Countercurrent Streams

At pH 4.8 and 50 C, semi-continuous countercurrent saccharification was performed using a-cellulose. Every second day, solids and liquids were transferred countercurrently and liquid samples were taken to determine sugar concentration in each stage. Train 1 (5 mg protein/g biomass, 8 stages) achieved 87.8% glucose conversion and 102 g/L total sugar. Train 2 (2 mg/g, 8 stages) achieved 56.1% glucose conversion and 65 g/L total sugar. Train 3 (2 mg/g, 16 bottles) achieved 73.6% glucose conversion and 67 g/L total sugar. Compared to 5-day batch saccharification, to achieve the same glucose conversion, enzyme requirements were reduced by factors of 16.8, 8, and 20.5 for Trains 1, 2, and 3, respectively. Further improvements can be realized by changing the enzyme addition point and increasing the number of stages.

Using the sugar platform, enzymes are a major cost contributor in biofuel production. Conventionally, enzymatic saccharification is performed in batch. To more efficiently use enzymes, a new continuous countercurrent method is explored. Pseudo-continuous countercurrent saccharification was performed on lime-pretreated corn stover at enzyme loadings of 1 mg CTec3/g dry biomass and (1 mg CTec3 þ 1 mg HTec3)/g dry biomass and the results were compared with batch. To achieve the same glucan conversion as compared to batch, countercurrent saccharification reduced enzyme loading by 1.6 and 1.4 times at 1 mg protein/g biomass and 2 mg protein/g biomass, respectively. In batch saccharification, the effect of hemicellulase addition was investigated. In countercurrent saccharification, as compared to only 1 mg CTec3/g biomass loading, adding 1 mg HTec3/g biomass increased glucose and xylose yields by 6% and 12%, respectively. The effect of product sugars on enzyme inhibition was studied in batch saccharification.

Corn stover was pretreated with submerged lime plus shock, a mechanical treatment that subjects biomass to a detonation wave. In a series of bottles, pretreated corn stover was countercurrently sac-charified with enzyme loadings of CTec3 (1 mg protein/g dry biomass), CTec3 (1 mg protein/g dry biomass) þ HTec3 (1 mg protein/g dry biomass), and CTec3 (2 mg protein/g dry biomass) þ HTec3 (2 mg protein/g dry biomass). To reach a given glucan conversion at low enzyme loadings, countercurrent saccharification reduced enzyme loadings by 1.9 times compared with batch saccharification but was not helpful at high enzyme loadings. To preserve the sugars during saccharification, volatile anti-microbials (chloroform and essential oils from thyme and oregano) prevent the growth of contaminating microorganisms. A simple packed column is proposed to perform commercial-scale countercurrent saccharification.