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Water Environment & Technology (WE&T) is the premier magazine for the water quality field. WE&T provides information on what professionals demand:
cutting-edge technologies, innovative solutions, operations and maintenance, regulatory and legislative impacts, and professional development. |
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June 2007, Vol. 19, No. 6 |
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Plant Profile
Fairfield–Suisun Sewer District Wastewater Treatment Plant
Location: Fairfield, Calif.
Startup date: October 1976
Service population: 135,000
Number of employees: 34
Design flow: 17.5 mgd (66,200 m3/d)
Average flow: 15.7 mgd (59,400 m3/d)
Peak flow: 85 mgd (320,000 m3/d)
Annual operating cost: $6.7 million) |
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The 17.5-mgd (66,200-m3/d) Fairfield–Suisun Sewer District Wastewater Treatment Plant (Fairfield, Calif.) faces unique challenges because it sits adjacent to the Suisun Marsh, the largest brackish water marsh on the West Coast. The plant must meet stringent requirements for discharge to the marsh and for reclamation, such as 10 mg/L biochemical oxygen demand (BOD), 10 mg/L suspended solids (SS), and less than 2.0 mg/L ammonia. The plant typically produces BOD and SS levels less than 2.0 mg/L and ammonia less than 0.2 mg/L.
Brewery effluent contributes 40% of the influent BOD load, 17% of the SS load and 8% of the flow. Travis Air Force Base contributes about 12% of the plant flow. The remainder is residential, commercial, and light industrial.
Influent is directed to the plant through force mains from three major pumping stations. Treatment begins with mechanical bar screening and grit removal in aerated grit chambers, followed by primary sedimentation.
Primary effluent then is directed to three oxidation towers for initial removal of soluble organics. Solids from the oxidation towers are removed in intermediate clarifiers, and the flow enters four aeration basins for activated sludge treatment, which is operated in nitrification mode.
Final clarifiers remove solids prior to tertiary filtration. Finally, the effluent is disinfected via gaseous chlorine. Within the next few years, the plant plans to phase out the chlorine gas in favor of ultraviolet disinfection.
After treatment, the effluent flows to onsite reservoirs for agricultural and municipal irrigation or to an outfall discharging to the marsh.
Solids from the intermediate clarifiers and activated sludge tanks are thickened via air flotation and combined with primary sludge for anaerobic digestion. Digester gas is used to fuel cogeneration engines to produce power for a portion of the plant and heat for the digesters. Digested solids are dewatered on solar drying beds during warm weather and on plate-and-frame filter presses during the rainy season.
The resulting biosolids meet Class B regulations and are utilized as alternative daily cover at the local landfill. The district is investigating thermal drying or composting the solids as supplemental methods of disposal or beneficial use.
The plant is publicly owned, but day-to-day operations and maintenance are contracted out. The district |
The Jelly Belly Candy Co. (Fairfield, Calif.) trucks its waste directly to the wastewater treatment plant, rather than sending it down the sewer. The waste is offloaded to this specially constructed holding tank and then metered into the anaerobic digesters. (Photo: Fairfield–Suisun Sewer District staff) | handles all engineering, regulatory, laboratory, construction, and major maintenance, while the contractor focuses on daily operations and preventive and corrective maintenance. This public–private partnership has worked well for the district for more than 30 years.
Working With Industries
Fairfield is home to the Jelly Belly Candy Co., and the district has worked with the factory to find a win–win option for high-strength candy waste. Jelly Belly trucks its waste directly to the plant, rather than sending it down the sewer. The waste is offloaded to a specially constructed holding tank and then metered into the anaerobic digesters. This arrangement lowers costs for the candy company and generates additional gas in the digestion process.
The plant has a similar arrangement with Superstore Industries, a local dairy processing plant, for its high-strength wastes.
©2007 Water Environment Federation. All rights reserved. |
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