Limitations of a membrane gradostat bioreactor designed for enzyme production from biofilms of Phanerochaete chrysosporium S. K. O. Ntwampe, M. S. Sheldon and H. Volschenk ABSTRACT S. K. O. Ntwampe M. S. Sheldon Department of Chemical Engineering, Faculty of Engineering, Cape Peninsula University of Technology, P.O. Box 652, Cape Town 8000, South Africa E-mail: Ntwampes@cput.ac.za; Sheldonm@cput.ac.za H. Volschenk Department of Microbiology, University of Stellenbosch, Private Bag X1, Matieland 7602, South Africa E-mail: Volschenkh@sun.ac.za 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 mm was identified after 264 h, with the anaerobic zone thickness reaching ,1,943 mm 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 b-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. Key words | biofilms, lignin peroxidase, manganese peroxidase, membrane bioreactor, Phanerochaete chrysosporium ABBREVIATIONS DCP Dichlorophenol DO Dissolved oxygen ECS Extra capillary space LiP Lignin peroxidase MCMGR Multicapillary membrane gradostat bioreactor MDA Malondialdehyde MGR Membrane gradostat bioreactor MnP Manganese peroxidase SCMGR Single capillary membrane gradostat bioreactor P. chrysosporium Phanerochaete chrysosporium ROS Reactive oxygen species INTRODUCTION A white-rot fungus, Phanerochaete chrysosporium was identified as having the potential to degrade various compounds found in industrial effluents. It produces extracellular enzymes, manganese peroxidase (MnP) and lignin peroxidase (LiP), that can degrade aromatic compounds and remove colour compounds from effluents. In recent publications, the fungus was used: 1) as a biosorbant for removing 2,4 dichlorophenol (2,4-DCP; Wu & Yu 2007); 2) to degrade azo dye in-vitro using its extracellular enzymes (Yu et al. 2006); and 3) to degrade a middle fraction diesel fuel residue (Kaunly & Hur 2006). doi: 10.2166/wst.2008.586 2259 Q IWA Publishing 2008 Water Science & Technology—WST | 58.11 | 2008