Decolourisation of industrial wastewaters of textile dyeing industry by photocatalysis

Abstract

The feasibility of photocatalytic decolourisation of real textile dyeing rinse wastewaters (RWWs) collected from the low salt cotton textile dyeing industry was studied, using two grades of titanium dioxide (TiO₂) under ultraviolet (UV) and solar light sources. The effects of <i>p</i>H in the range of 6-10, catalyst concentration in the range of 0.05-0.5 g/L for indoor

UV studies and 0.25- 2.0 g/L for outdoor solar studies and catalyst reuse for twenty cycles were studied on photocatalytic decolourisation of four batches of industrial RWWs. Since the RWWs contained more than one dye, their colour measurements were done at multiple wavelengths of 436, 525 and 620 nm. In order to compare the effect of the operating variables on rinse wastewaters, the reaction time at 436 nm was taken into consideration since the reaction time necessary was the maximum at 436 nm. It is concluded that the decolourisation of RWWs could be carried out at the natural pH itself. A catalyst concentration of 1 g/L was found to be necessary in solar studies, whereas only one tenth of 1 g/L was needed for UV studies. The titanium dioxides were found to maintain their photoactivity during reuse for 20 cycles.