(446g) Production of Polyhydroxybutyrate from Forest Residue Using a Chemical-Free Pretreatment

Polyhydroxybutyrate (PHB) is a class of biodegradable and biocompatible biopolymers, which is one of the alternatives to degradation-recalcitrant petroleum-based plastics. PHB production and application have been limited on a commercial scale despite considerable interest and effort, mostly because of high production costs. Abundant and low-cost lignocellulosic biomass can be used as carbon sources to lower the overall bioplastic production cost. Forest residue biomass (FRB) generated from harvesting operations, including tops, branches and low-grade wood material, is one of the lowest cost and abundantly available feedstock to produce sugars that can be subsequently fermented to produce PHB. However, FRB has a recalcitrance structure which makes a pretreatment step necessary to improve the biomass hydrolysis efficiency. Conventional pretreatment processes use acids or alkalis at high temperatures and pressures, which results in high energy use and the formation of intermediate compounds inhibitory to fermentative microorganisms. Alternatively, biomass can be pretreated using a sequential hydrothermal pretreatment-disk refining process and obtain hydrolysis yields similar to those from chemically pretreated biomass. The objective of this work is to optimize the two-stage hydrothermal pretreatment conditions to maximize sugar yields for PHB production. The pretreatment experiments were performed using a central composite design for three variables: temperature (160-200 ℃), time (10-20 min), and solid loading (10-20 %). Hydrothermally pretreated biomass was disk milled and hydrolyzed using commercial cellulase and hemicellulase enzymes. The sugar yields of pretreated biomass were higher than untreated biomass for all pretreatment conditions. The high severity pretreatment (213.6℃, 15 min, and 15% solid loading) resulted in more than 95% glucan conversion. However, pretreatment at these conditions resulted in only 21% hemicellulose recovery after hydrolysis, due to sugar degradation. The pretreatment conditions of 194.8℃, 12.9 min, and 13.4% solid loading were found optimum for maximizing the total sugar conversions (87.8%). The hydrolysate obtained from the hydrolysis of biomass pretreated at these optimized conditions will be evaluated as the carbon source for PHB synthesis by Recombinant Escherichia coli LSBJ and the results will be compared with the PHB yield from pure sugars.