Microfiltration membrane cleaning

Depth membrane filters are usually preferred for in-line filtration. As particles are trapped within the membrane, the permeability falls, and the pressure required to maintain a useful filtrate flow increases until, at some point, the membrane must be replaced. The useful life of the membrane is proportional to the particle loading of the feed solution. A typical application of in-line depth microfiltration membranes is final polishing of ultrapure water just prior to use. Screen membrane filters are preferred for the cross-flow microfiltration systems shown in Figure 7.1(b). Because screen filters collect the retained particles on the surface of the membrane, the recirculating fluid helps to keep the filter clean. 

Microfiltration processing for clarification and defatting of cheese whey, for selective separation and concentration of micellar caseins from milk for various purposes, for fractionation of caseins and their peptides, for recovery of native whey proteins from milk, for gentle sterilization of milk to produce extended shelf fife liquid milk and cheese milk, for fractionation of globular milk fat and its components, for the reduction of microorganisms in cheese brine, and for the removal of colloidal particles in membrane cleaning solutions. 

Al-Obeidani, S., Al-Hinai, H., Goosen, M.F.A., Sablani, S., Taniguchi, Y., and Okamura, H. 2008. Chemical cleaning of oU contaminated polyethylene hollow fiber microfiltration membranes. J Membr Sci. 307 299-308. 

There are few, if any, materials that provide sufficient flux during microfiltration for cleaning to be unnecessary. The type of cleaning depends on the type of fouling that has caused the flux rate to decline. Section 10.4 illustrated the types of resistances that occur in membrane filtration, and the necessary cleaning depends on which of these resistances dominate. In the most ideal filtration the flux decline is due solely to a loose deposit formed on top of the membrane. The deposit can, therefore, be dislodged firom the membrane by a siniple mechanical shock, such as momentarily lowering the... 

Microfiltration membranes are typically periodically cleaned by backpulsing these membranes. This can be accomplished through a variety of ways, some incorporating air and some using just product water or water containing a small amount of hypochlorite. Some immersed-membrane systems also use diffused air to agitate the membranes and prevent solids from caking on the membrane surface. 

Operational costs are primarily associated with power and vary from 50 to 120 hp/mgd. Pretreatment chemicals include coagulants, and when biofonhng is a problem, hypochlorite solution can be used on some membranes for cleaning. Citric acid can also be used for membranes that do not tolerate chlorine. Microfiltration membranes are typically not compatible with polymer addition, which is not reqnired, since even small pin floes cannot permeate the membranes. 

Direct Visual Observation of Microfiltration Membrane Fouling and Cleaning... 

Blanpain-Avet P, Migdal JF, Benezech T (2004) The effect of multiple fouling and cleaning cycles on a tubular ceramic microfiltration membrane fouled with a whey protein concentrate-membrane performance and cleaning efficiency. Food Bioprod Process 82(C3) 231-243. doi 10.1205/fbio.82.3.231.44182... 

A.2 Cross-Flow, Dead-End Configurations Microfiltration and UF systems are operated in two possible filtration modes. Figure 6.10 shows the cross-flow configuration in which the feed water is pumped tangential to the membrane. Clean water passes the membrane while the water that does not permeate is recirculated as concentrate and combined with additional feed water. To control the concentration of the sohds in the recirculation loop, a portion of the concentrate is discharged at a specific rate. In dead-end or direct filtration, all the feed water passes through the membrane. Therefore, the recovery is 100%, and a small fraction is used periodically for backwash in the system (5-15%). 

Pretreatment For most membrane applications, particularly for RO and NF, pretreatment of the feed is essential. If pretreatment is inadequate, success will be transient. For most applications, pretreatment is location specific. Well water is easier to treat than surface water and that is particularly true for sea wells. A reducing (anaerobic) environment is preferred. If heavy metals are present in the feed even in small amounts, they may catalyze membrane degradation. If surface sources are treated, chlorination followed by thorough dechlorination is required for high-performance membranes [Riley in Baker et al., op. cit., p. 5-29]. It is normal to adjust pH and add antisealants to prevent deposition of carbonates and siillates on the membrane. Iron can be a major problem, and equipment selection to avoid iron contamination is required. Freshly precipitated iron oxide fouls membranes and reqiiires an expensive cleaning procedure to remove. Humic acid is another foulant, and if it is present, conventional flocculation and filtration are normally used to remove it. The same treatment is appropriate for other colloidal materials. Ultrafiltration or microfiltration are excellent pretreatments, but in general they are... 

Among the numerous approaches studied so far to minimize such phenomena in ED, it is worth citing pretreatment of the feed solution by coagulation (De Korosy et al., 1970) or microfiltration (MF) or ultrafiltration membrane processing (Ferrarini, 2001 Lewandowski et al., 1999 Pinacci et al., 2004), turbulence in the compartments, optimization of the process conditions, as well as modification of the membrane properties (Grebenyuk et al., 1998). However, all these methods are partially effective and hydraulic or chemical cleaning-in-place (CIP) is still needed today, thus... 

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