Evaluation of greenhouse gas emissions from sludge treatment in Apulia, Southern Italy

The paper reports the greenhouse gas (GHG) evaluation emitted by the sludge treatment of 185 municipal wastewater treatment plant in South Italy and different upgrade Scenarios aimed to reduce GHG emissions. CO2, CH4 and N2O emissions have been analyzed from each treatment station in the sludge line: thickener, aerobic and anaerobic digestion, dewatering. The analysis includes the evaluation of GHG in terms of CO2 equivalent undirect emission due to electrical consumptions and the chemical consumption based on polymer utilization in dewatering station. Three Scenarios have been evaluated: SC1 (Current Estimation) with the gas produced in the anaerobic digester is burned off via flaring, without any energy recovery; SC2 (Dewatering Upgrade): increased % dewatering operations, and SC3 (Dewatering Upgrade + Biogas Recovery): increased dewatering efficiency and methane recovery for biogas production. The analysis demonstrated that the adoption of anaerobic digestion resulted in a higher level of dewaterability in comparison with aerobic digestion at WWTPs, leading to a reduction in the volume of sludge requiring disposal. This was accompanied by an estimated marginal increase in the production of CO₂eq per ton of dry Solid Sludge. Consequently, the Scenario involving anaerobic digestion resulted in a substantial reduction of 11.2% in greenhouse gas (GHG) emissions, thereby reducing the total emissions of sludge from anaerobic-based WWTPs to 1917 kgCO₂eq/tDS.