AWWA ACE56266

Conventional water treatment technologies perform well in removing arsenate (As(V)), but they largely fail to control arsenite (As(III)), which needs to be oxidized prior to treatment (e.g., by coagulation with ferric chloride or adsorption on alumina or iron oxide). Oxidants such as chlorine or chlorine dioxide rapidly convert As(III) to As(V), but their use requires storage facilities, delivery devices and other units. These chemicals are also associated with the formation of unwanted byproducts. However, electrochemical (EC) oxidation does not require any chemicals to be stored or delivered but employs two or more electrodes to pass electric current through the solution. EC systems can potentially be made simple and compact at reasonable cost. Previous research has shown EC technology performs well in arsenite oxidation. However, effects of important components of water quality (e.g., Fe2+, Mn2+, HCO3-, Cl-) remain to be explained in adequate detail. These species can either directly participate in electrode reactions or accelerate/inhibit the EC arsenite oxidation through other mechanisms. The goal of this study was to explore and quantify their influence. The EC oxidation of arsenite was studied using a micro-flow EC cell (ElectroCell AB, Sweden). The areas of the cathode and anode were 10 cm2. The cell was used without any separation of the anodic and cathodic compartments. The main anode materials chosen for the experiments were MnO2 and DSA/O2 (Dimensionally Stable Anode, ElectroCell AB). A stainless steel plate was used as the cathode in all cases. The inter-electrode distance was 0.5 cm. The EC current density was varied from <1 to 3 mA/cm2. The conversion of arsenite to arsenate was calculated based on the relevant arsenic speciation data. The arsenite was separated using anionic exchange resin ASB-1 after pH adjustment to pH 3.3+/-0.1. Five bed volumes of sample were passed through the packed-bed column; only the last 6 mL were collected for arsenic analysis. Analyses for arsenic were carried out using an inductively coupled argon plasma (ICP) atomic emission spectrophotometer. To convert arsenite and arsenate to arsine, the sample was mixed on-line with 0.1% sodium borohydride in 1 M NaOH prior to the injection into the ICP torch. Analyses for free chlorine were done in accordance with HACH method 1470 using a HACH DR/4000U spectrophotometer. Includes 3 references, table, figures.

Product Details

Edition:

Vol. - No.

Published:

06/16/2002

Number of Pages:

5

File Size:

1 file , 290 KB