Effect of loading types on performance characteristics of a trickle-bed bioreactor and biofilter during styrene/acetone vapor biofiltration.

A 2:1 (w/w) mixture of styrene (STY) and acetone (AC) was subjected to lab-scale biofiltration under varied loading in both a trickle bed reactor (TBR) and biofilter (BF) to investigate substrate interactions and determine the limits of biofiltration efficiency of typical binary air pollutant mixtures containing both hydrophobic and polar components. A comparison of the STY/AC mixture degradation in the TBR and BF revealed higher pollutant removal efficiencies and degradation rates in the TBR, with the pollutant concentrations increasing up to the overloading limit. The maximum styrene degradation rates were 12 and 8 gc m(-3) h(-1) for the TBR and BF, respectively. However, the order of performance switched in favor of the BF when the loading was conducted by increasing air flow rate while keeping the inlet styrene concentration (Cin) constant in contrast to loading by increasing Cin. This switch may be due to a drastic difference in the effective surface area between these two reactors, so the biofilter becomes the reactor of choice when the rate-limiting step switches from biochemical processes to mass transfer by changing the loading mode. The presence of acetone in the mixture decreased the efficiency of styrene degradation and its degradation rate at high loadings. When the overloading was lifted by lowering the pollutant inlet concentrations, short-term back-stripping of both substrates in both reactors into the outlet air was observed, with a subsequent gradual recovery taking several hours and days in the BF and TBR, respectively. Removal of excess biomass from the TBR significantly improved the reactor performance. Identification of the cultivable strains, which was performed on Day 763 of continuous operation, showed the presence of 7 G(-) bacteria, 2 G(+) bacteria and 4 fungi. Flies and larvae of Lycoriella nigripes survived half a year of the biofilter operation by feeding on the biofilm resulting in the maintenance of a nearly constant pressure drop.

A two-stage combined trickle bed reactor/biofilter for treatment of styrene/acetone vapor mixtures.

Performance of a two-stage biofiltration system was investigated for removal of styrene-acetone mixtures. High steady-state acetone loadings (above C(in)(Ac) = 0.5 g.m(-3) corresponding to the loadings > 34.5 g.m(-3).h(-1)) resulted in a significant inhibition of the system's performance in both acetone and styrene removal. This inhibition was shown to result from the acetone accumulation within the upstream trickle-bed bioreactor (TBR) circulating mineral medium, which was observed by direct chromatographic measurements. Placing a biofilter (BF) downstream to this TBR overcomes the inhibition as long as the biofilter has a sufficient bed height. A different kind of inhibition of styrene biodegradation was observed within the biofilter at very high acetone loadings (above C(in)(Ac) = 1.1 g.m(-3) or 76 g.m(-3).h(-1) loading). In addition to steady-state measurements, dynamic tests confirmed that the reactor overloading can be readily overcome, once the accumulated acetone in the TBR fluids is degraded. No sizable metabolite accumulation in the medium was observed for either TBR or BF. Analyses of the biodegradation activities of microbial isolates from the biofilm corroborated the trends observed for the two-stage biofiltration system, particularly the occurrence of an inhibition threshold by excess acetone.

Biofiltration of gasoline and diesel aliphatic hydrocarbons.

The ability of a biofilm to switch between the mixtures of mostly aromatic and aliphatic hydrocarbons was investigated to assess biofiltration efficiency and potential substrate interactions. A switch from gasoline, which consisted of both aliphatic and aromatic hydrocarbons, to a mixture of volatile diesel n-alkanes resulted in a significant increase in biofiltration efficiency, despite the lack of readily biodegradable aromatic hydrocarbons in the diesel mixture. This improved biofilter performance was shown to be the result of the presence of larger size (C9-C(12)) linear alkanes in diesel, which turned out to be more degradable than their shorter-chain (C6-C8) homologues in gasoline. The evidence obtained from both biofiltration-based and independent microbiological tests indicated that the rate was limited by biochemical reactions, with the inhibition of shorter chain alkane biodegradation by their larger size homologues as corroborated by a significant substrate specialization along the biofilter bed. These observations were explained by the lack of specific enzymes designed for the oxidation of short-chain alkanes as opposed to their longer carbon chain homologues.

Interactions among mononitrophenol isomers during biodegradation of their mixtures.

Continuous aerobic biodegradation of 4-NP, 3-NP and 2-NP mixture was monitored in a packed bed reactor in simulated wastewater with a mixed microbial culture immobilized on expanded slate. Substrate loading was varied by increasing the concentration of one isomer while keeping the other two at constant levels, all at a constant residence time of 60 min. At large concentrations, all of the individual NP isomers suppressed the degradation rates of the other isomers at steady state; however, the observed patterns and threshold concentrations were different for all three substrates. As a result, conditions were determined for stable and efficient removal of NP mixtures. Changes of the biofilm composition during a long-term operation were identified.

Biofiltration of a styrene/acetone vapor mixture in two reactor types under conditions of styrene overloading

This aim of study was to compare the performance of a biofilter (BF) and trickle bed reactor (TBR) under increased styrene loading with a constant acetone load, 2 gc/m3/h. At styrene loading rates up to 30 gc/m3/h, the BF showed higher styrene removal than TBR. However, the BF efficiency started to drop beyond this threshold loading and could never reach steady state, whereas the TBR continued to yield a 50% styrene removal. The acetone removal remained constant (93-98%) in both the reactors at any styrene loading. Once the overloading was lifted, the BF recovered within 26 min, whereas the TBR efficiency bounced back only to 95%, gradually returning to complete removal only in 10 h.

Biodegradation of nitroglycerin and ethylene glycol dinitrate by free and immobilized mixed cultures.

Aerobic biodegradation of nitroglycerin (NG) and ethylene glycol dinitrate (EGDN), both as individual substrates and in their mixture, was tested using batch or fed-batch cultivation with free suspended cells enriched from a soil sample subjected to a long-term contamination with explosives. EGDN was degraded only in the presence of glycerol as a co-substrate whereas NG could serve as a sole carbon, energy and nitrogen source for growth, its degradation being only slightly boosted by either glycerol or pyruvate. NG was not sufficient as a co-substrate for microbial growth on EGDN; furthermore, the presence of EGDN inhibited the NG degradation. The growth inhibition by both NG and EGDN was alleviated by the addition of glycerol. At an optimum nitroglycerin concentration of 30 mg/L, a maximum specific degradation rate of 60.9 ± 1.8 mg/gdw/h was observed. The biodegradation of both pollutants occurred with a release of nitrite. A method was developed for growing substantial amounts of NG-degrading biomass in the presence of glycerol for its immobilization on expanded slate in a pot-scale packed-bed reactor. Preliminary reactor tests were conducted in a continuous operation mode yielding a 70-90% NG biodegradation up to a load of 20 mg/L/h, with a removal rate up to 16 mg/L/h.

Pollutant interactions during the biodegradation of phenolic mixtures with either 2- or 3-mononitrophenol in a continuously operated packed bed reactor.

Pollutant interactions during the aerobic biodegradation of phenolic mixtures with either 2-nitrophenol (2-NP) or 3-nitrophenol (3-NP) by a NP-adapted microbial consortium in simulated wastewater were studied in a packed-bed bench scale bioreactor continuously operated in a flow mode. Phenol/2-NP and phenol/3-NP mixtures with varied phenol/nitrophenol ratios were shown to exhibit different biodegradability patterns. The presence of 2-NP led to a much lower overall elimination capacity and lower process stability in comparison to mixtures with 3-NP. In contrast to the expected greater degradation of a more biodegradable substrate in mixtures, phenol was degraded with a lower efficiency at higher phenol concentrations than NPs, although this difference became less pronounced with the gradual biofilm adaptation to phenol. This unusual substrate interaction, which appears to be common in the biotreatment of substituted phenol mixtures, was explained by prior biofilm adaptation to less degradable substrates, NPs. The biofilm composition was significantly altered during the long-term reactor operation. Although eukaryotes were not present in the inoculum, four fungal species were isolated from the biofilm after 1.5 years of operation. Of the initially present strains, only Chryseobacterium sp. and several Pseudomonas species persisted till the end of operation.

Biodegradation of a mixture of mononitrophenols in a packed-bed aerobic reactor.

Aerobic biodegradation of individual mononitrophenols (4-, 3- and 2-NPs) and their mixture in simulated wastewater was investigated in a packed-bed bench scale bioreactor continuously operated in a flow mode, with a mixed microbial culture adsorbed on expanded slate. Under a low, suboptimal hydraulic retention time (HRT) of 30 min the reactor removed more than 3 g.L(-1).day(-1) of the NP mixture while maintaining a > 85-90% removal efficiency (RE). Under higher HRT values, starting at 45 min, more than 2 g.L(-1).day(-1) of the NP mixture were removed with an RE > 98%. Significant substrate interactions were observed; the addition of other NPs caused the saturation of 2-NP catabolic capacity whereas the addition of 2-NP caused the de-saturation of the 4- and 3-NP catabolic capacity. 3- and 4-NPs appeared to be removed independently, i.e., by different enzyme systems. After ten months of operation, the biofilm composition was significantly altered to become predominantly bacterial. Only one originally inoculated strain remained indicating microbial contamination followed by a genetic material exchange.

Microbial monitoring and performance evaluation for H2S biological air emissions control at a wastewater lift station in South Texas, USA.

A pilot-scale biological sequential treatment system consisting of a biotrickling filter and two biofilters was installed at Waste Water Lift Station # 64 in Brownsville, Texas, USA to evaluate the performance of the system being loaded with variable concentrations of wastewater hydrogen sulfide (H(2)S) emissions. In this study, the effectiveness of sulfur oxidizing bacteria along with the distribution of various sulfur species and their correlation with the performance of the biofilters was evaluated. The biofilters were packed with engineered media consisting of plastic cylinders with compacted organic material which was supplied by Met-Pro Environmental Air Solutions (formerly Bio·Reaction Industries). The overall performance of the pilot-scale biological sequential treatment system with an Empty Bed Residence Time (EBRT) of 60s and the overall performance of the biofilter unit with an EBRT of 35s developed a removal efficiency of > 99% at H(2)S levels up to 500 ppm. A decrease in performance over time was observed in the first and second sections of the first biofilter unit with the third section of the biofilter unit ultimately becoming the most robust unit removing most of the pollutant. The second biofilter unit was not needed and subsequently removed from the system. The number of CFUs in sulfur oxidizing T.thioparus selective media grew significantly in all four sections of the biofilter over the two months of pilot operation of the biological unit. The sulfur oxidizer growth rates appeared to be highest at low total sulfur content and at slightly acidic pH levels. This study has implications for improving the understanding of the distribution of sulfur oxidizing bacteria throughout the length of the biofilter columns, which can be used to further optimize performance and estimate breakthrough at these very high H(2)S input loadings.

Parameters affecting HS emissions removal and re-circulating water quality in a pilot-scale sequential biological treatment system at a wastewater lift station in Brownsville, Texas, USA.

In this study, a pilot-scale sequential biological treatment system combining a biotrickling filter and biofilter was used to optimize the removal of variable emission H(2)S loadings ranging from 30 to 120 g m(-3) h(-1)at a wastewater lift station in Brownsville, Texas USA. The biotrickling filter recycle water pH remained between 2.0 to 3.0 during the four months of unit operation and the overall removal efficiency for H(2)S was >99%. The biotrickling filter removal efficiency was 70 ± 8%, with an elimination capacity of 10 to 80 g m(-3) h(-1) while the biofilter elimination capacity ranged from 10 to 40 g m(-3) h(-1). The sequential treatment system was operated initially at an Empty Bed Residence Time (EBRT) of 120 s (50 s for the biotrickling filter and 70 s for biofilter) for two months and then at an EBRT of 60 s (25 s for biotrickling filter and 35s for biofilter) for the remainder of the operating period; remarkably, there was only a slight decrease in removal efficiency at 60 s EBRT. In order to qualitatively evaluate the changes in recycle water quality in the system on the performance of the unit in precipitating sulfur species, the equilibrium chemical model, Visual MINTEQ was employed. The model predicted speciation results based on the feed water quality and sulfur loadings, and also forecast some iron-sulfur complexes which have potential to form some complex precipitates. This research demonstrated that low pH re-circulating water quality in the biological treatment of H(2)S was possible without compromising the high removal efficiency, and that an improved understanding of the recycle water chemistry of the trickling unit of a sequential treatment system could be useful in the overall optimization of the process.

Preferences in removal of aliphatic and aromatic gasoline components by biofiltration under varied loading.

Removal of gasoline vapors from waste air was investigated in a bench-scale perlite biofilter for three aromatic-to-aliphatic mass ratios (62/38, 92/8 and 44/56) under different loads, varied by changing both the substrate inlet concentration and air flow rate. The measurement of concentration profiles along the bed height allowed for an assessment of interactions between the aromatic and aliphatic fractions of gasoline. Variations in both the inlet concentrations and empty bed residence time significantly influenced the removal of aliphatic gasoline components. Except for the lowest organic loads, the whole biofilter bed was required for achieving an acceptable removal efficiency of aliphatic hydrocarbons. The presence of large amounts of aromatics negatively impacted the removal of aliphatics. By contrast, the aromatic gasoline components were near-completely removed from any mixtures; the bulk of them were degraded in the first (out of three) biofilter section, even at high concentrations of aliphatic hydrocarbons. The observed effect was shown to be due to competitive interactions of aliphatic and aromatic components, which is consistent with the biological steps being rate limiting. Mass transfer, particularly for aliphatic components due to their high Henry's law constants, was shown to be rate-limiting under extreme scenarios, such as low loading rates and EBRT.

Biofiltration of gasoline and ethanol-amended gasoline vapors.

Assuming the projected increase in use of ethanol as a biofuel, the current study was conducted to compare the biofiltration efficiencies for plain and 25% ethanol-containing gasoline. Two biofilters were operated in a downflow mode for 7 months, one of them being compost-based whereas the other using a synthetic packing material, granulated tire rubber, inoculated with gasoline-degrading microorganisms. Inlet concentrations measured as total hydrocarbon (TH) ranged from 1.9 to 5.8 g m(-3) at a constant empty bed retention time of 6.84 min. Contrary to the expectations based on microbiological considerations, ethanol-amended gasoline was more readily biodegraded than plain hydrocarbons, with the respective steady state elimination capacities of 26-43 and 14-18 gTH m(-3) h(-1) for the compost biofilter. The efficiency of both biofilters significantly declined upon the application of higher loads of plain gasoline, yet immediately recovering when switched back to ethanol-blended gasoline. The unexpected effect of ethanol in promoting gasoline biodegradation was explained by increasing hydrocarbon partitioning into the aqueous phase, with mass transfer being rate limiting for the bulk of components. The tire rubber biofilter, after a long acclimation, surpassed the compost biofilter in performance, presumably due to the 'buffering' effect of this packing material increasing the accessibility of gasoline hydrocarbons to the biofilm. With improved substrate mass transfer, biodegradable hydrocarbons were removed in the tire rubber biofilter's first reactor stage, with most of the remaining poorly degradable smaller-size hydrocarbons being degraded in the second stage.

Biofiltration of paint solvent mixtures in two reactor types: overloading by polar components.

Steady-state performances of a trickle bed reactor (TBR) and a biofilter (BF) in loading experiments with increasing inlet concentrations of polar solvents, acetone, methyl ethyl ketone, methyl isobutyl ketone and n-butyl acetate, were investigated, along with the system's dynamic responses. Throughout the entire experimentation time, a constant loading rate of aromatic components of 4 g(c)·m(-3)·h(-1) was maintained to observe the interactions between the polar substrates and aromatic hydrocarbons. Under low combined substrate loadings, the BF outperformed TBR not only in the removal of aromatic hydrocarbons but also in the removal of polar substrates. However, increasing the loading rate of polar components above the threshold value of 31-36 g(c)·m(-3)·h(-1) resulted in a steep and significant drop in the removal efficiencies of both polar (except for butyl acetate) and hydrophobic components, which was more pronounced in the BF; so the relative TBR/BF efficiency became reversed under such overloading conditions. A step-drop of the overall OL(POLAR) (combined loading by polar air pollutants) from overloading values to 7 g(c)·m(-3)·h(-1) resulted in an increase of all pollutant removal efficiencies, although in TBR the recovery was preceded by lag periods lasting between 5 min (methyl ethyl ketone) to 3.7 h (acetone). The occurrence of lag periods in the TBR recovery was, in part, due to the saturation of mineral medium with water-soluble polar solvents, particularly, acetone. The observed bioreactor behavior was consistent with the biological steps being rate-limiting.

Activation and detoxification metabolism of urban air pollutants 2-nitrobenzanthrone and carcinogenic 3-nitrobenzanthrone by rat and mouse hepatic microsomes.

OBJECTIVES: 2-Nitrobenzanthrone (2-NBA) has recently been detected in ambient air particulate matter. Its isomer 3-nitrobenzanthrone (3-NBA) is a potent mutagen and suspected human carcinogen identified in diesel exhaust. Understanding which enzymes are involved in metabolism of these toxicants is important in the assessment of individual susceptibility. Here, metabolism of 2-NBA and 3-NBA by rat and mouse hepatic microsomes containing cytochromes P450 (CYPs), their reductase (NADPH:CYP reductase), and NADH:cytochrome b5 reductase was investigated under anaerobic and aerobic conditions. In addition, using the same microsomal systems, 2-NBA and 3-NBA were evaluated to be enzymatically activated under anaerobic conditions to species generating 2-NBA- and 3-NBA-derived DNA adducts. METHODS: High performance liquid chromatography (HPLC) with ultraviolet (UV) detection was employed for the separation and characterization of 2-NBA and 3-NBA metabolites formed by hepatic microsomes of rats and mice under the anaerobic and aerobic conditions. Microsomal systems isolated from the liver of the control (untreated) rats and rats pretreated with Sudan I, ß-naphthoflavone (ß-NF), phenobarbital (PB), ethanol and pregnenolon 16α-carbonitrile (PCN), the inducers of cytochromes P450 (CYP) 1A1, 1A1/2, 2B, 2E1 and 3A, respectively, were used in this study. Microsomes of mouse models, a control mouse line (wild-type, WT) and Hepatic Cytochrome P450 Reductase Null (HRN) mice with deleted gene of NADPH:CYP reductase in the liver, thus absenting this enzyme in their livers, were also employed. To detect and quantify the 2-NBA- and 3-NBA-derived DNA adducts, the 32P postlabeling technique was used. RESULTS: Both reductive metabolite of 3-NBA, 3-aminobenzanthrone (3-ABA), found to be formed predominantly under the anaerobic conditions, and two 3-NBA oxidative metabolites, whose structures have not yet been investigated, were formed by several microsomal systems used in the study. Whereas a 3-NBA reductive metabolite, 3-ABA, was found only in the microsomal systems of control rats, the rats treated with ß-NF and PB, and microsomes of WT and HRN mice, all hepatic microsomes tested in the study were capable of activating this carcinogen under the reductive conditions to form DNA adducts. A stability of a reactive intermediate of 3-NBA, N-hydroxy-3-aminobenzanthrone that is formed during 3-NBA reduction to 3-ABA, to form nitrenium (and/or carbenium) ions binding to DNA in individual microsomes as well as binding of these ions to proteins of these microsomes, might be the reasons explaining this phenomenon. In contrast to 3-NBA, its isomer 2-NBA was not metabolized by any of the used enzymatic systems both under the anaerobic and aerobic conditions. Likewise, no DNA adducts were detectable after reaction of 2-NBA in these systems with DNA. CONCLUSIONS: The results found in this study, the first report on the metabolism of 2-NBA and 3-NBA by rat and mouse hepatic microsomes demonstrate that 3-NBA, in contrast to 2-NBA, is reductively activated to form 3-NBA-derived DNA adducts by these enzymatic systems. NADPH:CYP reductase can be responsible for formation of these DNA adducts in rat livers, while NADH:cytochrome b5 reductase can contribute to this process in livers of HRN mice.

Isolation and partial characterization of extracellular NADPH-dependent phenol hydroxylase oxidizing phenol to catechol in Comamonas testosteroni.

OBJECTIVE: Comamonas testosteroni Pb50 is a microorganism that possesses high tolerance for phenol and shows strong phenol degrading activity. This bacterial strain is capable of utilizing phenol as the sole carbon and energy source. Although examples are known in which the C. testosteroni utilizes phenol for growth or metabolism, much less information are known on the nature of the phenol-oxidizing enzymes in this microorganism. Therefore, the occurrence and cellular location of phenol hydroxylase (EC 1.14.13.7), the enzyme participating in the first step of phenol degradation, catalyzing its hydroxylation to catechol in a bacterial Comamonas testosteroni Pb50 strain grown in the presence of phenol as a sole carbon and energy source are the aims of this study. METHODS: Combination of fractionation with polyethylene glycol 6000 and gel permeation chromatography on columns of Sepharose 4B and Sephacryl S-300 was used for isolation of phenol hydroxylase detectable in the medium in which C. testosteroni was cultivated. The sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and gel chromatography on Sephacryl S-300 were used to evaluate the molecular mass of the enzyme. The enzyme activity was followed by HPLC (phenol consumption and/or catechol formation). RESULTS: Whereas low activity of phenol hydroxylase was detected in cytosol isolated from C. testosteroni, more than 16-fold higher activity of this enzyme was found in the medium in which C. testosteroni was cultivated. The presence of phenol hydroxylase extracellular activity suggests that this microorganism may secrete the enzyme into the extracellular medium. Using the procedure consisting of fractionation with polyethylene glycol 6000 and gel permeation chromatography on columns of Sepharose 4B and Sephacryl S-300, the enzyme was isolated from the medium to homogeneity. The formation of catechol mediated by purified phenol hydroxylase is strictly dependent on the presence of NADPH, which indicates that this enzyme is the NADPH-dependent phenol hydroxylase. The enzyme is a homotetramer having a molecular mass of 240 000, consisting of four subunits having a molecular mass of 60 000. The optimum pH of the enzyme for the phenol oxidation is pH 7.6. CONCLUSION: The results are the first report showing isolation and partial characterization of extracellular NADPH-dependent phenol hydroxylase of a bacterial C. testosteroni Pb50 strain capable of oxidizing phenol to catechol. The data demonstrate the progress in resolving the enzymes responsible for the first step of phenol degradation by bacteria.

Factors influencing the aerobic biodegradation of 2,4-dinitrotoluene in continuous packed bed reactors.

Factors affecting continuous 2,4-DNT degradation by an immobilized mixed microbial culture were investigated including the cell adaptation to this toxic substrate, 4-NT co-degradation, packing material porosity and substrate mass loading. Experiments were carried out in two packed bed reactors, with poraver (porous glass) and expanded slate as packing materials, using a concurrent water-air flow with ample oxygen. Running the system as a batch reactor with re-circulated medium showed that the immobilized cells adapted to higher 2,4-DNT concentrations yielding higher substrate biodegradation rates. The 2,4-DNT removal rate further increased, up to 180-265 mg L(-1)d(-1), when the immobilized biomass cultivation was switched to a continuous mode. The type of the packing material influenced the 2,4-DNT removal rate, apparently due to the difference in biofilm development. Significant changes in the biofilm composition were observed compared to the original inoculum despite poor biofilm growth.

Aerobic degradation of 2,4-dinitrotoluene by individual bacterial strains and defined mixed population in submerged cultures.

The degradation efficiencies of isomeric mononitrotoluenes (2- and 4-NTs) and dinitrotoluenes (2,4-DNT and 2,6-DNT) by either individual bacterial strains (Bacillus cereus NDT4, Pseudomonas putida NDT1, Pseudomonas fluorescens NDT2, and Achromobacter sp. NDT3) or their mixture were compared in submerged batch cultivations. The mixed culture degraded 2,4-DNT nearly 50 times faster than any of the individual strains. The mixed culture also demonstrated significantly shorter lag periods in 2,4-DNT degradation, a lack of nitrite or organic intermediates accumulation in the liquid medium and the ability to degrade a broader spectrum of nitrotoluenes over a wider concentration range. The presence of both readily degradable 2-NT (or 4-NT) and poorly degradable 2,6-DNT in the medium negatively affected 2,4-DNT biodegradation. However, the mixed bacterial culture still effectively degraded 2,4-DNT with only slightly lower rates under these unfavorable conditions, thus showing potential for the remediation of 2,4-DNT contaminated sites.

Respirometry kinetics of phenol oxidation by Comamonas testosteroni Pb50 under various conditions of nutritional stress

Kinetics of phenol biodegradation using suspended biomass of Comamonas testosteroni Pb50 (monoculture) was measured under conditions of nutrient abundance, limitation, and prolonged cell starvation in a fed-batch reactor, with phenol being the sole carbon and energy source. The pre-washed cells were applied for measurement of the phenol and oxygen uptake rates at varied starting phenol concentrations with the kinetic parameters calculated using the Haldane model. The results revealed that nutrient limitation significantly suppressed the maximum value of exogenous respiration rate while the endogenous respiration rate, affinity and tolerance to phenol increased. By contrast, cell starvation resulted in a drop of both the exogenous and endogenous respiration rates by an order of magnitude.

Biofiltration of paint solvent mixtures in two reactor types: overloading by hydrophobic components.

Steady-state performance characteristics of a trickle bed reactor (TBR) and a biofilter (BF) in loading experiments with increasing toluene/xylenes inlet concentrations while maintaining a constant loading rate of hydrophilic components (methyl ethyl and methyl isobutyl ketones, acetone, and n-butyl acetate) of 4 g m⁻³ h⁻¹ were evaluated and compared, along with the systems' dynamic responses. At the same combined substrate loading of 55 g m⁻³ h⁻¹ for both reactors, the TBR achieved more than 1.5 times higher overall removal efficiency (RE(W)) than the BF. Increasing the loading rate of aromatics resulted in a gradual decrease of their REs. The degradation rates of acetone and n-butyl acetate were also inhibited at higher loads of aromatics, thus revealing a competition in cell catabolism. A step-drop in loading of aromatics resulted in an immediate increase of RE(W) with variations in the TBR, while the new steady-state value in the BF took 6-7 h to achieve. The TBR consistently showed a greater performance than BF in removing toluene and xylenes. Increasing the loading rate of aromatics resulted in a gradual decrease of their REs. The degradation rates of acetone and n-butyl acetate were also lower at higher OL(AROM), revealing a competition in the cell catabolism. The results obtained are consistent with the proposed hypothesis of greater toxic effects under low water content, i.e., in the biofilter, caused by aromatic hydrocarbons in the presence of polar ketones and esters, which may improve the hydrocarbon partitioning into the aqueous phase.