Water Supply Vol 2 No 2 pp 281–288 © IWA Publishing 2002
A low cost technique of arsenic removal from drinking water by coagulation using ferric chloride salt and alum
M.M.T. Khan*, K. Yamamoto** and M.F. Ahmed***
*Department of Urban Engineering, The University of Tokyo, 7-3-1, Hongo, Bunkyo, Tokyo 113-8656, Japan. (E-mail: taimur@env.t.u-tokyo.ac.jp)
**Environmental Science Center, The University of Tokyo, 7-3-1, Hongo, Bunkyo, Tokyo 113-0033, Japan. (E-mail: yamamoto@esc.u-tokyo.ac.jp)
***Department of Civil Engineering, Bangladesh University of Engineering and Technology, Dhaka 1000, Bangladesh. (E-mail: fahmed@ce.buet.edu)
ABSTRACT
A variety of treatment processes have been used for arsenic removal from water. In a laboratory study using natural (tubewell) water, ferric chloride salt and alum were used, which are the most studied and widely used flocculents in water treatment due to their low price, comfortable availability and low risk usability. The solubility of arsenate(III) is much more than arsenite(V). Arsenate(III) was converted into arsenite(V) by proper oxidation using bleaching powder as an oxidizing agent before coagulation. The concentrations of ferric chloride salt and alum dose were varied from 10 mg/l to 200 mg/l, and pH was varied from 4 to 9. After intensive investigation, it was found that at pH 7 and for 100 mg/l to 125 mg/l dose of alum, the removal efficiency of arsenic and iron were around 82 to 86% and 92 to 95% respectively. Again, the optimum removal of arsenic and iron were around 90 to 93% and 97 to 100% respectively at pH 7 for 200 mg/l of ferric chloride salt. This research was carried out not only to observe the removal efficiency of arsenic, but also iron. Because most of the tubewells in Bangladesh, sometimes, contain higher amount of iron.
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