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 °C and 22 ± 1 °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 °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 °C) the inactivation rate increased with SODIS/H2O2 > SODIS > H2O2-assisted 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 °C) when UVA- and solar-based AOPs were employed compared to 22 ± 1 °C. The treatment with SODIS proved to be more effective in Finland than in Spain. The effect of the low temperature (6 ± 1 °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 (€ m−3) by 1.3–3.3 times. The mechanism of observed enhanced disinfection at low water temperature (6 ± 1 °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.