Codigestie

Codigestie, or co-digestion, refers to the anaerobic digestion of two or more organic substrates in a single digester to produce biogas. By combining substrates with complementary properties, codigestion can increase methane yield, improve process stability, and enable more efficient waste management than digestion of a single feedstock.

Common substrates include animal manure, agricultural residues, food waste, fats/oils/greases, septic sludge, brewery and dairy effluents, and municipal organic waste. The mixture is designed to balance nutrients such as the carbon-to-nitrogen ratio, trace elements, and moisture content.

Benefits include higher biogas production and better substrate utilization, improved digestion stability, and greater flexibility in feedstock supply. Economic and environmental advantages include reduced waste disposal costs and potential greenhouse gas emissions reductions, as well as nutrient-rich digestate that can be used as fertilizer if regulated.

Operational considerations include the selection of compatible substrates, optimization of feed ratios, and careful ramping of organic loading to avoid inhibitors. Challenges encompass ammonia inhibition from nitrogen-rich materials, inhibition from long-chain fatty acids from fats, salt and heavy metal content, and variability in waste composition. Process control often requires monitoring of soluble organic loading, pH, alkalinity, ammonia, and volatile fatty acids.

Applications are widespread in municipal and industrial anaerobic digestion facilities to treat mixed wastes and boost biogas production. Codigestion is part of broader waste-to-energy and nutrient-recovery strategies and can be tailored to regional waste streams and regulatory requirements.