Influence of pH and Temperature on the Survival of Coliforms and Enteric Pathogens When Exposed to Chloramine

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Abstract
The expts. were designed to cover conditions which might obtain in water plant operation and were done with attention to the chemical purity of the solns. used and the bacteriological identity of cultures at the beginning and end of the tests. A total of 193 series was run, in which the pH was varied from 6.5 to 10.5 to cover the range possible in natural water supplies; and temps, of 2-6[degree]C and 20-25 [degree]C were chosen as representing naturally oc-curring extremes. C1:N ratios were varied from 0.5:1 to 6:1, and in some instances through the range of 6:1 to 10:1 also. Organisms tested included Eberthella typhosa, Escherichia coli, Aerobacter aerogenes, Pseudomonas pyocyaneus, Shigella dysenteriae, S. sonnei, and several vars. of 5. paradysenteriae. Chloramines required a 25 times greater quantity than free Cl to obtain 100% kills, or 100 times the exposure period, if amts. were equal. 20 min. was the minimum time required for 100% kills with chloramine residuals of 1.2 ppm. Increased H-ion conc. and higher temps. enhanced the effectiveness of the bactericidal action. Under certain conditions some strains of E. typhosa were slightly more resistant than some strains of E. coli, but not more so than A. aerogenes. Presence of excessive amts. of ammonia N (Cl2: N ratios to 1:25) did not markedly reduce the bactericidal efficiency of the resultant chloramines, nor did the length of time of contact of the 2 components with each other alter the bactericidal properties.

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