A technology for pilot production of bacterial cellulose from oat hulls

The complete production cycle of bacterial cellulose (BC) was studied on a pilot scale. Oat hulls, a globally abundant agricultural residue, was utilized as the feedstock. A technology for producing BC from oat hulls has been developed herein and involves four process operations: exclusive chemical pretreatment with HNO3, enzymatic saccharification, mixed-culture fermentation, and purification. The HNO3 pretreatment was studied under atmospheric pressure at concentrations of 2-6 wt%. The optimum HNO3 concentration for pretreatment of oat hulls was found to be 4 wt%. The pretreatment was run in a 250-L vessel to furnish a pulp in 37.5% yield with 71.5% Kurschner cellulose content. The resultant pulp was well hydrolyzable: enzymatic saccharification with commercial enzymes at an initial solid loading of 30.0 g/L resulted in 79.5% reducing sugar (RS) yield. However, the test synthesis of BC using Medusomyces gisevii showed a very low yield of only 3.5%. It was therefore decided to improve the pulp with the aid of 4 wt% NaOH, whereupon oat-hull cellulose was obtained in 24% yield comprising 93.2% alpha-cellulose. The enzymatic saccharification of oat-hull cellulose ended with 73.5% RS yield. The test synthesis of BC exhibited 11% yield. Then, the biotechnological stages were scaled up: enzymatic saccharification of oat-hull cellulose was performed in a 100-L fermentor, and BC synthesis in the resultant hydrolyzate was run in a Binder KB-400 incubator. After purification, the BC yield was 10% of the RS concentration. BC was composed of 100% cellulose I alpha-allomorph and had 93% crystallinity index. The BC production from oat hulls was thus scaled up successfully with an optimistic BC yield: 80.5 tons of 98%-wet hydrogel per 100 tons of oat hulls.