From a local viewpoint, the part of AFBR and AnMBR completed
the transformation of organic carbon. The phase of practical
domestic wastewater digestion is in the AFBR, and the result was
good–there was an accumulation of VFAs in the effluent of AFBR
at each temperature. With the step decrease of temperature, the
accumulation of VFAs was more (Fig. 2). Therefore, there were enough
VFAs flowing into AnMBR for methanogens, but the methanogenic
process in AnMBR was not completed (Fig. 3). In fact, the
phenomenon of the separation of acidogenic and methanogenic
processes in an anaerobic process has been observed after longterm
operation (Zhu et al., 2008). And the variety of VFA along a
reactor makes it clear that the acidogenic and methanogenic are
separated. An incomplete methanogenic process may lead to a
harsh environment. In this study, a step dropped temperature is
obviously negatively to methanogens activity. What’s more, attached
growth in AnMBR systems may not be favorable for active
microorganisms, especially at a low temperature. It is not difficult
to speculate that the environmental conditions on cake layer are
not good for attached growth. The methanogenic activity of biofilm
is generally lower due to the shear force by cross flow on the cake
layer, especially at a lower temperature. Another study showed the
same conclusion, the microbial activity of suspended sludge
continuously increased, while that of attached sludge gradually
decreased at a lower temperature (Ho and Sung, 2010).