Can solar water-treatment really help in the fight against water shortages?

In the face of increasing global population, rising industrialization and the inescapable reality of climate change, the demand for access to clean, safe water has never been greater. Solar wastewater remediation technologies and solar water-treatment have the potential to contribute significantly towards affordable and sustainable solutions to this seemingly intractable problem. They do this by using solar energy to treat water from sources that previously would have been considered unsuitable for further use. In this article we reveal the basic principles surrounding the design and application of solar remediation reactors for urban wastewater treatment and reuse and then show how even simpler technologies are being used in low-income communities to provide affordable and safe potable water

Evaluation of Solar Disinfection of E. coli Under Sub-Saharan Field Conditions Using a 25 Litre Borosilicate Glass Batch Reactor Fitted with a Compound Parabolic Collector.

The bacterial inactivation efficacy of a solar water disinfection (SODIS) reactor consisting of a 25L borosilicate glass tube fitted with a compound parabolic collector (BGTR-CPC) was assessed under equatorial weather conditions in Uganda. The SODIS BGTR-CPC was tested over a 17-month period in Sub-Saharan conditions in Kampala, Uganda. The BGTR-CPC was filled with natural water from a nearby protected well. A wild strain of Escherichia coli isolated from local natural water was added to the reactor to give a starting population of between 105 and 107 CFU/100ml. This spiked water was exposed to natural sunlight. Satisfactory bacterial inactivation (log10 reduction values \u3e6 units or inactivation to below the limit of detection (/100ml.)) was observed for 11 of 13 experiments. Rainfall and overcast/cloudy conditions were factors on both of the occasions when incomplete inactivation was observed. In conclusion, the use of CPC SODIS technology is suitable for treating drinking water both at household level and institutional level in Sub-Saharan and other similar tropical climates if careful consideration of the cloud cover and rainfall is taken into account

Nitrogen and Copper doped solar light active TiO2 photocatalyst for water decontamination

A novel class of photocatalytic coating capable of degrading bacterial and chemical contaminants in the presence of visible sunlight wavelengths was produced by depositing a stable photocatalytic TiO2 film on the internal lumen of glass bottles via a sol gel method. This coating was prepared in either undoped form or doped with nitrogen and/or copper to produce visible light-active TiO2 films which were annealed at 600 °C and were characterized by Raman, UV-Vis, and X-ray photoelectron spectroscopy. The presence of doped and undoped TiO2 films was found to accelerate the degradation of methylene blue in the presence of natural sunlight, while copper-doped TiO2 films were found to accelerate bacterial inactivation (of E. coli and E. faecalis) in the presence of natural sunlight

Solar photocatalysis for water disinfection: Materials and reactor design

As of 2010, access to clean drinking water is a human right according to UN regulations. Nevertheless, the number of people living in areas without safe drinking water is predicted to increase by three billion by the end of this decade. Several recent cases of E. coli and Cryptosporidium contamination in drinking water are also reported in a number of advanced countries. Therefore ensuring the potability of drinking water is urgent, but highly challenging to both the developing and developed world in the future. A combination of solar disinfection and photocatalysis technology offers real possibilities for removing lethal pathogenic microroganisms from drinking water. The time taken for the conventional SODIS process can be greatly reduced by semiconductor (e.g. TiO2, ZnO, nano-heterojunctions) based photocatalysis. This review addresses the fundamental reaction mechanism, advances in materials synthesis and selection and recent developments in the reactor design for solar energy driven photocatalysis using titanium dioxide. The major advantage of using photo-reactors is that they enhance disinfection by increasing photon flux into the photocatalyst. Other major factors affecting such efficiency of solar-based photocatalysis such as the illuminated volume/total volume ratio, catalyst load and flow rate, are discussed in detail. The significance of using immobilised catalysts over the catalyst powder in slurries is also highlighted. It is noted that, despite encouraging early field studies, the commercialisation and mass production of solar photocatalysis systems remains highly challenging. Recommendations for future directions for addressing issues such as mass transfer, requirement of a standard test method, photo-reactors design and visible light absorption by TiO2 coatings are also discussed

Life cycle assessment comparison of point-of-use water treatment technologies: solar water disinfection (SODIS), boiling water, and chlorination

Numerous different point-of-use (POU) water treatment technologies exist that can remove, reduce or inactivate microbial pathogens present in untreated drinking water. However, there have been uncertainties as to which technology is best suited to rural populations. Environmental impacts of these technologies can bring further threats to rural communities, so the life cycle assessment (LCA) approach is frequently used to compare different POU water treatment technologies. The present study uses LCA to compare three treatment options: solar water disinfection (SODIS) using a Transparent Jerrycan (TJC), boiling, and chlorination. A life cycle inventory database is created for each stage, calculating the embodied energy and transportation energy considering daily reliance for all the technologies. Direct carbon dioxide emission at the point of use of energy/fuel, particulate matter formation and smog formation analysis can help to implement the most appropriate technology. The life-cycle assessment in this study indicates that when considering the environmental impact associated with providing sufficient safe drinking water for a family of six over a period of 6 months, SODIS has been found to have better sustainability credentials as a water treatment technology (6.0 kg CO2e per functional unit) with low contribution in all the three impact categories, followed by chlorination (9.8 kg CO2 e per functional unit) and boiling water (6808 kg CO2e per functional unit)

Capability of 19-litre polycarbonate plastic water cooler containers for efficient solar water disinfection (SODIS): field case studies in India, Bahrain and Spain.

The small treated volume (typically ~2 litres) associated with polyethylene terephthalate (PET) bottles that are most frequently used in solar water disinfection (SODIS), is a major obstacle to uptake of this water treatment technology in the developing world. In order to address this problem we have conducted a series of experiments in Spain, Bahrain and India, to assess the efficacy of large volume (19 litres) transparent plastic (polycarbonate) water cooler/dispenser containers (WDCs) as SODIS reactors to inactivate Escherichia coli and Enterococcus faecalis, under strong natural sunlight. Reduction values of 6 log10 units (LRV = 6.0) have been observed using WDCs in each location. Additional comparisons between 2-L PET bottles and 19-L indicate that WDCs provide bacterial inactivation similar in both systems. SODIS disinfection experiments in turbid water (100 NTU) in both reactors showed very good inactivation efficiency. LRVs of 7.2 and 7.8 were obtained for E. coli in WDC and 2-L PET bottles, respectively, and in the case of E. faecalis LRV = 5.7 and 7.9 were observed. These studies demonstrate that under conditions of strong sunlight and mild temperature, 19 litre water dispenser containers can be used to provide adequate volumes of SODIS treated water for households or larger community applications such as schools or clinics in the developing world

A Transdisciplinary Methodology for Introducing Solar Water Disinfection to Rural Communities in Malawi-Formative Research Findings

Despite the increasing volume of evidence demonstrating the efficacy of solar water disinfection (SODIS) as a household water treatment technology, there still appear to be significant barriers to uptake in developing countries. The potential of SODIS is often treated with skepticism in terms of effective treatment, volume, and safety, and is dismissed in preference for more accepted technologies such as ceramic filters and dose chlorination. As part of WATERSPOUTT (EU H2020 688928), our study used a transdisciplinary methodology to cocreate an innovative SODIS system in rural Malawi. The formative work focused on the design of 1) an appropriate and acceptable system and 2) a context-specific intervention delivery program using a behavior-centered design. Initial research identified specific water needs and challenges, which were discussed along with a cocreation process with potential end users, through a series of shared dialogue workshops (SDWs). Specifications from end users outlined a desire for higher volume systems (20 L) that were “familiar” and could be manufactured locally. Development of the “SODIS bucket” was then undertaken by design experts and local manufacturers, with input from end users and subject to controlled testing to ensure efficacy and safety. Concurrent data were collated using questionnaires (n = 777 households), water point mapping (n = 121), water quality testing (n = 46), and behavior change modeling (n = 100 households). These identified specific contextual issues (hydrogeology, water access, gender roles, social capital, and socioeconomic status), and behavioral determinants (normative, ability, and self-regulation factors) that informed the development and delivery mechanism for the implementation toolkit. Integr Environ Assess Manag 2020;16:871–884

Transforming practice, transforming practitioners:reflections on the TQFE in Scotland

This study offers reflections on the TQFE in Scotland as an example of the transformative professional learning model as identified by various authors. The focus of this study is the professional learning of lecturers in Scotland’s colleges. Informed by wider considerations of teacher education more broadly, it will be of particular interest to those supporting a transformative model of professional learning in a variety of educational contexts. The research was undertaken as a collaborative initiative between each of the three universities which offer the TQFE in Scotland. Qualitative data are drawn from former TQFE participants and college mentors, and thematic analysis used to gain further insight from participant interviews. Findings highlight the transformative nature of the TQFE with an impact that is beyond the currency of the TQFE programme duration. The provision of transformative professional learning opportunities is now imperative given various pressures and tensions around the development of educators more generally and within contemporary Scottish Further Education in particular. Such pressures and tensions include: the varied demands within the Professional Standards for Lecturers in Scotland’s Colleges, and the need for professional learning for college lecturers to go beyond a competency or tool-kit based approach and to be sustainable

Weathering of plastic SODIS containers and the impact of ageing on their lifetime and disinfection efficacy

This work aims to study the ageing of plastic materials suitable for manufacturing solar water disinfection (SODIS) containers, such as PET, polymethylmethacrylate (PMMA), and polypropylene (PP) with and without UV-stabiliser. The evolution of mechanical and optical properties, and disinfection rates were studied over different weathering periods. PMMA and PP with a 1% content by weight of UV-stabiliser were shown to be excellent candidate materials for manufacturing SODIS devices, since they presented stable optical and mechanical properties, and both transmit UVB radiation. Since PMMA is a UV resistant but fragile, easily scratched material with a lifetime above one year, it should be selected for static SODIS devices, while PP with 1% of UV-stabiliser should be chosen for portable devices because of its great resistance and elasticity for up to nine months of solar exposure. Both materials were considered profitable on the basis of their lifetime/costs ratio. PET showed great mechanical properties for one year but, in contrast, suffered of a deterioration of its optical properties and disinfection rates. PP without UV-stabilisers suffered a dramatic degradation after a very short exposure of 2 months. Finally, a kinetic model that considers the radiation spectral distribution (thus, the transmittance spectra of the plastics as a function of the ageing time) is proposed to estimate the required solar exposure time to achieve water disinfection for the proposed plastic SODIS containers. A good agreement between predicted and experimental data was achieved, especially for containers manufactured with PET and both PPs (errors below 25%)

Evaluation of transparent 20L polyproylene 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 effective, 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