Enhanced removal of mixed VOCs with different hydrophobicities by Tween 20 in a biotrickling filter: Kinetic analysis and biofilm characteristics

Biofiltration of toluene and ethyl acetate mixture by a fungal-bacterial biofilter: Performance and community structure analysis

The inhibitory effect of hydrophilic volatile organic compounds (VOCs) on hydrophobic VOCs removal was found to be efficiently reduced by the fungal-bacterial biofilters (F&B-BFs) developed in the present study. Overall, the toluene and ethyl acetate mixture removal efficiencies (REs) and elimination capacities (ECs) of F&B-BFs were superior to those of bacterial biofilters (B-BFs). The REs for toluene and ethyl acetate were 32.5 ± 0.8 % and 74.6 ± 1.0 %, respectively, for F&B-BFs, in comparison to 8.0 ± 0.3 % and 60 ± 1.3 % for B-BFs. The ECs for toluene and ethyl acetate were 13.0 g m-3 h-1 and 149.2 g m-3 h-1, respectively, for the F&B-BF, compared to 3.2 g m-3 h-1 and 119.6 g m-3 h-1 for the B-BFs. This was achieved at a constant empty bed residence time (EBRT) of 45 s. F&B-BFs exhibited a superior mineralization efficiencies (MEs) compared to B-BFs for a VOC mixture of toluene and ethyl acetate (≈36.1 % vs ~ 29.6 %). This is attributed to the direct capture of VOCs by the presence of fungi, increased the contact time between VOCs and VOCs-degrading bacteria, and even distribution of VOCs-degrading bacteria in the F&B-BFs. Moreover, compared with B-BFs, the coupling effect of genus Pseudomonas degradation, and unclassified_f_Herpotrichiellaceae and unclassified_p_Ascomycota adsorption of F&B-BF resulted in a reduction in the impact of the presence of hydrophilic VOCs on the removal of hydrophobic VOCs, thereby enhancing the biofiltration performance of mixtures of hydrophilic and hydrophobic VOCs.

Synchronous removal of gaseous toluene and benzene and degradation process shifts in microbial fuel cell-biotrickling filter system

Illustrating the biodegradation processes of multi-component volatile organic compounds (VOCs) will expedite the implication of biotechnology in purifying industrial exhaust. Here, performance shifts of microbial fuel cell and biotrickling filter combined system (MFC-BTF) are investigated for removing single and dual components of toluene and benzene. Synchronous removal of toluene (95 %) and benzene (97 %) are achieved by MFC-BTF accompanied with the output current of 0.41 mA. Elevated content of extracellular polymeric substance facilitates the mass transfer of benzene with the presence of toluene. Strains of Bacteroidota, Proteobacteria and Chloroflexi contribute to the removal of dual components VOCs. Empty bed reaction time and the VOCs concentration are the important factors influencing their dissolution in the system. The biodegradation of toluene and benzene proceeds with 2-hydroxymuconic semialdehyde and o-hydroxybenzoic acid as the main intermediates. These results provide a comprehensive understanding of multi-component VOCs removal by MFC-BTF and guide the system design, optimization, and scale-up.

Chemical structure of hydrocarbons significantly affects removal performance and microbial responses in gas biotrickling filters

The control of emissions of short-chain hydrocarbons with different structures is critical for the petrochemical industry. Herein, three two-carbon-containing (C2) hydrocarbons, ethane, ethylene, and acetylene, were chosen as pollutants to study the effects of chemical structure of hydrocarbons on removal performance and microbial responses in biotrickling filters. Results showed that the removal efficiency (RE) of C2 hydrocarbons followed the sequence of acetylene > ethane > ethylene. When the inlet loading rate was 30 g/(m3·h) and the empty bed residence time was 60 s, the RE of ethane, ethylene, and acetylene was 57 ± 4.0 %, 49 ± 1.0 %, and 84 ± 2.7 %, respectively. The high water solubility resulted in the high removal of C2 hydrocarbons, while a low surface tension enhanced the removal of C2 hydrocarbons. Additionally, the microbial community, enzyme activity, and extracellular properties of microorganisms also contributed to the difference in C2 hydrocarbon removal. These results could be referred for the effective control of light hydrocarbon emissions.

Effect of toluene on m-xylene removal in a biotrickling filter: Performance, biofilm characteristics, and microbial analysis

Hydrophobic volatile organic compounds (VOCs) pose a challenge to the removal efficiency in biotrickling filters (BTFs). The addition of relatively hydrophilic substances presents a promising approach for enhancing the elimination of hydrophobic VOCs. In this study, toluene was introduced into the BTF system alongside m-xylene, and their mixing ratios were changed to explore the interactions and mechanisms under different conditions. The result showed that the most pronounced synergistic interaction occurred when the mixing concentration ratio of m-xylene and toluene was 2:1. The removal efficiency (RE) of m-xylene increased from 88% to 97%, and the elimination capacity (EC) of m-xylene changed from 64 to 72 g m-3 h-1. Under this condition, there was a notable increase in biomass, extracellular polymeric substance (EPS) content, and relative hydrophobicity. Microbial diversity was enhanced observably with Berkeleyces and Mycobacterium potentially playing a positive role in co-degradation. Meanwhile, microbial metabolic function prediction indicated a significant enhancement in metabolic functions. Therefore, the introduction of relatively hydrophilic VOCs represents an effective strategy for enhancing the removal of hydrophobic VOCs in the BTFs.

Addition of (bio)surfactants in the biofiltration of hydrophobic volatile organic compounds in air

The removal of volatile organic compounds (VOCs) in air is of utmost importance to safeguard both environmental quality and human well-being. However, the low aqueous solubility of hydrophobic VOCs results in poor removal in waste gas biofilters (BFs). In this study, we evaluated the addition of (bio)surfactants in three BFs (BF1 and BF2 mixture of compost and wood chips (C + WC), and BF3 filled with expanded perlite) to enhance the removal of cyclohexane and hexane from a polluted gas stream. Experiments were carried out to select two (bio)surfactants (i.e., Tween 80 and saponin) out of five (sodium dodecyl sulfate (SDS), Tween 80, surfactin, rhamnolipid and saponin) from a physical-chemical (i.e., decreasing VOC gas-liquid partitioning) and biological (i.e., the ability of the microbial consortium to grow on the (bio)surfactants) point of view. The results show that adding Tween 80 at 1 critical micelle concentration (CMC) had a slight positive effect on the removal of both VOCs, in BF1 (e.g., 7.0 ± 0.6 g cyclohexane m-3 h-1, 85 ± 2% at 163 s; compared to 6.7 ± 0.4 g cyclohexane m-3 h-1, 76 ± 2% at 163 s and 0 CMC) and BF2 (e.g., 4.3 ± 0.4 g hexane m-3 h-1, 27 ± 2% at 82 s; compared to 3.1 ± 0.7 g hexane m-3 h-1, 16 ± 4% at 82 s and 0 CMC), but a negative effect in BF3 at either 1, 3 and 9 CMC (e.g., 2.4 ± 0.4 g hexane m-3 h-1, 30 ± 4% at 163 s and 1 CMC; compared to 4.6 ± 1.0 g hexane m-3 h-1, 43 ± 8% at 163 s and 0 CMC). In contrast, the performance of all BFs improved with the addition of saponin, particularly at 3 CMC. Notably, in BF3, the elimination capacity (EC) and removal efficiency (RE) doubled for both VOCs (i.e., 9.1 ± 0.6 g cyclohexane m-3 h-1, 49 ± 3%; 4.3 ± 0.3 g hexane m-3 h-1, 25 ± 3%) compared to no biosurfactant addition (i.e., 4.5 ± 0.4 g cyclohexane m-3 h-1, 23 ± 3%; hexane 2.2 ± 0.5 g m-3 h-1, 10 ± 2%) at 82 s. Moreover, the addition of the (bio)surfactants led to a shift in the microbial consortia, with a different response in BF1-BF2 compared to BF3. This study evaluates for the first time the use of saponin in BFs, it demonstrates that cyclohexane and hexane RE can be improved by (bio)surfactant addition, and it provides recommendations for future studies in this field.