Zero-Valent Iron-Enhanced Nitrogen and Phosphorus Removal Performance and Mechanisms in a GAO-Dominated System

Zero-valent iron (ZVI) improves nitrogen and phosphorus removal efficiency in municipal wastewater treatment systems. However, its effects on glycogen-accumulating organisms (GAOs) and the mechanisms of action are still not fully understood. This study investigated the influence of ZVI on GAOs by assessing its effect on the performance of a denitrification reactor dominated by Candidatus Competibacter sp. (with a relative abundance of 46.33%). After ZVI addition, the reactor harbored the iron-autotrophic denitrifying bacterium Ferruginibacter sp. (0.38%), the iron-reducing bacterium Pseudomonas sp. (0.26%), and the iron-oxidizing bacterium Comamonas sp. (0.26%). This effectively integrated ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) with heterotrophic denitrification alongside iron ammonium oxidation and nitrate-dependent ferrous oxidation. The integrated approach decreased aeration duration while improving the removal efficiency of PO43-P (98.01 ± 2.54%) and total inorganic nitrogen (TIN) (62.01 ± 1.45%). The combined of ZVI in systems predominantly occupied by GAOs enhanced the carbon storage capacity of the bacteria.