Comparison of UV/TiO2 and UV/H2O2 processes in an annular photoreactor for removal of micropollutants: Influence of water parameters on metaldehyde removal, quantum yields and energy consumption

Advanced oxidation processes have proven their efficacy in the removal of micropollutants but the role of background constituents on the kinetics of degradation is not well understood. Investigation into the role of alkalinity and background organic matter as defined by three surrogate compounds – serine, leucine and resorcinol – on the degradation of metaldehyde was conducted with a continuous flow photoreactor operated as either UV/TiO2 or UV/H2O2. Background organic compounds inhibited the process through scavenging such that reaction rates were on average reduced by 19%. Modelling the radiation field enabled the quantum yield to be determined indicating that metaldehyde contributed to 0.1% of the total quantum yield under realistic background organic matter concentrations. Examination of models in term of electrical energy per order suggested that ideal reactor width of 9 mm for TiO2 and 11.7 cm are required.

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► Whilst background organic matter and alkalinity act as OH scavengers during UV/H2O2, alkalinity inhibits the UV/TiO2 process due to TiO2 aggregation.
► UV/TiO2 is a much more effective process than UV/H2O2 at absorbing photons.
► However, greater quantum yields are observed in the UV/H2O2 process.
► The electrical energy consumption can be reduced by improving the rate of photon absorption in the reaction space.