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     

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     

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     

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     

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     

Biotrickling filtration of air contaminated with ethanol

A biotrickling filter (BTF) for treating high ethanol loads was operated for one year and the effect of operating conditions was studied. The BTF was operated in a range of ethanol inlet concentrations of 0.2–15.0 g m^?3 and at three different residence times (30, 65 and 130 s). The experiments show that removal efficiency decreased with increasing ethanol inlet concentration and decreasing air residence time. Removal efficiency varied in the range of 60–100%. A maximum elimination capacity of 970 g m^?3 h^?1 was obtained for an inlet load of 1610 g m^?3 h^?1. At a constant residence time, the carbon dioxide (CO₂) production rate varied with ethanol inlet concentration. BTF presented the maximum CO₂ production rate in the range of inlet concentration of 3.0–7.0 g m^?3. Two strategies for controlling biomass accumulation were applied: one consisted in periodical washing; the other combined periodical washing with nutrient starvation by consuming less water and energy. Both strategies led to maintaining the BTF stable, with high adaptability and reproducibility. Copyright © 2007 Society of Chemical Industry     

Methane and carbon dioxide emissions and nitrogen turnover during liquid manure storage

Animal slurry stored in-house and outside is a significant source of atmospheric methane (CH₄). The CH₄ source strength of stored slurry is greatly affected by temperature. To improve emission calculations on a global scale there is a need for knowledge about the relationship between production of CH₄ in slurry and temperature. In this study, the filling of slurry channels was reproduced in the laboratory by gradually filling 1 m-high PVC vessels during 9 days followed by incubation for 100–200 days. A preliminary test showed that little CH₄ was produced from animal slurry during 10 days of incubation at 20°C, if no inoculum (slurry incubated anaerobically at the test temperature for 1.5–2 months) was present. However, the addition of 7.6% inoculum supported an immediate production of CH₄. Vessels amended with inoculum and gradually filled with cattle or pig slurry were then incubated at 10, 15 and 20°C. Methane production from stored pig and cattle slurry was not significant at temperatures below 15°C, where CO₂ was the main product of decomposition processes. In contrast, the anaerobic production of CH₄ was high and significant relative to the production of CO₂ at 20°C. Peak emissions of CH₄ averaging 0.012 and 0.02 g C h⁻¹ kg⁻¹ volatile solids (VS) were reached within about 10 days at 10 and 15°C, respectively. At 20°C, the emission of CH₄ from pig slurry was about 0.01 g C h⁻¹ kg⁻¹ for 10 days, and thereafter emissions increased to about 0.10 g C h⁻¹ kg⁻¹ VS. For cattle slurry a peak emission of 0.08 g C h⁻¹ kg⁻¹ VS was measured after 180 days. Degradation of organic nitrogen (N) in cattle slurry was related to the reduction of organic material as reflected in CO₂ and CH₄ emission. The mineralization of organic N during storage represented 10–80% of organic N in cattle slurry, and 40–80% of the organic N in pig slurry.     

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     

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     

Characterization of an organic filter medium for the biofiltration treatment of air contaminated with 1,2‐dichlorobenzene

Laboratory experiments were conducted to determine the potential for removing 1,2‐dichlorobenzene (1,2‐DCB) in gaseous phase by biofiltration. Experiments were carried out over 8 months in a steel tank (0.45 m³) using an organic filter medium composed of peat, maple wood chips, chicken manure and 1,2‐DCB‐contaminated soil. During the first 6 months, the biofilter was operated without injecting 1,2‐DCB in order to characterize the physicochemical, mechanical and microbiological properties of the filter bed. The results revealed that it is an excellent medium for both microbial development (up to 10⁹ cells for heterotrophic bacteria) and long‐term stability with a limited drop of pressure (30 cm of water) and no clogging. Over the final 2 months, the biofilter treated air laden with 1,2‐DCB (0.30 and 0.75 g m^?3) and the maximum elimination capacity reached was 9 g m^?3 h^?1 (inlet load of 13 g m^?3 h^?1), which represented 69% efficiency. Elimination performance was strongly dependent upon inlet concentration, sorption/desorption and biodegradation phenomena occurring in the filter medium. Sorption/desorption and biodegradation mechanisms during the start‐up period were characterized using the elimination efficiency (%). At the beginning of the 1,2‐DCB injection, the microorganisms were strongly impacted and sorption/desorption phenomena prevailed. With the decrease of the inlet concentration, biodegradation progressively increased to become the most important mechanism. It was concluded that biofiltration possesses an excellent potential for treating volatile chlorinated benzene, known to be recalcitrant to biodegradation. Copyright © 2003 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     

Biodegradation of aromatic hydrocarbons in a compost biofilter

Two laboratory‐scale biofilters filled with the same type of packing material were operated at different gas flow rates and influent concentrations of toluene and xylene in order to investigate their performance in treating waste gas streams. The columns contained a mixture of municipal compost as a base material and wood chips as a bulking agent in an 80:20 ratio; the porosity was 54%. Microbial acclimation was achieved by addition of nutrient‐enriched solution along with pollutants for a week by daily mixing and natural aeration. During the start‐up of the systems with inlet concentrations of 20 and 70 ppm for toluene and xylene, respectively, high biomass growth resulted in pressure drops in excess of 2000 Pam^?1. Under steady state conditions, the response of each biofilter to variations in contaminant mass loading was studied by either changing the influent concentration or flow rate of the inlet waste stream. The results show that organic loading rates of up to 110 and 150 gm^?3h^?1 can be handled without any indication of the elimination capacity being saturated. However, maintaining the pressure drop below 1000 Pam^?1 to avoid operational problems, optimal organic loading rates for toluene and xylene of 78 ± 8 and 80 ± 14 gm^?3h^?1 respectively are suggested for an HRT value of 60 s. Under these conditions, elimination capacities of 73 ± 4 and 73 ± 14 gm^?3h^?1 and removal efficiencies of 94 ± 6% and 91 ± 8% were achieved for toluene and xylene, respectively. Copyright © 2003 Society of Chemical Industry     

Emissions of CH4, N2O, NH3 and odorants from pig slurry during winter and summer storage

Manure storage contributes significantly to greenhouse gas (GHG), NH₃ and odour emissions from intensive livestock production. A pilot-scale facility with eight 6.5-m³ slurry storage units was used to quantify emissions of CH₄, N₂O, NH₃, and odorants from pig slurry during winter and summer storage. Pig slurry was stored with or without a straw crust, and with or without interception of precipitation, i.e., four treatments, in two randomized blocks. Emissions of total reduced S (mainly H₂S) and p-cresol, but not skatole, were reduced by the straw crust. Total GHG emissions were 0.01–0.02 kg CO₂ eq m^?3 day^?1 during a 45-day winter storage, and 1.1–1.3 kg CO₂ eq m^?3 day^?1 during a 58-day summer storage period independent of storage conditions; the GHG balance was dominated by CH₄ emissions. Nitrous oxide emissions occurred only during summer storage where, apparently, emissions were related to the water balance of the surface crust. An N₂O emission factor for slurry storage with a straw crust was estimated at 0.002–0.004. There was no evidence for a reduction of CH₄ emissions with a crust. Current Intergovernmental Panel on Climate Change recommendations for N₂O and CH₄ emission factors are discussed.     

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     

Methane oxidation in soils with different textures and land use

Intact core samples from soils with different textures and land use were tested for their capacity to oxidise methane. The soil cores were taken from arable land, grassland and forest. It was found that coarse textured soils (6.74–16.38 μg CH₄ m^-2 h^-1) showed a higher methane uptake rate than fine textured soils (4.66–5.34 μg CH₄ m^-2 h^-1). Increasing soil tortuosity was thought to reduce the methane oxidation rate in fine textured soils. The oxidation rate of forest soils (16.32–16.38 μg CH₄ m^-2 h^-1), even with a pH below 4.5, was very pronounced and higher than arable land (11.40–14.47 μg CH₄ m^-2 h^-1) and grassland (6.74–9.30 μg CH₄ m^-2 h^-1). Within the same textural class arable land showed a faster methane uptake rate than grassland. In grassland with a fine texture, even methane production was observed. Nitrogen availability and turnover in these land use systems were thought to cause the different oxidation rates. Decreasing the moisture content slowed down the oxidation rate in all soils. This could be caused by an increased N turnover and a starvation of the methanotrophic bacteria. This revised version was published online in August 2006 with corrections to the Cover Date.     

Ultraviolet‐ray treatment of polysulfone membranes on the O2/N2 and CO2/CH4 separation performance

UV irradiation on polysulfone (PSF) membranes was studied to improve their gas‐separation properties. Membranes with 19–25% PSF contents were prepared by the phase‐inversion method, and the membrane surface was modified with UV rays with a wavelength of 312 nm and a power of 360 µw/cm². Measurements of gas permeation were conducted with pure carbon dioxide (CO₂), methane (CH₄), oxygen (O₂), and nitrogen (N₂) gases under 3–8 bar pressure at 25°C. Fourier transform infrared spectrometry revealed that the polar functional groups of hydroxyl and carbonyl were introduced by UV irradiation. The water contact angle of the treated membrane was reduced from 70–75° to 10–12° after 12 h of UV exposure. Scanning electron microscopy observation showed that the dense skin layer increased as the polymer concentration increased. After UV treatment, the permeation of O₂ decreased from 0.4–3.4 to 0.2–2.3 m³ m^?2 h^?1 bar^?1, whereas that of N₂, CO₂, and CH₄ increased for all of the pressures used from 0.1–1.7 m³ m^?2 h^?1 bar^?1 to about 0.1–3.4 m³ m^?2 h^?1 bar^?1; this depended on the applied pressure and the PSF content. As a result, the selectivity ratio of O₂/N₂ decreased from 1.9–7.8 to 0.6–1.5, whereas that of CO₂/CH₄ increased from 0.9–2.6 to 1.1–6.1. Moreover, the O₂/N₂ and CO₂/CH₄ of the untreated and the treated membranes decreased with increasing pressure and increased with increasing polymer concentration. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42074.     

Comparison of chemical wet scrubbers and biofiltration for control of volatile organic compounds using GC/MS techniques and kinetic analysis

Increasing public concerns and EPA air regulations in non‐attainment zones necessitate the remediation of volatile organic compounds (VOCs) generated in the poultry‐rendering industry. Wet scrubbers using chlorine dioxide (ClO₂) have low overall removal efficiencies due to lack of reactivity with aldehydes. Contrary to wet scrubbers, a biofilter system successfully treated the aldehyde fraction, based on GC/MS analysis of inlet and outlet streams. Total VOC removal efficiencies ranged from 40 to 100% for the biofilter, kinetic analysis indicated that the overall removal capacity approached 25 g m⁻³ h⁻¹, and aldehyde removal efficiency was significantly higher compared with chemical wet scrubbers. Process temperatures monitored in critical unit operations upstream from the biofilter varied significantly during operation, rising as much as 30 °C within a few minutes. However, the outlet air temperature of a high intensity scrubber remained relatively constant at 40 °C, although the inlet air temperature fluctuated from 50 to 65 °C during monitoring. These data suggest a hybrid process combining a wet scrubber and biofilter in series could be used to improve overall VOC removal efficiencies and process stability. Copyright © 2005 Society of Chemical Industry     

Mathematical modelling of the alcoholic fermentation of glucose by Zymomonas mobilis mobilis

The kinetics of alcoholic fermentation of a strain of Zymomonas mobilis, isolated from sugarcane juice, has been studied with the objective of determining the constansts of a non-structured mathematical model that represents the fermentation process. Assays in batch and in continuous culture have been carried out with different initial concentrations of glucose. The final concentrations of glucose, ethanol and biomass were determined. The following kinetic parameters were obtained: μ_max, 0·5 h^?1; K_s, 4·64 g dm^?3; P_max, 106 g dm^?3; Y_x/s, 0·0265 g g^?1; m, 1·4 g g^?1 h^?1; α, 17·38 g g^?1; β, 0·69 g g^?1 h^?1.     

Removal of dimethyl sulfide in a thermophilic membrane bioreactor

BACKGROUND: Several sources such as the paper and pulp industry and waste treatment plants emit waste gases containing volatile organic sulfur compounds at elevated temperature. Since cooling the hot gases increases the operational cost of biological reactors, application of thermophilic microorganisms could be a cost‐effective solution. The objectives of this study were to investigate the possibility of removal of dimethyl sulfide from waste gases under thermophilic conditions (52 °C) in a membrane bioreactor and to examine the long‐term stability of the reactor at elevated temperature. The effects of operating conditions such as gas residence time, nutrient supply, temperature decrease and short‐term shutdown on elimination capacity were investigated. RESULTS: A maximum elimination capacity of 54 g m^?3 h^?1 (0.108 g m^?2 h^?1) was obtained at a mass loading rate of 64 g m^?3 h^?1 (0.128 g m^?2 h^?1) with a removal efficiency of 84% at a gas residence time of 24 s. The long‐term operation of the thermophilic membrane bioreactor was followed for 9 months. Although the removal efficiency decreased to 50% after 3 months of continuous operation, it recovered (>96%) after the excess biomass was removed by applying high‐velocity liquid recirculation. CONCLUSION: This study demonstrated that the dimethyl sulfide removal is possible in a thermophilic membrane bioreactor with an elimination capacity of 54 g m^?3 h^?1 (0.108 g m^?2 h^?1) at a gas residence time of 24 s. Copyright © 2008 Society of Chemical Industry     

Synthesis of a new type poly(vinyl alcohol)/peat/bamboo charcoal/KNO3 composite bead used as biofilter material

A new type poly(vinyl alcohol) (PVA)/peat/bamboo charcoal (BC)/KNO₃ composite bead was prepared, which has a diameter of 2.4–6.0 mm and a density of 1.133 g/cm³ and is a porous spherical particle. The biochemical kinetic behaviors of n‐butyl acetate in PVA/peat/BC/KNO₃ spherical composite bead biofilter (BC biofilter) and PVA/peat/granular activated carbon (GAC)/KNO₃ spherical composite bead biofilter (GAC biofilter) were investigated. The values of half‐saturation constant K_s for BC biofilter and GAC biofilter were 27.89 and 27.95 ppm, respectively. The values of maximum reaction rate V_m for BC biofilter and GAC biofilter were 13.49 and 13.65 ppm/s, respectively. Zero‐order kinetic with the diffusion limitation was regarded as the most adequate biochemical reaction model for the two biofilters. The microbial growth rate and biochemical reaction rate for two biofilters were inhibited at higher inlet concentration, and the degree of inhibitive effect was more pronounced in the inlet concentration range of 100–800 ppm. The biochemical kinetic behaviors of the two biofilters were similar. The maximum elimination capacity of BC biofilter and GAC biofilter were 111.65 and 122.67 g C/h m³ bed volume, respectively. The PVA/peat/BC/KNO₃ composite bead was suitable as a biofilter material. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011