Photocatalytic ozonation of wastewater: a review

Industrialization is inducing water pollution by pharmaceuticals, fertilizers and cosmetics. Many emerging pollutants are non-biodegradable, toxic and recalcitrant to conventional wastewater treatments, thus calling for improved remediation techniques such as advanced oxidation processes which allow complete mineralization of pollutants. Here we review advanced oxidation processes with focus on ozonation and photocatalysis for the degradation of organic and microbial contaminants in wastewaters. Ozonation efficiency is limited by ozone-resistant pollutants, whereas photocatalysis is slow due to charge recombination, yet photocatalytic ozonation overcomes these limitations. Photocatalytic ozonation indeed shows synergy indices of up to 5.8 for treating wastewaters. This resulted in faster reaction kinetics, enhanced pollutant degradation with mineralization achieved in most cases, and reduction of toxicity up to 100%. We also discuss energy requirements.