Scenarios for treatment of sewage sludge from municipal wastewater treatment plants in Hanoi towards energy efficiency and resource recovery

Abstract

Wastewater treatment plants (WWTPs) generate significant amount of sewage sludge (SS). Besides, faecal sludge (FS) generated from popularly existing septic tanks in cities need also adequate treatment. Selection of appropriate sludge treatment options is among most challenging wastewater management issues for fast growing cities. The case study has selected the central part of Hanoi city, with expected population of 2,145,437 persons by 2030, total design capacity of WWTPs 588,300 m3/day, whereas different options of SS and FS management were analysed. The calculation results shown that an energy required for operation of sludge treatment processes in scenarios 2, 3 and 4 could be fully self-sufficient. Besides, with total energy demand for operation of WWTPs was of 311,799 kWh/day, 21.3% (scenario 2), 99.3% (scenario 3) or 71.3% (scenario 4) of demand could be covered by remaining biogas produced from anaerobic co-digestion of SS and FS. A conventional SS treatment process, dewatering by centrifuge and dumping dewatered sludge to the landfill (scenario 1) did not generate any energy but required an energy of 17,371 kWh/day for SS treatment and dumping. Anaerobic co-digestion of SS, FS, other organic fractions, can be a promising sludge management solution aiming at energy efficiency and resource recovery.