Anaerobic digestibility and SMAmax tests were performed at
a temperature of 30 1C for the sludge in the UASB reactor at
the end of each operational phase. The digestibility and the
SMAmax were carried out for a mixture of the sludge from
each sampling port in the reactor. The anaerobic digestibility
tests were performed in 250mL serum bottles and each
bottle contained 150mL of sludge followed by flushing with
nitrogen gas for 5min to guarantee anaerobic conditions. The
tests were carried out without inoculum addition. Therefore,
the anaerobic digestibility was determined after long period
of 76, 84 and 79 days for the sludge of phases 1, 2 and 3,
respectively. The SMAmax was measured according to Elmitwalli
et al. (2002b), but by measuring CODdis depletion
(instead of acetate depletion) to simplify the test. The SMAmax
was determined based on the CODdis depletion in the second
feed with an initial acetate concentration of 1.5 g COD/L for
each feed and a sludge concentration of 2 g VS/L. The
anaerobic digestibility and SMAmax tests were done in
duplicate for each sample.