Assessment of solar photocatalysis using Ag/BiVO4 at pilot solar Compound Parabolic Collector for inactivation of pathogens in well water and secondary effluents

Advanced oxidation processes (AOPs), such as photocatalysis driven by natural sunlight have been demonstrated to be a promising technology for degradation of hazardous chemical compounds and inactivation of microorganisms in water. Among already exiting photocatalysts, for solar water treatment, currently visible light-active photocatalysts such as bismuth vanadate (BiVO₄), have received much attention from researchers. This work reports on the capacity of new synthetized Ag modified BiVO₄ composite to inactivate E. coli, E. faecalis and spores of F. solani in different water matrices. Proof of principle experiments performed at laboratory scale (200 mL of distilled water in stirred tank reactor) demonstrated the capability of this photocatalyst to inactivate those pathogens. A range of Ag loadings were investigated, demonstrating that 15% of Ag was the best option for water disinfection under natural sunlight.  Although, TiO₂-P25 is a better material for the solar photocatalytic disinfection of water under real sun.  The cytotoxic effect of Ag/BiVO₄ composites was investigated by testing its cytotoxicity in human dermal fibroblasts (HDF). This result was supported also by the lack of bactericidal effect of the composites as it was demonstrated to not compromise the viability of E. coli, E. faecalis and F. solani spores in dark (1 g L⁻¹of Ag(15%)/BiVO₄) for 3 h in the case of E. coli and for 5 h for the others. Up-scaling the treatment to CPC flow-reactor of 10 L was successfully done in distilled water and well water; meanwhile inactivation of microorganism in secondary effluent (SE) from a Municipal Wastewater Treatment Plant was achieved only in the case of naturally occurring E. coli.  Several concentrations of catalyst were investigated, and best inactivation efficiency was found to be 1 g L⁻¹ for all microorganisms, solar reactors and water matrices. The influence of chemical composition of the water matrix was also investigated. The presence of high concentrations of carbonates/bicarbonates (in well water) did not affect significantly the photocatalytic efficiency; while natural organic matter (in SE) strongly limited the process probably due to the competitiveness for the radicals generated.