Computer applications in bioprocessing.

Biotechnologists have stayed at the forefront for practical applications for computing. As hardware and software for computing have evolved, the latest advances have found eager users in the area of bioprocessing. Accomplishments and their significance can be appreciated by tracing the history and the interplay between the computing tools and the problems that have been solved in bioprocessing.

Growth of yeast colonies on solid media.

Colonies on nutrient agar of the aerobic yeast Candida utilis show linear increases in diameter and height with time throughout most of the growth cycle. The concentration of glucose in the agar has a negligible effect on radial growth rate although an increase in the glucose concentration prolongs the linear radial growth phase. The rate of increase in height of the colony is proportional to the square root of the initial glucose concentration. A new model that considers both glucose diffusion and oxygen diffusion in the colony is consistent with the observed colony profiles.

Enzyme management in the Iotech process.

In the Iotech process, steam explosion of wood chips potentials hydrolysis of the cellulose by enzymes. A small portion of the exploded wood is used as substrate for the production of enzymes for hydrolysis of the remaining wood. Explosions conditions degrade some of the hemicellulose, creating factors (probably related to furfural) that impair enzymatic hydrolysis and destabilized the cellulases. Fortunately, simple washing with water permits more rapid hydrolysis while enzyme stability is greatly improved. Enzymes can be recovered from the hydrolysis residue by adjusting the pH to neutrality, and additional enzymes from hydrolysis filtrate can be adsorbed on fresh exploded wood en route to hydrolysis. A simple mass balance calculation shows proportions of various activities in a mix of fresh and recycled enzymes.

Biomass refining.

Processes for refining biomass from trees or from agricultural residues are fast approaching commercialization. Advances have been made in acidic and enzymatic hydrolysis of the cellulose component of biomass and in some newer processes for biomass refining which leave the lignin fraction relatively intact. Rather than low-priced fuels, which have received the most publicity, initial targets will be products with more profit potential, such as chemicals and molasses. Curtailment of government support for alcohol fuel programs is not crucial, because private investment is taking biomass refining from the pilot plant to the demonstration scale.

Inhibition of cellulases by impurities in Steam-Exploded wood.

Steam explosion of hardwood chips produces impurities that reduce the activity and stability of cellulases. Washing the exploded wood with water removes the inhibitors and permits hydrolysis equivalent to that with purified cellulose.

Hanging magnetic stirrer which minimizes cell disruption.

A magnetic stirring bar enclosed in tubing forms a large paddle which produces good mixing at slow rotational speeds. It is suspended above the bottom of the vessel and cannot grind cells or become misaligned.