Two-phase bioconversion product recovery by microfiltration I. Steady state studies

Abstract

Recovery of an aqueous bioconversion product from complex, two‐phase Pseudomonas putida broths containing 20% (v/v) soybean oil presents a significant challenge for downstream processing. Although not used before in multiple‐phase separation for complex biotech products, crossflow filtration employing ceramic filters is one of the most attractive options which allow the design of integrated, continuous bioconversion processes. As a first attempt, we studied multichannel, monolithic ceramic membranes of different nominal pore sizes and lumen diameters under steady‐state conditions. The best performance was obtained with 0.2‐μm‐pore/3‐mm‐lumen membrane, which completely rejected both cells and oil droplets from the permeate, creating a clear aqueous product stream. Although the same separation was achieved, the 50K molecular weight cut‐off (MWCO) ultrafilter showed greater irreversible but similar reversible resistance, in addition to an order‐of‐magnitude higher membrane resistance. Larger nominal pore microfilters, such as 0.45 and 1.0 μm, experienced both cell and oil leakage even at low transmembrane pressure (10 psig). Attributed to greater shear at the same recirculation rate, smaller lumen filters did provide greater permeate flux. However, for practical purposes, the 0.2‐μm‐pore/4‐mm‐lumen ceramic membrane was chosen for further evaluation. Transmembrane pressures up to 50 psig provided only marginal gains in filtration performance, whereas increasing shear rate resulted in linear increases in steady‐state flux, presumably due to formation of shear‐sensitive, complex gel/oil/cell layer near the membrane surface. A nominal shear rate of 9200 s−1 and 20 psig transmembrane pressure were chosen as optimal operating conditions. Additional studies in a clean system revealed that as low as 5% (v/v) soybean oil in deionized (DI) water resulted in an order‐of‐magnitude decline in steady‐state permeate flux. Breakthrough of oil droplets occurred at 35 psig transmembrane pressure. The severe fouling and breakthrough phenomena disappeared in the presence of washed cells for transmembrane pressure up to 43 psig, implying an oil/cell layer coating the membrane surface, thus preventing oil penetration. Serious membrane fouling was also experienced in microfiltration of oil‐free, cell‐free supernatant and oil‐free whole broth. Consequently, soluble proteins/surfactants were suspected to be the major membrane foulants. Interestingly, soybean oil up to 30% (v/v) enhanced the flux, presumably through complicated interactions with the major foulants. Regeneration of membrane was best achieved with protease and hot caustic/bleach treatments, supporting the hypothesized fouling mechanisms mentioned above. This work provides process and system information for batch microfiltration runs in the future, to be reported elsewhere as Part II of this work. © 1998 John Wiley & Sons, Inc. Biotechnol Bioeng 57: 631–641, 1998

Effect of Flow Configuration and Membrane Characteristics on Membrane Fouling in a Novel Multicoaxial Hollow‐Fiber Bioartificial Liver

“…The flux time course from the cross flow configuration (FIG. 2C) was consistent with other membrane-fouling studies in hollow-fiber bioreactors, 3,15 where there is an initial exponential decrease due to fouling, followed by a plateau over which flux remains relatively constant. In this study, a plateau was reached by 48 h (FIG.…”

Studies on the interaction of fermentation and microfiltration operations: Erythromycin recovery fromSaccharopolyspora erythraea fermentation broths

“…The carbon source in the SCM is glucose, a small water-soluble molecule that will have little effect on the subsequent microfiltration of the broth. In contrast, oil is a known foulant of microfiltration membranes (Conrad and Lee, 1998) and because there may be residual oil left at the desired harvest time of the fermentation, (approximately 2.5 gL −1 at the maximum erythromycin concentration), it will have a negative effect on the permeate flux and may also influence antibiotic transmission. The OBM also contains another insoluble component, soya flour.…”

“…In the case of crossflow microfiltration, this may occur due to a reduction in permeate flux or reduced transmission of the target molecule through the membrane. Several studies have observed the effects of individual media components on microfiltration operations, for example antifoams (Liew et al, 1997), and oils (Conrad and Lee, 1998). However, these investigations did not take into account the effects of these components on both the fermentation and recovery processes and the interactions between them.…”

Effect of stirring and pump on membrane processing of Aspergillus carbonarius culture broth for polygalacturonase

“…These systems fitted with various types of pumps, such as peristaltic, centrifugal, diaphragm, lobe and gear pumps have been used for processing microbial suspensions containing enzymes/proteins [6][7][8][9][10][11]. Even cross-flow systems encounter problems while processing enzyme feed stock owing to adsorption losses at the membrane surface and inactivation due to shear stress associated with pumping and high turbulence through the device and changes in the ionic environment [12,13].…”