Fueling the future: Co-digestion as a strategic tool for municipal and private wastewater facilities

Co-digestion involves combining more than one type of energy-packed organic solid waste, such as food scraps, fats, oils and grease (FOG), and feeding it into a single anaerobic digestion (AD) system. These oxygen-free tanks are teeming with microorganisms that break down the waste and regenerate to produce biogas. This biogas, rich in methane, rises to the top of the tank and can either be cleaned and upgraded into renewable natural gas (RNG) - a direct substitute for fossil fuel-based natural gas, or used with minimal biogas cleaning as a fuel for cogeneration applications. This renewable natural gas can then be sold and integrated into natural gas systems or used directly by the companies that produce it to offset energy requirements. 

The larger the tank, the greater the potential biogas yield. Wastewater treatment plants can introduce food waste into their existing sludge digesters to amplify gas production by up to three times due to the high energy density of food waste. 

Across the United States and Canada, state and provincial regulations are increasingly restricting organic waste from entering landfills. These policies are driven by the urgent need to reduce methane emissions generated during the slow decomposition of organic matter in landfills. At the same time, they promote alternative strategies, such as composting and anaerobic digestion, that offer scalable, sustainable solutions for waste diversion and energy recovery. 

As a result, municipalities and private haulers are shifting away from traditional disposal methods and embracing co-digestion as a viable path forward. This approach not only helps meet regulatory mandates but also generates clean energy and reduces reliance on landfills.

Why it matters for municipalities: 

Municipalities can unlock the full potential of their wastewater infrastructure through co-digestion.

• Environmental compliance: Co-digestion helps meet mandates like California’s SB 1383 by diverting food waste from landfills and reducing methane emissions.
• Infrastructure optimization: Many municipal wastewater treatment plants have underused anaerobic digesters and biogas systems. Co-digestion allows for better utilization without major capital investment and at the utility’s control of incoming feed stocks.
• Public benefit: Producing renewable energy onsite supports sustainability goals and can reduce municipal energy costs, with co-digestion potentially enabling facilities to generate more energy than they consume through enhanced biogas output.
• Funding opportunities: Federal and state grants are available to support co-digestion initiatives, making it financially viable for public utilities.

Why it matters for private operators: 

Co-digestion has the potential to turn waste into revenue and resilience for private-sector organizations.

• Revenue generation: Tipping fees from food waste generators and monetization of biogas through on-site power production or RNG sales. 
• RIN credits: Under the EPA’s Renewable Fuel Standard, operators could earn D3 and D5 credits, boosting financial returns. 
• Operational efficiency: Food waste has 2 - 3x the methane potential of biosolids, increasing energy recovery and system output. 
• Flexibility and control: Private facilities can design systems around specific feedstocks and scale quickly to meet market demand. 

While the benefits are compelling, co-digestion projects face hurdles: 

• Capacity management: Digesters must maintain operational balance. Overloading can restrict the opportunity for future growth for facility outputs. However, this can be overcome with effective planning, and once a facility is nearing its capacity, the revenue generated through the RNG output can aid in funding biosolids and the related wastewater treatment facility expansion. Our multidisciplinary teams provide strategic guidance to help facilities optimize capacity and unlock new revenue streams. 
• Feedstock consistency: We design preprocessing systems to support uniform feedstock quality. We also assist organizations in selecting the optimal feedstock specifications to maximize energy output and maintain long-term operational efficiency. 
• Capital constraints: Many wastewater facilities face upfront investment barriers when considering co-digestion projects. We help bridge this gap by facilitating public-private partnerships and developer-led financing models tailored to the wastewater sector. Whether it's upgrading existing digesters or integrating new feedstock streams, we work with clients to structure financially viable solutions.  

• Uncharted territory: With any unknown variable, beginning a new venture can be daunting. With proper due diligence assessments and strategic input, we help businesses and municipalities understand their opportunities, form a viable business case and identify risks that can lead to a sound financial investment decision.

At GHD, we see co-digestion not just as a technical solution, but as a strategic lever for long-term success. Municipalities and private operators alike are under pressure to meet sustainability goals, comply with landfill restrictions and optimize aging infrastructure. Co-digestion offers a way to do all three, while generating new revenue streams. 

We help our clients take a proactive approach by: 

• Assessing infrastructure readiness: We evaluate existing assets to identify underutilized capacity and opportunities for integration. 
• Developing business cases: Our team conducts comprehensive analyses of financial returns, regulatory incentives and operational impacts to facilitate informed investment decisions. 
• Forming strategic partnerships: We connect clients with developers, funders and feedstock suppliers to accelerate project timelines. 
• Navigating policy shifts: As regulations evolve, we help clients stay ahead of compliance and position themselves as leaders in clean energy production. 

Facilities that act now can transform waste liabilities into energy assets and gain a competitive edge in a rapidly changing landscape. Let us help you lead the way. Contact us to discuss your project.