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  • 1
    Electronic Resource
    Electronic Resource
    Fouling effects of yeast culture with antifoam agents on microfilters (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 53 (1997), S. 10-16 
    Details
    ISSN: 0006-3592
    Keywords: microfiltration ; fouling ; yeast ; antifoam agents ; depressurization ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The fouling effects of yeast fermentation broths of Candida utilis in the presence of various commercial antifoam agents (PPG2000, B5600, and G832) up to 4.0 mL/L were studied, using Millipore polyvinylidene fluoride 0.22-μm hydrophilic membranes (GVWP), in a stirred-cell system at 50 kPa and 700 rpm. PPG2000, which has a low value of work of adhesion (Wa of 0.81 mN/m), gave a steady flux of broth of 29 L/(h m2) and was found to have no significant fouling effect on the microfiltration of broth. G832, which has a high Wa, (26.0 mN/m) reduced the flux of the broth to 17 L/(h m2); i.e., by 42% when only 1.0 mL/L was used. However, B5600, which has a Wa of 14.3 mN/m, was found to enhance the flux of broth to 54 L/(h m2); i.e., by 86%, due to the preferential adsorption of the B5600 components onto the hydrophobic cell contents released. These results were reinforced by the depressurization experiments performed with both hydrophilic (GVWP) and hydrophobic (GVHP) membranes, using both young and aged broths. B5600 was found to be the optimum antifoam agent in this study in terms of membrane performance and defoaming efficiency. © 1997 John Wiley & Sons, Inc.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Hydraulic resistance and fouling of microfilters by Candida utilis in fermentation broth (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 48 (1995), S. 108-117 
    Details
    ISSN: 0006-3592
    Keywords: microfiltration ; hydrulic resistance ; fouling ; yeast ; depressurization ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The hydraulic resistance and membrane fouling effects of Candida utilis in fermentation broth were investigated using Millipore PVDF 0.22-μm membranes (GVWP and GVHP) in a stirred-cell system at 50 kPa and 700 rpm. With the various components of broth, spent medium, which contains colloidal particles and macromolecules having sizes (0.32 to 2.67 μm) comparable with the membrane pores (actual range 0.26 to 0.63 μm), was found to be the major contributing factor to the membrane fouling by broth through pore plugging. This led the spent medium to exhibit the highest hydraulic resistance (Rsm of 5.8E + 12 m-1) and percentage flux loss (81.0%) when compared with either intact cells alone in buffer or to whole broth. Intact cells appeared to physically block and protect the pores without significant adhesion, because of the relatively hydrophilic nature of their cell walls (hydrophobicity of 5.9% at hour 36), resulting in the lowest hydraulic resistance (Rsbc of 7.5E + 11m-1) and percentage flux loss (19.3%).However, the hydraulic resistance and percentage flux loss of broth increased as cells aged. This was attributed to the increase in particle loading (intact cells by 15.37%, released cell contents and cell fragments) and in the hydrophobicity of cell walls. Autoclaved broth, lysed broth and aged broth, which contained a larger portion of colloidal particles and released cell contents caused a more pronounced fouling effect. This was revealed by the absence of flux recovery after depressurization with continuous stirring, even when a hydrophilic membrane was used. Furthermore, the hydrophobicity of C. utilis was found to increase with yeast extract present in medium, and use of hydrophobic membranes helped enhance the fouling effect. Overall, the degree of irreversible membrane fouling could be revealed by the value of Rsm/Rt′ and the hydraulic resistance, which resulted from concentration polarrzation, could be revealed by the value of Rc/Rt′ where Rt = Rm + Rsm + Rc′ and Rm is the clean membrane resistance. © 1995 John Wiley & Sons, Inc.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260480204
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  • 3
    Electronic Resource
    Electronic Resource
    Fouling of microfiltration membranes by broth-free antifoam agents (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 56 (1997), S. 89-98 
    Details
    ISSN: 0006-3592
    Keywords: antifoam agents ; hydraulic resistance ; membrane fouling ; FESEM photographs ; PVDF membranes ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The fouling tendencies of seven commercial antifoam agents used with microfiltration membranes were investigated in a stirred cell. Parameters such as viscosity, oil droplet size distribution, contact angle, work of adhesion (Wa), membrane type, operating pressure, and feed concentration were examined. The results show that a silicone-based antifoam, G832, gave a significantly lower flux (≤100 L h-1 m-2) than the polypropylene glycol antifoam PPG2000 (1500-2500 L h-1 m-2) over the concentrations from 0.5 to 4.0 mL L-1 at 50 kPa, 700 rpm, and 25°C. The significantly lower flux attained by the antifoam G832 was attributed to a number of factors, such as its greater viscosity (1.25 × 10-3 kg m-1 s-1 compared with 1.05 × 10-3 kg m-1 s-1 for PPG2000), a smaller average oil droplet size (0.28 vs. 0.65 μm) comparable to the membrane pore size distribution (0.26-0.62 μm), a higher contact angle (98 vs. 51°); and a significantly larger value of work of adhesion (26.0 vs. 0.81 mN m-1). The different magnitudes of membrane adsorption by these antifoam agents, as reflected by their values of work of adhesion, were also observed in the field emission scanning electronic microscopy photographs. In terms of membrane type, the inorganic Anopore alumina membrane was found to offer a higher PPG flux than the organic Millipore polyvinyl difluoride (PVDF) membranes (both hydrophilic and hydrophobic). Furthermore, the mixed-type antifoams (B5600, B426, and G832) were found to give an increased hydraulic resistance and fouling percentage with an increase in pressure or feed concentration. Conversely for PPG2000, a reduction of the hydraulic resistance and fouling percentage was observed with increases of these two parameters. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 89-98, 1997.
    Additional Material: 9 Ill.
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