Linking performance to microbiology in biofilters treating dimethyl sulphide in the presence and absence of methanol

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.

Aerobic degradation of high tetramethylammonium hydroxide (TMAH) and its impacts on nitrification and microbial community

Tetramethylammonium hydroxide (TMAH) was often used as developer in the high-tech industries. Information regarding biological treatment of high TMAH-containing wastewater is limited. This study investigated aerobic degradation of high TMAH, its impacts on nitrification, and microbial community in a sequencing batch reactor (SBR). The initial TMAH concentrations of SBR gradually increased from 200 to 4666 mg L^-1 (equivalent to 31 to 718 mg-N L^-1) to enrich microbial community for aerobic TMAH degradation and nitrification. The results indicated that the aerobic specific TMAH degradation rates followed the Monod-type kinetics with a maximum specific TMAH degradation rate of 2.184 mg N hour^-1 g volatile suspended solid (VSS)^-1 and the half-saturation coefficient of 175.1 mg N L^-1. After TMAH degradation and ammonia release, the lag time for the onset of nitrification highly correlated with initial TMAH fed for the SBR. According to the microbial community analysis using next generation sequencing (NGS), potential aerobic TMAH-degraders including Mycobacterium sp. and Hypomicrobium sp. were enriched in the aerobic SBR. The results of real-time quantitative polymerase chain reaction (qPCR) and reverse transcript (RT)-qPCR indicated that Hyphomicrobium sp. may be able to utilize both TMAH and its degradation intermediates such as trimethylamine (TMA), while Thiobacillus sp. can only utilize TMAH. The qPCR and RT-qPCR results suggested that TMAH may inhibit nitrification by inactive expression of amoA gene and the intermediates of TMAH degradation may compete ammonia monooxygenase (AMO) enzyme with ammonia for nitrification inhibition.

Biological treatment of DMSO-containing wastewater from semiconductor industry under aerobic and methanogenic conditions

This study evaluated biological treatment of dimethyl sulfoxide (DMSO)-containing wastewater from semiconductor industry under aerobic and anaerobic conditions. DMSO concentration as higher as 1.5 g/L did not inhibit DMSO degradation efficiency in aerobic membrane bioreactor (MBR), while specific DMSO degradation rate at different initial DMSO-to-biomass (S₀/X₀) ratios from batch tests seemed to follow the Haldane-type kinetics. According to the microbial community analysis, Proteobacteria decreased from 88.2% to 26% as influent DMSO concentration increased, while Bacteroidetes, Parcubacteria, Saccharibacteria increased. Within the Bacteroidetes class, Flavobacterium and Laribacter genus significantly increased from less than 0.05%-26.8% and 13.4%, respectively, which might both be related to the DMS degradation. Hyphomicrobium and Thiobacillus, known as aerobic DMSO and DMS degraders, instead, decreased at higher DMSO conditions. Under methanogenic conditions, batch results implied DMSO concentrations higher than 3 g/L could be inhibitory, while DMSO and COD removal achieved 100% and 93%, respectively, using a pilot-scale anaerobic fluidized bed membrane bioreactor (AFMBR) with influent DMSO below 1.5 g/L. Results of terminal restriction fragment length polymorphism (TRFLP) analysis targeting on mcrA functional gene revealed that Methanomethylovorans sp. was dominant in AFMBR after 54 days of operation, indicating its importance on degrading DMS and mathanethiol (MT).

Vegetation successfully prevents oxidization of sulfide minerals in mine tailings

The oxidization of metal sulfide in tailings causes acid mine drainage. However, it remains unclear whether vegetation prevents the oxidization of metal sulfides. The oxidization characteristics and microbial indices of the tailings in the presence of various plant species were investigated to explore the effects of vegetation on the oxidization of sulfide minerals in tailings. The pH, reducing sulfur, free iron oxides (Fed), chemical oxygen consumption (COC) and biological oxygen consumption (BOC) were measured. Key iron- and sulfur-oxidizing bacteria (Acidithiobacillus spp., Leptospirillum spp. and Thiobacillus spp.) were quantified using real-time PCR. The results indicate that vegetation growing on tailings can effectively prevent the oxidization of sulfide minerals in tailings. A higher pH and reducing-sulfur content and lower Fed were observed in the 0-30 cm depth interval in the presence of vegetation compared to bare tailings (BT). The COC gradually decreased with depth in all of the soil profiles; specifically, the COC rapidly decreased in the 10-20 cm interval in the presence of vegetation but gradually decreased in the BT profiles. Imperata cylindrica (IC) and Chrysopogon zizanoides (CZ) profiles contained the highest BOC in the 10-20 cm interval. The abundance of key iron- and sulfur-oxidizing bacteria in the vegetated tailings were significantly lower than in the BT; in particular, IC was associated with the lowest iron- and sulfur-oxidizing bacterial abundance. In conclusion, vegetation successfully prevented the oxidization of sulfide minerals in the tailings, and Imperata cylindrica is the most effective in reducing the number of iron- and sulfur-oxidizing bacteria and helped to prevent the oxidization of sulfide minerals in the long term.

Characterization of the novel dimethyl sulfide-degrading bacterium Alcaligenes sp. SY1 and its biochemical degradation pathway

Recently, the biodegradation of volatile organic sulfur compounds (VOSCs) has become a burgeoning field, with a growing focus on the reduction of VOSCs. The reduction of VOSCs encompasses both organic emission control and odor control. Herein, Alcaligenes sp. SY1 was isolated from active sludge and found to utilize dimethyl sulfide (DMS) as a growth substrate in a mineral salt medium. Response surface methodology (RSM) analysis was applied to optimize the incubation conditions. The following conditions for optimal degradation were identified: temperature 27.03°C; pH 7.80; inoculum salinity 0.84%; and initial DMS concentration 1585.39 μM. Under these conditions, approximately 99% of the DMS was degraded within 30 h of incubation. Two metabolic compounds were detected and identified by gas chromatography-mass spectrometry (GC-MS): dimethyl disulfide (DMDS) and dimethyl trisulfide (DMTS). The DMS degradation kinetics for different concentrations were evaluated using the Haldane-Andrews model and the pseudo first-order model. The maximum specific growth rate and degradation rate of Alcaligenes sp. SY1 were 0.17 h(-1) and 0.63 gs gx(-1)h(-1). A possible degradation pathway is proposed, and the results suggest that Alcaligenes sp. SY1 has the potential to control odor emissions under aerobic conditions.

Pharmaceutically active compounds: Their removal during slow sand filtration and their impact on slow sand filtration bacterial removal

Slow sand filtration (SSF) has been widely used as a means of providing potable water due to its efficacy, low cost, and minimal maintenance. Advances in analytical instrumentation have revealed the occurrence of pharmaceutically active compounds (PhACs) in surface water as well as in groundwater. It is unclear if the presence of these compounds in the feed water can interfere with the performances of an SSF unit. The aim of this work was to examine i) the ability of two SSF units to remove six PhACs (caffeine, carbamazepine, 17-β estradiol [E2], estrone [E1], gemfibrozil, and phenazone), and ii) the impact of these PhACs on the removal of bacteria by two SSF units. The presence of PhACs in feed water for SSF can occur in surface waters impacted by wastewater or leakage from sewers and septic tanks, as well as in developing countries where unregulated use and improper disposal are prevalent. Two pilot-scale SSF units were used during the study. Unit B1 was fed with stream water with 1% of primary effluent added, while unit B2 was fed with stream water alone. Although limited removal (<10%) of carbamazepine, gemfibrozil, and phenazone occurred, the complete removal of caffeine, and the partial removal (11-92%) of E2 and E1 were observed in the two SSF units. The results of this study suggest that the occurrence of the selected PhACs, probably estrogens and caffeine, in the feed water at 50 μg L(-1) affected the ability of the schmutzdecke to remove total coliform and Escherichia coli. The bacterial removal achieved within the schmutzdecke dropped from 95% to less than 20% by the end of the study. This decrease in removal may be related to the change in the microbial community within the schmutzdecke. A diverse microbial community, including Bacteroidetes and several classes of Proteobacteria, was replaced by a microbial community in which Gammaproteobacteria was the predominant phylum (99%). Despite the low removal achieved within the schmutzdecke, removal of total coliform and E. coli greater than 99% occurred after both SSF units throughout the study. Bacterial removal occurred in the upper half of the sand filter. This was probably due to a diverse microbial community established in the packing material, in which Bacteroidetes (13-25%), Acidobacteria (7-17%) and several classes of Proteobacteria (35-52%) (Alpha-, Beta-, Delta-, and Gammaproteobacteria) were the predominant phyla.

Potentialities of coupling biological processes (biotrickler/biofilter) for the degradation of a mixture of sulphur compounds

This study deals with the potential of biological processes combining a biotrickler and a biofilter to treat a mixture of sulphur-reduced compounds including dimethyl sulphide (DMS), dimethyl disulphide (DMDS) and hydrogen sulphide (H2S). As a reference, duplicated biofilters were implemented, and operating conditions were similar for all bioprocesses. The first step of this work was to determine the efficiency removal level achieved for each compound of the mixture and in a second step, to assess the longitudinal distribution of biodegradation activities and evaluate the total bacteria, Hyphomicrobium sp. and Thiobacillus thioparus densities along the bed height. A complete removal of hydrogen sulphide is reached at the start of the experiment within the first stage (biotrickler) of the coupling. This study highlighted that the coupling of a biotrickling filter and a biofilter is an interesting way to improve both removal efficiency levels (15-20% more) and kinetics of recalcitrant sulphur compounds such as DMS and DMDS. The total cell densities remained similar (around 1 × 10(10) 16S recombinant DNA (rDNA) copies g dry packing material) for duplicated biofilters and the biofilter below the biotrickling filter. The relative abundances of Hyphomicrobium sp. and T. thioparus have been estimated to an average of 10 ± 7.0 and 0.23 ± 0.07%, respectively, for all biofilters. Further investigation should allow achieving complete removal of DMS by starting the organic sulphur compound degradation within the first stage and surveying microbial community structure colonizing this complex system.

Linking TFT-LCD wastewater treatment performance to microbial population abundance of Hyphomicrobium and Thiobacillus spp

This study investigated the linkage between performance of two full-scale membrane bioreactor (MBR) systems treating thin-film transistor liquid crystal display (TFT-LCD) wastewater and the population dynamics of dimethylsulfoxide (DMSO)/dimethylsulfide (DMS) degrading bacteria. High DMSO degradation efficiencies were achieved in both MBRs, while the levels of nitrification inhibition due to DMS production from DMSO degradation were different in the two MBRs. The results of real-time PCR targeting on DMSO/DMS degrading populations, including Hyphomicrobium and Thiobacillus spp., indicated that a higher DMSO oxidation efficiency occurred at a higher Hyphomicrobium spp. abundance in the systems, suggesting that Hyphomicrobium spp. may be more important for complete DMSO oxidation to sulfate compared with Thiobacillus spp. Furthermore, Thiobacillus spp. was more abundant during poor nitrification, while Hyphomicrobium spp. was more abundant during good nitrification. It is suggested that microbial population of DMSO/DMS degrading bacteria is closely linking to both DMSO/DMS degradation efficiency and nitrification performance.

Enrichment and characterization of a bacterial culture that can degrade 4-aminopyridine

Background

The agrichemical 4-aminopyridine is used as a bird repellent in crop fields and has an epileptogenic action in a variety of animals, including man and mouse. 4-Aminopyridine is biodegraded in the environment through an unknown mechanism.

Results

A 4-aminopyridine-degrading enrichment culture utilized 4-aminopyridine as a carbon, nitrogen, and energy source, generating 4-amino-3-hydroxypyridine, 3,4-dihydroxypyridine, and formate as intermediates. 4-Amino-3-hydroxypyridine could not be further metabolized and probably accumulated as a dead-end product in the culture. Biodegradability tests and partial sequence analysis of the enrichment culture indicated that 4-aminopyridine was mainly degraded via 3,4-dihydroxypyridine and that the metabolite is probably cleaved by 3-hydroxy-4-pyridone dioxygenase. Seven culturable predominant bacterial strains (strains 4AP-A to 4AP-G) were isolated on nutrient agar plates. Changes in the bacterial populations of 4-aminopyridine, 3,4-dihydroxypyridine, or formate/ammonium chloride enrichment cultures were monitored by denaturing gradient gel electrophoresis (DGGE) profiling of PCR-amplified 16S rRNA gene fragments. Sequence analysis of the 16S rRNA gene fragments derived from predominant DGGE bands indicated that Pseudomonas nitroreducens 4AP-A and Enterobacter sp. 4AP-G were predominant in the three tested enrichment cultures and that the unculturable strains Hyphomicrobium sp. 4AP-Y and Elizabethkingia sp. 4AP-Z were predominant in 4-aminopyridine and formate/ammonium chloride enrichment cultures and in the 3,4-dihydroxypyridine enrichment culture, respectively. Among the culturable strains, strain 4AP-A could utilize 3,4-dihydroxypyridine as a growth substrate. Although we could not isolate strain 4AP-Y on several media, PCR-DGGE analysis and microscopy indicated that the unique bi-polar filamentous bacterial cells gradually became more dominant with increasing 4-aminopyridine concentration in the medium.

Conclusions

Hyphomicrobium sp. 4AP-Y, P. nitroreducens 4AP-A, and Elizabethkingia sp. 4AP-Z probably play important roles in 4-aminopyridine degradation in crop fields. In the enrichment culture, 3,4-dihydroxypyridine and its metabolites including formate might be shared as growth substrates and maintain the enrichment culture, including these indispensable strains.

High-rate denitrification using polyethylene glycol gel carriers entrapping heterotrophic denitrifying bacteria

This study evaluated the nitrogen removal performance of polyethylene glycol (PEG) gel carriers containing entrapped heterotrophic denitrifying bacteria. A laboratory-scale denitrification reactor was operated for treatment of synthetic nitrate wastewater. The nitrogen removal activity gradually increased in continuous feed experiments, reaching 4.4 kg N m(-3) d(-1) on day 16 (30 °C). A maximum nitrogen removal rate of 5.1 kg N m(-3) d(-1) was observed. A high nitrogen removal efficiency of 92% on average was observed at a high loading rate. In batch experiments, the denitrifying gel carriers were characterized by temperature. Nitrate and total nitrogen removal activities both increased with increasing temperature, reaching a maximum at 37 and 43 °C, respectively. Apparent activation energies for nitrate and nitrite reduction were 52.1 and 71.9 kJ mol(-1), respectively. Clone library analysis performed on the basis of the 16S rRNA gene revealed that Hyphomicrobium was mainly involved in denitrification in the methanol-fed denitrification reactors.

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 13.2 g m(-3) h(-1). Methanol LRs varied from 4.6 to 64.5 g m(-3) h(-1) and from 2.3 to 45.2 g m(-3) h(-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 CO(2) 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 13.2 g m(-3) h(-1). For n-hexane LR greater than 13.2 g m(-3) h(-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.

Rapid acclimation of methanogenic granular sludge into denitrifying sulfide removal granules

Rapid formation of denitrifying sulfide removal granules is of practical interest to start up an expanded granular sludge bed reactor for wastewater treatment. This study demonstrates that methanogenic granules can be easily acclimated into DSR granules in one day, removing all 1.30 kg m(-3) d(-1) sulfide and converting >90% of 0.56 kg-Nm(-3)d(-1) nitrate into di-nitrogen gas. Under high loadings, reactor performance, however, declined. Under high loading rates, sulfide first inhibited the heterotrophic denitrifier (Caldithrix sp.), thereby accumulating nitrite in the system; the autotrophic denitrifier (Pseudomonas sp. C23) was then inhibited by accumulated nitrite, leading to breakdown of the entire DSR process.

Integrating microbial ecology in bioprocess understanding: the case of gas biofiltration

Biofilters are packed-bed bioreactors where contaminants, once transferred from the gas phase to the biofilm, are oxidized by diverse and complex communities of attached microorganisms. Over the last decade, more and more studies aimed at opening the back box of biofiltration by unraveling the biodiversity-ecosystem function relationship. In this review, we report the insights provided by the microbial ecology approach in biofilters and we emphasize the parallels existing with other engineered ecosystems used for wastewater treatment, as they all constitute relevant model ecosystems to explore ecological issues. We considered three characteristic ecological indicators: the density, the diversity, and the structure of the microbial community. Special attention was paid to the temporal and spatial dynamics of each indicator, insofar as it can disclose the potential relationship, or absence of relation, with any operating or functional parameter. We also focused on the impact of disturbance regime on the microbial community structure, in terms of resistance, resilience, and memory. This literature review led to mitigated conclusions in terms of biodiversity-ecosystem function relationship. Depending on the environmental system itself and the way it is investigated, the spatial and temporal dynamics of the microbial community can be either correlated (e.g., spatial stratification) or uncoupled (e.g., temporal instability) to the ecosystem function. This lack of generality shows the limits of current 16S approach in complex ecosystems, where a functional approach may be more suitable.

Growth kinetics of Hyphomicrobium and Thiobacillus spp. in mixed cultures degrading dimethyl sulfide and methanol

The growth kinetics of Hyphomicrobium spp. and Thiobacillus spp. on dimethyl sulfide (DMS) and methanol (in the case of Hyphomicrobium spp.) in an enrichment culture created from a biofilter cotreating DMS and methanol were studied. Specific growth rates of 0.099 h(-1) and 0.11 h(-1) were determined for Hyphomicrobium spp. and Thiobacillus spp., respectively, growing on DMS at pH 7. These specific growth rates are double the highest maximum specific growth rate for bacterial growth on DMS reported to date in the literature. When the pH of the medium was decreased from pH 7 to pH 5, the specific growth rate of Hyphomicrobium spp. decreased by 85%, with a near 100-fold decline in the yield of Hyphomicrobium 16S rRNA gene copies in the mixed culture. Through the same pH shift, the specific growth rate and 16S rRNA gene yield of Thiobacillus spp. remained similar. When methanol was used as a substrate, the specific growth rate of Hyphomicrobium spp. declined much less over the same pH range (up to 30%) while the yield of 16S rRNA gene copies declined by only 50%. Switching from an NH(4)(+)-N-based source to a NO(3)(-)-N-based source resulted in the same trends for the specific growth rate of these microorganisms with respect to pH. This suggests that pH has far more impact on the growth kinetics of these microorganisms than the nitrogen source. The results of these mixed-culture batch experiments indicate that the increased DMS removal rates observed in previous studies of biofilters cotreating DMS and methanol are due to the proliferation of DMS-degrading Hyphomicrobium spp. on methanol at pH levels not conducive to high growth rates on DMS alone.