Cleaning in membrane filtration systems

Abstract

A method of cleaning permeable, hollow membranes (6) in an arrangement of the type wherein a pressure differential is applied across the walls (15) of the permeable, hollow membranes (6) immersed in a liquid suspension, the liquid suspension being applied to the outer surface of the porous hollow membranes (6) to induce and sustain filtration through the membrane walls (15) wherein some of the liquid suspension passes through the walls (15) of the membranes (6) to be drawn off as clarified liquid or permeate from the hollow membrane lumens (7), and at least some of the solids are retained on or in the hollow membranes (6) or otherwise as suspended solids within the liquid surrounding the membranes (6). The method of cleaning comprises the steps of applying a cleaning solution (14) to one side of the membrane wall (15); applying a pressure differential across the membrane wall (15) to cause flow of the cleaning solution (14) through the wall (15) from the one side of the membrane wall (15) to the other side of the membrane wall (15) and applying a reverse pressure differential across the membrane wall (15) to cause flow of the cleaning solution (14) through the wall (15) from the other side of the membrane wall (15) back to the one side of the membrane wall (15). A method of determining the amount of chemical cleaning solution required is also disclosed.

Description

FIELD OF THE INVENTION [0001] The present invention relates to the backwashing of hollow permeable membranes used in membrane filtration systems and, in particular, to an improved method of backwashing and cleaning the hollow permeable membranes. BACKGROUND ART [0002] Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of common general knowledge in the field. [0003] Known backwash systems include those described in our earlier International Application No. WO93 / 02779 the subject matter of which is incorporated herein by cross-reference. [0004] During cleaning of membranes, cleaning solutions are often flowed through the membranes and their permeable walls to clean foulants from the membranes. Applying the cleaning solution under pressure assists the removal of foulants from the surface. [0005] The typical known cleaning procedure for membranes involves cleaning the membranes in...

AI Technical Summary

Benefits of technology

[0056] For preference, the predetermined value approximates a steady-state value of membrane resistance. Preferably, the membranes are microfiltration or ultrafiltration type membranes.

Problems solved by technology

This often results in a one process fits all approach where a standard chemical cleaning stage is applied regardless of the amount of fouling.

This can lead to large amounts of cleaning solution being used unnecessarily with the effect of additional cost and environmental impact in disposing of the waste solution after cleaning is complete.

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