Energy recovery from the anaerobic co-digestion of ricotta cheese whey and dairy cattle manure

Abstract

This study evaluated biogas production, methane concentration and yield, as well as the potential for energy production of anaerobic co-digestion of ricotta cheese whey and dairy cattle manure in 60 L plug flow reactors. Four reactors were operated: three with different proportions of ricotta cheese whey (20, 40, and 80%) and a control reactor containing only dairy cattle manure. The reactors were operated for 106 days, with a hydraulic retention time of 30 days. In all reactors, pH remained near neutrality, and alkalinity stayed above 2,500 mg L⁻¹. Notably, only the reactor with 80% ricotta cheese whey demonstrated more efficient removal of total solids, volatile solids, biochemical oxygen demand, and chemical oxygen demand, with average reductions of 54, 69, 69, and 78%, respectively. However, the reactor operated with 40% ricotta cheese whey produced the highest accumulated biogas volume, surpassing the 80% ricotta cheese whey reactor by 36 L, with a realistic extrapolation of electricity production estimated at 1.67 kWh m^-³. Although methane yields were close to theoretical maximum values and methane concentrations showed no significant differences between treatments, the results confirm the effectiveness of anaerobic co-digestion in the treating of agro-industrial waste. The 40% ricotta cheese whey and 60% dairy cattle manure ratio stands as a promising alternative for biogas production.