Methods for determining the methane generation potential and methane generation rate constant for the FOD model: a review

In the first order decay (FOD) model of landfill methane generation, the methane generation potential (L₀) and methane generation rate constant (k) for both bulk municipal solid waste (MSW) and individual waste components have been determined by a variety of approaches throughout various literature. Differences in the determination methods for L₀ and k are related to differences in our understanding of the waste decomposition dynamics. A thorough understanding of the various available methods for determining L₀ and k values is critical for comparative study and the drawing of valid conclusions. The aim of this paper is to review the literature on the available determining methods and the ranges for L₀ and k values of both bulk MSW and individual waste components, while focusing on understanding the decomposition of waste, including the role of lignin. L₀ estimates in the literature are highly variable and have been derived from theoretical stoichiometric calculations, laboratory experiments, or actual field measurements. The lignin concentration in waste is correlated with the fraction of total degradable organic carbon (DOC_f) that will actually anaerobically degrade in the landfill. The k value has been determined by precipitation rates, laboratory simulations, aged-defined waste sample, and model fitting or regression analysis using actual gas data. However, the lignin concentration does not correlate well with the k value, presumably due to the impact of lignin arrangement and structure on cellulose bioavailability and degradation rate. In sum, this review summarizes the literature on the measurement of L₀ and k values, including the dynamics and decomposition of bulk MSW and individual waste components within landfills.