Disinfection of urban effluents using solar TiO2 photocatalysis: A study of significance of dissolved oxygen, temperature, type of microorganism and water matrix

• Thermal effect between 15 and 45 °C on urban waste water photocatalytic disinfection was investigated.
• Air injection in the solar photocatalytic disinfecting treatment was analyzed.
• Enhancement of water disinfection with air injection was observed for Escherichia coli and Fusarium solani.
• The important role of water temperature and dissolved oxygen on disinfection efficiency was confirmed using solar pilot CPC reactors.

The enhancement of current technologies used to treat polluted water is one of the most important challenges in water research. The application of physico-chemical treatments could reduce the load of chemical and biological pollutants present in WW reducing the pressure over water requirements, allowing the reclaim of the treated water. Advanced Oxidation Processes (AOPs) and, in particular, photocatalysis using titanium dioxide (TiO2) have shown a great potential for chemicals removal as well as for pathogens reduction in water. Moreover, the use of solar Compound Parabolic Collectors (CPC) reactors has been also shown to be very effective for water treatment purpose by solar photocatalysis. Nevertheless, the effects of some key parameters in photocatalytic disinfection have not been already investigated at pilot scale in solar reactors; like dissolved oxygen concentration, water temperature, water matrix composition and the type of microorganism. The roles of these parameters in photocatalytic processes are individually known for chemicals degradation, but their relative significance in water photocatalytic disinfection has been never studied at pilot scale. The aim of this work was to investigate the influence of these parameters on the disinfection efficiency using a solar 60 L-CPC reactor with suspended TiO2 (100 mg/L). The following variables were experimentally evaluated: injection of air in the reactor (160 L/h); different controlled temperatures (15, 25, 35 and 45 °C); two very different models of water pathogen, Escherichia coli (model of fecal water contamination) and Fusarium solani spores (a highly phytopathogenic fungus); and the chemical composition of the water comparing urban WW effluents (UWWE) and simulated urban WW effluent (SUWWE). The increase of water temperature (from 15 to 45 °C) had a benefit on the disinfection rate for both pathogens in all the experimental conditions evaluated. The air injection led to an important enhancement on the inactivation efficiency, which was stronger for F. solani spores, the most resistant microorganisms to TiO2 photocatalysis. The composition of the water matrix significantly affected the efficiency of the photocatalytic treatment, showing a better inactivation rate in SUWWE than for UWWE.

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