The effect of CO2 enrichment of ADs was investigated for food
waste and sewage sludge. An enhancement of CH4 production
was observed, demonstrating the potential of ADs to utilise additional
CO2. When treating food waste, CO2 enrichment increased
the CH4 yield by up to 13%. For sewage sludge, CH4 production
increases of 96–138% were obtained during the first 24 h of digestion.
Associated CO2 reductions of 3–11% for food waste and 8–34%
for sewage sludge were estimated. The different substrate response
to CO2 observed could indicate that CO2 enrichment enhanced the
acetoclastic pathway of CH4 formation.