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).