3.1.3. Power generation
The SMFCs operated at short circuited mode that is with zero
external resistance did not produce any sustainable power. However,
in order to facilitate comparison of electrochemical behavior,
the maximum power produced during polarization was compared
for these SMFCs. The one which produced more power during
polarization certainly had better electrochemical behavior with
better biofilm developed on electrodes, and hence contributed
more for organic matter removal due to electrochemistry rather
than removal of organic matter due to substrate utilization by
suspended microbes. Power generation was also observed to be
proportional to pH (Fig. 3). Power produced from a SMFC operated
with feed pH of 6.5 was 3.96 mWm−2 and for SMFC operated at
feed pH of 8.5, it was 4.52 mWm−2 (Table 1). Lower pH might have
reduced the enrichment of electrogenic bacteria during biofilm formation
on the electrode. This has reduced the power generation at
acidic pH despite of higher COD removal efficiency obtained during
this operation. Researchers have found that the acidic pH reduces
electricity production. Gil et al. (2003) and He et al. (2008) have
reported that low pH (5 and 6) resulted in lower electricity generation.
The optimal pH range for chosen MFC configuration was
reported to be between 7 and 8 (Gil et al., 2003) and 8 and 10 (He
et al., 2008). Ren et al. (2007) reported that significant decrease in
power production occurred when the final pH, i.e., the pH in anodecompartment dropped to 5.2 due to the acidic products of fermentation
and power production was quickly resumed when the pH
was increased to 7.0. Yuan et al. (2011) reported that most electrochemically
active biofilm is achieved under alkaline condition. They
have demonstrated that larger numbers of bacteria were attached
to anode at pH 9.0 when compared to that at pH of 5.0.