Nutritionally Limited Biofouling in Spiral-Wound RO Elements

Abstract

Operating on municipal tap water, a two-stage reverse osmosis (RO) unit producing boiler feed makeup water for a power plant in North America experienced an increasing feed-side pressure drop after about a week in operation. Cleanings did not restore the pressure drop to its original value. On restart after cleaning, the pressure drop continued increasing during operation. Water permeability and salt rejection of the RO elements were not significantly affected by the fouling problem. After about five months of operation, the feed-side pressure was about double the initial pressure and about four times higher than predicted. All six elements in the first-stage housing and the first and last elements in the second-stage housing were returned to the manufacturer for inspection. The eight elements were tested for feed-side pressure drop and water and sodium chloride permeabilities. The leading element was autopsied, and two elements were aggressively cleaned. Study results and suggestions to reduce biofouling are detailed in this article.