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

Abstract

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.