Waste sludge from shipping docks as a catalyst to remove amoxicillin in water with hydrogen peroxide and ultrasound

The waste sludge from shipping docks contains important elements that can be used as a catalyst after proper processing. The purpose of this study was to remove of amoxicillin (AMX) from the aquatic environment using waste sludge from shipping docks as catalyst in the presence of hydrogen peroxide/ultrasound waves. The catalyst was produced by treating waste sludge at 400 °C for 2 h. N₂ adsorption, SEM, XRD, XRF, and FTIR techniques characterized the structural and physical properties of the catalyst. The BET-specific surface area of the catalyst reduced after AMX removal from 4.4 m²/g to 3.6 m²/g. To determine the optimal removal conditions, the parameters of the design of experiments were pH (5-9), contaminant concentration (5-100 mg/L), catalyst dosage (0.5-6 g/L), and concentration of hydrogen peroxide (10-100 mM). The maximum removal of AMX (98%) was obtained in the catalyst/hydrogen peroxide/ultrasound system at pH 5, catalyst dose of 4.5 g/L, H₂O₂ concentration of 50 mM, AMX concentration of 5 mg/L, and contact time of 60 min. The kinetics of removal of AMX from urine (k = 0.026 1/min), hospital wastewater (k = 0.021 1/min), and distilled water (k = 0.067 1/min) followed a first-order kinetic model (R²>0.91). The catalyst was reused up to 8 times and the AMX removal decreased to 45% in the last use. The byproducts and reaction pathway of AMX degradation were also investigated. The results clearly show that to achieve high pollutant removal rate the H₂O₂/ultrasound and catalyst/ultrasound synergy plays a key role.