processes in the three rectors, which resulted in the increasing
of the VFA concentration. A high amount of CODdis
and VFAs in the effluent in all the three reactors showed
that methanogenesis was limiting the overall conversion
of organic matter to methane in all the three reactors. The
increasing VFAs concentration, which corresponded with
the decrease in HRT, indicated that methanogenesis was
going on in the reactors, although the process was slow and
negligible at 16◦C.
All sludges produced methane in batch assays with or
without different substrates, with the results presented in
Table 4. SMAs with acetate were highest and similar to
all sludges, approximately 20mL CH4 g−1 VS day−1 for
sludges in R1 and R2, 18mL CH4 g−1 VS day−1 for sludges
in R3. SMAs of R1 sludges with influent were higher than
those of R2 and R3 sludges in all the three operation phases.