Solar-Enhanced Advanced Oxidation Processes for Water Treatment: Simultaneous Removal of Pathogens and Chemical Pollutants

Abstract

The review explores the feasibility of simultaneous removal of pathogens and chemical pollutants by solar-enhanced advanced oxidation processes (AOPs). The AOPs are based on in-situ generation of reactive oxygen species (ROS), most notably hydroxyl radicals •OH, that are capable of destroying both pollutant molecules and pathogen cells. The review presents evidence of simultaneous removal of pathogens and chemical pollutants by photocatalytic processes, namely TiO2 photocatalysis and photo-Fenton. Complex water matrices with high loads of pathogens and chemical pollutants negatively affect the efficiency of disinfection and pollutant removal. This is due to competition between chemical substances and pathogens for generated ROS. Other possible negative effects include light screening, competitive photon absorption, adsorption on the catalyst surface (thereby inhibiting its photocatalytic activity), etc. Besides, some matrix components may serve as nutrients for pathogens, thus hindering the disinfection process. Each type of water/wastewater would require a tailor-made approach and the variables that were shown to influence the processes-catalyst/oxidant concentrations, incident radiation flux, and pH-need to be adjusted in order to achieve the required degree of pollutant and pathogen removal. Overall, the solar-enhanced AOPs hold promise as an environmentally-friendly way to substitute or supplement conventional water/wastewater treatment, particularly in areas without access to centralized drinking water or sewage/wastewater treatment facilities.

Keywords: TiO2 photocatalysis; disinfection; pathogen inactivation; photo-Fenton; pollutant degradation; simultaneous removal; solar-enhanced AOPs; water/wastewater treatment.

Figure 1

Effect of resorcinol (10 mg/L) on inactivation of bacteria in (a) photo-Fenton and (b) TiO₂ photocatalytic processes. Solar simulator light intensity: 1000 W/m, initial bacteria concentration: 10⁶ CFU/mL. Photo-Fenton parameters: Fe³⁺: 1 mg/L, and H₂O₂: 60 mg/L, initial pH = 5.0. TiO₂ photocatalysis: TiO₂ concentration: 1.0 g/L. Reproduced from [26] with permission of The Royal Society of Chemistry (RSC) on behalf of the Centre National de la Recherche Scientifique (CNRS) and the RSC.

Figure 2

Kinetic constant for E. coli inactivation and initial reaction rate of methylene blue oxidation as a function of TiO₂ concentration. Reproduced from [39] with permission from Elsevier.

Figure 3

Kinetic constant for E. coli inactivation and initial reaction rate of methylene blue oxidation as a function of incident radiation. Reproduced from [39] with permission from Elsevier.