BIOL 448B Grant Proposal:
Evaluating the potential of Solar Water Disinfection (SODIS)
as a method of preventing diarrheal infections in the developing
Due Date: March 17, 2008
The goal of this grant proposal is to investigate the potential of Solar Water Disinfection (SODIS) as
a way of preventing tropical diarrheal infections such as those caused by enteric bacterial pathogens
such as Escherichia coli, Vibrio cholerae, Salmonella typhimurium and Shigella dysenteriae, the
causative agent of dysentery (Berney et al. 2006, Kehoe et al. 2004). This method is cheap and easy
to disseminate in developing world countries where these diseases are prevalent. Preliminary research
has shown that this method of disinfection is promising as it uses solar UV-A radiation and
temperature to inactivate pathogens causing diarrhea as opposed to harmful chemicals or complicated
and expensive technological solutions.
At least one third of the population in developing countries has no access to safe and reliable drinking
water supplies (Wegelin et al. 1994). The lack of adequate water supply and sanitation facilities
causes a serious health hazard and exposes many to the risk of water-borne diseases. There are about
4 billion cases of diarrhea each year, out of which 2.5 million cases end in death (Wegelin et al.
1994). Every day about 6000 children die of dehydration due to diarrhea. It is estimated that it would
cost over $150 billion in public funds for full water supply coverage in developing countries
(Wegelin et al. 1994). Several low cost household methods of water disinfection have been proposed
including boiling of water, disinfection with chlorine and filtration. However these methods,
respectively, require energy (often requiring the use of firewood), are dosage dependent and produce
an undesirable taste, and are unaffordable (Wegelin et al. 1994). These problems call for the
development and expansion of alternative treatment techniques that are inexpensive, effective,
practical, and simple enough to be applied by individuals or households.
FIG 1: World map showing the disproportionate distribution of cholera prevalence in
the tropical regions, predominantly in the developing world.
Solar water disinfection (SODIS) is considered to be such an alternative. The treatment
process is a simple technology using the temperature and UV-A exposure of solar radiation to
inactivate and destroy pathogenic bacteria present in water in a low cost and sustainable manner.
Recent studies have also shown that the inactivation of fecal bacteria in sunlight is strongly
dependent upon the formation of free radicals derived from dissolved oxygen via solar photo-
oxidation (Reed et al. 2000). This indicates that vigorous mixing of the water in transparent plastic
containers may also play an important role in disinfection (Reed et al. 2000). This method may be
used to treat approximately 10-15 litres per family per day (Wegelin et al. 1994). Solar water
disinfection is not without limitations however. Solar radiation is dependent on the geographic
location and climatic conditions, and undergoes diurnal and annual variations. We intend to use this
study to investigate these differences and maximize the potential implementation of this technology.
FIG 2: World map showing the global distribution of solar radiation as measured in
kWh/m2. Areas with a 4 kWh/m2 in total radiation would be appropriate areas to
investigate SODIS (taking into account factors like weather and geographical
Previous research has shown that solar disinfection of water is an inexpensive, effective, and
acceptable method of increasing water safety in a resource limited environment, and can significantly
decrease diarrheal morbidity in children. However, most of this research is based on a small sampling
of particular cohorts. While the success of this technology has been investigated in a number of
diverse regions around the world, no one study has proposed to simultaneously monitor a global set
of cohorts. There are several requisite specifications that need to be met for this technology to be
successful which will determine where these cohorts will be set up. Simultaneously. SODIS requires
a specific amount of exposure to radiation and high temperature from the sun (Sommer et al. 1997,
Wegelin et al. 1994). The container needs to be exposed to the sun for 6 hours if the sky is bright or
up to 50% cloudy (Wegelin et al. 1994). Alternatively, if a water temperature of at least 50°C is
reached, an exposure time of 1 hour is sufficient. If the sky is 100% cloudy then the container needs
to be exposed to the sun for two consecutive days (Sommer et al. 1997). During days of continuous
rainfall, such as the monsoon period, SODIS does not perform satisfactorily and rainwater harvesting
is recommended during these days. The most favourable region for SODIS lies between latitudes 15°
North or South (N/S) and 35° N/S (Conroy et al. 1999, Hobbins 2003). These semi-arid regions are
characterized by high solar radiation and limited cloud coverage and rainfall (3000 hours sunshine
per year). The second most favourable region lies between the equator and latitude 15° N/S where the
scattered radiation in this region is quite high (2500 hours sunshine per year)(Conroy et al. 2006).
FIG 3 A/B: Photographs of a typical community SODIS setup in a variety of diverse
communities Uzbekistan (left) and Kenya (right).
UV-A light produces reactive oxygen species, which can damage nucleic acids, proteins or
other life-supporting cell structures (Berney et al. 2006). It was also found that broad-spectrum UV-A
light blocks the electron transport chain, inactivates transport systems, interferes with metabolic
energy production and can cause a general increase in permeability of the membrane (Berney et al.
2006). Furthermore, direct inhibition of certain enzymes (e.g. catalase) has also been observed
(Berney et al. 2006).
It is also important to consider the initial turbidity of the water that you are attempting to
disinfect. Previous studies have shown that suspended particles in the water reduce the penetration of
solar radiation into the water and protect microorganisms from being irradiated. According to this
research, SODIS requires relatively clear water with a turbidity of less than 30 NTU. Some
researchers have proposed using the visibility of a simple logo at the bottom of the container as an
easy way of determining 30 NTU of turbidity (Reed et al. 2000). In water with higher turbidity than
30 NTU pathogens will have to be inactivated by the temperature rather than radiation (>50°C for at
least an hour) or the water has to be filtered before being exposed to the sun (Reed et al. 2000).
Various types of transparent plastic materials are good transmitters of light in the UV and
visible range of the solar spectrum. Plastic bottles made from PET (PolyEthylene Terephtalate) are
preferred because they contain less UV-stabilizers than PVC (PolyVinylChloride) bottles. Ageing of
plastic bottles (due to mechanical scratches and due to photoproducts) leads to a reduction of UV
transmittance that will reduce the efficiency of SODIS. Heavily scratched or old, blind bottles should
be replaced. Glass bottles can be used for SODIS (although window glass cannot be used to create
shallow large containers since it does not transmit UV-radiation adequately).
FIG 4: An example of an educational pamphlet (this one is in Indonesian) that would
accompany the bottles for community distribution.
We will set up approximately 10-20 cohorts in different parts of the world including Latin America,
Asia, Africa and the Middle East in countries within latitudes specified by the latitudes in the
‘Background section’ (Conroy et al. 1999). We will identify these cohorts (and the control regions)
based on collaborations with NGOs that are already working in the regions of interest. This will
greatly facilitate data collection and monitoring. We have chosen to perform this study in many
multiple regions around the world because different areas have different water-borne pathogens and
different amounts of UV-A exposure and temperature. In order to monitor the effects of the usage of
SODIS and find statistically significant results, we will find appropriate control regions (close
geographically, similar access to water and medical care, similar UV-A exposure and temperature)
where we will monitor the epidemiology of water-borne illnesses over the same time frame (Rose et
al. 2006). Water samples will be taken using sterile containers and either tested immediately for
physiochemical characteristics (turbidity, temperature and dissolved oxygen) or transported in
darkness, within one hour of sampling for analysis of fecal bacteria and solar experimentation at local
laboratories (Reed et al. 2000). These samples will also be tested for the presence of chemical
contaminants that may have leached from the water bottles while they were exposed to solar
Obtaining more results in this area will further aid in assuring the complete safety of this
technology in producing water that is safe for human consumption. This is an important aspect of the
project because, while conclusive results have been shown in terms of bacterial inactivation and
disease prevention, the lack of extensive research in the area of chemical leaching is a barrier to
extensive dissemination of this technology (Kehoe et al. 2001). If it is deemed at any point in the
experimental timeline that there is the potential for dangerous levels of chemical contaminants (i.e.
potential carcinogens), alternate container materials will be investigated such as glass or other types
of plastic (Kehoe et al. 2001). Other factors that have been identified as barriers to the extensive
global implementation of SODIS in developing countries are a lack of trust in the results that bacteria
can be killed just by exposure, the length of time required to adequately disinfect the water, and the
water’s taste and smell (particularly for those using plastic bags) (Martín-Domíngueza et al. 2005).
We hope to address these concerns through the extensive nature of our study and will partner with
other groups and professions involved in similar endeavours (ex. work with engineers to develop
solar panels to expedite the process, provide rainwater barrels for countries where they experience
monsoons during part of the year, or work with chemists who are developing safer and less odourous
containers) (Kehoe et al. 2001).
Our hypothesis is that SODIS will provide a safe, cheap and effective way to prevent bacterial
diarrheal infections in the developing world and in doing so will reduce morbidity and mortality
related to these infections in the experimental areas (compared to control areas with no SODIS
protocol in place).In order to test this hypothesis we will collect statistics from local hospitals or
clinics regarding the prevalence of common bacterial diarrheal infections. There will be staff
monitoring and local reporting in villages without access to medical care (Martín-Domíngueza et al.
2005, Rose et al. 2006)). Additionally, periodic testing of water for viability of known water-borne
pathogens and testing of water for presence of chemicals leached from plastic water bottles.
By looking at a number of different cohorts in different areas of the world, we will be able to
gain a better understanding of the universality and generalizability of the SODIS results (i.e. we
expect a decrease in morbidity and mortality resulting from diarrheal complications in groups using
SODIS vs. the control groups). This research will also investigate potential long term effects of using
this disinfection method as it will measure the amount of chemicals leached from the plastic water
bottles after varying lengths of time. By taking samples of the water at different times and in different
areas (i.e. Southeast Asia vs. South America), this study will help to elucidate which microorganisms
are destroyed by SODIS and why this method may work better in some areas compared to others.
In a world where at least one third of the population in developing countries has no access to safe and
reliable drinking water supplies, it is clear that there is great need for simple and creative solutions to
this problem (Wegelin et al. 1994). While approximately 6000 children die of dehydration due to
diarrhea, we cannot wait for improvements in infrastructure to address this issue (Wegelin et al.1994,
Conroy et al. 1996). SODIS has the potential to be an immediate solution for a desperately pressing
problem in places where improving healthcare and sanitation infrastructure is not an feasible option
(at least in the short term) (Wegelin et al. 1994). The potential to improve life expectancy, quality of
life and productivity for millions of the world’s most impoverished is staggering. Diarrheal infections
have numerous implications beyond just dehydration, including but not limited to HIV/AIDS
medication absorption, malnutrition including micronutrient deficiencies that can lead to
immunocompromisation, blindness, anemia and developmental disabilities. Diarrheal disease plays a
critical role in the vicious cycle of poverty and disease and for a relatively small investment in plastic
bottles and education campaigns; SODIS could have a huge impact. This study will help us gain a
greater understanding of this potential and will also address some important questions of safety. With
this extensive survey of many different global communities, we will be able to influence policy and
establish connections allover the world to promote other types of community-based healthcare and
link them with other resources (Rose et al. 2006).
Berney, M., Weilenmann, H.-U., and Egli, T. 2007. Adaptiation to UVA radiation of E.coli growing
in continuous culture. Journal of Photochemistry and Photobiology B:Biology. 86:149-159.
Berney, M., Weilenmann, H.-U., Simonetti, A., and Egli, T. 2006. Efficacy of solar disinfection of
Escherichia coli, Shigella flexneri, Salmonella Typhimurium and Vibrio cholerae. Journal of Applied
Microbiology. 101: 828-836.
Conroy, R.M., Meegan, M.E., Joyce, T., McGuigan, K., and Barnes, J. 1999. Solar disinfection of
water reduces diarrhoeal disease: an update. Arch Dis Child. 81:337-338.
Conroy R.M., Meegan M.E., Joyce T.M., McGuigan K.G., and Barnes J. 2001. Use of solar
disinfection protects children under 6 years from cholera. Arch Dis Child, 85:293-295.
Dejung S., Wegelin M., Fuentes I., Almanza G., Jarro R., Navarro L., Arias G., Urquieta E., Torrico
A., Fenandez W., Iriarte M., Birrer Ch., Stahel W.A. 2007. Effect of solar water disinfection (SODIS)
on model microorganisms under improved and field SODIS conditions. Journal of Water Supply:
Research and Technology. AQUA . 56(4): 245–256.
Hobbins M. 2003. The SODIS Health Impact Study, Ph.D. Thesis, Swiss Tropical Institute Basel.
Kehoe, S.C., Barer, M.R., Devlin, L.O., and McGuigan, M.G. 2004. Batch process solar disinfection
is an efficient means of disinfecting drinking water contaminated with Shigella dysenteriae type 1.
Letters in Applied Microbiology. 38: 410-414.
Kehoe, S.C., Joyce, T.M., Ibrahim, P., Gillepsie, J.B., Shahar, R.A., and McGuigan, K.G. 2001.
Effect of agitation, turbidity, aluminum foil reflectors and container volume on the inactivation
efficiency of batch-process solar disinfectors. Water Research. 35(4): 1061-1065.
Martín-Domíngueza A., Alarcón-Herrerab T., Martín-Domínguezb I.R., González-Herrera A.2005.
Efficiency in the disinfection of water for human consumption in rural communities using solar
radiation. Solar Energy.78: 31-40.
Reed, R.H., Mani, S.K., and Meyer, V. 2000. Solar photo-oxidative disinfection of drinking water:
preliminary field observations. Letters in Applied Microbiology. 30:432-436.
Rose, A., Roy, S., Abraham, V., Holgren, G., George, K., et al. 2006. Solar disinfection of water for
diarrhoel prevention in southern India. Arch Dis Child. 91:139-141.
Sommer, B., Marino, A., Solarte, Y., Salas, M.L., Dierolf, C., et al. 1997. SODIS – an emerging
water treatment process. J Water SRT – Aqua. 46(3):127-137.
Wegelin, M., Canonica, S., Mechsner, K., Fleischmann, T., Pesaro, F., and Metzler, A. 1994. Solar
water disinfection: scope of the process and analysis of raditation experiments. J Water SRT –Aqua.