Nutrient removal through pyrrhotite autotrophic denitrification: Implications for eutrophication control.

This study investigated nutrient removal kinetics and main influencing factors of natural pyrrhotite autotrophic denitrification (PAD), and nutrient removal performance and the microbial community in the PAD biofilter (PADB). Results demonstrated that both NO and PO in wastewater were nearly completely removed, and biological N removal and chemical P removal took place simultaneously in the PAD process. NO removal kinetics of the PAD can be described with half-order kinetics. The PAD was effective across a wide temperature range of 11-34 °C, initial NO-N range of 13-52 mg·L and PO-P below 60 mg·L. Both NO and PO decreased gradually with wastewater flowing along the PADB. The PADB operation results show that at 12 h HRT, when the PADB treated wastewater containing 30.95 ± 0.97 mg·L of NO and 3.02 ± 0.10 mg·L of PO-P, the effluent contained 1.15 ± 2.08 and 0.09 ± 0.11 mg·L of NO-N and PO-P on average, respectively. In the PADB the dominant bacteria were Thiobacillus and Sulfurimonas, which used pyrrhotite as the electron donor to reduce NO. The relative abundance of Thiobacillus at the bottom of the PADB increased from 0.81% to 58.65% and that of Sulfurimonas decreased from 97.22% to 12.30%, with exposure to pyrrhotite. From the bottom to the top of the PADB, the relative abundance of Thiobacillus increased from 58.65% to 86.23% and Sulfurimonas decreased from 12.30% to 0.52%. Technologies based on the PAD are promising ways to control eutrophication.