Zero-Valent Iron-Enhanced Nutrient Removal in Simultaneous Nitrification Denitrification and Phosphorus Removal Process: Performance, Microbial Community and Potential Mechanism

The efficacy of zero-valent iron (ZVI) for the simultaneous nitrification denitrification and phosphorus removal (SNDPR) process is unclear, although it has been shown in numerous studies to help improve nitrate removal in biological wastewater treatment systems. This study investigated the response of the SNDPR process to ZVI addition in an anaerobic/aerobic/anoxic (An/O/A)-sequencing batch reactor (SBR). The results indicated that ZVI addition could promote the removal of phosphorus and total inorganic nitrogen (TIN). The phosphorus removal by ZVI was mainly attributed to iron precipitation due to the in situ oxidation of ZVI by oxygen or nitrate. The TIN removal by ZVI was attributed to the chemical denitrification reaction, which reduces nitrate to nitrite and nitrogen gas. The nanoscale zero-valent iron (nZVI) was more favorable for TIN removal than microscale zero-valent iron (mZVI) in the SNDPR process. The average removal efficiency of PO43−-P and TIN increased from 50.37 ± 7.55% to 99.29 ± 1.24% and 73.15 ± 5.92% to 76.75 ± 5.05% with nZVI addition. The relative abundance of Dechloromonas sp. decreased by 0.65% and that of Nitrospira sp. increased by 3.78% with the addition of ZVI, indicating that ZVI could weaken the activity of polyphosphate-accumulating organisms (PAOs) and promote the activity of nitrite-oxidizing bacteria. These results provide a new and environmentally friendly approach for applying ZVI in SNDPR systems, reducing the dependence on organic carbon sources.