To investigate the performance for MSFU treatment, the
experiment was performed at an OLR of 3.1 kg-
VS m3 day1 and HRT of 11 days in this stage. The biogas
production decreased gradually during the initial period,
and then increased to 579 L kg1-VS added. The methane
content of 76% was the same as in Stage 1. The removal of
VS was 58% and that of COD was 59% (Table 2). The
removal of COD in Stages 1 and 2 was relatively lower than
that reported in previous work (Boopathy, 1998). This is
probably because the digested effluent was discharged
immediately after the source material was fed in, and this
resulted in that a part of the digested sludge floated into
the digested effluent. The pH in the fermentation reactor
decreased slightly, but was kept at 8.0 in this stage.