Treatment of wastewater by TiO2 and photo-Fenton
Many industrial activities had failed to carry out adequate treatment of wastewater due to a shortage of available on-site systems. As a result of the IPPC Directive, suitable cost-efficient technologies became highly sought after. The CADOX project investigated both the photo-Fenton and titanium dioxide (TiO2) photocatalytic treatments for wastewater heavily contaminated with non-biodegradable chlorinated solvents (NBCS). Both systems aroused interest because they used sunlight to generate hydroxyl radicals with a semiconductor which absorbs UV radiation when immersed in water. It was shown that both systems were feasible for treating water contaminated with NBCS. However, if the process was to be carried out on a large scale it would not be possible to make the photoreactor airtight. Therefore, anaerobic conditions were strictly applied during TiO2 treatment to prevent NBCS being released to the atmosphere. The photo-Fenton method was considered more appropriate for large-scale operations. Photo-Fenton uses Fenton's reagent which comprises hydrogen peroxide and an iron catalyst. Great care was taken to ensure that the reactor operated at the correct temperature, as this affected the production of NBCS and reaction rate. The initial concentration of hydrogen peroxide was also a key factor in controlling NBCS photocatalytic treatment.
