Urban waste to natural gas: supplementing natural gas supply from a municipal methane recovery plant

Abstract

This report is prepared for Architects, Engineers and Planners interested in Solids Waste Management and concerned about three problems currently facing urban centres in some of the more developed nations. These problems are: 1 increasing production of solids waste per capita; 2 increasing environmental pollution of watersheds and coastal waters through management of solids waste; and 3 increasing energy consumption per capita coupled with diminishing reserves of non-renewable fossil fuels. The report provides one solution available to meet these problems - the anaerobic digestion of sewage sludge with the organic fraction of refuse from urban population to provide the marketable products of synthetic natural gas and organic soil conditioner. The report contains three main sections: 1 an experiement in the anaerobic digestion of a mixture of sewage and refuse to determine factors in methane gas production; 2 a prediction method for the design and operation of plant to maximize residual gas production; and 3 the preliminary design of a municipal methane recovery plant. It was found that the digestion of sewage and refuse was quite feasible, with gas production of 0.02 m3/Kg V.S./day of calorific value of 33.35 megajoules per cubic metre. From the prediction method it was found that a large part of gas produced could be available for supplementing existing natural gas supplies. Finally, it appears technically feasible to provide the recycling of organic resources as part of an urban scale methane recovery plant.