Solar Water Disinfection Could Kill Even More Germs with New High-Tech Coating

October 23rd, 2009 by Tina Casey

Solar water disinfection is an idea so simple, it hurts. Now a Georgia Tech scientist may be on to a new high-tech twist that could make this no-cost, zero emission ultraviolet (UV) water disinfection method even more quick and effective.

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Solar disinfection is a proven method of killing germs in drinking water by exposing it to direct sunlight in a clear plastic or glass bottle. Dr. Jaehong Kim of the Georgia Institute of Technology has just been awarded a $100,000 innovation grant by the Water Environment Research Foundation for his work in developing a new coating that could be applied to bottles to shorten the solar disinfection process and improve its effectiveness. Though not (yet) practical for large volumes of water, solar disinfection has proven to be a sustainable answer for people in remote locations or impoverished areas that lack the resources to disinfect their drinking water through other means.

Solar Disinfection and Upconversion Phosphers

Dr. Kim’s innovation is to adapt upconversion phosphers for use in coating the bottles used in solar disinfection. Upconversion phosphors are materials that absorb light near the infrared end of the scale and convert it into visible red, green, and blue light. The high brightness combined with the durability of the emitting material make upconversion phosphors a cost-effective candidate for commercial use, and they were originally developed for laser optics. Dr. Kim will be developing phosphors that could be used to create antibacterial surfaces.

Solar Disinfection and Sustainability

As applied to small volumes of water, it’s hard to beat solar disinfection. The only capital outlay is the cost of the bottles. The process requires no fuel and no chemicals. Just fill a bottle with water, park it in the sun for six hours and the germs are killed. Solar disinfection works on waterborne pathogens in three ways, including ultraviolet (UV) disinfection, a physical process in which the UV wavelength starts a photochemical reaction that targets the DNA of bacteria. The UV process works on Cryptosporidia, Giardia, and other parasites that can resist chemical treatment. Water suppliers are searching for reliable, non-chemical water treatments that are not subject to price spikes, shortages, and the vagaries of world commodities markets, so large-scale UV radiation has become a focus of attention. However, conventional UV disinfection is energy intensive (it requires UV lamps), and it is unavailable to many communities. Another alternative would be to boil the water, but many communities lack the fuel resources to depend on boiled water consistently.

Solar Disinfection and Magic Wands

SODIS, the international organization that promotes solar disinfection, points to numerous studies that prove the method’s effectiveness. It has also recently collected the endorsements of UNICEF, the Red Cross, and the World Health Organization. Though it almost sounds like magic, solar disinfection is not a miracle cure-all, and SODIS emphasizes the importance of thorough education and training, as well as the selection of water supplies that are appropriate for this kind of treatment. Like conventional ultraviolet disinfection, solar disinfection only works on water that is relatively free of suspended solids (low turbidity water). It effectively kills germs, but it does address chemical pollutants such as fertilizers. And, it must be used correctly and consistently in order to achieve the desired result, which is to relieve communities from waterborne diseases leading to diarrhea. Though concerns have been raised regarding PET plastic bottles in general, SODIS’s research has revealed no risk involved in the solar disinfection method due to its short storage times and low heat.

Image: marcelometal on flickr.com.









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