Reduction of Methane Emission From Landfill Through Microbial Activities in Cover Soil: A Brief Review

Abstract

Scientifically designed landfill or open dumpsites are used for disposal of municipal solid waste (MSW) in many developed and developing countries. These two systems pose two environmental challenges such as generation of landfill leachate and emission of greenhouse gases (GHGs). Because the GHG emission has been considered to be a global threat, various options have been tried to mitigate the emission of GHGs, especially methane (CH 4 ). The capture and disposal of the landfill gas (LFG) emanating from landfills is technically difficult and costly. The conventional methods for reducing LFG consist of flaring or combustion with energy recovery in engines. Due to the technical difficulties and/or high cost associated with these conventional possibilities, many other alternatives are being investigated. Among these, microbial oxidation of CH 4 stands as a cost-effective candidate to minimize the GHG emission from landfills to the atmosphere. Many researchers have worked in this area and the results are encouraging. This paper is an attempt to review this candidate.

Methane emissions as energy reservoir: Context, scope, causes and mitigation strategies

“…Differences among landfill specific organism groups include the ability to co-metabolize other non-CH4 organic compounds, CH4 consumption rates, O2 requirements, the CH4 concentration that triggers oxidation, temperature and moisture change resiliency, and the release of various extracellular chemicals (at least partially to address internal production of formaldehyde) [212]. These extracellular chemicals can clog soil pores and prevent organisms from accessing gas [193]. In general, methanotropes transform more CH4 in summer than winter [139].…”

“…But not all constituents degrade even under these optimal anaerobic conditions [201]. In landfills, with plastic wraps, differential and uneven exposure to water, and other factors, it is clear that most degradable compounds do not evolve into CH4 in sanitary landfills [191], at least partly due to isolation from water flows carrying nutrients [193], so that, in a sense, landfills constitute a carbon sequestration vehicle for time periods of decades to centuries [201]. It has been argued eventually the organic matter will decay, although it may take millennia [187].…”

“…Under mesophilic (~35°C) conditions, the efficiency is expected to reach~75% [193]. The state of the wastes, including differing origins (industrial, commercial, residential) and whether they are shredded will affect degradation [193]; recent preferences in the US for tightly baled and wrapped bundles of wastes that enhance transportability are likely to suppress degradation, as well.…”

“…There are two ways to assimilate CH4. Type I methanotropes (eight genera in Methylococcaceae) assimilate formaldehyde via the ribulose monophosphate pathway, but Type II methanotropes (four genera in Methylocystacecae) assimilate formaldehyde through the serine pathway [193]. Approximately 50% of CH4 affected by these microbes is assimilated, and the remainder is oxidized, providing metabolic energy [181].…”

“…Water flows are also likely to be the best means to transport nutrients and organic substrates [193], so wastes outside of flow paths or isolated from other wastes inside plastic bags are unlikely to degrade quickly, if at all. Since collected wastes are mostly aerobic, the microbial communities must either be facultative or able to survive long exposures to oxic conditions.…”