Viridi, Casella partner on Maine RNG facility

Viridi Energy, a Wilmington, Delaware-based renewable natural gas (RNG) platform, has acquired a legacy biosolids digester plant in Brunswick, Maine, with plans to convert the site into a waste-to-RNG facility.

The company has partnered with Rutland, Vermont-based Casella Waste Systems Inc., which will manage feedstock collection and delivery logistics for an estimated 85,000 tons of biosolids per year collected from a network of wastewater treatment plants.

Viridi says the facility will help power the local community while offering a solution for managing biosolids and supporting compliance for local regulations aimed at mitigating per- and polyfluoroalkyl substance (PFAS) contamination.

At the Brunswick facility, anaerobic digestion will convert the biosolids into enough energy to heat more than 3,000 homes for a year, Viridi says. The facility will also supply electricity to Brunswick Landing, a 3,300-acre campus hosting commercial, industrial and professional office space.

“Viridi continues to lead the industry with innovative solutions that help overcome challenges in both the waste management and energy sectors, and this project signals the team’s ongoing emphasis on diversifying our waste feedstocks and expanding our processing capabilities to meet growing renewable energy needs,” Viridi CEO Dan Crouse says.

"We are excited to be working with Casella, whose established track record in successfully managing multifaceted waste streams will be pivotal to our success. Casella has been at the forefront of finding a sustainable solution to this issue since the law prohibiting land application of biosolids was enacted and has played a significant role in bringing this vital piece of infrastructure online.”

With Maine law now prohibiting the practice of land-applying biosolids digestate in agricultural settings because of PFAS concerns, Viridi says wastewater treatment facilities are facing the choice between two alternatives: trucking the material long distances or landfilling it, where it requires stabilization and takes up space.

The company says the anaerobic digestion solution offered at Viridi's Brunswick facility is expected to reduce the volume of the biosolids by nearly 90 percent, from 85,000 wet tons down to 10,000 tons once the material has been digested and dried. Once processed, Casella will transport the postprocess digestate to landfill.

“Our agreement with Viridi represents a major step toward finding a sustainable solution for Maine’s biosolids,” Casella CEO and Chairman John Casella says. “The need for efficient, responsible biosolids treatment and disposal solutions has never been more pressing. We are pleased to be working with Viridi to provide a comprehensive approach for managing this waste stream in a safe, sustainable and beneficial way.”

Viridi currently is conducting siting, permitting and environmental due diligence at the Brunswick site. Retrofit construction of the Brunswick facility is expected to be complete by the second half of 2025, with full operations slated to commence in 2026.

As previously reported by Waste Today, Viridi partnered with American Organics Energy (AOE) in 2023 to develop a waste-to-RNG project in New York. According to Viridi, the project will generate emissions reductions equivalent to approximately 100,000 tons of CO₂ per year.