Degradation of Linseed Oil Vapors by Soil Bacteria in Trickling Biofilters

Oxidation products of linseed oil were produced by impinging a stream of air onto the surface of pure linseed oil and injecting the vapor-laden air into soil percolation columns to enrich the population of bacteria capable of degrading linseed oil vapors. As the populations of bacteria increased, the linseed oil vapors were consumed by these organisms, and the air that emerged from the columns was free of linseed oil contaminants. Five different kinds of bacteria capable of growing on the linseed oil oxidation products as sole source of carbon and energy were found and isolated in pure culture. Chromatographic analyses showed that individual organisms removed specific components of the vapor at specific rates, but none was able to remove them all within a 30-day period of time. When the five were grown together and presented the linseed oil vapor, all vapor constituents were utilized, and the rate of utilization was greater than that seen when the isolates were tested in pure culture. This indicated that the five organisms operated as a bacterial consortium in the degradation of linseed oil vapors. Trickling biofilters prepared from pregrown populations of the five organisms challenged with linseed oil vapors were able to remove all volatile constituents found in linseed oil vapor. Bioremediation of the air was complete and it was accomplished in a single pass of the air through the filter.

This work shows that bacteria found in the soil are capable of degrading linseed oil vapors and that they can be grown in the laboratory and used successfully in bench scale trickling biofilters.     

Steady-state and transient-state performance of a biotrickling filter treating chlorobenzene-containing waste gas

Biotrickling filter (BTF) technology was applied for the treatment of waste gas containing a mixture of chlorobenzene and 1,2-dichlorobenzene. An adapted microbial community was immobilised on a structured packing material. The strategy followed was to reach high removal efficiencies at initially low mass loading rates followed by an increase of the latter. This procedure was successful and resulted in a short start-up period of only 2 weeks. A 3-month operation under steady-state conditions showed good performance, with >95% removal efficiency at a mass loading rate of 1,800 g m^–3 day^–1. Dimensionless concentration profiles showed that the chlorobenzenes were simultaneously degraded. Low dissolved organic carbon of 15 mg l^–1 and stoichiometric chloride concentrations in the trickling liquid indicated complete mineralisation of the pollutant. Transient-state experiments with five times higher mass loading rates caused a decrease in the removal efficiency that recovered rapidly once the mass loading rate returned to its original steady-state level. A progressive increase of the mass loading rate in a long-term performance experiment showed that the removal efficiency could be kept stable between 95 and 99% at loads of up to 5,200 g m^–3 day^–1 over several days. Above this mass loading rate, the elimination capacity did not increase any further. These results demonstrated that with a well-adapted inoculum and optimal operation parameters, a BTF system with excellent performance and stability that efficiently removes a mixture of cholorobenzene vapours from air can be obtained.     

The use of pine bark and natural zeolite as biofilter media to remove animal rendering process odours

Studies of odour-control pilot-scale biofilters at a rendering plant were conducted for five years. The biofilters contained different sizes of crushed pine bark or a mixture of zeolite and crushed bark, and treated the exhaust gases from direct-fired meal dryers. The exhaust gases were odorous and contained significant smoke. The odour concentration of the rendering process air ranged between 50,000 and 307,200 OU m(-3). Odour-removal performance measurements of the biofilters were undertaken on five occasions using forced-choice dynamic-dilution olfactometry. Biofilter odour-removal efficiencies of between 80% and 99% were measured at various influent odour concentrations and air loading rates. There was no obvious deterioration in performance of these biofilters between various sampling times in the five year study period. The biofilters also reduced the "offensiveness" of the odour. The fine crushed bark biofilter generally reduced odour concentration more efficiently than the coarse bark biofilter. The additions of zeolite to the bark medium in the biofilter had little effect on the odour-removal performance. An increase in air loading rate produced only a very small decrease in odour-removal performance. The pilot-scale biofilters had smoke removal efficiencies between 71% and 100%. Finely crushed bark removed smoke more effectively than coarsely crushed bark. Drainage from the biofilters contained significant concentrations of pollutants, suggesting that controlled leaching has potential to remove accumulated substances in biofilter media from rendering gas emissions and increase the longevity of a biofilter system.     

Influence of the water content and water activity on styrene degradation by Exophiala jeanselmei in biofilters

 The performance at low water availability of styrene-degrading biofilters with the fungus Exophiala jeanselmei growing on perlite, the inert support, was investigated. E. jeanselmei degrades styrene at a water activity of 0.91–1. In biofilters, the styrene elimination capacity at a water activity of 0.91 is 5% of the maximal elimination capacity of 79 g m^-3 h^-1 (water activity 1). Application of dry air results in a rapid loss of styrene degradation activity, even at 40%–60% (w/w) water in the filter bed and at a water activity of 1. Humidification of the gas and an additional supply of water to the filter bed are necessary to maintain a high and stable styrene elimination capacity. Received: 7 August 1995 / Received revision: 29 January 1996 / Accepted: 5 February 1996     

Intermittent trickling bed filter for the removal of methyl ethyl ketone and methyl isobutyl ketone

Biodegradations of methyl ethyl ketone and methyl isobutyl ketone were performed in intermittent biotrickling filter beds (ITBF) operated at two different trickling periods: 12 h/day (ITBF-12) and 30 min/day (ITBF-0.5). Ralstonia sp. MG1 was able to degrade both ketones as evidenced by growth kinetic experiments. Results show that trickling period is an important parameter to achieve high removal performance and to maintain the robustness of Ralstonia sp. MG1. Overall, ITBF-12 outperformed ITBF-0.5 regardless of the target compound. ITBF-12 had high performance recovery at various inlet gas concentrations. The higher carbon dioxide production rates in ITBF-12 suggest higher microbial activity than in ITBF-0.5. Additionally, lower concentrations of absorbed volatile organic compound (VOC) in trickling solutions of ITBF-12 systems also indicate VOC removal through biodegradation. Pressure drop levels in ITBF-12 were relatively higher than in ITBF-0.5 systems, which can be attributed to the decrease in packed bed porosity as Ralstonia sp. MG1 grew well in ITBF-12. Nonetheless, the obtained pressure drop levels did not have any adverse effect on the performance of ITBF-12. Biokinetic constants were also obtained which indicated that ITBF-12 performed better than ITBF-0.5 and other conventional biotrickling filter systems.     

Biofilter performance and characterization of a biocatalyst degrading alkylbenzene gases

A biofilter treating alkylbenzene vapors was characterized for its optimal running conditions and kinetic parame-ters. Kinetics of the continuous biofilter were compared to batch kinetic data obtained with biofilm samples as well as with defined microbial consortia and with pure culture isolates from the biofilter. Both bacteria and fungi were present in the bioreactor. Five strains were isolated. Two bacteria, Bacillus and Pseudomonas, were shown to be dominant, as well as a Trichosporon strain which could, however, hardly grow on alkylbenzenes in pure culture. The remaining two strains were most often overgrown by the other three organisms in liquid phase batch cultures μ _max, K_S, K_I values and biodegradation rates were calculated and compared for the difterent mixed and pure cultures. Since filter bed acidification was observed during biofiltration studies reaching a pH of about 4, experiments were also undertaken to study the influence of pH on performance of the different cultures. Biodegradation and growth were possible in all cases, over the pH range 3.5–7.0 at appreciable rates, both with mixed cultures and with pure bacterial cultures. Under certain conditions, microbial activity was even observed in the presence of alkylbenzenes down to pH 2.5 with mixed cultures, which is quite unusual and explains the ability of the present biocatalyst to remove alkylbenzenes with high efficiency in biofilters under acidic conditions.     

An experimental and modeling study on the removal of mono-chlorobenzene vapor in biotrickling filters

Removal of mono-chlorobenzene (m-CB) vapor from airstreams was studied in a biotrickling filter (BTF) operating under counter-current flow of the air and liquid streams. Experiments were performed under various values of inlet m-CB concentration, air and/or liquid volumetric flow rates, and pH of the recirculating liquid. Conversion of m-CB was never below 70% and at low concentrations exceeded 90%. A maximum removal rate of about 60 gm-3-reactor h-1 was observed. Conversion of m-CB was found to increase as the values of liquid and air flow rate increase and decrease, respectively. The effects of pH and frequency of medium replenishment on BTF performance were also investigated. The process was successfully described with a detailed mathematical model, which accounts for mass transfer and kinetic effects based on m-CB and oxygen availability. Solution of the model equations yielded m-CB and oxygen concentration profiles in all three phases (airstream, liquid, biofilm). It is predicted that oxygen has a controling effect on the process at high inlet m-CB concentrations. From independent, suspended culture, experiments it was found that m-CB biodegradation follows Andrews inhibitory kinetics. The kinetic constants were found to remain practically unchanged after the culture was used in BTF experiments for 8 months. Copyright 1998 John Wiley & Sons, Inc.     

A model study based on experiments on toluene removal under high load condition in biofilters

As a control measure for substrate inhibition phenomenon in biofilters caused by toxic gases with high concentration, an appropriate mathematical model is required to calculate gas concentrations at various positions within and outside biofilms. Thus validation of the Deshussess model, Devinny–Hodge model and Luong Model were carried out for high toluene load conditions, and the results were examined for their veracity. Calculated concentrations using the modified Deshussess model, which considers sorption volume of carriers, approximated to measurements. This appears to mean the contribution of porosity in inorganic ceramic carriers to the biological removal of toluene vapor. Since toluene removal capacities for high liquid concentrations, which were calculated using the Luong model, approximated to the measurements, the generality and usefulness of the Luong model in predicting the substrate elimination capacity in biofilters with substrate inhibition appear to be manifested. Simplified Devinny–Hodge model turned out to be not applicable to predicting gas concentration along longitudinal axis of biofilters with high gas load. Various model parameters, needed for modeling studies, including critical toluene load per unit biomass and time, maximum toluene degradation rate, half velocity toluene concentration, and maximum toluene concentration in liquid, above which biodegradation is inhibited, were experimentally determined.     

Gaseous TCE and PCE removal by an activated carbon biofilter

Gaseous trichloroethylene (TCE) and tetrachloroethylene (PCE) are emitted in the treatment of contaminated groundwaters with air stripping and/or the remediation of contaminated soils using vapor extraction techniques. This study investigated the application of biofiltration using cometabolic process to remediate gaseous TCE and PCE that are highly recalcitrant to biodegradation. The investigation was conducted using two specially built stainless steel columns, one for TCE and the other for PCE, packed with granular activated carbon (GAC) coated with phenol-oxidizing microorganisms at residence times of 1.5–7 min. Two activated carbon biofilters were fed with phenol at a specific concentration along with a nutrient solution to optimize the various catalyzed biochemical reactions. The removal efficiency of gaseous TCE was 100% at a residence time of 7 min and average inlet concentration of 85 ppm. For gaseous PCE, 100% removal efficiency was obtained at residence times of 4–7 min and average concentrations of 47–84 ppm. It was found that phenol fed to the biofilters was completely utilized by the phenol-oxidizing microorganisms, as an indirect indicator of the microorganisms growth in the biofilters, throughout the period of the biofilter operation. Transformation yields of gaseous TCE and PCE were about 8–48 g of TCE/g of phenol and 6–25 g of PCE/g of phenol, depending on different residence times. It was found that adsorption by GAC and absorption by the influent nutrient solution were a minor negligible mechanism for TCE and PCE removal in the activated carbon biofilters.     

Isolation of a dimethylsulfide-utilizingHyphomicrobium species and its application in biofiltration of polluted air

The methylotrophic bacteriumHyphomicrobium VS was enriched and isolated, using activated sewage sludge as inoculum in mineral medium containing dimethylsulfide (DMS) at a low concentration to prevent toxicity. DMS concentrations above 1 mM proved to be growth inhibiting.Hyphomicrobium VS could use DMS, dimethylsulfoxide (DMSO), methanol, formaldehyde, formate, and methylated amines as carbon and energy source. Carbon was assimilated via the serine pathway. DMS-grown cells respired sulfide, thiosulfate, methanethiol, dimethyldisulfide and dimethyltrisulfide.To testHyphomicrobium VS for application in biofiltration of air polluted with volatile sulfur compounds two laboratory scale trickling biofilters with polyurethane and lava stone as carrier material were started up by inoculation with this bacterium. Both methanol- and DMS-grown cells could be used. Only a short adaptation period was needed. Short term experiments showed that high concentrations of DMS (1–2 µmol 1^–1) were removed very efficiently by the biofilters at space velocities up to 100 h^–1.Abbreviations VSC volatile sulfur compounds - DMS dimethylsulfide - DMDS dimethyldisulfide - DMTS dimethyltrisulfide - MT methanethiol - DMSO dimethylsulfoxide     

Dynamic responses of biofilters to changes in the operating conditions in the process of removing toluene and xylene from air

The dynamic behaviour of biofilters intended to remove toluene and xylene from air was studied during transient states. Laboratory scale biofilters were filled with a mixture of peat, bark and wood and inoculated with a mixed microbial population. Toluene and xylene were applied both as single pollutants and as mixtures. Attention was focused on the evaluation of the following transients: the response of biofilters to step changes and peaks in pollutant concentrations, the effect of changes between single and multiple pollutant loadings and the response to shutdown periods. The biofilters demonstrated a good dynamic stability during transient states induced by change in inlet pollutant concentrations. Their time periods did not exceed three hours. No interaction between xylene and toluene degradation was observed during changes in loading with single pollutants or their mixture. The performance interruptions lasting less than 24 hours were found to have no significant influence on the removal efficiency of biofilters. When the biofilters were reacclimated after longer starvation periods, a short temporary decrease in efficiency whose minimum and duration were proportional to the length of a preceding shutdown period was observed. The longest starvation period (7 days) resulted in a reacclimation lasting 7 hours only. Adaptations of a microbial population to new operating conditions as well as sorption/desorption processes were suggested as the main factors influencing the dynamic reponse characteristics.     

Toluene biodegradation rates in unsaturated soil systems versus liquid batches and their relevance to field conditions

Contaminant biodegradation in unsaturated soils may reduce the risks of vapor intrusion. However, the reported rates show large variability and are often derived from slurry experiments that are not representative of unsaturated conditions. Here, different laboratory setups are used to derive the biodegradation capacity of an unsaturated soil layer through which gaseous toluene migrates from the water table upwards. Experiments in static unsaturated soil microcosms at 6–30 % water-filled porosity (WFP) and unsaturated soil columns at 9, 14, and 27 % WFP were compared with liquid batches containing the same culture of Alicycliphilus denitrificans. The biodegradation rates for the liquid batches were orders of magnitude lower than for the other setups. Hence, liquid batches do not necessarily reflect optimal conditions for bacteria; either oxygen or toluene mass transfer at the cell scale or the absence of soil–water–air interfaces seemed to be limiting bacterial activity. For the column setup, the rates were limited by mass supply. The microcosm results could be described by apparent first-order biodegradation constants that increased with WFP or through a numerical model that included biodegradation as a first-order process taking place in the liquid phase only. The model liquid phase first-order rates varied between 6.25 and 20 h^?1 and were not related to the water content. Substrate availability was the primary factor limiting bioactivity, with evidence for physiological stress at the lowest water-filled porosity. The presented approach is useful to derive liquid phase biodegradation rates from experimental data and to include biodegradation in vapor intrusion models.     

Total Aromatic Content in Petroleum Solvents Modifies Headspace Benzene Vapor Concentrations: Implications for Exposure Assessments

This study evaluates how equilibrium vapor concentrations above petroleum solvent mixtures are affected by total aromatic content and the implications for estimating benzene vapor exposures. Headspace vapor concentrations over mixtures with liquid benzene content ranging from 0.001 to 1.0% and varying percentages of 1,2,4-trimethylbenzene and n-nonane were studied using a direct-injection gas chromatography/flame ionization detection method that showed good precision. The measured values were compared to predictions based on Raoult's Law, with and without non-ideality corrections using activity coefficients. Ratios of vapor to liquid benzene concentrations decreased with increasing total aromatic content; that is, mixtures with 10% to 20% trimethylbenzene simulating non-hydrotreated mineral spirits had much lower ratios compared to the ≥99% aliphatic mixtures that simulate hydrotreated mineral spirits. Positive deviations from Raoult's Law were greatest at liquid benzene concentrations less than 0.1%, particularly in the predominantly aliphatic mixtures. Correcting for non-ideality using activity coefficients resulted in predicted vapor concentrations that were closer to measured values. The data indicate that higher aromatic content and higher liquid benzene content suppress benzene vapor concentrations due to benzene's greater affinity for similar aromatic molecules in solution. Benzene exposure reconstructions should consider actual composition of the historic material with respect to aromatic content.     

The influence of NaCl on the degradation rate of dichloromethane byHyphomicrobium sp.

The degradation of dichloromethane by the pure strainHyphomicrobium GJ21 and by an enrichment culture, isolated from a continuously operating biological trickling filter system, as well as the corresponding growth rates of these organisms were investigated in several batch experiments. By fitting the experimental data to generally accepted theoretical expressions for microbial growth, the maximum growth rates were determined. The effect of NaCl was investigated at salt concentrations varying from 0 to 1000 mM. Furthermore the dichloromethane degradation was investigated separately in experiments in which a high initial biomass concentration was applied. The results show that microbial growth is strongly inhibited by increased NaCl concentrations (50% reduction of _max at 200–250 mM NaCl), while a certain degree of adaptation has taken place within an operational system eliminating dichloromethane. A critical NaCl concentration for growth of 600 mM was found for the microbial culture isolated from an operational trickling filter, while a value of 375 mM was found for the pure cultureHyphomicrobium GJ21. The substrate degradation appears to be much less susceptible to inhibition by NaCl. Even at 800 mM NaCl relatively high substrate degradation rates are still observed, although this process is again dependent on the NaCl concentration. Here the substrate elimination is due to the maintenance requirements of the microorganisms. The inhibition of the dichloromethane elimination was also investigated in a laboratory scale trickling filter. The results of these experiments confirmed those obtained in the batch experiments. At NaCl concentrations exceeding 600 mM a considerable elimination of dichloromethane was still observed for during several months of operation. These observations indicate that the inhibition of microbial growth offers a significant control parameter against excessive biomass growth in biological trickling filters for waste gas treatment.     

Trickling Filters and Biofilm Reactor Modelling

Tricking filters are biofilm reactors commonly used for biological removal of nitrogen and organic matter. A review of published and unpublished material on the function, microbiology, design and operation of trickling filters is given. This is followed by more general dynamic biofilm reactor modelling, i.e. models for rotating biological contactors, different types of biofilters, moving beds as well as trickling filters.     

Establishing oil-degrading biofilms on gravel particles and glass plates

A method is described for “artificially” establishing biofilms rich in hydrocarbon degrading bacteria on gravel particles and glass plates. The microbial consortia in the biofilms included in additions, filamentous cyanobacteria, picoplankton and diatoms. Phototrophic microorganisms were pioneer colonizers. Hydrocarbon utilizing bacteria, namely Acinetobacter calcoaceticus and nocardioforms were in part attached to filaments of cyanobacteria. In batch cultures, it was shown that those artificial biofilms had an attenuation effect on crude-oil in contaminated sea water samples. The potential use of these biofilms for preparing trickling filters (gravel particles), and in bioreactors (glass plates) for attenuating hydrocarbons in oily liquid wastes before their disposal in the open environment is suggested and discussed.     

Biomass control in waste air biotrickling filters by protozoan predation

Two protozoan species as well as an uncharacterized protozoan consortium were added to a toluene-degrading biotrickling filter to investigate protozoan predation as a means of biomass control. Wet biomass formation in 23.6-L reactors over a 77-day period was reduced from 13.875 kg in a control biotrickling filter to 11.795 kg in a biotrickling filter enriched with protozoa. The average toluene vapor elimination capacity at 1 g/m3 toluene and 64 m3/(m3. h) was 31.1 g/(m3. h) in the control and 32.2 g/(m3. h) in the biotrickling filter enriched with protozoa. At higher toluene inlet concentrations, toluene degradation rates increased and were slightly higher in the biotrickling filter enriched with protozoa. The lower rate of biomass accumulation after the addition of protozoa was due to an increase of carbon mineralization (68% as compared to 61% in the control). Apparent biomass yield coefficients in the control and enriched trickling filter were 0.72 and 0.59 g dry biomass/g toluene, respectively. The results show that protozoan predation may be a useful tool to control biomass in biotrickling filters, however, further stimulation of predation of the biomass immobilized in the reactor is required to ensure long-term stability of biotrickling filters.     

Biodegradation of N-Nitrosodimethylamine in Aqueous and Soil Systems

N-Nitrosodimethylamine (NDMA) was mineralized by microorganisms in aqueous and soil systems. Initial rates of mineralization (micrograms per milliliter per day) were calculated for a wide range of initial concentrations of NDMA (micrograms per milliliter to picograms per milliliter). Log-log plots of the data were fitted with both linear and nonlinear least-squares analyses; however, linear models provided better fits for the kinetic data in all cases. The slopes of the linear fits were not significantly different than 1.0 (P < 0.05); thus, first-order reaction kinetics were in effect over the range of concentrations tested, and saturation kinetics were not achieved. Rate constants (day⁻¹) and total percent mineralized increased with decreasing initial concentrations of NDMA. Rates of mineralization were reduced in aqueous systems when supplemental carbon was available, whereas in soils, percentages of organic matter and supplemental carbon had little effect on rates of mineralization. Implications of these results for predictions of rates and threshold limits of mineralization activity in natural systems are discussed. A laboratory scale simulated trickling filter containing an activated charcoal bed provided a suitable environment for mineralization of NDMA at concentrations of 50 and 100 μg/ml on a continuous basis. NDMA was not toxic to natural populations of microorganisms at concentrations up to 10 mg/ml. Using high-pressure liquid chromatography coupled with radioactivity detection, we identified formaldehyde and methylamine as intermediates produced during the biodegradation of NDMA.     

Shift of microbial community in gas-phase biofilters with different inocula,inlet loads and nitrogen sources

The research on gaseous VOCs biofilters has often concentrated on process optimization. However, the microbial community change upon operating conditions is not well understood. In this study, three lab-scale biofilters treating gaseous toluene were operated for 66 days with different inocula under changes in inlet loads and nitrogen sources. Three biofilters were inoculated with activated sludge, river sediment or microbial consortia, respectively. The microbial community differed a lot initially but gradually deviated toward similar structures with the same dominant microorganisms, i.e. Proteobacteria, Actinobacteria (phylum level) and Rhodococcus,Pseudomonas(genus level). Among three biofilters, the two biofilters inoculated with activated sludge and river sediment showed higher microbial diversity, better VOCs removal performance and higher metabolic activity. Higher relative abundance of Alcanivorax (3% compared with lower than 0.03%), Pimelobacte (0.05% compared with lower than 0.01%)were detected under low inlet load, and Zoogloea(0.1%), Alkaliphilus(0.2%) were detected when the inlet load was increased. the abundance of Pseudomonasdecreased from 14% to 2% when ammonia was used as nitrogen source instead of nitrate, meanwhile the abundance of Bacillus and Gordoniaincreased from 0.01% to 0.05% and 0.8% to 5.8% respectively. Some special organisms were observed i.e. the intestinal microorganism.