Abstract
Dexamethasone (DXM) is a widely used anti-inflammatory corticosteroid that is frequently detected in the water bodies due to its immense consumption and incomplete removal during wastewater treatment. The potential eco-toxicity of pharmaceutical pollutants and their insufficient removal in conventional wastewater treatments have provoked researchers to investigate and develop novel and highly efficient treatment systems. The present study aimed to develop a synergistic advanced oxidation system based on electro-peroxone coupled with ultrasonic irradiation (EP/US process) for the degradation of dexamethasone (DXM) from water medium and an EP/US process assisted with granular activated carbon (GAC) for the remediation of real pharmaceutical wastewater. The effects of various experimental parameters such as pH, operating time, US power, applied current, and supporting electrolyte (Na2SO4) were systematically investigated by using response surface methodology based on central composite design (RSM-CCD), and results established that the complete degradation of DEX was attained at pH 9, operating time 25 min, US power 300 W/L, applied current 420 mA, and supporting electrolyte 0.05 M. The results of analysis of variance and regression analysis revealed that the second-order polynomial equation is more suitable (R2 = 0.9981 and p-value = 0.0004) to predict removal efficiency and describe the oxidation process. Under optimized experimental condition, the integrated EP/US process provided synergy and lessenergyconsumption compared to individual EP and US processes. The removal efficiency of TOC and COD reached 44.2% and 70.8% after 25 min reaction and increased to 78.7 % and 94.4%, respectively, as contact time increased to 50 min. Also, average oxidation state (AOS) and carbon oxidation state (COS) values increased from 0.22 to 3.28 and 3.78, respectively. Scavenger tests disclosed that HO• radical is the predominant reactive free radical generated in the EP/US system, and LC-MS analysis indicated that different intermediates are produced during DEX decomposition. The EP/US system increased the BOD/COD ratio of real pharmaceutical wastewater from 0.27 to 0.5 during 100 min treatment time, while in the presence of GAC, the EP/US process showed better results. Overall, the present study highlights that the coupling of EP/US processes noticeably improves the DEX abatement rate from water medium, and GAC can improve the efficiency of this process for pharmaceutical wastewater treatment. The findings of the present study propose the EP/US and EP/US/GAC systems as promising efficient alternatives for treating persistentpharmaceutical wastewater.
Published Version
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