Tobermolite effects on methane removal activity and microbial community of a lab-scale soil biocover

Laboratory scale bioreactor designs in the processes of methane bioconversion: Mini-review

Global methane emissions have been steadily increasing over the past few decades, exerting a negative effect on the environment. Biogas from landfills and sewage treatment plants is the main anthropogenic source of methane. This makes methane bioconversion one of the priority areas of biotechnology. This process involves the production of biochemical compounds from non-food sources through microbiological synthesis. Methanotrophic bacteria are a promising tool for methane bioconversion due to their ability to use this greenhouse gas and to produce protein-rich biomass, as well as a broad range of useful organic compounds. Currently, methane is used not only to produce biomass and chemical compounds, but also to increase the efficiency of water and solid waste treatment. However, the use of gaseous substrates in biotechnological processes is associated with some difficulties. The low solubility of methane in water is one of the major problems. Different approaches have been involved to encounter these challenges, including different bioreactor and gas distribution designs, solid carriers and bulk sorbents, as well as varying air/oxygen supply, the ratio of volumetric flow rate of gas mixture to its consumption rate, etc. The aim of this review was to summarize the current data on different bioreactor designs and the aspects of their applications for methane bioconversion and wastewater treatment. The bioreactors used in these processes must meet a number of requirements such as low methane emission, improved gas exchange surface, and controlled substrate supply to the reaction zone.

Design and shelf stability assessment of bacterial agents for simultaneous removal of methane and odors

Two types of solid bacterial agents for the simultaneous removal of methane and odor were designed using humic soil (De-MO-1) and the mixture of humic soil and tobermolite (De-MO-2) as biocarriers. The bacterial consortium, having the removability of methane and dimethyl sulfide (DMS), was immobilized in the biocarriers, and then stored at room temperature for 375 days without additional treatment. Although the lag period, of which the incubation time required for removing methane and DMS, tended to increase over the storage period, the removability of methane and DMS was maintained during 375 days in both bacterial agents. Key bacteria associated with the removal of methane and odors (Streptomyces, Promicromonospora, Paracoccus, Lysobacter, Sphingopyxis and Methylosystis) could keep their abundance during the storage period. The richness and evenness values of the bacterial communities in De-MO-1 and De-MO-2 ranged 4.89 ∼ 6.50 and 0.89 ∼ 0.98, respectively, indicating that high bacterial diversity was maintained during the storage period. The results suggest that De-MO-1 and De-MO-2, designed for the simultaneous removal of methane and odors, had shelf stabilities over one year.

Biocomplex textile as an alternative daily cover for the simultaneous mitigation of methane and malodorous compounds

Space-saving biocomplex textiles, which can be used as covers or rolled up as needed, have been demonstrated as alternative daily covers for the simultaneous mitigation of greenhouse gases (GHGs) and odors in landfills. The biocomplex textiles were made by inserting inorganic biocarriers (perlite (P), tobermolite (T) and their mixture (P/T)) between nonwoven fabrics. Methane (CH₄) and dimethyl sulfide (DMS) were used as model compounds for GHGs and odors, and a CH₄ and DMS co-degrading microbial consortium was used as an inoculum source. CH₄ and DMS could be biologically degraded by methanotrophs and sulfur-oxidizing bacteria in the biocomplex textiles. Both biocomplex textiles made with either P or T were able to maintain the removability for CH₄ and DMS after storage for 70 days, although their removal efficiencies for CH₄ and DMS were 70-71% and 62-65% of those before storage, respectively. CH₄ and DMS were simultaneously removed in lab-scale landfill simulation reactors employed with the biocomplex textiles. After 17 days of starvation, only 2-3 days were needed to recover their removability. Among the 3 kinds of biocarriers evaluated, the biocomplex textile generated using the P/T showed the highest removability and was the most stable. The maximum elimination capacities of the biocomplex textile generated with the P/T were 11.5 g-CH₄·m^-2-fabric·d^-1 and 0.5 g-DMS·m^-2-fabric·d^-1, respectively. These results suggest that the biocomplex textiles are promising alternative daily covers to mitigate the emission of greenhouse gas and odor in operational landfills.

Seasonal characteristics of odor and methane mitigation and the bacterial community dynamics in an on-site biocover at a sanitary landfill

Landfills are key anthropogenic emission sources for odors and methane. For simultaneous mitigation of odors and methane emitted from landfills, a pilot-scale biocover (soil:perlite:earthworm cast:compost, 6:2:1:1, v/v) was constructed at a sanitary landfill in South Korea, and the biocover performance and its bacterial community dynamics were monitored for 240 days. The removal efficiencies of odor and methane were evaluated to compare the odor dilution ratios or methane concentrations at the biocover surface and landfill soil cover surface where the biocover was not installed. The odor removal efficiency was maintained above 85% in all seasons. The odor dilution ratios ranged from 300 to 3000 at the biocover surface, but they were 6694-20,801 at the landfill soil cover surface. Additionally, the methane removal efficiency was influenced by the ambient temperature; the methane removal efficiency in winter was 35-43%, while the methane removability was enhanced to 85%, 86%, and 96% in spring, early summer, and late summer, respectively. The ratio of methanotrophs to total bacterial community increased with increasing ambient temperature from 5.4% (in winter) to 12.8-14.8% (in summer). In winter, non-methanotrophs, such as Acinetobacter (8.8%), Rhodanobacter (7.5%), Pedobacter (7.5%), and Arthrobacter (5.7%), were abundant. However, in late summer, Methylobacter (8.8%), Methylocaldum (3.4%), Mycobacterium (1.1%), and Desulviicoccus (0.9%) were the dominant bacteria. Methylobacter was the dominant methanotroph in all seasons. These seasonal characteristics of the on-site biocover performance and its bacterial community are useful for designing a full-scale biocover for the simultaneous mitigation of odors and methane at landfills.