Evaluation of Titanium dioxide photocatalytic technology for the treatment of reactive Black 5 dye in synthetic and real greywater effluents

Reuse of alternative water sources is gaining impetus as an acceptable integrated water resources management practice due to the scarcity of freshwater resources, particularly in urban centres where population is dense and freshwater supply is limited. This study investigated on the practical application of titanium dioxide (TiO2) photocatalytic treatment technology as a standalone system for the removal of Reactive Black 5 (RB5) dye, which usually causes a serious aesthetic problem that depresses the wider social acceptance of greywater recycling and reuse schemes. An optimization study was conducted on the photocatalytic degradation of RB5 dye in synthetic greywater effluent (i.e. aqueous RB5 in distilled water), in order to understand the effects of different photoreactor parameters on the degradation kinetics. It was found that the optimum photoreactor operating conditions are at TiO2 loading of 0.1 g/L, pH 5, initial RB5 concentration of 1 ppm and without compressed air sparging. Results showed that a 97% removal of RB5 was evident after 150 min of photocatalytic reaction in synthetic greywater effluent. With the established optimum photoreactor conditions, the photocatalytic degradation kinetics of RB5 dye in real greywater effluent was subsequently investigated. Results showed that the photocatalytic degradation of RB5 in real greywater effluent has a lower removal efficiency of 76% even after 330 min of reaction. It was hypothesized that the presence of other water pollutants in real greywater effluent could compete for the surface binding sites owing to the non-specific nature of TiO2 photocatalytic reaction. Thus, other greywater quality parameters such as oil and grease (O&G), chemical oxygen demand (COD), biological oxygen demand (BOD5), total nitrogen (TN) and total number of Escherichia coli were also monitored. Monitoring results showed that the parallel removal efficiencies of 60% O&G, 54% COD, 69% BOD5, 41% TN and 100% E. coli were evident, which have proven the impact of water impurities in real greywater effluent that could lower the photocatalytic degradation efficiency of RB5.