Long-term operation of the pilot scale two-stage anaerobic digestion of municipal biowaste in Ho Chi Minh City.

A pilot-scale two-stage anaerobic digestion system, which includes a feed tank (0.4 m), a hydrolysis reactor (1.2 m) followed by a methane fermenter (4.0 m) was set up and run at the municipal solid waste landfill located in Ho Chi Minh City (HCMC), Vietnam. The feed that was separated from urban organic solid waste was collected at households and restaurants in District 1, HCMC. This study aimed to investigate the resource recovery performance of the pilot two-stage anaerobic digestion system, in terms of carbon recovery via biogas production and nutrient recovery from digestate. The average organic loading rate (OLR) of the system was step increased from 1.6 kg volatile solids (VS)·m·d, 2.5 kg VS·m·d and 3.8 kg VS·m·d during 400 days of operation. During the long-term operation at three OLRs, pH values and alkalinity were stable at both hydrolysis and methanogenesis stages without any addition of alkalinity for the methanogenesis phase. High buildup of propanoic acid and total volatile fatty acid concentrations in the fermenter did not drop pH values and inhibit the methanogenic process at high OLRs (2.5-3.8 kg VS m·d). The obtained total chemical oxygen demand (tCOD) removal performance was 83-87% at the OLRs ranging from 2.5 kg VS·m·d and 3.8 kg VS·m·d, respectively. The highest biogas yield of 263 ± 64 L·kg tCOD removed obtained at OLR of 2.5 kg VS·m·d. It is expected that a full scale 2S-AD plant with capacity of 5200 tons day of biowaste collected currently from municipal solid waste in HCMC may create daily electricity of 552 MWh, thermal energy of 630 MWh, and recovery of 16.1 tons of NH-N, 11.4 tons of organic-N, and 2.1 tons of TP as both organic liquid and solid fertilizers.