Reverse osmosis fermentation broths

STY is high for a fermentative procedure and ranges from 140 g L-1 d 1 for a continuous tank reactor to 1.2 kg IT1 d 1 in a continuous tower reactor with cell recycle. Depending on the ethanol tolerance of the production species, ethanol is produced to a concentration of 12-20%. The ethanol is traditionally recovered from the fermentation broth via an energy-intensive distillation step, but it is sought to replace the latter by pervaporation or reversed osmosis [25]. 

Several methods have been explored for the economical recovery of lactic acid from fermentation broth including extraction with solvent, electrodialysis, ion-exchange adsorption (see [14] for review), and reverse osmosis [15]. Wang et al. 

The potential of membrane separation techniques (such as cross-flow microfiltration(MF), ultrafiltration (UF), Reverse Osmosis (RO)and electrodialysis (ED) ) and membrane reactors in the treatment of fermentation broths are huge. The synergistic effects obtainable by designing the overall biotechnological process combining various membrane technique are particularly significant. 

Abstract The processes of lactic acid production include two key stages, which are (a) fermentation and (h) product recovery. In this study, fiee cell of Bifidobacterium longum was used to produce lactic acid from cheese whey. The produced lactic acid was then separated and purified from the fermentation broth using combination of nanofiltration and reverse osmosis membranes. Nanofiltration membrane with a molecular weight cutofif of 100-400 Da was used to separate lactic acid from lactose and cells in the cheese whey fermentation broth in the first step. The obtained permeate from the above nanofiltration is mainly composed of lactic acid and water, which was then concentrated with a reverse osmosis membrane in the second step. Among the tested nanofiltration membranes, HL membrane from GE Osmonics has the highest lactose retention (97 1%). In the reverse osmosis process, the ADF membrane could retain 100% of lactic acid to obtain permeate with water only. The effect of membrane and pressure on permeate flux and retention of lactose/lactic acid was also reported in this paper. 

The objectives of this study were (1) to evaluate the performance of nanofiltration filtration membrane for separation of lactose from lactic acid in the fermentation broth and (2) to evaluate the performance of reverse osmosis for lactic acid concentration in the permeate of the nanofiltration. The diagram for the proposed process for lactic acid production and separation was shown in Fig. 1. 

Combined nanofiltration and reverse osmosis membranes could successfully separate and concentrate lactic acid from cheese whey fermentation broth. Nanofiltration membrane could retain about 97% of lactose to obtain permeate mainly containing lactic acid and water. The highest lactose retention of 97% was obtained with the HL membrane. The tested reverse osmosis membranes successfully separated lactic acid from water. Nearly 100% of lactic acid retention was obtained with the ADF membrane. 

Numerous endeavors have been implemented in fermentation process development in order to alleviate the solvent-induced inhibitory effects and thus improve the fermentation productivity. Usually, the selective removal of fermentation products was integrated simultaneously into the fermentation process in order to maintain a low solvent concentration in the fermentation broth. Many online butanol removal techniques have been reported with various advantages and efficiencies, including liquid-liquid extraction, perstraction, gas stripping, pervaporation, adsorption, reverse osmosis, etc. 

Timmer, J. M. K., Kromkamp, J., Robbertsen, T. (1994). Lactic acid separation from fermentation broths by reverse osmosis and nanofiltration. Journal of Membrane Science, 92, 185-197. 

In the next step, the filtered fermentation broth is contacted with an extracting solvent in a mbter-setder type of device (Section 6.4.1.2) the solvent extracts the antibiotic from the broth, aiong with many reiated and nonrelated compounds. Countercurrent extracting cascades in the form of centrifugal extractors are employed (Section 8.1.4, Figure 8.1.35) to reduce the contact/residence time. This process is often called product isolation in that the product has been isoiated from the broth however, the solvent extraction process extracts other compounds as well fram the broth. Often, adsorption (Section 7.1.1) as well as membrane processes such as ultrafiltration and reverse osmosis may be used (Sections 7.2.1.3 and 7.2-1.2). Sometimes, such a step results in a significant increase in product concentration. 

It is useful now to identify the concentration of the antibiotic product (i.e. the titer) during the different steps identified earlier (Belter et al., 1988). The product concentration level in the fermentation broth may vary between 0.1 and 5 g/liter. Removal of insolubles via microfiltration, rotary vacuum filter and centrifuging increases the product concentration marginally, in the range of 1-5 g/liter. Product isolation via solvent extraction enhances the product concentration to 5-50 g/liter. Purification by chromatography or crystallization leads to a product concentration level between 50 and 200 g/liter. The polishing step may not enhance the concentration in general much, but it certainly improves the purity. If a membrane process such as reverse osmosis is used to concentrate a very dilute solution of the antibiotic, 10-30 times the initial concentration may be achieved. 

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