The landfill is an inexpensive way of municipal solid waste (MSW) management and contributes extensively to the total carbon budget and global climate change. Three landfills from two geographically distinct metro- cities of India were taken as model systems to create microcosms and study their physiochemistry, microbiology, and carbon emission. The microcosm experiments revealed that facultative anaerobic bacterial community showing the dominance in the beginning but with the progression of anoxia and anaerobic conditions, methanogenesis prevailed, resulting in a clear shift towards the abundance of methanogens especially the members of Methanosarcina, Methanocorpusculum, and Methanoculleus (70-90% of the total microbial population). Geochemical data showed a wide range of heterogeneity in landfills\' composition located even in the same city. In past, greenhouse gas emission from landfills is mainly estimated using different models which lack accuracy. As limited information is available as of now, this study can elicit researcher interest for in-depth characterization of microbial diversity and carbon emission from landfills. The microcosm model presented in the current study is a robust and straightforward method of accurate estimation of amounts of different types of gases release from landfill. It can also be extrapolate for estimation of different gases release from actual landfill sites by setting the on-site experiments.
UNASSIGNED: The online version contains supplementary material available at 10.1007/s12088-021-00995-7.

Most commonly, next generation sequencing-based microbiome studies are performed on the total DNA (totDNA) pool; however, this consists of extracellular- (exDNA) and intracellular (iDNA) DNA fractions. By investigating the microbiomes of different anaerobic digesters over time, we found that totDNA suggested lower species richness considering all and/or only common species and yielded fewer unique reads as compared to iDNA. Additionally, exDNA-derived sequences were more similar to those from totDNA than from iDNA and, finally, iDNA showed the best performance in tracking temporal changes in microbial communities. We postulate that abundant sequences present within the exDNA fraction mask the overall results of totDNA and provide evidence that exDNA has the potential to qualitatively bias microbiome studies at least in the anaerobic digester environment as it contains information about cells that were lysed hours or days ago. iDNA, however, was found to be more appropriate in providing reliable genetic information about potentially alive as well as rare microbes within the target habitat.

This study investigated the operation of ex-situ biological methanation at two thermophilic temperatures (55°C and 65°C). Methane composition of 85-88% was obtained and volumetric productivities of 0.45 and 0.4LCH4/Lreactor were observed at 55°C and 65°C after 24h respectively. It is postulated that at 55°C the process operated as a mixed culture as the residual organic substrates in the starting inoculum were still available. These were consumed prior to the assessment at 65°C; thus the methanogens were now dependent on gaseous substrates CO2 and H2. The experiment was repeated at 65°C with fresh inoculum (a mixed culture); methane composition and volumetric productivity of 92% and 0.46LCH4/Lreactor were achieved in 24h. Methanothermobacter species represent likely and resilient candidates for thermophilic biogas upgrading.