PHOSPHATE REMOVAL BY FERROUS IRON IN THE PRESENCE OF DISSOLVED OXYGEN: CHARACTERISTICS AND KINETICS INVESTIGATIONS

This study examined the kinetics of phosphate removal during Fe(II) oxidation, and the quantitative relationship between phosphate removal and Fe(II) oxidation in synthetic wastewater. The phosphate removal rate increased with the increase of DO and Fe(II)(0) but firstly increased and then decreased with pH. The reaction kinetics of phosphate removal as a function of DO, Fe(II)(0) and pH all followed pseudo-first-order kinetics. For the tested DO conditions, quantitative relationship between k(P) and k(Fe) was described by the equation: k(p) = 0.6024 k(Fe)+0.0004. For the tested Fe(II)(0) conditions, the evolution of k(P) versus k(Fe) was expressed by two equations: k(p) =1.9573 k(Fe) - 0.0233 (Fe(II)(0) from 10 to 30 mg/L) and k(p) =13.252 k(Fe) - 0.2215 (Fe(II)(0) from 30 to 45 mg/L). For the tested pH conditions, relationship between k(p) and k(Fe) followed two equations: k(p)= 0.5911 k(Fe) - 0.0001 (pH from 6.0 to 8.0) and k(p) = 0.2274 k(Fe) + 0.4401 (pH from 8.0 to 9.0). The precipitates formed at higher DO tended to be more compact, and featured by relatively bigger size, thus it resulted in better solid-liquid separation.