Field Dechlorination Studies at Bureau of Water Works, Portland

Field Dechlorination Studies at Bureau of Water Works, Portland 

Portland Bureau of Water Works uses combined cWorine for disinfection. The tests conducted at Portland were similar to those at Tacoma, except in the following aspects Tests using all the chemicals, except sodium sulfite, were conducted at stoichiometric concentrations only a 100 ft hose, rather than a diffuser, was provided for mixing of chemicals with the water the released water traveled along a well-paved surface for 1000 ft prior to discharging into a storm drain leading to a storage pond. 

When no dechlorination chemical was added, the chlorine concentration decreased from 1.05 to 0.95 mg/L after 1000 feet (Fig. 2). This indicated that only a small amount (0.1 mg/L) of the chloramines dissipated through chlorine demand of paved surfaces. Sodium bisulfite, sodium sulfite, ascorbic acid, and sodium ascorbate neutralized all detectable chlorine to below 0.1 mg/L within 2 ft downstream of the mixing hose (approx 2 s). Sodium thiosulfate neutralized more than 80% of the chlorine within 2 ft. However, chlorine concentrations decreased below 0.1 mg/L (the discharge limit in most states) after about 500 ft (elapsed time 3 min, 2 s). Calcium thiosulfate neutralized 60% of the chlorine within 2 ft and neutralized 90% of the chlorine after 1000 ft (elapsed time 7 min, 10s). 

At concentrations used in this study, none of the chemicals appeared to affect the pH of the Portland Water Bureau water appreciably. 

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