Treatment of pharmaceutical wastewater using photocatalytic reactor and hybrid system integrated with biofilm based process: Mechanistic insights and degradation pathways

Abstract

Diclofenac and tetracycline, the pharmaceutically active compounds, are ubiquitously found in water bodies. The inability of conventional processes has mandated the use of advanced treatment techniques. This study has demonstrated the use of sulfur-doped g-C3N4/ZnO (SCZ) catalyst for removing diclofenac and tetracycline and achieved ∼94 % and ∼97 % degradation efficiencies, respectively, in 240 min using UV light (wavelength: 320–400 nm). The SCZ catalyst exhibited enhanced mineralization efficiency (∼95 %) in 600 min and reusability (11 cycles) for targeted contaminants. The physicochemical characterization of the used catalyst depicted the presence of crystalline structures, defects, and roughness, similar to that of the pristine catalyst. The degradation pathways of diclofenac and tetracycline delineated the possible reaction mechanisms for the transformed product formations. The SCZ catalyst was used in the continuous photocatalytic reactor to treat synthetic and real wastewater spiked with pharmaceuticals. Additionally, moving and stationary bed bioreactor-sedimentation tank was coupled with the continuous photocatalytic reactor removing suspended and biodegradable impurities, which enhanced the organic removal efficiency from ∼70–94 %. The SCZ catalyst showed ∼85 % degradation efficiency for the targeted pharmaceutical compounds from the solution mixture. The results of this study suggest that SCZ catalyst and the hybrid photocatalytic system can be a promising solution for the treatment of pharmaceuticals from real wastewater.