RECIRCULATING CALCIUM HYDROXIDE SOLUTION: A PRACTICAL CHOICE FOR ON-FARM HIGH SOLIDS LIGNOCELLULOSE PRETREATMENT

Pretreatment is a necessary step in the utilization of lignocellulosic biomass for biochemical conversion to higher value products. There are multiple chemical choices for industrial settings, however on-farm choices are constrained to near ambient conditions with minimal specialized equipment, training, and limited waste disposal. Calcium hydroxide (lime) is suitable for on-farm use. This work presents the novel idea of pretreating biomass by recirculating a filtered, saturated lime solution in an up-flow, high solids (14-16% w/w) configuration at ambient conditions. In this system, lime solids were efficiently consumed, post-pretreatment washing of substrate did not significantly improve glucose yields, and energy and resources were conserved. Pretreatment effectiveness was assessed by glucose yield comparisons for both switchgrass and corn stover. Using mean glucose yields from 5mm corn stover, lime pretreatment required 350kgs of dry stover to produce 100kgs glucose at a chemical cost of $8.67 while NaOH required 300kgs at a cost of $22.38. The recirculation concept was used to enzymatically hydrolyze pretreated substrate in-situ with an initial solids content of 14-16% (w/w). The bulk in-situ hydrolysis produced mean glucose yields ~70% greater than an NREL hydrolysis modified to 16% (w/w) solids and reached ~77% of the yield of an NREL hydrolysis at 2.7% (w/w) solids