## 1 Introduction  
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]. Water quality is a topical issue in public health due to concerns emanating from the indiscriminate discharge of inadequately treated sewage into water bodies, which is deleterious to human health and the environment [2; 3]. The lack of access to good quality water increasingly impaired by the presence of waterborne pathogens continues to be a major contributor to the disease 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. Commonly 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]. Ozone is highly efficient in the inactivation of viruses, bacteria and protozoa but decomposes rapidly. It also, requires special operation, and potentially forms bromate as a by-product in waters containing bromide [9,10]. Chlorine is a potent oxidant which causes the destruction of nucleic acids and cell membranes and it is an attractive option for disinfection due to its ease of handling, low capital cost and production of residual chlorine [11,12]. However, limitations in the use of chlorine include the production of off-tastes and odours, and potential formation of disinfection by-products (DBPs) such as trihalomethanes (THMs), Haloactic acids (HAAs), Haloacetylnitrile (HAN) and nitrosodimethylamine (NDMA) [13, 14, 15]. In addition, recovery of chlorine tolerant microbial pathogens at low chlorine dosages has been reported [16, 17, 18, 19]. The \(Ct\) concept (disinfection concentration \(C\) multiplied by the contact time \(t\) over defined time intervals) has been used to model the effieicency of many disinfection systems [20, 21, 22]. The detailed impact of disinfectant concentrations and exposure times required to sufficiently control microbial pathogens of public health hazards are useful in developing regulations and treatment strategies [6] and have been described by the \(Ct\) concept. Published data on \(Ct\) values include 21.7, 18.5 and 52.6 mg/L-min free chlorine for 3 log\({}_{10}\) inactivation of total coliforms, _Enterococcus_ and _Salmonella_ species [23] and 48.99-194.7 mg/L-min free chlorine for strains of _Aspergillus_ and _Penicillium_[22]. Water regulatory bodies have prescribed guidelines for effluent discharge into water bodies [24]. For example, the South Africa water regulation stipulates a maximum contaminant level (MCL) of zero for total coliforms including _E. coli_ and a residual chlorine concentration of 0.25 mg/L for effluent discharge into water bodies [25]. Microbiological parameters for routine monitoring of water do not regulate for all pathogens but rather stipulate indicator organisms, including _E. coli_, that specify a contamination problem with a disinfection step [1,16,21]. Strains of _E. coli_ such as enterohemorrhagic _E. coli_ O157:H7 have been associated with various outbreaks of waterborne and foodborne diseases such as bloody diarrhoea, haemolytic-uremic syndrome and sometimes death in immune-compromised individuals [26]. Previous studies have demonstrated the susceptibility of _E. coli_ to chlorine. For example, a bench-scale inactivation study examined the inactivation of pathogenic and wild strains _E.