Cyclic Adsorption/Regeneration of Methylene Blue onto Prickly Pear Seeds Waste in a Fixed-Bed Column

The aim of this work is to highlight the effectiveness of the prickly pear seeds waste biomass (PPSW) as adsorbent to eliminate methylene blue (MB) dye from aqueous solution using fixed-bed column adsorption. A Batch study was conducted to prove the adsorption potential of the newly biosorbent. The adsorption isotherms were realized at three temperature (30, 40 and 50 °C) and medium pH and were modeled by the Langmuir and Freundlich models. The results confirmed that the adsorption of MB on PPSW was an exothermic reaction and well described by the Freundlich model. In Dynamic study, the effect of several parameters was investigated including the inlet concentration (20–120 mg/L), bed height (5–10 cm) and flow rate (1.8–10 mL/min). The obtained breakthrough curves (BTC) indicated that the breakthrough time and the removal efficiency increased from 8.5 to 26.9 min and from 22.46 to 32.15%, respectively, with the increasing of the bed height. Moreover, as the flow rate increased from 1.8 to 10 mL/min, the observed efficiency in dye removal declined from 54.5 to 22.48%. For modeling of adsorption dynamics, the application of empirical models such as Thomas, Yoon-Nelson and Clark gave a good approximation of experimental behavior with an error that didn’t exceed 2%, except for that of BDST which was not suitable for some operating conditions. A Regeneration study also was performed on saturated PPSW with different agents such as distilled water at 70 °C, ethanol, acetic acid and sodium hydroxide. The results showed that the regeneration with chemical agents doubled the adsorption capacity since it activated the biomass, otherwise the regeneration by distilled water ensured a constant adsorption capacity for almost 4 cycles.