Electrophoretically deposited TiO2 layers for efficient photocatalytic degradation of antibiotic mixture in greywater

Efficient removal of pharmaceuticals from greywater is crucial to enable its application for non-potable use. TiO2 photocatalysis is a promising environmentally friendly way of streamlining their complete degradation. However, dispersed TiO2 nanopowders are unsuitable for greywater treatment procedures because they require separation and may aggregate, thereby losing photocatalytic activity. Thus, TiO2 nanopowders (anatase 5 and 100 nm, AEROXIDE (R) P 25) were immobilized into layers by quantitative electrophoretic deposition. The layer ability to degrade the commonly used antibiotics ampicillin and sulfathiazole in deionized water was monitored using HPLC-PDA analysis and compared with that of the respective nanopowders. All layers attained total conversion of the initial antibiotics (limit of detection 50-100 mu g L-1) with the highest degradation rate constant corresponding to 66 x 10(-4) min(-1) for AEROXIDE (R) P25 layer. To evaluate the efficiency of the prepared layers under more realistic conditions, collected greywater was treated in a membrane bioreactor, spiked with an equimolar antibiotic mixture, and subjected to photocatalysis. The overall reaction rate constants were calculated as 54, 15 and 75 x 10(-4) min(-1) for 5 and 100 nm anatase and AEROXIDE (R) P25 layers, respectively; the best-performing layer achieved complete removal and 68 % total mineralization of the antibiotic mixture in greywater within 7 and 24 h, respectively. For this layer, the developed regeneration method recovered min. 94 % of the original photocatalytic activity, enabling its reusability. These results suggest that our presented deposition method provides layers capable of degrading antibiotic mixtures in greywater effectively and is suitable for upscaling due to its low cost and simplicity.