Metagenomics illuminated the mechanism of enhanced nitrogen removal and vivianite recovery induced by zero-valent iron in partial-denitrification/anammox process

•A strategy of ZVI combined with acetic acid to optimize the PD/A process is proposed.•Vivianite is the main product of P recovery in PD/A supplied with novel method.•ZVI-induced DNRA pathway played an important role in high-rate of nitrogen removal.•ZVI acting as new electron donor reduced the dependence of PD/A on organics.