Abstract
Methane production during solid waste decomposition is a typical methanogen-mediated and enzyme-catalyzed anaerobic digestion (AD). Methanogen community dynamics and metabolic diversity during the decomposition are not known. In this study, we investigated methanogen community dynamics and methanogenic pathways during solid waste decomposition in a bioreactor using high-throughput Illumina MiSeq sequencing and phylogenetic investigation of communities by reconstruction of unobserved states (PICRUSt), respectively. We also related the methanogen community differences with solid waste and leachate physiochemical parameters. Results showed that the percentage of biodegradable matter (BDM) in solid waste decreased from 55 ± 5% in aerobic phase (AP) to 30 ± 2% in anaerobic acid phase (ACP), and to 13 ± 11% in methanogenic phase (MP), resulting in 76% BDM consumption by microbes. Methanogen community structure varied in AP, ACP, and MP, showing that Methanomicrobiales and Methanosarcinales were dominant in AP and MP and archaea E2 was abundant in ACP. Each phase had abundant core methanogen orders, genera, and species with significant difference (p < 0.05). Redundancy analysis showed that biochemical oxygen demand (BOD5) and nitrate significantly influenced methanogen community composition, suggesting that methanogen community structure is nutrient-dependent. Two methanogenic pathways including acetoclastic and hydrogenotrophic pathways with associated functional genes differed at three phases. ACP had the lowest abundance of these genes, indicating that methanogenesis was inhibited in acidogenesis. Abundant hydrogenotrophic and acetoclastic methanogenesis functional genes in MP and AP are in response to the abundance of Methanomicrobiales and Methanosarcinales. The findings provide previously unidentified insight into the mechanism of methanogen community structure and function during solid waste bioconversion for methane.
Highlights
The world is facing the challenges of energy shortage and climate change
Methanogen community structure varied in aerobic phase (AP), acid phase (ACP), and methanogenic phase (MP), showing that Methanomicrobiales and Methanosarcinales were dominant in AP and MP and archaea E2 was abundant in ACP
Abundant hydrogenotrophic and acetoclastic methanogenesis functional genes in MP and AP are in response to the abundance of Methanomicrobiales and Methanosarcinales
Summary
Various innovation techniques are developing to produce and recover clean energy such as methane (Niu et al, 2014; Li et al, 2017b). Municipal solid waste (MSW) landfills are an important methane resource, representing 22% of global anthropogenic emissions (IPCC, 2013). Powell et al (2016) investigated 850 landfills in the United States and found that the CH4 emissions from landfills are largely underestimated (262 million tons vs 121 million tons estimated by United States EPA), suggesting that more bioenergy is stored in landfills. Methane production (methanogenesis) in solid waste decomposition is a typical methanogen-mediated and enzymecatalyzed anaerobic digestion. Methanogenesis uses carbon such as acetic acid and carbon dioxide as the terminal electron acceptor to produce methane. Understanding the underlying mechanism of methanogen community dynamics and metabolic diversity during solid waste decomposition is critical for methane production and recovery
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