The removal of hydroxychloroquine and oseltamivir from wastewater using a simulated lab-scale bio-photocatalytic wastewater treatment plant: Activated sludge coupled with calixarene@Nb₂CT_x@g-C₃N₄ photocatalytic system

The increasing concerns on water and environmental quality due to the continuous excessive release of antiviral drugs into water systems have received notable attention world-wide. Thus, the development of sustainable environmental remediation technologies is of interest amongst researchers. Herein, a hyphenated bio-photo degradation system was engineered, utilizing activated sludge and a 5-Calixarene@Nb₂CT_x@g-C₃N₄ photocatalytic reactor set-up. The activated sludge was acclimatized to synthetic wastewater for 25 days, reaching COD removal of above 80 %. Mixed liquor suspended solids (MLSSs) and mixed liquor volatile suspended solids (MLVSSs) used to monitor the concentration of suspended solids and the amount of volatile suspended solids reached optimum values of about 2500 mg.L^-1, where ideal MLVSSs values of 70–80 % of MLSSs were reached to give MLVSSs/MLSSs ratios of 0.7–0.8. In a 250 mL working solution, the optimum photoreactor parameters were pH 4, 20 mg catalyst loading, and an initial pollutant concentration of 5 mg.L^-1. In the hyphenated system, the biodegradation efficiency of 62.5 and 58.1 % for hydroxychloroquine (HCQ) sulphate and oseltamivir (OS) phosphate were obtained, respectively. Photodegradation using 5-CxNbCN increased the removal efficiency to 97.3 and 92.6 % for HCQ and OS, correspondingly. The major contributing reactive oxygen species (ROS) towards the removal of HCQ and OS were e⁻ and •O₂⁻ charge carriers. Degradation efficiency was reduced from 80.8 % (control) to 30.7 % in the presence of p-benzoquinone (e⁻ and •O₂⁻quencher). Plausible OS and HCQ photodegradation fragments were identified using liquid chromatography mass spectrometry (LC-MS/MS). The parent OS and HCQ ARVs decomposed into smaller organic molecules 3-hydroxycyclohexa-2,5‑dien-1-ylium (m/z = 95.05) and 2-aminobenzaldehyde (m/z = 121.05), respectively. This study paves the way towards the realization of practical applicability of solar-powered photocatalysis in conventional WWTPs.