Airlift reactor-based heterogeneous catalytic ozonation using CuO@Leca for biodegradability enhancement of quercetin-rich pharmaceutical effluent

Abstract

Herbal pharmaceutical effluent (HPE) is distinguished by its high content of natural flavonoids such as Quercetin. Heterogeneous catalytic ozonation (HCO) in an airlift reactor (600 mL) was applied to degrade Quercetin in an aqueous environment using copper oxide-loaded light-expanded clay aggregate (CuO@Leca). Prepared catalyst was characterized by BET, XRD, FTIR, EDS, and SEM analysis, while GC–MS and UV–visible spectroscopy were used to evaluate HPE characterizations. In the first part of experiments, the influence of three main variables, namely CuO loading (0–20 wt%), pH (4–10), and ozonation time (5–35 min) was optimized on Quercetin removal efficiency from synthetic HPE. The results showed a significant increase (2–5 times) in Quercetin degradation using HCO compared to ozonation alone. Meanwhile, an 86.34 % removal was achieved at pH 7.4 and high level of other variables. In the second part of the experiments, real HPE was subjected to HCO under the optimal CuO loading determined in the first part of experiments. Significant reduction was achieved in Quercetin concentration (84 %), TSS (96 %), turbidity (92 %), COD (86 %), and BOD (80 %), alongside an improvement in HPE biodegradability from 0.41 to 0.59. The liquid flow in the riser of airlift reactor promotes the dispersion and direct reactions of ozone, while the catalyst-ozone interactions in the downcomer accelerate ozone decomposition and generation of reactive species, leading to the formation of smaller and more biodegradable compounds such as flavonol, chalcone, flavone, flavanon, flavan-3-ol, oxonium, and phenol. The suggested catalytic reactor is practically interested than slurry configuration. The spent catalyst was regenerated via aerobic calcination at 450 °C for 2 h, showing ∼9 % efficiency loss after four recycling cycles.