Anawat Pinisakul <br/><br/>
Application of electro-chemical process for treatment of arsenic-contaminated water 

 - Bangkok :  Asian Institute of Technology,  2002 
 - 134 p. 
 - Dissertation ;  no. EV-02-03 .
 - Asian Institute of Technology.  Dissertation ;  no. EV-02-3 .
<br/><br/> A dissertation submitted in partial fulfil~ment of the reqqirements for the degree of Doctor of Technical Science,  Inter-University Program on Environmental Toxicology, Technology and Management, Asian Institute of Technology;  Chulabhorn Research Institute and Mahidol University   
<br/><br/>Thesis (Ph.D.) - Asian Institute of Technology, 2002 
<br/><br/> This research was conducted to investigate the efficiency, chemical reactions and mechanisms of arsenic (As) removal from a contaminated water by using the electrochemical treatment (ECT) process. For a synthetic As-contaminated water, within the following operating conditions : initial As-concentration of 0.5-5 mg/L, area of electrode plate/volume ofECT reactor of 0.02 cm2/cm3, 0.1 M KCl, electrical gradient of200 volt/m and initial pH higher than 3, the laboratory-scale ECT reactors operating in batch mode were able to reduce As to be within 0.01 mg/L in 15-20 min, making the treated water suitable for use in shrimp culture. For a contaminated groundwater containing As about 0.135-1.072 mg/L, the batch ECT reactors were effective in reducing the As to be within 0.01 mg/Lin 5 min. The Cr salt was found to yield better As removal efficiencies than the N03- salt because, chemically, N03- ions interfere with the production of OH- and Fe(OH)3, the compound mainly responsible for As removal. A first-order reaction model for As removal, incorporating parameters such as area of electrode plate/volume of ECT reactor, conductivity and electrical gradient, was developed which was found feasible in predicting As removal efficiency by the ECT process. The continuous ECT reactor was found to be equally effective in treating the Ascontaminated water, but due to the continuous As input, it required longer operation time than that of the batch operation. However; because of the continuous mixing condition, it required less power and electi'ode consumptions than those of the batch reactors in achieving the same As removal efficiency. The ECT sludge characteristics were analyzed by X-ray fluorescence (XRF) and X-ray diffractometric (XRD) methods. The results revealed maghemite (Fe203) and angellelite (Fe<iAs20 11) to be the major compounds present in the precipitated ECT sludge generated from both in the synthetic water and contaminated groundwater. The percent Fe203 and Fe<iAs20 11 (as As20 3) contents of the dried ECT sludge were 98.29% and 0.26% for the synthetic As-contaminated water and 90-95% and 0.07-0.14% for the contaminated groundwater, respectively. A mass balance analysis of the As removal in the ECT process revealed the follows : As incorporation in and adsorption on the ECT sludge, 73.3 ± 14.6%; As conversion to arsine (AsH3) gas, 10.6 ± 4.3%; As adsorption on the electrode plates and reactor walls, 0.4 ± 0.4%; As residual in the supernatant, 0.3 ± 0.1 % and As unaccounted for, 15 .4 ± 11.2%. From the adsorption/desorption experiments and Freundlich isotherm analysis, the ECT sludge was found to possess less As adsorption capacity than other absorbents, such as activated carbon and rice husk, but it appeared to have strong adsorptive bond and less As desorption potential. The operation cost of the ECT process in treating the As-contaminated water was calculated to be slightly lower than that of the chemical precipitation process using FeCh as coagulant. This lower cost was probably due to the high efficiency of the ECT reactions in producing that ECT sludge that was effective in removing the As compounds by adsorption and incorporation in the ECT sludge. Overall, the ECT process was found to be a feasible technology in treating the As-contaminated groundwater in southern Thailand and the treated effluent was found to have characteristics suitable for use in low-salinity shrimp culture, and, based on literature data, should not cause toxicity to the slu·imps or create serious environmental impact to the nearby environment. 
<br/><br/><label>Subjects--Topical Terms: </label><br/>Water--Pollution<br/>Water--Purification