Ultrasound enhanced removal of lead from wastewater by hazelnut shell: an experimental design methodology

The present work aimed to investigate the possibility to enhance Pb(II) removal from wastewater by ultrasound-assisted adsorption using unmodified hazelnut shell, as locally and readily available agricultural waste. The main objective was to optimize operational parameters, to allow efficient (fast and low-cost) lead removal. Thus, parameters as contact time, initial Pb(II) concentration and wastewater temperature were investigated in batch operation and optimized using response surface methodology. The obtained results indicated high adsorption efficiency, between 91.6 and 97.3%, even for very short contact time (4–10 min) and for relatively large particles of grounded shell (particle size between 0.5 and 0.63 mm). Furthermore, it was found that the initial Pb(II) concentration is the most important factor in this process: a higher initial concentration of Pb(II) determined a higher removal efficiency. The linear forms of Langmuir and Freundlich isotherms were applied for different values of temperature and initial Pb(II) concentration. In all cases, based on the obtained values of the correlation coefficient, Langmuir model fitted better the isotherms of ultrasound-assisted adsorption. Overall, this study can be regarded as positive background for ultrasound-assisted adsorption as industrial-scale application.