Short Ozonation of Lignocellulosic Waste as Energetically Favorable Pretreatment

Lignocellulosic waste (here municipal trimmings) is a promising sustainable feedstock for ethanol production, but requires costly and polluting pretreatment, often resulting in toxic by-products. Ozonation, nonpolluting, effective pretreatment method, is not used commercially due to high energy requirements of ozone production at high ozone doses needed. Our results, however, demonstrated that low-dose ozonation (15 min, accumulated TOD = 318 mg L⁻¹) of water-submerged waste resulted in improved enzymatic saccharification efficiency (31% of cellulose) compared to a non-ozonated sample (12%) although only 20% of the lignin was removed. Ozonation up to 90 min resulted in better conversion however exceptionally long ozonation (6 h and beyond) resulted in reduced conversion. These results suggest that contrary to common hypothesis, short ozonation could offer an effective and feasible pretreatment method for high sugar release without the need for delignification. In addition, the ozonation process was accompanied by changes in absorbance, mainly at 280 nm, making it a useful tool for process monitoring. Net calculated energy balance was positive for all ozonation regimes, with increased process efficiency at lower ozone doses. Furthermore, ozonation can be generated on-site and on demand, enabling decentralized pretreatment operated near the feed source, thus overcoming transportation costs.