Back-wash fluid

Fortunately, hollow fibers may be cleaned by back-washing which tends to compensate for their propensity to foul. Manufacturers of tubes, plate and frame units, and spiral wound modules do not recommend back-washing due to problems with membrane delamination and glue line seal rupture. Because hollow fibers are self-supporting and hold up well under the compression force of a reverse transmembrane pressure drop, they can easily withstand back-wash pressures of 15 to 20 psi. However, the back-wash fluid should be filtered to remove any particles which would tend to lodge in the porous wall of the fiber. 

The permeate itself is often the ideal back-wash fluid since it has been through the membrane once. Unfortunately, permeate by itself will not always restore the flux (see Figure 3.71) and more aggressive cleaning solutions must be used. An auxiliary pump and filter must be provided to deliver the cleaning solution under pressure through the permeate port to the shell side of the module. The materials back-flushed will exit from the fiber lumen and must be discharged from the system so as not to redeposit on the walls of the fiber. 

The test organism may be placed on the skin, e.g. on the back of the hand, and the preparation to be evaluated placed on the same area. After a given time interval the area is swabbed with sterile cotton wool and the swab incubated in a suitable medium or washed in a suitable fluid, and viable counts are subsequently made. 

Several unit processes can be used in the washing process. The soil is mixed with washing agents and extraction agents that remove the contaminants from the soil and transfer them to the extraction fluid. The soil and washwater are then separated. The soil can be further rinsed with clean water. The soil is removed as clean product, ready to put back into the original excavation, and the washwater is ready to be treated by conventional wastewater treatment processes as addressed in the next subsection. 

Add the primary antibody to the living cells at 4°C in BSA-PBS, and incubate for 30 min (1-mL vol for a 35-mm dish). Do not pipet directly onto the cells, but add antibody solutions at the edge of the dish, and add wash solutions from a wide-mouth bottle or beaker to minimize the potential of removing cells by too vigorous a fluid stream. Do not allow the cells to dry at any step. Rock the dish back and forth to maintain coverage over the cells if the antibody solution volume is too small see Note 7). 

Fig. 6.2-23 CIP of fluid-bed granulation units a) principle of automatic cleaning, b) principle of washable pulse blow-back filters and view into the filter area of a unit, c) metal cartridge filter, d) hydraulically extendable washing nozzles (courtesy Clatt, Binzen, Germany)... 

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