Inhibition of the respiratory chain reactions in denitrifying EBPR biomass under simultaneous presence of acetate and electron acceptor

•Simultaneous presence of electron donor and acceptor inhibited phosphorus uptake.•PAOs stored exogenous carbon as PHAs irrespectively to their previous PHAs content.•Bacterial ATP requirements are met by oxidative phosphorylation when polyphosphate is limited.•PHAs utilization appears to be directly linked to polyphosphate synthesis. In this study, the deterioration of the typical EBPR (Enhanced Biological Phosphorus Removal) process due to the simultaneous presence of electron donor (external substrate) and electron acceptor (oxygen or nitrate) was investigated by using a PAOs (Polyphosphate Accumulating Organisms)-enriched biomass grown in a modified DEPHANOX system. Intracellular and extracellular constituents were monitored in batch tests under different electron donor and acceptor conditions and specific oxygen and nitrogen uptake rates were evaluated. Results showed that phosphorus uptake was inhibited during the simultaneous presence of electron donor (acetate) and acceptor (O2/NO3−) in the mixed liquor. In the presence of acetate, PHAs and glycogen were produced under both aerobic and anoxic conditions irrespectively to the PHAs amount already stored intracellularly. The Krebs cycle reactions and oxidative phosphorylation provided the reduced coenzymes and energy required for PHAs synthesis when biomass polyphosphate content was low. On the contrary, polyphosphate cleavage provided the ATP required for PHAs synthesis in the presence of high biomass polyphosphate content. Inhibition of the respiratory chain reactions was observed when biomass with high polyphosphate and low PHAs content was subjected to simultaneous presence of electron donor and acceptor. PHAs utilization rather than glycogen degradation appears to favor phosphate accumulation since no polyphosphate synthesis occurred in the absence of PHAs reserves.