The cities of Aurora, Colorado and El Paso, Texas demonstrated through laboratory and plant
studies the synergistic benefits of combined treatment of chlorine dioxide and chlorine in
reducing chlorite levels and THM levels in the distribution system. Gordon Finch, in the late
1990s, has already showed synergistic disinfection benefits from sequential addition of chlorine
dioxide and chlorine for Cryptosporidium sp. inactivation at lower CT levels than for chlorine
dioxide alone. Similarly, this paper demonstrates the synergistic benefits of additional THM
and chlorite reduction from combined disinfectants. Aurora was able to meet lower chlorite and
THM levels by mixing chlorine at various ratios with chlorine dioxide. Similarly, El Paso mixed
chlorine with chlorine dioxide doses from 3 to 7.5 mg/L using ferrous chloride for chlorite
reduction in order to reduce THMs significantly more compared to chlorine dioxide alone. It was
shown that chlorine preferentially reacts with the chlorite byproduct from the chlorine dioxide
dose, and thereby lowered the chlorite level instead of it reacting first with THM precursors.
Linear regression equations were developed to predict THMs with R<sup>2</sup> levels greater than 0.90
based on various independent variable levels for TOC, pH, chlorine dioxide dose, chlorine dose,
and contact times. Because chlorine is synergistic with chlorine dioxide and satisfies some of
the chlorine dioxide demand, the treatment cost can be lower for meeting disinfection and
disinfection byproduct goals compared to using higher chlorine dioxide dosages alone in
pretreatment. By combining these oxidants in water treatment, their advantages can be
maximized while their disadvantages can be minimized. Includes 7 references, tables, figures.
| Edition : | Vol. - No. |
| File Size : | 1
file
, 930 KB |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 17 |
| Published : | 11/01/2009 |
