Inactivation of simulated aquaculture stream bacteria at low temperature using advanced UVA- and solar-based oxidation methods

Abstract

In this work the effect of water temperature (6 +/- 1 degrees C and 22 +/- 1 degrees C) on inactivation of bacteria (104 -106 CFU mL-1; Pseudomonas spp., Aeromonas spp. and Enterobacter spp.) in simulated aquaculture streams (SAS) using UVA based advanced oxidation processes (AOP) (H2O2-assisted UVA; photocatalysis; H2O2-assisted photocatalysis) and solar driven AOPs (H2O2-assisted solar disinfection, SODIS) was studied. Efficiency at 22 degrees C in terms of inactivation rate was higher using H2O2-assisted photocatalysis (H2O2/UVA-TiO2/polysiloxane) > H2O2-assisted UVA disinfection (UVA/H2O2 - 10 mg L-1) > photocatalysis (UVA-TiO2/polysiloxane) > UVA disinfection. At low temperature (6 degrees C) the inactivation rate increased with SODIS/H2O2 > SODIS > H2O2assisted UVA disinfection (UVA/H2O2 - 10 mg L-1) > H2O2-assisted photocatalysis (H2O2/UVA-TiO2/polysiloxane) > photocatalysis (UVA-TiO2/polysiloxane). The main results indicate that the inactivation rates increased when hydrogen peroxide (10 mg L-1) was used during H2O2-assisted UVA disinfection and photocatalysis. In addition, exposure of SAS to hydrogen peroxide for 24 h (in absence of light) at room temperature decreased the subsequent exposure UVA irradiation dose by almost four times. Drastic increase of inactivation rate was observed at low water temperature (6 +/- 1 degrees C) when UVA- and solarbased AOPs were employed compared to 22 +/- 1 degrees C. The treatment with SODIS proved to be more effective in Finland than in Spain. The effect of the low temperature (6 +/- 1 degrees C) was proposed as a critical factor during UVA disinfection (UVA/H2O2 and photocatalysis) that can increase the disinfection rate constant (kmax) by 1.3-5.2 times, leading to a reduction of the treatment costs ( euro m-3) by 1.3-3.3 times. The mechanism of observed enhanced disinfection at low water temperature (6 +/- 1 degrees C) when natural solar light and UVA are employed as irradiation sources for UVA/H2O2 and photocatalytic bacteria inactivation was proposed. No regrowth was observed in case of H2O2-assisted AOPs.