Design and Economic Evaluation of a Prototype Biogas Plant Fed by Restaurant Food Waste

Abstract

Food waste and other biodegradable matter in the municipal solid waste stream are a source of environmental and public health concern in cities of developing countries. Anaerobic digestion applied to urban solid organic waste treatment is an option to address those issues and to produce biogas, a renewable energy source. This paper presents the design and economic evaluation of a prototype biogas plant fed by food waste from a restaurant in Mexico City. On average, the restaurant produces 40.5 kg/day of food waste with 23.0% total solids (TS) and 94.2% total volatile solids (TVS). With this amount of food waste, around 69.2 L/day of feeding substrate with 12.7% TVS are produced. Considering an operating temperature of 20°C, total anaerobic digester volume required was calculated at 6.0 m 3 . Plant design comprises a continuous stirred tank reactor (1 m 3 ) coupled with a conventional digester (5 m 3 ). Organic loading rate and hydraulic retention time were 1.9 kg-TVS/(m 3 ∙day) and 86 days, respectively. The plant is expected to produce 6.1 m 3 /day of biogas for use as a cooking fuel at the same restaurant, leading to LP gas savings of 692 kg/year. Plant investment cost was estimated at MXN 129,000 (~9,550 USD). Economic evaluation showed that the biogas plant profitability is highly dependent on LP gas price and its annual growth rate. The prototype biogas plant described here is a step forward in the conception of a biogas facility suitable for cities in developing countries to collaborate in solving their environmental, public health, and energy concerns.