The concentrations of chlorine dioxide (CI02), chlorine, chlorite (CIO2),
and chlorate (CI03) were evaluated following pretreatment of raw water by CI02
at water treatment plants in New Castle, Pennsylvania; Charleston, West Virginia;
Skagit, Washington; and Columbus, Georgia. Chlorite and chlorate
concentrations were unaffected by any of the water treatment processes and did
not vary as a function of time of travel in the distribution system. Chlorine
dioxide, which was analyzed on-site at two water treatment plants, reformed in the
clear well and in the distribution system following post chlorination.
The chlorite-removal capability of powdered activated carbon (PAC) was
evaluated in both laboratory- and pilot-scale studies. Chlorite removal by PAC in
laboratory studies decreased with increasing pH over a range from pH 5.5 to 7.5
and varied with the type of PAC. Chlorite was reduced to chloride at pHs
ranging from 5.5 to 7.5, but CI03- formed at the pH 5.5 through 6.0. The pilot plant
study; which was conducted at Newport News, Virginia; evaluated CI02
removal by PAC enmeshed in a floc blanket in a pulsed-bed, solids-contact
clarifier. An average of 27 percent of the CI02 was removed when the PAC dose
was 10 mg/L PAC and 57 percent when it was 20 mg/L PAC. Chlorate was not
removed by PAC, but the concentrations could be reduced if the CIOz generator
was properly operated.
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