Accelerating lignocellulosic anaerobic digestion by cotreatment using the ball mill

Mechanical disruption of lignocellulosic biomass during fermentation, or cotreatment, has recently been introduced as an alternative to thermochemical pretreatment for enhancing biologically-mediated solubilization of cellulosic biomass. Cotreatment has been shown to be effective in increasing biomass digestibility in pure culture fermentation systems using Clostridium thermocellum (Paye et al., 2016, Balch et al., 2017). Here we explore the application of cotreatment to a mixed, anaerobic methanogenic cultures. An anaerobic digester was operated in semi-continuous mode with senescent switchgrass as the feedstock. Once the reactor reached steady-state, partially digested material from it was extracted and subjected to cotreatment using a ball mill. Following milling, another round of fermentation was performed on this partially digested and milled material. Biomass solubilization was determined by measuring methane production rates and consumption of sugars. In order to assess the feasibility of this milling process, energy consumption of the mill was measured during the cotreatment process. Particle size measurement was conducted to assess the extent of cotreatment milling on the biomass particles. Reported results include the extent to which cotreatment enhances methane production in mixed culture systems, the rate of solubilization of biomass, energy efficiency of the mill as a fraction of the total energy in the biomass, particle size change.