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Water Safety Conference 2010. M.T. Amin, H. Kim, M.Y. Han. Enhancing SODIS for safe drinking water supplies from collected rainwater. Contents. 1. Introduction. 2. Materials and Methods. 3. Results and Discussion. 4. Conclusions. Introduction. Background. < Tailand >. < Uganda >.

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Water Safety

Conference 2010

M.T. Amin, H. Kim, M.Y. Han

Enhancing SODIS for safe drinking water supplies from collected rainwater





Materials and Methods


Results and Discussion




< Tailand >

< Uganda >

  • Lots of countries have water shortage problems over the world

  • Rainwater harvesting (RWH) can be alternative water resource to these countries

  • Because RWH system is simple to install and manage, this system has been spread to water shortage areas.








drain pipe


What is rainwater harvesting system?

Rainwater as drinking water?

  • Rainwater can’t be used as drinking water for the possibility of microbial contamination.

  • At least one-third of the population in developing countries has no access to safe drinking water

Simple disinfection method can make and supplysafe drinking water by rainwater

Solar Disinfection (SODIS)

  • Inactivation of microorganisms by UV-A-radiation and thermal treatment

  • Suited for providing safe drinking water in rural and semi-urban communities in developing countries

  • Promoted by the World Health Organization (WHO)

Limitation of SODIS

  • Few scientific and engineering data for rainwater disinfection

  • Only strong sunlight radiation for about 6~8 h daily is adequate for the complete disinfection

SOCO-DIS (Solar Collector Disinfection) system

  • Improving SODIS to achieve more concentrated sunlight radiation and temperature effects


  • To compare the efficiency of SOCO-DIS with that of SODIS

  • To optimize the developed SOCO-DIS system by investigating the effects of a variety of factors.- base surface- box angles- pH- turbidity

Sample collection site

* RWH : Rainwater harvesting system

The quality of rainwater samples

Main target

  • Samples were always collected from the same outlet point, about 1.35 m from the base of the tank

  • The reason for the different initial values of all the parameters is the effect of the season and residential time in the tank

  • These are used as the standard initial values for the rainwater samples in this study.

Weather conditions

  • Weather conditions are categorized into three different types, depending upon low, medium and high sunlight radiations.

  • The temperature difference is about 2~4 0C, with the great temperature rise in the SOCO-DIS system.

  • Effective temperature about 50OC observed only under strong weather conditions in SOCO-DIS

Outline of experiment

0.25 m


0.75 m


0.75*0.25 m




0.35 m

  • Consist of five wooden components covered by aluminum

  • A maximum theoretical concentration of three times the solar radiation is achieved

  • 1.7 L rainwater sample was contained to 2 L PET bottle.

  • Aluminum foil is placed under the PET bottle for reflection



Reflective PET bottle (SODIS)

SOCO-DIS system

TC, FC, E-Coli, HPC was observed

Results and Discussion

1- The effects of weather condition

2- The effects of base surfaces

3- The effects of box angles

4- The effects of initial pH

5- The effects of initial turbidity

The effects of weather condition

  • Disinfection exhibited three stages of treatment depending upon the sunlight intensity with middle stage being critical.

  • Synergistic effects of radiations and temp. are evident under strong weather conditions where rainwater is disinfected completely.



200 500 850

200 500 850

The effects of weather condition

  • In case of SODIS, no parameter met the potable guideline values

  • SOCO-DIS system proved ineffective under weak weather conditions mostly because the synergistic effects of radiations and temperatures are absent

  • The difference of disinfection efficiency of SOCO-DIS system is about 20-30% with that of simple SODIS mostly because of the enhanced effects of concentrated radiations

The effects of base surfaces

  • Disinfection efficiency of SOCO-DIS system with different base surfaces including reflective, absorptive, and transmissive (Trans.) is evaluated and compared under moderate sunlight conditions.

  • The thermal effects have not significantly contributed by comparing the results of absorptive base surface with that of reflective base surface where disinfection efficiency is more.

  • With insignificant thermal or synergistic effects because of low temperature, it can be concluded that UV radiation effects are prominent under moderate sunlight conditions.

The effects of box angles

  • To improve the amount of radiation reaching the water, the solar box is kept an angle of 370 (Latitude of the location=mid-day position of sun) .

  • Solar box with continuous changing of direction with respect to the sun’s position is the best choice due to minimized shading effects of open wings of box, but it would require more labor work.

  • The best selection, thus, would be the inclined position of box for optimum disinfection efficiency.

The effects of initial pH

  • Rainwater with acidic pH offered best disinfection efficiency for SOCO-DIS system for all microbial parameters without any exception.

  • TC and HPC, which were not removed under standard sampling conditions of neutral pH, are also inactivated completely at low pH values.

  • Overall disinfection efficiency increased from 10 to 20% by decreasing pH values from basic to neutral and then acidic states, respectively.

The effects of initial turbidity

  • SODIS showed poor performance for all microbial parameters at higher turbidity and disinfection efficiency decreased by almost 10-20%.

  • Low turbidity sample show better results although this difference is insignificant up to may be 20NTU.

  • This could be due to the loss of UV due to scattering & absorption by particles


  • Disinfection efficiency of the SOCO-DIS is 20~30 % better than SODIS and it managed complete disinfection under strong and even moderate weather condition

  • Optimized SOCO-DIS design and operation conditions- Reflective base: 10~15 % better than absorptive and transmissive surface- Inclined position: 10% better than horizontal position- low pH: improving the efficiency from 10 to 20 %- low turbidity: decrease the efficiency by 10 to 15 %

Further study

Social acceptability of rainwater as drinking water

  • Even though there is excellent technology, it has no meaning without social acceptability.

  • Therefore, effort to change unwelcome attitude should be followed to use rainwater as drinking water.

Rainwater challenge

  • Water tasting event was held with tap water, bottled water and treated rainwater

  • People vote there sticker to the most acceptable water as drinking water

Tap water


Bottled water