Browsing by Author "Bester, Carmen"
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- ItemInvestigating the efficacy of sodium hypochlorite, calcium hypochlorite and peracetic acid on environmental Escherichia coli strains(Stellenbosch : Stellenbosch University, 2015-12) Bester, Carmen; Sigge, G. O.; Lamprecht, Corne; Stellenbosch University. Faculty of Agrisciences. Dept. of Food Science.ENGLISH ABSTRACT: The intake of enteric pathogens such as Escherichia coli (E. coli) may lead to serious foodborne illnesses in humans. Previous research has reported high levels of faecal contamination in various Western Cape rivers which make these sources unsuitable for irrigation purposes. This emphasises the urgency for feasible on-farm treatment options to disinfect river water prior to irrigation. Chemical disinfection is a popular choice for general water disinfection. This study, therefore, focussed on the potential application of peracetic acid (PAA) and chlorine in the treatment of irrigation water. Initially, the efficacy of an emerging water disinfectant, peracetic acid, was investigated. Research was based on the evaluation of PAA disinfection on reference and environmental E. coli strains (in saline solution). Environmental E. coli strains were more resistant than reference E. coli strains to PAA (6 mg.L-1 for 5 and 15 min). Strain variation was particularly evident at a contact time of 5 min. The most resistant strain was environmental E. coli strain F11.2 (1.54 log reduction) and the least resistant was ATCC 25922 (4.50 log reduction). The effect of lower PAA doses (0.5, 1.5, 3.0, 4.5 and 6.0 mg.L-1) and longer contact times (5, 15 and 25 min) were tested against the most resistant strain (E. coli F11.2). It was observed that PAA concentrations ranging between 0.5 – 3.0 mg.L-1 were ineffective (< 1.5 log reduction) in reducing E. coli over a contact period of 25 min and did not reach the 3 log reduction target. Higher PAA doses (4.5 – 6.0 mg.L-1) resulted in increased log reductions (4.94 – 5.5 log reduction) after 15 – 25 min of disinfection. Following this, two sources of chlorine were studied: Granular calcium hypochlorite (Ca(OCl)2) and liquid sodium hypochlorite (NaOCl) (6, 9 and 12 mg.L-1 for 30, 60, 90 and 120 min) (in saline solution). Compared to environmental E. coli strains (M53, F11.2, MJ56 and MJ58), the ATCC E. coli (25922 and 35218) strains were always more susceptible to chlorine. After NaOCl treatment (12 mg.L-1, 120 min), ATCC 25922 was totally inactivated compared to MJ58 which showed a reduction of 0.37 log only. The 3 log target reduction level was never reached by any of the environmental strains after chlorine (NaOCl) treatment at 6 – 12 mg.L-1 (120 min contact time). The most resistant strain (E. coli MJ58) was inactivated (> 4 log reduction) in saline when a chlorine treatment of 24 mg.L-1 (NaOCl) was applied (30 min contact time). The impact of river water quality on chlorine (NaOCl) and PAA disinfection efficiency was also evaluated. Results indicated that the Plankenburg River is severely contaminated with E. coli levels exceeding the limit of 1 000 faecal coliforms per 100 mL. Subsequent chlorine (3.0 – 6.0 mg.L-1, 120 min) and PAA disinfection (3.0 – 4.5 mg.L-1, 25 min) resulted in E. coli levels being lowered to within these guidelines. Generally, chlorine disinfection resulted in higher log reductions (heterotrophic microorganisms, total coliforms and E. coli) compared to PAA disinfection. The effectiveness of PAA was impacted to a greater extent by water quality compared to chlorine. The microbiological and physico-chemical parameters of river water fluctuated to varying extents on different days. Chlorine was found to be a highly versatile disinfectant as it was efficient within the range of water quality parameters reported in this study. Chlorine and PAA are considered potential disinfectants for the treatment of river water prior to irrigation. The quality of river water can differ between various river sources. Treatment efficacy should, therefore, be evaluated individually for each specific source of water as the effect water quality has on the chemical disinfection efficiency can vary greatly.