o-Xylene removal using one- and two-phase partitioning biotrickling filters: steady/transient-state performance and microbial community

Study on Gaseous Chlorobenzene Treatment by a Bio-Trickling Filter: Degradation Mechanism and Microbial Community

Large-flow waste gas generated from the pharmaceutical and chemical industry usually contains low concentrations of VOCs (volatile organic compounds), and it is also the key factor that presents challenges in terms of disposal. To date, due to the limitations of mass transfer rate and microbial degradation ability, the degradation performance of VOCs using the biological method has not been ideal. Therefore, in this study, the sludge from a chlorobenzene-containing wastewater treatment plant was inoculated into our experimental bio-trickling filter (BTF) to explore the feasibility of domestication and degradation of gaseous chlorobenzene by highly active microorganisms. The kinetics of its mass transfer reaction and microbial community dynamics were also discussed. Moreover, the main process parameters of BTF for chlorobenzene degradation were optimized. The results showed that the degradation effect of chlorobenzene reached more than 85% at an inlet concentration of chlorobenzene 700 mg·m−3, oxygen concentration of 10%, and an empty bed retention time (EBRT) of 80 s. The mass transfer kinetic analysis indicated that the process of chlorobenzene degradation in the BTF occurred between the zero-stage reaction and the first-stage reaction. This BTF contributed significantly to the biodegradability of chlorobenzene, overcoming the limitation of gas-to-liquid/solid mass transfer of chlorobenzene. The analysis of the species diversity showed that Thermomonas, Petrimona, Comana, and Ottowia were typical organic-matter-degrading bacteria that degraded chlorobenzene efficiently with xylene present.

Evaluation of Parallel-Series Configurations of Two-Phase Partitioning Biotrickling Filtration and Biotrickling Filtration for Treating Styrene Gas-Phase Emissions

The removal of styrene from industrial representative gaseous emissions was studied using two reactors connected in series: a two-phase partitioning biotrickling filter (TPPB-BTF) and a conventional biotrickling filter (BTF). The system was operated under industrial conditions, which included steady and transient conditions and intermittent spraying. Silicone oil was used in the TPPB-BTF with a quantity as low as 25 mL L−1, promoting a faster start-up compared to the BTF. By working at a styrene loading of 30 g m−3 h−1, nearly complete removal efficiency (RE) was obtained. In addition, the removal was not adversely impacted by using non-steady emission patterns such as overnight shutdowns (97% RE) and oscillating concentrations (95% RE), demonstrating its viability for industrial applications. After 2 months from inoculation, two additional configurations (reverse series BTF + TPPB-BTF and parallel) were tested, showing the series configuration as the best approach to consistently achieve RE > 95%. After 51 days of operation, high throughput sequencing revealed a sharp decrease in the bacterial diversity. In both reactors, the microorganisms belonging to the Comamonadaceae family were predominant and other styrene degraders such as Pseudomonadaceae proliferated preferably in the first reactor.

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.

Shift of microbial diversity and function in high-efficiency performance biotrickling filter for gaseous xylene treatment

Xylene is the main component of many volatile industrial pollution sources, and the use of biotechnology to remove volatile organic compounds (VOCs) has become a growing trend. In this study, a biotrickling filter for gaseous xylene treatment was developed using activated sludge as raw material to study the biodegradation process of xylene. Reaction conditions were optimized, and long-term operation was performed. The optimal pH was 7.0, gas-liquid ratio was 15:1 (v/v), and temperature was 25 °C. High-throughput sequencing technique was carried out to analyze microbial communities in the top, middle, and bottom layers of the reactor. Characteristics of microbial diversity were elucidated, and microbial functions were predicted. The result showed that the removal efficiency (RE) was stable at 86%-91%, the maximum elimination capacity (EC) was 303.61 g·m^-3·hr^-1, residence time was 33.75 sec, and the initial inlet xylene concentration was 3000 mg·m^-3, which was the highest known degradation concentration reported. Kinetic analysis of the xylene degradation indicated that it was a very high-efficiency-activity bioprocess. The r_max was 1059.8 g·m^-3·hr^-1, and K_s value was 4.78 g·m^-3 in stationary phase. In addition, microbial community structures in the bottom and top layers were significantly different: Pseudomonas was the dominant genus in the bottom layer, whereas Sphingobium was dominant in the top layer. The results showed that intermediate metabolites of xylene could affect the distribution of community structure. Pseudomonas sp. can adapt to high concentration xylene-contaminated environments. Implications: We combined domesticated active sludge and reinforced microbial agent on biotrickling filter. This system performed continuously under a reduced residence time at 33.75 sec and high elimination capacity at 303.61 g·m^-3·hr^-1 in the biotrickling reactor for about 260 days. In this case, predomestication combined with reinforcing of microorganisms was very important to obtaining high-efficiency results. Analysis of microbial diversity and functional prediction indicated a gradient distribution along with the concentration of xylene. This implied a rational design of microbial reagent and optimizing the inoculation of different sites of reactor could reduce the preparation period of the technology.

Enhanced biological removal of intermittent VOCs and deciphering the roles of sodium alginate and polyvinyl alcohol in biofilm formation

Developing a robust biofilm is a prerequisite for a biotrickling filter to obtain the good performance in removing volatile organic compounds (VOCs). But the biofilm formation can be seriously disturbed under intermittent loading condition due to carbon starvation stress in idle time. In this study, a biotrickling filter, with its packing materials being modified by 3% sodium alginate and 5% polyvinyl alcohol (v/v = 1:3), was employed to treat intermittent VOCs. Results showed that the removal efficiencies of toluene, ethylbenzene, p-xylene, m-xylene, and o-xylene was significantly enhanced in the BTF compared to the control one. Under relatively lower inlet loading, nearly complete removal of the five pollutants was achieved. A quantitative analysis showed that the concentration of total organic compound (TOC) in the leachate maintained at a high level, and had a strongly positive correlation with the divergence of microbial communities. The capacity of biofilm formation in the BTF was approximately four-fold higher than the control BTF, while the quantity of EPS secreted was more than ten-fold. EPS comprised largely of protein, and to less extent, polysaccharide. The biofilm formed on the modified packing materials maintained higher levels of microbial diversity and stability, even when modifiers were complete depleted or the VOCs inlet loading was increased. This study highlights the importance of packing materials for reducing the gap in performance between laboratory and industrial applications of BTFs.

Evaluation on the removal performance of dichloromethane and toluene from waste gases using an airlift packing reactor

Biological removal of dichloromethane (DCM) from pharmaceutical industry is limited by its recalcitrance. In this study, an airlift packing reactor (ALPR), which combined the suspended and fixed-film microbial growth system, was set up to remove DCM and co-existed toluene. The removal performance of the ALPR for DCM was greater than traditional airlift reactor (ALR). The maximum elimination capacity (EC_max) of the ALPR for DCM reached 108 g m^-3 h^-1 with removal efficiency (RE) of 41%, increased by 145% if compared to the ALR. The EC_max for toluene was 172 g m^-3 h^-1 with RE of 70%, decreased by 25% if compared to the ALR, which was mainly due to the higher liquid-phase biomass in the ALR. The results of high-throughput sequencing showed that the microbial composition on the packings of the ALPR had a large difference from its liquid-phase or the liquid-phase of the ALR. Gemmobacter, Rhizomicrobium, Chitinophaga, Vampirovibrio, and Fodinicurvata were genera with great abundance fixed on the packings and Rhizomicrobium, Chitinophaga, Vampirovibrio, and Fodinicurvata are first to be reported in VOCs biological removal. This study indicated that the ALPR can augment the microbial community and effectively improve the removal of recalcitrant VOCs.