Wastewater treatment and cogeneration project wins international award

ATLANTA—Environmental engineering firm Brown and Caldwell (BC) and the Columbus (Ga.) Water Works (CWW) won the International Water Association’s 2008 Global Project Innovation Superior Achievement Award for their work on the Columbus Biosolids Flow-Through Thermophilic Treatment (CBFT³) and Cogeneration System Project.

To retrofit an existing wastewater treatment plant with anaerobic digesters, CWW and BC developed the CBFT³ process to convert the existing mesophilic digestion process to low-cost, Class A thermophilic digestion and produce Class A biosolids. The CBFT³ reduces required batch processing times from 24 hours to 30 minutes, saving CWW approximately $3 million in capital costs.

Cogeneration is being implemented that incorporates state-of-the-art, lean-burn engine-generator technology to produce about 40 percent of the treatment plant’s electricity demand using biogas (digester gas) that would otherwise be flared. These new engines offer roughly 20 percent more power than previous generation engines or 60 percent more power than microturbines with low exhaust emissions.

The CBFT³ and Cogeneration project is under construction and represents the culmination of more than six years of research and engineering evaluations that BC said will advance anaerobic digestion.

"The project is revolutionary in that it is the first thermophilic anaerobic digestion process in North America to be run entirely off heat derived from digester gas-fueled power generation," said BC’s Principal Investigator John Willis. "Coupled with other gains, generation of this Green Power will result in a net carbon offset of 9,500 metric tons as CO₂ per year for this 40-mgd treatment facility."

Other green innovations include the following:

• using all of the biogas from digesters to generate renewable thermal and electrical energy;
• heating the raw solids by first using heat recovered as digesting thermophilic biosolids are cooled to mesophilic temperatures in the TPAD system;
• continuing to heat solids to thermophilic temperatures and maintaining digesters at this level using heat recovered from the engines used to generate power; and
• treating digester gas to remove water, siloxanes, hydrogen sulfide, and particulates to levels required for the advanced engine-generators.

The project also won the International Water Association’s 2008 grand prize in the Applied Research category, as well as the grand prize for research in the American Academy of Environmental Engineers’ Excellence in Environmental Engineering awards competition in 2007.