Wastewater chlorination disinfection, chlorine dosages

Table 3 gives recommended ranges of chlorine dosages for disinfection of various wastewaters. Recommended minimum bactericidal chlorine residuals are given in Table 4. Data in Table 4 are based on water temperatures between 20 C to 25 C after a 10-minute contact for free chlorine and a 60 minute contact for combined available chlorine. 

Chlorine may be fed into the wastewater automatically, with the dosage depending on the degree of treatment. The wastewater then flows into a tank, where it usually is held for about 30 min to allow the chlorine to react with the pathogens (Fig. 1). Chlorine often is used either as a gas, or a solid or liquid compound. Liquid chlorine, or hypochlorite, has been used mostly in small systems (fewer than 5000 persons), or in large systems, where safety concerns related to handling chlorine gas outweigh economic concerns. The use of chlorine has proven to be a very effective means of disinfection. 

For wastewater treatment, the recommended chlorine dosage for disinfection purposes should produce a chlorine residual of 0.5-1 mg/L after a specified contact time. Effective contact time of not less than 15 min at peak flow is recommended. Practical chlorine dosages recommended for wastewater disinfection and odor control are presented in below ... 

Because ozone, chlorine, and UV are all common disinfectants in both drinking water and wastewater treatment, the formation and subsequent conversion of transformation products in wastewater can be similar to those observed in drinking water (as discussed above). However, much higher disinfectant or oxidant dosage would typically be required in wastewater due to the scavenging of the oxidant (or UV) by the much more concentrated background constituents in wastewater as compared to drinking water. 

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