Chlorine Tolerance and Inactivation of Escherichia coli recovered from Wastewater Treatment Plants in the Eastern Cape, South Africa

Abstract

Featured Application: This study examined the tolerance of Escherichia coli isolates, a fecal indicator of water contamination, to chlorine as a common water disinfectant and the effectiveness of chlorine at different concentrations in eliminating E. coli in wastewater effluent. Data obtained can be used as baseline monitoring data for future epidemiological surveillances that could further enhance the control of E. coli and some bacteria species of public health concern in wastewater treatment plants and ensure protection of public and environmental health.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 (R 2 > 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.

Evaluation of Fecal Coliform Prevalence and Physicochemical Indicators in the Effluent from a Wastewater Treatment Plant in the North-West Province, South Africa

“…The final effluent compliance was about 3.57% when measured against zero E. coli count/100 mL of the special limit. The high free chlorine concentration detected confirmed that the dosed chlorine was more than sufficient and possibly indicated the presence of chlorine resistant strains [ 18 ]. The presence of resistant microorganisms pose significant risk to public health.…”

“…The presence of resistant microorganisms pose significant risk to public health. Studies have shown stress mechanisms [ 18 , 42 , 43 ] and resistance genes mechanisms [ 44 , 45 ] advancing in the resistance of E. coli to disinfection by chlorine. As the final effluent samples, the samples collected prior to disinfection were also analyzed to determine the number of organisms expected to be eradicated.…”

“…E. coli is a preferred indicator organism to monitor the bacteriological quality of wastewater [ 15 ]. On the other hand, inadequately treated effluent may contain hazardous elements [ 16 , 17 , 18 ] which place sufficient treatment technologies/processes [ 19 ] at the cornerstone of any WWTP. Some of the hazardous elements are in the form of heavy metals and the most commonly reported include arsenic, lead, mercury and cadmium [ 20 , 21 ] which are known to be carcinogenic and mutagenic [ 22 ].…”

The Best-Practice Organism for Single-Species Studies of Antimicrobial Efficacy against Biofilms Is Pseudomonas aeruginosa

“…The previous review found that the most commonly tested organisms were in the class Gammaproteobacteria in the genus Escherichia . Escherichia was likely tested most often because it is a model bacterial organism and because it is a common fecal contamination indicator used in water treatment [ 100 , 101 ]. Pseudomonas was identified as the next most commonly used organism in the previous semi-systematic review.…”

Bioremediation of Fracking: Novel Hybrid Biofilm System Using Synthetically Engineered Curli Fibres

“…To control of E. coli and curli fiber contamination, several controls and environmental precautions will be put in place, as discussed in Table 2. As a further precautionary measure, E. coli contamination will be detected using standard methods and the water will be treated with 1.5 mg/L of chlorine, a potent disinfectant [18].…”