Removal of pyridine using ultrasound assisted and conventional batch adsorption based on tea waste residue as biosorbent

Abstract

The current study deals with comparison of ultrasound assisted adsorption and conventional batch adsorption using biosorbent based on tea waste residue (TWR) with an objective to develop novel treatment approach for effective removal of pyridine. The characterization of TWR was performed using FTIR and SEM to get clear insight into the associated functional groups and the morphology. In addition, point of zero charge was also established and oxygen functional groups were detected using Boehm titration method. Ultrasound assisted adsorption was studied in ultrasonic bath (25 kHz frequency) under varying conditions of pH (2–10), TWR dose (0.5–4 g/L) treatment time (0 to 120 min for ultrasound assisted and 0 to 200 min for conventional approach), temperature (283 K–313 K), power (15 W–150 W) and initial concentration (10 mg/L– 150 mg/L). Maximum removal and pyridine uptake obtained for ultrasound assisted adsorption was 98.2% and 37.38 mg/g respectively at optimized conditions of pH of 6, TWR loading of 2.5 g/L, temperature of 303 K, treatment time of 90 min and power of 120 W. Conventional batch adsorption studies performed at fixed 150 rpm as shaking speed revealed that maximum removal and maximum pyridine uptake was obtained as 92.25% and 33.72 mg/g respectively under similar optimum conditions but in treatment time of 160 min required to reach equilibrium. Pseudo second order kinetic model was the best fit for both adsorption approaches. Langmuir adsorption isotherm model for conventional batch adsorption and both Langmuir and Temkin isotherm for ultrasound assisted adsorption were also found suitable. Thermodynamic parameters as ∆G, ∆H and ∆S were evaluated for both adsorption approaches and it was established that the ∆G and ∆S values for ultrasound assisted adsorption for all temperatures and isotherms are higher compared to conventional batch adsorption. Overall, ultrasound was demonstrated as effective means to improve adsorption leading to enhanced extent of adsorption and lower treatment time.