The effect of free nitrous acid on key anaerobic processes in enhanced biological phosphorus removal systems

► FNA has a detrimental effect on the anaerobic metabolism of both PAOs and GAOs. ► FNA has a stronger adverse effect on acetate uptake by PAOs than by GAOs. ► FNA causes faster depletion of the anaerobic energy pool of PAO than that of GAOs. ► FNA may potentially provide a competitive advantage to GAOs over PAOs.