Effect mechanism of micron-scale zero-valent iron enhanced pyrite-driven denitrification biofilter for nitrogen and phosphorus removal

This study aims to explore the effect mechanism of micron-scale zero-valent iron (mZVI) to improve nitrogen and phosphorus removal in a pyrite (FeS 2 )-driven denitrification biofilter (DNBF) for the secondary effluent treatment. Two similar DNBFs (DNBF-A with FeS 2 as fillers and DNBF-B with the mixture mZVI and FeS 2 as carrier) were developed. The results showed that NO 3 − –N, total nitrogen (TN) and PO 4 3− –P removal efficiencies were up to 91.64%, 67.44% and 80.26% in DNBF-B, which were obviously higher than those of DNBF-A (with NO 3 − –N, TN and PO 4 3− –P removal efficiencies of 38.39%, 44.89% and 53.02%, respectively). Kinetic analysis of both PO 4 3− –P and NO 3 − –N showed an increase in the rate constant (K) for DNBF-B compared to DNBF-A. The addition of mZVI not only improved the electron transport system activity (ETSA), but also achieved system Fe(II)/Fe(III) redox cycle in DNBF-B. In addition, the high-throughput sequencing analysis indicated that the addition of mZVI could obviously stimulate the enrichment of functional bacteria, such as Thiobacillus (11.99%), Mesotoga (7.50%), JGI-0000079D21 (6.37%), norank_f__Bacteroidetes_vadinHA17 (6.19%), Aquimonas (5.93%) and Arenimonas (3.97%). These genus played the important role in nitrogen and phosphorus removal in DNBF-B. Addition mZVI in the FeS 2 -driven denitrification biofilter is highly promising for TN and TP removal during secondary effluent treatment.