Solvent-free membrane extraction of volatile fatty acids from acidogenic fermentation.

Diversification of anaerobic digestion into higher value products, namely volatile fatty acids (VFAs), is receiving interest. One of the biggest challenges with this is recovery of the VFAs. Membrane extraction can be used, and a novel process configuration using a non-porous silicone membrane and water for an extractant is proposed here. This process would enable the reduction in the number of downstream unit operations compared to other membrane extraction processes. Selective recovery in favour of longer chain VFAs was demonstrated. Testing with a synthetic solution resulted in an overall mass transfer coefficient of 0.088 µm s-1 for butyric acid, and 0.157 µm s-1 when fermentation broth was used. This indicates this process is not hindered by fouling, but improved somehow. Although the preliminary economic analysis showed this process to require a larger membrane area compared to porous membrane alternatives, it also has a significantly reduced cost associated with the extractant.

Applied in situ product recovery in ABE fermentation.

The production of biobutanol is hindered by the product's toxicity to the bacteria, which limits the productivity of the process. In situ product recovery of butanol can improve the productivity by removing the source of inhibition. This paper reviews in situ product recovery techniques applied to the acetone butanol ethanol fermentation in a stirred tank reactor. Methods of in situ recovery include gas stripping, vacuum fermentation, pervaporation, liquid-liquid extraction, perstraction, and adsorption, all of which have been investigated for the acetone, butanol, and ethanol fermentation. All techniques have shown an improvement in substrate utilization, yield, productivity or both. Different fermentation modes favored different techniques. For batch processing gas stripping and pervaporation were most favorable, but in fed-batch fermentations gas stripping and adsorption were most promising. During continuous processing perstraction appeared to offer the best improvement. The use of hybrid techniques can increase the final product concentration beyond that of single-stage techniques. Therefore, the selection of an in situ product recovery technique would require comparable information on the energy demand and economics of the process. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 33:563-579, 2017.

A comparison of the energy use of in situ product recovery techniques for the Acetone Butanol Ethanol fermentation.

The productivity of the Acetone Butanol Ethanol (ABE) fermentation can be significantly increased by application of various in situ product recovery (ISPR) techniques. There are numerous technically viable processes, but it is not clear which is the most economically viable in practice. There is little available information about the energy requirements and economics of ISPR for the ABE fermentation. This work compares various ISPR techniques based on UniSim process simulations of the ABE fermentation. The simulations provide information on the process energy and separation efficiency, which is fed into an economic assessment. Perstraction was the only technique to reduce the energy demand below that of a batch process, by approximately 5%. Perstraction also had the highest profit increase over a batch process, by 175%. However, perstraction is an immature technology, so would need significant development before being integrated to an industrial process.