DESIGN OF ODOR CONTROL AT A POTW TREATING SEAWEED PROCESSING WASTES

The City of Rockland, Maine owns and operates a 2.9 million gallons per day (mgd) publicly owned treatment works (POTW) discharging treated effluent to the Class SC Rockland Harbor. The POTW provides secondary treatment using primary clarification followed by conventional activated sludge. Raw primary and thickened waste activated sludges are dewatered and transported off-site to a contract disposal facility. Treatment will also be provided at the POTW for consolidated combined sewer overflow (CSO) discharges utilizing a swirl concentrator followed by high rate disinfection and dechlorination.The City receives approximately 70 percent of the design organic loading from a seaweed processor. The remaining 30 percent of the design organic loading to the POTW is from conventional domestic sewer users. The seaweed processor produces carrageenan, a food additive. The wastewater from the seaweed processor occasionally has characteristics which cause the solids in the aeration tank to agglomerate and settle to the floor of the basin. The thick, viscous blanket which forms cannot be resuspended with the mechanical aeration equipment. After the blanket becomes septic it floats to the surface, causing severe off-site odors. The wastewater from the seaweed processor historically entered the POTW via the interceptor sewers.Following the upgrade the industrial wastewater from the seaweed processor will enter the POTW via a separate 8-inch force main. The force main can discharge to the following locations within the POTW:Aerated Equalization TankPrimary ClarificationAeration Tank InfluentThe upgraded Aeration Tanks include an anoxic zone with submersible mixers and internal mixed liquor recirculation, followed by an aerobic zone utilizing new fine bubble type diffused aeration.The new odor control system at the upgraded POTW will treat foul air from the following locations:Influent Pump Station WetwellHeadworksPrimary Clarifier Flow Distribution StructurePrimary ClarifiersAeration Tank Inlet Channel and Industrial Wastewater Equalization TankAnoxic and Aerobic Aeration TanksSecondary Clarifier Flow Distribution StructureReturn Sludge WetwellGravity Belt Thickener RoomAerated Sludge Holding TanksBelt Filter Press RoomSludge Truck Loading BuildingOdor control chemical addition is provided at the POTW in the following locations:Sodium Hypochlorite to the influent sewageFerric Chloride to the CSO treatment system, and influent sewageHydrogen Peroxide to the industrial wastewater equalization tank, and aeration tank influentThis paper will review the unique design considerations created by the seaweed processing wastes and impacts on the design of the odor control, and chemical addition systems.