Successful Application of Submerged Ultra Filtration Membranes to Meet Stringent NPDES Permit Limits for Stormwater Overflows

Stormwater discharges from an industrial aerospace complex located in Ventura County,
California require substantial treatment in order to meet the stringent NPDES permit
limits. Overflows are generated during heavy rain events when onsite storage pond
capacities are exceeded. Multiple treatment configurations have been tested to remove the
constituents of concern (COCs) below the permit limits. Past experiences have indicated
that chemical treatment with rapid clarification consistently produced water quality close
to the permit limits. Therefore, additional treatment is required to fully meet the treatment
goals. Ultrafiltration (UF) membranes were tested for this effect during a pilot study
conducted to determine performance of a submerged membrane unit. Effluent from the
rapid clarification unit (i.e., Kruger’s ACTIFLO) was further treated with multimedia
filters and used as influent to the membrane pilot. The submerged UF membrane was
able to remove approximately 99% of the influent turbidity. Ultimately, the submerged
UF membrane proved to be a viable treatment alternative that consistently removed
COCs below their NPDES permit limits, which in this particular case are even more
stringent than drinking water limits for certain COCs.