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The development of a cost-effective hydrolysis for crude cellulose is an essential part of biorefinery developments. To establish such high solid hydrolysis, a new solid state reactor with static mixing is used. However, concentrations >10% (w/w) cause a rate and yield reduction of enzymatic hydrolysis. By optimizing the synergetic activity of cellulolytic enzymes at solid concentrations of 9%, 17% and 23% (w/w) of crude Organosolv cellulose, glucose concentrations of 57, 113 and 152 g L⁻¹ are reached. However, the glucose yield decreases from 0.81 to 0.72gg⁻¹ at 17% (w/w). Optimal conditions for hydrolysis scale-up under minimal enzyme addition are identified. As result, at 23% (w/w) crude cellulose the glucose yield increases from 0.29 to 0.49gg⁻¹. As proof of its applicability, biobutanol, succinic and itaconic acid are produced with the crude hydrolysate. The potential of the substrate is proven e.g. by a high butanol yield of 0.33gg⁻¹.
Due to the interfering effects of acetic acid in many fermentation processes, a gas-diffusion technique was developed for the online determination of acetic acid. The measurements were accomplished with a flow diffusion analysis (FDA) unit from the TRACE Analytics GmbH, Braunschweig, Germany. The diffusion analysis is based on the UV-absorbance of acetic acid at 205 nm. The measurement was achieved by the separation of an acceptor and a carrier stream (acidified fermentation broth) using a gas permeable polytetrafluoroethylene (PTFE) membrane, whereby broth constituents that would otherwise disturb the UV-measurement of acetic acid, are held back efficiently. Merely, the fermentation by-products, e.g. formic acid, is capable of diffusing through the membrane. While formic acid can disturb the measurement, carbon dioxide does not absorb at 205 nm. The method operates with time-dependent sample enrichment. During the analysis, a small volume of the acceptor stream is stopped for a defined time interval in the acceptor chamber. During this period, the gaseous acetic acid diffuses through the membrane and is enriched in the acceptor chamber. Subsequently after the enrichment, the acceptor stream flows through a UV-detector. The intensity of the signal is proportional to the acetic acid concentration. Online measurements in bioreactors via a sterile filtration probe have been accomplished. A linear calibration in the range of 0.5–5.0 g/L acetic acid with a relative standard deviation of <5 % was obtained. A sampling rate of 8 samples per hour was possible. The system was applied for the determination of acetic acid in E. coli fermentation broth. The instrument is easy to clean, very user-friendly and does not require any toxic or expensive reagents.
Biotechnological downstream processing is usually an elaborate procedure, requiring a multitude of unit operations to isolate the target component. Besides the disadvantageous space-time yield, the risks of cross-contaminations and product loss grow fast with the complexity of the isolation procedure. A significant reduction of unit operations can be achieved by application of magnetic particles, especially if these are functionalized with affinity ligands. As magnetic susceptible materials are highly uncommon in biotechnological processes, target binding and selective separation of such particles from fermentation or reactions broths can be done in a single step. Since the magnetizable particles can be produced from iron salts and low priced polymers, a single-use implementation of these systems is highly conceivable. In this article, the principles of magnetizable particles, their synthesis and functionalization are explained. Furthermore, applications in the area of reaction engineering, microfluidics and downstream processing are discussed focusing on established single-use technologies and development potential.