Photochemical Oxidation of Complex Organic Contaminants in Water

Various complex organic pollutants resist conventional wastewater treatments. Thus, it is not possible to assure that water and wastewater treatment plants achieve the adequate removal of such organic contaminants, increasing the risk for human health and ecosystems. In this work, we have studied the capacity of the photochemical treatment for the degradation of complex organic pollutants in water. Selected dyes and pesticides were tested for their possible degradation by UV-C light. All the tested compounds were decomposed by the UV-C. The dyes malachite green and indigo carmine were completely degraded in 17 h whereas the tested pesticides (thiamethoxam, pyriproxifen, difenoconazol, and phosmet) were only partially degraded in 8 h. A detailed study with thiamethoxam proved that the UV-C light was able to decompose the molecule in just 15–30 min, and then the degradation products were oxidized with the UV light but at a much slower rate. The chemical oxygen demand showed no or minor removal of organic matter in water, proving that the photochemical oxidation was not able to mineralize the organic compounds.