Landfill gas extraction and purification techniques

Abstract

Landfill Gas (LFG) is mainly composed of methane and carbon dioxide and some other compounds like hydrogen sulphide, water vapor, etc. in trace level. The gas is, basically, generated as an end product of anaerobic decomposition of solid wastes containing organic matter. Studies indicate that LFG production ranges between 0.05 and 0.40 m3 of LFG per kilogram of solid waste (Ham, 1989). There are a number of different ways of collecting gas from landfills. The main part of the collection system includes vertical extraction wells and/or horizontal trenches; headers and piping system; and blower and compressor for creating pressure gradient so that the gas flow is induced. Purification of LFG is important whereby the gas is upgraded to biomethane with relatively higher energy value. There are a number of available techniques designed to upgrade LFG to biomethane by removing the impurities such as CO2, H2S, moisture, etc. Generally, the paper discusses landfill gas generation, gas extraction and purifications techniques. Compositions of LFG and gas generation processes are discussed. Inline with this, different models for estimating the rate of LFG generation are analyzed. Landfill gas generation model of U.S. EPA along with other common quantifying models are explored. The study of LFG extraction and collection systems includes design considerations for LFG collection schemes, gas capture augmenting techniques, and the prediction of gas collection efficiency. An in depth assessment of purification processes of LFG along with upgrading of the LFG to biomethane of different grades is carried out. The discussion on gas purification methods is conducted in accordance with the type of LFG composition, level of treatment required, quality of LFG expected, and the final application of the LFG and biomethane.