Plug flow approaching novel reactor employing in-situ dual effect of photocatalysis and photo-Fenton for the degradation of metronidazole

Abstract

The novel concept of fixed-bed in-situ continuous reactor approaching plug flow (PFR) has been employed for the degradation of Metronidazole (MTZ). Axial dispersion model has been employed to validate the exit age distribution. PFR modeled reactor was employed with novel composite beads composed of fuller’s earth and foundry sand encompassing the properties of the in-situ dual effect of both photocatalysis and photo-Fenton. The optimization was performed under the solar irradiations using reactors in series. Significant reduction in treatment time was achieved as dual effect took only 45 min for 84% removal optimized at three reactors in series with flow rate of 8 L h−1, 75% area covered by the beads.Whereas individual processes of photo-Fenton and photocatalysis engaged nearly 3.5 h for merely 45% removal. The in-situ dual process exhibited 84% synergy, calculated in terms of the rate constant, over the individual processes. Various parameters including flow rate, number of reactors, H2O2 dose, the surface area covered by the beads, etc were optimized. 55% reduction in COD after the third reactor (in once-through mode) and formation of various ions substantiated the mineralization of MTZ into various small compounds. Results were extended to real effluent treatment using once through plug flow reactor approach. The tentative mechanism for the degradation of MTZ was also proposed. The industry viability of the reported process was demonstrated by recycling the composite beads up to 80 cycles and evaluating the approximate cost for the removal of the drug. Various characterizations like SEM, XRD, EDS, FT-IR, DRS confirmed the in-situ dual process.