Simultaneous methanethiol and dimethyl sulfide removal in a single-stage biotrickling filter packed with polyurethane foam: Performance, parameters and microbial community analysis

Swelling problems in immobilized filler: an improvement method and comparative study of the effect of different fillers on biotrickling filters

Immobilized fillers have been increasingly utilized in biotrickling filters (BTFs) due to their positive impact on shock load resistance and recovery performance. However, due to the inherent characteristics of its immobilized carrier, the immobilized filler is prone to swelling during the long-term operation of the system, resulting in increased pressure drop. Polyurethane (PU) sponge was used as the cross-linked skeleton of immobilized filler and compared with direct emulsified cross-linked immobilized filler for treating ethylbenzene gas. In the early stage, both fillers can maintain good performance despite changes in the inlet concentration and short-term stagnation. However, on the 107th day of operation, the immobilized filler experienced swelling, and the pressure drop sharply increased to 137.2 Pa, while the PU immobilized filler was still able to maintain a low-pressure drop level. The results of the microbial diversity analysis revealed that the microbial community structure of PU immobilized fillers remained relatively stable when responding to the fluctuations in operating conditions. PU sponges as the skeleton can effectively prolong the service life of the immobilized filler and improve the performance of the biotrickling filter.

Cellulosimicrobium sp. Strain L1: A Study on the Optimization of the Conditions and Performance of a Combined Biological Trickling Filter for Hydrogen Sulfide Degradation

Sulfide is a toxic and hazardous substance in the agricultural environment, which can cause damage to humans and livestock when exposed to large amounts of air. In this study, we performed one-factor optimization of the culture conditions and culture fractions of the Cellulosimicrobium sp. strain L1 and combined it with a biological trickling filter cell for the degradation of hydrogen sulfide for 24 consecutive days. The degradation effect of strain L1 and the biological trickling filter (BTF) on hydrogen sulfide was investigated, and the changes in intermediate products in the degradation process were briefly analyzed. The results showed that strain L1 had the highest conversion efficiency when incubated with 3 g/L sucrose as the carbon source and 1 g/L NH4Cl as the nitrogen source at a temperature of 35 °C, an initial pH of 5, and a NaCl concentration of 1%. The concentration of thiosulfate increased and then decreased during the degradation process, and the concentration of sulfate increased continuously. When strain L1 was applied to the biological trickling filter, it could degrade 359.53 mg/m3 of H2S. This study provides a deeper understanding of sulfide degradation in biological trickling filters and helps promote the development of desulfurization technology and the treatment of malodorous gasses produced by the accumulation of large quantities of livestock manure.

Simultaneous removal of ammonia and sulfur odorants in biotrickling filters and N2O production

Research on the stability evaluation of biotrickling filters (BTFs) under harsh conditions and the bacterial adaptation process still needs to be improved. Herein, BTFs with polypropylene plastic (PP) and ceramic raschig rings (CRR) were investigated for a better understanding of the biodegradation of ammonia (NH3), hydrogen sulfide (H2S), and dimethyl sulfide (DMS). The results showed an excellent performance in removal efficiency (RE) for NH3 (91.6 %-99.9 %), H2S (RE: 55.3 %-99.5 %), and DMS (RE: 10.6 %-99.9 %). It was found that a more apparent positive correlation between N2O emission and pressure drop in CRR BTF (R2 = 0.92) than in PP BTF (R2 = 0.79) (P < 0.01). Low temperature promotes an increase in the abundance ofComamonasandBacillus. The polysaccharides in PP and CRR reactors decreased by 78.6 % and 68.1 % when temperature reduced from 25℃ to 8℃. This work provides a novel insight into understanding bacterial survival under harsh BTF environments.

Management of methyl mercaptan contained in waste gases - an overview

Methyl mercaptan is a typical volatile organosulfur pollutant contained in many gases emitted by urban waste treatment, various industries, natural gas handling, refining processes, and energy production. This work is a comprehensive overview of the scientific and practical aspects related to the management of methyl mercaptan pollution. The main techniques, including absorption, adsorption, oxidation, and biological treatments, are examined in detail. For each method, its capability as well as the technical advantages and drawbacks have been highlighted. The emerging methods developed for the removal of methyl mercaptan from natural gas are also reviewed. These methods are based on the catalytic conversion of CH3SH to hydrocarbons and H2S.

Biofiltration of gaseous mixtures of dimethyl sulfide, dimethyl disulfide and dimethyl trisulfide: Effect of operational conditions and microbial analysis

The efficient removal of volatile sulfur compounds (VSCs), such as dimethyl sulfide (DMS), dimethyl disulfide (DMDS) and dimethyl trisulfide (DMTS), is crucial due to their foul odor and corrosive potential in sewer systems. Biofilters (BFs) offer promise for VSCs removal, but face challenges related to pH control and changing conditions at full scale. Two BFs, operated under acidophilic conditions for 78 days, were evaluated for their performance at varying inlet concentrations and empty bed residence times (EBRTs). BF1, incorporating 4-6 mm marble limestone for pH control, outperformed BF2, which used NaHCO3 in the nutrient solution. BF1 displayed better resilience, maintained a stable pH of 4.6 ± 0.6, and achieved higher maximum elimination capacities (ECmax, 41 mg DMS m-3 h-1 (RE 38.3%), 146 mg DMDS m-3 h-1 (RE 83.1%), 47 mg DMTS m-3 h-1 (RE 93.1%)) at an EBRT of 56 s compared to BF2 (9 mg DMS m-3 h-1 (RE 7.1%), 9 mg DMDS m-3 h-1 (RE 4.8%) and 11 mg DMTS m-3 h-1 (RE 26.6%)). BF2 exhibited pH stratification and decreased performance after feeding interruptions. The biodegradability of VSCs followed the order DMTS > DMDS > DMS, and several microorganisms were identified contributing to VSCs degradation in BF1, including Bacillus (14%), Mycobacterium (11%), Acidiphilium (7%), and Acidobacterium (3%).

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.

Synergy effects of Methylomonas koyamae and Hyphomicrobium methylovorum under methanethiol stress

Methanotrophs are able to metabolize volatile organic sulfur compounds (VOSCs), excrete organic carbon during CH₄ oxidation, and influence microbial community structure and function of the ecosystem. In return, microbial community structure and environmental factors can affect the growth metabolism of methanotrophs. In this study, Methylomonas koyamae and Hyphomicrobium methylovorum were used for model organisms, and methanethiol (MT) was chosen for a typical VOSC to investigate the synergy effects under VOSC stress. The results showed that when Hyphomicrobium methylovorum was co-cultured with Methylomonas koyamae in the medium with CH₄ used as the carbon source, the co-culture had better MT tolerance relative to Methylomonas koyamae and oxidized all CH₄ within 120 h, even at the initial MT concentration of 2000 mg m^-3. The optimal co-culture ratios of Methylomonas koyamae to Hyphomicrobium methylovorum were 4:1-12:1. Although MT could be converted spontaneously to dimethyl disulfide (DMDS), H₂S, and CS₂ in air, faster losses of MT, DMDS, H₂S, and CS₂ were observed in each strain mono-culture and the co-culture. Compared with Hyphomicrobium methylovorum, MT was degraded more quickly in the Methylomonas koyamae culture. During the co-culture, the CH₄ oxidation process of Methylomonas koyamae could provide carbon and energy sources for the growth of Hyphomicrobium methylovorum, while Hyphomicrobium methylovorum oxidized MT to help Methylomonas koyamae detoxify. These findings are helpful to understand the synergy effects of Methylomonas koyamae and Hyphomicrobium methylovorum under MT stress and enrich the role of methanotrophs in the sulfur biogeochemical cycle. KEY POINTS: • The co-culture of Methylomonas and Hyphomicrobium has better tolerance to CH₃SH. • Methylomonas can provide carbon sources for the growth of Hyphomicrobium. • The co-culture of Methylomonas and Hyphomicrobium enhances the removal of CH₄ and CH₃SH.

N-acetylation of toxic aromatic amines by fungi: Strain screening, cytotoxicity and genotoxicity evaluation, and application in bioremediation of 3,4-dichloroaniline

Aromatic amines (AA) are one of the most commonly used classes of compounds in industry and the most common pollutants found in both soil and water. 3,4-Dichloaniline (3,4-DCA) is a persistent residue of the phenylurea herbicide in the environment. In this study, we used a colorimetric method as a new approach to screen 12 filamentous fungal strains of the genera Aspergillus, Chaetomium, Cladosporium, and Mucor to assess their capacity to perform AA N-acetylation since it is considered a potential tool in environmental bioremediation. Subsequently, the selected strains were biotransformed with different AA substrates to evaluate the product yield. The strains Aspergillus niveus 43, Aspergillus terreus 31, and Cladosporium cladosporioides showed higher efficiencies in the biotransformation of 3,4-DCA at 500 µM into its N-acetylated product. These fungal strains also showed great potential to reduce the phytotoxicity of 3,4-DCA in experiments using Lactuca sativa seeds. Furthermore, N-acetylation was shown to be effective in reducing the cytotoxic and genotoxic effects of 3,4-DCA and other AA in the immortalized human keratinocyte (HaCaT) cell line. The isolated products after biotransformation showed that fungi of the genera Aspergillus and Cladosporium appeared to have N-acetylation as the first and main AA detoxification mechanism. Finally, A. terreus 31 showed the highest 3,4-DCA bioremediation potential, and future research can be carried out on the application of this strain to form microbial consortia with great potential for the elimination of toxic AA from the environment.

Super enhancement of methanethiol biodegradation by new isolated Pseudomonas sp. coupling silicone particles

A new strain, Pseudomonas sp. SJ-1, which was able to remove model odorous organics methanethiol (MT) has been isolated from the wastewater treatment plant and identified via 16S rRNA analysis. Initial MT concentration, temperature and pH played an important role in MT removal, and up to 100% of 260 mg L^-1 of MT could be removed within 11 h under the optimum conditions (30 °C, pH 7.0) with an average degradation rate of 23.6 mg L^-1 h^-1, which was the highest one in literature so far. The silicone particles were added as the non-aqueous phases (NAP) to enhance the performance of MT degradation. The results indicated that the maximum degradation rate and specific cell growth of strain SJ-1 were 2.36 times and 1.31 times by Haldane kinetic model analysis in the NAP added test. The SO₄^2- was identified as the major intermediate and CO₂ as a final product in MT biodegradation. Overall, this is the first report that a newly isolated Pseudomonas sp. could use high concentration MT as sole energy source and carbon source and its activity could be enhanced by adding NAP. The results provide a suggestion for the development of more effective and reliable biological treatment processes.

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.

Evaluation of continuous and intermittent trickling strategies for the removal of hydrogen sulfide in a biotrickling filter

Biotrickling filter (BTF) is a widely applied bioreactor for odour abatement in sewer networks. The trickling strategy is vital for maintaining a sound operation of BTF. This study employed a lab-scale BTF packed with granular activated carbon at a short empty bed residence time of 6 s and pH 1-2 to evaluate different trickling strategies, i.e., continuous trickling (different velocities) and intermittent trickling (different trickling intervals), in terms of the removal of hydrogen sulfide (H₂S), bed pressure drop, H₂S oxidation products and microbial community. The H₂S removal performance decreased with the trickling velocity (∼3.6 m/h) in BTF. In addition, three intermittent trickling strategies, i.e., 10-min trickling per 24 h, 8 h, and 2 h, were investigated. The H₂S elimination capacity deteriorated after about 2 weeks under both 10-min trickling per 24 h and 8 h. For both intermittent (10-min trickling per 2 h) and continuous trickling, the BTF exhibited nearly 100 % H₂S removal for inlet H₂S concentrations<100 ppmv, but intermittent BTF showed better removal performance than continuous trickling when inlet H₂S increased to 120-190 ppmv. Furthermore, the bed pressure drops were 333 and 3888 Pa/m for non-trickling and trickling periods, respectively, which makes intermittent BTF save 83 % energy consumption of the blower compared with continuous tirckling. However, intermittent BTF exhibited transient H₂S breakthrough (<1 ppmv) during trickling periods. Moreover, elemental sulfur and sulfate were major products of H₂S oxidation and Acidithiobacillus was the dominant genus in both intermittent and continuous trickling BTF. A mathematical model was calibrated for the intermittent BTF and a sensitivity analysis was performed on the model. It shows mass transfer parameters determine the H₂S removal. Overall, intermittent trickling strategy is promising for improving odour abatement performance and reducing the operating cost of the BTF.

Optimization of acrylic-styrene latex-based biofilms as a platform for biological indoor air treatment

Biotechnologies have emerged as a promising solution for indoor air purification with the potential to overcome the inherent limitations of indoor air treatment. These limitations include the low concentrations and variability of pollutants and mass-transfer problems caused by pollutant hydrophobicity. A new latex-based biocoating was herein optimized for the abatement of the volatile organic compounds (VOCs) toluene, trichloroethylene, n-hexane, and α-pinene using acclimated activated sludge dominated by members of the phylum Patescibacteria. The influence of the water content, the presence of water absorbing compounds, the latex pretreatment, the biomass concentration, and the pollutant load was tested on VOC removal efficiency (RE) by varying the formulation of the mixtures. Overall, hexane and trichloroethylene removal was low (<30%), while high REs (>90%) were consistently recorded for toluene and pinene. The assays demonstrated the benefits of operating at high water content in the biocoating, either by including mineral medium or water absorbing compounds in the latex-biomass mixtures. The performance of the latex-based biocoating was likely limited by VOC mass-transfer rather than by biomass concentration in the biocoating. The latex-based biocoating supported a superior toluene and pinene removal than biomass in suspension when VOC loading rate was increased by a factor of 4.

Enhanced removal of hydrophobic volatile organic compounds in biofilters and biotrickling filters: A review on the use of surfactants and the addition of hydrophilic compounds

The use of biological reactors to remove volatile organic compounds (VOCs) from waste gas streams has proven to be a cost-effective and sustainable technique. However, hydrophobic VOCs exhibit low removal, mainly due to their limited bioavailability for the microorganisms. Different strategies to enhance their removal in bio(trickling)filters have been developed with promising results. In this review, two strategies, i.e. the use of surfactants and hydrophilic compounds, for enhancing the removal of hydrophobic VOCs in bio(trickling)filters are discussed. The complexity of the processes and mechanisms behind both strategies are addressed to fully understand and exploit their potential and rapid implementation at full-scale. Mass transfer and biological aspects are discussed for each strategy, and an in-depth comparison between studies carried out over the last two decades has been performed. This review identifies additional strategies to further improve the application of (bio)surfactants and/or hydrophilic VOCs, and it provides recommendations for future studies in this field.

Biotrickling filter for the removal of volatile sulfur compounds from sewers: A review

Volatile sulfur compounds (VSCs) were identified as the dominant priority odorants emitted from sewers, including hydrogen sulfide (H₂S), methyl mercaptan (MM), dimethyl disulfide (DMDS) and dimethyl sulfide (DMS). Biotrickling filter (BTF) is a widely-applied technology for odour abatement in sewers because of its relatively low operating cost and efficient H₂S removal. The authors review the mechanisms and performance of BTF for the removal of these four VSCs, and discuss the key influencing factors including of empty bed residence time (EBRT), pH, temperature, nutrients, water content, trickling operation and packing materials. Besides, measures to improve the VSCs removal in BTF are proposed in the context of key influencing factors. Finally, the review assesses the new challenges of BTF for sewer emissions treatment, namely with respect to the performance of BTF for greenhouse gases (GHG) treatment.

Microbial analysis for the ammonium removal from landfill leachate in an aerobic granular sludge sequencing batch reactor

In this study, a laboratory-scale sequencing batch reactor (SBR) equipped with aerobic granular sludge (AGS) technology was continuously operated for 220 days to remove ammonium from an existing landfill leachate. The ammonium removal was characterized by polymerase chain reaction (PCR)-denaturing gradient gel electrophoresis (DGGE) technology. This method helped to analyze the long-term community structural stability of ammonia-oxidizing bacteria (AOB), nitrite-oxidizing bacteria (NOB) and denitrifying bacteria (DB) throughout the experiment. Simultaneously, 16S rRNA gene cloning and sequencing analysis identified the dominant species of different microbial species. Experimental results confirmed that ammonium removal was inhibited at the high nitrogen loading rate (NLR) stage while the low NLR stage achieved satisfactory ammonium removal. Moreover, the findings demonstrated that functionally stable wastewater treatment bioreactors facilitated the occurrence of stable microbial community structures.