Economic and CO2 avoided emissions analysis of WWTP biogas recovery and its use in a small power plant in Brazil

An anaerobic wastewater treatment generates at the end of its process an anaerobic biomass, also known as anaerobic sludge, and a major sub product, the biogas, composed mainly by methane (CH4) and carbonic gas (CO2). The biogas needs to be collected in order to be flared or used in another process, especially because it cannot be released directly into the atmosphere due to methane gas and its high global warming potential. Nevertheless, when this gas is burnt, an energy vector for micro generation is discarded. In the present work was designed a thermal power plant using the biogas produced in an anaerobic wastewater treatment plant (WWTP) through an implementation methodology that considers the population growth according to a southeast ordinary Brazilian city. The energy production potential, avoided CO2 emissions due to the biogas burnt and the possibility of using this energy to supply the WWTP's internal demand consumption were analyzed, as well as the project's economic viability and the arising benefits from carbon credits, calculated in three scenarios. The data of calculus were based on the Brazilian sales tariffs obtained from Brazilian National Electric Energy Agency - ANEEL, where: i) T1 = 64.9 [US$/MWh] (average tariff on Brazilian energy auction A-5); ii) T2 = 86.47 [US$/MWh] (average tariff for thermal power plants in the same auction), and iii) the third scenario, in which the energy produced would be consumed by the WWTP's internal demand. The economic viability was only achieved in second and third scenarios, being intensified in the scenario that WWTP's internal demand is supplied using the energy generated in the biogas plant.