Application of solar photocatalytic ozonation in water treatment using supported TiO2

Abstract

TiO2 P25 supported on mullite ceramic foams (CF) and glass raschig rings (GR), have been prepared by dip-coating with calcination at 500 °C. The (photo) catalytic activity of these materials in the degradation of N, N-diethyl-m-toluamide (DEET) by different AOPs, in ultrapure water or in a secondary effluent, has been tested. Under the conditions applied, for a given process, the performance of CF and GR supported catalysts was similar, and a slight improvement was observed only from 1 to 2 TiO2 coatings, indicating that, regardless of the support, after the second coating the amount of TiO2 (2.4 and 0.49 wt% for CF and GR, respectively), was in excess with respect to the solar UV photon flux and/or the ozone entering the reactor. Ozonation was the most effective process for DEET and A254nm removal, whereas solar photocatalytic ozonation led to the highest carboxylates formation and mineralization rates. At pH < 8.5, the presence of 5 mg L−1 PO43- or 20 mg L−1 IC as HCO3-/CO3= had no effect on DOC removal by this system, but some HO· scavenging effect was noticed when 40 mg L−1 IC was present, more markedly at pH > 8.5. The impact of the water matrix (ultrapure water, DOC0 15 mg L−1; or a secondary effluent, DOC0 11 mg L−1 and IC0 20 mg L−1), on the effectiveness of photocatalytic oxidation was high, and low for photocatalytic ozonation (45–50% DOC removed from both matrices after 2 h). After several cycles of use, almost no loss of activity of the supported materials was observed. By comparing the characterization results of fresh/used materials their stability is deduced.