Recent modifications to the aircraft paint stripping and washing operations performed at this aircraft washrack resulted in significant changes to the characteristics of the process wastewater that is generated. This washrack wastewater stream is the primary contributor of both organic
and heavy metal loads at the facility's Industrial Wastewater Treatment Plant (IWTP). Following characterization of the wastewater and establishment of the design basis, an evaluation of alternatives led to the conclusion that biomembrane activated sludge appeared to be the most suitable
treatment alternative for this wastewater. Biomembrane activated sludge is activated sludge treatment coupled with ultrafiltration membrane separation of mixed liquor suspended solids (MLSS). Pilot testing was performed to confirm the applicability of the process and to facilitate development
of operating parameters and design parameters for a full-scale system. After a period of acclimation, the biomembrane activated sludge pilot test unit demonstrated it could produce a high quality effluent that exceeded the discharge requirements. Removal efficiencies for total toxic organics
(TTO), chemical oxygen demand (COD), biochemical oxygen demand (BOD), and total organic carbon (TOC) were each greater than 98 percent. There were no signs of incompatibility between the membrane and the washrack wastewater. Membrane flux rates were sustained at 10 gallons per square foot
per day with little increase in operating pressure. The effluent total suspended solids (TSS) concentrations were less than 1 milligram per liter (mg/L). Long solids residence times (SRTs) were achievable in this activated sludge system because the use of an ultrafiltration membrane for
final solids separation resulted in low observed yields without concern for the settleability issues associated with conventional activated sludge systems.
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