The pathway of the organic in IAFMBR was obviously changed
with temperature (Fig. 3). About 13.6%, 16.9% and 24.7% of
CODinfluent were transferred to VFAs at 35, 25 and 15 C, separately,
and about 53.1%, 55.4% and 39.5% were removed in the form of
methane, respectively. The part of CODVFAs in the effluent gradually
increased as the temperature was reduced. While lowering operational
temperature from 35 to 15 C, the accumulation of acetic
acid in the effluent increased sharply (the contribution of acetic
acid for CODVFAs was 56.2% and 72.7%). A logical explanation to
acetic acid accumulation should be the decrease of methanogens
activity. However, it was noteworthy that the part of COD removed
in the form of methane increased from 53.1% to 55.4% when temperature
dropped from 35 to 25 C, combined with an increase of
CODVFAs from 13.6% to 16.9%. The mesophilic temperature (25 C)
did not seem to negatively influence the methane production of
IAFMBR. Moreover, although more than 50% of the influent COD
was converted into methane, only part of which was collected in
the form of gas, about 21.6%, 28.6% and 45.2% of methane was dissolved
into the water. In order to improve the utilization of methane
in practical application, it is necessary to set a gas–water
separator to recover methane dissolved in water.