Food Waste Digester Redesign, Retrofitting, Substantial Completion and Startup


The Montrose team was initially engaged as an Owner’s Representative to provide an independent assessment of ongoing design, engineering and construction progress at a confidential food waste digester that was designed to take in over 175,000 tons of food waste per year and generate 5.2 megawatts of electricity. Following the delivery of the initial assessment to the project owner, Montrose was subsequently selected to take over the responsibilities and scope of work from the lead EPC firm. Based on prior work that had been completed, Montrose was tasked with significantly redesigning portions of the facility, procuring new equipment, providing construction management services and then starting up and operating the facility using an in-house operations and maintenance team.


The primary mandate of the client was twofold: (1) to ensure that the facility was designed as an “omnivore” and was able to accept a wide variety of organic food waste feedstock that would be delivered with varying levels of contamination, original packaging, configurations and overall solids content, and (2) given that the project had already been designed, was well into the construction phase and had incurred significant delays, to work as expeditiously and cost-effectively as possible.

The primary challenges for the project fell into three areas. First, the prior EPC contractor had progressed significantly with their scope, so the Montrose team had to demo some parts of their work,  while also seamlessly syncing the new work, equipment and systems together with what was already on site. Second, parts of the facility were simultaneously already being started up, including the digesters themselves, so the Montrose team had to continue operating portions of the facility throughout the redesign and construction phase. Lastly, given all of the modifications that were being implemented, it was very important to work closely with local regulators on amendments and clarifications to the environmental permits, and the Montrose team would need to maintain close communication with the regulatory staff to help translate how new designs and equipment would impact current environmental limits placed on the facility.


Montrose developed a scope of work, budget and staffing plan for approaching the project. The scope included developing a new mass balance for the facility, broadening the accepted feedstock mix, upgrading the feedstock receiving building, which included the installation of Scott Turbo Separators, biopulper upgrades, installation of new centrifuges and a Dissolved Air Flotation (DAF) system, as well as leading the commissioning for multiple pieces of equipment that had been previously installed.

Concurrent with the execution of the scope of work of the Engineering, Design and Construction Management team, the Montrose Operations and Maintenance team took over the operational portions of the facility and began to staff a dedicated, on-site O&M team for plant startup and long-term operations. With the completion of the redesign and upgrade work, the plant proceeded with start-up using a feedstock mix of source separated organics, fats, oils and greases (FOG), food processing and production waste, and fully-packaged, out-of-specification consumer goods. The plant is also staffed and operated, full-time, by the Montrose Operations and Maintenance team.

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