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SODIS-An emerging water treatment process

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Abstract

This article comprises the work of several research teams which analysed the effectiveness of solar water disinfection (SODIS) in various laboratory and field investigations carried out at different test sites over the last five years. SODIS was applied as batch and continuous flow process (SODIS reactor). The process is most effective with a water temperature of at least 50 °C. Transparent plastic bags allow a 3-log reduction (99.9%) of faecal coliforms and Vibrio cholerae through heating and radiation at an UV-A dose of 54 Wh/m2 over a period of 140 min. The SODIS reactor produces around 100 L of drinking water per square metre of solar collector and day.
... A simple alternative to treat water for human consumption is solar disinfection (SODIS), which uses UV radiation to inactivate pathogens present in the water. Although, technically, SODIS can use glass containers, due to the greater weight, fragility and expense of this material, traditionally, users tend to reuse polyethylene tetraphlanate (PET) bottlesmostly of 1.5 or 2 Lor even plastic bags, since these resources are more easily accessed by lower income communities (Acra et al. 1984;Wegelin et al. 1994;Reed 1997;Sommer et al. 1997;Oates et al. 2003;Dessie et al. 2014;Jin et al. 2020). Previous studies indicated exposure times required for 100% of pathogen removal spanning from about 3 to 48 h, depending on the intensity of sunlight, pathogen concentration, turbidity and cloud cover conditions (McGuigan et al. 2012;Haider et al. 2014). ...
... On the other hand, Figure 4(b) shows EC decay in a sunny day, with I g and T increasing from about 190 to 750 W/m² and 26 to 48°C, respectively, and EC decreasing from 122 MPN/100 mL to below the detection limit. Note that in this case, 100% removal efficiency was reached within 2.5 h with an average solar radiation of about 410 W/m², which is below the minimum of 500 W/m² recommended in the literature for bacterial inactivation (Sommer et al. 1997;Oates et al. 2003;Haider et al. 2014). Finally, Figure 4(c) shows EC decay in a rainy day, where I g and T increased from about 90 to 370 W/m² and 27 to 32°C, respectively, while EC decreased from 120 MPN/100 mL to below the detection limit. ...
... The rectangular shape may favor a more perpendicular incidence of solar radiation over the glass sheet surface, while the small water depth (5 cm) may contribute to a more efficient heat transfer from top to bottom. Observe that conventional SODIS devices such as PET bottles or plastic bags usually present a curvilinear surface and water depths larger than 5 cm (Sommer et al. 1997;Oates et al. 2003;Dessie et al. 2014;Loeb et al. 2015). ...
Article
We conducted field, laboratory and modeling studies to evaluate the efficiency of a new solar disinfection (SODIS) device called Aqualuz for the removal of Escherichia coli (EC) from cistern water in the Brazilian semiarid, for different solar exposure–water temperature conditions. The results indicated EC contamination (100–300 MPN/100 mL) in all tests performed. As compared to the literature, lower exposure times (2.5–4.0 h) and solar radiations (250–410 W/m²) were sufficient for EC elimination. Then, assuming the complete-mix approach and first-order kinetics, it was possible to adjust EC decay rate constants (k) considering three different models: constant k-value, k as a function of water temperature and a new formulation for k as a function of both solar radiation and water temperature. All models performed well with normalized root mean squared logarithmic error (NRMSLE) lower than 20%, but the best fitting was obtained with the new approach. A new relationship between solar radiation and water temperature was also obtained, which allowed model simulations of EC decay for 34 municipalities in the Brazilian northeast, resulting in a color map for the region depicting the exposure periods of 1.8–5.6 h for reaching a 3-log reduction. HIGHLIGHTS We conducted field, laboratory and modeling studies to evaluate the efficiency of a new solar disinfection device called Aqualuz for the removal of Escherichia coli (EC) from cistern water in the Brazilian semiarid.; We carried experiments in different solar exposure-water temperature conditions.; Assuming the complete-mix approach and first-order kinetics, it was possible to adjust EC decay rate constants (k).;
... Downes and Blunt (1877) [1], reported the bactericidal effect of sunlight. Acra et al. (1984) [2], initiated research practically on solar disinfection for drinking water and oral rehydration solution in late 1970s [3,4]. SODIS technique in drinking water is fed in transparent bottles which exposed to sunlight upto 8 hours and there is subsequent inactivation of micro-organisms and viruses [4,5,6]. ...
... Acra et al. (1984) [2], initiated research practically on solar disinfection for drinking water and oral rehydration solution in late 1970s [3,4]. SODIS technique in drinking water is fed in transparent bottles which exposed to sunlight upto 8 hours and there is subsequent inactivation of micro-organisms and viruses [4,5,6]. SODIS have advantages simple, no chemical consumption, no harmful by products, low energy requirement, inexpensive and environmentally sustainable method [7,8]. ...
... SODIS application under natural conditions demonstrated that for the inactivation of E.Coli, FC and TC temperature is significant [9]. UV-A radiation of the spectrum of sunlight is mainly responsible for the inactivation microorganisms (bacteria and viruses) [4]. UV-A radiation at the same time increased in the mortality of microorganism occurred when temperatures exceeds 45°C [3,10,11,12]. ...
Experiment Findings
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Recently SODIS is looked upon as a potential alternative for disinfecting low strength grey water for inactivation of microorganisms with research mainly focused towards enhancement of inactivation efficiency. The present study was aimed to enhance inactivation efficiency of SODIS through gaining relatively higher temperature by introducing aluminum foil reflectors (reflective rear surface). Investigation were carried out at a constant flowrate 135 ml/min, varying turbidity (30, 25, 20, 15 and 10 NTU) and radiation intensity 550.55 ± 26.55 W/m 2 at glass tubes of SODIS treatment unit inclined at 45 o. At the end of the contact time of 8hours, about average 21.53 % gain of temperature was obtained with reflective rear surface and the inactivation efficiency was about 36.54% for Escherichia Coli (E Coli), 60.62% for Feacal Coliform (F C) and Total Coliform (TC) for 57.58% when absorptive rear surface was kept and 77.54% for E.Coli, 94.79 % for FC and 94.64 % for TC when reflective rear surface was kept. Overall enhancement in inactivation efficiency of 41%, 34.17% and 37.06 % for E.Coli, FC and TC were obtained respectively when aluminum foil was used as reflective rear surface.
... The effectiveness of SODIS was found to be the best in locations with significant amounts of strong sunlight during midday, mostly located around the equator [76]. Various studies have been conducted to overcome the weather issue in term of partially sunny or during cold season and enhance SODIS; Sommer et al. [77] suggested using darker containers or painting the underside of them with black to enhance the thermal disinfection. However, this could increase the water temperature, but it will prevent the penetration of solar irradiation through the water and minimize the action of endogenous photo-inactivation (through the action of UVB) [62]. ...
Article
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Poor access to drinking water, sanitation, and hygiene has always been a major concern and a main challenge facing humanity even in the current century. A third of the global population lacks access to microbiologically safe drinking water, especially in rural and poor areas that lack proper treatment facilities. Solar water disinfection (SODIS) is widely proven by the World Health Organization as an accepted method for inactivating waterborne pathogens. A significant number of studies have recently been conducted regarding its effectiveness and how to overcome its limitations, by using water pretreatment steps either by physical, chemical, and biological factors or the integration of photocatalysis in SODIS processes. This review covers the role of solar disinfection in water treatment applications, going through different water treatment approaches including physical, chemical, and biological, and discusses the inactivation mechanisms of water pathogens including bacteria, viruses, and even protozoa and fungi. The review also addresses the latest advances in different pre-treatment modifications to enhance the treatment performance of the SODIS process in addition to the main limitations and challenges.
... Several research groups started analyzing SODIS efficiency in batch and continuous reactors, at different temperatures, radiation intensities, UV-A doses, etc. [32]. ...
Article
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“Ensure access to water for all”, states Goal 6 of the UN’s Sustainable Development Goals. This worldwide challenge requires identifying the best water disinfection method for each scenario. Traditional methods have limitations, which include low effectiveness towards certain pathogens and the formation of disinfection byproducts. Solar-driven methods, such as solar water disinfection (SODIS) or solar photocatalysis, are novel, effective, and financially and environmentally sustainable alternatives. We have conducted a critical study of publications in the field of water disinfection using solar energy and, hereby, present the first bibliometric analysis of scientific literature from Elsevier’s Scopus database within the last 20 years. Results show that in this area of growing interest USA, Spain, and China are the most productive countries in terms of publishing, yet Europe hosts the most highly recognized research groups, i.e., Spain, Switzerland, Ireland, and UK. We have also reviewed the journals in which researchers mostly publish and, using a systematic approach to determine the actual research trends and gaps, we have analyzed the capacity of these publications to answer key research questions, pinpointing six clusters of keywords in relation to the main research challenges, open areas, and new applications that lie ahead. Most publications focused on SODIS and photocatalytic nanomaterials, while a limited number focused on ensuring adequate water disinfection levels, testing regulated microbial indicators and emerging pathogens, and real-world applications, which include complex matrices, large scale processes, and exhaustive cost evaluation.
... Solar disinfection (SODIS) is a standard water treatment method used by communities where access to safe drinking water is a problem [1]. Water is exposed to sunlight radiation in a transparent container, usually a bottle or bag (typically of 1.5 or 2 L volume) for at least 6 h under sunny conditions. ...
Article
This paper studies the worldwide applicability of solar water disinfection (SODIS) technology through a novel parameter: the SODIS potential. This parameter is defined as the inverse ratio between the required exposure time to achieve a four log disinfection of E. coli and the six hours recommended by the standard SODIS protocol. The E. coli inactivation kinetics was predicted by fitting the results under different temperature and incident radiation to a semi-empirical inactivation model, including a synergy term between bacterial stress sources (light/heat). To estimate the SODIS potential, a solar calculator was developed based on the Sun's position, atmospheric extinction, cloud-cover, and elevation. The time-varying total incident radiation available at any location worldwide was estimated for each day along the year during sunlight hours. The time-varying temperature was also estimated from minimum and maximum values, introducing its dynamic variation along with the solar exposure of the water. Both incident radiation and temperature values are input into the kinetic model to estimate the disinfection rate. Based on these values, the number of batch disinfections that can reach the goal of 99.99% bacterial elimination in 1 day and the minimum daily time required to achieve this goal is computed; the latter is finally transformed to the SODIS potential. The results of the study, illustrated as contours indicating the SODIS potential and other relevant indicators overlayed on a world map, confirm that latitude has a significant contribution to the SODIS potential, with the highest values close to the equator. However, the results also highlight the importance of temperature and cloud-cover, with critical differences between equal latitude regions.
... This radiation intensity threshold is associated with 3 log reduction unit of bacterial pathogens at a water temperature of 30°C and water turbidity of 30 NTU. SODIS is most effective at water temperature values above 50°C, at which the radiation threshold required for complete inactivation could be lowered by as much as two-thirds (Sommer et al., 1997). Such elevated water temperature values are easily achievable in the tropics by painting the underside of the SODIS bottles black or exposing them on an absorptive background. ...
Article
Solar disinfection (SODIS) involves exposing water stored in transparent polyethylene terephthalate (PET) containers to the sun for about 6 h of strong sunlight, after which the water is rendered safe for consumption. This study investigated the seasonal effect of reactor characteristics on the inactivation kinetics/constant of faecal coliforms by conducting a 23 factorial experiment, involving two levels of PET bottle size, PET bottle thickness, and PET bottle rear surface, uniquely combined to form 8 SODIS reactors/experimental units. The faecal coliform population of hourly samples taken from the 8 SODIS reactors showed that the inactivation kinetics/constant depends on the irradiation energy and maximum water temperature as dictated by the reactor characteristics. The average rate constant of the reflective reactors (1.37 ± 0.43 h-1) was significantly better (p < 0.001) than the absorptive reactors (1.17 ± 0.59 h-1) between June and October. The average rate constant of the small PET bottles (1.73 ± 0.65 h-1) is significantly higher (p < 0.002) than the large PET bottles (1.46 ± 0.51 h-1) from December to May; while the average rate constant of the light PET bottles (1.58 ± 0.64 h-1) is significantly better (p < 0.001) than the thick PET bottles (1.41 ± 0.52 h-1) year-round. Analyses of results confirmed a two-way interaction effect between PET bottle size and PET bottle thickness and between PET bottle rear surface and PET bottle thickness for periods with average radiation intensity of 450–500 W∙m−2. Although container size and thickness were the most significant factors, combining light PET bottles with absorptive rear-surface could extend the applicability of SODIS to regions that fall short of the recommended radiation intensity threshold of 500 W∙m−2 for 5 h.
... Parabolic dish configuration (Adapted fromSommer, Marino, Solarte, Salas, Dierolf, Valiente, Mora, Rechsteiner, Setter, Wirojanagud & Ajarmeh, 1997) ...
Conference Paper
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In this paper, we highlight the effects of contaminated water on humans as well as the crisis of water supply and distribution of potable water in many areas of developing countries. While water is the most important substance on earth and a primary human need, contaminated water can cause and spread diseases. It is, therefore, necessary to ensure that water is purified and decontaminated for daily use at a low cost. The design of solar-powered water purification systems is thus regarded as an important means of producing clean water. Solar energy poses no polluting effect and has become a dependable energy source for usage. The design of a solar-powered water purification system is based totally on the thermal method by using the thermal heating system principle which converts sunlight rays into heat. The most vital aspect is the absorption of heat to induce evaporation of water. Research shows that flat plate collectors produce heat at relatively low temperatures (27°C to 60°C) and are commonly used to heat liquids. A solar-powered water purification system consists of a solar collector that absorbs sunlight to ensure vaporisation, which is the first stage of purifying and a filter that removes contaminants. Four different concepts have been developed. A detailed description of the components and the operation of the systems constitute the main contribution of this paper.
... 13 A significant amount of research has been directed toward discovering new ways to enhance SODIS, thereby increasing the efficacy of this low-cost and simple water treatment technique. Such examples include the use of solar concentrators/reflectors to enhance radiation exposure, 14,15 painting the underside of plastic bottles black to enhance thermal disinfection, 16 and using chemical additives such as citric acid or riboflavin, which may be photochemically activated. 17,18 We highlight, however, that the addition of a high functioning photocatalyst has the potential to enhance SODIS to a far greater degree than the aforementioned methods, rendering this a perfect context in which to optimize PWT materials and systems ( Figure 2). ...
Article
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This Viewpoint article in ACS Catalysis expresses the importance of applying photocatalytic water treatment materials to the solar disinfection of real world water samples in areas that struggle to obtain a reliable supply of clean drinking water.
Article
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Solar disinfection (SODIS) is a simple and low-cost household water treatment (HWT) option used for disinfection of drinking water. In this study, the bacterial inactivation potential of SODIS was evaluated under the solar irradiance observed in different seasons in Bangladesh according to WHO evaluation protocol of HWT, and the SODIS experiments were conducted for both transmissive and reflective reactors using PET bottles and plastic bags. In summer, log reduction value (LRV) more than 5 was observed for the transmissive PET reactors for 6 to 8 hr exposure to sunlight and the treated water complied with the microbial standard of zero colony forming units/100 mL in drinking water. In monsoon and winter, LRV > 4 can be achieved for 16 hr and 8 hr exposure to sunlight, respectively, using reflective reactors. The plastic bag was found to be more effective than PET. A safe exposure time was estimated from the Weibull model to be maintained for SODIS application to achieve 4.0 LRV and also to prevent the re-growth of microorganisms in the treated water. A significant re-growth of microorganisms was observed in the treated water, thus SODIS with other HWT processes can be recommended for use in communities with an unsafe drinking water supply. HIGHLIGHTS Address the effectiveness of SODIS under the local irradiance observed in Bangladesh.; Used both reflective and transmissive reactors.; Complete inactivation achieved under strong sunlight condition.; Reflective reactors are more effective.; A safe exposure time was estimated.;
Article
Universal access to basic drinking water services remains elusive, especially for rural communities of low- and lower-middle income countries where financial constraints restrict the implementation of existing drinking water development approaches. With the need for cheaper and more accessible point-of-use water treatment technologies, this study proposes a near-zero cost modification for solar disinfection (SODIS) using a suite of natural, plant-sourced photosensitizers to produce singlet oxygen and accelerate microbial inactivation under simulated sunlight. Chlorophyll, curcumin, and Saint John’s Wort extract are applied with edible dispersants, enhancing the inactivation of bacteriophage MS2, a human enteric virus surrogate. Chlorophyll exhibited the most dramatic enhancement, increasing the disinfection rate up to 180 times that of SODIS alone. The potential for this approach to be successfully applied in different geographic regions was evaluated using the experimentally obtained disinfection kinetics and annual average daytime surface sunlight intensity data across the globe. The findings suggest that locally sourced natural photosensitizers and dispersants (e.g., chlorophyll extracted from alfalfa and saponin extracted from quinoa husks) can be a particularly useful point-of-use water disinfection technology for rural regions of low- and lower-middle income countries that have been previously underserved by safe water initiatives.
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