A large, Midwestern oil refinery installed two identical, 110’ diameter S&L Model R OXIGEST® treatment systems to solve a groundwater treatment problem on-site. Each plant incorporates aeration, clarification, and effluent holding, treating peak flows of 7.2 MGD combined; 4.3 MGD in each plant.
The plant operates with a Food-to-Mass (F/M) typical of extended aeration conditions while the hydraulic retention time is 4.2 to 6.25 hours. The (F/M) ranges from 0.05 to 0.15 lbs BOD5 /d/lb MLVSS. Because of this low loading, the system operates in the endogenous respiration phase of the bacterial growth cycle, resulting in high BTEX removal and low sludge production. Based on input from the refinery and the designer, the system provides the capability to infuse powdered activated carbon for possible future use in the aeration zone.