Keywords: chlorinated hydrocarbons, heterogeneous photocatalysis, titanium dioxide, water purification, water pollution, degradation rate
Advanced technology for water purification by heterogeneous photocatalysis
The TiO2 photocatalytic degradation of 2,4-dichlorophenol (2,4-DCP) and pentachlorophenol (PCP) was examined using a prototype photoreactor fabricated by Nulite. The degradation of both pollutants proved very efficient as in 12 min it was possible to bring the concentration of 2,4-DCP from 10 to 0.5 p.p.m. and in a separate experiment the concentration of PCP from 100 to 0.5 p.p.b. The effect of flow rate on the degradation of 2,4-DCP in both single pass and multi-pass operation modes was investigated. In single pass experiments, the conversion (%) of 2,4-DCP initially decreased with increasing flow rate and levelled up at about 1-1.5 l/min. This indicates that the reactor operates more efficiently at higher flow rates. In the multi-pass experiments, the degradation rate of 2,4-DCP increases non-linearly with the flow rate. The effect of concentration (1.2-20 p.p.m.) on the degradation of 2,4-DCP was also investigated. The degradation rate of 2,4-DCP increases and the degradation rate constant decreases with increasing concentration of 2,4-DCP. The results are explained in terms of surface heterogeneity of TiO2. Partial removal of oxygen by bubbling nitrogen into the feed stream just before the photoreactor decreased the degradation rate markedly, whilst introducing oxygen or air increased the degradation rate considerably.