Mesophilic and thermophilic biotreatment of BTEX-polluted air in reactors

This study compares the removal of a mixture of benzene, toluene, ethylbenzene, and all three xylene isomers (BTEX) in mesophilic and thermophilic (50 degrees C) bioreactors. In the mesophilic reactor fungi became dominant after long-term operation, while bacteria dominated in the thermophilic unit. Microbial acclimation was achieved by exposing the biofilters to initial BTEX loads of 2-15 g m(-3) h(-1), at an empty bed residence time of 96 s. After adaptation, the elimination capacities ranged from 3 to 188 g m(-3) h(-1), depending on the inlet load, for the mesophilic biofilter with removal efficiencies reaching 96%. On the other hand, in the thermophilic reactor the average removal efficiency was 83% with a maximum elimination capacity of 218 g m(-3) h(-1). There was a clear positive relationship between temperature gradients as well as CO(2) production and elimination capacities across the biofilters. The gas phase was sampled at different depths along the reactors observing that the percentage pollutant removal in each section was strongly dependant on the load applied. The fate of individual alkylbenzene compounds was checked, showing the unusually high biodegradation rate of benzene at high loads under thermophilic conditions (100%) compared to its very low removal in the mesophilic reactor at such load (<10%). Such difference was less pronounced for the other pollutants. After 210 days of operation, the dry biomass content for the mesophilic and thermophilic reactors were 0.300 and 0.114 g g(-1) (support), respectively, reaching higher removals under thermophilic conditions with a lower biomass accumulation, that is, lower pressure drop.     

Start-up and the effect of gaseous ammonia additions on a biofilter for the elimination of toluene vapors

Biotechnological techniques, including biofilters and biotrickling filters are increasingly used to treat air polluted with VOCs (Volatile Organic Compounds). In this work, the start-up, the effect of the gaseous ammonia addition on the toluene removal rate, and the problems of the heat accumulation on the performance of a laboratory scale biofilter were studied. The packing material was sterilized peat enriched with a mineral medium and inoculated with an adapted consortium (two yeast and five bacteria). Start-up showed a short adaptation period and an increased toluene elimination capacity (EC) up to a maximum of 190 g/m3/h. This was related to increased CO2 outlet concentration and temperature gradients between the packed bed and the inlet (Tm-Tin). These events were associated with the growth of the microbial population. The biofilter EC decreased thereafter, to attain a steady state of 8 g/m3/h. At this point, gaseous ammonia was added. EC increased up to 80 g/m3/h, with simultaneous increases on the CO2 concentration and (Tm-Tin). Two weeks after the ammonia addition, the new steady state was 30 g/m3/h. In a second ammonia addition, the maximum EC attained was 40 g/m3/h, and the biofilter was in steady state at 25 g/m3/h. Carbon, heat, and water balances were made through 88 d of biofilter operation. Emitted CO2 was about 44.5% of the theoretical value relative to the total toluene oxidation, but accumulated carbon was found as biomass, easily biodegradable material, and carbonates. Heat and water balances showed strong variations depending on EC. For 88 d the total metabolic heat was -181.2 x 10(3) Kcal/m3, and water evaporation was found to be 56.5 kg/m3. Evidence of nitrogen limitation, drying, and heterogeneities were found in this study.     

Correlation of biological activity and reactor performance in biofiltration of toluene with the fungus Paecilomyces variotii CBS115145

A biofiltration system inoculated with the mold Paecilomyces variotii CBS115145 showed a toluene elimination capacity (EC) of around 250 g/m3 of biofilter/h, which was higher than the values usually reported for bacteria. P. variotii assimilated m- and p-cresols but not the o isomer. Initial toluene hydroxylation occurred both on the methyl group and through the p-cresol pathway. These results were corroborated by detecting benzyl alcohol, benzaldehyde, and p-cresol as volatile intermediates. In liquid cultures with toluene as a substrate, the activity of toluene oxygenase (TO) was 5.6 nmol of O2/min/mg of biomass, and that of benzyl alcohol dehydrogenase was 16.2 nmol of NADH/min/mg of protein. Toluene biodegradation determined from the TO activity in the biofilter depended on the biomass distribution and the substrate concentration. The specific enzymatic activity decreased from 6.3 to 1.9 nmol of O2/min/mg of biomass along the reactor. Good agreement was found between the EC calculated from the TO activity and the EC measured on the biofilter. The results were confirmed by short-time biofiltration experiments. Average EC measured in different biofiltration experiments and EC calculated from the TO activity showed a linear relation, suggesting that in the biofilters, EC was limited by biological reaction. As the enzymatic activities of P. variotii were similar to those reported for bacteria, the high performance of the fungal biofilters can possibly be explained by the increased transfer of the hydrophobic compounds, including oxygen, from the gas phase to the mycelia, overcoming the transfer problems associated with the flat bacterial biofilms.     

Toluene gas phase biofiltration by Paecilomyces lilacinus and isolation and identification of a hydrophobin protein produced thereof

Paecilomyces lilacinus consumed toluene as the sole carbon source in a gas-phase biofilter packed with perlite obtaining an average elimination capacity of 50 g m(-3) h(-1), a removal efficiency of 53%, and a final biomass of 31.6 mg biomass g dry support(-1). Hydrophobin proteins from the mycelium produced in the biofilter were purified by formic acid extraction and precipitated by electrobubbling, and the molecular weight was found to be 10.6 +/- 0.3 kDa. The peptide mass fingerprinting analysis of the purified hydrophobin by matrix-assisted laser desorption/ionization time-of-flight resulted in the identification of two peptides that presented high homology with sequences of class I hydrophobin proteins from other ascomycetous fungi when compared against the National Center for Biotechnology Information database. The yield of hydrophobin (PLHYD) from P. lilacinus was 1.1 mg PLHYD g biomass(-1). These proteins modified the hydrophobicity of Teflon by lowering the contact angle from 130.1 (+/-2) degrees to 57.0 (+/-5) degrees supporting hot sodium dodecyl sulfate washing. This work is the first report about biodegradation of toluene by the nematophagous fungus P. lilacinus in a gas-phase biofilter and the identification of its hydrophobin protein.     

Biofiltration of toluene-contaminated air using an agro by-product-based filter bed

An innovative, coir-pith-based, filter bed for degrading vapor phase toluene in a gas biofilter over 160 days without any external nutrient supply is reported in this study. Indigenous microflora present in the coir pith as well as in the aerobic sludge added at the start-up stage metabolized the toluene, and correspondingly, CO₂ was produced in the biofilter. Inlet toluene concentration in the range of 0.75 to 2.63 g/m³ was supplied to the biofilter in short acclimation periods. The maximum elimination capacity achieved was 96.75 g/m³·h at 120.72 g/m³·h loading where around 60% was recovered as CO₂. The filter bed maintained a stable low-pressure drop (0–4 mm H₂O), neutral pH range (6.5–7.5), and moisture content of 60–80% (w/w) throughout the period. In addition to toluene-degrading microbial community, a grazing fauna including rotifer, bacteriovoric nematode, tardigrade, and fly larvae were also present in the filter bed. The overall performance of the biofilter bed in pollutant removal and sustainability was analyzed in this study.     

Biofiltration of ethylbenzene vapours: influence of the packing material

In order to investigate suitable packing materials, a soil amendment composed of granular high mineralized peat (35% organic content) locally available has been evaluated as carrier material for biofiltration of volatile organic compounds in air by comparison with a fibrous peat (95% organic content). Both supports were tested to eliminate ethylbenzene from air streams in laboratory-scale reactors inoculated with a two-month conditioned culture. In pseudo-steady state operation, experiments at various ethylbenzene inlet loads (ILs) were carried out. Maximum elimination capacity of about 120 g m(-3) h(-1) for an IL of 135 g m(-3) h(-1) was obtained for the fibrous peat. The soil amendment reactor achieved a maximum elimination capacity of about 45 g m(-3) h(-1) for an inlet load of 55 g m(-3) h(-1). Ottengraf-van den Oever model was applied to the prediction of the performance of both biofilters. The influence of gas flow rate was also studied: the fibrous peat reactor kept near complete removal efficiency for empty bed residence times greater than 1 min. For the soil amendment reactor, an empty bed residence time greater than 2 min was needed to achieve adequate removal efficiency. Concentration profiles along the biofilter were also compared: elimination occurred in the whole fibrous peat biofilter, while in the soil amendment reactor the biodegradation only occurred in the first 65% part of the biofilter. Results indicated that soil amendment material, previously selected to increase the organic content, would have potential application as biofilter carrier to treat moderate VOC inlet loads.     

Improving hexane removal by enhancing fungal development in a microbial consortium biofilter

The removal of hydrophobic pollutants in biofilters is often limited by gas liquid mass transfer to the biotic aqueous phase where biodegradation occurs. It has been proposed that the use of fungi may improve their removal efficiency. To confirm this, the uptake of hexane vapors was investigated in 2.6-L perlite-packed biofilters, inoculated with a mixed culture containing bacteria and fungi, which were operated under neutral or acid conditions. For a hexane inlet load of around 140 g.m-3.h-1, elimination capacities (EC) of 60 and 100 g.m-3.h-1 were respectively reached with the neutral and acid systems. Increasing the inlet hexane load showed that the maximum EC obtained in the acid biofilter (150 g.m-3.h-1) was twice greater than in the neutral filter. The addition of bacterial inhibitors had no significant effect on EC in the acid system. The biomass in the acid biofilter was 187 mg.g-1 (dry perlite) without an important pressure drop (26.5 mm of water.m-1reactor). The greater efficiency obtained with the acid biofilter can be related to the hydrophobic aerial hyphae which are in direct contact with the gas and can absorb the hydrophobic compounds faster than the flat bacterial biofilms. Two fungi were isolated from the acid biofilter and were identified as Cladosporium and Fusarium spp. Hexane EC of 40 g.m-3.h-1 for Cladosporium sp. and 50 g.m-3.h-1 for Fusarium sp. were obtained in short time experiments in small biofilters (0.230 L). A biomass content around 30 mg.g-1 (dry perlite) showed the potential for hexane biofiltration of the strains.     

Correlation of Biological Activity and Reactor Performance in Biofiltration of Toluene with the Fungus Paecilomyces variotii CBS115145

A biofiltration system inoculated with the mold Paecilomyces variotii CBS115145 showed a toluene elimination capacity (EC) of around 250 g/m³ of biofilter/h, which was higher than the values usually reported for bacteria. P. variotii assimilated m- and p-cresols but not the o isomer. Initial toluene hydroxylation occurred both on the methyl group and through the p-cresol pathway. These results were corroborated by detecting benzyl alcohol, benzaldehyde, and p-cresol as volatile intermediates. In liquid cultures with toluene as a substrate, the activity of toluene oxygenase (TO) was 5.6 nmol of O₂/min/mg of biomass, and that of benzyl alcohol dehydrogenase was 16.2 nmol of NADH/min/mg of protein. Toluene biodegradation determined from the TO activity in the biofilter depended on the biomass distribution and the substrate concentration. The specific enzymatic activity decreased from 6.3 to 1.9 nmol of O₂/min/mg of biomass along the reactor. Good agreement was found between the EC calculated from the TO activity and the EC measured on the biofilter. The results were confirmed by short-time biofiltration experiments. Average EC measured in different biofiltration experiments and EC calculated from the TO activity showed a linear relation, suggesting that in the biofilters, EC was limited by biological reaction. As the enzymatic activities of P. variotii were similar to those reported for bacteria, the high performance of the fungal biofilters can possibly be explained by the increased transfer of the hydrophobic compounds, including oxygen, from the gas phase to the mycelia, overcoming the transfer problems associated with the flat bacterial biofilms.     

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.     

Toluene removal from waste air using a flat composite membrane bioreactor

In this report, gaseous toluene biodegradation results in a flat composite membrane reactor inoculated with Pseudomonas putida TVA8 are presented. Preliminary abiotic experiments showed that transport of toluene through the membrane was linearly and negatively correlated with the gas residence time (tau). During a 339-day biofiltration experiment, the influence of gas residence time (2-24 sec) and mass loading rate (B(v); 10-483 g x m(-3) h(-1)) on the toluene elimination capacity was investigated. A maximum elimination capacity (EC(max)) of 397 g x m(-3) h(-1) was achieved at tau = 24 sec and B(v) = 473 g x m(-3) h(-1). Expressed per unit membrane area, the EC(m,max) was 0.793 g x m(-2) h(-1), which is five times higher than results obtained with other membrane bioreactor experiments in the same range of loading rates. At low gas residence times, reactor performance was limited by mass transfer. Toluene concentration profiles along the membrane were measured for several biotic and abiotic conditions. For inlet concentrations (C(in)) up to 1 g x m(-3), more than 90% was eliminated at 15 cm from the reactor inlet. For C(in) > 1.65 g x m(-3), longer membranes are necessary to obtain these high removal efficiencies.     

Removal of n-hexane by Fusarium solani with a gas-phase biofilter

A gas-phase biofilter inoculated with the fungus Fusarium solani, isolated from a consortium grown on hexane vapors, was used to degrade this compound. The biofilter, packed with perlite and operated with an empty bed residence time of 60 s, was supplied with hexane concentrations between 0.5 gm(-3) and 11 gm(-3). Biofilter performance was evaluated over 100 days of operation. Several strategies for supplying the nutritive mineral medium were assayed to maintain favorable conditions for the fungal growth and activity. The Fusarium system was able to sustain an average elimination capacity of 90 gm(-3)(reactor) h(-1) with a maximum of 130 gm(-3)(reactor) h(-1) . The mass transfer limitations due to high biomass development in the biofilter were confirmed in batch experiments. Bacterial contamination was observed, but experiments in the biofilter and in batch reactors using selective inhibitors and controlled pH confirmed the predominant role of the fungus. Results indicate that fungal biofilters can be an effective alternative to conventional abatement technologies for treating hydrophobic compounds.     

Fungal removal of gaseous hexane in biofilters packed with poly(ethylene carbonate) pine sawdust or peat composites

The removal of volatile organic compounds (VOC) in biofilters packed with organic filter beds, such as peat moss (PM) and pine sawdust (PS), frequently presents drawbacks associated to the collapse of internal structures affecting the long-term operation. Poly(ethylene ether carbonate) (PEEC) groups grafted to these organic carriers cross linked with 4,4'-methylenebis(phenylisocyanate) (MDI) permitted fiber aggregation into specific shapes and with excellent hexane sorption performance. Modified peat moss (IPM) showed very favorable characteristics for rapid microbial development. Water-holding capacity in addition to hexane adsorption almost equal to the dry samples was obtained. Pilot scale hexane biofiltration experiments were performed with the composites after inoculation with the filamentous fungus Fusarium solani. During the operation of the biofilter under non-aseptic conditions, the addition of bacterial antibiotics did not have a relevant effect on hexane removal, confirming the role of fungi in the uptake of hexane and that bacterial growth was intrinsically limited by an adequate performance of the composites. IPM biofilter had a start-up period of 8-13 days with concurrent CO(2) production of approximately 90 g m(-3) h(-1) at day 11. The final pressure drop after 70 days of operation was 5.3 mmH(2)O m(-1) reactor. For modified pine sawdust (IPS) packed biofilter, 5 days were required to develop an EC of about 100 g m(-3) h(-1) with an inlet hexane load of approximately 190 g m(-3) h(-1). Under similar conditions, 12-17 days were required to observe a significant start-up in the reference perlite biofilter to reach gradually an EC of approximately 100 g m(-3) h(-1) at day 32. Under typical biofiltration conditions, the physical-chemical properties of the modified supports maintained a minimum water activity (a(w)) of 0.925 and a pH between 4 and 5.5, which allowed the preferential fungal development and limited bacterial growth.     

Treatment of waste gas containing diethyldisulphide (DEDS) in a bench scale biofilter

Waste gas containing diethyldisulphide (DEDS) is generated from various industries including pulp and paper, refinery, rayon and molasses based distilleries, etc. DEDS has odour threshold detection with an average concentration of 10(-9)mg/m(3) at 25 degrees C. DEDS is toxic to bacteria, fungus and also to mammals when exposed for a long period. Waste gas containing DEDS require proper treatment prior to discharge into the environment. DEDS containing waste gas was treated in a biofilter, packed with compost along with wooden chips and enriched with DEDS degrading microorganisms. The biofilter could remove DEDS to the extent of 94+/-5% at a loading of 1.60 g/m(3)/h with an empty bed retention time of 150s. At optimal operating conditions, the average moisture content required by the biofilter was in the range of 60-65%. The biodegradative products of DEDS were thiosulphate and sulphate.     

Biotreatment of a gas-phase volatile mixture from fibreglass and composite manufacturing industries

Acetone, toluene and styrene (ATS) are representative air pollutants emanating during the production process in fibreglass and composite manufacturing industries. In this study, the performance of a steady-state biofilter inoculated with the fungus Sporothrix variecibatus was tested at different empty bed residence times (EBRTs), and at different inlet concentrations of ATS, corresponding to total pollutant loading rates ranging from 30 to 490 gm(-3)hour(-1). Styrene was somewhat better removed (47-100%) in the biofilter than acetone (34-100%) and toluene (42-100%), with maximum elimination capacities (EC(max)) of 108, 72 and 144 gm(-3)hour(-1), for ATS, respectively. Besides, it was observed that, although increasing the concentration of ATS decreased their removal, the presence of toluene also decreased the EC(max) of both acetone and toluene in the ternary mixture. During transient operations, the biofilter was subjected to intermittent shutdown and re-start operations where the gas-phase pollutant flow was stopped for either 5 or 16d. It was observed that, for longer shutdown periods (16d), the biofilter required nearly 8-10d to reach similar removal patterns to those observed before the shutdown phase. Batch biodegradation tests were conducted, using Sporothrix-like microorganisms present in the leachate of the biofilter, with a mixture of ATS as the sole carbon source. Complete removal of ATS was observed within the test period of 168 hours. Styrene was degraded faster, with a specific substrate utilization rate of 0.9 mg styrenemg biomass(-1)hour(-1), followed by toluene (0.6) and acetone (0.44). The effectiveness of the biofilter to reach high total EC (321.3 gm(-3)hour(-1)), and withstand transient operations shows the robustness of this fungal-bioreactor and its suitability to handle emissions from a fibreglass and composite manufacturing industry.     

Microbiological and kinetic aspects of a biofilter for the removal of toluene from waste gases

Microbiological and kinetic aspects of a biofilter inoculated with a consortium of five bacteria and two yeast adapted to remove toluene vapors were investigated. Initially the toluene sorption isotherm on peat and the effect of different environmental conditions on the toluene consumption rates of this consortium were measured. The fast start-up of the biofilter and the decay in the elimination capacity (EC) were reproduced using microcosm assays with toluene successive additions. Nutrient limitation and a large degree of heterogeneity were also detected. EC values, extrapolated from microcosms, were higher than biofilter EC when it was operating close to 100% efficiency but tended to relate better as the biofilter EC diminished. In studies on the microbial evolution in the biofilter, an increase in the cell count and variation in the ecology of the consortium were noted. Bacterial counts up to 10 x 10(11) cfu/gdry peat were found in 88 days, which corresponds to about a 10(4) increase from inoculum. Observations with SEM showed a nonuniform biofilm development on the support and the presence of an extracellular material. The results obtained in this work demonstrated that activity measurement in microcosms concomitant to the biofilter operation could be an important tool for understanding, predicting and improving the biofiltration performance. Copyright 1999 John Wiley & Sons, Inc.     

Long-term performance of peat biofilters treating ethyl acetate, toluene, and its mixture in air

Three laboratory-scale peat biofilters were operated at 90 s empty bed residence time (EBRT) for over a year. Biodegradation of ethyl acetate, toluene, or a 1:1 mixture were investigated. In first stage, inlet concentration was progressively increased from 0.4 to 4.5 g/m(3). The maximum elimination capacity (EC) found for ethyl acetate was 190 gC/m(3).h, and it was not affected by toluene. The maximum EC found for toluene as a sole contaminant was 150 gC/m(3).h, but the presence of ethyl acetate decreased the toluene maximum EC to 80 gC/m(3).h. From respirometry monitoring, values of 3.19 g CO(2)/gC and 3.06 g CO(2)/gC for pure ethyl acetate and pure toluene, respectively, were found, with overall yield coefficients of 0.13 g dry biomass produced per gram ethyl acetate consumed and 0.28 g dry biomass produced per gram toluene consumed. CO(2) production in the 1:1 mixture was successfully simulated. Dynamics of living and dead cells were monitored in four sections of the biofilters. Concentrations ranged between 2.6 x 10(9) and 3.0 x 10(10) cells per gram-dry peat for total bacteria, and 2.4 x 10(9)-1.9 x 10(10) cells per gram-dry peat for living bacteria. At high loads loss of bacterial density in the inlet zones, and increase in the dead cells percentages up to 60% was observed. In second stage, long-term performance at an inlet concentration of 1.5 g/m(3) was evaluated to show the process feasibility. Good agreement with previous data was obtained in terms of EC and CO(2) production. Restoration of living cells proportion was also observed.     

Controlled biomass formation and kinetics of toluene degradation in a bioscrubber and in a reactor with a periodically moved trickle-bed

The kinetics of degradation of toluene from a model waste gas and of biomass formation were examined in a bioscrubber operated under different nutrient limitations with a mixed culture. The applicability of the kinetics of continuous cultivation of the mixed culture was examined for a special trickle-bed reactor with a periodically moved filter bed. The efficiency of toluene elimination of the bioscrubber was 50 to 57% and depended on the toluene mass transfer as evident from a constant productivity of 0.026 g dry cell weight/L . h over the dilution rate. Under potassium limitation the biomass productivity was reduced by 60% to 0.011 g dry cell weight/L . h at a dilution rate of 0.013/h. Conversely, at low dilution rates the specific toluene degradation rates increased. Excess biomass in a trickle-bed reactor causes reduction of interfacial area and mass transfer, and increase in pressure drop. To avoid these disadvantages, the trickle-bed was moved periodically and biomass was removed with outflowing medium. The concentration of steady state biomass fixed on polyamide beads decreased hyperbolically with the dilution rate. Also, the efficiency of toluene degradation decreased from 72 to 56% with increasing dilution rate while the productivity increased. Potassium limitation generally caused a reduction in biomass, productivity, and yield while the specific degradation increased with dilution rate. This allowed the application of the principles of the chemostat to the trickle-bed reactor described here, for toluene degradation from waste gases. (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 686-692, 1997.     

Thermophilic biofiltration of benzene and toluene

In the current studies, we characterized the degradation of a hot mixture of benzene and toluene (BT) gases by a thermophilic biofilter using polyurethane as packing material and high-temperature compost as a microbial source. We also examined the effect of supplementing the biofilter with yeast extract (YE). We found that YE substantially enhanced microbial activity in the thermophilic biofilter. The degrading activity of the biofilter supplied with YE was stable during long-term operation (approximately 100 d) without accumulating excess biomass. The maximum elimination capacity (1,650 g x m(-3) h(-1)) in the biofilter supplemented with YE was 3.5 times higher than that in the biofilter without YE (470 g g x m(-3) h(-1)). At similar retention times, the capacity to eliminate BT for the YE-supplemented biofilter was higher than for previously reported mesophilic biofilters. Thus, thermophilic biofiltration can be used to degrade hydrophobic compounds such as a BT mixture. Finally, 16S rDNA polymerase chain reaction-DGGE (PCR-DGGE) fingerprinting revealed that the thermophilic bacteria in the biofilter included Rubrobacter sp. and Mycobacterium sp.     

Prevention of clogging in a biological trickle-bed reactor removing toluene from contaminated air

Removal of organic compounds like toluene from waste gases with a trickle-bed reactor can result in clogging of the reactor due to the formation of an excessive amount of biomass. We therefore limited the amount of nutrients available for growth, to prevent clogging of the reactor. As a consequence of this nutrient limitation a lower removal rate was observed. However, when a fungal culture was used to inoculate the reactor, the toluene removal rate under nutrient limiting conditions was higher. Over a period of 375 days, an average removal rate of 27 g C/(m(3) h) was obtained with the reactor inoculated with the fungal culture. From the carbon balance over the reactor and the nitrogen availability it was concluded that, under these nutrient-limited conditions, large amounts of carbohydrates are probably formed. We also studied the application of a NaOH wash to remove excess biomass, as a method to prevent clogging. Under these conditions an average toluene removal rate of 35 g C/(m(3) h) was obtained. After about 50 days there was no net increase in the biomass content of the reactor. The amount of biomass which was formed in the reactor equaled the amount removed by the NaOH wash. (c) 1996 John Wiley & Sons, Inc.     

Parameters affecting performance and modeling of biofilters treating alkylbenzene-polluted air

Both short-term and long-term biofiltration experiments were undertaken with a biofilter inoculated with a defined microbial consortium and treating an alkylbenzene mixture. The results obtained with such a biofilter in short-term experiments were very similar to those obtained with a biofilter inoculated with a non-defined mixed culture, in terms of maximum elimination capacities (70-72 g m(-3) h(-1)) and the corresponding removal efficiencies (>95%). However, in long-term experiments, a better performance was reached, with a maximum elimination capacity of 120 g m(-3) h(-1), corresponding to a removal efficiency >99% after 2 years of operation. Inoculation proved to be useful for shortening the start-up period. In the long term, it appeared that biomass distribution was not homogenous along the biofilter, which in some cases resulted in a bad fit between simple model equations and experimental data.