Resuscitation of Bacteria after Dechlorination of Treated Drinking Water

Abstract

Small-scale household water treatment techniques, using branded chlorine-based products have been recognized as low-cost means of reducing the heavy burden of diarrhoea and other water-borne diseases, especially among populations with inadequate or no access to improved water supplies. However, factors influencing the efficacy of these products are scarcely investigated. This study evaluated the influence of initial bacterial load and dechlorination idiosyncrasy on the efficacy of Water Care® in drinking water disinfection. Results indicated that the initial cell populations (102, 104and 106 cells/ml) had significant influence on the efficacy of WaterCare® at the concentrations investigated (0.4 and 0.6 µl ml-1), although there was a near complete inactivation (cell reduction >4 log CFU/ml) of pathogens (Escherichia coli and Salmonella typhi) at over 150 minutes post-contact in water. Subsequent dechlorination of the hypochlorite-treated water (applied at 0.1, 0.2, 0.3, 0.4, 0.5, 0.6 and 0.7 µl ml-1 for 30 minutes) resulted in resuscitation of bacteria (Escherichia coli, Salmonella typhi, Proteus vulgaris and Shigella dysenteriae added at 1.2×106 cells ml-1). Bacterial regrowth was demonstrated after 1440 minutes post-dechlorination for Salmonella typhi or after at least 120 minutes for the other test organisms, particularly at the lower disinfectant concentration levels (0.1\x960.3 µl ml-1). While the use of Water Care® at the recommended dosage (0.4 µl ml-1 or 10 ml to 25 l of clean water for 30 minutes) may produce microbiologically safe water and thus, drastically reduce the incidents of diarrhoea and other water-borne diseases, it is advised that higher doses be used to supply residual disinfectant to prevent resuscitation of inactivated bacteria.