Chlorine Tolerance and Inactivation of Escherichia coli recovered from Wastewater Treatment Plants in the Eastern Cape, South Africa

摘要

This study investigated the survival of Escherichia coli ( E. coli ) recovered from secondary effluents of two wastewater treatment plants in the Eastern Cape Province, South Africa, in the presence of different chlorine concentrations. The bacterial survival, chlorine lethal dose and inactivation kinetics at lethal doses were examined. The bacterial isolates were identified by 16S rRNA gene sequencing. Comparison of the nucleotide sequences of 16S rRNA gene of bacteria with known taxa in the GenBank revealed the bacterial isolates to belong to Escherichia coli. At the recommended free chlorine of 0.5 mg/L, reduction of E. coli isolates ( n = 20) initial bacterial concentration of 8.35–8.75 log was within a range of 3.88–6.0 log at chlorine residuals of 0.14–0.44 mg/L after 30 min. At higher doses, a marked reduction ( p < 0.05) in the viability of E. coli isolates was achieved with a greater than 7.3 log inactivation of the bacterial population. Inactivation kinetics revealed a high rate of bacterial kill over time ( R 2 > 0.9) at chlorine dose of 1.5 mg/L. This study indicates poor removal of bacteria at free chlorine at 0.5 mg/L and a greater efficacy of 1.5 mg/L in checking E. coli tolerance.