Foam balls, membrane cleaning

Cleaning is frequently aided mechanically. Foam balls scour the center of tubes, and hoUow-filter systems can be back-flushed. HoUow fibers and membranes attached to rigid supports can be back-pressured, thereby eliminating the pressure drop that holds redispersed films on the membrane surface. 

In radioactive waste treatment, significant operational aspects include the following. Since the operation requires the use of high pressures, there is a need to ensure control of the activity release from possible leaks. As with evaporation, pretreatment of the feed may be necessary to prevent scaling, and where dirty waters are to be fed directly it would be advisable to consider the use of equipment with larger membrane flow channels, which would permit periodic foam ball cleaning of the membrane surface. 

The tubular membrane (TM) modules shown in Figure 1.20 are 1.5—3 cm in diameter and have the lowest surface area. Tubular membranes are usually preferred to HF and SW membranes for high sohds (>0.5%) industrial wastewater apphcations TM modules are less prone to severe polarisation and fouling since they are operated under turbulent flow conditions (Re >3000). The TM module is best suited for feeds with high suspended sohds because it can handle particulates and can be physically cleaned with foam balls. Although TM plants consume 50% more power than HF or SW plants, TM are relatively inexpensive and have a longer life. 

Hydraulic energy in the form of high flow velocity in the feed channel. Ideally, cleaning should be done at turbulent conditions, i.e. Re >2100, which is only possible with tubular membranes. Sometimes foam balls are used to scrape dirt from the surface of tubular membranes, as shown in Figure 2.38. 

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