Cedar Rapids/Linn County Bioreactor
Cedar Rapids, Iowa

The Cedar Rapids/ Linn County Solid Waste Agency, at the recommendation of a citizen’s Focus Group, determined that the use of a bioreactor cell should be evaluated as a long-term waste management option to reach the State of Iowa’s 50 percent diversion goal. Foth and E&A Environmental Consultants were retained to design, permit, and develop operating requirements for a bioreactor cell pilot project.

The Cedar Rapids/Linn County bioreactor is a research bioreactor used to determine the rate of waste decomposition when leachate and other liquids are recirculated back through the waste. This bioreactor is unique since one-half of the bioreactor contains wastewater treatment plant sludges. This bioreactor will also examine the concept of sustainable landfilling, the concept of constructing a series of bioreactor cells. Each year’s waste is placed in a separate cell to be bioreacted for seven years. After seven years, the waste is removed, screened and the non-decomposible waste placed in an inerts landfill. The cell is then reused. This sustainable landfilling will reduce the amount of land needed for landfilling.

The bioreactor was constructed in 1998; filling of the two cells was completed in 1999; capping with an exposed polypropylene cap was completed in 2000; and the first full year of bioreactor operations was 2001.

The Cedar Rapids/Linn County bioreactor project concluded in 2006. Portions of the waste were excavated and screened to determine the level of decomposition, what wastes did not decompose and if the decomposed fraction has beneficial reuse.

Challenges:

• Cold weather bioreactor operations
• Wind uplift of exposed synthetic cap
• Demonstrating low-cost bioreactor effectiveness

Benefits:

• The Cedar Rapids/Linn County bioreactor was contructed using landfill staff and several innovative features including:
  – Horizontal gas collection system
  – Exposed synthetic cap with wind uplift ballast
  system
  – Targeted leachate recirculation system
  – Biofilter landfill gas odor control system
• The Cedar Rapids/Linn County bioreactor received the innovating project of the year for 2003 from ISOSWO Iowa SWANA chapter).
• Results from the Cedar Rapids/Linn County bioreactor indicate bioreactor technology can be effectively used in cold climates. The rate of decomposition of waste is accelerated by the bioreactor as evidenced by time capsules removed from the bioreactor in 2002, 2003 and 2004. Also, landfill gas production appears to be accelerated by using bioreactor technology.