A biochemical hypothesis explaining the response of enhanced biological phosphorus removal biomass to organic substrates.

Anaerobic/aerobic batch experiments were conducted with a variety of volatile fatty (VFAs) and amino acids on two sequencing batch reactor populations displaying enhanced biological phosphorus removal. The batch experiments were consistent between the two systems and with the past literature: acetic and isovaleric acid were the most efficient substrates, and propionic acid was the least efficient of the 2-5 carbon VFAs (lack of acclimation was ruled out). A survey of the engineering and biochemical literature revealed that both acetic and isovaleric acid resulted in a negative reaction redox balance (i.e. it requires reducing equivalents such as NADH2) during their biotransformation to polyhydroxyalkanoates (PHAs). In addition, the survey indicated that acetic and isovaleric acid resulted in 3HB rather than 3HV or 3H2MV formation. Two possible hypotheses were put forward for evaluation: (1) it was hypothesized that a negative intracellular redox balance might result in higher PHA content since PHA biosynthesis could be sustained under anaerobic conditions (no NADH2 build up), and/or (2) it was hypothesized that 3HB resulted in greater P-uptake than other PHA forms such as 3HV.