Enhanced coagulation process by Fe-Mn bimetal nano-oxides in combination with inorganic polymer coagulants for improving As(V) removal from contaminated water

Abstract

This study investigated the efficient removal of As(V) from contaminated water using enhanced coagulation by Fe-Mn bimetal nano-oxides in combination with poly-ferric chloride (PFC) and poly-aluminum chloride (PAC). The effects of coagulant dose, initial pH, initial As(V) concentration, Fe-Mn nano-oxide dose and flocs properties were investigated. The results showed that the combination of coagulants and nano-oxides significantly increased the As(V) removal efficiency in the optimal coagulants doses (25 mg/L). The As(V) removal efficiencies for PAC and PFC were 82.93% and 88.22% and for PFC + Fe-Mn and PAC + Fe-Mn were increased to 96.83% and 98.26%, respectively. The residual As(V) concentration was decreased to ˂10 μg/L in the presence of Fe-Mn nano-oxides. The best removal efficiencies for PAC + Fe-Mn and PFC + Fe-Mn were in pH 7 and 9, respectively. Based on FESEM - EDX analysis, the combined floc formation by coagulants - nano-oxides and the existence of Fe, Mn and As elements in the precipitated flocs was confirmed, and the PFC + Fe-Mn flocs were more uniform and bigger than PAC + Fe-Mn flocs. Total Fe and Al residual concentrations in optimum dose of PAC + Fe-Mn and PFC + Fe-Mn were 0.15 and 0.25 mg/L and Cl− residue concentrations were 6.87 and 4.72 mg/L, respectively. Therefore, the combination of Fe-Mn bimetal nano-oxides with PFC and PAC coagulants can be a suitable option to improve the removal of As(V) from the contaminated water resources.