Solar technology to purify water

The sun is the motor of life on our planet, not only do plants get light energy and transform it into chemical energy, releasing oxygen in the process, also humans have been able to convert the sun’s energy into electric energy for domestic use and now also they use sunlight to induce chemical reactions in order to purify polluted water.

The Biobío Region has an average solar radiation of 1400-1700 kWh/m2 per year in winter and 1700-1900 kWh/m2 per year in summer. This flow is at least 2 times higher in UV radiation than that used in the Solar Platform of Almeria (PSA in Spanish) in Spain, the largest and most important solar platform in the European Community. With these data, UDT promoted two projects that are currently under development, “Solar photoreactor for the treatment of polluted waters in rural areas and their use for human consumption” of the Energy Access Fund (FAE in Spanish), Ministry of Energy, and the “Solar photoreactor for treatment of water polluted with heavy metals and dangerous anions” of Innova Chile CORFO.

Dr. Juan Matos, researcher in the Biomaterials Department of UDT, who heads these initiatives, explains that for both projects solar photocatalysts of the CPC type were developed, consisting of anodized aluminum panels and borosilicate tubes, through which water and photoactive materials circulate. These photoreactors are connected to a water tank and the water recirculates through a diaphragm pump. These devices are installed within UDT facilities connected to the tip system; decontaminated water will be used for irrigation of green areas.

“One of the photoreactors is used to perform oxidation of emerging contaminating molecules and pathogenic microorganisms, generating ultra pure water and CO2. The other is designed to reduce toxic metals such as arsenic, chromium, cadmium, mercury, etc., where precious metals such as gold, platinum and silver can be recovered. Both photoreactors use 2 different types of biochars containing titanium, produced at UDT, in order to perform oxidation or reduction reactions, according to the purposes”, says the researcher.

This technology is feasible to be transferred to the industry and reach the homes of Chilean people. “We have calculated that to treat 65,000 liters of water, we need 100 square meters of photoreactors. That amount of water corresponds to the average consumption of a 10-story building with 4 apartments per floor and the reactors would occupy about a quarter of the roof area of the building that is normally an unused area”, explains the scientist. In addition, the operating costs are practically the same as those of the conventional plants by reverse osmosis in the order of $0.8 the liter of treated water.

The technologies currently used in water treatment plants – activated sludge, filtration and reverse osmosis – do not remove pollutants, but rather store them in filters that need to be replaced periodically, and many also end up in rivers, streams or accumulated in groundwater. Photocatalysis is the most efficient technique known to date, to eliminate emerging molecules and microorganisms dangerous to health.