Ozonation as Biomass Pretreatment for Ethanol Production - Studying Tannic Acid as a Model

Lignocellulosic biomass is a promising feedstock for production of ethanol. Such wastes are rich in cellulose and hemicellulose, but also in lignin that inhibits the activity of cellulolytic enzymes. Ozonation is a well-established process for removal of phenols (such as lignin) but total removal requires high dose of ozone, making the process energy inefficient. We have studied this process using a semi-batch ozonation system containing high concertation aqueous Tannic Acid solution (60g/L) as a lignin model, followed by addition of carboxymethyl cellulose (CMC) and testing for saccharification activity by cellulase.

Full phenol removal (and 18% removal of dissolved organic carbon) took more than 3 hours ozonation (TOD > 11,000 mgO₃/L). The phenol removal demonstrated triple-phase kinetics with two transition points. Interestingly, full cellulase activity was recovered near the first transition point, after only 3-10 min ozonation (TOD = 142-348 mgO₃/L), and removal of only ~50% of the phenol and only 3% of the dissolved organic carbon. These results demonstrated that short ozonation could offer an energy efficient pretreatment for lignocellulose and full phenol degradation is not necessary, dramatically reducing energy costs, and could promote a new, economic and competitive pretreatment process that will suit future industrial applications.

Reference: Peretz R., Gerchman Y. and Mamane H. (2017), Ozonation of tannic acid to model biomass pretreatment for bioethanol production, Bioresource Technology, 241: 1060-1066