Wastewater Disinfection with Chlorine Dioxide

Introduction

Chlorine dioxide (ClO2) is effective as both a disinfectant and an oxidant in wastewater

treatment. It has several distinct chemical advantages compared to the traditional use of chlorine in wastewater treatment.disinfectant and bactericide, equal or superior to

chlorine on a mass dosage basis.

Its efficacy has been well documented   in the laboratory, in pilot studies and in full-scale studies using potable and wastewater.

Unlike chlorine,chlorine dioxide does not hydrolyze in water.

Therefore, its germicidal activity is relatively constant over a broad pH range. At pH 6.5,

doses of 0.25 mg/L of chlorine dioxide and chlorine produce comparable one-minute kill rates for the bacterium Escherichia coli. At pH 8.5, chlorine dioxide maintains that same killrate, but chlorine requires five times as long.

Thus, chlorine dioxide should be considered as a primary disinfectant for high pH, lime-softened waters.Chlorine dioxide is as effective as chlorine indestroying coliform populations in wastewatereffluents, and is superior to chlorine in thetreatment of viruses commonly found in secondary wastewater effluents。

When Poliovirus I and a native coliphage weresubjected to these two disinfectants, a 2 mg/Ldose of chlorine dioxide produced a much lowersurvival rate than did a 10 mg/L dose ofchlorine2. Chlorine dioxide has also been shownto be effective in killing other infectious bacteria such as Staphylococcus aureus and Salmonella.

When applied for disinfection (as opposed tooxidation), a disinfectant must provide specifiedlevels of microorganism kills or inactivations asmeasured by reductions of coliforms, heterotrophic plate count organisms and Legionella bacteria.

Feed Requirements

The required dosages will vary with water conditions and the degree of contamination

present. For most municipal and other wastewater systems, a chlorine dioxide residual

concentration of up to 5 ppm is sufficient to provide adequate disinfection.

For sulfide odor control, between pH 5-9, aminimum of 5.2 ppm (wt) of chlorine dioxide

should be applied to oxidize 1 ppm of sulfide (measured as sulfide ion). For phenol

destruction, at pH less than 8, 1.5 ppm chlorinedioxide will oxidize 1 ppm phenol; at pH greaterthan 10, 3.3 ppm chlorine dioxide will oxidize 1ppm phenol.