Photocatalytic ozonation of wastewater: a review
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REVIEW
Photocatalytic ozonation of wastewater: a review Achisa C. Mecha1 · Martha N. Chollom2 Received: 9 December 2019 / Accepted: 1 June 2020 © Springer Nature Switzerland AG 2020
Abstract 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. Keywords Advanced oxidation processes · Degradation · Photocatalytic ozonation · Toxicity · Wastewater
Introduction The protection of natural water resources and development of new technologies for water and wastewater treatment for reuse are key priorities of the twenty-first century. The environmental degradation caused by emerging biorecalcitrant organic compounds such as pharmaceuticals, cosmetics, fertilizers and resistant microbial pollutants is a global concern resulting in scarcity of fresh water in various parts of the world (Valério et al. 2020). However, the current conventional wastewater treatment technologies are often not effective in meeting the stringent effluent standards targeting the removal of emerging contaminants (Dewil et al. 2017). There is need to develop more effective treatment technologies that satisfy a range of requirements such as complete removal of biorecalcitrant organic pollutants, inactivation of resistant pathogens, less costly, energy efficient and environmentally friendly (Singh 2012; Mecha et al. 2017a, b). In this regard, advanced oxidation processes, especially those driven by solar light, have great potential in wastewater * Achisa C. Mecha [email protected] 1
Department of Chemical and Process Engineering, Moi University, Eldoret, Kenya
Department of Chemical Engineering, Durban University of Technology, Durban, South Africa
2
remediation targeting emerging contaminants (Rizzo et al. 2019; Rodríguez et al. 2019). The advanced oxidation processes are destructive technologies which degrade contaminants. However, despite their overall high degradation efficiency, large-scale practical implementation has not been realized (Matafonova and Batoev 2018). This is partly due to high process costs since they are energy intensive. Also information regarding their performance is not standardized, for instance, a direct comparis
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