Comparison of the effectiveness of photon-based oxidation processes in a pilot falling film photoreactor

Progress on the exploitation of photon-based oxidation processes for the treatment and purification of water and wastewater could be achieved by combining the most effective oxidation processes with optimal reactor designs. In this work, the effectiveness of six different photon-based processes on the oxidation of a model organic pollutant-salicylic acid-was studied in a pilot plant falling film photoreactor designed for optimal light absorption. The photon-based processes studied were UVA-photocatalysi- s, UVA-photocatalysis-peroxidation, UVC-photolysis, UVC-photolysis-peroxida- tion, UVC-photocatalysis-photolysis, and UVC-photocatalysis-photolysis-pero- xidation. The effects of major process variables on each of these processes were examined. The highest oxidation rates were obtained with concomitant photocatalysis, photolysis, and UV-peroxidation. The oxidation rates of salicylic acid obtained by this combined process were 1 order of magnitude higher than with UVA-photocatalysis alone, 2-fold higher than UVA-photocatalysis-peroxidation, and 3-fold higher than UVC-photolysis- -peroxidation. In addition, a high degree of mineralization of salicylic acid was obtained. An economic analysis shows the cost of treatment by this combined process to be much lower than that of other processes, making this process a suitable photon-based oxidation technology for further development and commercialization.