Effect of pre‐treatments based on UV photocatalysis and photo‐oxidation on toluene biofiltration performance

BACKGROUND: The integration of UV photocatalysis and biofiltration seems to be a promising combination of technologies for the removal of hydrophobic and poorly biodegradable air pollutants. The influence of pre‐treatments based on UV_{254 nm} photocatalysis and photo‐oxidation on the biofiltration of toluene as a target compound was evaluated in a controlled long‐term experimental study using different system configurations: a standalone biofilter, a combined UV photocatalytic reactor‐biofilter, and a combined UV photo‐oxidation reactor (without catalyst)‐biofilter. RESULTS: Under the operational conditions used (residence time of 2.7 s and toluene concentrations 600–1200 mg C m^?3), relatively low removal efficiencies (6–3%) were reached in the photocatalytic reactor and no degradation of toluene was found when the photo‐oxidation reactor was operated without catalyst. A noticeable improvement in the performance of the biofilter combined with a photocatalytic reactor was observed, and the elimination capacity of the biological process increased by more than 12 g C h^?1 m^?3 at the inlet loads studied of 50–100 g C h^?1 m^?3. No positive effect on toluene removal was observed for the combination of UV photoreactor and biofilter. CONCLUSIONS: Biofilter pre‐treatment based on UV_{254 nm} photocatalysis showed promising results for the removal of hydrophobic and recalcitrant air pollutants, providing synergistic improvement in the removal of toluene. Copyright © 2011 Society of Chemical Industry     

Influence of nitrogen on the degradation of toluene in a compost‐based biofilter

Two identical laboratory‐scale bioreactors were operated simultaneously, each treating an input air flow rate of 1 m³ h^?1. The biofilters consisted of multi‐stage columns, each stage packed with a compost‐based filtering material, which was not previously inoculated. The toluene inlet concentration was fixed at 1.5 g m^?3 of air. Apart from the necessary carbon, the elements nitrogen, phosphorus, sulfur, potassium and other micro‐elements are also essential for microbial metabolism. These were distributed throughout the filter bed material by periodic ‘irrigations’ with various test nutrient solutions. The performance of each biofilter was quantified by determining its toluene removal efficiency, and elimination capacity. Nutrient solution nitrogen levels were varied from 0 to 6.0 g dm^?3, which led to elimination capacities of up to 50 g m^?3 h^?1 being obtained for a toluene inlet load of 80 g m^?3 h^?1. A theoretical analysis also confirmed that the optimum nitrogen solution concentration lays in the range 4.0–6.0 g dm^?3. Validation of the irrigation mode was achieved by watering each biofilter stage individually. Vertical stage‐by‐stage stratification of the biofilter performance was not detected, ie each filter bed section removed the same amount of pollutant, the elimination capacity per stage being about 16 g m^?3 h^?1 per section of column. © 2001 Society of Chemical Industry     

A Study of the Biofiltration of High‐Loads of Toluene in Air: Carbon and Water Balances,Temperature Changes and Nitrogen Effect

Biodegradable atmospheric pollutants, released at low to moderate concentrations, can be removed by biofiltration. In this work, a laboratory‐scale compost‐based biofilter has been evaluated for the removal of high levels of toluene in air (～ 4.0 g.m^?3). By applying a variable nitrogen input in the irrigation solution, it was shown that the biodegradation extent can be controlled through the nutrient supply. The maximum elimination capacity achieved was 135 g.m^?3.h^?1, for a N‐concentration of 3.0 g of N.L^?1. A quantitative analysis of the bioreaction aspects (stoichiometry, temperature) led to the determination of the water flow rates associated with the toluene oxidation. Thus, it was estimated that some 530 to 800 g of water.day^?1 were lost at the bioreactor outlet, but were balanced by the irrigation system.     

Simultaneous treatment of methane and swine slurry by biofiltration

BACKGROUND: The piggery industry is important both worldwide and in Canada, but localized production of large quantities of swine slurry causes severe environmental problems such as aquatic pollution and greenhouse gas emissions. The main objective of this study was to determine whether it is possible to simultaneously treat methane (CH₄) and swine slurry using an inorganic biofilter. RESULTS: A novel biofilter was designed to overcome the inhibition of CH₄ biodegradation by swine slurry. The CH₄ elimination capacity increased with the inlet load and a maximum value of 18.8 ± 1.0 g m^?3 h^?1 was obtained at an inlet load of 46.7 ± 0.9 g m^?3 h^?1 and a CH₄ concentration of 3.3 g m^?3. Four pure strains of fungi were used in an attempt to improve the removal of CH₄, but no significant effect was observed. Between 0.35 and 3.4 g m^?3, the CH₄ concentration had no effect on swine slurry treatment with removal efficiencies of 67 ± 10% for organic carbon and 70 ± 7% for ammonium. The influence of the slurry supply was analyzed and the best results were obtained with a supply method of six doses of 50 mL per day. CONCLUSION: Even though the results were lower than those obtained for the biofiltration of CH₄ alone, this study demonstrated the feasibility of treating CH₄ and swine slurry with the same biofilter using a novel design. Copyright © 2012 Society of Chemical Industry     

Elimination of chlorobenzene vapors from air in a compost‐based biofilter

In this work, the removal of monochlorobenzene (CB) vapors from air was studied, for the first time, in a non‐inoculated, laboratory‐scale, aerobic biofilter. The influence of three parameters on the bioprocess has been evaluated: the rate of nitrogen supplied to the bed, the inlet concentration of CB, and the flow rate. The CB inlet concentration was varied between 0.3 and 3.2 g m^?3, at a constant flow rate of 1.0 m³ h^?1. Removal rates of greater than 90% were achieved for CB inlet concentrations of up to 1.2 g m^?3. Then the flow rate was varied from 0.5 to 3.0 m³ h^?1 with a constant inlet concentration (1.2 g m^?3). Maximum elimination capacities (70 g m^?3 h^?1) were reached for contact times of greater than 60 s. The study of varying flow rates also permitted evaluation of a first order macrokinetic constant (1.1 × 10^?2 s^?1) for the CB biodegradation. Finally, the optimum nitrogen input value was found to lie between 0.3 and 0.4 g N h^?1 and gave rise to elimination capacities as high as 70 g m^?3 h^?1 for an inlet load of near 80 g m^?3 h^?1. Copyright © 2003 Society of Chemical Industry     

A trickling fibrous-bed bioreactor for biofiltration of benzene in air

A novel trickling fibrous-bed bioreactor was developed for biofiltration to remove pollutants present in contaminated air. Air containing benzene as the sole carbon source was effectively treated with a coculture of Pseudomonas putida and Pseudomonas fluorescens immobilized in the trickling biofilter, which was wetted with a liquid medium containing only inorganic mineral salts. When the inlet benzene concentration (C_gi) was 0·37 g m⁻³, the benzene removal efficiency in the biofilter was greater than 90% at an empty bed retention time (EBRT) of 8 min or a superficial air flow rate of 1·8 m³ m⁻² h⁻¹. In general, the removal efficiency decreased but the elimination capacity of the biofilter increased with increasing the inlet benzene concentration and the air (feed) flow rate. It was also found that the removal efficiency decreased but the elimination capacity increased with an increase in the loading capacity, which is equal to the inlet concentration divided by EBRT. The maximum elimination capacity achieved in this study was ∽11·5 g m⁻³ h⁻¹ when the inlet benzene concentration was 1·7 g m⁻³ and the superficial air flow rate was 3·62 m³ m⁻² h⁻¹. A simple mathematical model based on the first-order reaction kinetics was developed to simulate the biofiltration performance. The apparent first order parameter K_l in this model was found to be linearly related to the inlet benzene concentration (K_l=4·64−1·38 C_gi). The model can be used to predict the benzene removal efficiency and elimination capacity of the biofilter for benzene loading capacity up to ∽30 g m⁻³ h⁻¹. Using this model, the maximum elimination capacity for the biofilter was estimated to be 12·3 g m⁻³ h⁻¹, and the critical loading capacity was found to be 14 g m⁻³ h⁻¹. The biofilter had a fast response to process condition changes and was stable for long-term operation; no degeneration or clogging of the biofilter was encountered during the 3-month period studied. The biofilter also had a relatively low pressure drop of 750 Pa m⁻¹ at a high superficial air flow rate of 7·21 m³ m⁻² h⁻¹, indicating a good potential for further scale up for industrial applications. © 1998 Society of Chemical Industry     

Treatment of air polluted with high concentrations of toluene and xylene in a pilot-scale biofilter

Air biofiltration is now under active consideration for the removal of the volatile organic compounds from air polluted streams. In order to investigate the performance of this newly developed technology, a biofiltration pilot unit was operated for a continuous period of 8 months. The biofilter column was packed with commercially conditioned peat. At start-up, the filter bed was inoculated with four species of microorganisms. The resulting biofilter was fed with air contaminated with toluene, xylene or a mixture of toluene and xylene. The maximum elimination capacities attained were 165 g m⁻³ h⁻¹ for toluene, 66 g m⁻³ h⁻¹ for xylene and 115 g m⁻³ h⁻¹ for the mixture of toluene and xylene. These specific performances exceed the values published in the technical and commercial literature for similar processes. Xylene isomers were degraded in decreasing order of reactivity, m-xylene, p-xylene, o-xylene. In the case of air polluted with a toluene and xylene mixture, it was noticed that the metabolism of toluene biodegradation was inhibited by the presence of xylene. Characterization of the biofilm microbial populations after several weeks of operation showed that the dominant strains among the isolated culturable strains from the biofilm, even if different from the initially inoculated strains, had at least one physiological property favoring degradation of aromatic organic rings. The performance of the biofilter was found to be dependent on the temperature of the filter media and the pressure drop through the bed. Finally, a steady state mathematical model was tested in order to theoretically describe the experimental results. This model is used to illustrate the operating diffusion and reaction regimes at steady state for the case of each pollutant. © 1998 Society of Chemical Industry     

A new synthetic biofiltration material: poly(vinyl alcohol)/pig manure compost composite beads

Poly(vinyl alcohol) (PVA)/pig manure compost composite beads proved suitable as a biofilter material in a biofiltration process. The composite bead is a porous spherical particle with a diameter between 2.4 and 6.0 mm and a density of 0.96 g cm^?3. It contains 9.43 mg P g^?1 dry solid and 12.1 mg N g^?1 dry solid. The equilibrium moisture contents of the PVA/compost composite beads bed for adsorption and holding experiments are 50.5% and 54.6% by wet basis, respectively, which correspond to the optimal filter material required and could sustain the biological activity. The PVA/pig manure compost composite beads bed has higher moisture‐holding capacity and compression strength than the pig manure compost bed. The PVA/compost composite beads have buffer capacity and could keep the filter bed at pH 6.9–7.2 during operating. The percentage of ethyl acetate removed could stay at over 99% for 40 days of operation as the PVA/pig manure compost composite beads adsorbed inorganic nitrate nutrient. The maximum elimination capacity of the PVA/pig manure compost composite beads filters at the loading rate of 0.71 kg ethyl acetate m^?3‐bed h^?1 is 0.71 kg ethyl acetate m^?3‐bed h^?1. Copyright © 2005 Society of Chemical Industry     

Removal of TEX vapours from air in a peat biofilter: influence of inlet concentration and inlet load

This paper presents the results of the study of the removal of toluene, ethylbenzene, and o‐xylene (TEX) by biofiltration using a commercial peat as filter‐bed material. Runs with a single organic compound in air, and with the mixture of TEX in air, were carried out for at least 55 days in laboratory‐scale reactors inoculated with a conditioned culture. The influence of organic compound inlet load and of gas flow rate on the biofilter's performance was studied, including relatively high values of pollutant inlet concentration (up to 4.3 gC m^?3 for ethylbenzene, 3.2 gC m^?3 for toluene, and 2.7 gC m^?3 for o‐xylene). Results obtained show maximum elimination capacities of 65 gC m^?3 h^?1 for o‐xylene, 90 gC m^?3 h^?1 for toluene, and 100 gC m^?3 h^?1 for ethylbenzene, and high removal efficiency (>90%) even for moderately elevated concentrations: 3.0, 2.5 and 1.8 gC m^?3 for ethylbenzene, toluene and o‐xylene, respectively. The behaviour of the TEX mixture was in good agreement with the results obtained for the runs in which only one organic compound was present. Ethylbenzene and toluene are degraded easier than o‐xylene, and inhibitory effects due to the presence of multiple substrates were not observed. Copyright © 2005 Society of Chemical Industry     

Removal of monochlorobenzene from air in a trickling biofilter at high loading rates

BACKGROUND: In this study, the biofiltration of air streams laden with monochlorobenzene (MCB) vapours was investigated using a trickling biofilter operated co‐currently. The device was filled with ceramic material and inoculated with an acclimated microbial culture. A neutralization process was carried out in a separate unit using crushed oyster shells. Long‐term biofilter performance was evaluated over a 10‐month period of continuous experiments under different influent pollutant concentrations from 0.10 to 1.75 g m^?3, sequentially stepped up through three different apparent air residence times of 60, 30, and 15 s. RESULTS: Pollutant removal was shown to be complete at influent concentrations up to 1.25, 0.75 and 0.20 g m^?3, and apparent air residence times of 60, 30, and 15 s, respectively. The maximum elimination capacity was found to be 95.0 g m_PM^?3 h^?1 for an influent concentration of 1.0 g m^?3 and an apparent air residence time of 30 s, corresponding to a loading rate of 120.0 g m_PM^?3 h^?1. Monochlorobenzene and biomass concentration profiles along the biofilter evidenced the dependence of microbial concentration distribution on the pollutant loading rate and the existence of a linear relationship between biomass concentration and specific pollutant removal rate, regardless of the operating conditions applied. A macrokinetic analysis shows that the MCB removal rate is zeroth order for low values of MCB concentration. A critical value of MCB concentration exists at all superficial air velocity at which the biomass growth is inhibited. A simple kinetic model is developed which is able to describe the inhibition behaviour under any operating conditions. CONCLUSION: The experimental results indicated that the system was effective and stable under various working conditions and over a long operating period, provided that the loading conditions corresponding to substrate inhibition of microbial growth are not exceeded. Copyright © 2012 Society of Chemical Industry     

Coupling ultraviolet photolysis and biofiltration for enhanced degradation of aromatic air pollutants

Coupling UV photolysis and biofiltration was evaluated as an effective treatment strategy for the enhanced degradation of hardly biodegradable aromatic volatile organic compounds (VOCs). o‐Xylene, a recalcitrant and poorly water‐soluble VOC, was used as a model compound and treated in two parallel treatment systems with and without UV pretreatment. Contaminated streams with flow rates of 0.186–0.384 m³ h^?1 and inlet o‐xylene concentrations of up to 0.22 g m^?3 were passed through the treatment system. About 20% (between 10 and 35%) of o‐xylene was converted into water‐soluble intermediates during the UV photolysis stage, which partially oxidized o‐xylene to more water‐soluble and biodegradable byproducts. The untreated contaminant along with the byproducts of UV photolysis was then removed effectively in the biofiltration stage, with improvements of up to 100% compared with the control biofiltration process. The results suggested that combined UV photolysis–biofiltration is promising as an effective technique to eliminate hydrophobic and recalcitrant organic compounds from contaminated air steams. Copyright © 2005 Society of Chemical Industry     

Biofiltration of volatile organic compound using two packing materials: Kinetics and modelling

The performance of two laboratory scale biofilters, packed with pressmud (BF1) and sugarcane bagasse (BF2), was evaluated for gas phase ethylacetate removal under various operating conditions. Biofilters were inoculated with mixed culture obtained from pharmaceutical wastewater sludge. Experiments were carried out at different flow rates (0.03, 0.06, 0.09 and 0.12 m³ h^?1) and inlet ethylacetate concentrations (0.2, 0.4, 0.6 and 1.2 gm^?3). Maximum removal efficiency (RE) of 100% and 98% was achieved at an inlet concentration of 0.2 gm^?3 and gas flow rate of 0.03 m³ h^?1 in BF1 and BF2, respectively. A maximum elimination capacity (EC) of 66.6 gm^?3 h^?1 and 64.1 gm^?3 h^?1 was obtained in BF1 and BF2, respectively, at an inlet concentration of 0.8 gm^?3 and a gas flow rate of 0.12 m³ h^?1. The kinetics of biofiltration of ethylacetate was studied by using Ottengraf and van den Oever model. The kinetic modelling gives an insight into the mechanism of biofiltration. The modified Ottengraf model, which was also tested, demonstrated good agreement between calculated and experimental data.     

Experimental and neural model analysis of styrene removal from polluted air in a biofilter

BACKGROUND: Biofilters are efficient systems for treating malodorous emissions. The mechanism involved during pollutant transfer and subsequent biotransformation within a biofilm is a complex process. The use of artificial neural networks to model the performance of biofilters using easily measurable state variables appears to be an effective alternative to conventional phenomenological modelling. RESULTS: An artificial neural network model was used to predict the extent of styrene removal in a perlite‐biofilter inoculated with a mixed microbial culture. After a 43 day biofilter acclimation period, styrene removal experiments were carried out by subjecting the bioreactor to different flow rates (0.15–0.9 m³ h^?1) and concentrations (0.5–17.2 g m^?3), that correspond to inlet loading rates up to 1390 g m^?3 h^?1. During the different phases of continuous biofilter operation, greater than 92% styrene removal was achievable for loading rates up to 250 g m^?3 h^?1. A back propagation neural network algorithm was applied to model and predict the removal efficiency (%) of this process using inlet concentration (g m^?3) and unit flow (h^?1) as input variables. The data points were divided into training (115 × 3) and testing set (42 × 3). The most reliable condition for the network was selected by a trial and error approach and by estimating the determination coefficient (R²) value (0.98) achieved during prediction of the testing set. CONCLUSION: The results showed that a simple neural network based model with a topology of 2–4–1 was able to efficiently predict the styrene removal performance in the biofilter. Through sensitivity analysis, the most influential input parameter affecting styrene removal was ascertained to be the flow rate. Copyright © 2009 Society of Chemical Industry     

Performance evaluation of a water/silicone oil two‐phase partitioning bioreactor using Rhodococcus erythropolis T902.1 to remove volatile organic compounds from gaseous effluents

BACKGROUND: In the framework of biological processes used for waste gas treatment, the impact of the inoculum size on the start‐up performance needs to be better evaluated. Moreover, only a few studies have investigated the behaviour of elimination capacity and biomass viability in a two‐phase partitioning bioreactor (TPPB) used for waste gas treatment. Lastly, the impact of ethanol as a co‐substrate remains misunderstood. RESULTS: Firstly, no benefit of inoculation with a high cellular density (>1.5 g L^?1) was observed in terms of start‐up performance. Secondly, the TPPB was monitored for 38 days to characterise its behaviour under several operational conditions. The removal efficiency remained above 63% for an inlet concentration of 7 g isopropylbenzene (IPB) m^?3 and at some time points reached 92% during an intermittent loading phase (10 h day^?1), corresponding to a mean elimination capacity of 4 × 10^?3 g L^?1 min^?1 (240 g m^?3 h^?1) for a mean IPB inlet load of 6.19 × 10^?3 g L^?1 min^?1 (390 g m^?3 h^?1). Under continuous IPB loading, the performance of the TPPB declined, but the period of biomass acclimatisation to this operational condition was shorter than 5 days. The biomass grew to approximately 10 g L^?1 but the cellular viability changed greatly during the experiment, suggesting an endorespiration phenomenon in the bioreactor. It was also shown that simultaneous degradation of IPB and ethanol occurred, suggesting that ethanol improves the biodegradation process without causing oxygen depletion. CONCLUSION: A water/silicone oil TPPB with ethanol as co‐substrate allowed the removal of a high inlet load of IPB during an experiment lasting 38 days. Copyright © 2008 Society of Chemical Industry     

Biofiltration of toluene in the absence and the presence of ethyl acetate under continuous and intermittent loading

BACKGROUND: Two peat biofilters were used for the removal of toluene from air for one year. One biofilter was fed with pure toluene and the other received 1:1 (by weight) ethyl acetate:toluene mixture. RESULTS: The biofilters were operated under continuous loading: the toluene inlet load (IL) at which 80% removal occurred was 116 g m^?3 h^?1 at 57 s gas residence time. Maximum elimination capacity of 360 g m^?3 h^?1 was obtained at an IL of 745 g m^?3 h^?1. The elimination of toluene was inhibited by the presence of ethyl acetate. Intermittent loading, with pollutants supplied for 16 h/day, 5 days/week, did not significantly affect the removal efficiency (RE). Biomass was fully activated in 2 h after night closures, but 6 h were required to recover RE after weekend closures. Live cell density remained relatively constant over the operational period, while the dead cell fraction increased. Finally, a 15 day starvation period was applied and operation then re‐started. Performance was restored with similar re‐acclimatization period to that after weekend closures, and a reduction in dead cell fraction was observed. CONCLUSION: This study demonstrates the capacity of the system to handle intermittent loading conditions that are common in industrial practices, including long‐term starvation. Copyright © 2008 Society of Chemical Industry     

Biological treatment of a contaminated gaseous emission from a paint and varnish plant—from laboratory studies to pilot‐scale operation

A Vapour‐Phase Bioreactor (VPB), namely a biotrickling filter, was scaled‐up and operated in‐situ for the treatment of gaseous emissions from a paint and varnish industrial plant. A microbial culture able to degrade the target compounds was enriched and a laboratory‐scale VPB was established in order to evaluate the treatment's performance. The VPB presented removal efficiencies higher than 90% when exposed to Organic Loads (OL) of ca 50 g h^?1 m^?3 of reactor. The VPB was exposed to dynamic conditions often found in‐situ (eg night and weekend shutdown periods) and showed a fast capacity to recover, with and without mineral medium recirculation. After a prolonged interruption period (10 months), the VPB was not able to cope with OL of ca 25 g h^?1 m^?3 of reactor and re‐inoculation was required in order to recover the treatment performance. The VPB also showed limited treatment when exposed to higher OL (ca 500 g h^?1 m^?3 of reactor). The VPB was then scaled‐up and a 3 m³ VPB was operated in‐situ, showing removal efficiencies higher than 50% when exposed to an OL of c 5 g h^?1 m^?3 of reactor, thus complying with current legal demands. The addition of a maintenance feed was shown to be a useful tool for VPB pilot‐scale operation when shutdown periods occurred. A factorial design of experiments was carried out, which allowed reduction to one‐tenth of the initial supply of the main mineral medium constituents, namely phosphate buffer, ammonium and magnesium salts, and also elimination of the metal supplement. Overall, the VPBs were shown to be robust equipment, being able to respond actively to dynamic treatment scenarios, particularly night and weekend shutdown periods. Copyright © 2003 Society of Chemical Industry     

Treatment performance of volatile organic sulfide compounds by the immobilized microorganisms of B350 group in a biotrickling filter

BACKGROUND: In this work, the feasibility of biodegradation and the removal performance of sole and mixed odorous vapors, such as dimethyl disulfide (DMDS), methyl phenyl sulfide (MPS), and ethanethiol (EtSH) in an EtSH‐acclimated biotrickling filter seeded with commercially available B350 microorganisms, were investigated. RESULTS: Removal efficiencies (REs) for DMDS as a sole substrate were evaluated under different inlet concentrations and empty bed residence times (EBRT), 100% RE was achieved at concentration below 0.4 g m^?3 at EBRT 110 s. In addition, 100% RE was obtained for binary EtSH and DMDS (3:2) at the same EBRT. According to the Michaelis–Menten type kinetic equation, the maximum removal rates (V_max) were calculated as 28.7 and 13.9 g m^?3 h^?1 for DMDS and MPS as sole substrate, respectively, while V_max was 22.1 and 10.1 g m^?3 h^?1 for DMDS and MPS in the presence of EtSH and EtSH‐DMDS mixture, respectively. After 5 and 20 days starvation, the re‐acclimation times were only 2 and 8 days, respectively, for the binary system. An EtSH:DMDS:MPS (3:2:1) ternary mixture was removed efficiently by the rebooted system after starvation. CONCLUSION: The proposed system can be applied to cost‐effectively decompose a mixture of volatile organic sulfide compounds at pilot scale. Copyright © 2011 Society of Chemical Industry     

Treatment of methanol vapours in biofilters packed with inert materials

BACKGROUND: Methanol is a major pollutant emitted in Canada. Methanol is toxic to humans and it is associated with environmental problems such as smog generation. Biofiltration is a treatment method of considerable interest for controlling methanol emissions, because of its characteristics: no production of hazardous wastes, low energy consumption and low operating costs. The present study analyzed the effects of porous and non‐porous packing materials, the nitrogen concentration in nutrient solution and the methanol inlet load on biofilter performance and biofilm characteristics. RESULTS: The biofilter packed with porous material presented a removal efficiency up to 95%, which was higher than the 35% removal efficiency with the non‐porous material. Inlet load (IL) influenced the biomass and carbon dioxide production rates. The critical inlet load (IL_crit) occurred at 80 g m^?3 h^?1. The cellular densities of methylotrophs and non‐methylotrophs were affected by all operating variables examined. CONCLUSION: Biofiltration can be applied for controlling methanol emissions with high removal efficiency. The cellular density of methylotrophs is correlated with the performance of the biofilter. Copyright © 2008 Society of Chemical Industry     

Effect of inlet mass loading,water and total bacteria count on methanol elimination using upward flow and downward flow biofilters

An upward flow biofilter and a downward flow biofilter using compost for removing methanol from air were investigated to compare the biofilter performance and to realize the advantages of using downward flow biofilters for accessibility to water make‐up. Both the upward flow and downward flow columns showed similar performance in terms of elimination capacity (EC) versus inlet mass loading (IC). The maximum elimination capacity (EC) from these two biofilters was approximately 101 g m⁻³ h⁻¹ with an optimum methanol loading rate at inlet (IC) of 169 g m⁻³ h⁻¹ (7.5 g m⁻³ of methanol with superficial velocity of 7.6 m h⁻¹). The effect of water movement within the bed on elimination capacity was monitored. In addition, it was found that when the water content in the compost was below 35% by weight, microbial activity was impaired. Once the compost media had dried, it became hydrophobic and could be rewetted only with great difficulty. Total bacteria count was performed on compost samples during the entire operation. The relationship between elimination capacity and total bacteria count was reported. Similar trends were shown by the variations of elimination capacity and total bacteria count with methanol loading: both initially increase, go through a plateau, then decrease with loading. © 2000 Society of Chemical Industry     

RDX biodegradation column study: influence of ubiquitous electron acceptors on anaerobic biotransformation of RDX

A series of column studies, with aquifer material from the former Nebraska Ordinance Plant (NOP), were performed to explore the phenomenon of electron competition from ubiquitous inorganic electron acceptors (nitrate and sulfate) present in contaminated groundwater. Acetate was used as a source of readily biodegradable carbon in all of the treatment‐column systems. Influent hexahydro‐1, 3, 5‐trinitro‐1, 3, 5‐triazine (RDX) concentrations (1–1.8 mg dm^?3) were completely removed to below detection levels of 20 µg dm^?3 in all treatment‐column systems without any nitroso‐metabolites. In the control‐column system (with no carbon amendment) significant levels (～30% of the inlet molar RDX) of nitroso‐substituted RDX derivates were observed in the effluent stream. The estimated first‐order biodegradation rate coefficient for RDX was highest (0.79 h^?1) in the treatment‐column system where acetate was the only amendment, about 52 times higher than the rate coefficient (0.015 h^?1) obtained in the control‐column system. The presence of sulfate (100 mg dm^?3) in influent groundwater temporarily delayed the onset of RDX biotransformation without any adverse effects on overall RDX biotransformation. Coexistence of low (100 mg dm^?3) nitrate levels in the influent feed water reduced the first‐order biodegradation rate coefficient obtained in the absence of nitrate by about 80% to 0.16 h^?1. These nitrate levels, however, were low to halt the RDX biodegradation probably because the available carbon levels were high enough to exceed the demands for nitrate reduction. High levels of nitrate (500 mg dm^?3) initially halted RDX removal, and significantly reduced the rate of RDX biotransformation by about 98% to 0.02 h^?1, thereby increasing the half‐life from 0.9 h in the absence of nitrate to about 32 h, with noticeable levels of untreated RDX in the effluent stream. Contrary to the expectations, the presence of ammonium in conjunction with acetate resulted in a lower (0.09 h^?1) biodegradation rate coefficient as compared with the one obtained in the absence of ammonium. Copyright © 2003 Society of Chemical Industry