Solar system for water purification

Slide 1: 

USE OF SOLAR ENERGY IN DISINFECTION OF DRINKING WATER Mr. Santosh Jathar (Pune, Maharashtra, India) santoshnjathar@yahoo.co.in

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The World Health Organization estimates that more than one billion people lack access to safe drinking water, resulting in millions of deaths each year from water-related diseases such as diarrhoea “The mission of Safe Water Systems is to significantly improve the health and quality of life for millions of people worldwide.”

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Sunlight is used to disinfect water in plastic bottles

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Basic Question About Solar Water disinfection System (SODIS) What health benefits can be directly associated with using solar disinfected drinking water in developing countries? What factors influence people and communities to decide to adopt or reject SODIS in preference to some other household water treatment technology such as boiling, chlorination, filtration? Can the basic solar disinfection technique be improved with a range of simple and cost-effective enhancement technologies? Are there any important waterborne diseases that are not susceptible to SODIS?

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Figure 6.2 EFFECT OF TEMP.

Temperature : 

Temperature Figure 6.1

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Important Factors. Location (Position) of Solar Unit:- The unit should be located at such a place where maximum time the direct sunlight will be available. Turbidity of Water :- The turbidity of water should be low. If turbidity of water is high then disinfection could not be possible. Availability of Sunlight:- At day time maximum sunlight should be available. Cloudy interval direct affects on disinfection process, in that time organisms recovers themselves.

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Some Scientific Facts Sunlight exposure is considered to be the most important cause of “Natural Disinfection" in surface water environments. The Solar Water heating was determined to be a superior disinfectant of water based on its ability to inactivate more than 99.999% of fecal indicator bacteria The UV-B portion of the solar spectrum is the most bactericidal, causing direct (photo- biological) DNA damage. In the present experimental study, the effect of solar radiation on the elimination of bacteria in water, especially in surface water, was studied. The influence of depth and UV-B transmittance of water was determined. Comparing Escherichia coli, Enterococcus faceless, Pseudomonas aeruginosa and Staphylococcus aureus, Enterococcus faecalis proved to be the most resistant organism.

Some Scientific Facts : 

Some Scientific Facts Pseudomonas aeruginosa was shown to be the most sensitive indicator bacterium among the tested microorganisms. Results show a significant correlation between radiation intensity and reduction rates. Best elimination of microorganisms occurs on the water surface; with increasing water depth, there is less UV radiation to inactivate bacteria. High turbidity substantially reduces UV-B transmittance in water causing decreased elimination efficiency. The results of the present study show that sunlight, given an appropriate intensity and good water transparency is suitable to inactivate fecal indicator bacteria within a few hours in surface waters and therefore also in bathing waters.

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1 Water supply tank; 2 Solar water disinfection reactor; 3 Temp. regulation valve; 4 Solar heater; 5 Heat exchanger; 6 Storage tank; Schematic Diagram of the Modified Solar Water Disinfection Reactor

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Result of Experiments The results also indicate that the exposure time needed to reach 99.99% reduction depends on the irradiance of UV radiation and the temperature. The time to obtain this reduction varied between one hour at high UV & temp. irradiances, very low turbidity and high temp. to seven hrs at low UV radiation The average exposure time needed to reach 99.99% reduction at average conditions encountered during testing was six hours. This exposure time decreased rapidly with reduction in the turbidity level and elevation of water temperature. The results from this study indicate that temperature affects the degree of water disinfection by natural UV radiation. As the temperature of the water increased the time needed to obtain maximum bacterial inactivation is reduced.

Merits of Technique : 

Merits of Technique This Technique is Simple & Easy to Apply. This Technique is economical. No dangerous, Toxic or Hazardous by-product are produced.

De-Merits of Technique : 

De-Merits of Technique X The method requires strong sunlight and can only treat limited volumes of water. X If the bacteria are not completely inactivated by the sunlight, the dark periods give them time to recover from the radiation damage, making them more resistant when reilluminated. X It is found that Organisms inactivation depends on the total dose of sunlight rather than the light's intensity. (Cont.)

De-Merits of Technique : 

De-Merits of Technique X Turbidity of water decreases the penetration of solar radiation into water & protects micro-organisms from being Irradiated. SODIS is reduced in Turbid water. X Solar radiation however is unevenly distributed &varies in intensity from one geographical location to another depending on latitude, season & time of the day. . (Cont.)

De-Merits of Technique : 

De-Merits of Technique X In many places the solar units are located on roof so it requires electricity. In all Rural areas where electricity is not easily available or absent(Load shading) will not be able to use the unit. X After disinfection of water proper storage is important rather than it increases the chances of post contamination. (In chlorination the residual chlorine reduces the chances of post contamination.) . (Cont.)

De-Merits of Technique : 

De-Merits of Technique X After heating the water, the taste of water is changed (tasteless).Also the oxygen content of water is reduced.