Immobilisation of TiO₂ for combined photocatalytic-biological azo dye degradation

The biodegradability of the azo dye Remazol Red RR (100 mg/l) was evaluated using unadapted activated sludge and the experiment confirmed the recalcitrance of the dye. Using a combination of photocatalysis and an aerobic biological step, the biodegradability was improved significantly and complete removal of both colour and COD were achieved. Furthermore, TiO₂ was successfully immobilised on borosilicate glass slides by calcination, which facilitates reuse of the catalyst. The catalytic activity of the immobilised TiO₂ was close to that of suspended TiO₂. A reduced activity was however observed when the TiO₂ slides were used repeatedly. When comparing NaOH, calcination and UV irradiation for regeneration of the TiO₂ slides, immersion in NaOH was shown to be the most efficient method.