A correct cleaning is the key for a long PERMEABILITY AND SELECTIVITY of a membrane. Infact a mechanical cleaning reduces both membrane occlusion and frequency of chemical cleaning extending the life of the membrane and reducing the operational costs. The “backwash” technology is a mechanical cleaning method that can effectively avoid the fouling effect of the filter membranes. “Fouling” is the obstacle that limits the efficiency of the filtration processes: it reduces the permeability of the membrane with an increase in operating and maintenance costs. Many techniques have been tested over the years to avoid fouling of membranes and backwash (although it is not effective in removing advanced stages of fouling that are irreversible) has numerous advantages in combination with chemical cleaning. The use of Backwash is convenient because it is done during the filtration cycle, it allows an high productivity and it reduces the frequency of chemical cleaning. This leads to an extended life of the membrane. The Backwash is a mechanical cleaning action of the membrane carried out by means of a flow of filtered product which is push back against the normal flow. In this way, the colmating gel-layer formed on the surface of the dirty side of the membrane is “detached”. The picture shows the effects of the backwash on a filtration cycle. Curve 1 represents the flow without the use of the backwash, Curve 2 with its use. The average flow of permeate over time is higher and longer thanks to the use of the backwash.
Is backwash really efficient?
Too frequent use of the backwash can result in a significant reduction in net permeate flow, while on the other hand a backwash too short or with a too low frequency is not effective to remove or prevent membrane fouling. Only an optimization of the working conditions therefore produces a real benefit with an higher permeate rate over time. The optimal operating conditions in Bared crossflow filters arise from years of experience near customers and allow to obtain filtration cycles of up to 70 working hours without interruptions.
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