Membrane cleaning advantages

Chapter 13.2 discussed techniques and chemicals used for cleaning of RO membranes. This section discusses the merits of on-site verses off-site membrane cleaning. Table 15.4 summarizes the advantages and limitations of on-site and off-site membrane cleaning. 

Advantages Minimal filtration pretreatment Easier membrane cleaning Higher surface area means more filtration area per fiber True cross flow velocity minimizes concentration polarization and membrane fouling When no air is utilized for backwashing the less fiber movement leads to breakage of fewer fibers Can be created with a variety of inside fiber diamters... 

The major advantages of the tubular reverse osmosis configuration are the ability to tolerate high suspended solids concentrations in the feed and the possibility of mechanical membrane cleaning. The disadvantages are the excessive number of tube end fittings in proportion to the active membrane area in each pressure vessel, the bulkiness of the reverse osmosis plant and the high cost. 

Spiral wound membranes offer advantages such as compactness, good membrane surface/volume and low capital/operating cost ratios. Nevertheless, they are not suitable for viscous fluid and are difficult to clean. 

J3.2 Tubular The tubular configuration is an extension of the hollow fiber, but with larger diameter (up to 25 mm) tubes (Fig. 6.6). The flow is inside-out similar to hoUow-fiber membranes. The advantage of tubular membrane is that feed water with a high level of suspended sohds can be processed and the system is easy to clean mechanically. However, mbular membranes are more costly than hollow-fiber membrane modules. The tubular configuration is widely used in the food and beverage industries and for industrial wastewater treatment. 

RO membrane performance in the utility industry is a function of two major factors the membrane material and the configuration of the membrane module. Most utility applications use either spiral-wound or hollow-fiber elements. Hollow-fiber elements are particularly prone to fouling and, once fouled, are hard to clean. Thus, applications that employ these fibers require a great deal of pretreatment to remove all suspended and colloidal material in the feed stream. Spiral-wound modules (refer to Figure 50), due to their relative resistance to fouling, have a broader range of applications. A major advantage of the hollow-fiber modules, however, is the fact that they can pack 5000 ft of surface area in a 1 ft volume, while a spiral wound module can only contain 300 ftVff. 

The basis of ultrafiltration is that a liquor is passed through a membrane many times until the required concentration of the permeate is attained. Fouling of the membrane can be a problem and regular cleaning and disinfection of the membrane is recommended. Ultrafiltration of poly(vinyl alcohol) and starch sizes offers economic advantages over... 

Each type of device has specific advantages and disadvantages. The batch emulsification is suitable for laboratory-scale investigations. The construction of the device is simple and handling during emulsification as well as for cleaning. Crossflow membrane emulsification is used when it is important that a proper adjustment of all process parameters and larger amounts of emulsion have to be produced. 

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