Greenhouse gas emissions from urban wastewater treatment systems in Managua, Nicaragua

ABSTRACT Graphical abstract of eight wastewater treatment plants in Managua, showing treatment types and emissions; anaerobic systems produce more methane, while aerobic systems produce more carbon dioxide. This study presents the first comprehensive assessment of greenhouse gas (GHG) emissions from decentralized sewered urban wastewater treatment systems (WWTS) in Nicaragua, focusing on eight representative plants in Managua's southern lake basin. It estimates CH4 and N2O emissions using IPCC methodologies, combining field surveys with historical data from 2013 to 2024 to quantify emissions from small-scale systems. The WWTS – including extended aeration, UASB reactors, biodigesters, and MBBR technologies – collectively emitted 8,113.33 kg CO2-eq/day (2.96 Gg CO2-eq/year), representing 0.353% of Nicaragua's wastewater sector emissions. Anaerobic systems (WWTS 2/3/6/8) dominated methane (CH4) release (60–85% of footprint, up to 76.1 m3 CH4/day), while energy-intensive aerobic plants (WWTS 1/7) showed the highest CO2 emissions (309.28 kg/day at 0.264 kWh/m3). N2O emissions (0.005 kg N2O-N/kg N removed) peaked at 0.364 kg/day in systems with nitrogen removal. This study addresses important data gaps regarding decentralized wastewater treatment systems (WWTS) in developing regions with limited data and offers a framework for aligning wastewater management with climate objectives. The findings highlight the urgent need for localized emission factors and capacity building to reduce greenhouse gas (GHG) emissions from the rapidly growing urban sanitation infrastructure in Nicaragua.