Backwashing, Backflushing, and Operation Mode

The relatively large pores of MF allow the removal of the deposit using air backflush or permeate backwash. Crossflow, rather than dead-end filtration mode, can be used to control the thickness of the 

Permeate backwash is a possible means to remove cake deposit in UF. The choice of a more hy drophilic membrane can decrease adsorption significantly and changes in the solution chemistry can impact on the deposit structure and porosity. 

Nakatsuka and Ase (1995) found backwash most effective if the backwash pressure is more than double the operating pressure. An increase in crossflow velocity also lead to higher flux, but at the cost of higher energy consumption. Hagmeyer et al. (1996) optimised the backwash interval to 30 sec every 30 minutes. Efficiency could be further increased with the duration and frequency, but at the cost of recovery. 

Bian et al (1999) reduced the concentration polarisation and fouling in NF by vibrations. Mallubhotla et al (1998) reduced the concentration polarisation by constructing helical modules from tubular membranes. 

a key factor is pretreatment, which can be conventional sand filtration, MF, or UF. It is believed however, that conventional filtration does not remove particulate matter sufficiently to prevent severe fouling. 

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