Assessment of integrated binary process by coupling photocatalysis and photo-Fenton for the removal of cephalexin from aqueous solution

Abstract

A novel concept of integrated process by coupling photocatalysis and photo-Fenton especially in fixed mode has been presented in the current study for the removal of recalcitrant pharmaceuticals like cephalexin (CEX) from aqueous solution in reduced treatment time. Waste materials like foundry sand (FS) was used as a substitute for iron along with TiO2. The parametric optimization was carried out in slurry mode using Box–Behnken design model (BBD) and response surface methodology. For fixed-bed studies, support materials of varying shapes (hollow circular disk, rectangular slabs, spherical beads) were prepared using clay in conjunction with FS for TiO2 immobilization. Different supports were compared on the basis of degradation efficiency, exposed surface area of catalyst as well as their recyclability capacity for the degradation of CEX. Iron was leaching by default from the supports during the degradation process which contributed simultaneously to photo-Fenton process along with photocatalysis. Spherical beads with 0.0265 m2 exposed surface area of catalyst and better recyclability efficiency (10 cycles) yielded best degradation efficiency (80%) of CEX after 240 min of treatment time. The presence of iron along with TiO2 on the surface of beads was confirmed through TGA, SEM/EDS, XRD, DRS and FTIR. The mineralization of CEX was validated through quantification of nitrite, nitrate and sulfate ions along with reduction in COD. A tentative pathway for the degradation of CEX was also proposed based on the identification of intermediates through GC–MS analysis.