Role of Adsorption in the Removal of Diclofenac in Wastewater by Activated Sludge

ABSTRACT Diclofenac (DCF) is one of the prevalent pharmaceutical contaminants detected in municipal wastewater treatment plants. This research aimed to study the role of adsorption mechanisms in DCF removal in wastewater and the potential of using dried activated sludge (AS) as an adsorbent. Wastewater obtained from the facility was spiked with 1 and 10 mg L −1 of DCF, and the removal was observed in batch experiments conducted in the laboratory. The DCF removal efficiencies of 90.9% and 89.7% by AS were obtained in 48 h for 1 and 10 mg L −1 of DCF, respectively. Role of adsorption was then observed by adsorption experiments with dried biomass of the AS at the same DCF concentrations. The adsorption process was found to be pH and sludge dosage dependent. Sludge had the highest adsorption capacity in the DCF solution at the neutral pH 7 (14.4 × 10 −2  mg g −1 ), followed by pH 10 (12.3 × 10 −2  mg g −1 ), then pH 4 (4.0 × 10 −2  mg g −1 ). The adsorption capacity reduced as the sludge dose increased whilst the removal percentage increased as the sludge dosage increased from 35.1% to 53.5%, and 71.3% for 1, 2, and 4 g of sludge, respectively. The adsorption was better fitted to a pseudo‐second‐order kinetic model with R 2 values > 0.98 and was dominated by the chemisorption process. The findings from this study have shown that adsorption is one of the key mechanisms of DCF removal in a municipal wastewater treatment plant, and the dried activated sludge has a potential as a DCF adsorbent.