The process is more stable when the volatile fatty acid
(VFA) concentrations approach a minimal level, which can be taken as an indication that a sufficient methanogenic population
exists and sufficient time is available to minimize hydrogen
and VFA concentrations.
Performance of phosphorus accumulating organisms (PAOs)
Biological phosphorus removal can occur in the activated
sludge process if aerobic phosphorus accumulating organisms
(PAOs) are present in the system.
The stimulation of the
growth of organisms can be achieved if anaerobic and aerobic
conditions alternate in turns, and volatile fatty acids (VFAs)
are added or formed in the anaerobic condition by the fermenting
bacteria .