Contribution of bacterial biodiversity on the operational performance of a styrene biotrickling filter

A review of the recent progress in biotrickling filters: packing materials, gases, micro-organisms, and CFD

Organic pollutants in the air have serious consequences on both human health and the environment. Among the various methods for removing organic pollution gas, biotrickling filters (BTFs) are becoming more and more popular due to their cost-effective advantages. BTF can effectively degrade organic pollutants without producing secondary pollutants. In the current research on the removal of organic pollutants by BTF, improving the performance of BTF has always been a research hotspot. Researchers have conducted studies from different aspects to improve the removal performance of BTF for organic pollutants. Including research on the performance of BTF using different packing materials, research on the removal of various mixed pollutant gases by BTF, research on microbial communities in BTF, and other studies that can improve the performance of BTF. Moreover, computational fluid dynamics (CFD) was introduced to study the microscopic process of BTF removal of organic pollutants. CFD is a simulation tool widely used in aerospace, automotive, and industrial production. In the study of BTF removal of organic pollutants, CFD can simulate the fluid movement, mass transfer process, and biodegradation process in BTF in a visual way. This review will summarize the development of BTFs from four aspects: packing materials, mixed gases, micro-organisms, and CFD, in order to provide a reference and direction for the future optimization of BTFs.

Bioelectrochemical Purification of Biomass Polymer Derived Furfural Wastewater and Its Electric Energy Recovery

With the increasing environmental pollution caused by waste polymers, the conversion of polymer components in biomass into valuable products is of great significance for waste management and resource recovery. A two-stage microbial fuel cell (MFC) was used to treat furfural wastewater in this study. The maximum output voltage was 240-250 mV and the power generation time in an operation cycle was 286 h. The degradation efficiency of furfural reached 99-100% (furfural concentration at 300-3000 mg/L) and was slightly reduced to 91% at 7000 mg/L. In addition, the BOD/COD ratio of the furfural wastewater increased from 0.31 to 0.48 after MFC processing. The molecular analysis of the anodic bacterial isolates indicated that the phylogenetic bacterial mixture was dominated by five active anaerobic bacteria with a similarity percentage above 99% for each strain: Burkholderia (B. burdella), Clostridium sensu stricto (Cymbidaceae), Klebsiella (Klebsiella), Ethanoligenens (anaerobic genus), and Acidocella (anaerobic genus); the mixture exhibited good properties to carry out bioelectricity generation in the microbial fuel cell. This indicates that the MFC has effectively degraded furfural for pollutant removal and power generation and is a promising clean method to treat furfural pollution in industry wastewater.

Application of loofah and insects in a bio-trickling filter to relieve clogging

Bio-trickling filters (BTFs) use an inert filler to purify pollutants making them prone to clogging due to bacterial accumulation. To investigate the performance of a non-inert filler in BTF and its cooperation with insects to relieve clogging, a vertical BTF was constructed with a loofah/Pall ring/polydimethylsiloxane composite filler and selected bacteria to purify toluene. The BTF was started up within 17 d and restarted within 3 d after starvation for 12-16 d. Its average removal efficiency was >90% at steady state. The maximum elimination capacity of 86.4 g·(m³·h)^-1 was obtained at a volume capacity of 96.2 g·(m³·h)^-1. The introduction of holometabolous insects (Clogmia albipunctata) rapidly removed the biofilm and accelerated the degradation of the loofah, which alleviated clogging. Furthermore, confocal laser scanning microscope (CLSM) observations showed that the biofilm polysaccharides were difficult to remove, while lipids were readily lost. Analysis of microbial diversity over time and space revealed that the dominant bacterium, Comamonas, was replaced by diverse microflora with no obvious dominant genus. Insect introduction and loofah migration had little effect on the evolution of microflora. This study provides a promising approach to operating BTFs with less clogging.

Performance of a packed-bed anode bio-electrochemical reactor for power generation and for removal of gaseous acetone

The packed anode bioelectrochemical system (Pa-BES) developed in this study is a type of BES that introduces waste gas into a cathode and then into an anode, thereby providing the cathode with sufficient oxygen and reducing the amount of oxygen to the anode to promote the output of electricity. When the empty-bed residence time was 45 s and the liquid flowrate was 35 mL/s, the system achieved optimal performance. Under these conditions, removal efficiency, mineralization efficiency, voltage output, and power density were 93.86%, 93.37%, 296.3 mV, and 321.12 mW/m³, respectively. The acetone in the waste gas was almost completely converted into carbon dioxide, indicating that Pa-BES can effectively remove acetone and has the potential to be used in practical situations. A cyclic voltammetry analysis revealed that the packings exhibited clear redox peaks, indicating that the Pa-BES has outstanding biodegradation and power generation abilities. Through microbial community dynamics, numerous organics degraders, electrochemically active bacteria, nitrifying and denitrifying bacteria were found, and the spatial distribution of these microbes were identified. Among them, Xanthobacter, Bryobacter, Mycobacteriums and Terrimonawas were able to decompose acetone or other organic substances, with Xanthobacter dominating. Bacterium_OLB10 and Ferruginibacter are the electrochemically active bacteria in Pa-BES, while Ferruginibacter is the most abundant in the main anode, which is responsible for electron collection and transfer.

Effects of Water Content and Irrigation of Packing Materials on the Performance of Biofilters and Biotrickling Filters: A Review

Biofilters (BFs) and biotrickling filters (BTFs) are two types of bioreactors used for treatment of volatile organic compounds (VOCs). Both BFs and BTFs use packing materials in which various microorganisms are immobilised. The water phase in BFs is stationary and used to maintain the humidity of packing materials, while BTFs have a mobile liquid phase. Optimisation of irrigation of packing materials is crucial for effective performance of BFs and BTFs. A literature review is presented on the influence of water content of packing materials on the biofiltration efficiency of various pollutants. Different configurations of BFs and BTFs and their influence on moisture distribution in packing materials were discussed. The review also presents various packing materials and their irrigation control strategies applied in recent biofiltration studies. The sources of this review included recent research articles from scientific journals and several review articles discussing BFs and BTFs.

Highly efficient degradation of hydrogen sulfide, styrene, and m-xylene in a bio-trickling filter

Controlling the release of malodorous gas discharged from wastewater treatment plants (WWTPs) has become an urgent environmental problem in recent years. In this study, a bio-trickling filter (BTF) inoculated with microorganisms acclimated to activated sludge in a WWTP was used as the degradation equipment. A continuous degradation experiment with hydrogen sulfide, styrene, and m-xylene in the BTF lasted for 84 days (12 weeks). The degradation capacities of the BTF for hydrogen sulfide, styrene, and m-xylene were evaluated, and the synergy and inhibition among the substrates during biodegradation are discussed. The results indicated that the degradation efficiencies of the BTF were as high as 99.2% for hydrogen sulfide, 94.6% for styrene, and 100.0% for m-xylene. When the empty bed residence time was 30 s, the maximum elimination capacities (EC) achieved for hydrogen sulfide was 38 g m^-3 h^-1, for styrene was 200 g m^-3 h^-1, and for m-xylene was 75 g m^-3 h^-1. Furthermore, the microbial species and quantity of microorganisms in the middle and top of the BTF were much higher than those at the bottom of the BTF. A variety of microorganisms in the BTF can efficiently degrade the typical and highly toxic malodorous gases released from WWTPs. This study can help increase the understanding of the degradation of a mixture of sulfur-containing substances and aromatic hydrocarbons in BTF degradation and promote the development of technologies for the reduction of a complex mixture of malodorous gas emissions from organic wastewater treatment.

Water condition in biotrickling filtration for the efficient removal of gaseous contaminants

Biofiltration (BF) facilitates the removal of organic and inorganic compounds through microbial reactions. Water is one of the most important elements in biotrickling filters that provides moisture and nutrients to microbial biofilms. The maintenance of proper trickle watering is very critical in biotrickling filtration because the flow rate of the trickling water significantly influences contaminant removal, and its optimal control is associated with various physicochemical and biological mechanisms. The lack of water leads to the drying of the media, creating several issues, including the restricted absorption of hydrophilic contaminants and the inhibition of microbial activities, which ultimately deteriorates the overall contaminant removal efficiency (RE). Conversely, an excess of water limits the mass transfer of oxygen or hydrophobic gases. In-depth analysis is required to elucidate the role of trickle water in the overall performance of biotrickling filters. The processes involved in the treatment of various polluted gases under specific water conditions have been summarized in this study. Recent microscopic studies on biofilms were reviewed to explain the process by which water stress influences the biological mechanisms involved in the treatment of hydrophobic contaminated gases. In order to maintain an effective mass transfer, hydrodynamic and biofilm conditions, a coherent understanding of water stress and the development of extracellular polymeric substances (EPS) in biofilms is necessary. Future studies on the realistic local distribution of hydrodynamic patterns (trickle flow, water film thickness, and wet efficiency), integrated with biofilm distributions, should be conducted with respect to EPS development.

Effects of filler voidage on pressure drop and microbial community evolution in fungal bio-trickling filters

Bio-trickling filters (BTFs) can be used to remediate pollution by volatile organic compounds such as toluene. To investigate the effect of filler voidage on pressure drop (△P), two parallel BTFs were constructed using ceramsite with different voidages (47.5% for BTF1 and 55% for BTF2) and inoculated with Fusarium fungus to purify toluene. Commutation and stagnation operations were explored as ways to relieve △P. In BTF1, commutation temporarily relieved △P and maintained it for 7 days. Implementing stagnation on the 178th day for 69 days effectively reduced the △P from 720 Pa/m to below 20 Pa/m, which was maintained for 36 days. Compared with BTF1, the filler in BTF2 effectively delayed the increase in △P for 70 days or more and ensured stable operation for as long as 174 days. High-throughput sequencing revealed that Fusarium was mainly replaced by Protoctista, Fronsecaea and other fungi in both BTFs, although there were significant differences in their microbial communities. The influences of commutation and stagnation operations on fungal evolution were more obvious in BTF2, in relation to both time and space. The results provide guidance for designing better BTFs to treat hazardous pollutants.

Low-dosage ozonation in gas-phase biofilter promotes community diversity and robustness

BACKGROUND

The ozonation of biofilters is known to alleviate clogging and pressure drop issues while maintaining removal performances in biofiltration systems treating gaseous volatile organic compounds (VOCs). The effects of ozone on the biofilter microbiome in terms of biodiversity, community structure, metabolic abilities, and dominant taxa correlated with performance remain largely unknown.

METHODS

This study investigated two biofilters treating high-concentration toluene operating in parallel, with one acting as control and the other exposed to low-dosage (200 mg/m³) ozonation. The microbial community diversity, metabolic rates of different carbon sources, functional predictions, and microbial co-occurrence networks of both communities were examined.

RESULTS

Consistently higher biodiversity of over 30% was observed in the microbiome after ozonation, with increased overall metabolic abilities for amino acids and carboxylic acids. The relative abundance of species with reported stress-tolerant and biofilm-forming abilities significantly increased, with a consortium of changes in predicted biological pathways, including shifts in degradation pathways of intermediate compounds, while the correlation of top ASVs and genus with performance indicators showed diversifications in microbiota responsible for toluene degradation. A co-occurrence network of the community showed a decrease in average path distance and average betweenness with ozonation.

CONCLUSION

Major degrading species highly correlated with performance shifted after ozonation. Increases in microbial biodiversity, coupled with improvements in metabolizing performances of multiple carbon sources including organic acids could explain the consistent performance commonly seen in the ozonation of biofilters despite the decrease in biomass, while avoiding acid buildup in long-term operation. The increased presence of stress-tolerant microbes in the microbiome coupled with the decentralization of the co-occurrence network suggest that ozonation could not only ameliorate clogging issues but also provide a microbiome more robust to loading shock seen in full-scale biofilters. Video abstract.

Degradation of the mixture of ethyl formate, propionic aldehyde, and acetone by Aeromonas salmonicida: A novel microorganism screened from biomass generated in the citric acid fermentation industry

Microorganisms play important roles in the degradation of volatile organic compounds. Aeromonas salmonicida strain (AEP-3) generated from biomass in the citric acid fermentation industry was screened and subjected to denaturing gradient gel electrophoresis (DGGE) fingerprinting and 16S rDNA gene sequencing. The growth conditions of AEP-3 in Luria-Bertani broth were optimized at 25 °C and approximately pH 7. AEP-3 was used to degrade ethyl formate, propionic aldehyde, or acetone alone and their mixture. The concentrations of ethyl formate, propionic aldehyde, and acetone were below 7500, 600, and 800 mg L^-1, respectively, and their maximum degradation efficiencies were 100%, 92.41%, and 34.75%. AEP-3 first degraded acetone and propionic aldehyde in the mixture, followed by ethyl formate. The degradation pathways of these organic compounds in the mixture and their substrate interactions during degradation were explored. Propionic aldehyde was first converted into propionic acid in the metabolic process and was involved in the subsequent carboxylic acid cycle. By contrast, ethyl formate was first hydrolyzed into formic acid and ethanol. Then, formic acid participated in the cyclic metabolism of carboxylic acid, whereas, ethanol was hydrolyzed into acetaldehyde and acetic acid through alcohol and aldehyde dehydrogenase. Additionally, acetone directly interacted with nitrate in the medium under the action of hydrogen ions and produced carbon dioxide, water, and nitrogen. Overall, this study provides a new degrading bacterium biodegradability toward the exhaust gas of citric acid fermentation.

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.