SODIS

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Application example from Indonesia

SODIS (abbreviation for example, lar Water Dis infection ) is a process for water disinfection and is based on the germicidal effect of UV-A radiation in the sunlight. The WHO recommends SODIS as an effective method for treating water at the household level. SODIS is used in an increasing number of households in numerous developing countries .

Working principle

The SODIS method uses the disinfecting effect of UV-A light (wavelength 320–440 nm) from solar radiation. If the irradiation is long enough, common pathogens ( diarrhea , cholera, etc.) are largely killed. At temperatures above 50 ° C, a strong synergistic effect of UV-A radiation and heat can be observed, which further increases the efficiency of SODIS.

application

PET beverage bottles are best for using SODIS in developing countries. Unlike window glass, PET and bottle glass allow UV light to pass through. The diameter of a drinking bottle with a content of max. 3 liters roughly corresponds to the effective penetration depth of UV-A radiation.

Microbially polluted water is filled into PET bottles. For oxygen saturation, the bottle can first be filled three-quarters of the way, shaken for 20 seconds and then completely filled. The bottle is closed and left horizontally in direct sunlight for six hours. If the sky is overcast, the bottles should be left exposed for two days.

+ Recommended duration of exposure of the SODIS bottles
Weather conditions Recommended exposure time
Sunny - 50% overcast 6 hours
50–100% covered 2 days
Constant rain limited effectiveness, the consumption of rainwater is recommended.

In addition to SODIS, there are other methods of water treatment at household level. Boiling water is an effective and widespread method, but it often involves a great deal of effort in obtaining fuel. Chlorination and filtration also achieve good disinfection, but they also do not achieve complete sterilization of the water.

Methods for decentralized water treatment can play an important role for people who would remain without access to clean drinking water for years even with an accelerated expansion of the centralized water supply. The selection of the appropriate method should be based on criteria such as effectiveness, cost efficiency, the occurrence of specific types of pollution (e.g. chemical pollutants, salinity, turbidity), workload and user preferences. Organizations nowadays rely on a range of different water treatment methods in projects for decentralized water treatment, including treatment with chlorine, the use of water filters and the boiling of water in addition to the SODIS process.

Research and Development

The SODIS method was developed by Professor Aftim Acra at the American University of Beirut in 1980 and tested for years in Switzerland by Eawag (the water research institute of the ETH Domain ).

Research on the effectiveness of SODIS, and in particular clinical studies on the effectiveness of the method, is also being carried out at the Royal College of Surgeons in Ireland (Ronan Conroy, Kevin McGuigan , T Michael Elmore-Meegan ).

The long-standing head of the SODIS project at Eawag, Martin Wegelin , was awarded the Swiss Red Cross Prize for Humanitarian Achievements in 2006.

Elsa Sanchez , director of the Fundación Sodis , received the United Nations' "Water best Practices" award in 2012 for her work to spread the Sodis method in four districts in the department of Cochabamba in Bolivia .

Impact on the health of water users

The effectiveness of SODIS in inactivating diarrhea-causing bacteria and viruses has been shown in many studies. Studies on the reduction of diarrheal diseases through the use of SODIS show a reducing effect of 30–80%. The transmission of diarrheal diseases can also take place via other channels in addition to drinking water (food, hands) and depends heavily on the sanitary facilities and general hygiene.

criticism

In a three-year study by the Swiss Tropical Institute , the effectiveness of SODIS in Bolivia could not be statistically proven. The researchers attribute this to the poor and inconsistent use of SODIS. The study was published in PLoS Medicine .

Critical Factors

The effectiveness of SODIS depends crucially on the exposure time. If the water is not exposed to sunlight for long enough, consumption - as with untreated water - can lead to illness and diarrhea. The effectiveness of SODIS is also limited in the case of high turbidity. If the turbidity exceeds 30  NTU , the water should be filtered before using SODIS. In developing countries, the availability of PET bottles is a critical factor for the use of SODIS.

The following factors should also be considered:

  • Bottle material: Certain types of glass (window glass) and PVC absorb UV-A light and are therefore not suitable for SODIS. Commercially available bottles made of PET or glass are recommended. However, the handling of PET bottles is much more pleasant.
  • Lifetime of PET bottles: The efficiency of SODIS also depends on the condition of the PET bottle. Badly scratched bottles (e.g. by cleaning with sand) have a reduced permeability for UV-A light and should be replaced.
  • Shape of the container: The intensity of the UV-A radiation decreases sharply with the depth of penetration into the water. At a depth of 10 cm (with a cloudiness of 26 NTU) the intensity of the UV-A radiation is still 50%. Commercially available PET bottles (0.5–2 liters) are best suited for SODIS.
  • Oxygen : The presence of oxygen in the water is desirable in the SODIS process due to the formation of reactive radicals from UV-A radiation. Oxygen also has a positive effect on the taste of the water; in contrast to boiled water, SODIS water saturated with oxygen tastes fresh. Oxygen saturation can be achieved by shaking the 3/4 full bottles prior to exposure to sunlight. Water from rivers, wells or water pipes usually contains enough oxygen and does not need to be aerated.
  • Release of Chemicals from Bottle Material: The possibility of chemical release from PET bottles into water is sometimes portrayed as a potential health risk. The danger from antimony (a catalyst in PET polymerisation) is, however, considered to be rather low. Current studies show that the critical factors for the increased diffusion of antimony from PET bottles are long storage and increased water temperature. The Eawag (Swiss Federal Institute for Aquatic Science and Technology) assumes that “the storage of 6 hours and the temperature development of well below 85 ° C did not exceed the 6 ppb from the study by Westerhoff et al. will cause. " This estimate is based on the experience that the maximum achievable temperature is not above 60 ° C when uncovered and a maximum of SODIS method beyond 65 ° C with covered.
  • The plasticizers ( adipates and phthalates ) also found in some studies do not come from the PET itself and can only get into the water or the PET itself through cross-contamination . New studies find concentrations of plasticizers in the water from PET bottles well below the WHO limit values.

Worldwide application

The SODIS process has been used and tested in over 30 countries since 2001. In 2011, a worldwide cooperation project between EAWAG and Helvetas Swiss Intercooperation led to the widespread use of the SODIS process, as part of which water treatment projects were supported and carried out in 26 countries. a. in Ethiopia , Bhutan , Bolivia , Burkina Faso , Ecuador , El Salvador , Ghana , Guatemala , Guinea , Honduras , India , Indonesia , Cambodia , Cameroon , Kenya , Congo , Laos , Malawi , Mozambique , Nepal , Nicaragua , Pakistan , Peru , Philippines , Zambia , Senegal , Sierra Leone , Zimbabwe , Sri Lanka , Tanzania , Togo , Uganda , Uzbekistan and Vietnam and has already reached over two million people. It was shown that water contaminated with causers of diarrheal diseases was safe to drink after treatment. In the test areas, diarrhea, cholera, salmonella and similar diseases have decreased significantly.

SODIS projects are financed by the SOLAQUA Foundation , Fundación Sodis , Aktion Sodis, Helvetas Swiss Intercooperation , various Lions clubs , Rotary clubs, Migros and the Michel Comte Water Foundation .

Individual evidence

  1. ↑ Solar water disinfection
  2. ↑ SODIS: This is how it works
  3. ↑ International Decade for Action 'Water for Life' 2005-2015. Water for Life Voices: Voices from the field: case studies, Elsa Sanchez. Retrieved May 28, 2019 .
  4. ↑ Aftim Acra, Yester Karahagopian, Zeina Raffoul, and Rashid Dajani (1980). Disinfection of Oral Rehydration Solutions by Sunlight. The Lancet , Vol. 316 (No. 8206), pp. 1257-1258.
  5. ↑ Report on NZZ Online
  6. ↑ 'Water for Life' UN-Water Best Practices Award. 2012 edition: Ceremony. Retrieved May 31, 2019 .
  7. ↑ Conroy RM, Meegan ME, Joyce T., McGuigan K., Barnes J. (1996), Solar disinfection of drinking water and diarrhea in Maasai children: a controlled field trial , In: The Lancet , Vol. 348
  8. ↑ Conroy RM, Meegan ME, Joyce T., McGuigan K., Barnes J. (1999), Solar disinfection of water reduces diarrhoeal disease, an update , In: Arch Dis Child , Vol. 81.
  9. ^ Conroy RM, Meegan ME, Joyce TM, McGuigan KG, Barnes J. (2001) Use of solar disinfection protects children under 6 years from cholera . In: Arch Dis Child ; 85: 293-295
  10. ↑ Rose A. et al. (2006). Solar disinfection of water for diarrheal prevention in Southern India . In: Arch Dis Child , 91 (2): 139-141]
  11. ↑ Hobbins M. (2003). The SODIS Health Impact Study, Ph.D. Thesis, Swiss Tropical Institute Basel
  12. ↑ A flop from plastic. NZZ am Sonntag , accessed on August 21, 2009 .
  13. ^ Solar Drinking Water Disinfection (SODIS) to Reduce Childhood Diarrhea in Rural Bolivia: A Cluster-Randomized, Controlled Trial. PloS Medicine, accessed August 21, 2009 .
  14. ↑ SODIS Fact Sheet: Materials: Plastic versus Glass Bottles , accessed on February 16, 2015.
  15. ↑ Westerhoff et al .: Antimony leaching from polyethylene terephthalate (PET) plastic used for bottled drinking water , Water Research , Elsevier, 42 (2008), page 551 ff.
  16. ↑ Montuori, P., Jover, E., Morgantini, M., Bayona, JM and Triassi, M. (2007). HTUAssessing human exposure to phthalic acid and phthalate esters from mineral water stored in polyethylene terephthalate and glass bottlesUTH. Food Additives & Contaminants 25 (4), 511 - 518
  17. ↑ SODIS: ABOUT US. Retrieved May 28, 2019 .

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