RETHINK MEMBRANE CHOICE
When it's finally time to replace RO membrane elements that handle fouling-prone water, check into technological developments introduced by membrane manufacturers to help mitigate fouling. For example, there's been a growing acceptance that elements with 34-mil spacers foul less quickly and are easier to clean than those with thinner spacers.
Membrane manufacturers continue to innovate in their quest to optimize spacer geometry and thus flush the membrane surface more effectively. Work also is advancing to improve the fouling-resistant properties of the spacer material and membrane surface.
All these development efforts aim to extend the time between cleanings, improve the effectiveness of cleaning, and lengthen the overall lifetime of the membranes. Plants benefit from lower operating costs via: 1) decreased consumption of cleaning chemicals due to less frequent cleanings, 2) less electricity use due to slower increases in feed pressure, and 3) reduced membrane replacement costs due to longer life.
As this article has stressed, timely and proper membrane maintenance is necessary to ultimately achieve the lowest operating costs.
Monitor the condition of the plant, normalize and assess the data, and use the results to decide when to clean so membrane performance isn't irreversibly reduced.
Before starting to clean, determine the type of fouling and its location so you can use the proper cleaning chemical. Cleaning at more extreme pH is much more effective — but first always check the membrane manufacturer's literature for pH (and temperature) limits for cleaning.
Waiting too long to clean will shorten membrane life and cost far more than appropriate cleaning to keep membranes healthy.
GREGG POPPE is a global application development specialist at Dow Water & Process Solutions, Edina, Minn. E-mail him at email@example.com.