Memcor Membrane Bioreactor Products – From Research to Commercialization
Fufang Zha, USFilter / Memcor, 1 Memtec Parkway, Windsor 2756, Australia

Abstract：USFilter Memcor’s MBR products have been in market for years now. In this paper, the author describes the distinct features of the Memcor MBR process and the main MBR products available from USFilter.

Introduction
　　With the increasing water shortage and more stringent discharge limit, membrane bioreactor (MBR) is playing more and more important role in the treatment and recycle of wastewater. Since the first publication of submerged membrane bioreactor by Professor Yamamoto et al in 1989 [1], the technology has advanced very rapidly. Nowadays, there are many commercial MBR products in the market place and hundreds of full MBR plants are in operation worldwide.
Memcor’s research on MBR
　　MBR research conducted in Memcor R&D was directly focusing on overcoming the problems occurring in the MBR plants.
　　When the MBR technology first emerged, one of the major attractions was considered to be the simple process by immersing membranes in the bioreactor to replace the conventional clarifiers. Air is injected to the bottom of modules to scour the membranes and prevent significant fouling. The membranes behave like a physical barrier to completely reject the suspended solids and eliminate the trouble of sludge bulking encountered in the conventional wastewater treatment processes.
　　The in-tank MBR process with air scouring looks simple, but problems appeared in the full scale plant operation.
　　1. Difficulty to perform full chemical clean on membranes. No matter what type of membranes is used in MBR, the membrane eventually requires chemical clean to fully recover its permeability after operation for a certain period of time. One way to perform such a clean is to backwash the membrane with a high concentration chemical solution. If this method can not recover the membrane’s performance, then
the modules have to be removed from the bioreactor and cleaned in separate tanks. This cleaning strategy has several obvious negatives: (1) Injecting chemicals, normally high concentration of chlorine, will disturb the biological activities and generally create serious foaming problem; (2) Removal of modules out of the aerobic tank into another tank for cleaning causes a long down time and involves operators’ directly handling of modules covered with sludge (non-friendly environment). Alexander et al [2] described the cassette-by-cassette clean was expensive, labour intensive and potentially problematic for the membranes.
　　2. Passive mass transfer in the membrane system. In an MBR system, the membranes filter biomass containing high suspended solids >8,000 mg/L. As the clean water is filtered through the membrane, more solids are left on the surface and in the vicinity. The higher SS concentration, the higher viscosity and hence the higher resistance to the membrane to filter. The limited surface refreshment is achieved through the mass transfer with the bulk phase. This process is, however, hindered if the membranes are packed densely. Such a passive refreshment process limits the membrane packing density in modules and in tanks. Loosely packed membranes will require more air to effectively scour the membranes [3] and to increase the membrane tank volume.
　　To overcome the above issues, Memcor introduced a novel cleaning method by using a mixture of air and mixed liquor, instead of using air bubbles only, to scour the membranes. Figure 1 illustrates such a concept. The air and mixed liquor are both introduced to a chamber located at the bottom of the membrane module. Inside the mixing chamber, the two phases are mixed and flow into the bundles of the membranes. The air bubbles effectively scour the membranes and the semi crossflow of mixed liquor along the membranes continuously delivers the refresh mixed liquor to the membrane surface, minimizing the solid concentration polarization at the membrane surface and
therefore reducing the filtration resistance.
　　The process described above has been validated in various pilots and full scale MBR plants. Figure 2 shows the result from a pilot study conducted at Memcor R&D site in Windsor, Australia. During three-month operation, the membrane’s permeability was stable at a flux of 30 lmh. No blockage in the system occurred during the test, even at the two events of power blackout.

MemJet^TM Immersed Membrane Bioreactor Systems
　　After years of research and development on the MBR process, Memcor launched its MBR product in 2001 and MemJetTM is registered as the trade name for MBR product.The product has the features of
　　1) Unique patented two-phase efficient cleaning process
　　2) Positive fluid transfer into fiber bundles and uniform distribution of flow and solids;
　　3) Cross-flow dynamics minimize energy consumption;
　　4) Automated, in-place membrane cleaning process;
　　5) Small footprint required for the membrane system;
　　6) Safe environment for plant operators.
Membrane and Modules
　　The Memcor hollow fiber membrane used in the MemJetTM MBR is hydrophilic and chlorine tolerant. The membrane can generally achieve the filtrate quality of
　　Turbidity <0.2 NTU
　　TSS <1 mg/L
　　Faecal coliform <2 cfu/100 mL
　　The study has also demonstrated a log reduction of viruses greater than 4.
　　Hollow fibers are potted into modules. Memcor supplies two types of modules for MBR applications: B10R and B30R. The latter is mainly used for large scale plants. The effective membrane surface areas are 10 and 37 m2 respectively for B10R and B30R.
MemJet System
　　The MBR modules are assembled into racks. Each rack can accommodate a maximum of 40 B10R or 16 B30R modules. Figure 3 is a snapshot of a rack of 40 B10R modules.

　　The racks are then installed in parallel in membrane tanks. Depending on the size of a plant, the number of racks per membrane tank is determined to meet the flow capacity.
Figure 3 Memcor MBR Rack
MBR XPress^TM
　　MBR XPress^TM is a complete, pre-engineered membrane bioreactor from USFilter. The system is available in 100, 200, 300 and 400 m3/day sizes. The packed plant system is a robust wastewater treatment process with inherent features designed to reduce maintenance and provide reliable and efficient wastewater treatment for small scale applications.
　　A sketch of the system is shown in Figure 4. The system can be offloaded quickly and efficiently at the wastewater treatment site. The standard system removes COD/BOD, nitrogen, SS, turbidity and bacteria. Phosphorus removal is achieved through a combination of chemical dosing and biological activities.

Conclusion
　　Through years of research and development, USFilter Memcor has successfully applied its MBR products into the market. With distinct features, the Memcor MBR products are designed to be suitable for the treatment of wastewater from small packed systems to large scale plants. The R&D team continues to work on the cost reduction to achieve high quality treated effluent from MBR but with competitive price against the conventional treatment processes.

References：
1. K. Yamamoto, M. Hiasa, T. Mahmood and T. Matsuo, Direct solid-liquid separation using hollow fiber membrane in an activated sludge aeration tank, Wat.Sci. Tech., Vol. 21, p43, 1989.
2. K. Alexander, B. McBride, R. Jackson and J.Wade, Membrane bioreactor design: problems and solutions for a plant upgrade in Anthem, Arizona, Proceedings of WEFTEC 2001, Session 3.
3. T. Ueda, K. Hata, Y. Kikuoka and O. Seino, Effects of aeration on suction pressure in a submerged membrane bioreactgor, Wat. Res. Vol. 3, P489, 1997.