Scrap Iron Filings assisted nitrate and phosphate removal in low C/N waters using mixed microbial culture

* Microbes enhance denitrification under varying DO concentrations and SIF dosages. * Abiotic nitrate reduction rates are proportional to SIF age and dosage. * Over 80% of the simultaneously loaded NO 3 −-N and PO 4 3 − is removed biologically. This study focuses on identifying the factors under which mixed microbial seeds assist bio-chemical denitrification when Scrap Iron Filings (SIF) are used as electron donors and adsorbents in low C/N ratio waters. Batch studies were conducted in abiotic and biotic reactors containing fresh and aged SIF under different dissolved oxygen concentrations with NO 3 −-N and/or PO 4 3 - influent(s) and their nitrate/phosphate removal and by-product formations were studied. Batch reactors were seeded with a homogenized mixed microbial inoculum procured from natural sludges which were enriched over 6 months under denitrifying conditions in the presence of SIF. Results indicated that when influent containing 40 mg/L of NO 3 −-N was treated with 5 g SIF, 79.9% nitrate reduction was observed in 8 days abiotically and 100% removal was accomplished in 20 days when the reactor was seeded. Both abiotic and seeded reactors removed more than 92% PO 4 3 − under high DO conditions in 12 days. Abiotic and biochemical removal of NO 3 −-N and abiotic removal of PO 4 3 − were higher under independent NO 3 −-N/PO 4 3 − loading, while 99% PO 4 3 - was removed biochemically under combined NO 3 −-N and PO 4 3 − loading. This study furthers the understandings of nitrate and phosphate removal in Zero Valent Iron (ZVI) assisted mixed microbial systems to encourage the application of SIF-supported bio-chemical processes in the simultaneous removals of these pollutants.