Membrane recycle bioreactor

By resorting to the so-called membrane recycle bioreactors (MBR) (Bubbico et al., 1997 Enzminger and Asenjo, 1986), continuous recycling of the culture broth through crossflow MF modules allows removal of the inhibiting metabolites, this helping to maximize cell density in the bioreactor, as well as bioproduct formation rate. Further ED treatment of MF permeates gives rise to two streams, a diluted one to be recycled back into the bioreactor, and a concentrated one to be supplementary refined. 

Bubbico, R., Lo Presti, S., and Moresi, M. 1997. Repeated batch citrate production by Yarrowia lipolytica in a membrane recycle bioreactor. In Engineering Food at ICEF7. Part I (R. Jowitt, ed.), pp. B21-B24. Sheffield Academic Press, Sheffield, UK. 

A process flow diagram for producing ethanol and lactic acid from cheese whey by fermentation with the aid of a membrane recycle bioreactor (MRB) is shown in Figure 3.26 [23]. The UF permeate (WPC in the retentate) contains lactose, nonprotein nitrogen and dissolved salts and is then concentrated by RO to the desired sugar... 

Figure 3.26 Processing of cheese whey using multiple membrane systems and a membrane recycle bioreactor. Source Cheryan, Copyright 1998 from Ultrafiltration and Microfiltration Handbook by M. Cheryan. Reproduced by permission of Routledge/Taylor Francis Group, LLC.

Escobar et al (2001) did a complete study in which pilot plant trials were conducted in a corn wet mill with a 7000-L membrane recycle bioreactor (MRB) that integrated ceramic microflltration membranes in a semi-closed loop configuration with a stirred-tank reactor. Residence times of 7.5-10 h... 

Mehaia M A, Cheryan M, (1986), Lactic acid from acid whey permeate in a membrane recycle bioreactor . Enzyme and Microbial Technology, 8(5), 289-292. 

Added productivity of lactic acid fermentations can be achieved by combining continuous systems with mechanisms that allow higher bacterial cell concentrationsResearch is concentrated on two mechanisms (1) membrane recycle bioreactors (MRBs) and (2) immobilized cell systems (ICSs). The MRB consists of a continuous stirred-tank reactor in a semiclosed loop with a hollow fiber, tubular, flat, or cross flow membrane unit that allows cell and lactic acid separation and recycle of cells back to the bioreactor. The results of a number of laboratory studies with various MRB systems demonstrate the effect of high cell concentrations on raising lactic acid productivity (Litchfield 1996). O Table 1.12 lists examples of published results employing various MRB systems. 

Examples of lactic acid production in membrane recycle bioreactors... 

The production of substances that preserve the food from contamination or from oxidation is another important field of membrane bioreactor. For example, the production of high amounts of propionic acid, commonly used as antifungal substance, was carried out by a continuous stirred-tank reactor associated with ultrafiltration cell recycle and a nanofiltration membrane [51] or the production of gluconic acid by the use of glucose oxidase in a bioreactor using P E S membranes [52]. Lactic acid is widely used as an acidulant, flavor additive, and preservative in the food, pharmaceutical, leather, and textile industries. As an intermediate product in mammalian metabolism, L( +) lactic acid is more important in the food industry than the D(—) isomer. The performance of an improved fermentation system, that is, a membrane cell-recycle bioreactors MCRB was studied [53, 54], the maximum productivity of 31.5 g/Lh was recorded, 10 times greater than the counterpart of the batch-fed fermentation [54]. 

Kubota A process for treating mnnicipal wastes, incorporating a membrane throngh which the liqnor is recycled to a bioreactor. Eight plants were operating in 1996. Developed in Japan. 

A key consideration in development of all multi-step bioprocesses is the type of bioreactor it may be necessary to accommodate a range of conditions including compartmentalization of the enzymes, cofactor recycle, adequate oxygen supply, variable temperature and pH requirements, and differential substrate feed rates. Examples described below include a range of different reactors, of which membrane bioreactors are clearly often particularly useful. 

A great deal of research work has been carried out to enhance bioreactor productivity (2 14 kg m 3h 1) using cell recycle via membrane processing (Boyaval and Corre, 1987 Boyaval et al., 1994) and recovering propionic acid by monopolar or bipolar ED (Boyaval et al., 1993 Weier et al., 1992 Zhang et al., 1993). 

Curcio S, Calabro V, Iorio G (2006) A theoretical and experimental analysis of a membrane bioreactor performance in recycle configuration. J Membr Sci 273 129-142... 

Goulas AK, Cooper JM, Grandison AS, Rastall RA (2004) Synthesis of isomaltooligosac-charides and oligodextrans in a recycle membrane bioreactor by the combined use of dextransucrase and dextranase. Biotechnol Bioeng 88 778-787... 

Papeterie du Rhin, Paper Roll Mill, France. In 1999, Veolia Water STI installed an MBR with Zeeweed ultrafiltration membranes (pore size 0.04 p.m) in Papeterie du Rhin s paper roll mill in France (Table 35.1). Recycled (not deinked) paper is used as the raw material. The bioreactor (1500 m ) is operated at a mixed liquor suspended solids (MLSS) content of 12-16 g/L. Brockmann and Praderie [58] report an average flux of 15 L/(m h) at a pressure of 0.15 bar over a 1 year filtration period. The wastewater from the mill is first prescreened with dmm screens, then sent to an equalization basin, from which it is pumped directly into the bioreactor. Table 35.6 summarizes the performance of the MBR process. The pressure used to draw the water through the membrane is 7-55 kPa. The filtrate is partly recycled as process water [27,57,58]. 

The waters in question are pumped to a membrane bioreactor equipped with an air injection system, where part of the feed is recycled, making it move across a membrane ultrafiltration system, to prevent the presence of suspended microelements in the later phase of reverse osmosis. From the ultrafiltration process, two streams are obtained a concentrated stream of salts and microbial mass, which is recycled to the bioreactor, and a permeate stream that passes to the reverse osmosis plant. 

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