Foam FeSO₄ modified limestone sulfur concrete for non-stink and high-rate nitrogen and phosphorus removal from...

Aiming at disadvantages of conventional sulfur-limestone autotrophic denitrification system, such as producing stink (H₂S) and low-rate nitrogen and phosphorus removal from wastewater with low C/N, foam FeSO₄ modified limestone sulfur concrete (FFLSC) was prepared. Experimental parameters of FFLSC biofilter, such as hydraulic retention time (HRT), influent NO₃^--N, additional alkalinity and COD addition, were tested. For wastewater without COD, FFLSC biofilter could simultaneously remove TON (NO₃^--N+NO₂^--N) from 22.63 to 0.73 mg/L and PO₄^3--P from 0.98 to 0.34 mg/L, respectively, and H₂S was not detected at HRT 1 h, and obtain the highest TON removal rate 1514.88 mg/L/d at HRT 0.25 h with effluent TON 6.80 mg/L. The longer the HRT, the higher N and P removal, but the more the H₂S production. Additional alkalinity and COD addition could enhance N removal largely. But H₂S production increased with COD addition increasing. FFLSC biofilter was a sulfur-based mixotrophic denitrification reactor with non-ignorable biological sulfate reduction and hydrolysis. FeSO₄ in FFLSC accelerated N removal by providing additional Fe²⁺and SO₃^2- autotrophic denitrification, prevented H₂S production by FeS formation, increased P removal by precipitation of FePO₄. FFLSC is a promising material for non-stink and high-rate nitrogen and phosphorus removal from wastewater.