Effect of photocatalyst type on oxidation of ersatz water using a photocatalytic reactor with slurry separation

Previous work demonstrated that the Photo-Cat® developed by Purifics is capable of reducing the total organic carbon (TOC) concentration of 51 mg/L to below 0.5 ppm using Degussa P25 titanium dioxide (TiO₂) as a photocatalyst. The work also showed that ammonium bicarbonate had a detrimental effect on the rate of photocatalytic oxidation, but did not prevent the system from reaching the potable water specification. Nanometer sized Degussa P25 is very popular and quite frequently used as a benchmark of performance in literature, but it may not be the most effective for oxidizing all waste streams. It is critical that each component of the water recovery system be optimized for power consumption and the effectiveness of the photocatalyst plays an important role in accomplishing this. The difficulty of separating the nanometer sized particles has lead many researchers including the authors to experiment with immobilizing the TiO₂ in a high surface area substrate like mesoporous silica pellets. These pellets have a specific surface area of approximately 400 m²/g compared to 50 m²/g for Degussa P25. The present work has shown that substituting ground mesoporous silica impregnated with TiO₂ for Degussa P25 results in a doubling of the reaction rate for the air evaporation system (AES) ersatz, whereas there is only a 24% increase for the biological water processor effluent (BWP). Interference by dextran, a polymer has been proposed as a possible mechanism for the diminished photocatalytic activity.