Effects of Particle Size of Food Waste on Methane Gas Production and Dewaterability of Digestate in Co-digestion with Dairy Manure

Natural biodegradation of organic matter under anaerobic conditions is estimated to release 590–800million tons of methane into the atmosphere annually. Biogas recovery systems exploit these biochemical processes to decompose various types of biomass, with the generated biogas potentially providing an energy source. Co-digestion of food waste and dairy manure has been predicted as the most efficient approach to making economic use of cattle slurry digestion. Higher organic loading and process stability is achieved through co-digestion. Reduced particle size of food waste caused a corresponding increase in biogas production and methane yield. The average biogas production rate is 1.85, 1.82 and 1.78 L/L/d in the digesters with fine, medium and coarse particle size of food waste, respectively. Biogas composition is analyzed by gas chromatography with methane composition ranging from 72, 68 to 67% in the three digesters, respectively. Time-to-filter the digestate decreased gradually, indicating improved dewaterability with time. Three 2-L complete-mix anaerobic digesters are operated for co-digestion of domestic food waste and dairy manure (50%: 50% by VS) at 36 ± 1 ⁰C. The food waste is shredded through cutting plates with different diameters (2.5, 4 and 8 mm) for the three digesters, respectively. The digesters are seeded with municipal anaerobic digester sludge and anaerobically digested dairy manure. Total solids in the substrates ranged from 11.3% in the dairy manure and, 30.4 – 32.1% in the food waste. The study is intended to advance feasibility of co-digesting food waste and dairy manure as a sustainable waste management strategy