One of the most critical health problems during natural and human induced disasters is finding safe drinking water. Disease and illnesses result from contaminated water supplies, poor hygiene, lack of safe water for washing, and/or environmental conditions that support water borne diseases.
What is Solar Water Disinfection
There is no simple solution for these problems in the midst of crisis; but there is a little known but effective water treatment process that has enormous potential. Solar disinfection (SODIS) is economical, requires no exotic or expensive chemicals, and does not require expensive and limited fuels for boiling water (Lawand et al., 1988). Solar disinfection uses the near ultra-violet radiation of the sun, 300-400 nm wavelength, to kill pathogens (Acra et al., 1984).
Before it is solarized cloudy water should be filtered (cloth or?) and/or allowed to settle. The water is then placed in a thin-walled plastic container that transmits a high percentage of UV radiation. One liter water bottles of Type 1 plastic PETE will work. Clear glass will also work but takes longer. The bottles are placed where they will receive full sun. Six hours of bright sun are desirable. In most arid lands this is not a problem. Directions could be printed on bottle labels.
UVA radiation from the sun is lethal against many bacteria, and UVB radiation is good against bacteria, viruses, and some protozoa (Garcia-gil et al. 2021). Studies showed complete destruction of Salmonella enteritidis and S. typhi in just 60 minutes, S. flexneri in just 15 minutes, Escherichia coli in 75 minutes, and comparable results against a number of other pathogens.
Treated water should be consumed within the 24 hours following exposure since bacteria can regrow in the dark if the water is stored (Garcia-Gil et al, 2021). Cloudy water (turbidity) decreases the solar disinfection efficiency and prolongs treatment time. Since the water is generally treated, stored, and often drunk from the same container, there is a decreased risk of recontamination.
Solar disinfection offers a worthwhile reduction in disease risk under real life conditions, but is not a panacea (Mcguigan et al., 1999). A central problem is the difficulty people have in matching laboratory protocols around family life. People may not leave the water in the sun long enough before drinking it. Well designed and presented studies show what can be done. The compliance in a study in Ethiopia was 91% and the incidence of diarrhea in children under 5 was cut in half (Bitwe et al.,2018).
Solar Disinfection of Food
This process can also be of benefit with solid foods. The food, such as bread, is covered with a clear plastic lid and placed in the full sun. The tabag, as it is known in the Sudan, has been found to kill most intestinal bacteria and could help protect pilgrims and large crowds at religious gatherings.
Solar Ovens
A wide range of solar ovens have also been developed to cook food or heat water. Most work very well. The challenge is more often social than technical. Most advocates of solar cookers have failed to take into account the impact their product may have on people’s cultural, social, and economic lives. Project proponents that provided solar ovens to people were often disappointing when the ovens weren’t used.
Future Perspectives
Further research is urgently needed on the effectiveness of solar disinfection against viruses, giardia, other parasites and pathogens. The added effect from a reflective backboard should be studied. The impact of combining solar disinfection with antimicrobial extracts of common herbs is also of interest. The potential added benefits from including small amounts of tea, herbs, and other traditional medicines that are bactericides, virucides, and amebicides, would be of particular interest (Soliman et al., 2021). If these local resources and SODIS can provide disinfection comparable to chlorination, the benefits would be enormous. Research has been limited because there is no marketable gadget to sell.
References
Acra, A., Raffoul, Z., Karahagopian, Y. 1984. Solar disinfection of drinking water and oral rehydration solutions. UNICEF. Beirut, Lebanon. 56 p.
Bitew, B. D., Gete, Y. K , Biks, G. A.., Takele, T. A. 2018. The effect of SODIS water treatment intervention at the household level in reducing diarrheal incidence among children under 5 years of age: a cluster randomized controlled trial in Dabat district, northwest Ethiopia. Trials. July 31. 19(1):412. doi: 10.1186/s13063-018-2797-y. PMID: 30064489; PMCID: PMC6069566.
Lawand, T.A., Alward, R, Odeyemi, R. O., Hahn, J., Kandpal, T. C., Ayoub, J. 1988. Solar water disinfection : proceedings of a workshop held at the Brace Research Institute, Montreal, Quebec, Canada, 15-17 August. https://www.ircwash.org/sites/default/files/254.1-90SO-7144.pdf
García-Gil Á, García-Muñoz, R. A. McGuigan, K. C., Marugán, J. 2021. Solar Water Disinfection to Produce Safe Drinking Water: A Review of Parameters, Enhancements, and Modelling Approaches to Make SODIS Faster and Safer. Molecules. 2021 Jun 5;26(11):3431. doi: 10.3390/molecules26113431. PMID: 34198857; PMCID: PMC8201346.
Mcguigan, K., Joyce, T. M., Conroy. R. M. 1999. Solar disinfection: use of sunlight to decontaminate drinking water in developing countries. Journal of Medical Microbiology 48:785-787. DOI: 10.1099/00222615-48-9-785
Soliman, M. M., Elsaba, Y. M., Soliman, M. S.A. et al. 2024. Composition and antimicrobial activity of Rosmarinus officinalis L. and Artemisia monosperma L. leaf essential oils and methanolic extracts from plants grown in normal and saline habitats in Egypt. Science Reports 14:7342.
El Agil, A. A. R., Erwa, H.H. 1974. Decontamination of foodstuffs by solar energy: bacterial counts in food samples following exposure to sunlight in airtight containers. IRCS 2, 1270.
Sarangi, A., Sarangi, A., Sahoo, S. S., Nayak, J., Mallik, R. K. 2024. Advancements and global perspectives in solar cooking technology: A comprehensive review. Energy Nexus. 13:100266, https://doi.org/10.1016/j.nexus.2023.100266.
