Analysis of the economic viability of the use of biogas produced in wastewater treatment plants to generate electrical energy

Basic sanitation in developing countries such as Brazil still needs many investments today to meet the population appropriately. Therefore, the study of technologies that can facilitate the deployment of sewage treatment systems becomes essential. In this sense, the objective of this study was to evaluate the energy potential and the economic viability of the operation efficiency of biogas from anaerobic digestion of sewage and sewage sludge in wastewater treatment plants in the state of Minas Gerais, Brazil. Economic analysis was considered for the local legislation that establishes a system of energy compensation for distributed generation. The potential for reducing emissions of greenhouse gases (GHG) with the application of the methane recovery system was always estimated. For the biogas production calculations, real data on the volume of treated sewage and the population served with sanitary sewage were presented in a report by the local authority. The results indicated that the methane recovery system is feasible in most cities above 50,000 inhabitants, 86% of the municipalities with a population between 50,000 and 150,000 inhabitants, 67% of the municipalities with a population between 150,000 and 250,000 inhabitants and 100% of the municipalities with a population exceeding 250,000 inhabitants; these showed positive NPV and IRR, greater than the rate of attractiveness (8%). The time needed for return on investment (payback) in municipalities where the investment was feasible was 1.25 years for cities with a population of more than 250,000 inhabitants, 4.49 years for cities with a population between 150,000 and 250,000 inhabitants, 2.08 years for cities with a population between 50,000 and 150,000 inhabitants and 7.97 years for cities with a population of less than 50,000 inhabitants. In addition, a potential for electricity generation in the state of Minas Gerais of approximately 47,140 MWh per year and a potential reduction in emissions of GHG close to 325,800 tCO2eq/year with the deployment of the system was identified.