Council Bluffs, IA

Wastewater Digester Improvements

  • Client City of Council Bluffs
  • Type Wastewater
  • Services Evaluation, Design, Construction
  • Project Manager Keith Hobson, P.E., BCEE
  • Project Engineer Laurie Twitchell, P.E., BCEE

CHALLENGE

The anaerobic digesters were built with the original plant in the 1970s. In 2009, FOX evaluated and designed improvements and repairs to the entire digester complex, including structural repairs to the primary and secondary digester covers, replacement of the sludge heating and gas safety equipment, and upgrade of the electrical and control equipment. Through the repair and commissioning of the existing covers instead of replacement, the city was able to save significant costs and provide reliable digestion and gas collection.

2. Digester cover on the ground 3. Working inside the digester cover

SOLUTION

FOX Engineering was hired in 2009 to evaluate the capacity of the anaerobic digester complex, as well as the electrical and structural integrity of two existing secondary digesters and the associated equipment in the entire digester complex. The study included assessment of the existing floating gasholder covers, biogas safety equipment, sludge pumping and heating system, and the digester gas use and waste gas burner.

FOX looked at alternative methods of biogas holding and utilization. It was determined that the existing, almost 40 year old, floating covers were in need of extensive structural repair, but still had many years of service left. Replacement steel covers or membrane covers were also evaluated. The sludge heating systems (heat exchanger/boilers) were deemed at the end of their useful life and required replacement with new, more efficient equipment. In addition, new grinders were installed upstream of the sludge recycle pumps and a new motor control center was recommended. All of the original gas safety equipment is being replaced.

For this project, each gasholder digester cover was removed and placed onto the ground with a large crane so that the contractor could complete the repairs to the covers and tanks, sandblast and repaint, and then replace it in the digester.

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Outcome

Through the repair and commissioning of the existing covers instead of replacement, the city was able to save significant costs and provide reliable digestion and gas collection.

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