Assessment of chlorine tolerant bacteria recovered from wastewater effluent in Eastern Cape Province, South Africa
Mojisola C. Owoseni 1,2,3* and Anthony I. Okoh 2,3
1 – Department of Microbiology, Federal University Lafia, PMB 146, Nasarawa State, Nigeria.
2 – SAMRC Microbial Water Quality Monitoring Centre, University of Fort Hare Alice, 5700 South Africa.
3 – Applied and Environmental Microbiology Research Group, Department of Biochemistry and Microbiology, University of Fort Hare, Alice 5700, South Africa.
*Corresponding author’s email: firstname.lastname@example.org; telephone: +2349034509990
The transmission of chlorine tolerant pathogens to waterbodies via discharge of inadequately treated wastewater effluents can contribute to outbreak of infectious diseases. This study investigated the chlorine tolerance of some bacterial pathogens recovered from final effluents of two wastewater treatment plants in the Eastern Cape, South Africa. Secondary effluent samples were collected from the clarifier of two wastewater treatment plants in Eastern Cape Province.
The bacterial survival (n=20) at the recommended chlorine dosage (0.5 ml), lethal dose (n=3) and inactivation kinetics (n=3) at lethal doses were examined. Bacterial isolates (n=20) were confirmed by PCR assay and isolates (n=3) which showed the highest chlorine tolerance were further identified using the 16S rRNA gene sequence. Nucleotide sequences were compared to known sequences in the GenBank and submitted to the Basic Local Alignment Search tools (BLAST) search engine at the NCBI GenBank.
Data was analysed using Analysis of variance (ANOVA) and linear regression. Bacterial isolates (n=20) screened at the recommended dose of 0.5 mg/l were inactivated within a range of 4.71 – 6.02 log at chlorine residuals of 0.04 – 0.42 mg/l after 30 min. The bacterial isolates with the highest survival were identified as Klebsiella sp., Bacillus sp. and Staphylococcus sp. Higher chlorine doses (0.75 – 1.5mg/l) showed a marked reduction (p < 0.05) in the viability of bacterial isolates from 0.67 to 1 log. Inactivation kinetics showed a high rate of bacterial kill (R = 0.85 – 0.98) in 30 min contact time at 0.75 – 1.5 mg/l chlorine dose.
Disinfection at 0.5 mg/l chlorine indicates a poor removal efficiency of bacterial isolates while increasing the disinfection dose to 0.75 – 1.5 mg/l increased the inactivation rate. Data obtained suggests a need to review 2 current chlorine standards for wastewater treatment especially in resource-poor countries dependent on cost-effective disinfectant for wastewater treatment.
Keywords: Bacterial pathogens; wastewater effluent; chlorine tolerance; lethal dose;inactivation kinetics.