Solids Thickening, Dewatering and Odor Control at Plants 1 and 2
The Orange County Sanitation District is implementing a $2.4 billion capital improvement program to provide full secondary treatment at Plants 1 and 2, supply water to the GWR System, and improve the condition and reliability of its treatment plants. As part of this program, HDR is providing design, construction and start-up services for both liquid treatment and solids handling facilities at Plant 1.
The liquid treatment improvements involved converting the existing activated sludge facility to remove ammonia-nitrogen. This modification improved the water quality provided to the GWR System and resolved a number of reliability, condition, capacity, and hydraulic issues. Key elements of the project included retrofitting the aeration basins with new diffusers, baffles and process piping; retrofitting 14 secondary clarifiers with new mechanisms; building 2 new secondary clarifiers; adding process air blowers; expanding sludge pumping capacity; and extensive upgrades to the electrical and control systems. A key consideration was the hydraulic interface between the activated sludge system and the GWR System facility. The design and construction was completed on a fast-track basis to fulfill OCSD's schedule commitments to the GWR System project. In fact the concept development, predesign and final design for this $35 million project was completed in only 11 months. A carefully-planned construction sequence was developed to maintain capacity and permit compliance during construction.
For solids handling, HDR is designing a new $100 million thickening, dewatering and odor control facility. This facility will replace the DAFTs with thickening centrifuges and replace the belt filter presses with dewatering centrifuges. Key project components include sludge pumping, sludge cake conveyance, centrate conveyance, chemical handling, foul air ventilation and utility water systems. The project required renovation of existing structures and construction of new structures.
As part of this project, HDR has updated the flow and load projections for Plant 1, and developed mass balance models for the liquid treatment and solids processing facilities. These analyses address the Plant 1 interfaces with the GWR System and GAP facilities, including consideration of recycle streams.