Integrated Membrane Processes for Separation and Purification of Organic Acid from a Biomass Fermentation Process

During biomass (e.g., waste wood chips) decomposition under an anaerobic fermentation process, organic acids such as acetic acid and butyric acid are continuously produced from controlled microbial activity. Since the accumulation of organic acids hinders the microbial metabolism in the fermentation broths, the organic acids should be removed by using appropriate separation processes. A few separation processes such as extraction, electrodialysis, and distillation have been reported, but they still have many limitations such as high energy input and environmental problems (e.g., toxic chemical effluents). The integrated membrane processes proposed here, including the three steps of (1) clarification of fermentation broth, (2) organic acid separation, and (3) dewatering, can be applied to achieve energy-efficient and environmentally friendly organic acid removal and recovery. First, microorganisms and large insoluble particles in fermentation feed can be mostly removed by clarification steps using microfiltration or ultrafiltration processes. In this study, we focused only on organic acid separation and dewatering processes using nanofiltration and forward osmosis membrane processes. Using nanofiltration (or high-flux reverse osmosis) membranes, aqueous organic acids can be selectively separated from pretreated fermentation feed solutions while other organics and many salts can be rejected using these processes by varying pH conditions in the feed. Finally, a low-energy-consuming forward osmosis process was applied for dewatering in the aqueous organic acid solutions to concentrate organic acid. The concentrated organic acid was successfully obtained by using conventional desalination and/or commercial forward osmosis membranes.