Anaerobic digestion in northern Italy: the situation in Piemonte Region

At a time of growing global energy demands, there has been increasing interest in green energy production through agricultural feedstock anaerobic digestion (A.D.) and several plants have been constructed in Italy. With the financial support of the National Biofuels Programme “Probio-biogas”, a survey was carried out on Piemonte territory to have a figure of the number, efficiency and typology of anaerobic digestion plants. Four representative biogas plants running on Piemonte Region were monitored by DEIAFA – Torino University. For each plant the following parameters were recorded on regular basis: feedstock typology and chemical characteristics, organic loading rate, hydraulic retention time, operative temperatures, daily biogas yield and biogas composition, CHP functioning hours, operative problems arisen at the plants and digestate management. The monitoring activity highlighted long retention times (100 days) at three on four plants. They were fed with big amounts of energy crops that represented up to the 64% of the daily organic loading rate. The plants management – in terms of organic loading rate – was not efficient leading to an average production of electric energy often 15-20% lower than the potential one. All the electric energy is utilized within the farm or sold to the grid, whereas on average the 90% of the thermic energy is dissipated. The volume of the digestate storage tanks were not sufficient to fulfil the storage autonomy required by the current national normative (120-180days) as they allowed on average 50-100 days of storage only. Furthermore all the storage tanks were uncovered leading to a risk of high biogas emission to the atmosphere.