Methane production and bromatological characteristics of the different fractions of organic municipal solid waste

In some countries, garden trimmings are not considered part of urban solid wastes. Lignocellulosic substances contribute to heterogeneity, complicating the analysis of the organic fraction of municipal solid waste (OFMSW) and, subsequently, for methane production. Some of the substances contained in OFMSW are readily biodegradable, and others are not. This work analyses OFMSW from Mexico City and the methane production from its separate components. From OFMSW, nine fractions were visually identified and separated. Including bromatological and fibre analysis, the characterisation of OFMSW and its components was made to determine how the different substances influence methane production. Together, branches, dry leaves, fresh garden trimmings, unsorted wastes (mainly garden trimmings), kitchen paper, and waste vegetables represent 56 % of OFMSW in weight. Fruit waste and unsorted organics contribute to 60 % of the total methane production. Except for branches and dry leaves, methane production increases inversely with the content of lignocellulosic compounds. Animal waste, having the highest concentrations of proteins and lipids and the lowest in lignocellulosic substances, is characterised by the highest level of methane production. Fibre-rich fractions in OFMSW contributed with little or no methane production. Higher concentrations of lignocellulosic substances in the fractions resulted in lower methane production rates.