Enhancing the energetic potential of Mediterranean food waste by anaerobic co-digestion with sewage sludge

Mediterranean Food Waste (FW) with high Carbon/Nitrogen (C/N) ratio (approximate to 31) and a biodegradability (BD) above 75%, were anaerobically co-digested with Sewage Sludge (SS), in both batch and semicontinuous processing systems. Biochemical Methane Potential (BMP) tests were carried out for five mixture ratios (VS basis). The highest methane yield was obtained for the Food Waste to Sewage Sludge (FW/SS) ratio of 3:1, reaching a Specific Methane Production (SMP) of of 452 ml CH4/g VSadded. Moreover, this ratio has shown a BD of 40%, twofold lower than the one obtained for digestion of FW alone. Applying the semi-continuous process, a methane yield of 200 ml CH4/g VS was obtained at the high Organic Loading Rate (OLR) of 8 g VS/L center dot day, indicating a good performance of the system facing a high daily feeding. A predictive study of the energy efficiency of this system provided an estimated daily production of 1.4 kilowatt-hour electricity load (KWh(el))/kg VS(added)and 2.2 kilowatt-hour thermal load (KWh(th))/kg VSadded.