De-Bugging the Plant - Managing Reverse Osmosis Biofouling at a Groundwater Treatment Plant

Last Modified: Feb 25, 2015


  • Myriam Cardenas, Gary Richinick – City of Santa Monica
  • Troy Walker – Hazen and Sawyer

Biological fouling is one of the scourges of reverse osmosis membrane plant operation. Once established, biological fouling can be difficult and expensive to remove. Even when it is removed, it can quickly re-establish, resulting in increased energy costs, increased chemical costs, loss of production as a result of cleaning downtime and a significant burden for operation teams.

Chloramine dosing has long been established as an effective strategy for biological fouling control for reverse osmosis in wastewater reuse applications. While almost ubiquitous in those applications, for groundwater treatment applications, the use of chloramine is not as widespread. Previous studies (Lozier 2005) using chloramine on surface and groundwater RO systems showed undesirable increase in salt transport, which can adversely impact treated water quality and decrease usable membrane life. This effect was hypothesized as possibly resulting from iron catalysis of the chloramine to more potent oxidants, such as free chlorine, which may have oxidized the polyamide membrane structure.

Commissioned in 2010, the ArcadiaWater Treatment Plant treats local groundwater to provide up to 10 MGD of treated water as part of the City of Santa Monica’s drinking water supply. The plant removes iron and manganese, and then treats a portion of the water with reverse osmosis as a softening process to achieve desired levels of hardness. Shortly following commissioning, biological fouling occurred first at the pretreatment cartridge filters before spreading to the reverse osmosis units themselves.

This paper will discuss the process and results of plant troubleshooting the City used to overcome this fouling, including the successful implementation of chloramine dosing and provide salient lessons learned for both groundwater plant design and operation.

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