Project : General Mills, Inc. Yogurt to Methane Gas-to-Energy

General Mills, Inc. -- Murfreesboro, Tennessee

This project encompassed the benefits of a waste-to-energy case study addressing combined heat and power (CHP) generation fueled by the vertical start-up of a 6.5 MG anaerobic reactor for industrial wastewater pretreatment in the food service industry.

The project was defined by five goals:

  1. Compliance with industrial pretreatment discharge limitation
  2. Elimination of off-site waste disposal
  3. Reduced energy and operating expenses
  4. Use of design-build delivery method
  5. Securing of federal energy investment tax credit

Two operations existed on the site that produced 605,000 gallons per day of process wastewater, required off-site disposal at considerable expense, generated discharges under an industrial discharge permit, and consumed large amounts of energy.

Optimization of the site encompassed anaerobic pretreatment and an energy recovery evaluation and plan. Anaerobic pretreatment lowered overall sludge production and improved the average effluent quality as well as generating methane gas. The energy recovery evaluation was based upon proof of the gas asset and considered multiple alternatives, which were evaluated using an economic model to determine the internal rate of return (IRR). A sensitivity analysis was performed to evaluate the impact of sensitive factors on IRR.

The energy recovery plan included gas compression and drying at the digester site, a single containerized engine-generator with provisions for an additional unit as well as excess biogas to flare or direct firing in a boiler for process heating. Design and construction was completed with power production within six months of notice to proceed.

Awards Received:

  • 2017 ACEC New York - Diamond Award, Energy
Services Provided by CHA:
  • Mechanical, Electrical and Plumbing (MEP) Engineering
  • Water and Wastewater Engineering
  • Thermal Generation 
  • Structural Engineering
  • Civil/Site Survey
  • Archaeological Exploration
  • Design-Build