Destruction and entrainment of microplastics in ozonation and wet oxidation processes

The global environmental worsening of microplastic (MP) pollution, particularly in water bodies, urges the search for treatments that can remove MPs from wastewaters, and, with this aim several processes have been investigated in the last years. This work analyses the use of wet oxidation and ozonation to remove real MPs from water, recovered from a wastewater treatment plant (WWTP). After 5 h of treatment, MP removals of 86.3 +/- 1.7 % and 45.2 +/- 1.3 % have been achieved by wet oxidation and ozonation, respectively. To know if the removal achieved was by reaction or by entrainment, similar experiments using inert gases have been carried out. A MP removal of 5.5 +/- 2.0 % was obtained substituting O2 by N2 in wet oxidation setup and 43.4 +/- 1.1 % when ozone was substituted by air. These results proved that most part of removal obtained by ozonation was due to entrainment of MP by the gas bubbling in an open reactor, whereas in the case of wet oxidation in a closed reactor chemical degradation was the main responsible for MP removal. Kinetic constants for the global processes were obtained and a model for MP entrainment has been proposed obtaining the kinetic constants for both, chemical reaction and entrainment. In the case of wet oxidation experiments, kinetic constants of 0.018 +/- 0.007 h-1 and 0.395 +/- 0.055 h-1 have been obtained for entrainment and chemical degradation, respectively. Finally, it has been shown that entrainment and chemical reaction occurred together with MP fragmentation.

Automated summary

This study analyzes the application of wet oxidation and ozonation in the removal of microplastics from wastewater. It was found that wet oxidation can remove approximately 86.3% of microplastics, while ozonation can remove approximately 45.2% of microplastics. Further experiments showed that ozonation mainly removes microplastics through gas bubbling, while wet oxidation mainly removes microplastics through chemical degradation. Finally, it was also found that the removal of microplastics is accompanied by fragmentation.