Investigating the efficacy of sodium hypochlorite, calcium hypochlorite and peracetic acid on environmental Escherichia coli strains

Bester, Carmen (2015-12)

Thesis (MSc)--Stellenbosch University, 2015.

Thesis

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.

AFRIKAANSE OPSOMMING: Die inname van ingewandspatogene soos Escherichia coli (E. coli) kan lei tot ernstige voedselgedraagde siekteuitbrake in mense. Vorige navorsing rapporteer hoë vlakke van fekale kontaminasie in menigte Wes-Kaapse riviere wat hierdie bronne ongeskik maak vir besproeiingsdoeleindes. Dit beklemtoon die dringendheid vir geskikte behandelingsmetodes op plaasvlak om rivierwater te dekontamineer voor besproeiing. Chemiese behandeling is ‘n populêre keuse vir algemene water dekontaminering. Die fokus van hierdie studie was daarom gerig op die potensiële toepassing van perasynsuur (PAA) en chloor vir die behandeling van besproeiingswater. Die effektiwiteit van ‘n opkomende behandelingsmiddel, perasynsuur, is aanvanklik bestudeer. Navorsing is gebasseer op die evaluasie van PAA behandeling op verwysingsisolate (ATCC) en omgewingsisolate van E. coli (in soutoplossing). Omgewingsisolate was meer weerstandbiedend teen PAA as die ATCC isolate (6 mg.L-1 vir 5 en 15 min). Die variasie tussen E. coli isolate was veral duidelik by ‘n kontaktyd van 5 min. Escherichia coli F11.2 (1.54 log reduksie) en ATCC 25922 (4.50 log reduksie) was onderskeidelik die mees weerstandbiedende en mees sensitiewe verwysingsisolate wat getoets is. Die effek van laer PAA dosisse (0.5, 1.5, 3.0, 4.5 en 6.0 mg.L-1) en langer kontaktye (5, 15 en 25 min) is getoets teen die mees weerstandbiedende isolaat (E. coli F11.2). Daar is waargeneem dat konsentrasies wat wissel tussen 0.5 – 3.0 mg.L-1 oneffektief was (< 1.5 log reduksie) in die vermindering van E. coli oor ‘n kontaktyd van 25 min en het ook nie die 3 log reduksieteiken bereik nie. Hoër PAA dosisse (4.5 – 6.0 mg.L-1) het gelei tot verhoogde log reduksies (4.94 – 5.5 log reduksie) na 15 – 25 min van behandeling. Na aanleiding hiervan is twee chloorbronne bestudeer: Granulêre kalsium hipochloriet (Ca(OCl)2); en natrium hipochloriet (NaOCl) (6, 9 en 12 mg.L-1 vir 30, 60, 90 en 120 min) (in soutoplossing). Die ATCC (25922 en 35218) isolate was altyd meer vatbaar vir chloor in vergelyking met omgewingsisolate (M53, F11.2, MJ56 en MJ58). Na NaOCl behandeling (12 mg.L-1, 120 min) was ATCC 25922 totaal geïnaktiveer in vergelyking met MJ58 wat slegs ‘n reduksie van 0.37 log getoon het. Die 3 log reduksieteiken is nooit bereik nie, selfs na ‘n chloor (NaOCl) behandeling van 6 – 12 mg.L-1 (120 min kontaktyd), vir enige van die omgewingsisolate nie. Die mees weerstandbiedende isolaat (E. coli MJ58) is geïnaktiveer (> 4 log reduksie) in soutoplossing nadat ‘n behandeling van 24 mg.L-1 (NaOCl) (30 min kontaktyd) toegepas is. Die impak van rivierwaterkwaliteit op die behandelingsdoeltreffendheid van chloor (NaOCl) en PAA is ook geëvalueer. Resultate het getoon dat die Plankenburg Rivier ernstig besoedel is met E. coli vlakke bo die riglyn van 1 000 fekale kolivorms per 100 mL. Die daaropvolgende chloor (3.0 – 6.0 mg.L-1, 120 min) en PAA behandelings (3.0 – 4.5 mg.L-1, 25 min) het daartoe gelei dat E. coli vlakke verlaag was tot onder hierdie riglyn. Chloor behandeling het oor die algemeen gelei tot hoër log reduksies (heterotrofiese mikroorganismes, totale kolivorms en E. coli) in vergelyking met PAA behandeling. Die effektiwiteit van PAA is tot ‘n groter mate beïnvloed deur die rivierwaterkwaliteit in vergelyking met die effektiwiteit van chloor. Die mikrobiologiese en fisies-chemiese parameters van rivierwater het varieer op verskillende dae. Daar was gevind dat chloor ‘n hoogs veelsydige behandeling is as gevolg van die doeltreffendheid by die reeks waterkwaliteitparameters berig in hierdie navorsing. Beide chloor en PAA kan beskou word as potensiële behandelings metodes vir rivierwater voor besproeiing. Die kwaliteit van rivierwater kan verskil tussen verskeie rivierbronne. Die effek van waterkwaliteit op die chemiese behandelingseffektiwiteit kan dus varieer, en daarom moet die behandelingsdoeltreffendheid individueel geëvalueer word vir elke spesifieke waterbron.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/98057
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