Biogas production from switchgrass under experimental conditions simulating U.S. digester operations.

Area of Science:

• Environmental Science
• Biotechnology
• Chemical Engineering

Background:

• Lignocellulosic feedstocks offer high energy potential and have been co-digested with biosolids in Europe.
• The U.S. anaerobic digester capacity for co-digesting lignocellulosic materials remains uncertain.
• Operational challenges may arise when integrating these feedstocks into existing U.S. digester systems.

Purpose of the Study:

• To evaluate the co-digestion of switchgrass with sewage biosolids under U.S. anaerobic digester conditions.
• To determine the feasibility and operational impacts of lignocellulosic feedstock co-digestion.
• To identify effective pretreatment methods for switchgrass in anaerobic digestion.

Main Methods:

• Laboratory-scale co-digestion experiments were conducted using switchgrass and sewage biosolids.
• Switchgrass was prepared using fine-grinding and ensiling pretreatment methods.
• Digester performance was monitored for methane yield, solids removal, and operational stability.

Main Results:

• Finely-ground and ensiled switchgrass co-digested effectively with biosolids up to 4% solids, yielding high methane and energy conversion efficiencies.
• Acceptable volatile solids (VS) removal was maintained, with no observed solids accumulation, mixing problems, or floating debris.
• Coarsely ground switchgrass resulted in low methane yields and operational issues even at 2% solids.

Conclusions:

• Fine-grinding switchgrass is energy-intensive and potentially cost-prohibitive for U.S. anaerobic digesters.
• Ensiling shows promise but requires further study at full-scale to differentiate particle size effects.
• Low-cost pretreatment methods are needed to facilitate lignocellulosic feedstock co-digestion in current U.S. systems.