Biorefining of high ligno-cellulosic waste biomass via pyrolysis coupled with anaerobic digestion. An LCA study

The sustainable processing of biomass into a spectrum of products and energy is the goal of a biorefinery. Sustainability is key in this process and all biorefineries should be designed for sustainability along the entire value chain. A laboratory-scale plant has been built by the University of Bologna, coupling pyrolysis and anaerobic digestion, in order to treat high ligno-cellulosic waste biomass. This technology set can bring a wider range of exploitable residual biomasses in anaerobic digestion. A life cycle assessment has been conducted on the use of corn stover in this experimental plant. The assessment included changes in land-use and soil carbon stock, biochar application to agricultural soils, biomass collection and pre-treatment, and biochar valorization as fertilizer and for carbon storage. The system is compared to a fossil reference system providing the same set of products. Results show that the process can yield a net energy gain and reduce GHG emissions, but high variability affects some key parameters, such as the energy required by the pyrolyzer and the biogas output from the anaerobic digester. As for the carbon balance, a relevant contribution is given by carbon storage in biochar.