Technical Notes

S DIS Technical Note # 14SODIS Use:Guidelines to Increase EfficiencyBACKGROUND INFORMATION SUMMARYTreatment efficiency can be increased by a sound application of SODIS. One important method is toenhance water heating through the use of half-blackened bottles and black zinc sheets as support of thebottlesIn the field, the process is not applied under strictlycontrolled conditions, the material and methods usedare often not optimal, the raw water pollution is generallymuch lower and the handling of the treated waterfrequently inadequate.Optimizing water heatingThe treatment efficiency can be increased by applyingsimple methods as listed below. Our method is to usehalf-blackened plastic bottles which achieve approx.5°C higher water temperature as compared tounpainted bottles (see Figure 1). Another method is toplace the plastic bottles on a black zinc sheet instead oflaying them on a floor. This arrangement will alsoincrease the temperature by approx. 5°C (see Figure 2).Both methods have the effect that the microorganismsare longer exposed to a period of increased temperatureby a faster heating up of the water. This willenhance the inactivation effects.Factors that reduce the efficiency• Turbid water• Bottles with low UV-A transmittance• Low air temperature• Cloudy sky• Bottle placed upright instead of horizontalMethods to enhance the efficency• Use raw water with low turbidity• Use half-side black painted plastic bottles• Place container to a place which is exposed to thesun the full day• Place the container on a corrugated zinc sheet• Expose containers for two consecutive days oncloudy days• Replace old and scratched bottlesWater Temperature (°C)10:0010:1510:3010:4511:0011:1511:3011:4512:0012:1512:3012:4513:0013:1513:3013:4514:0014:1514:3014:4515:00Figure 1. Comparison of water temperature in half-blackenedSODIS bottles and clear bottles (cement floor, no black zincsheet, no wind protection).Water Temperature (°C)555045403530255550454035302511.00painted bottleunpainted bottleTimerangepaintedbottlerangeunpaintedbottle11.1511.3011.4512.0012.1512.3012.4513.0013.1513.3013.4514.0014.1514.3014.4515.00Weather Condition(% cloudiness)TimePainted BottleUnpainted Bottle100%90%80%70%60%50%40%30%20%10%0%Weather Condition(% cloudiness)Figure 2. Water temperature in painted and unpainted SODISbottles placed on a black zinc sheet. The bars illustrate thecloudiness.REFERENCESSODIS News No. 3, August 1998. [R13]Yayasan Dian Desa (1997). Solar Disinfection System - FieldStudy. Final Report. [FInd3]Ueberlandstr. 133, CH-8600 Duebendorf / Switzerland http://www.sodis.chPhone +41-1-823 50 19 Fax: +41-1-823 53 99 http://www.sandec.ch