Efficient recovery of TiO2 and Pt-doped TiO2 photocatalysts in wastewater treatment using a pilot-scale cross-flow ultrafiltration membrane system

Despite the high efficacy of photocatalysts in wastewater treatment, their pilot plant and industrial-scale applications are scanty. The photocatalysts must be recovered for their reuse to minimize the treatment cost and also to avoid secondary water pollution due to the presence of catalyst particles. Herein, we have studied the recovery of TiO2 and Pt-doped TiO2 (Pt/TiO2) photocatalysts using a pilot scale cross-flow ultrafiltration (CF-UF) membrane system with a nominal area of 2 m2 and pore size of 75 kDa. The photocatalysts recovery was conducted at a 0.032–0.105 m s−1 cross flow velocity (CFV) and transmembrane pressure (TMP) drop of 0.6–1.05 kg cm−2. The wettability studies revealed that the membrane is more hydrophilic from the inside (water contact angle, θ = 54.1°) than the outer surface (θ = 77.3°) with an inner diameter of 0.78 mm and a thickness of 0.21 mm. Pure water flux (PWF), permeate flux, and catalyst recovery (%) decreased with increased pH and catalyst concentration. The flux was reduced from 11.12 ± 0.15 to 10.56 ± 0.17 and 10.37 ± 0.19 L m−2 h−1 during the recovery of TiO2 and Pt/TiO2 (50 mg/L), respectively. The recovery of about 99.74 ± 0.13 and 99.41 ± 0.29 % of TiO2 and Pt/TiO2 (50 mg/L), respectively, was achieved at the optimized pH 5. Membrane fouling and flux recovery studies revealed excellent antifouling properties of the membrane with a maximum of 9.86 ± 0.04 % reversible fouling and a minimum of 98.78 ± 0.20 % flux recovery. The hydrodynamic diameters of both catalyst particles increased in the reject and backflush streams with right-tailed lognormal distribution.