Rice straw and sugarcane bagasse as supporting co-substrates for lack of food waste in industrial anaerobic digesters

The rapid diffusion of full-scale anaerobic mono-digestion plants of separately collected food waste (FW) in Italy will probably lead to a lack of organic material to feed industrial digesters in the coming years. This study aims to evaluate the industrial FW anaerobic co-digestion with rice straw (RS) and sugarcane bagasse (SB) as a valid and sustainable alternative to FW mono-digestion. Batch tests showed the highest cumulative methane yield for FW mono-digestion and a progressive decrease in specific biomethane production for co-digestion with increasing fraction of agricultural waste in the mixtures with FW. Subsequent pilot plant tests determined a biomethane production of 0.462 m3/kg of volatile solids (VS) equal to 0.370 m3/kg of total solids (TS) fed for FW mono-digestion, while a biomethane production of 0.360 m3/kgVS and 0.352 m3/kgVS equal to 0.288 m3/kgTS and 0.283 m3/kgTS for FW/RS (90:10) and FW/SB (90:10) co-digestion. For each ton fed to full-scale digester, co-digestion of FW/RS (90:10) and FW/SB (90:10) showed a profit increase of €5.5 and €3.8, a decrease in CO2eq emissions of 123 kg and 121 kg and a reduction of 1.12 kg and 1.13 kg in fine particulate matter (PM2.5eq) production. Replacing 10 % of FW with the same amount of RS or SB for a full-scale anaerobic co-digestion process resulted in both economic and environmental gain compared to the mono-digestion with 10 % less FW fed. The sustainability of FW co-digestion with RS and SB at industrial level was demonstrated by scaling up the results obtained to a pilot scale.