Membrane filtration is a very effective way to remove dissolved substances in water. However, the membranes can become quickly clogged or fouled if the water has not been pre-treated appropriately. First, suspended solids 5 micron and larger need to be removed. This may involve a single step using a 5 micron multi-media filter. Or, if the concentration of suspended solids is high, a clarifier, a DAF (Dissolved Air Flotation) unit, or a hydro-cyclone filter may be needed prior to the multi-media filter in order to remove the larger suspended solids.
Once the particles larger than 5 micron have been removed and any remaining smaller particles are at a low concentration, attention has to turn to the removal of dissolved organics. This is accomplished by installing an activated carbon filter. In cases where the water going to the membranes is hard, a water softener should also be part of the treatment process.
This may sound like a long, complicated process, but pre-treating water before it reaches membranes is essential to maintain optimum efficiency of the membranes and minimize maintenance and replacement. A water analysis, including a particle size distribution, would go a long way in helping Broken Arrow understand which pre-treatment steps are needed to solve its current problem. Algae is an immediate problem, but it may not be the only issue that should be addressed.