Constructed wetlands applied for wastewater treatment from a low carbon sanitation perspective

Abstract

Wastewater treatment plants (WWTP) can be a greater or lesser source of greenhouse gases depending on the technology used. In Brazil, most small and medium-sized municipalities served by sewage services adopt anaerobic processes, whose methane generation potential can be up to 80 times higher than that associated with aerobic processes. Considering demographic, geographic and socioeconomical aspects of Brazilian cities and facing the challenge of switching to a low-carbon economy, constructed wetlands (CW) emerges as an important process for wastewater treatment in municipalities with up to 20,000 inhabitants. Based on the Intergovernmental Panel on Climate Change (IPCC) guidelines for greenhouse gas (GHG) inventories, this study aimed at analyzing the potential impact on GHG emissions reduction by the entry of  CW systems in the Brazilian wastewater treatment infrastructure. Assuming a universal sanitation coverage, methane emissions from municipal WWTP were estimated for three different infrastructure scenarios, each one with different participation of CW systems. The control scenario represents the maintenance of the wastewater treatment technologies currently adopted nationwide, and was considered as a baseline for methane emission reduction calculation in the other two scenarios. The results suggested that by switching the use of UASB reactors by CW systems, the methane emissions in the wastewater treatment infrastructure as a whole could be reduced by more than 10%, a value that represents approximately 867 million tons of carbon dioxide equivalent that are no longer emitted annually. In terms of carbon credits, this reduction could represent an average revenue of US$ 35 million per year.