Pyrrhotite-sulfur-limestone composite for high rate nitrogen and phosphorus removal from wastewater: Column study.

Pyrrhotite-sulfur-limestone composite (PSLC) was prepared and PSLC autotrophic denitrification biofilter (PSLCAD) was constructed with PSLC particle (2-4.75 mm) in this study. During treating synthetic, municipal and industrial secondary effluent, PSLCAD showed good NO-N and PO-P removal, and the highest TON (Total oxidized nitrogen) removal rate of PSLCAD was up to 1749.91 mg/L/d. At HRT 0.5 h, and influent NO-N 21.09 mg/L, TON removal rate was up to 1005.12 mg/L with effluent NO-N 0.10 mg/L. PSLCAD achieved effluent PO-P below 0.2 mg/L when influent PO-P was around 0.5 mg/L. HRT down to 0.5 h had no negative impacts on N removal. Effluent pH below 7 was harmful to denitrification performance of PSLCAD. TON removal rate increased with influent NO-N increasing, but influent NO-N over 103.55 mg/L decreased NO-N removal rate. In PSLCAD biofilter, the most dominant bacteria were Thiobacillus and Sulfurimonas, and they played the most important role in denitrification, but the abundance of heterotrophic denitrifiers was also quite high. PO was mainly removed through precipitate of Fe-P in PSLCAD. The synergistic effects between pyrrhotite and sulfur autotrophic denitrification were much enhanced, and that caused PSLCAD to achieve high rate N and P removal.