminant in pink water, which was to be co-metabolized with 560-mg/l ethanol. Granular activated carbon was used as the attachment medium for biological growth. TNT was reduced to a variety of compounds, mainly 2,4,6-triaminotoluene (2,4,6-TAT), 2,4-diamino-6-nitrotoluene (2,4-DA-6-NT), 2,6-diamino-4-nitrotoluene (2,6-DA-4-NT), 2-amino-4,6-dinitrotoluene (2-A-4,6-DNT), and 4-amino-2, 6-dinitrotoluene (4-A-2,6-DNT). These conversions resulted through the oxidation of ethanol to carbon dioxide under anoxic conditions, or reduction to methane under methanogenic conditions. The anaerobic reactor was charged with 1.0 kg of 16x20 U.S. Mesh Granular Activated Carbon (GAC) and was pre-loaded with 200g of TNT prior to the addition of the mixed seed culture. During the first three weeks of operation, ethanol was completely degraded and no methane was produced. Effluent inorganic carbon revealed stoichiometric conversion of the feed ethanol to dissolved inorganic carbon with accumulation of carbon dioxide in the headspace of the reactor. GAC extraction showed incremental reduction of the nitro groups to amino groups, with 2,4,6-TAT as the final product. After three weeks, the oxygen from the nitro groups was depleted and methane production commenced. The reproducibility of this phenomenon was confirmed by repeating the experiment in the same manner using anidentical AFBR. Furthermore, serum bottle tests were conducted usingTNT loading ratios of 0.2, 0.4, 0.8, 1.0 g-TNT/g-GAC as well as experiments in the absence of GAC. Similar behavior to that of the columns was observed, with degradation rates varying according to the particular condition. GAC greatly enhanced the degradation rates and the higher TNT loading resulted in slower degradation rates of ethanol. [ABSTRACT FROM AUTHOR]

The objective of this work is to develop a fundamental mathematical model that describes the biodegradation of volatile organic compounds(VOCs) in gas phase trickle-bed biofilters, and to estimate the unknown model parameters. The mathematical model considers a three-phase system (biofilm, water, and gas phase), non-uniform bacterial population, and one limiting substrate. Two pilot-scale trickle-bed biofilters were operated to remove the VOC diethyl ether from a waste gas stream. Experimental results from this system were used to estimate the unknown parameters of the steady-state model: the maximum rate of substrate utilization mu m Xf/Y, the Monod constant, Ks, and the ether biofilm/water diffusivity ratio, rd. While the value of mu m Xf/Y was uniquely determined, the values of Ks and rd were highly correlated. High values of the Monod constant and the ether diffusivity in the biofilm gave similar predictions to those corresponding to low values of both parameters. Batch studies were used to estimate the value of Ks without mass transfer limitations showing that Ks < 1 mg/L=2.6 mg COD/L. Using this information and biofilter operating data the true values of Ks and rd were determined. [ABSTRACT FROM AUTHOR]

Bioremediation of oil spills on beaches commonly involves the addition of nutrients (especially nitrogen and phosphorus) to stimulate thegrowth of indigenous oil-degrading bacteria. Very little informationis available regarding the relationship between nutrient concentration and the rate of oil biodegradation. This information is necessary to design an appropriate nutrient delivery technology. We used continuous-flow beach microcosms containing heptadecane-coated sand (2.0 g per kg of dry sand) to evaluate the effect of nitrate concentration on the hydrocarbon biodegradation rate. Heptadecane biodegradation wasdetermined by monitoring oxygen consumption and carbon dioxide production in the microcosms. The maximum biodegradation occurred at 2.5 mg nitrate-N l-1. Nitrogen recycling by the biomass was evidenced by the presence of microbial activity at zero influent nitrateconcentration. [ABSTRACT FROM AUTHOR]

An integrated reactor system has been developed to remediate pentachlorophenol (PCP) containing wastes using sequential anaerobic and aerobic biodegradation. Anaerobically, PCP was degraded to predominatelyequimolar concentrations (>99%) of monochlorophenol (MCP) in two GACfluidized bed reactors at Empty Bed Contact Times (EBCTs) ranging from 18.6 to 1.15 hours. However, at lower EBCTs, MCP concentrations decreased to less than 10% of the influent PCP concentration suggestingmineralization. The optimal EBCT was determined to be 2.3 hours based on PCP conversion to MCPs and stable reactor operation. Decreasing the EBCT fourfold did not inhibit degradation of PCP and its intermediates, thus allowing removal of PCP at much lower detention time and resulting in a significant cost advantage. Analytical grade PCP was fed via syringe pumps into two fluidized bed reactors at influent concentrations of 100 mg/l and 200 mg/l, respectively. Acting as the primary substrate, ethanol was also fed into the reactors at concentrations of 697 and 1388 mg/l. Effluent PCP and chlorinated phenolic compounds were analyzed weekly to evaluate reactor performance. Biodegradation pathways were also identified. 3-chlorophenol (CP) was the predominant MCP and varied simultaneously with 3,5-dichlorophenol (DCP) concentrations. Likewise, 4-CP concentrations varied simultaneously with3,4-DCP concentrations. A second stage aerobic GAC fluidized bed reactor was added after the anaerobic reactor to completely mineralize the remaining MCP and phenols. Data show no presence of phenol and MCPin the effluent or on the GAC. Overall, the chemical oxygen demand (COD) fed to the system was reduced from 75 g/d in the influent to less than 1.5 g/d in the effluent. [ABSTRACT FROM AUTHOR]

Successful bioremediation of oil-contaminated beaches requires maintenance of a sufficient quantity of growth-limiting nutrients in contact with the oiled beach material. A conservative tracer study was conducted on a moderate-energy, sandy beach on Delaware Bay to estimate the washout rate for dissolved nutrients from the bioremediation zoneat different stages during the lunar tidal cycle. When an aqueous solution of the conservative tracer (LiNO3) was applied to the beach surface in the upper intertidal zone at the full moon spring tide, it was completely removed within one day. When it was applied at neap tide, however, the tracer persisted in the bioremediation zone for several days. The amount of nutrient remaining in the bioremediation zone was highly correlated with the maximum extent to which the treated area had previously been submerged by water at high tide: submergence resulted in nearly complete removal of dissolved compounds from the bioremediation zone. This high rate of nutrient washout was confirmed by daily monitoring of nutrient concentrations in the bioremediation zone during an oil-spill bioremediation field study that was conductedon a nearby beach. [ABSTRACT FROM AUTHOR]

A kinetic model that describes the anaerobic cometabolism of 2,4-dinitrtoluene (DNT) with ethanol as the primary substrate has been developed based on experimental results. The kinetic parameters were estimated using the Levenberg-Marquardt algorithm. 2,4-DNT is anaerobically biotransformed to 2,4-diaminotoluene (DAT) via 4-amino-2-nitrotoluene (4-A-2-NT) and 2-amino-4-nitrotoluene (2-A-4-NT) by the bacteria whose growth is supported by utilizing ethanol. 2,4-DNT shows inhibition to its own biotransformation. It also exhibits a very strong competitive inhibition to further biotransformation of 4-A-2-NT and 2-A-4-NT. All the aromatics in the system, 2,4-DNT, 4-A-2-NT, 2-A-4-NT, and2,4-DAT, inhibit the conversion of ethanol. Hydrogen produced from the acetogenesis of ethanol is utilized for the transformation of the nitroaromatics. The utilization of hydrogen and acetate by methanogenic bacteria is very strongly inhibited by the presence of the nitroaromatics. Acetate exhibits strong competitive inhibition to the biodegradation of propionate. [ABSTRACT FROM AUTHOR]