Trickle-bed Air Biofilter Research Articles

Role of Fungal Biomass in N-Hexane Biofiltration

The biofiltration of n-hexane is studied to optimize determinants factors of hydrophobic VOC filtration efficiency. Four trickle-bed air biofilters (TBABs) were employed; two of which were supplied with nutrients buffered at a neutral pH, while another two at an acidic pH of 4 to induce and enhance fungal growth. The loading rate of n-hexane was kept constant in all TBABs at 13 g/m3/h. At each pH levels studied, the biomass of the TBABs was pre-acclimated using different ratios of n-hexane and methanol. The fungal biomass responsible for the degradation of n-hexane was then examined and quantified. Dichloran Rose Bengal Chloramphenicol agar was used for fungi quantification, and optical microscopy for classification. Effluent biomass was validated by measuring volatile suspended solids. Fungal counts resulting from n-hexane biodegradation were related to nitrate and carbon consumption. It was found that n-hexane elimination capacity closely followed biomass growth, and reached a steady-state at an optimum biomass density of roughly 3000 cfu/ml. Major shifts in fungal species were observed in all TBABs. Dominant fungal species grew slowly to become the most numerous, and were found to provide maximum elimination capacity, although TBABs pre-acclimated to higher methanol concentrations took less time to reach this steady-state. It was concluded, therefore, that steady and monitored growth of TBAB biomass is an essential factor in maximizing fungi’s ability to metabolize VOCs and that a new ecological biofiltration model may be the most effective at VOC purification. Keywords

Biofiltration of Chloroform in a Trickle Bed Air Biofilter Under Acidic Conditions.

In this paper, the application of biofiltration is investigated for controlled removal of gas phase chloroform through cometabolic degradation with ethanol. A trickle bed air biofilter (TBAB) operated under acidic pH 4 is subjected to aerobic biodegradation of chloroform and ethanol. The TBAB is composed of pelleted diatomaceous earth filter media inoculated with filamentous fungi species, which served as the principle biodegrading microorganism. The removal efficiencies of 5 ppmv of chloroform mixed with different ratios of ethanol as cometabolite (25, 50, 100, 150, and 200 ppmv) ranged between 69.9 and 80.9%. The removal efficiency, reaction rate kinetics, and the elimination capacity increased proportionately with an increase in the cometabolite concentration. The carbon recovery from the TBAB amounted to 69.6% of the total carbon input. It is postulated that the remaining carbon contributed to excess biomass yield within the system. Biomass control strategies such as starvation and stagnation were employed at different phases of the experiment. The chloroform removal kinetics provided a maximum reaction rate constant of 0.0018 s-1. The highest ratio of chemical oxygen demand (COD)removal/nitrogenutilization was observed at 14.5. This study provides significant evidence that the biodegradation of a highly chlorinated methane can be favored by cometabolism in a fungi-based TBAB.

Removal characteristics and mass balance analysis of ammonia in trickle bed air biofilter packed with polyurethane foam

Removal characteristics and mass balance analysis of ammonia in trickle bed air biofilter packed with polyurethane foam

Biological removal of chloroform in a controlled trickle bed air biofilter (Session 9)

Biological removal of chloroform in a controlled trickle bed air biofilter (Session 9)

Treatment of Dynamic Mixture of n-Hexane, Benzene, and Methanol and Fungi Community Characterization in an Integrated Scheme of Cyclic Adsorption/Desorption Beds and Trickle Bed Air Biofilter

This study investigates the effect of volatile organic compound (VOC) feed fluctuations on trickle bed air biofilters (TBABs) and the ability of a two-bed adsorption/desorption unit in dampening fluctuations. A mixture of n-hexane, benzene, and methanol with concentration ratios of 1:3:6.6 was fed to two parallel TBABs. To simulate feed fluctuations, four different square waves were applied. The total VOC loading rates (LRs) varied from 28.4 to 107.3 g/m3 h. The average concentration of VOCs applied to both TBABs was within allowable limits as determined in an earlier study. One TBAB was preceded by a two-bed cyclic adsorption/desorption unit (integrated unit), while the other TBAB (control unit) was directly subjected to the high and low peaks. n-Hexane elimination in the integrated unit was steady, and stable performance was obtained (75%-89%) based on the LRs, whereas the control unit showed erratic performance. The other two VOCs were mostly removed.

Biodegradation of a Ternary Mixture of Hydrophobic and Hydrophilic VOCs in Trickle Bed Air Biofilters

The main objective of this study was to evaluate the degradation of a ternary mixture of n-hexane, benzene, and methanol fed to two Trickle Bed Air Biofilters (TBABs) designated as “A” and “B”. Both TBABs were loaded with pelletized diatomaceous earth support media and run at an empty bed residence time (EBRT) of 120 s. TBABs “A” and “B” were operated at pH 4 and fed with n-hexane:benzene:methanol (CH:CB:CM) concentrations ratios of 1:3:10 and 1:3:6.6, respectively under different loading rates. The influent total loading rates varied from 39.2 to 117.7 g/m3h and from 32 to 96.4 g/m3h for TBABs “A” and “B”, respectively. In both TBABs, methanol and benzene were the most eliminated volatile organic compounds (VOCs), while the removal of n-hexane was controlled by the VOCs ratios. Higher removal efficiencies were obtained for the VOCs ratio of 1:3:6.6 corresponding to a total VOCs load of 96.4 g/m3h. The addition of VOCs mixture to the TBABs resulted in change of the fungi community within the TBABs as compared to the fungi community when the TBABs were previously receiving only n-hexane as a sole substrate.

Treatment of hydrophobic VOCs in trickling bed air biofilter: Emphasis on long-term effect of initial alternate use of hydrophilic VOCs and microbial species evolution

The main research objective of this study is to enhance the removal of recalcitrant compounds that are not readily bioavailable due to limiting mass transfer rate between the liquid and gas phases. Four trickle-bed air biofilters (TBABs), loaded with pelletized diatomaceous earth support media, were run at an empty bed residence time (EBRT) of 120 sec. After an acclimation period at constant loading rate (LR) of n-hexane (13.2 g m−3 hr−1) and intermittent feeding of methanol, n-hexane influent LR was then increased in step-wise fashion to 47.7 g m−3 hr−1 for biofilters receiving acidic nutrients (pH 4), and to 36.3 g m−3 hr−1 for biofilters receiving nutrient at pH 7. The results have shown that for TBABs receiving nutrient at pH 4, greater elimination capacities were obtained as compared to TBABs working at pH 7. n-Hexane removal efficiency of more than 84% at LR up to 47.7 g m−3 hr−1 was obtained for pH 4 nutrient-fed biofilters, while for biofilters with nutrients fed at pH 7, the removal efficiency did not exceed 64% for n-hexane LR of 36.3 g m−3 hr−1. The microbial analysis revealed that no fungal community was detected in TBABs run at neutral pH. The fungi communities that were initially acclimating TBABs run at pH 4, namely, Aspergillus niger and Fusarium solani, were not detected at the end of the experiment, while Gibberella moniliformis (Fusarium verticillioides) genus became the dominant species. Gibberella moniliformis (Fusarium verticillioides) was present along all the biofilter media and sustained very high n-hexane elimination at steady-state condition.Implications:With growing apprehension about sustainability and environmental protection, with limited resources available, and with the passage of the 1990 Amendments to the Clean Air Act, there is more need for using air pollution control techniques that are sound economically and proven environmentally friendly. Biofiltration systems, namely, trickle-bed air biofilters, were for decades recognized as efficient in treating air pollutants. Thus, the application of this technique over a wide industrial spectrum would certainly contribute to reduction of hazardous gas emissions.

Impact of alternate use of methanol on n-hexane biofiltration and microbial community structure diversity

The impact of introducing and suspending methanol on n-hexane biodegradation in trickle-bed-air-biofilters (TBABs) and the associated changes in microbial biodiversity is evaluated in this study. Four TBABs with n-hexane loading rate of 13.2g/m3h were evaluated. Two TBABs operated at pH 4 and the remaining at pH 7. The concentration ratios of methanol to n-hexane were 3:1 and 5:1, providing methanol loading rates of 37.7 and 64.5g/m3h, respectively. The removal efficiency (RE) of n-hexane in presence of methanol under pH 4 fluctuated between 81±5.7% and 88±11.6%. While for TBABs operating under pH 7, the RE varied between 34±12.7% and 69±11.2%. Methanol suspension triggered n-hexane REs of 93% and 82% for TBABs operating at pH 4 and pH 7, respectively. 16S and 18S rDNA sequencing analysis suggested that methanol inhibited n-hexane biodegrading microorganisms, while its suspension enhanced the microbial community diversity and promoted enrichment of the functional microorganisms degrading n-hexane.

Biological treatment of n-hexane and methanol in trickle bed air biofilters under acidic conditions

This study focuses on evaluating the degradation of n-hexane/methanol mixture in trickle-bed-air-biofilters (TBABs). Two different concentration ratios of methanol:n-hexane were evaluated (3:1) for TBAB “A” and (5:1) for TBAB “B”. Both TBABs were run and fed with nutrients buffered at pH 4 for encouraging the growth of fungi. The TBABs were loaded with pelletized diatomaceous earth support media and were run at an empty bed residence time of 120s. n-Hexane loading rates (LRs) ranged from 0.9 to 13.2g/m3h for both TBABs. The corresponding methanol LRs varied from 2.3 to 37.7g/m3h and from 4.6 to 64.5g/m3h for TBABs “A” and “B”, respectively. Experimental results have shown that the degradation of n-hexane in presence of methanol is enhanced for n-hexane LRs less than 10.6g/m3h as compared to previous study for sole-fed n-hexane, but for n-hexane LRs of 13.2g/m3h, the performance of TBABs in eliminating n-hexane depended on the methanol to n-hexane ratios. The impact was less severe for TBAB “A” (RE 85%) as compared to TBAB “B” (RE 72%). This is attributed to the high LRs of methanol in TBAB “B”. n-Hexane performance stability was another advantage attained.

Effect of methanol on the biofiltration of n-hexane

This study investigated the removal of recalcitrant compounds in the presence of a hydrophilic compound. n-Hexane is used as a model compound to represent hydrophobic compounds. Methanol has been introduced in mixture with n-hexane in order to increase the bioavailability of n-hexane in trickle-bed-air-biofilters (TBABs). The mixing ratios investigated were: 70% methanol:30% n-hexane, and 80% methanol:20% n-hexane by volume. n-Hexane loading rates (LRs) ranged from 0.9 to 13.2gm−3h−1. Methanol LRs varied from 4.6 to 64.5gm−3h−1 and from 2.3 to 45.2gm−3h−1 depending upon the mixing ratio used. Biofilter performance, effect of mixing ratios of methanol to n-hexane, removal profile along biofilter depth, COD/nitrogen consumption and CO2 production were studied under continuous loading operation conditions. Results have shown that the degradation of n-hexane is significantly enhanced by the presence of methanol for n-hexane LRs less than 13.2gm−3h−1. For n-hexane LR greater than 13.2gm−3h−1, even though methanol had impacted n-hexane biodegradation, its removal efficiency was higher than our previous study for biodegradation of n-hexane alone, in presence of surfactant, or in presence of benzene. On the other hand, the degradation of methanol was not impacted by the presence of n-hexane.

Treatment of Benzene and n-Hexane Mixtures in Trickle-Bed Air Biofilters

ABSTRACT Trickle-bed air biofilters (TBABs) are suitable for treatment of hydrophilic volatile organic compounds, but they pose a challenge for hydrophobic compounds. Three laboratory-scale TBABs were used for the treatment of an airstream contaminated with different ratios of n-hexane and benzene mixtures. The ratios studied were 1:1, 2:1, and 1:3 n-hexane:benzene by volume. Each TBAB was operated at a pH of 4 and a temperature of 20 °C. The use of acidic-buffered nutrient solution was targeted for changing the microorganism consortium to fungi as the main biodegradation element. The experimental plan was designed to investigate the long-term performance of the TBABs with an emphasis on different mixture loading rates, removal efficiency with TBAB depth, volatile suspended solids, and carbon mass balance closure. n-Hexane loading rate was kept constant in the TBABs for comparison reasons and ranged from 4 to 22 g/(m3.hr). Corresponding benzene loadings ranged from 4 to 43 g/(m3.hr). Generally, benzene behavior in the TBAB was superior to that of n-hexane because of its higher solubility. n-Hexane showed improved performance in the 2:1 mixing ratio as compared with the other two ratios. IMPLICATIONS The use of biofilters is a cheap and attractive option; however, their application is limited because of several challenges. One of them is the reluctance of hydrophobic compounds for biodegradation and the coexistence of other compounds in air emissions. This paper evaluated the impact of different mixing ratios of two hydrophobic compounds and the effect of increasing influent concentration. Finally, a comparison is provided on the best performance attained for these hydrophobic compounds as single solutes. The results of this study will aid in the design and operation of full-scale biofilters.

Treatment of dynamic mixture of hexane and benzene vapors in a Trickle Bed Air Biofilter integrated with cyclic adsorption/desorption beds

One of the main challenges that face successful biofiltration is the erratic loading pattern and long starvation periods. However, such patterns are common in practical applications. In order to provide long-term stable operation of a biofilter under these conditions, a cyclic adsorption/desorption beds system with flow switching was installed prior to a biofilter. Different square waves of a mixture containing n-hexane and benzene at a 2:1 ratio were applied to the cyclic adsorption/desorption beds and then fed to a biofilter. The performance of this integrated system was compared to a biofilter unit receiving the same feed of both VOCs. The cyclic adsorption/desorption beds unit successfully achieved its goal of stabilizing erratic loading even with very sharp peaks at the influent concentration equalizing influent concentrations ranging from 10–470 ppmv for n-hexane to 30–1410 ppmv for benzene. The study included different peak concentrations with durations ranging from 6 to 20 min. The cyclic beds buffered the fluctuating influent load and the followed biofilter had all the time a continuous stable flow. Another advantage achieved by the cyclic adsorption/desorption beds was the uninterrupted feed to the biofilter even during the starvation where there was no influent in the feed. The results of the integrated system with regard to removal efficiency and kinetics are comparable to published results with continuous feed studies at the same loading rates. The removal efficiency for benzene had a minimum of 85% while for n-hexane ranged from 50% to 77% according to the loading rate. The control unit showed very erratic performance highlighting the benefit of the utilization of the cyclic adsorption/desorption beds. The biofilter was more adaptable to concentration changes in benzene than n-hexane.

Treatment of waste gas from the breather vent of a vertical fixed roof p-xylene storage tank by a trickle-bed air biofilter

This study applied a pilot-scale trickle-bed air biofilter (TBAB) system for treating waste gas emitted from the breather vent of a vertical fixed roof storage tank containing p-xylene (p-X) liquid. The volatile organic compound (VOC) concentration of the waste gas was related to ambient temperature as well as solar radiation, peaking at above 6300 ppmv of p-X and 25000 ppmv of total hydrocarbons during the hours of 8 AM to 3 PM. When the activated carbon adsorber was employed as a VOC buffer, the peak waste gas VOC concentration was significantly reduced resulting in a stably and efficiently performing TBAB system. The pressure drop appeared to be low, reflecting that the TBAB system could be employed in the prolonged operation with a low running penalty. These advantages suggest that the TBAB system is a cost-effective treatment technology for VOC emission from a fixed roof storage tank.

Removal of benzene under acidic conditions in a controlled Trickle Bed Air Biofilter

Trickle Bed Air Biofilters (TBABs) are considered to be economical and environmental-friendly for treatment of Volatile Organic Compounds (VOCs). Hydrophilic VOCs are easily degradable while hydrophobic ones pose a great challenge for adequate treatment due to the transfer of the VOC to the liquid phase. In this study the utilization of acidic pH is proposed for the treatment of benzene vapors. The acidic pH would encourage the growth of fungi as the main consortium. A TBAB operated at pH 4 was used for the treatment of an air stream contaminated with benzene under different loading rates ranging from 37 to 76.8g/(m3h). The purpose of introducing fungi was to compare the performance with traditional TBAB operating under neutral pH in order to assess the biodegradation of benzene in mixtures with other compounds favoring acidic conditions. The experimental plan was designed to assess long-term performance with emphasis based on different benzene loading rates, removal efficiency with TBAB depth, and carbon mass balance closure. At benzene loading rate of 64g/(m3h), the removal efficiency was 90%. At the maximum loading rate of 77g/(m3h), the removal efficiency was 75% marking the maximum elimination capacity for the TBAB at 58.8g/(m3h). Operating at acidic pH successfully supported the degradation of benzene in TBAB. It is worthwhile to note that benzene appears in mixtures with n-hexane and toluene, which are reported to be better degraded under such conditions.

Nitrogen utilization and biomass yield in trickle bed air biofilters

Nitrogen utilization and subsequent biomass yield were investigated in four independent lab-scale trickle bed air biofilters (TBABs) fed with different VOCs substrate. The VOCs considered were two aromatic (toluene, styrene) and two oxygenated (methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK)). Long-term observations of TBABs performances show that more nitrogen was required to sustain high VOC removal, but the one fed with a high loading of VOC utilized much more nitrogen for sustaining biomass yield. The ratio N consumption/N growth was an effective indicator in evaluating nitrogen utilization in the system. Substrate VOC availability in the system was significant in determining nitrogen utilization and biomass yield. VOC substrate availability in the TBAB system was effectively identified by using maximum practical concentrations in the biofilm. Biomass yield coefficient, which was driven from the regression analysis between CO 2 production rate and substrate consumption rate, was effective in evaluating the TBAB performance with respect to nitrogen utilization and VOC removal. Biomass yield coefficients (g biomass/g substrate, dry weight basis) were observed to be 0.668, 0.642, 0.737, and 0.939 for toluene, styrene, MEK, and MIBK, respectively.

A comparative study for destruction of n-hexane in Trickle Bed Air Biofilters

Trickle Bed Air Biofilter (TBAB) could be an attractive treatment option for removal of hydrophobic Volatile Organic Compounds (VOCs) from air streams. In this study, three independent parallel laboratory-scale TBABs were run simultaneously to degrade n-hexane, a hydrophobic VOC known to be difficult to degrade. The loading rate of n-hexane varied from 13.4 and 47.7 g/(m 3 h) (1.14–4.04 kg COD/(m 3 day)). The experimental plan was designed to operate one TBAB at pH 7, another at pH 7 utilizing surfactant for enhancing the solubility of n-hexane, and finally a third one operating at pH 4 to promote fungi growth. Elimination capacities up to 38.7 g/(m 3 h) (3.28 kg COD/(m 3 day)) were observed with a removal efficiency of 90% for the TBAB operating at pH 4. The operating conditions for the TBABs include 120 s of Empty Bed Residence Time (EBRT), 1.4 L/min air flow rate and fixed temperature of 20 °C. Biomass control within the TBAB was investigated through two strategies, namely, stagnation (off flow for 2 days/week) and flow switching.

Biofiltration of n‐hexane in the presence of benzene vapors

AbstractBACKGROUND: Degrading hydrophobic volatile organic compounds in biofilters is very challenging. Previous research in our laboratories examined the degradation of hydrophobic contaminants by several methods including changing the empty bed resident time, utilization of surfactants and change of the microorganism consortium. As n‐hexane is considered relatively soluble in benzene and alongside benzene is more soluble in water, it was anticipated that a mixture of both volatile organic compounds fed to a trickle bed air biofilters (TBABs) would lead to an improved performance of n‐hexane degradation.RESULTS: The ratio of benzene:n‐hexane studied was 2:1 by volume, corresponding to a concentration ratio of 3:1, respectively. The TBAB was operated at pH 4 to provide favorable conditions for fungi growth. The effects of changing loading rates ranging from 20 to 80 g m−3 h−1 on the biofilter performance, acclimation period, and removal profile along biofilter depth, nitrogen consumption and CO2 production were studied under continuous loading operation conditions and compared to previous data of TBABs degrading single feed of benzene and n‐hexane separately.CONCLUSIONS: Results have shown that the degradation of n‐hexane is significantly impacted by the presence of benzene; however, the degradation of benzene was not impacted to the same extent as n‐hexane. Copyright © 2010 Society of Chemical Industry

역세척공정을 이용한 Trickle Bed Air Biofilter의 혼합VOCs 분해특성 및 물질수지 고찰

VOC mixture was fed to a trickle bed air biofilter (TBAB) with step-change in influent mixture concentrations from 50 ppmv to 1,000 ppmv, corresponding to loadings of <TEX>$5.7\;g/m^3/hr$</TEX> to <TEX>$114.1\;g/m^3/hr$</TEX>. VOC mixture was an equimolar ratio of two aromatic VOCs, i.e., toluene and styrene, and two oxygenated VOCs, i.e., methyl ethyl ketone (MEK) and methyl isobutyl ketone (MIBK). The TBAB system employed backwashing as biomass control. The experimental results showed that a critical loading rate for VOC mixture removal was determined to be about <TEX>$60\;g/m^3/hr$</TEX>, and critical loading rates for individual VOCs in the mixture were different. Specifically, toluene content in the mixture played a major role in the biofilter overall performance. As VOC mixture was fed beyond the critical loading rate, reacclimation of the biofilter to reach the 99% removal efficiency following backwashing was delayed, which was a critical factor in the biofilter performance. In the mass balance analysis, 63.8% of the carbon equivalent in VOCs removal was used for <TEX>$CO_2$</TEX> production during the experimental runs. The 82.6% nitrogen utilized in the biofilter was contributed to microbial cell synthesis. The obtained results were compared against consistently high efficient performance of TBAB for VOC mixture by employing backwashing as biomass control.

Biological treatment of benzene in a controlled trickle bed air biofilter

Trickle bed air biofilters (TBABs) are suitable for treatment of relatively high volumes of volatile organic compounds due to their controlled environment. A laboratory-scale TBAB was used for the treatment of an air stream contaminated with benzene under different loading rates (LRs) ranging from 7.2 to 76.8 g m −3 h −1. The TBAB was operated at pH 7 and 25 °C. Consistent long-term performance of the benzene TBAB depends on various factors one of which is the excess amount of biomass accumulated within the bed. Three experimental strategies for biomass control were employed in the study: weekly backwashing for 1 h, starvation (no benzene feed for a period of 2 d/week) and stagnation (no benzene, air and nutrient flow for a period of 2 d/week). The experimental plan was designed to investigate the long-term performance of the TBAB with emphasis on the empty bed resident time (EBRT), different benzene LRs, removal efficiency with TBAB depth, volatile suspended solids and carbon mass balance closure. For benzene loading up to 34.1 g m −3 h −1, removal efficiency consistently over 98% was achieved. At the maximum LR 76.8 g m −3 h −1 the removal efficiency was still above 80% by utilizing stagnation strategy for 2 d and gas flow switching once per week as means of biomass control. Backwashing once per week provided less efficient performance as compared to stagnation while starvation showed the worst performance. EBRT at 120 s provided the best performance while EBRT at 90 s showed slightly lower performance.

Effect of Changing VOC Influent Composition on the Microbial Community Structure of TBABs

Microbial communities in trickle bed air biofilters (TBABs) were evaluated under conditions of interchanging the feed volatile organic compounds (VOCs) and VOC mixtures. Three independent TBABs (Biofilter “A,” “B,” and “C”) were run under interchanging VOCs conditions with different initial VOCs. Two aromatic compounds (toluene and styrene) and two oxygenated compounds (methyl ethyl ketone (MEK) and methyl isobutyl ketone (MIBK)) were interchanged as single solutes. Two other TBABs “D” and “E” were run for two VOC mixtures. Biofilter “D” had a VOC mixture with equal molar ratio of the four components and Biofilter “E” received a VOC mixture with its composition based on EPA 2003 emission report. Denaturing gradient gel electrophoresis (DGGE) analysis of 16S rRNA genes was used to assess the microbial richness in TBABs for treating the VOC mixtures and the impact of interchanging VOCs on the bacterial community structure in the biofilters. The results from DGGE indicated that the microbial community structure in the biofilter was different after each interchange of VOCs. Some bands of microbial species faded and some bands were strengthened. For the two TBABs treating VOC mixtures, the microbial species did not show significant difference, but the richness among these species was different from each other.