Seawater desalination by reverse osmosis (RO) provides a solution to the increasing scarcity of drinking water supplies. However, RO membranes are subject to biological fouling when conditions are conducive to growth and proliferation of bacteria. Operation and maintenance consequences are costly. Given these challenges, does biodegradable and easily assimilable organic carbon (AOC) contribute to biological fouling of RO membranes used for seawater desalination? This hypothesis was evaluated using a novel bioluminescent assimilable organic carbon (AOC) test to identify the relationship between biofouling and seawater biodegradability by: Investigating biofouling potential at full, pilot and bench scale seawater RO conditions; evaluate the impact of oxidants on AOC formation; and assess pretreatment chemicals for AOC formation potential. The results of the full scale plant data analysis revealed statistically significant correlations (<i>p</i> &lt; 0.01) when AOC was used as a predictor variable for the increased differential pressure (4 – 8 psi from September – December, 2012) and the 53% decrease in specific flux through the RO membranes. RO membrane biological fouling occurred when the median AOC was 50 µg/L. In a comparison test using 30 - 1000 µg/L AOC, fouling was detected on more portions of the membrane when AOC was higher. Application of antiscaling, cleaning and dechlorinating agents in most solutions and recommended doses increased AOC. AOC was also a reaction byproduct of commonly used disinfectants, such as chlorine, chlorine dioxide and ozone in antiscalant solutions or with naturally occurring organic carbon. Increases in biodegradability and Polyphosphonates and polymer-based antiscalants increased AOC by &lt; 30 µg/L but phosphate-based antiscalants increased AOC nearly 100 µg/L AOC. Depending on the active chemical or impurities, antiscalants increase the biofouling potential of the RO feed despite the targeted application for controlling inorganic fouling. Besides creating more effective organic carbon removal, recommendations are presented from the study to help control AOC levels in the RO feed and ultimately reduce the occurrence of Ro membrane biofouling.

Using luminescence to determine the impact of assimilable organic carbon on biological fouling of reverse osmosis membranes in seawater desalination

250th National Meeting (2015)

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