As(III) Oxidation by Active Chlorine and Subsequent Removal of As(V) by Al13 Polymer Coagulation Using a Novel Dual Function Reagent

An electrochemically prepared water treatment reagent containing a high concentration of Al-13 polymer and active chlorine (PACC) showed promising potential for the removal of As(III) due to the combined function of oxidation and coagulation. The results indicated that PACC was effective for As(III) removal through oxidation by the active chlorine and subsequent removal of As(V) by coagulation with the Al-13 polymer. The As(III) was oxidized to As(V) by active chlorine in PACC, with a stoichiometric rate of 0.99 mg Cl-2/mg As(III). The Al-13 polymer was the most active Al species responsible for As(V) removal in PACC. To meet As drinking water standards the stoichiometric weight ratio of Cl-2/Al within PACC was 0.09 for the treatment of As(III). Considering the process of As(III) oxidation and As(V) coagulation together, the optimal pH conditions for the removal of As by PACC was within the neutral range, which facilitated the reaction of As(III) with active chlorine and favored the formation of Al hydroxide flocs. The presence of humic acid reduced the As(III) removal efficiency of PACC due to its negative influence on subsequent As(V) coagulation, and disinfection byproduct yields were very low in the presence of insufficient or stoichiometric active chlorine.