Contaminant effects on the photo-oxidation of greywater over titania film catalysts

One strategy for reducing water demand is by matching water quality to water need, through increased use of treated greywater to replace potable water in non-potable applications. Greywater processing, using photo-oxidation over TiO2 films, results in catalytic activity, which can be either enhanced or inhibited by xenobiotic contaminants found within the greywater stream. Analysis of film pre-treatment and reaction conditions indicated that photoactivation was caused in part by contact of the films with water and in some instances by degradation products produced during the initial cycle of photodegradation. Using a model probe for photoactivity, degradation over such films exhibited pseudo-first order kinetics. However, after catalyst re-cycling, the kinetics deviated from first order, with the films becoming increasingly more photoactive. Aging of these films over a prolonged period of time did not alter film photocatalytic activity and prior exposure of the films to UV irradiation in water actually decreased subsequent photocatalytic activity of the films compared with the un-irradiated films. Some greywater components, such as polyethylene glycol, enhanced the photodegradation rate of the model probe in both the initial and subsequent cycles, whereas others, such as sodium stearate, were more complex; the initial photodegradation rate was initially inhibited but then enhanced over subsequent photocatalytic cycles. Ionic phosphate has a strong inhibitory effect under all conditions tested. The results indicate that even minor components, at concentrations typically found in household effluents, may have a critical effect on the photocatalytic activity of titania films during processing of greywater.