Membrane Bioreactor (mbr) as an Advanced Wastewater Treatment Technology
Types of Membrane Bioreactor Configurations
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TRICHLUCTHUADAT LIEN 1, TRICHLUCTHUADAT LIEN 1, TRICHLUCTHUADAT LIEN 1, TRICHLUCTHUADAT LIEN 1
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- Fig. 1 Side-stream MBR with external pressure-driven membrane filtration Fig. 2 Submerged MBR with internal vacuum-driven membrane filtration Table 1
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Types of Membrane Bioreactor Configurations Membrane separation is carried out either by pressure-driven filtration in side-stream MBRs (Fig. 1) or with vacuum-driven membranes immersed di- rectly into the bioreactor, which operates in dead-end mode (Fig. 2) in sub- merged MBRs. The more common MBR configuration for wastewater treat- ment is the latter one, with immersed membranes, although a side-stream configuration is also possible, with wastewater pumped through the mem- brane module and then returned to the bioreactor. The energy consumption required for filtration in submerged MBR is significantly lower (Table 1). Both configurations need a shear over the mem- brane surface to prevent membrane fouling with the constituents of mixed liquor. Side-stream MBRs provide this shear through pumping, as with most other membrane processes, whereas immersed processes employ aeration in the bioreactor to provide it. Shear enhancement is critical in promot- 42 J. Radjenovi´c et al. Fig. 1 Side-stream MBR with external pressure-driven membrane filtration Fig. 2 Submerged MBR with internal vacuum-driven membrane filtration Table 1 Comparison of filtration conditions for tubular and immersed MBRs [8] Side-stream Submerged membrane tubular membrane Manufacturer Zenon Zenon Model Permaflow Z-8 ZeeWeed ZW-500 Surface area [m 2 ] 2 46 Permeate flux [L m –2 h –1 ] 50–100 20–50 Pressure [bar] 4 0,2–0,5 Air flow rate [m 3 h –1 ] – 40 Energy for filtration [kWh m –3 ] 4–12 0.3–0.6 ing permeate flux and suppressing membrane fouling, but generating shear also demands energy, which is probably the reason for submerged config- uration predominance. Also, in side-stream MBR module fouling is more pronounced, due to its higher permeate flux. Pumping of activated sludge in- duces shear stress to microbial flocs, causing them to break-up, which leads to a decrease in particle size and releasing of foulant material from the flocs [7]. Membrane Bioreactor (MBR) as an Advanced Wastewater Treatment Technology 43 This may significantly promote the membrane fouling rate. In Table 1 filtra- tion conditions are presented for tubular and immersed MBRs [8]. The configurations of MBR are based on either planar or cylindrical geom- etry. There are five principal membrane configurations currently employed in practice: 1. Hollow fiber (HF) 2. Spiral-wound 3. Plate-and-frame (i.e., flat sheet (FS)) 4. Pleated filter cartridge 5. Tubular. In the HF module, large amounts of HF membranes make a bundle, and the ends of the fibers are sealed in epoxy block connected with the outside of the housing (Fig. 3). The water can flow from the inside to the outside of the membrane, and also from the outside to the inside, which is produced differ- ently by different manufacturers. These membranes can work under pressure and under vacuum (Fig. 4). The spiral-wound configuration is mostly used for the NF and RO process. The membranes are wound around the perforated tube through which perme- ate goes out (Fig. 5). The spiral-wound modules are manufactured in standard dimensions by all major manufacturers, which makes their installation eas- ier and membrane production less costly. Many membrane modules can be installed together in series or parallel in plants with high capacity (Fig. 6). Plate-and-frame membrane modules comprise of FS membranes with sep- arators and/or support membranes. The pieces of these sheets are clamped onto a plate. The water flows across the membrane and permeate is being col- lected through pipes emerging from the interior of the membrane module in a process that operates under vacuum (Fig. 7). There are also membrane configurations such as plated filter cartridge and tubular module, but they are not so widely used as the other three mod- Fig. 3 Hollow-fiber (HF) membrane module |