ABSTRACT
As. We have observed that the oxidation of As(III) by conventional aeration (cascade, sprinkler etc.) is ineffective in oxidizing As(III) to As(V). Therefore, we use permanganate in the form of either KMnO4 or NaMnO4 as chemical oxidant to rapidly oxidize the As(III) concentration in raw water. Regarding the permanganate, the selection of this oxidizing agent was made after carrying out a series of labscale investigations which provided us with a clear evidence of its superior performance compared to other commonly used chemical oxidants in drinking water production industry. It must be noted that in comparison to KMnO4, NaMnO4 is more easy and safe to handle during operation. Therefore, if available, use of NaMnO4 should get priority. Dosing of permanganate not only increases the rate of As(III) oxidation to As(V), but also Fe(II) to Fe(III). The iron hydroxide flocs [Fe(OH)3(s)] sorb As(V). A significant amount of As(V) is also coprecipitated with Fe(OH)3(s). When As is present in relatively high concentration, addition of additional Fe becomes necessary and we have observed in our lab-scale experiments that adding Fe as Fe(III) is more effective compared to adding Fe(II).
