Photocatalytic inactivation of Enterobacter cloacae and Escherichia coli using titanium dioxide supported on two substrates

The antibacterial photocatalytic activity of TiO2 supported over two types of substrates, borosilicate glass tubes (TiO2/SiO2-borosilicate glass tubes (BGT)) and low-density polyethylene pellets (TiO2-LDPE pellets), which were placed in a compound parabolic collectors (CPC) reactor, was evaluated against Enterobacter cloacae and Escherichia coli under sunlight. Three solar photocatalytic systems were assessed, suspended TiO2, TiO2/SiO2-BGT and TiO2-LDPE pellets, at three initial bacterial concentrations, 1 × 105; 1 × 103; 1 × 101 CFU/mL of E. coli and total bacteria (E. cloacae and E. coli). The solar photo-inactivation of E. coli was achieved after two hours with 7.2 kJ/L of UV-A, while total bacteria required four hours and 16.5 kJ/L of UV-A. Inactivation order of E. coli was determined, as follows, suspended TiO2/sunlight (50 mg/L) > TiO2-LDPE pellets/sunlight (52 mg/L) > TiO2/SiO2-BGT/sunlight (59 mg/L), the best E. coli. inactivation rate was obtained with TiO2-LDPE pellets/sunlight, within 4.5 kJ/L and 90 min. The highest total bacteria inactivation rate was found for TiO2/sunlight (50 mg/L) and TiO2-LDPE pellets/sunlight (52 mg/L), within 11.2 kJ/L and 180 min. TiO2 deposited over LDPE pellets was the most effective material, which can be successfully used for water disinfection applications. Bacterial regrowth was assessed 24 h after all photocatalytic treatments, none of those microorganisms showed any recovery above the detection limit (2 CFU/mL).