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.
Keywords: azo dyes, biodegradation, immobilisation, photocatalysis, regeneration, titanium dioxide