Photocatalytic oxidation as a secondary treatment method following wet airoxidation

Photocatalytic oxidation is investigated. as a potential secondary treatmen t method to follow wet air oxidation (WAO). The rates of photocatalytic oxi dation of acetic acid and 2-chlorobiphenyl in aqueous solution were studied under continuous flow conditions in a small diameter cylindrical borosilic ate reactor packed with highly porous TiO2 particles at temperatures up to 160 degrees C and pressures up to 20 atm. These compounds are of particular interest because they are recalcitrant to conventional WAO. Specific atten tion is paid to the effects of oxygen concentration, pH, and temperature on reaction rates. Results show that solution pH may play an important role i n the selective oxidation of compound in a mixed waste stream. 8-Chlorobiph enyl was selectively oxidized in the presence of much higher concentrations of acetic acid by maintaining a neutral to basic pH. Moreover, the depende nce of the rate of mineralization of acetic acid on oxygen is strongly infl uenced by pH. At low pH, high dissolved oxygen concentrations were required to achieve the limiting oxidation rate. Temperature affects the intrinsic rate of react;ion, the extent of substrate adsorption, and the light intens ity. Each of these effects can be accurately modeled using a modified form of a Langmuir-Hinshelwood-Hougen-Watson kinetic rate expression that pertai ns to a mechanism involving noncompetitive adsorption on two different type s of sites.