Greenhouse gases emissions accounting for typical sewage sludge digestion with energy utilization and residue land application in China

About 20 million tonnes of sludge (with 80% moisture content) is discharged by the sewage treatment plants per year in China, which, if not treated properly, can be a significant source of greenhouse gases (GHGs) emissions. Anaerobic digestion is a conventional sewage sludge treatment method and will continue to be one of the main technologies in the following years. This research has taken into consideration GHGs emissions from typical processes of sludge thickening + anaerobic digestion + dewatering + residue land application in China. Fossil CO2, biogenic CO2, CH4, and avoided CO2 as the main objects is discussed respectively. The results show that the total CO2-eq is about 1133 kg/t DM (including the biogenic CO2), while the net CO2-eq is about 372 kg/t DM (excluding the biogenic CO2). An anaerobic digestion unit as the main GHGs emission source occupies more than 91% CO2-eq of the whole process. The use of biogas is important for achieving carbon dioxide emission reductions, which could reach about 24% of the total CO2-eq reduction.

► GHGs emissions from sludge digestion + residue land use in China were calculated. ► The AD unit contributes more than 97% of total biogenic GHGs emissions. ► AD with methane recovery is attractive for sludge GHGs emissions reduction.