Anaerobic co-digestion of grass and cow manure: kinetic modeling comparison and GHG emission reduction

Abstract Grass is a highly desirable substrate for anaerobic digestion because of its higher biodegradability and biogas/methane yield. It contains a large amount of organic matter, which can be digested anaerobically to produce biogas. Anaerobic co-digestion of grass, cow manure and sludge was studied under mesophilic conditions for 65 days. Experiments were performed on a feed ratio of grass/manure 5, 10, 15, 20, 25%, respectively. During the experiments the volume and concentration of biogas and methane were recorded daily. The maximum cumulative biogas and methane yield was obtained as 331.75 mLbiogas/gVS and 206.64 mLCH4/gVS for 25% ratio. Also, the results of the experiments were tested on the three different kinetics model which are the first order kinetic model, modified Gompertz model and Logistics model. As a result of the study, it was found that by using grass waste 1.2.109 kWh/year electricity may be produced and 1.106 tons/year CO2 greenhouse gas emission may be reduced.