Arsenic removal from a high-arsenic wastewater using in situ formed Fe-Mn binary oxide combined with coagulation by poly-aluminum chloride.

In this study, in situ formed Fe-Mn binary oxide (FMBO) was applied to treat a practical high-arsenic wastewater (5.81 mg/L). FMBO exhibited a remarkable removal capacity towards both As(III) and As(V), achieving a removal efficiency over 99.5%. However, the FMBO-As particles could not be sufficiently separated by gravitational sedimentation due to their low sizes and negative charges, as being indicated from laser particle size and zeta-potential analysis. Thus, poly-aluminum chloride (PACl) was introduced as a coagulant to facilitate the solid-liquid separation, and it remarkably improved As removal efficiencies. Results of scanning electron microscope (SEM) revealed that PACl contributed to the formation of precipitates with larger sizes and compact surfaces, which was favorable to sedimentation. Moreover, residual soluble As was removed by PACl hydroxides. The optimum dosages of FMBO and PACl were determined to be 60 mg/L and 80 mg/L, respectively. Additionally, the secondary pollution was minimized in FMBO-PACl process. Based on these bench-scale results, a full-scale treatment process was proposed to successfully treat 40,000 m(3) of high-arsenic wastewater in a municipal wastewater treatment plant (MWWTP). The average As concentration in the effluent was about 0.015 mg/L. FMBO-PACl process showed the advantages of high effectiveness, low cost, safety, and ease for operation.