Assessment of the microbial quality of various domestic rainwater harvesting systems and the suitability of a nano based treatment method

- Malema, Mokaba Shirley

Title
Assessment of the microbial quality of various domestic rainwater harvesting systems and the suitability of a nano based treatment method
Creator
Malema, Mokaba Shirley
ThesisAdvisor
Tandlich, R
ThesisAdvisor
Ubomba-Jaswa, Eunice
Date
2020
Type
thesis
Type
text
Type
Thesis
Type
Doctoral
Type
PhD
Identifier
http://hdl.handle.net/10962/110218
Identifier
vital:33249
Identifier
https://dx.doi.org/10.21504/10962/110218
Description
Thesis (PhD)--Rhodes University, Faculty of Science, Chemistry, 2020.
Description
In most developing countries, people from rural and peri-urban settlements depend on harvested rainwater (HRW) as an alternative water source for drinking and other household purposes. Despite this reliance, there is little monitoring of the microbial quality of HRW in these areas. The most important issue in relation to using untreated harvested rainwater for drinking and other domestic purposes is the potential public health risks associated with microbial pathogens. Unlike chemical contamination, microbial contamination my lead to disease occurring rapidly, hence the need for frequent monitoring. Thus, the current study investigated the microbial quality of various domestic rainwater harvesting systems and the suitability of a nano based treatment method. The first experiments involved determining the microbial (Escherichia coli) and physicochemical quality (pH, turbidity, nitrate and chemical oxygen demand (COD)) of HRW in the Eastern Cape Province, South Africa. Samples were collected from 11 tanks situated at the Rhodes University, Kenton-on-sea (coastal) and in homes in the Grahamstown area on a weekly basis between June and September 2016. The Colilert-18®/Quanti-tray® 2000 system was used for enumeration of E. coli while physicochemical parameters were measured using commercial kits. Results showed that all samples were contaminated with varying concentrations of E. coli ranging from 7 to 1055 MPN/100 mL. Physicochemical analysis revealed that pH ranged from 5.6 to 7.6 and Turbidity values obtained for all tanks were below 5 NTU except for tank 4 (5.12 ± 4.96 NTU) and 7 (5.58 ± 8.19 NTU). Nitrate levels (range: 5.95 to 28.12 mg L-1) and COD (range: 66.53 to 191.12 mg L-1) were higher than the recommended South African drinking water quality guidelines in most of the tanks. In the second experiments, the objective was to determine whether a modified hydrogen sulphide (H2S) test kit with an improved detection rate is an effective preliminary screening qualitative test that can be used for rainwater quality monitoring. The hydrogen sulphide method is a low-cost microbiological field-based test which can be used in areas where water testing facilities are limited. Harvested rainwater samples were collected from various tanks in the Eastern Cape and tested for contaminants of faecal origin using the modified hydrogen sulphide test kit, Colilert-18/Quanti-tray®/2000 and membrane filtration technique. Faecal coliforms were measured using membrane filtration, E. coli was measured using Colilert and correspondence rates were calculated with results of the improved hydrogen sulphide test kit. E. coli results ranged from <1 – >2419.6 MPN/100 mL while the faecal coliforms ranged from 0 – >300 CFU/mL. The agreement rate with hydrogen sulphide test and membrane filtration was 88% while the agreement rate for the Colilert and hydrogen sulphide test was 76%. The third experiments investigated the prevalence of pathogenic E. coli strains and their antimicrobial resistance patterns in HRW tanks in the Eastern Cape, South Africa. E. coli isolates obtained in the first experiments were further screened for their virulence potentials using polymerase chain reaction (PCR) and subsequently tested for antibiotic resistance using the disc-diffusion method against 11 antibiotics. The pathotype most detected was the neonatal meningitis E. coli (NMEC) (ibeA 28%) while pathotype enteroaggregative E. coli (EAEC) was not detected. The highest resistance of the E. coli isolates was observed against Cephalothin (76%). All tested pathotypes were susceptible to Gentamicin, and 52% demonstrated multiple-antibiotic resistance (MAR). The fourth experiments shed light on the occurrence of Legionella, zoonotic and fungal pathogens in the rainwater harvesting systems (RWHS) situated in different regions of South Africa. Rainwater samples were collected in urban and semi-urban areas from tanks situated in various areas in South Africa (Johannesburg, Pretoria and Grahamstown). Pathogenic organisms investigated were Salmonella, Shigella, Vibrio cholerae, Legionella and fungal isolates. Pure isolates were obtained and screened using PCR. Results revealed the presence of pathogenic bacteria and fungi in all the tested RWHS. In Grahamstown the most detected pathogen was Salmonella (73%) while Vibrio Cholerae was not detected. All the tested pathogens were present from the RWHS situated in Pretoria. Shigella was not detected from the RWHS in Johannesburg while others were detected. Identification of fungal isolates from HRW showed the presence of pathogenic fungi such as Aspergillus fumigatus, Cryptococcus laurentii, Aureobasidium pullulans and Mucor circinelloides. The last experiments, focussed on exploring a suitable treatment method for HRW where a nano compound quaternary imidazolium modified montmorillonite (MMT) was used as a potential household rainwater treatment option. Harvested rainwater samples were collected from the RWHS situated at the Council for Scientific and Industrial Research (CSIR), Pretoria South Africa. River and borehole water samples were included in the study to check the efficiency of the treatment method on various water sources. River water samples were collected from Olifants River, Witbank, South Africa while borehole water was collected from a privately-owned borehole in Pretoria. For inoculation studies, all the water sources were sterilised in batches of 1 and 2 L and inoculated with approximately 107 CFU/mL of overnight E. coli. Approximately 200 mg of the quaternary imidazolium modified MMT was added to the inoculated water and samples collected immediately after inoculation (time 0) and thereafter every hour for 5 hrs. The analyses were further conducted using unsterilised water samples (total bacterial count) and 500 mg of the treatment material. Complete inactivation of E. coli in sterilised HRW was achieved in 2 hrs for the 2 L water samples and 3 hrs for the 1 L water samples. Sterilised river water achieved complete E. coli inactivation in 4 hrs for the 1 L and 5 hrs for the 2 L samples while borehole water samples achieved complete E. coli inactivation in 5 hrs (2 L) and 6 hrs for the 1 L samples. In the unsterilised water sources (total bacteria), complete bacterial inactivation was observed in 5 hrs for both the 1 and 2 L harvested rainwater samples, 6 hrs in river water samples (both 1 and 2 L) and 8 hrs for borehole water samples (1 and 2 L). The results suggest that the treatment option was more efficient in harvested rainwater (required less time for bacterial inactivation compared to river and borehole water). The results of the current study are of public health concern since the use of untreated HRW for potable purposes may pose a risk of transmission of pathogenic and antimicrobial-resistant E. coli and other pathogenic organisms such as Salmonella, Shigella and Vibrio cholerae. It is therefore recommended that in cases where the tested harvested rainwater is used for potable purposes, simple treatment methods such as boiling and SODIS be applied so the harvested rainwater is fit for human consumption.
Format
computer, online resource, application/pdf, 1 online resource (149 pages)
Publisher
Rhodes University, Faculty of Science, Biotechnology Innovation Centre (RUBIC)
Language
English
Rights
Malema, Mokaba Shirley
Rights
All rights reserved.
Person PID
https://orcid.org/0000-0002-1085-5921
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