The hybrid process TiO₂/PAC: performance of membrane filtration

In investigations concerning the photocatalytic degradation by TiO₂ usually filter discs with a pore size of 0.22 μm and 0.45 μm are used for the removal of photocatalyst particles in aqueous suspensions. In this study the effective rejection of suspended particles by microfiltration in different types of membrane modules and with different membrane materials was investigated. Furthermore, Powdered Activated Carbon (PAC), which can be used to gain an increase in photocatalytic degradation rates, was investigated concerning its influence on the membrane performance. It is shown that by membrane filtration with a pore size above 0.1 μm, irrespective of the experimental conditions, no complete removal can be achieved. However, UV irradiation was found to improve the removal efficiency for all types of tested membrane materials. The addition of PAC also led to a higher performance of membrane filtration with regard to particle rejection. In long-term experiments with a hollow fibre membrane module in the presence of PAC a five-fold decrease of TiO₂ particles in the permeate could be proven. Besides, it was shown that added PAC can shield the membrane regarding the abrasivity of TiO₂, which could otherwise lead to the destruction of the membrane. Therewith PAC exhibits another crucial advantage besides its synergetic effect in photodegradation.