Effective Pretreatment of Heavy Metal-Contaminated Biomass Using a Low-Cost Ionic Liquid (Triethylammonium Hydrogen Sulfate): Optimization by Response Surface Methodology Box-Behnken Design

Recently, dealing with generated heavy metal contaminated biomasses (HMCBs) harvested from phytoextraction process has drawn increasing attention. In this study, the feasibility of an HMCB (willow) pretreatment using a low-cost ionic liquid (IL), namely, triethylammonium hydrogen sulfate [TEA] [HSO4], is investigated to remove the high contents of HMs prior to further thermochemical and biological valorization. The operating variables were temperature (75-105 degrees C), IL:biomass (10:1-30:1) ratio, and time (4-8 h) with constant feedstock particle size (0.35 mm). According to results obtained from response surface methodology-Box Behnken design (RSM-BBD), the optimum conditions of the IL-based pretreatment of HMCB for maximum HMs' removal are temperature, 93 degrees C; IL:biomass ratio, 30:1; and time, 7.12 h. Under the optimum conditions, the IL is found to solubilize lignin and hemicellulose respectively about 70.54% and 92.56%; and subsequently, effective removal of HMs from HMCB is obtained (Cu, 100%; Zn, 88.77%; Mn, 79.70%; Fe, 73.11%; Cd, 70.42%; AI, 34.53%; and Cr, 18.17%), while Pb removal is negligible. The average amount of confidence intervals of developed models is similar to 95%, and generally, the ratio of IL:biomass shows a higher effect on the efficiency of biomass fractionation and HMs' removal, compared with temperature and time; however, interactions between the operating parameters are negligible.