Effect of zero-valent iron and its oxidation products as alternative electron donor on the partial denitrification performance

In this study, zero-valent iron (ZVI) was utilized as an alternative electron donor in the partial denitrification (PD) process to achieve stable nitrite (NO 2 - -N) accumulation, thereby enabling cost-effective treatment strategy for low carbon-to-nitrogen ratio (C/N) wastewater. Results demonstrated that under the optimal molar ratio of ZVI to nitrate (NO 3 - -N) (ZVI/N) of 2/3, the C/N of PD system reduced from conventional range of 2.5–3.0–2.0, saved 20% of carbon demand. Under C/N was 2, the NO 2 - -N transition rate (NTR) was 62.90 ± 7.71%, which was not significantly different from that of C/N was 2.5. Additionally, during the operation of the PD system, the addition of ZVI affected the characteristics of EPS and the response of the microbial community. Although the total EPS content decreased during the ZVI addition phase, changes of the composition of EPS indicated that the microorganisms adapted to the altered iron ion-rich environment. Furthermore, the relative abundance of PD functional bacteria ( Thauera ) rose from 4.44% to 21.15%, enhanced stability of system under low-carbon conditions. This study demonstrated that ZVI significantly reduced carbon source demand for PD process, provided viable technical pathway for low C/N wastewater treatment.