The size of the digester and hydraulic retention times also influence viability. Larger digesters allow long hydraulic retention times for top biogas yields, while it may be harder to break even with smaller digesters. When there is inadequate feedstock, nearby operations may pool feedstocks to keep a large digester busy or employ numerous other anaerobic variations to boost productivity.

Because of a global fertilizer shortage, nearby agricultural operations may be willing to pay for an AD operation's nutrient-rich liquid digestate, the sludge left over after treatment. Liquid digestate is routinely applied directly to fields, and an additional dewatering process can create more stable dry fertilizer products. Anaerobic digestion also has the potential for electrical and thermal energy generation, renewable natural gas generation, and even hydrogen generation.

In the United States, the landmark Inflation Reduction Act (IRA) of 2022 was passed to slow inflation by investing in American energy production and clean energy. It established a stand-alone Investment Tax Credit (ITC) of 30% to offset CAPEX for the construction of qualified biogas property systems.

Projects that started construction in 2020 through October 2022 are entitled to the full 30% credit, while projects that start later must meet wage and apprenticeship rules to get the full credit. Qualified biogas projects typically start at 6% for basic biogas utilization, and quickly increase to 30% with certain wage requirements. An additional 10% can be realized for projects that use domestically sourced material, and another 10% is tied to selected energy sites.

Under the IRA, a "qualified biogas property" is a property with a system that converts organics/biomass into gas at 52% methane or higher, concentrates it to that strength, or cleans and conditions the gas. The gas must be recovered for sale or productive use. Construction of qualified biogas property must be started by December 31, 2024.

While there are too many variables to give a fixed answer, average wastewater contains five times more energy than is needed to power the wastewater treatment process. High-load streams may contain even more. Waste-to-energy systems frequently use recovered energy to fuel the treatment process, with energy left over to generate electricity, or fuel other industrial processes or vehicles. Biogas from anaerobic digestion can also be sold externally. In the European Union, the market for biogas is fully mature, with biomethane – refined biogas – accounting for 17% of the gas used for road transport on the continent.

Frequently, operations that produce high-strength wastewater rely on municipal wastewater treatment systems, which may raise bills when effluents overstress treatment plants. Many Fluence anaerobic digestion clients initially explored it due to excessive utility costs and have been able to realize significant savings on municipal wastewater treatment.

And, when biogas generated on-site by digesters is used to fuel boilers and electrical generators to power processes, it lowers electricity and natural gas bills.