Membrane Bioreactor (MBR) Research at UNSW

The membrane bioreactor (MBR) can no longer be considered as a novel process. This reliable and efficient technology has become a legitimate alternative to conventional activated sludge processes and an option of choice for many domestic and industrial applications. More background information on MBR is available here and in the recent review "Fouling in membrane bioreactors used in wastewater treatment" published in the Journal of Membrane Science (vol 284, 2006, pp 17-53).

At UNSW, the UNESCO Centre for Membrane Science and Technology investigates many aspects of the MBR operation, maintenance and optimisation. Some of these studies are based on the collaboration with the Centre for Water and Waste Technology (School of Civil and Environmental Engineering). Check their website http://www.cwwt.unsw.edu.au/ for more MBR projects.

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CURRENT PROJECTS

Although many studies assessed fouling behaviour in MBRs, in-situ or direct observation of the fouling layer has not yet been possible. The observation of the fouling layer resulting from the filtration of model solutions allowed better understanding of MBR fouling intensity and mechanisms. In this study, alginate has been used as a model for polysaccharide (one of the main foulants in MBRs). Three visualisation techniques, confocal laser scanning microscopy (CLSM), environmental scanning electron microscopy (ESEM), and direct observation (DO) will be tested to observe the fouling behaviour of alginate (alone and in mixture). Detailed studies of EPS filtration under controlled operation can provide a better understanding of fouling propensity and mechanisms process in MBR operation. In this study, alginate was used as model foulant for polysaccharides, bovine serum albumin (BSA) for proteins analogue while bentonite and yeast (washed and unwashed) were representing suspended solids content. Fouling behaviours and rejection propensities were assessed for mixture solutions and provided explanations on fouling mechanisms of carbohydrate and its interaction with protein and membrane in MBR systems. Following a detailed protocol for the fractionation of the fouling layers into three distinct sections, biopolymeric analyses of the foulant is possible. Preliminary results indicated that the upper fouling fraction consists of a porous, loosely bound cake layer with a similar composition than the biomass flocs. The intermediate fraction, which consists of equal parts of soluble molecular products (SMP) and biomass aggregates, features a higher concentration of carbohydrates and possibly acts as a linkage between the cake layer and irreversible fouling layer. The lower fraction, representing the irreversible fouling fraction and predominantly consisting of SMP, features a relative higher concentration of strongly bound proteins. In an effort to better understand membrane stability and to optimise its lifetime, new physical and chemical cleaning strategies are to be assessed for MBR operation. The benefits and limitations of relaxation, continuous and backwash modes will be compared with some more complex filtration cycles. A series of enzymatic cleaning agents are also to be assessed to limit fouling in MBRs. For more details about these projects, contact Pierre Le-Clech or A/Prof Vicki Chen. The optimisation of MBR units requires knowledge of the membrane fouling, mixing and biokinetics. MBRs are designed mainly based on the biokinetic and membrane fouling considerations even though the hydrodynamics within an MBR system is of critical importance to the performance of the system. Consequently, the effect of the flow regime in the MBR process unit has been an insufficiently understood aspect of MBR design.

This project aims to examine the hydrodynamics of MBRs using two different methods: experimental tracer studies to derive the Residence Time Distribution (RTD) and process modelling based on Computational Fluid Dynamics (CFD). The tracer studies will be performed upon 6 different full-scale and pilot-scale MBRs of differing configurations (i.e. inside/outside submerged membranes, with/without pre sedimentation and hollowfibre/flatsheet membranes). Apart from RTD analysis the tracer studies can be used for validation of the CFD model. This model will account for aeration, sludge transport and the biokinetics and will allow detailed desktop design. More details could be found here.

This work is sponsored by the Australian Government's Department of Education, Science and Training and is participating in various sub-projects within the €5.9m EU MBR research project AMEDEUS "Accelerate Membrane Development for Urban Sewage Purification" http://www.mbr-network.eu. For more details about this project, contact Matthew Brannock.

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PAST PROJECTS

In this project high strength wastes were treated by an anaerobic UASB followed by a sequential batch aerobic reactor (SBR). The settled effluent was clarified by MF. This process can be operated as a net energy producer. We have examined the optimal flux conditions for sustainable operation. This work was supported by the CRC WMPC. This was an extension of the previous project where membranes were directly combined with the UASB. Of special interest has been the control of fouling. Our results have highlighted the important role of extracellular polymeric substances (EPS) in determining sustainable operating flux. Hollow fibre membrane systems are popular in many applications for microfiltration and ultrafiltration. We are especially studying the factors controlling performance, including fibre size, fibre orientation, imposed flux and bubbling conditions for MBR. This project was supported by a major International water company and an Ausaid scholarship.

Vicki Chen and Richard Stuetz (from Civil and Environmental Engineering) check the bench-scale MBR.

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