ReviewPerformance of the biotic systems for reducing methane emissions from landfill sites: A review

Today, solid waste landfilling is considered to be one of the major environmental concerns due to its significant methane (CH4) production. Although selecting landfill as a viable option for solid waste management should be given the last priority due to considerable greenhouse gas (GHG) emissions in comparison to other waste management technologies. However, it is still a popular way of monitoring solid waste production throughout the world. It is generally estimated that landfill gas (LFG) accounts for more than half of the GHG emissions from waste sectors, so it is globally regarded as a major environmental challenge. Therefore, it is vital to promote management techniques to reduce CH4 emission from landfills to address the global warming nuisance and decrease the human risks concerning LFG migration from landfill sites. Biotic oxidation of CH4 in landfill cover soil has been given utmost attention for mitigation of CH4 emissions over the recent years. CH4 oxidation is a process which naturally takes place through different layers of cover soil due to the profusion of methanotrophic organisms. The contribution of these bacteria to CH4 oxidation is affected by several environmental controlling factors. These factors include the nutrient requirement, and the operating conditions such as pH, temperature, and moisture content of the cover soil, which are considered to be the main bioreactor bed. The prolonged operation of the biotic systems was found to be adversely influenced by the self-degradability of the material, which resulted in more CH4 production rather than oxidation. Such conditions might result in the formation of pore-clogging exopolymeric substances (EPS) that restricts O2 penetration to the cover soil and CH4 oxidation potential. These issues resulted in the poor performance of the biotic systems and no potential solution has not been clearly presented in the literature. Therefore, the aim of this study was to review the recent field and laboratory studies associated with different types of soil and biotic systems. In addition, the advantages and disadvantages of every biotic process to reduce CH4 emission from landfill sites were also discussed.