Fouling submerged membranes

Ji, L. and Zhou, J. (2006) Influence of aeration on microbial polymers and membrane fouling in submerged membrane bioreactors. Journal of Membrane Science, 276, 168-177. 

The concept of the helical membrane module has been tested in a submerged membrane filtration mode with bubbling used for the membrane fouling control. Liu et al. [30] showed that the helical membrane with a twisted angle of 180° could achieve a 1.46-1.69 flux enhancement, compared to the membrane modules with 0° twisted angle, in the filtration of 500 mg/L kaolin suspension under a constant TMP of 2.8 and 3.2 kPa. The particle image velocimetry (PIV) analysis [31] showed that the tortured membrane surface of the helical membrane could generate rotational flow near the membrane surface and increase the wall shear rate. 

Germain, E., Stephenson, T., Pearce, R, Biomass characteristics and membrane aeration Toward a better understanding of membrane fouling in submerged membrane bioreactors (MBRs). Biotechnology and Bioengineering... 

Fan, F. S., Zhou, H. D. (2007). Interrelated effects of aeration and mixed liquor fractions on membrane fouling for submerged membrane bioreactor processes in wastewater treatment. Environmental Science Technology, 41(7), 2523-2528. 

In the case of PMRs with submerged membranes, the treatment can be conducted either in continuous or in intermittent suction mode. Intermittent permeation could improve permeate flux and reduce membrane fouling, as was described in Section 6.7.1. However, no significant difference between the quality of permeate obtained during continuous and intermittent operations was observed. Similarly, no significant influence of the intermittent frequency (IF) on the efficiency of organics removal in the PMRs was found (Chin et al., 2007a Ryu et al., 2005). 

The main drawback of pressurized PMRs is permeate flux decline and membrane fouling caused by Ti02 particles (compare Section 6.7 in Chapter 6). Considering the above findings, recent researches have been also addressed towards other configurations of PMRs, in which, instead of the pressurized membrane systems, submerged membrane modules are applied. 

The catalyst deposition on the membrane surface and fouling caused flux decUne during the photocatalytic process. To overcome these problems the depressurized (submerged) membrane system, in which the membrane module was located separately from the photoreactor, was studied. The achieved results showed pharmaceuticals abatement of 100% after ca. 20 min and mineralization of 44.5% after ca. 150 min in the retentate. The UF membrane used in the submerged system did not allow the rejection of GEM and of its oxidation products compared to the NF membranes of the pressurized system. 

Submerged membranes are typically operated at fixed (imposed) flux (/, ) This means that changes due to deposition/fouling are reflected in changes to TMP. So we can write... 

In membrane processing the application of surface shear is required to control concentration polarization and fouling for high solids feeds or to assist cake removal for batch membrane filtration of low solids feeds. For submerged membranes the common practice is to use two-phase bubbly flow to induce surface shear. This section deals with the role of bubbles as well as other hydrodynamic aspects of submerged membranes. 

The amount of air sparging required to control fouling in submerged membrane systems is an important operating cost. This is because the power required, P i, is a function of the... 

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