Simultaneous nitrate and phosphate removal from wastewater lacking organic matter through microbial oxidation of pyrrhotite coupled to nitrate reduction

• N and P were simultaneously removed from wastewater lacking organic matter.
• NO3 was reduced by autotrophic denitrification with pyrrhotite as the electron donor.
• Phosphate was mainly removed through formation of secondary minerals with Fe3+.
• N and P levels in wastewater can be reduced to 1.13 and 0.3 mg L−1 , respectively.

This study investigated the efficiency of a pyrrhotite autotrophic denitrification biofilter (PADB) technology for simultaneous N and P removal from wastewater lacking organic matter. A PADB was constructed with natural pyrrhotite as the biofilter medium and inoculated with autotrophic denitrifies enriched from anaerobic sludge. Over an operating period of 247 days, PADB efficiently removed NO3− and PO43− simultaneously from wastewater that lacked organic matter. The hydraulic retention time (HRT), and influent NO3− and PO43− concentrations affected the removal of NO3− and PO43−. A longer HRT led to lower concentrations of NO3− and PO43− in the effluent. The PO43− removal was influenced by NO3− removed; the more NO3− removed, the more PO43− removed. As the synthetic wastewater containing NO3−–N of 28 mg L−1 and PO43−–P of 6 mg L−1 in the absence of organic matter was treated by PADB at HRT of 24 h, total oxidized nitrogen (TON; NO2−–N + NO3−–N) and PO43−–P concentrations of effluent were as low as 1.13 and 0.28 mg L−1, respectively. When treatment of municipal wastewater treatment plant (WWTP) secondary effluent with TON of 21.11 mg L−1 and PO43−–P of 2.62 mg L−1 at HRT of 24 h, the effluent TON was 1.89 mg L−1 and PO43−–P was 0.34 mg L−1. PO43− was removed through the formation of secondary minerals with Fe and Ca. These secondary minerals contained elevated phosphorus, which presents a potential for P recovery from wastewater.

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