Impact of a methane emission tax on circular economy scenarios in small wastewater treatment plants

This paper analyzes the impact of methane emissions taxation on the recovery of the investments required for implementing technologies that use biogas energy in small wastewater treatment plants (WWTPs) in Brazil. It is based on the hypothesis that the adoption of a national methane emission tax policy would encourage small WWTPs to become sustainable power plants. The procedure involved 173 anaerobic plants to analyze: (a) methane production; (b) available useful energy; (c) investments and avoided costs for implementing STHIL system (thermal drying sludge) and motor generator (electricity generation); (d) financial impact for two scenarios (C1: no emissions tax; C2: with tax). Positive environmental and financial results were observed for WWTPs, varying according to the period of time analyzed for both technologies. Investments must be made in cogeneration in anaerobic WWTPs for achieving satisfactory results. Taxation must not be viewed simply as a punitive instrument; on the contrary, it should be seen as a tool to encourage continuous process improvement. The circular economy may support the enlargement of the wastewater collection and treatment system, guaranteeing widespread sanitation conditions in urban areas. However, the actual implementation of a methane emission tax in Brazil still requires many rounds of discussion among sanitation companies, government, and civil society, to establish emission limits, and unit taxes, as well as to consolidate a carbon trade to follow through with this decision in the sanitation sector.