Iron-carbon microelectrolysis coordinated advanced N and P removal from municipal tailwater: Unexpected N conversion and microbial characteristic

Abstract

The biochemical mechanisms that iron-carbon microelectrolysis (IC-ME) advanced and coordinated treating nitrogen (N) and phosphorus (P) from tailwater are not intensive. Depending on the optimal operating conditions of the iron carbon biofilter (ICBF), the interface P reaction, functional microbial community and characteristics were analyzed. Results demonstrated that iron (Fe) engaged in reaction with nitrate nitrogen (NO3−-N), facilitating the release of both nitrite nitrogen (NO2−-N) and ammonia nitrogen (NH4+-N) to 0.75 and 2.46 mg/L. Total nitrogen (TN) and total phosphorus (TP) were simultaneously removed lower than 10 and 0.3 mg/L under the optimum conditions i.e., gas water ratio of 15, empty bed contact time (EBCT) of 105 min, and backwashing cycle of 12 h. Microelectrolysis (ME) exhibited a robust capacity to degrade macromolecular pollutants, and P was predominantly eliminated via Fe3(PO4)2 and Fe4(PO4)3(OH)2 precipitation. Intriguingly, IC-ME did alter the microbial community composition, especially the Fe-containing microflora (Desulfuromonas, Azospira, Denitratisoma, Rhodobacter and Paludibaculum). The relatively high abundance of Gammaproteobacteria (29.67–38.3 %) promoted N transformation and the N cycle was mainly dominated by nitrogen respiration (1.95–3.39 %), nitrate reduction (2.06–3.45 %) and nitrate respiration (1.95–3.39 %). ME invigorated functional metabolism, thereby promoting organic carbon metabolism.