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A Megacity-Scale Analysis of Sludge Managementand Carbon Footprint in China
Summary
This analysis of sludge management and carbon footprint across Shanghai's 42 wastewater treatment plants found that the city produces more sludge per capita than other Chinese regions. Managing sludge effectively is important because sludge can contain concentrated microplastics removed from wastewater during treatment.
With the growing capacity of wastewater treated, a large amount of sludge has been generated in China. Shanghai has 42 wastewater treatment plants (WWTPs), with a total design capacity of 8.510 6 m 3 /day. The sludge production per Capita is higher than in other Chinese regions. The sludge management strategy has changed drastically over the past three years in Shanghai. As to the sludge treatment, deep dewatering technologies such as filter-press dewatering and vacuum filter-press dewatering are the most used methods. On the other hand, the ratio of sludge anaerobic digestion and aerobic composting is very low due to the poor sludge quality. Regarding sludge disposal, sludge landfill has been phasing out, but the ratio of sludge incineration has increased significantly. The carbon footprint results show landfill alternatives generally have more greenhouse gas (GHG) emissions than sludge incineration and land use alternatives. The average CO 2 per ton dry solids (DS) has reduced from 0.91 in 2019 to 0.67 ton CO 2 /t DS in 2020 thanks to the optimization of sludge disposal. This study suggests deep dewatering treatment followed by incineration is considered the reasonable and sustainable sludge management scenario in a megacity.