Flow rates and good chemistry are the critical factors in successfully cleaning membranes fouled by colloidal material. The high pH RoClean formulations contain dispersants that help push particles away from each other and away from the membrane surface, allowing a more effective clean.
The following are symptoms or indicators of silt and colloidal fouling:
- High pressure differential on elements.
- Surface water feed supply to system.
- High turbidity in feedwater.
- Element telescoping.
- Discoloration of the membranes.
Cleaning Approach
- Low pH clean with either RoClean P303 or L403 followed by a high pH clean with RoClean L211.
- Consider reverse flow and air sparging during cleaning procedure.
- Heat cleaning solution to maximum allowed by the membrane manufacturer.
Steps to preventing silt and colloidal fouling:
- Conduct SDI (Silt Density Index) and turbidity testing to determine colloidal fouling potential.
- Conduct laboratory filtration study to determine fouling potential, filterability of the water and optimum RoQuest® coagulant dosage.
- Consider a multi media pilot filter study.
- Using a microscope, inspect the spent SDI pads from the MMF feed and effluent to compare filter efficiency.
- Use properly designed multi media filtration and consider the need for air scour or surface wash.
- Consider the use of a coagulant to increase the effectiveness of the multi media filter.
- Use clarifiers or other filtration equipment for high turbidity waters.
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