Validation of large-volume batch solar reactors for the treatment of rainwater in field trials in sub-Saharan Africa

The efficiency of two large-volume batch solar reactors [Prototype I (140 L) and II (88 L)] in treating rainwater on-site in a local informal settlement and farming community was assessed. Untreated [Tank 1 and Tank 2-(First-flush)] and treated (Prototype I and II) tank water samples were routinely collected from each site and all the measured physico-chemical parameters (e.g. pH and turbidity, amongst others), anions (e.g. sulphate and chloride, amongst others) and cations (e.g. iron and lead, amongst others) were within national and international drinking water guidelines limits. Culture-based analysis indicated that Escherichia coli, total and faecal coliforms, enterococci and heterotrophic bacteria counts exceeded drinking water guideline limits in 61%, 100%, 45%, 24% and 100% of the untreated tank water samples collected from both sites. However, an 8 hour solar exposure treatment for both solar reactors was sufficient to reduce these indicator organisms to within national and international drinking water standards, with the exception of the heterotrophic bacteria which exceeded the drinking water standard limit in 43% of the samples treated with the Prototype I reactor (1 log reduction). Molecular viability analysis subsequently indicated that mean overall reductions of 75% and 74% were obtained for the analysed indicator organisms (E. coli and enterococci spp.) and opportunistic pathogens (Klebsiella spp., Legionella spp., Pseudomonas spp., Salmonella spp. and Cryptosporidium spp. oocysts) in the Prototype I and II solar reactors, respectively. The large-volume batch solar reactor prototypes could thus effectively provide four (88 L Prototype II) to seven (144 L Prototype I) people on a daily basis with the basic water requirement for human activities (20 L). Additionally, a generic Water Safety Plan was developed to aid practitioners in identifying risks and implement remedial actions in this type of installation in order to ensure the safety of the treated water

EMA-amplicon-based sequencing informs risk assessment analysis of water treatment systems

Illumina amplicon-based sequencing was coupled with ethidium monoazide bromide (EMA) pre-treatment to monitor the total viable bacterial community and subsequently identify and prioritise the target organisms for the health risk assessment of the untreated rainwater and rainwater treated using large-volume batch solar reactor prototypes installed in an informal settlement and rural farming community. Taxonomic assignments indicated that Legionella and Pseudomonas were the most frequently detected genera containing opportunistic bacterial pathogens in the untreated and treated rainwater at both sites. Additionally, Mycobacterium, Clostridium sensu stricto and Escherichia/Shigella displayed high (≥80%) detection frequencies in the untreated and/or treated rainwater samples at one or both sites. Numerous exposure scenarios (e.g. drinking, cleaning) were subsequently investigated and the health risk of using untreated and solar reactor treated rainwater in developing countries was quantified based on the presence of L. pneumophila, P. aeruginosa and E. coli. The solar reactor prototypes were able to reduce the health risk associated with E. coli and P. aeruginosa to below the 1 × 10−4 annual benchmark limit for all the non-potable uses of rainwater within the target communities (exception of showering for E. coli). However, the risk associated with intentional drinking of untreated or treated rainwater exceeded the benchmark limit (E. coli and P. aeruginosa). Additionally, while the solar reactor treatment reduced the risk associated with garden hosing and showering based on the presence of L. pneumophila, the risk estimates for both activities still exceeded the annual benchmark limit. The large-volume batch solar reactor prototypes were thus able to reduce the risk posed by the target bacteria for non-potable activities rainwater is commonly used for in water scarce regions of sub-Saharan Africa. This study highlights the need to assess water treatment systems in field trials using QMRA

Evaluation of transparent 20l polypropylene buckets for household solar water disinfection (SoDis) of drinking water in resource poor environments

Solar water disinfection (SODIS) is an appropriate technology for treating drinking water in developing communities, as it is e¬ective, low- or zero-cost, easy to use. The WHO recognises SODIS as an appropriate intervention to provide drinking water after manmade or natural disasters. Nevertheless, uptake is low due partially to the burden of using small volume polyethylene terephthalate (PET) bottles (1.5-2 L). A major challenge is to develop a low cost transparent container for disinfecting larger volumes of water. This study examines the capability of transparent polypropylene (PP) buckets of 5 and 20 litres volume, as SODIS containers using three waterborne pathogen indicator organisms: E. coli, MS2-phage and Cryptosporidium parvum oocysts

Design and evaluation of large volume transparent plastic containers for water remediation by solar disinfection

Solar water disinfection (SODIS) is a household drinking water treatmentwith a number of well-known benefits such as simplicity, efficiency and low cost. It consists of solar exposure of water stored in transparent containers (1–2 L) to direct sunlight for at least 6 hours, producing water that is safe for drinking. During recent years, much effort has been directed by the scientific community to increase the batch volume of treated water delivered by SODIS with the main objective of reducing the risk of waterborne disease in communities in resource-poor settings. In this context, this chapter reviews the latest research on the evaluation of common and novel materials employed for the design of larger-volume transparent containers (420 L) to be used for SODIS. The container design and performance of the materials developed are described from different perspectives, including microbial inactivation (bacteria, viruses and protozoan parasites), mathematical modelling of the microbicidal capacity of the container material based on optical characteristics, their lifespan and stability under natural sunlight as well as field experiences for implementation

Good optical transparency is not an essential requirement for effective solar water disinfection (SODIS) containers

The efficacy of 10 L polypropylene (PP) transparent jerry cans (TJCs) to inactivate E. coli, MS2-phage and Cryptosporidium parvum via solar water disinfection (SODIS) was tested in well water or general test water under natural sunlight. Food-safe PP was used to manufacture the TJCs and a clarifying agent was added to improve optical transparency in the UV–visible range. 10 L PP TJCs and 2 L polyethylene terephthalate (PET) bottles were filled with well water, spiked separately with (~106 CFU/mL of E. coli, ~106 PFU/mL of MS2 phage and 5 ×105C. parvum oocysts per litre) and exposed to natural sunlight for 6 h. While the 10 L PP TJC prototype had poorer transparency (UV-B 0.001%, UV-A 4.29%, and visible 92% for TJCs without clarifier and UV-B 1.36%,UV-A 8.01%, and visible 90.01% for TJCs with clarifier) than standard 2 L PET (UV-B 0.72%, UV-A 10–85%, and visible 80–90%); log reduction values (LRVs) > 5, 2 and 0.8 for E. coli, MS2-phage, and C. parvum, respectively, were observed for the TJCs within six hours respectively, which is a minimum standard for drinking water established by the World Health Organisation (WHO). We observed similar inactivation kinetics for all three organisms in PP TJCs and PET bottles despite the poorer optical transparency properties of the SODIS jerry cans. Therefore, for effective SODIS, container optical transparency is not as important as previously believed. We conclude that good visible transparency is not a necessary requirement for containers intended for SODIS use