Empty Bed Residence Time Research Articles

Interactions and microbial variations in a biotrickling filter treating low concentrations of hydrogen sulfide and ammonia

A lab-scale biotrickling filter (BTF) packed with porcelain Rasching ring and ceramsite was applied for co-treating of low concentrations of hydrogen sulfide (H2S) and ammonia (NH3), as major pollutants typically found in e.g., intensive livestock production facilities. In this study, the outlet gas concentrations of H2S and NH3 were used for indicators if the treated gas reached odor-free condition. Overall, excellent removal efficiencies were obtained for both H2S and NH3 in the BTF during Stage I (H2S alone) and Stage II (H2S and NH3). Specifically, the H2S outlet concentration was below the detection limit (∼3.6 ppbv) and the NH3 outlet concentration was less than 0.4 ppmv when the inlet concentrations of H2S and NH3 were around 1.8 ppmv and 35.3 ppmv, respectively. In this case, the running empty bed residence time was 10.2 s. During Stage II, the outlet H2S concentration was decreased significantly when the inlet NH3 concentration was increased, likely due to the influence by pH. Meanwhile, the outlet nitrous oxide (N2O) concentration was kept low (<2% NH3) during the experiment, suggesting a proper operation of the BTF. After the inlet gas shifted from H2S alone at Stage I to H2S and NH3 at Stage II, the main sulfur-oxidizing bacteria (SOB) species in the BTF switched from Acidithiobacillus to Thiobacillus.

Effect of hydrophobic fumed silica addition on a biofilter for pentane removal using SIFT-MS

Biofiltration is a typical air pollution control process for the treatment of volatile organic compounds (VOCs). Mass transfer of hydrophobic VOCs to the biofilm is limited which leads to low removal efficiency (RE). Aiming to enhance the transport of hydrophobic VOCs, the effect of hydrophobic fumed silica (HFS) addition to a biofilter (BF) for pentane removal was studied in this paper. The effect of HFS on pentane removal was evaluated by daily RE measurements and periodical headspace gas pentane pulse injections using SIFT-MS as analysis apparatus. The BF was operated during more than 100 days at an empty bed residence time (EBRT) of 120 s reaching an elimination capacity (EC) up to 93.8 g pentane m−3 h−1. At the last stage of the study, when a higher nutrient pulse and HFS to a concentration of 1.5% w/w wet were added, the BF showed better EC (46.3 ± 14.9 g pentane m−3 h−1; RE = 96.2%) compared to the previous stages (28.3 ± 4.4 g pentane m−3 h−1; RE = 68.3%). This overall performance improvement was in line with the short peak perturbation experiments carried out during the operational time which demonstrated, by net retention time (NRT) determination, to be a fast and reliable tool to gain insights into the behaviour of pollutants inside the BF and its state. Pentane demonstrated to have larger interactions with the packing material when HFS was added. NRT/EBRT ratio variated along the whole operational time, being larger at the last stage.

Dynamic performance of a fungal biofilter packed with perlite for the abatement of hexane polluted gas streams using SIFT-MS and packing characterization with advanced X-ray spectroscopy

The use of Fusarium solani fungi in an expanded perlite packed biofilter was investigated for the treatment of a hexane polluted waste gas stream using selected ion flow tube mass spectrometry (SIFT-MS). The latter analytical technique proved to be of utmost importance to evaluate the performance of the biofilter at high time resolution (seconds) under various transient conditions, analogous to industrial situations.The biofilter was operational for 277 days with inlet loads varying between 1 and 14 g m−3 h−1 and applying an empty bed residence time of 116 s. The results showed a positive behaviour of the biofilter against different types of disruptions such as: (i) changes in the relative humidity of the inlet gas, (ii) stopping the carbon supply for 1, 5 and 10 days, (iii) varying the inlet hexane concentration (step increases and intermittent pulses) and (iv) limiting the availability of nutrients.X-ray imaging (both conventional 2D μCT and X-ray fluorescence, XRF) was applied for the first time on biofilter media in order to get insight in the internal structure of expanded perlite and to visualise the biomass growth. The latter in combination with online porosity measurements using SIFT-MS provides fundamental information regarding the biofiltration process.

Preliminary Investigation of CO2 Sequestration by Chlorella sorokiniana TH01 in Single and Sequential Photobioreactors

Increasing accumulation of CO2 in the atmosphere mainly caused by fossil fuels combustion of human activities have resulted in adverse global warming. Therefore, searching for treatment methods for effective utilization of CO2 have received a great attention worldwide. Among various methods (e.g., adsorption, absorption, storage, membrane technologies, etc.) have been developed and applied, the sequestration of CO2 using microalgae has recently emerged as an alternatively sustainable approach. In this work, a green microalgal strain Chlorella sorokiniana TH01 was used to investigate its capability in sequestration of CO2 in laboratory scale. Results indicated that the C. sorokiniana TH01 grew well under a wide range of CO2 concentration from 0.04% to 20% with maximum growth was achieved under CO2 aeration of 15%. In a single photobioreactor (PBR) with 10 min empty bed residence time (EBRT), the C. sorokiniana TH01 only achieved CO2 fixation efficiency of 6.33% under continuous aeration of 15% CO2. Increasing number of PBRs to 15 and connected in a sequence enhanced mean CO2 fixation efficiency up to 82.64%. Moreover, the CO2 fixation efficiency was stable in the range of 78.67 to 91.34% in 10 following days of the cultivation. Removal efficiency of NO3--N and PO43--P reached 82.54 – 90.25% and 95.33 – 98.02%, respectively. Our trial data demonstrated that the C. sorokiniana TH01 strain is a promising microalgal for further research in simultaneous CO2 mitigation via CO2 sequestration from flue gas as well as nutrients recycling from wastewaters.&#x0D; Keywords: Carbon dioxide, C. sorokiniana TH01, Photobioreactors, Sequestration, Nutrients removal.

Screening and study of the degradation characteristics of efficient toluene degrading bacteria combinations

ABSTRACT In this paper, three effective toluene-degrading bacteria were obtained through acclimation and screening by using landfill leachate as the initial liquid strain. The three obtained bacteria were denoted as J1, J2 and J3, and identified as Pseudomonas, Bacillus and Staphylococcus, respectively. We then identified the optimal combination of these toluene-degrading bacteria in the laboratory. The combination of J1 + J3 (1:1) exhibited the highest toluene removal efficiency (RE). A vertical bio-trickling filter (BTF) packed with ceramsite was started by inoculation with the effective combination. The performance of the BTF in treating toluene under various operating conditions was investigated. After 17 days of operation, the toluene RE reached about 90% and the maximum elimination capacity reached 42.0 g m−3 h−1. The scanning electron microscope (SEM) showed that after the successful start-up of the BTF, the biofilm on the packing surface primarily consisted of Bacillus and Staphylococcus. During the stable state, the RE of the BTF was maintained above 80%, the shortest empty bed residence time was 34 s and toluene concentrations ranged between 300 and 800 mg m−3. The results indicate that the BTF started using the effective combination of bacteria described here is robust. This paper also provides a preliminary analysis of the mechanism of microbial degradation of pollutants in the BTF.

Multi-factorial analysis of the removal of dichloromethane and toluene in an airlift packing bioreactor

Biotechnology has proven effective in removing a wide variety of VOCs. In this study, the effects of pH (from 3 to 7), operating temperature (20−30 °C), empty bed residence time (EBRT, 10−40 s) and transient inlet concentration (400−4000 mg m−3) on the removal performance of an airlift packing bioreactor (ALPR) was investigated. The removal efficiency (RE) and stability of the ALPR was evaluated and compared with the conventional airlift bioreactor (ALR). The results showed that under the influence of single factor variation, the ALPR showed significant higher RE and better stability than the ALR in removing dichloromethane (DCM) and toluene. Besides, a factorial design was used to analyses the interaction of multiple factors and their influence on the removal of DCM and toluene in the ALPR and ALR. It shows that pH value has the most significant influence, and plays a crucial role in maintaining high RE of DCM and toluene in both of the ALPR and ALR. Temperature has a great effect on the removal of toluene. EBRT has certain effect on the removal of DCM in the ALPR. The transient concentration of a single substrate has a significant negative effect on the RE of this substrate, while it does not significantly affect the removal of another substrate in the ALPR. However, the steep increase of DCM concentration has an adverse effect on the RE of high concentration toluene in the ALR. The overall RE and degradation capacity of both toluene and DCM by the ALPR are much higher than that of the conventional ALR.

Release of formaldehyde during the biofiltration of methanol vapors in a peat biofilter inoculated with Pichia pastoris GS115

Methanol can be effectively removed from air by biofiltration (Shareefdeen et al., 1993; Babbitt et al., 2009 [1,2]). However, formaldehyde is one of the first metabolic intermediates in the consumption of methanol in methylotrophic microorganisms (Negruţa et al., 2010 [3]), and it can be released out of the cell constituting a secondary emission. The total removal of methanol was achieved up to input loads of 263 g m−3 h−1 and the maximum elimination capacity of the system was obtained at an empty bed residence times of 90 s and reached 330 g m−3 h−1 at an input methanol load of 414 g m−3 h−1 and 80% of removal efficiency. Formaldehyde was detected inside the biofilter when the input methanol load was above 212 g m−3 h−1. Biomass in the filter bed was able to degrade the formaldehyde generated, but with the increase of the methanol input load, the unconsumed formaldehyde was released outside the biofilter. The maximum concentration registered at the output of the system was 3.98 g m−3 when the methanol load was 672 g m−3 h−1 in an empty bed residence times of 60 s. Formaldehyde is produced inside a biofilter when methanol is treated in a biofiltration system inoculated with Pichia pastoris. Biomass present in the reactor is capable of degrading the formaldehyde generated as the concentration of methanol decreases. However, high methanol loads can lead to the generation and release of formaldehyde into the environment. How to cite: Guerrero K, Arancibia A, Caceres M, et al. Release of formaldehyde during the biofiltration of methanol vapors in a peat biofilter inoculated with Pichia pastoris GS115. Electron J Biotechnol 2019;40. https://doi.org/10.1016/j.ejbt.2019.04.003.

Performance evaluation and microbial community analysis of the composite filler micro-embedded with Pseudomonas putida for the biodegradation of toluene

The composite filler micro-embedded with Pseudomonas putida (P. putida) was prepared and the biodegradation performance of the filler was evaluated in a biofilter. Five phases were set up to evaluate the performance of the biofilter under different toluene inlet loadings and transient shock loadings. In particular, the microbial community structure in the biofilms and fillers was measured by sequence analysis of the 16S rRNA gene. The results show that the biofilter packed with the composite fillers was suitable for the biodegradation of toluene. The biofilter could start up quickly with high removal efficiency (RE), and remain above 90 % RE when the empty bed residence time (EBRT) was 18 s and the inlet loading rates were not higher than 41.4 g/(m3·h). Moreover, the biofilter could tolerate substantial transient shock loadings. The high removal efficiency and elimination capacity contributed to rich bacterial communities for the efficient degradation of toluene. The dominant microbial communities at the phylum level were mainly Firmicutes, Actinobacteria and Proteobacteria. It is noteworthy that the abundance of Bacteroidetes at phylum level and Chungangia and Stenotrophomonas at genus level increased significantly during the re-start period.

Performance evaluation of a biotrickling filter for the removal of gas-phase 1,2-dichlorobenzene: Influence of rhamnolipid and ferric ions

The aim of this study was to evaluate the influence of rhamnolipid (RL) and ferric ions on the performance of a biotrickling filter (BTF) for the removal of gas-phase 1,2-dichlorobenzene (o-DCB). A comprehensive investigation of microbial growth, pollutant solubility, extracellular polymeric substances (EPS) and enzymatic activity in o-DCB degradation by an isolated strain Bacillus cereus DL-1 with/without RL and Fe3+ were carried out using batch microcosm experiments. In addition, o-DCB removal performance, biofilm morphology, and microbial community structures in two identical lab-scale biotrickling filters (named BTF1 and BTF2) inoculated with strain DL-1 were studied. The batch microcosm experiments demonstrated that 120 mg L−1 RL and 4 mg L−1 Fe3+ could enhance the biodegradation of o-DCB, which may be due to promotion on bacterial growth, o-DCB solubilization, C12O enzyme activity, and polysaccharide (PS) and protein (PN) in EPS. Fourier transform infrared (FTIR) spectra indicated that the addition of RL with Fe3+ had notable effects on the functional groups of PS and PN in EPS. The experimental results in BTFs indicate that the removal efficiency of o-DCB decreased from 100% to 56.4% for BTF1, which was not fed with RL and Fe3+, and from 100% to 80.3% for BTF2, which was fed with RL and Fe3+, when the inlet loading rate increased from 4.88 to 102 g m−3 h−1 at an empty bed residence time of 60 s. In addition, the microbial adhesive strength and the microbial community structure were different among both BTFs, highlighting the positive effects of RL and Fe3+.

Two‐step method for the construction and start‐up of a fungal–bacterial biofilter for treating gaseous toluene

AbstractIn this study, a two‐step method was applied to build and start up a fungal–bacterial biofilter. The reactor was built by controlling pH and adding an antibiotic based on a conventional biofilter. A low pH (5.9) and the addition of chloramphenicol were favorable for the construction of the fungal–bacterial biofilter. The results illustrated that it took only 15 days to complete the start‐up of the fungal–bacterial biofilter. The removal efficiency (RE) and the mineralization rate (MR) were 93.0% and 77.6%, respectively, at a toluene concentration of 1,000 ± 112 mg m−3 and an empty bed residence time (EBRT) of 45 s. The new method effectively overcomes the unstable performance and nonuniversality of such a reactor, which was constructed by inoculating a pure fungal culture into a bacterial biofilter. Removal performance comparison and PICRUSt analysis showed that the higher the relative abundance of benzoate degradation‐related genes in activated sludge is, the more suitable the sludge is for inoculation. The increase in toluene MR and the apparent morphology and scanning electron microscopy (SEM) results of biofilms in the top layer of the fungal–bacterial biofilter suggest that the biofilter performance enhancement can be attributed to the ability of fungi to distribute toluene‐degrading bacteria.

Effect of concentration and gas flow rate on the removal of gas-phase trichloroethylene in a novel packed biofilter

A lab-scale biofilter system packed with a mixture of bamboo-clay and turkey litter compost (novel) was developed to remove trichloroethylene (TCE) vapor which was artificially generated. After 60 days of a start-up, the maximum removal efficiency of 90% achieved at a loading rate of 43 g m−3 h−1 with empty bed residence time (EBRT) of 1.6 min in continuous mode. About 65% of TCE eliminated at the first 18 cm of the bed height. During biofiltration, the pressure drop found to vary in acceptable ranges of 20–71 mmHg m−1. The carbon dioxide (CO2) production profile confirms that the TCE mineralized by mixed culture. The compost biofilter showed a quick response to the transient condition. The biokinetic constants estimated and explained the behavior of TCE biofiltration. This is the first study to provide a promising tool for the removal of a high concentrated TCE in a novel packed bed biofilter.

Simultaneous removal of siloxanes and H2S from biogas using an aerobic biotrickling filter

The feasibility of simultaneous removal of siloxane and H2S from biogas was investigated using an aerobic biotrickling filter (BTF). The biodegradation of H2S in the BTF followed a first-order kinetic model and more than 95 % H2S was eliminated within a residence time of 0.3 min. The removal of decamethylcyclopentasiloxane (D5) increased with longer empty bed residence time (EBRT). The partition test and microbial community analysis further reveals that up to 52 % removal of D5 was reached mainly by the chemical-absorption in acid recycling liquid. Finally, D5 was converted into mixtures of dimethylsilanediol (DMSD) and hexamethyldisiloxane (L2) via ring-opening hydrolysis in acid liquid and ring-shrinking polyreaction using CH4 derived from biogas. These operational characteristics demonstrate that the abiotic removal of D5, in addition to biological removal of H2S in an aerobic BTF can significantly decrease the siloxane loading to the downstream siloxane removing units.

Trimethylamine abatement in algal-bacterial photobioreactors.

Trimethylamine (TMA) is an odorous volatile organic compound emitted by industries. Algal-based biotechnologies have been proven as a feasible alternative for wastewater treatment, although their application to abate polluted air emissions is still scarce. This work comparatively assessed the removal of TMA in a conventional bacterial bubble column bioreactor (BC) and a novel algal-bacterial bubble column photobioreactor (PBC). The PBC exhibited a superior TMA abatement performance compared to the conventional BC. In this sense, the BC reached a removal efficiency (RE) and an elimination capacity (EC) of 78% and 12.1g TMA m-3h-1, respectively, while the PBC achieved a RE of 97% and a EC of 16.0g TMA m-3·h-1 at an empty bed residence time (EBRT) of 2min and a TMA concentration ~500mgm-3. The outstanding performance of the PBC allowed to reduce the operating EBRT to 1.5 and 1min while maintaining high REs of 98 and 94% and ECs of 21.2 and 28.1gm-3·h-1, respectively. Moreover, the PBC improved the quality of the gas and liquid effluents discharged, showing a net CO2 consumption and decreasing by ~ 30% the total nitrogen concentration in the liquid effluent via biomass assimilation. A high specialization of the bacterial community was observed in the PBC, Mumia and Aquamicrobium sp. being the most abundant genus within the main phyla identified. GraphicalAbstract.

Steady State, transient behavior and kinetic modeling of benzene removal in an aerobic biofilter

The performance of the benzene microbial biofilter conducted under both continuous and transient operations. Mixed culture retrieved from the cow dung compost and inoculated within the biofilter. After the acclimatization period, it was studied continuously for 35 days at different empty bed residence times (EBRT) and up to the benzene concentration of 1.72 g m−3. Elimination capacity (EC) evaluated at different inlet loading rates (ILR) of benzene. The removal efficiency attained ranging from 37 to 84 %. Besides, the pressure drop increased during the biofiltration due to the accumulation of biomass on the packing. The restoration of biological activity observed within a few days of transient operation. The production of carbon dioxide (CO2) increased with the increasing elimination capacity during the degradation in the biofilter. However, the kinetics of biofilter was investigated using the macrokinetic method and application of the Michaelis-Menten model. Theoretical biofilm thickness in the biofilter was calculated to be 1.89 mm. ECmax and ks was found to be 0.2777 g m3 sec-1 and 0.008 g m−3 with R2 of 0.865.

Effect of photocatalytic pretreatment on the biodegradation of n-hexane vapours in a biofilter

Hydrophobic volatile organic compounds (VOCs) such as n-hexane are not completely biodegradable by a single biofilter. So, in the present study, a photoreactor system packed with scoria granules coated with TiO2, as a pretreatment unit, was used for increasing the removal efficiency of n-hexane by a biofilter during an operation period of 191 days. The inlet and outlet concentration of n-hexane was analyzed with a gas chromatography coupled with a flame ionization detector (GC/FID). The results indicated that the removal efficiency of the single biofilter with input concentrations of 0.18 – 1 g/m3 at empty bed residence times (EBRTs) of 30, 60, and 120 s was 10.06%, 21.45%, and 46.8%, respectively. When the photoreactor was used as a pretreatment system, the removal efficiency of the combined system in corresponding EBRTs was improved to 39.79%, 63.08%, and 92.60%, respectively. The results proved that the combined system provided higher removal efficiencies than the single biofilter. Thus, the application of the photoreactor as a pretreatment step was much effective in increasing the removal efficiency of n-hexane from the polluted air by the biofilter.

Biodegradation of o-dichlorobenzene by Bacillus cereus DL-1：kinetics, degradation pathway, biodegradability and performance in biotrickling filter

ABSTRACT o -Dichlorobenzene could be mineralized as the sole carbon and energy source by Bacillus cereus DL-1. In this work, Haldane–Andrews and pseudo-first-order models were used to simulate the growth and degradation abilities of the strain. Two possible degradation pathways were identified by GC/MS intermediate and open-loop analysis. The removal efficiency (RE) of biotrickling filter (BTF) could reach 57.86% at the start phase. At the steady phase, the effects of empty bed residence time (EBRT), inlet gas concentration and intake load rate (ILR) on the performance of BTF have highlighted the potential of strain DL-1 for the treatment of o-dichlorobenzene.

On-Farm Testing of a Zeolite Filter to Capture Ammonia and Odors from a Dairy Manure Flushing System

Highlights A zeolite filter achieved 92% reduction in ammonia emissions from a dairy flushed manure pit. The reduction in odor concentration was 45% at a minimum filter residence time of 0.9 seconds. The on-farm filter and air collection structure over a manure pit demonstrated the applicability of the project. Abstract. The concentration of large numbers of animals in relatively small areas, high production output per animal unit, and concentration of animal excretions and air emissions are some of the characteristics of modern animal agriculture. Ammonia (NH3) and odors are among the most noticeable as well as locally and regionally problematic emissions generated by concentrated animal feeding operation (CAFO) dairy production systems. Zeolites are defined as aluminosilicates with open three-dimensional framework structures composed of corner-sharing TO4 tetrahedra, where T is Al or Si. Zeolites are able to lose or gain water reversibly and to exchange and retain cations, including NH3 and ammonium. This study demonstrated the design and performance of a zeolite filter treating the airstream from a flushed manure pit installed on-farm at a commercial dairy. Clinoptilolite zeolite mined in Idaho was used as the filter medium. The capacity of the filter to reduce NH3 emissions was tested at three, six, and 59 days of filter operation. Reduction of odor emissions was tested at six days of operation. NH3 emissions were reduced by 92% (p &amp;lt; 0.001) at three days of operation and by 42% (p = 0.13) at 59 days of operation. The ammonia concentration in the pre-treatment airstream from a dairy manure collection pit was relatively high at 5.287 ±0.04 mg NH3-N m-3 (p &amp;lt; 0.001). The odor concentration reduction was 45% (p = 0.001) at six days of operation with the minimum empty bed residence time of 0.9 s. Total trial running time was 59 days. The roof-like pit cover structure used for air collection and the zeolite filter were proven to be capable of operating in the harsh on-farm environment and to be adaptable to changing operating conditions within the dairy. Keywords: Air filtration, Ammonia, Clinoptilolite, Dairy, Manure, Odor, Zeolite

Improved degradation of n-hexane vapours using a hybrid system, a photoreactor packed with TiO2 coated-scoria granules and a multilayer biofilter.

Biofiltration of hydrophobic and/or recalcitrant volatile organic compounds such as n-hexane is imperfect. In the present study, we applied a hybrid system consisting of a photoreactor packed with scoria granules coated with TiO2 and a biofilter to improve the removal efficiency of n-hexane from the air stream. The experimental results showed that the hybrid system provided higher removal efficiencies than the single biofilter process with an inlet n-hexane concentration range of 0.11-1g-3 for empty bed residence times (EBRTs) of 30-120s in the hybrid system. The removal efficiency of the single biofilter in EBRTs of 30, 60 and 120s was 10.06%, 21.45%, and 45.98%, respectively. When the photoreactor was included as a pretreatment system (with residence time of 7-27s) and the overall EBRTs of the system was adjusted to 30, 60 and 120s, the removal efficiency of the hybrid system was increased to 39.79%, 63.08%, and 92.6%, respectively. The mass ratio of carbon dioxide produced as an indicator for n-hexane degradation in the hybrid system and the biofilter alone was 1.9 and 1.28, respectively. Bacterial community analysis with sequence analysis of 16S rDNA in the biofilter biomass revealed that Pseudomonas and Bacillus as predominant bacterial species were responsible for n-hexane biodegradation. Therefore, the application of the hybrid system is advantageous in enhanced n-hexane removal from the air stream.

Enhanced biodegradation of styrene vapors in the biotrickling filter inoculated with biosurfactant-generating bacteria under H2O2 stimulation

Biotrickling filters (BTFs) applied to hydrophobic volatile organic compounds (VOCs) suffer from limited mass transfer. Phase transfer kinetic and equilibrium effects limit the biodegradation of hydrophobic VOCs especially at high concentrations. This study evaluates two strategies for overcoming the problem. First, a natural process was used to enhance the aqueous availability of styrene, a hydrophobic VOC model, by inoculating the BTF with a mixture of biosurfactant–generating bacteria. This method achieved a maximum elimination capacity (ECmax) of 139 g m-3h−1 in the BTF at an empty bed residence time (EBRT) of 60s. The highest concentrations of the biosurfactants surfactin and rhamnolipid were 205 and 86 mg L-1, respectively, in this step. Sequencing 16S rRNA confirmed the presence of biosurfactant-producing bacteria capable of biodegrading styrene in the BTF including Bacillus sonorensis, Bacillus subtilis, Lysinibacillus sphaericus, Lysinibacillus fusiformis, Alcaligenes feacalis, Arthrobacter creatinolyticus, and Kocuria rosea. Second, the effect of adding H2O2 to the recycle liquid on the BTF performance was determined. The biodegradation and mineralization of styrene in the BTF operated at a loading rate of 266 g m-3h−1 and H2O2/styrene molar ratio of 0.05 with EBRT as short as 15 s were 94% and 53%, respectively, with the EC of 250 g m-3h−1. High concentrations of antioxidant enzymes (peroxidase and catalase: 56 and 7 U gbiomass-1, respectively) were produced and biosurfactant generation was increased in this step, contributing to enhanced styrene biodegradation and mineralization. The styrene biodegradation and mineralization values in the BTF in the last day operated under similar conditions but without H2O2 were 11.4% and 5.3%, respectively. The bacterial population had no considerable change in the BTF after adding H2O2. Accordingly, stimulating the BTF inoculated with biosurfactant-generating bacteria with H2O2 is a promising strategy for improving the biodegradation of hydrophobic VOCs.

Influence of phosphorus and trace metals in biofilters treating gaseous VOCs using a novel irrigation system

ABSTRACT Although the appropriate supply of nutrients has been extensively researched, more information is required on the effects of nutrients in treating gaseous volatile organic compounds (VOCs) in biofiltration. In this study, the effects of phosphorous and trace metals on gaseous toluene and methyl ethyl ketone (MEK) removal were investigated. The transfer of nutrients from the irrigation liquid to the packed bed, and the consumption and holding amount of nutrients in the packing material were observed during biofiltration. Under conditions of 20–24 s of empty bed residence time, MEK removal was 95% or more in all conditions of the biofiltration reactors, whereas toluene removal was affected by the operating conditions of the reactors. Consumption ratio of phosphorus to carbon was from 1.7 × 10−4 to 1.1 × 10−3 in the steady state of VOC removal under the conditions of this study. When gaseous VOC treatment was restarted after nine days of shutdown, a significant decline in toluene removal was observed by the reactor in which phosphorus supply was approximately one fifth of the amount in another reactor. Two types of irrigation systems, soaking and spraying, were compared and soaking irrigation achieved a more even distribution of nutrients held inside the packed bed. Soaking irrigation was expected to lead to higher VOC removal capacity by this distribution effect of nutrients, but toluene removal in the reactor with this irrigation was lower than that in the reactor with spraying irrigation. One of the possible reasons for this was the inhibition of nutrients transfer in the bottom part of the reactor. The trend of transfer in all ingredients from the irrigation liquid to the packed bed was synchronized on the whole; however, this transfer relatively tended to be high in nitrate and sodium and low in ammonium and phosphate. Implications: A major concern about using biofiltration systems to treat VOCs is the uncertainty regarding the appropriate nutrient supply to the filter bed to preserve microbial activity. This study showed that all the elements, except nitrogen, were retained sufficiently in the filter bed when a proper composition of nutrient solution was used for irrigation; however, phosphate addition may be needed when restarting a reactor from a prolonged period of shutdown. Distinct differences in the amount of transfer to the filter bed for different ingredients are probable, and may have to be taken into account when operating biofiltration reactors.