Accelerated methane oxidation cover system to reduce greenhouse gas emissions from MSW landfills in cold, semi-arid regions

Abstract

Many regional landfills for municipal solid waste (MSW) and industrial, commercial, institutional (ICI) wastes in cold, dry regions do not produce enough gas to support conventional gas extraction, treatment, and utilization or flaring. Yet, some solution is required to reduce emissions of methane and trace constituents to the atmosphere for the protection of the public and of the global climate. Methane oxidation, as a natural biochemical process, offers an opportunity to reduce methane emissions with a simple, passive alternative cover system. The goal of this article is to develop an effective design of Methane Oxidation Covers to achieve superior methane management performance while still producing equivalent closure conditions to conventional covers in semi-arid, cold climates. specifically, the goal is to reduce methane surface emissions by 50% to 80%, with no significant increase in leachate production compared with conventional covers of clay and topsoil.

A field pilot test of an alternative cover system with gas collection, methane oxidation and heat extraction was conducted on an operating MSW/ICI waste landfill in Western Canada from August 2001 to February 2005. The cool, semi-arid region experiences cold winters (down to minus 40^˚C) for up to 5 months of the year, and annual precipitation rates of 150 mm to 450 mm p.a., of which one third to one half falls as snow.

The need to direct gas from large surface areas to gas control zones of minimal area led to the configuration of the system of gas collection trenches connected to a central methane oxidation (MethOx) bed. The need to keep the bed above 5^˚C in winter required the development of a simple, passive heat transfer system.

The maintenance of suitable moisture contents and the restriction of percolation were accomplished by the choice of filter material and the layering of the bed over the gas percolation layer.

The test program was conducted in three phases from August 2001 to February 2005. In the first test phase, a methane oxidation bed of yardwaste compost performed well during the summer, but froze from November to April and did not resume oxidation until May. Oxygen was always present at or above 3%(vol.) and the moisture content remained above 25%(vol.) in the lower layer of the bed. The freezing temperature caused the most serious performance reduction. In the next phases of the study, a passive heating system was installed in an accelerated methane oxidation bed. Heat exchange from inside the landfill to the filter raised the bed temperature to 14 to 18^˚C during the third winter of the test. The moisture contents of 25% to 50% (v/v) in the bed were high, but the percolation rate was only 7.3 mm/a, or about 2% of total precipitation. The methane oxidation performance increased with the heating of the bed, from a 33% emission reduction in an unheated bed, up to 89% in a well heated filter bed. The achievement of high oxidation performance (over 80%), the complete reduction of surface emissions from the test area (to zero), and the low percolation rate through the filter bed (less that 2%) constitute a proof of principle for MethOx covers in cool, semi-arid climates. The possible improvement of the Alternative Cover System's performance by adding vegetation to the filter bed is currently being tested in the ongoing research project.