Kinetics of the removal of mono-chlorobenzene vapour from waste gases using a trickle bed air biofilter

The performance of a trickle bed air biofilter (TBAB) in the removal of mono-chlorobenzene (MCB) was evaluated in concentrations varying from 0.133 to 7.187 g m(-3) and at empty bed residence time (EBRT) varying from 37.7 to 188.52 s. More than 90% removal efficiency in the trickle bed air biofilter was achieved for the inlet MCB concentration up to 1.069 g m(-3) and EBRT less than 94.26 s. The trickle bed air biofilter was constructed with coal packing material, inoculated with a mixed consortium of activated sludge obtained from sewage treatment plant. The continuous performance of the removal of MCB in the trickle bed air biofilter was monitored for various gas concentrations, gas flow rates, and empty bed residence time. The experiment was conducted for a period of 75 days. The trickle bed air biofilter degrading MCB with an average elimination capacity of 80 g m(-3) h(-1) was obtained. The effect of starvation was also studied. After starvation period of 8 days, the degradation was low but recovered within a short period of time. Using macrokinetic determination method, the Michaelis-Menten kinetic constant K(m) and maximum reaction rate, r(max) evaluated as 0.121 g m(-3) s(-1) and 7.45 g m(-3), respectively.     

High loading toluene treatment in a compost based biofilter using up-flow and down-flow swing operation

A compost/ceramic (1:1, v/v) three section laboratory-scale biofilter inoculated with acclimated activated sludge was examined to treat high loading toluene vapors from a synthetic gas stream. The biofilter was operated continuously at different gas flow rates, 0.108-0.15m(3)h(-1), with inlet toluene concentrations ranging 0.5-13gm(-3). The overall performance of the biofilter was divided to seven stages according to the mode of operation (down-flow and up-flow) over a period of 102 days. Removal efficiencies ranging from 48 to 100% and elimination capacities ranging from 26 to 180gm(-3)h(-1) were observed depending on the initial loading rates and the mode of operations. A maximum elimination capacity of 180gm(-3)h(-1) was observed in the last period at an inlet toluene concentration of about 13gm(-3). The results showed that changing the mode of operation (up-flow and down-flow) periodically will improve the performance of the biofilter under high inlet toluene concentration (higher than 4gm(-3)). Results obtained in this study provide insight into the possibility of the biofilter to treat high inlet concentrations rather than low concentrations well known in the literature.     

Trimethylamine (TMA) biofiltration and transformation in biofilters

Bioremoval of trimethylamine (TMA) in two three-stage biofilters packed with compost (A) and sludge (B), respectively, was investigated. Both biofilters were operated with an influent TMA concentration of 19.2-57.2mgm(-3) for 67 days. Results showed that all of the inlet TMA could be removed by both biofilters. However, removal efficiency and transformation of TMA in each section of both biofilters was different. In the Introduction section, TMA removal efficiency and maximum elimination capacity of the compost medium were greater than those of sludge medium under higher inlet TMA concentration. In comparison with biofilter A, considerably higher NH(3) concentrations in effluent of all three sections in biofilter B were observed after day 19. Although, NO(2)(-)-N concentration in each section of biofilter A was relatively lower, NO(3)(-)-N content in each section of biofilter A increased after day 26, especially in the Materials and method section which increased remarkably due to a lesser amount of TMA and higher ammonia oxidation and nitrification in compost medium. In contrast, neither NO(2)(-)-N nor NO(3)(-)-N were detected in either section of biofilter B at any time throughout the course of the experiment. The cumulative results indicated that compost is more favorable for the growth of TMA-degrading and nitrifying bacteria as compared to the sludge and could be a highly suitable packing material for biodegradation and transformation of TMA.     

H2S and volatile fatty acids elimination by biofiltration: clean-up process for biogas potential use

In the present work, the main objective was to evaluate a biofiltration system for removing hydrogen sulfide (H(2)S) and volatile fatty acids (VFAs) contained in a gaseous stream from an anaerobic digestor (AD). The elimination of these compounds allowed the potential use of biogas while maintaining the methane (CH(4)) content throughout the process. The biodegradation of H(2)S was determined in the lava rock biofilter under two different empty bed residence times (EBRT). Inlet loadings lower than 200 g/m(3)h at an EBRT of 81 s yielded a complete removal, attaining an elimination capacity (EC) of 142 g/m(3)h, whereas at an EBRT of 31 s, a critical EC of 200 g/m(3)h was reached and the EC obtained exhibited a maximum value of 232 g/m(3)h. For 1500 ppmv of H(2)S, 99% removal was maintained during 90 days and complete biodegradation of VFAs was observed. A recovery of 60% as sulfate was obtained due to the constant excess of O(2) concentration in the system. Acetic and propionic acids as a sole source of carbon were also evaluated in the bioreactor at different inlet loadings (0-120 g/m(3)h) obtaining a complete removal (99%) for both. Microcosms biodegradation experiments conducted with VFAs demonstrated that acetic acid provided the highest biodegradation rate.     

Biofiltration and kinetic aspects of a biotrickling filter for the removal of paint solvent mixture laden air stream

In the present study, removal of methyl ethyl ketone (MEK), toluene, n-butyl acetate and o-xylene (MTBX) emitted from the paint industry was carried out in a coal based biotrickling filter. When the influent MTBX loadings were less than 120 gm(-3)h(-1), nearly 100% removal could be achieved. A maximum elimination capacity of 184.86 gm(-3)h(-1) was obtained at a MTBX load of 278.27 gm(-3)h(-1) with an empty bed residence time of 42.4s in phase V. Results showed that the condition was the most favorable for n-butyl acetate degradation followed by MEK, toluene and then o-xylene. The corresponding maximum removal rate, r(max) values of MTBX were calculated as 0.085, 0.033, 0.16 and 0.024 gm(-3)h(-1), respectively. Standard deviation of error in prediction of MEK, toluene and o-xylene removal were within limit of 10%, while in the case of n-butyl acetate this was approximately 60%. The MTBX concentration profiles along the depth were also determined by using convection-diffusion reaction (CDR) model. It was observed that at low concentration and low flow rate, the model is in good agreement with the experimental values for MEK, toluene and n-butyl acetate, but for o-xylene the model results deviated from the experimental.     

Treatment of xylene polluted air using press mud-based biofilter

In the present work, biofiltration of xylene vapors has been investigated on a laboratory scale biofilter packed with press mud as filter material inoculated with activated sludge from pharmaceutical industry. Four various gas flow rates, i.e. 0.03, 0.06, 0.09 and 0.12 m(3) h(-1), were tested for inlet xylene concentration ranging from 0.2 to 1.2 g m(-3). The biofilter proved to be highly efficient in the removal of xylene at a gas flow rate of 0.2m(3) h(-1) corresponding to a gas residence time of 2.8 min. For all the tested inlet concentrations, the removal efficiency decreased for high gas flow rates. For all the tested gas flow rates, a decrease in the removal efficiency was noticed for high xylene inlet concentration. The follow-up of carbon dioxide concentration profile through the biofilter revealed that the mass ratio of carbon dioxide produced to the xylene removed was approximately 2.52, which confirms complete degradation of xylene if one considers the fraction of the consumed organic carbon used for the microbial growth.     

Steady- and transient-state effects during the biological oxidation of gas-phase benzene in a continuously operated biofilter

Biofiltration is an aerobic degradation process in which a well-humidified contaminated air stream is passed through a porous packed medium that supports a thriving population of microbes. The removal of benzene vapor was investigated in a laboratory-scale biofilter packed with compost, inoculated with a mixed microbial consortium. This biofilter was operated continuously in six different phases for a period of 8 months at different flow rates, 0.024–0.144 m³ h⁻¹ with benzene concentrations ranging up to 1.7 g m⁻³. Under steady-state conditions, the removal efficiencies (REs) in the biofilter was consistently greater than 78% when benzene loading was less than 20 g m⁻³ h⁻¹. The maximum elimination capacity (EC) achieved in this study is 64 g m⁻³ h⁻¹ at an inlet loading rate of 128 g m⁻³ h⁻¹. The response of the biofilter to shutdown, restart operations and fluctuations in inlet concentration, and flow rate was determined by subjecting the biofilter to inlet loads of up to 120 g m⁻³ h⁻¹. The biofilter responded effectively to these loading conditions and was found to recover rapidly. The results from this study suggest that a compost biofilter is effective in treating benzene vapor under steady- and transient-conditions.     

Removal of styrene vapor from waste gases by a trickle-bed air biofilter

The trickle-bed air biofilter (TBAB) performance for the removal of high-strength styrene was evaluated under different gas flow rates and influent concentrations. Under pseudo-steady-state conditions, the elimination capacity increased but the removal efficiency decreased with the increase of styrene loading. More than 90 and 80% removal efficiencies were achieved for influent styrene loadings below 32 and 55g/m(3)/h, respectively. The TBAB appears to be an effective treatment process for controlling high-strength styrene emission under low-to-medium loading conditions, and the effectiveness could be maintained over 140 days of laboratory operation.     

Assessment of ethylene removal with Pseudomonas strains

This study investigated the biological removal of ethylene by Pseudomonas strains in a batch test and a biofilter column. In the batch test, no removal of ethylene was found in the absence of inoculated system, whereas more than 50% of the ethylene in the presence of inoculated system was degraded within 17 h, and completely removed after 25 h. The biofilter, packed with activated carbons, was capable of achieving ethylene removal efficiency as much as 100% at a residence time of 14 min and an inlet concentration of 331 mg m-3. Under the same conditions, carbon dioxide with a concentration of up to 1097 mg m-3 was produced. It was found that carbon dioxide was produced at a rate of 87 mg day-1, which corresponded to a volume of 0.05 L day-1. During operation with an inlet ethylene of 331 mg m-3, the maximum elimination capacity of the biofilter was 34 g C2H4 m-3 day-1. This biological system could reduce the ethylene concentration to levels below the threshold limit for the plant hormonal response (0.01 mg m-3), and provide an attractive treatment technology in horticultural storage facilities.     

Performance of low pH biofilters treating a paint solvent mixture: continuous and intermittent loading

Two biofilters packed with a reticulated polyurethane foam medium were inoculated with a compost-derived enrichment culture grown under acidic conditions (pH 3.0) and then operated over a period lasting 63 days. Both biofilters were supplied with a humidified gas stream containing a five-component mixture of acetone, methyl ethyl ketone, toluene, ethylbenzene, and p-xylene at a total VOC loading rate 80.3 gm(-3)h(-1) to simulate treatment of air emissions resulting from manufacture of reformulated paint. One biofilter was operated under continuous loading conditions and the other received intermittent loading with contaminants supplied only 8 h/day. Nutrient solution with pH 3.0 was supplied approximately once per week to provide nitrogen and other nutrients. Data are presented which demonstrate that undefined mixed cultures acclimated at low pH can successfully treat paint solvent mixtures in biofilters. The biofilter receiving continuous loading reached high overall removal efficiency (greater than 90% overall removal) 3 weeks after startup, and performance increased over time reaching overall removal in the range of 97-99% after 50 days. Performance of the intermittently loaded biofilter developed more slowly, requiring 6 weeks to stabilize at an overall removal efficiency in excess of 90%. In both biofilters, ketone components were more rapidly degraded than aromatic components, and removal of aromatic compounds was somewhat unstable even after 2 months of biofilter operation. Scanning electron microscopy (SEM) revealed that fungi dominated the microbial populations in both biofilters.     

Effects of adsorptive properties of biofilter packing materials on toluene removal

Various adsorptive materials, including granular activated carbon (GAC) and ground tire rubber (GTR), were mixed with compost in biofilters used for treating gaseous toluene, and the effects of the mixtures on the stability of biofilter performance were investigated. A transient loading test demonstrated that a sudden increase in inlet toluene loading was effectively attenuated in the compost/GAC biofilter, which was the most significant advantage of adding adsorptive materials to the biofilter packing media. Under steady conditions with inlet toluene loading rates of 18.8 and 37.5 g/m³/h, both the compost and the compost/GAC biofilters achieved overall toluene removal efficiencies greater than 99%. In the compost/GAC mixture, however, biodegradation activity declined as the GAC mass fraction increased. Because of the low water-holding capacity of GTR, the compost/ground tire mixture did not show a significant improvement in toluene removal efficiency throughout the entire operational period. Furthermore, nitrogen limitations affected system performance in all the biofilters, but an external nitrogen supply resulted in the recovery of the toluene removal efficiency only in the compost biofilter during the test periods. Consequently, the introduction of excessive adsorptive materials was unfavorable for long-term performance, suggesting that the mass ratio of the adsorptive materials in such mixtures should be carefully selected to achieve high and steady biofilter performance.     

Removal of p-xylene from an air stream in a hybrid biofilter

Biofiltration of an air stream containing p-xylene has been studied in a laboratory hybrid biofilter packed with a mixture of mature pig compost, forest soil and the packing material which was made of polyethylene (PE) and used in the moving bed biological reactor (MBBR) in wastewater treatment. Three flow rates, 9.17, 19.87 and 40.66 m(3)m(-2)h(-1), were investigated for p-xylene inlet concentration ranging from 0.1 to 3.3 g m(-3). A high elimination capacity of 80 g m(-3)h(-1) corresponding to removal efficiency of 96% was obtained at a flow rate of 9.17 m(3)m(-2)h(-1) (empty bed residence time of 132 s). At a flow rate of 40.66 m(3)m(-2)h(-1) (empty bed residence time of 30s), the maximum elimination capacity for p-xylene was 40 g m(-3)h(-1) and removal efficiencies were in the range of 47-100%. The production of carbon dioxide (P(CO(2))) is proportional to elimination capacity (EC) and the linear relation was formulated as P(CO(2))=1.65EC+15.58. Stable pH values ranging from 6.3 to 7.6 and low pressure drop values less than 0.2 cm H(2)O (19.6 Pa) of packing media in compost-based biofilter of hybrid biofilter were observed, which avoided acidification and compaction of packing media and sustained the activity of microorganism populations.     

Biofiltration of volatile ethanol using sugar cane bagasse inoculated with Candida utilis.

Candida utilis (C. utilis) growing on sugar cane bagasse complemented with a mineral salt solution was studied for gaseous ethanol removal in a biofilter. Ethanol loads from 93.7 to 511.9 g/h m(3) were used, by varying both inlet ethanol concentration (9.72 to 52.4 g/m(3)) and air flow rate (1.59 x 10(-3) to 2.86 x 10(-3) m(3)/h). At a loading rate of 93.7 g/h m(3), a steady-state was maintained for 300 h. Ethanol removal was complete, and 76.3% of the carbon consumed was found in carbon dioxide. At an higher aeration rate (ethanol load=153.8 g/h m(3)), the biofilter displayed an average removal efficiency (RE) of 70%, and an elimination capacity (EC) of 107.7 g/h m(3). Only 64.4% of the carbon consumed was used for CO(2) production. Acetaldehyde and ethyl acetate in the outlet gas attained 7.86 and 20.4% in terms of carbon balance, respectively. In both cases, the transient phase was less than one day. At a high inlet ethanol concentration (52.4 g/m(3)), no steady-state was observed and the process stopped during the third day. In the three cases, final biomass was poor, ranging from 10.5 to 14.8 mg/g dm. Final pH 4.0-4.6, indicated that acidifying non-volatile metabolites, such as acetate, accumulated in the reactor.     

A comparative assessment of biofiltration and activated sludge diffusion for odour abatement

The deodorization performance of a biofilter and an activated sludge diffusion (AS) system was comparatively evaluated in terms of removal efficiency (RE) and process stability at empty bed residence times (EBRT) ranging from 94 to 32s. Both bioreactors were fed with a synthetic odorous emission containing H(2)S, butanone and toluene at 23.6-43.3, 4.3-6.3 and 0.4-0.6 mg m(-3), respectively. While the outlet H(2)S concentration was always lower than 1.4 mg m(-3), the REs for butanone and toluene remained higher than 95% in both bioreactors regardless of the EBRT. The continuous supply of wastewater in the AS unit did not affect removal and appeared to be a requirement for efficient pollutant abatement. Despite the narrow carbon source spectrum treated, the AS system maintained a large bacterial diversity over time. Therefore, the results obtained confirmed the potential of AS systems as a robust and efficient biotechnology for odour treatment in WWTPs.     

An analysis of synergistic and antagonistic behavior during BTEX removal in batch system using response surface methodology

The removal of benzene, toluene, ethylbenzene and xylene (BTEX) as quaternary mixtures were studied in batch systems using a well-defined mixed microbial culture. The synergistic and antagonistic effects of total BTEX removal (BTEXT-RE) due to the presence of mixed substrate was evaluated through experiments designed by response surface methodology (RSM). The low and high concentrations of individual BTEX were 15 and 75 mg l(-1), respectively. The results showed that, increasing the concentration of xylene increased the cumulative BTEX removal (BTEXT-RE), however the reverse occurred when benzene concentrations were increased from low to high levels. A mixed response of increasing and decreasing trend in the BTEXT-RE value was observed when either of toluene or ethylbenzene concentration was increased. When the concentrations of individual BTEX compounds were 30 mg l(-1), the BTEXT-RE was about 58%. Complete BTEXT-RE was achieved at optimal BTEX concentrations of 48.1, 45.6, 49.3 and 56.6 mg l(-1). The RSM approach was found efficient in explaining the main, squared and interaction effects among individual BTEX concentrations on the BTEXT-RE in a more statistically meaningful way.     

Substrate interactions during anaerobic biodegradation of BTEX by the mixed cultures under nitrate reducing conditions

The enriched BTEX-degrading bacteria were used to investigate the substrate interactions during anaerobic biodegradation of all the possible BTEX binary combinations. Beneficial and detrimental substrate interactions were observed in comprehensive mixtures of benzene, toluene, ethylbenzene, o-xylene, m-xylene and p-xylene. The amendment of toluene or ethylbenzene could stimulate benzene degradation. Lower concentrations of m-xylene would enhance the degradation of benzene, whereas degradation of benzene was inhibited with higher concentrations of m-xylene. The simultaneous presence of toluene and ethylbenzene could stimulate the degradation of each other. The addition of toluene stimulated o-xylene degradation, whereas the amendment of ethylbenzene inhibited the degradation of o-xylene. Lower concentrations of toluene or ethylbenzene would enhance the degradation of m-xylene and p-xylene, whereas higher concentrations of toluene or ethylbenzene had a slight inhibitory effect on m-xylene and p-xylene degradation. The amendment of benzene, m-xylene or p-xylene would inhibit the degradation of other BTEX compounds. When the concentration of BTEX mixtures was over 150mg/l, the degradation of benzene, o-xylene, m-xylene and p-xylene was severely inhibited.     

Evaluation of gas removal and bacterial community diversity in a biofilter developed to treat composting exhaust gases

The performance of a new, but simply constructed, biofilter system, developed to purify composting exhaust air, was evaluated. The biofilter was packed with mature compost mixed with activated carbon and sludge sourced from a wastewater treatment plant. An alternating air flow system and a bioaerosol reduction device were designed to prevent pressure drop and reduce bioaerosol release. Experimental results demonstrated that satisfactory removal efficiencies of nitrogen-containing compounds, sulfur-containing compounds, fatty acids, total hydrocarbon and odor were achieved at an empty bed retention time (EBRT) of 30s. No significant acidification or alkalinity in the biofilter was observed, and the system was characterized by a small pressure drop and a low level of bioaerosol emission. Denaturing gradient gel electrophoresis (DGGE) and fluorescence in situ hybridization (FISH) techniques were used to uncover the changes in the bacterial community of the biofilter during the deodorization processes. A minimum of 16 bands were observed in the DGGE profile. Phylogenetic analysis revealed the phylum of Proteobacteria to be predominant, followed by Actinobacteria, Bacteroidetes, and Firmicutes, in descending order. However, the occurrence and predominance of specific bacterial species varied with the environmental conditions of the biofilter. Our results demonstrate - from both an engineering and biological point of view - the feasibility of the biofilter system described herein in purifying the gases derived from composting food waste.     

Evaluating the impact of water supply strategies on p-xylene biodegradation performance in an organic media-based biofilter

The influence of water irrigation on both the long-term and short-term performance of p-xylene biodegradation under several organic loading scenarios was investigated using an organic packing material composed of pelletised sawdust and pig manure. Process operation in a modular biofilter, using no external water supply other than the moisture from the saturated inlet air stream, showed poor p-xylene abatement efficiencies (≈33 ± 7%), while sustained irrigation every 25 days rendered a high removal efficiency (RE) for a critical loading rate of 120 g m(-3)h(-1). Periodic profiles of removal efficiency, temperature and moisture content were recorded throughout the biofilter column subsequent to each biofilter irrigation. Hence, higher p-xylene biodegradation rates were always initially recorded in the upper module, which resulted in a subsequent increase in temperature and a decrease in moisture content. This decrease in the moisture content in the upper module resulted in a higher removal rate in the middle module, while the moisture level in the lower module steadily increased as a result of water condensation. Based on these results, mass balance calculations performed using measured bed temperatures and relatively humidity values were successfully used to account for water balances in the biofilter over time. Finally, the absence of bed compaction after 550 days of continuous operation confirmed the suitability of this organic material for biofiltration processes.     

The effects of selected parameters on the nitric oxide removal by biofilter

A bench-scale biofilter was used to demonstrate the treatability of off-gas containing nitric oxide (NO) by examining selected operational parameters. After 6 days of operation, the biofilter reached to a steady state and NO reduction was significant, reducing from 200 ppm to 95 and 40 ppm after 6 and 40 days of continuous operation. The oxygen concentrations in the inlet would affect NO removal performance significantly; as oxygen content decreasing from 6% to 0%, the NO removal efficiency increased from 55% to 99%, indicating that oxygen inhibited the progress of denitrification. NO removal was inversely proportional to inlet NO concentration, removal efficiency decreased from 88% to 40 % as NO concentration increasing from 60 to 500 ppm. Column height would significant effect on the NO removal efficiency, under column height=6.5m and O(2)=6% conditions, 90% of removal efficiency was achievable. The effect of glucose added into biofilter would significantly enhance the NO removal efficiencies for both anaerobic and aerobic conditions of which 99% and 55%, respectively.     

Performance of a biofilter for the removal of high concentrations of styrene under steady and non-steady state conditions

The performance of a laboratory scale perlite biofilter inoculated with a mixed culture was evaluated for gas phase styrene removal under various operating conditions. Experiments were carried out by subjecting the biofilter to different flow rates (0.15–0.9 m³ h⁻¹) and concentrations (0.03–17.3 g m⁻³), corresponding to inlet loading rates varying from as low as 3 g m⁻³ h⁻¹ to as high as 1390 g m⁻³ h⁻¹. A maximum elimination capacity (EC) of 382 g m⁻³ h⁻¹ was achieved at an inlet loading rate of 464 g m⁻³ h⁻¹ with a removal efficiency of 82%. The high elimination capacity reached with this system could have been due to the dominant presence of filamentous fungi among others. The impact of relative humidity (RH) (30%, 60% and >92%) on the biofilter performance was evaluated at two constant loading rates, viz., 80 and 260 g m⁻³ h⁻¹, showing that inhibitory effects were only significant when combining the highest loads with the lowest relative humidities. Biomass distribution, moisture content and concentration profiles along the bed height were significantly dependent on the relative humidity of the inlet air and on the loading rate. The dynamic behaviour of the biofilter through vigorous short and long-term shock loads was tested at different process conditions. The biofilter was found to respond apace to rapid changes in loading conditions. The stability of the biomass within the reactor was apparent from the fast response of the biofilter to recuperate and handle intermittent shutdown and restart operations, either with or without nutrient addition.