Flat-sheet MBR

Zhang K, Cui Z, Field RW. Effect of bubble size and frequency on mass transfer in flat sheet MBR. J. Membr. Sci. 2009 332 30-37. 

The submerged MBR system is a small-footprint, single-process unit that can achieve a high-quality standard with low solids production. The membrane systems typically utilize either micro- or ultramembranes configured as hollow fibers, flat sheets, or tubes depending upon the manufacturer. Experience over the past decade has proved MBRs to be reliable and cost-effective for high-quality effluent applications, and relatively easy to maintain and operate. The key parameters for MBR... 

Figure 4.13. Aerated MBR for wastewater treatment. 1 feed tank 2 feed pump 3 reactor vessel and diffuser 4 hollow-fiber or flat-sheet membranes 5 air pump for diffuser or back-washing 6 permeate vacuum pump 7 permeate 8 air feed.

The Kubota MBR uses a flat-sheet manbrane made of polyolefin with a nonwoven cloth base. Each m brane cartridge consists of solid acrylonitrile butadiene styrene support plate with a spacer layer between it and a flat-sheet membrane on both sides. Permeate is drawn through the membrane from the bulk fluid by a partial vacuum applied within the membrane plate matrix while retaining the solids... 

As mentioned in Section 14.3, biofilm is heterogeneous and contains dead and living microorganisms. The images obtained by CLSM showed that dead bacteria accumulated in the sublayer in thickened biofilm on a flat sheet hydrophilic polypropylene membrane, used in MBR [61]. In other MBR-based studies, CLSM was used to assess the fouled membrane at different dissolved oxygen... 

As mentioned above there is no standardization in submerged membranes, and there are many commercial suppliers. For example, Judd (2006) describes 12 different MBRs using submerged membranes. The majority of submerged membranes are either hollow fibers (HF) or flat sheets (FS), as depicted in Figure 10.3. This seetion gives a brief description of the different submerged membrane eoneepts. 

The submerged flat-sheet systems are principally used for high solids content MBR applications. Table 10.3 summarizes the products from three suppliers, which are briefly... 

Huber The Huber MBR is radically different from aU other commercial submerged membrane systems, being based on a mechanically moved membrane. The Huber VRM (vacuum rotating membrane) uses flat-sheet membranes of polyethersulfone... 

Figure 10.10 Huber VRM rotating submerged flat-sheet module (MBR).

In MBRs bubbling also has a role in mixing the reactor contents, presumably through the induced liquid circulation [Eq. (10.11)]. There is some evidence from tracer studies that mixing induced by bubbles may be a httle more effective with submerged hollow fibers than flat-sheet membranes because the latter act as baffles in the vessel (Wang et al., 2008). 

Some insights into membrane failure can be found in the literature (Childress et al., 2005 Gijsbertsen et al., 2006). The frequency of failure will depend on applications, but Gijsbertsen et al. (2006) estimate annual rates in water treatment of 1-10 per million fibers. Higher rates would be anticipated in MBRs where membranes are subject to more fouling conditions and greater operational stresses. Even flat-sheet membranes used in MBRs are not immune to occasional failure (Cornel and Krause, 2003). 

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