May 28, 1914: Municipal Journal article. Disinfecting Philadelphia’s Water Supply. By Francis D. West. “Bleach was first used at Torresdale [now called the Samuel S. Baxter treatment plant] in the form of hypochlorite of soda, produced electrolytically, during September, 1909. Two cells manufactured by the National Laundry Co. were used. A current of 35 amperes at 110 volts was used to decompose a brine solution. The chlorine and soda were allowed to recombine and the temperature was so high (about 110° F) that chlorates were formed. The bleach was applied directly in front of the first valve of one of the preliminary filters operated at a 20 mgd rate, or about 1/4 normal.
The conclusions were in part that the bacterial efficiency of the filter was considerably less than that of filters operated at four times the rate without treatment.
Hypochlorite was again used in December 1910. Due to the fact that the bacterial efficiency of slow sand filters decreases considerably in cold weather and the fecal organism B. coli communis was present in the filtered water, it was decided to use chloride of lime to disinfect the water in the filtered water basin. Treatment was continued until April 1911, when it was stopped; was again started December 1911, and was continued without interruption until February, 1913.
Liquid chlorine was first used Nov. 26, 1913, in conjunction with chloride of lime about 90 lbs. of liquid and 800 lbs. of powder being used daily until Feb. 9, when the use of chloride of lime was stopped.