Performic acid pre-treatment of poplar biomasses grown on a contaminated area for enhanced enzymatic digestibility: A viable route to obtain fine-products and recovery of contaminants

Biomasses obtained from green remediation strategies can represent a new valuable feedstock for obtaining fine chemicals and/or next generation liquid fuels. A sustainable chain of technologies for recovering chemicals from poplar grown in a multi-contaminated area is presented here in this work. A pre-treatment based on the use of performic acid (generated in situ from formic acid and hydrogen peroxide) was designed and tested. The effect of this pre-treatment was measured in terms of delignification, the increased enzymatic digestibility of the solid residues, and final destination of the mineral components initially present in poplar biomass. Upon treatment with performic acid at 1.75, 3.5 and 7 M, the content of lignin in the residual biomasses resulted as being significantly reduced: 28.5, 92.8 and 100% of initial lignin were removed and dissolved. After this pre-treatment, most of minerals initially present in poplar biomass were dissolved during the generated aqueous phase. In concomitance, a large part of the initial lignin and xylose were also dissolved. The solid residues obtained from the pre-treatment phase were then subjected to hydrolysis. Enzymatic digestibility was proven to be already effective on samples pre-treated with 3.5 M performic acid at 55 °C. Indeed, even when lignin was not completely removed (>75%), the cellulose in the residual biomasses was completely hydrolysed in glucose through a commercial cellulase (from Trichoderma reesei). Finally, the aqueous solution obtained from enzymatic hydrolysis was effectively reacted in presence of AlCl3·6H2O (1%) and sulphuric acid (0.5%) at 150 °C for 45 min. A final yield of 68.2% of levulinic acid and 4.8% of hydroxymethyl furfural were eventually obtained. Through this process, not only were the majority of metals coming from the plant-assisted bioremediation process/strategy confined to an aqueous solution, but also residual poplar biomasses were valorised by generating platform molecules which might find applications in the production of fine-chemicals.