Disinfection of water and wastewater by TiO2 photocatalysis, sonolysis and UV-C irradiation

The efficacy of various advanced oxidation processes based on ultraviolet and ultrasound irradiation to inactivate Escherichia coli in sterile water and total coliforms (TCs) in biologically treated municipal wastewater was evaluated. H2O2-assisted UV-A/TiO2 photocatalysis (9 W lamp) could generally lead to nearly complete E. coli destruction in 20 min contact time with the extent of inactivation depending on the photocatalyst type and loading (in the range 0–0.75 g/L) and oxidant concentration (in the range 0–100 mg/L). Low frequency (in the range 24–80 kHz), high power (in the range 150–450 W) ultrasound irradiation provided by a horn-type sonicator was less effective than photocatalysis requiring longer contact times (i.e. 120 min) for E. coli inactivation. TiO2 photocatalysis, UV-C irradiation (11 W lamp), ultrasound irradiation, chlorination (in the range 1–5 mg/L chorine) and various combinations of them were tested concerning their ability to disinfect municipal effluents already subject to activated sludge treatment. Of these, UV-C irradiation was more efficient than the rest in achieving full and permanent (i.e. without bacteria regeneration) inactivation after short periods of contact time.