Techno-economic feasibility of anaerobic digestion of cheese whey in small Italian dairies and effect of ultrasound pre-treatment on methane yield.

In Friuli-Venezia Giulia plain (North-East of Italy), a significant number of small diaries is present; this study was aimed at evaluating technical and economic feasibility of diffused anaerobic digestion implementation at dairy level. Different kinds of cheese whey were characterized, and biochemical methane potential tests were executed. Good methane yields (up to 437.3 NmL CH4/g VSadded) were obtained, applying an inoculum-to-substrate ratio of 6. Ultrasound pre-treatment was investigated to evaluate an eventual increase in methane production and kinetics, varying applied ultrasonic energy: significant increases in methane yield (maximum +16.0%) and CH4 production kinetics (up to +46% increase after 3 days) were obtained at low ultrasonic energy of 251.4-693.7 Wh/kg VS, while at higher ultrasonic energy of 502.8-1387.5 Wh/kg VS no significant effect was visible. Energy consumption in selected dairies was analysed, to underline the impact of anaerobic digestion implementation on electric and thermal energy need, and it was concluded that through cheese whey anaerobic digestion it is possible to cover most of the dairies energy demand. Specific electric and thermal energy consumption were evaluated to be respectively in the range of 0.009-0.133 kWh/kg milk and 0.247-0.557 MJ/kg milk, while specific energy costs were calculated as 0.0079-0.0308 €/kg milk. For each analysed plant, digester volume to install and organic loading rate were hypothesized.