Improved methane removal in exhaust gas from biogas upgrading process using immobilized methane-oxidizing bacteria

Manipulating soil microbial community assembly by the cooperation of exogenous bacteria and biochar for establishing an efficient and healthy CH4 biofiltration system

Manipulating the methanotroph (MOB) composition and microbial diversity is a promising strategy to optimize the methane (CH4) biofiltration efficiency of an engineered landfill cover soil (LCS) system. Inoculating soil with exogenous MOB-rich bacteria and amending soil with biochar show strong manipulating potential, but how the two stimuli interactively shape the microbial community structure and diversity has not been clarified. Therefore, three types of soils with active CH4 activities, including paddy soil, river wetland soil, and LCS were selected for enriching MOB-dominated communities (abbreviated as B_PS, B_RWS, and B_LCS, respectively). They were then inoculated to LCS which was amended with two distinct biochar. Besides the aerobic CH4 oxidation efficiencies, the evolution of the three microbial communities during the MOB enrichment processes and their colonization in two-biochar amended LCS were obtained. During the MOB enriching, a lag phase in CH4 consumption was observed merely for B_LCS. Type II MOB Methylocystis was the primary MOB for both B_PS and B_LCS; while type I MOB dominated for B_RWS and the major species were altered by gas concentrations. Compared to biochar, a more critical role was demonstrated for the bacteria inoculation in determining the community diversity and function of LCS. Instead, biochar modified the community structures by mainly stimulating the dominant MOB but could induce stochastic processes in community assembly, possibly related to its inorganic nutrients. Particularly, combined with biochar advantages, the paddy soil-derived bacteria consortiums with diverse MOB species demonstrated the potent adaption to LCS niches, not only retaining the high CH4-oxidizing capacities but also shaping a community structure with more diverse soil function. The results provided new insights into the optimization of an engineered CH4-mitigation soil system by manipulating the soil microbiomes with the cooperation of exogenous bacteria and biochar.

A bio-augmented system with Methylosarcina sp. LC-4 immobilized on bio-carriers: Towards an integrated approach to mitigate and valorize methane emissions from landfills to biodiesel

Bio-augmented systems based on methanotrophs are indispensable in curbing anthropogenic methane emissions from engineered landfills or dumpsites to curtail rising levels of greenhouse gases. Using a defined methanotroph culture immobilized on an inert material-based bio-carrier makes it possible to harness these methane emissions for creating value-added products, thus contributing to the circular bio-economy. The methane oxidation capacity of the model methanotroph Methylosarcina sp. LC-4, a prospective organism for biodiesel production using methane present in landfill gas, immobilized on several inert bio-carriers, was evaluated to identify a bio-carrier that provided optimum conditions for the process. Among the several bio-carriers evaluated, perlite and vermiculite were selected due to their high specific surface area and superior water-holding capacity, which result in the retention of nutrients and biomass and higher methane elimination capacity. While perlite showed high biomass holding capacity and methane transport, vermiculite supported a high growth of methanotrophs. LC-4 immobilized on perlite and vermiculite as the bio-carrier showed maximum methane elimination capacity (MEC) of 291.3 g m-2 day-1 and 155.5 g m-2 day-1, respectively. The low bed height of only 0.13 m and a short start-up period of 2-4 days are promising for use as alternate daily cover in a landfill. The recovered biomass had 12% (w/w) fatty acid methyl ester (FAME), with a high fraction of (∼85%) of C14-C18 saturated and monounsaturated fatty acids, suitable for biodiesel production. The combination of perlite and vermiculite increased MEC and FAME content levels. The current study demonstrated a new bio-augmented system designed with a pure methanotroph for methane elimination with a short start-up time and the valorization of the assimilated methane.

Microbial protein production from sulfide-rich biogas through an enrichment of methane- and sulfur-oxidizing bacteria

This study evaluated the possibility of combining methane oxidizing bacteria (MOB) with sulfur oxidizing bacteria (SOB) to enable the utilization of sulfide-rich biogas for microbial protein production. For this purpose, a MOB-SOB mixed-culture enriched by feeding both methane and sulfide was benchmarked against an enrichment of solely MOB. Different CH₄:O₂ ratios, starting pH values, sulfide levels and nitrogen sources were tested and evaluated for the two enrichments. The MOB-SOB culture gave promising results in terms of both biomass yield (up to 0.07±0.01 g VSS/g CH₄-COD) and protein content (up to 73±5% of VSS) at 1500 ppm of equivalent H₂S. The latter enrichment was able to grow also under acidic pH (5.8-7.0), but as inhibited outside the optimal CH₄:O₂ ratio of 2:3. The obtained results show the capability of MOB-SOB mixed-cultures to directly upcycle sulfide-rich biogas into microbial protein potentially suited for feed, food or biobased product applications.

Batch Experiments Demonstrating a Two-Stage Bacterial Process Coupling Methanotrophic and Heterotrophic Bacteria for 1-Alkene Production From Methane

Methane (CH₄) is a sustainable carbon feedstock for value-added chemical production in aerobic CH₄-oxidizing bacteria (methanotrophs). Under substrate-limited (e.g., oxygen and nitrogen) conditions, CH₄ oxidation results in the production of various short-chain organic acids and platform chemicals. These CH₄-derived products could be broadened by utilizing them as feedstocks for heterotrophic bacteria. As a proof of concept, a two-stage system for CH₄ abatement and 1-alkene production was developed in this study. Type I and Type II methanotrophs, Methylobacter tundripaludum SV96 and Methylocystis rosea SV97, respectively, were investigated in batch tests under different CH₄ and air supplementation schemes. CH₄ oxidation under either microaerobic or aerobic conditions induced the production of formate, acetate, succinate, and malate in M. tundripaludum SV96, accounting for 4.8–7.0% of consumed carbon from CH₄ (C-CH₄), while M. rosea SV97 produced the same compounds except for malate, and with lower efficiency than M. tundripaludum SV96, accounting for 0.7–1.8% of consumed C-CH₄. For the first time, this study demonstrated the use of organic acid-rich spent media of methanotrophs cultivating engineered Acinetobacter baylyi ADP1 ‘tesA-undA cells for 1-alkene production. The highest yield of 1-undecene was obtained from the spent medium of M. tundripaludum SV96 at 68.9 ± 11.6 μmol mol C_substrate^–1. However, further large-scale studies on fermenters and their optimization are required to increase the production yields of organic acids in methanotrophs.

Impact of hydrogen sulfide on biochar in stimulating the methane oxidation capacity and microbial communities of landfill cover soil

Hydrogen sulfide (H₂S) can influence methanotrophic activities and be adsorbed by biochar (BC); however, the impact of H₂S on BC in stimulating the methane (CH₄) oxidation capacity of landfill cover soil (LCS) has not been clarified. Thus, batch incubation experiments were conducted to observe the effect of H₂S on the CH₄ oxidation capacity of and microbial communities in BC-amended LCS. Three landfill gas conditions were considered: 5 % CH₄ and 15 % oxygen (O₂) (5 M), 10 % CH₄ and 10 % O₂, and 20 % CH₄ and 5 % O₂ (20 M) by volume, with H₂S concentrations of 0, 100, 250, and 1000 ppm, respectively. Another series was conducted using LCS subjected to pre-H₂S saturation under the 20 M gas condition. In the 5 M gas condition suitable for the dominant methanotroph Methylocaldum (type I), the BC retained its ability to stimulate the CH₄ oxidation capacity of LCS (enhancement of 41-108 %) in the presence of H₂S. Additionally, when H₂S ≤ 250 ppm, the BC exhibited a relatively consistent impact of H₂S on both CH₄ oxidation capacity and microbial communities in LCS, independent of the CH₄ or O₂ concentrations. This result could be attributed to the different pathways of H₂S metabolism for the LCS and BC-amended LCS. Furthermore, when saturated adsorption of H₂S occurred for the LCS, the CH₄ oxidation capacity for BC-amended LCS was higher than that for non-amended LCS, which demonstrated the ability of BC in alleviating the inhibition of H₂S on CH₄ oxidation due to its excellent H₂S adsorption under even anoxic environments.

Novel biotechnologies for nitrogen removal and their coupling with gas emissions abatement in wastewater treatment facilities

Wastewaters contaminated with nitrogenous pollutants, derived from anthropogenic activities, have exacerbated our ecosystems sparking environmental problems, such as eutrophication and acidification of water reservoirs, emission of greenhouse gases, death of aquatic organisms, among others. Wastewater treatment facilities (WWTF) combining nitrification and denitrification, and lately partial nitrification coupled to anaerobic ammonium oxidation (anammox), have traditionally been applied for the removal of nitrogen from wastewaters. The present work provides a comprehensive review of the recent biotechnologies developed in which nitrogen-removing processes are relevant for the treatment of both wastewaters and gas emissions. These novel processes include the anammox process with alternative electron acceptors, such as sulfate (sulfammox), ferric iron (feammox), and anodes in microbial electrolysis cells (anodic anammox). New technologies that couple nitrate/nitrite reduction with the oxidation of methane, H₂S, volatile methyl siloxanes, and other volatile organic compounds are also described. The potential of these processes for (i) minimizing greenhouse gas emissions from WWTF, (ii) biogas purification, and (iii) air pollution control is critically discussed considering the factors that might trigger N₂O release during nitrate/nitrite reduction. Moreover, this review provides a discussion on the main challenges to tackle towards the consolidation of these novel biotechnologies.

Conversion of biogas to methanol by methanotrophs immobilized on chemically modified chitosan

In this study, chitosan modified with glutaraldehyde (GLA), 3-aminopropyltriethoxysilane (APTES), polyethyleneimine, and APTES followed by GLA (APTES-GLA) as a support material was used to improve methanol production from biogas. Among these support materials, chitosan-APTES-GLA showed the highest increase in immobilization yield and relative efficiency of Methylomicrobium album up to 56.4% and 97.7%, respectively. Maximum cell loading of 236 mg dry cell mass per g-support was observed for M. album., which is 7.7-fold higher than that of chitosan. The immobilized M. album maintained a 23.9-fold higher methanol production compared to free cells after 8 cycles of reuse; it also produced 6.92 mmol·L^-1 methanol from biogas that originated from anaerobic digestion of rice straw, thereby validating its industrial application. This is the first report on the immobilization of methanotrophs on chemically modified chitosans to improve cell loading and relative efficiency, and its potential applications in the conversion of greenhouse gases to methanol.

Proteinaceous methanotrophs for feed additive using biowaste as carbon and nutrients source

To achieve a sustainable production of food and feed production, inexpensive carbon and nutrient sources are needed. In the present study, biologically upgraded biogas is coupled with electrochemically extracted nitrogen from digested biowaste to cultivate mixed methanotrophs as protein source. Results showed that an increase from less than 5 μgCu²⁺/L to 100 μgCu²⁺/L increased the biomass production by 41%. Microbial analysis revealed that the dominated Methylomonas spp. followed by Methylophilus spp. created a specialized community for high CH₄ assimilation. Moreover, duplicate semi-continuous fermenters run for 120 days validating the efficiency of alternative carbon and nitrogen feedstocks at long-term operation. As for dry cell weight (DCW) production, more than 2.5 g-DCW/L were produced using biologically upgraded biogas and electrochemically extracted nitrogen. Furthermore, the protein content and amino acid profile (>50% of DCW) demonstrated that the microbial biomass pose the characteristics to be used as animal feed additive.

Methane Elimination Using Biofiltration Packed With Fly Ash Ceramsite as Support Material

Methane is a greenhouse gas and significantly contributes to global warming. Methane biofiltration with immobilized methane-oxidizing bacteria (MOB) is an efficient and eco-friendly approach for methane elimination. To achieve high methane elimination capacity (EC), it is necessary to use an exceptional support material to immobilize MOB. The MOB consortium was inoculated in biofilters to continuusly eliminate 1% (v/v) of methane. Results showed that the immobilized MOB cells outperformed than the suspended MOB cells. The biofilter packed with fly ash ceramsite (FAC) held the highest average methane EC of 4.628 g h^–1 m^–3, which was 33.4% higher than that of the biofilter with the suspended MOB cells. The qPCR revealed that FAC surface presented the highest pmoA gene abundance, which inferred that FAC surface immobilized the most MOB biomass. The XPS and contact angle measurement indicated that the desirable surface elemental composition and stronger surface hydrophilicity of FAC might favor MOB immobilization and accordingly improve methane elimination.

Biotransformation of methane into methanol by methanotrophs immobilized on coconut coir

This study aimed to establish a unique approach for the production of methanol from methane (CH₄) in the presence of paraffin oil mediated by methanotrophs immobilized on coconut coir (CC). Immobilization of different methanotrophs through covalent method increased the immobilization yield and relative efficiency for methanol production to 48.6% and 96.8%, respectively. In the presence of paraffin oil, methanol production was 1.6-fold higher by Methylocystis bryophila than by control. Compared to free cells, whole cells immobilized on CC showed higher stability for methanol production. Under repeated batch conditions, cumulative methanol production by immobilized cells and free cells, after eight cycles of reuse, was 52.9 and 30.9 mmol/L, respectively. This study effectively demonstrated the beneficial influence of lignocellulosic biowaste CC as support for immobilization of methanotrophs and paraffin oil on bioconversion of CH₄ to methanol.

Comparison of the methane-oxidizing capacity of landfill cover soil amended with biochar produced using different pyrolysis temperatures

The in-situ mitigation of methane (CH₄) in landfill gas using landfill cover soil (LCS) is a cost-effective approach, but its efficiency needs to be enhanced. In this study, we incorporated an enriched methane-oxidizing bacteria (MOB) consortium into LCS and established four biochar-amended LCS groups with biochar produced at 300 °C (BC300), 400 °C (BC400), 500 °C (BC500), and 600 °C (BC600). The purpose was to evaluate the CH₄ oxidation capacity of biochar-amended LCS after inoculation with MOB and to investigate how the physicochemical properties of biochar that are influenced by the pyrolysis temperature affect the performance and microbial activity of biochar-amended LCS. It was found that a 15% volume ratio (representing a mass ratio of 2.49%-2.78%) for biochar amendment in LCS enhanced CH₄ removal efficiency, with the highest removal observed to be 46% for BC400-amended LCS compared to 30% for the original LCS. In addition, CH₄ adsorption by the biochar was not observed, and a 15% mass ratio for biochar in the LCS had no or a negative impact. Besides improving the water-holding capacity and gas permeability of LCS, other possible advantages of biochar amendment in terms of CH₄ oxidization include greater retention of nutrients, electron acceptors, and exchangeable cations, as well as introducing iron ions. It was also found that CH₄ oxidation capacity and the methanotroph activity of biochar-amended LCS did not continue to increase with higher pyrolysis temperatures, even though higher micropore volumes and surface areas were obtained at higher pyrolysis temperatures. From this study, BC400 was identified as the optimal choice for the best performance in terms of enhancing both the CH₄ oxidation capacity of the amended LCS and the growth of type II methanotroph Methylocystaceae, which can possibly be attributed to having the highest cation exchange capacity of the four biochars.

Improved methane elimination by methane-oxidizing bacteria immobilized on modified oil shale semicoke

Methane is a greenhouse gas with significant global warming potential. The methane-oxidizing bacteria (MOB) immobilized on biocarrier could perform effectively and environmentally in methane elimination. To further improve the efficiencies of MOB immobilization and methane elimination, the surface biocompatibility of biocarrier needs to be improved. In this work, the oil shale semicoke (SC) was chemically modified by sodium p-styrenesulfonate hydrate (SS) and 2-(methacryloyloxy)ethyltrimethylammonium chloride (DMC) to promote surface hydrophilicity and positive charge, respectively. Results revealed that, under methane concentrations of ~10% (v/v) and ~0.5% (v/v), the MOB immobilized on semicoke modified with 1.0 mol L^-1 of SS permitted improved methane elimination capacities (ECs), which were 15.02% and 11.11% higher than that on SC, respectively. Additionally, under methane concentrations of ~10% (v/v) and ~0.5% (v/v), the MOB immobilized on semicoke modified with 0.4 mol L^-1 of DMC held superior ECs, which were 17.88% and 11.29% higher than that on SC, respectively. The qPCR analysis indicated that the MOB abundance on modified semicoke were higher than that on SC. In consequence, the surface biocompatibility of semicoke could be promoted by SS and DMC modifications, which potentially provided methods for other biocarriers to improve surface biocompatibility.

Methanol production from simulated biogas mixtures by co-immobilized Methylomonas methanica and Methylocella tundrae

In the present study, co-cultures of the methanotrophs Methylocella tundrae, Methyloferula stellata, and Methylomonas methanica were evaluated for improving methanol production with their application. Among the different combinations, the co-culture of M. tundrae and M. methanica increased methanol production to 4.87 mM using methane (CH₄) as feed. When simulated biogas mixtures were used as feed, the maximum methanol production was improved to 8.66, 8.45, and 9.65 mM by free and encapsulated co-cultures in 2% alginate and silica-gel, respectively. Under repeated batch conditions, free and immobilized co-cultures using alginate and silica-gel resulted in high cumulative production, up to 24.43, 35.95, and 47.35 mM, using simulated biohythane (CH₄ and hydrogen), respectively. This is the first report of methanol production from defined free and immobilized co-cultures using simulated biogas mixtures as feed.