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Corncob-derived biochar as a cleaner technology for microplastic removal and energy recovery in a continuous-flow filtration system
Summary
Researchers packed fixed-bed columns with corncob-derived biochar and passed polystyrene microplastic suspensions through them, achieving up to 97.85% removal efficiency at pH 9 via physical entrapment and hydrophobic interactions, while also demonstrating that spent biochar has increased energy value (31.82 MJ/kg) suitable for recovery.
Microplastic contamination is a critical environmental issue, highlighting the need for effective and sustainable treatment strategies. This study investigates the removal performance of polystyrene (PS) microplastics in a continuous-flow fixed-bed column packed with corncob-derived biochar. Corncob was selected as the precursor due to its simple preparation, absence of chemical additives, low cost, and wide availability. Removal efficiency was evaluated under varying pH, bed height, flow rate, and particle size. The highest efficiency was observed at pH 9, reaching 97.85% within 20 min. Bed height strongly influenced performance: the 0.5 cm bed reached clogging earlier, whereas the 1.5 cm bed maintained higher removal efficiency for a longer duration, achieving 97.85% at 20 min and declining to 64.62% after 300 min. Flow rate substantially affected efficiency, with 97.85%, 66.67%, and 73.66% observed at 1.0, 0.5, and 0.3 mL/min, respectively, after 20 min. Particle size also played a significant role, with efficiencies of 98.39%, 97.85%, and 61.45% for the >125–250 μm, 63–125 μm, and <63 μm fractions, respectively. Mechanistic analyses suggest that PS removal is likely governed by a combination of physical entrapment within inter-particle spaces, surface adsorption via hydrophobic and π–π interactions, and weak hydrogen bonding with oxygen-containing functional groups, inferred from FE-SEM and FTIR observations. Furthermore, energy valorization analysis demonstrated that the higher heating value of corncob increased from 19.86 to 28.06 MJ/kg after pyrolysis and further to 31.82 MJ/kg following PS filtration. Overall, corncob-derived biochar provides a low-cost, sustainable, and effective approach for microplastic removal, integrating filtration performance with energy recovery and supporting circular utilization of agricultural residues. • Corncob biochar removes PS microplastics in continuous-flow columns. • Up to 97.85% removal at pH 9 within 20 min. • Bed height, flow rate, and size govern efficiency and clogging. • Removal via entrapment, hydrophobic and π–π interactions. • Spent biochar gains HHV (to 31.82 MJ/kg) enabling energy recovery.