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Limitations of a membrane gradostat bioreactor designed for enzyme production from biofilms of Phanerochaete chrysosporium.

Growing interest has been shown in the continuous production of high-value products such as extracellular secondary metabolites used in the biotechnology, bioremediation and pharmaceutical industries. These high-value extracellular secondary metabolites are mostly produced in submerged fermentations. However, the use of continuous membrane bioreactors was determined to be highly productive. A novel membrane bioreactor, classified as a membrane gradostat reactor (MGR) was developed to immobilize biofilms to produce extracellular secondary metabolites continuously using an externally unskinned and internally skinned membrane. Anaerobic zones were identified in the MGR system when air was used for aeration. To improve the MGR system, limitations related to the performance of the bioreactor were determined using P. chrysosporium. A DO penetration depth of +/-450 microm was identified after 264 h, with the anaerobic zone thickness reaching approximately 1,943 microm in the immobilised biofilms. The penetration ratio, decreased from 0.42 after 72 h to 0.14 after 264 h. This led to the production of ethanol in the range of 10 to 56 mg/L in the MCMGR and 7 to 54 mg/L in SCMGR systems. This was attributed to an increase in beta-glucan within immobilised biofilms when an oxygen enriched aeration source was used. Increasing lipid peroxidation and trace element accumulation was observed with the use of an oxygen enriched aeration source.