EFFECT OF SEWAGE-SLUDGE ADDITION ON THE STARTUP OF THE ANAEROBIC-DIGESTION OF OFMSW

The performances and stabilities of three laboratory-scale semi-batch anaerobic digesters, operated at 35 degrees C, treating organic fracti on of municipal solid waste (OFMSW) and primary sewage sludge (PSS) mi xed at various ratios were compared during the start-up period. The OF MSW:PSS ratios in the feeds to the three digesters were 100:0, 80:20, and 60:40 on a total solids (TS) basis and their organic loading rates (OLR) were 5.2 kg VS m(-3) d(-1), 3.9 kg VS m(-3) d(-1), and 3.2 kg V S m(-3) d(-1), respectively. There were no indications of failure in a ny of the digesters. However, addition of primary sewage sludge signif icantly decreased the imbalances observed during the start-up and impr oved the process performance. The best performance in terms of specifi c gas production rate (SGPR) was obtained with a feedstock having an O FMSW:PSS ratio of 80:20. The use of inoculum from an operating anaerob ic digester enabled a quick start-up and the reactors were capable of handling high OLRs from the beginning of the experiment.