Dem-Con HZI Bioenergy proposes the construction of a new facility that will process organic materials through anaerobic digesters at its environmental campus in Shakopee. The proposed facility includes two anaerobic digesters that will process up to 75,419 tons per year of organic materials including yard waste, food scraps, and other scraps into natural gas and biochar, creating a sustainable alternative to landfilling these organics.
Our role
The MPCA has released the environmental assessment worksheet (EAW) for the Dem-Con anaerobic digestion facility. The EAW is coupled with a draft air permit to thoroughly assess the potential for significant environmental effects and implement measures to protect the environment and nearby residents.
Comment on this project
The comment period for the environmental assessment worksheet ended on Aug. 16, 2024. The 30-day comment period for the draft air permit continues through Aug. 29, 2024.
Location
The proposed facility will be located south of the existing Dem-Con Landfill, on the Dem-Con Environmental Campus in Shakopee. The comprehensive plan encompasses 27 acres, with permits already in place for 13 acres. These approved permits are tied to a landfill expansion for stormwater management (February 2023) and onsite mining (July 2020).
Project information
The anaerobic digestion facility will accept materials from Ramsey and Washington counties and other third-party sources.
In addition to the digesters, the facility plans to construct an enclosed flare, separate buildings for operations and offices, a digester storage bunker, liquid digestate dispatch/biogas holder, biochar storage area, truck scale, and stormwater management system that includes a pond and infiltration basin.
Dem-Con's EAW reviewed potential impacts on air, soils, groundwater, surface water, and other potential environmental impacts. Some key takeaways include:
- The project will produce an estimated 8,600 tons per year of biochar, a form of charcoal that can be used to improve soil health, lower greenhouse gas emissions, and improve soil moisture. The biochar will be sold to a third party for use as a soil amendment or remediation purposes.
- The project will use 3.5 million gallons of groundwater annually with the potential for using 8.8 million gallons.
- Per- and polyfluoroalkyl substances (PFAS) may be present in materials received by the facility. The amount of PFAS present in the facility’s produced output waste streams depends on the amount of PFAS in the organic materials received. The processes at the facility do not add PFAS to the end products.
- The project will produce renewable natural gas that will be compressed and sent to a pipeline (to be constructed) at the proposed gas interface station. This pipeline will be reviewed in an EAW at a later date.
Most air emissions from the facility will come from producing biochar. The air permit will authorize construction and operation of the facility and will require Dem-Con to install and maintain several controls to reduce air emissions including the following controls on the biochar process:
- Activated carbon injection (for mercury and dioxins/furans).
- A fabric filter baghouse (for particulate matter and heavy metals).
- A liquid scrubber (for acid gases, particulate matter, heavy metals, and dioxins/furans).
Next steps and timeline
The public is encouraged to comment on the EAW and draft air permit during the 30-day comment periods.
Dem-Con will begin construction on the facility after mining operations are completed. Dem-Con expects mining activity to finish in the fall of 2024 with construction of the project to follow reclamation activity, which includes grading within the site to drain and applying topsoil or other surfacing. The anaerobic digestion facility should be completed in 2026 or 2027. The useful life of the facility is estimated at 30 years.