Abstract
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 (R2 > 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.
Highlights
The growing demand for water for industrial, agricultural, environmental, municipal and domestic requirements has extended the requirements for an improvement in water treatment processes [1]
The nucleotide sequences of the three E. coli isolates were deposited in GenBank as E. coli South Africa Medical Research Council (SAMRC)-1, E. coli SAMRC-2 and E. coli SAMRC-3
This study evaluated the efficacy of chlorine disinfectant in the inactivation of some E. coli isolates recovered from secondary effluent samples from the clarifier of two selected wastewater treatment plants in the Eastern Cape Province, South Africa
Summary
The growing demand for water for industrial, agricultural, environmental, municipal and domestic requirements has extended the requirements for an improvement in water treatment processes [1]. Sci. 2017, 7, 810 burden, morbidity, the retardation of economic growth and the well-being of the populace in many developing countries [4]. The use of an efficient water treatment system that relies on technologically compatible, cost-effective disinfectants that minimizes the production of disinfectant by-products [5] offers a safe margin for wastewater reuse. Used disinfectants for water treatment include ultraviolet (UV) irradiation frequently used in large water and wastewater treatment plants which directly impairs the intracellular functions of microbial cells leading to growth inhibition and death [6]. UV irradiation does not produce disinfectant by-products [7], it is cost-intensive and requires large amounts of energy and frequent maintenance, including replacement of the UV lamps [8,9]
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