Wastewater management in the state of Alagoas, Brazil: greenhouse gas emissions and organic load removal efficiency of wastewater treatment plants

Abstract

Domestic and industrial wastewater treatment plants are categorized as anthropogenic sources of direct greenhouse gases (GHG) emissions. In this study, greenhouse gases emissions from the wastewater sector in the state of Alagoas – Brazil were estimated, and the efficiency of sewage treatment plants was evaluated, based on biochemical oxygen demand (BOD) removal. In addition, possible GHG emission scenarios for direct emission sources were evaluated. To evaluate these emissions, calculation tool developed by the GHG Protocol (scopes 1 and 2) and the Intergovernmental Panel on Climate Changes (IPCC) Guidelines were used. As a result, in 2018, a total of 66.524.76 tCO₂e was emitted, of which 52.677.53 tCO₂e were due to sewage treatment. Electricity consumption was responsible for emitting 13.023.77 tCO₂e. Among wastewater treatment systems, the most efficient for BOD removal was septic tank with stabilization ponds, with 80% removal efficiency. Through scenario evaluations, this study suggests that the replacement of current treatments by well-operated aerobic systems is the most effective strategy in reducing total GHG emissions from sewage wastewater treatment plants. The results obtained constitute a management tool, helping the company in the strategic planning to achieve sustainability.