Effect of chlorination on β-D-galactosidase activity of sewage bacteria and Escherichia coli

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Abstract
The effect of chlorine on β‐ D‐galactosidase activity of sewage bacteria and Escherichia coli was studied. β‐ D‐galactosidase activity of sewage was more resistant to chlorine than faecal coliform cultivability. At low initial dosage (0·05 mg Cl2 l−1) neither cultivability (colony‐forming units (cfu)), nor enzyme activity of E. coli suspensions were severely impaired. When initial chlorine concentration was increased to 0·1 mg Cl2 l−1, the cfu number decreased whereas enzyme activity remained high, i.e. the enzyme activity calculated cfu−1 increased. At higher chlorine doses both cfu and enzyme activity were reduced, but non‐cultivable cells retained assayable activity after chlorination. Mean values of the enzyme activity calculated cfu−1 decreased when the chlorine dosage was increased from 0·1 to 0·5 mg Cl2 l−1, but were not significantly different (P > 0·05) for dosages of 0·2–0·7 mg Cl2 l−1. After chlorination, β‐ D‐galactosidase activity of E. coli was less reduced than cfu and direct viable count numbers, but more reduced than 5‐cyano‐2‐3, ditolyl tetrazolium chloride and total cell counts, and the enzyme activity represented an alternative activity parameter of chlorinated samples.

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