Chemical techniques chlorine dioxide

The second option involves the use of a CIO2 scrubber. This is a technique presently used in the paper and pulp industry. In the scrubber, the chlorine dioxide reacts with another chemical, such as a sulphite, DMSO, white spirit or an alkaline hydrogen peroxide solution. The hydrogen peroxide solution is most suited to the process described in this chapter as there are no waste streams. The reaction of chlorine dioxide with the alkaline hydrogen peroxide solution is rapid [10]. The reaction equation is as follows ... 

If a strong chemical reducing agent is added somewhere in the treatment process after chlorine dioxide primary disinfection, then chlorine dioxide and chlorite ions can be reduced to chloride ion. This would leave only traces of chlorate ion in the water. This chemical reduction technique will allow much higher chlorine dioxide dosages to be apphed for oxidation and/or primary disinfection than the 1.2-1.4 mg/L currently recommended. 

The following sections discuss the primary biocide used today, chlorine, and alternative physical and chemical techniques to address membrane biofouling control. The most common alternative techniques examined here include chloramine, chlorine dioxide, ozone, UV, and non-oxidizing biocides such as DBNPA and isothiazolone. Table 8.12 summarizes advantages and limitations of these techniques (adapted from Kim, 2009). It is important to note that some of these biocides/disinfectants can contact the membranes, and others must be removed or destroyed before the water is introduced to the membrane system itself. 

Dechlorination is the process of converting highly reactive chlorine from these waters into less reactive chloride ions prior to disposal into receiving streams. Various chemical and nonchemical techniques are currently used for disposal of chlorinated waters by water and wastewater agencies. For example, wastewater treatment plants use sulfur dioxide gas or sodium metabisulfate to dechlorinate treated effluent prior to release into receiving streams. Many water utilities often use passive, non-chemical methods such as discharge to sanitary sewers for disposal of chlorinated waters. Impurities such as organics, iron, and sulfide in the sanitary sewer exert a chlorine demand and neutralize chlorine in the released water. 

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