Simultaneous removal of nitrogen and phosphorus from wastewater by means of FeS-based autotrophic denitrification

The efficacy of iron(II) sulfide (FeS)-based autotrophic denitrification in simultaneous nitrogen and phosphorus removal from wastewater was studied with batch experiments. It was efficient at a wide pH range of 5-9, and temperature range of 10-40 WC. The concentrations of NH⁴⁺-N, Mg²⁺ and HCO₃^- in the wastewater should be kept over 7.8, 0.24 and 30 mg L^-1 for efficient nitrate (NO₃^--N) reduction, respectively. The NO₃^--N removal rate increased from 0 to 82 mg L^-1 d^-1 and then leveled off when the NO₃^--N concentration increased from 0 to 415 mg L ^-1 and then to 700 mg L^-1, respectively. The NO ₃^--N removal rate quickly increased, leveled off, and then sharply decreased when the PO₄^3--P concentration increased from 0 to 0.1 mg L^-1, then to 114.0 mg L^-1, and further to 683.8 mg L^-1, respectively. The PO₄ ^3--P removal was over 98% when the PO₄^3--P concentration ranged 0-683.3 mg L^-1. During treatment of the secondary effluent of a local municipal wastewater treatment plant containing NO₃^--N of 14.9 mg L^-1 and total phosphorus (TP) of 3.9 mg L^-1, NO₃^--N was reduced to 1.1 mg L^-1 and TP was completely removed.