## 4 Conclusions  
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  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Bacterial Strains**} & \multirow{2}{*}{\(R^{2}\)} & \multirow{2}{*}{\(k\)} & \multicolumn{2}{c}{**Chlorine Exponent**} & \multicolumn{2}{c}{**Time Exponent**} \\ \cline{3-6}  & & & \(n\) & \(p\) & \(m\) & \(p\) \\ \hline _E. coli_ SAMRC-1 & 0.90 & \(-\)2.42 & 1.57 & 0.80 & \(-\)0.23 & 0.31 \\ _E. coli_ SAMRC-2 & 0.96 & \(-\)19.88 & 12.96 & 0.34 & \(-\)0.14 & 0.33 \\ _E. coli_ SAMRC-3 & 0.98 & \(-\)33.2 & 22.4 & 0.20 & 0.17 & 0.41 \\ \hline \hline \end{tabular} \(R^{2}\): coefficient of determination; \(k\): inactivation rate constant; \(n\): disinfection exponent; \(m\): time exponent; \(p\): probability level. All disinfection parameters were considered significant at \(p\) < 0.05, \(n\) = 3.  
\end{table}
Table 4: Inactivation of _E. coli_ as a function of chlorine dose (1.5 mg/L) and contact time (30 min) (Hom model: log (\(N/N_{0}\)) = \(-k^{n}T^{m}\)).  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Bacterial Strains**} & \multicolumn{4}{c}{**Free Chlorine (mg/L)**} \\ \cline{2-5}  & \(R^{2}\) & \(k\) & \(n\) & \(p\) \\ \hline _E. coli_ SAMRC-1 & 0.95 & \(-\)0.21 \(\pm\) 0.68 & \(-\)0.26 \(\pm\) 0.04 & 0.02 \\ _E. coli_ SAMRC-2 & 0.91 & \(-\)0.60 \(\pm\) 0.88 & \(-\)0.27 \(\pm\) 0.05 & 0.03 \\ _E. coli_ SAMRC-3 & 0.91 & \(-\)0.67 \(\pm\) 0.76 & \(-\)0.23 \(\pm\) 0.04 & 0.03 \\ \hline \hline \end{tabular} \(R^{2}\): coefficient of determination; \(k\): inactivation rate constant; \(n\): coefficient of dilution; \(p\): probability level of \(k\) values (considered significant at \(p\) < 0.05), \(n\) = 3.  
\end{table}
Table 3: Inactivation kinetics of _E. coli_ at chlorine concentrations of 1.5 mg/L (Chick–Watson model: \(\log N/N_{0}\) = \(-kC^{n}T\)).  
treatment plants in the Eastern Cape Province, South Africa. Treatment at 0.5 mg/L free chlorine was ineffective in eliminating bacteria isolates and the survival of _E. coli_ demonstrated a high level of _E. coli_ tolerance to chlorine in all the suspensions at the recommended dose of 0.5 mg/L. Further treatment at higher chlorine concentrations was more effective in inactivating _E. coli_ isolates and complete inactivation of _E. coli_ population was achieved at optimum dose of 1.5 mg/L. For optimization of disinfection processes, the chlorine dose required to achieve sufficient disinfection of wastewater appears to demand a review of current guidelines as observed for 0.5 mg/L free chlorine especially in resource-limited countries dependent on cost-effective and available disinfectant for wastewater treatment. These results demonstrate the potentials of 1.5 mg/L free chlorine obtained in this study as an effective dose to control _E. coli_ tolerance in chlorinated effluents and is hereby proposed.  
We are grateful to the South Africa Medical Research Council (SAMRC), the University of Fort Hare and Nigeria Tertiary Education Fund (TET Fund) for financial support.  
[PERSON] conceived the idea; [PERSON], [PERSON] and [PERSON] designed the experiments, [PERSON] performed the experiments, [PERSON] analyzed the data; [PERSON] and [PERSON] contributed reagents/materials/analytical tools; [PERSON] wrote the paper; [PERSON] reviewed the paper.  
The authors declare no conflict of interest. The funding sponsors had no role in the design of the study; in the collection, analyses and interpretation of data; in the writing of the manuscript, and in the decision to publish the results.