Enhanced arsenite removal through surface-catalyzed oxidative coagulation treatment

Area of Science:

• Environmental Science
• Water Treatment Technology
• Inorganic Chemistry

Background:

• Arsenic is a prevalent groundwater contaminant requiring effective removal strategies.
• Conventional coagulation and adsorption methods show limited efficiency for arsenite (As(III)) compared to arsenate (As(V)).
• Stringent water quality regulations necessitate improved arsenic removal technologies.

Purpose of the Study:

• To investigate the in situ oxidation of arsenite (As(III)) during coagulation.
• To evaluate the feasibility of Fe(II) or H2O2-assisted oxidative coagulation for arsenic removal.
• To optimize treatment conditions for enhanced As(III) removal efficiency.

Main Methods:

• Ferric chloride coagulation assisted by either Fe(II) or hydrogen peroxide (H2O2).
• Investigation of catalytic properties of Fe(III) hydroxide colloids in mediating As(III) oxidation.
• Radical quenching experiments to identify reactive species involved in arsenic removal.

Main Results:

• H2O2-assisted oxidative coagulation significantly enhanced arsenic retention across a broad pH range (4-9).
• Fe(II)-assisted coagulation showed minor improvements, with efficiency highly pH-dependent (optimal pH 7-9).
• Superoxide radical was identified as a key species in As(III) removal; phosphate inhibited removal, while carbonate and humic acid had minor impacts.

Conclusions:

• Low-dose H2O2 addition to ferric coagulant is a feasible strategy for improving As(III) removal in existing water treatment facilities.
• H2O2-assisted oxidative coagulation reliably achieves arsenic concentrations below the U.S. EPA regulatory limit.
• This method offers a practical solution for enhancing arsenite removal efficiency in drinking water treatment.