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CORESTA Congress, Shanghai, 2008, AP 10

Bioenergy from anaerobic digestion process for a more sustainable tobacco production

MIELE S.; ROSSI F.; BARGIACCHI E.
University of Pisa, Dpt of Agronomy and Agroecosystem Management (DAGA), Pisa, Italy

Presently, energy costs of Virginia Bright tobacco (VBt), especially for curing, are a major expense of this crop. To reduce these costs and benefit from an affordable source of "green" energy, to make the tobacco crop more sustainable, an anaerobic digestion plant is under construction at the Service Unit Giove of Fattoria Autonoma Tabacchi of Città di Castello (PG), one of the major VBt producers in Central Italy. Digestion is carried out in two digestion tanks where biogas (methane 60% v/v, carbon dioxide 39% v/v, and other gases) and digestated phase (7-10% w/w DM) are produced. Biogas (470 Nm3/h), after purification, is burned in a cogeneration plant to produce electricity (1 MWe) and heat (2.6 thermal MWh). Some 4-500 ha of maize and triticale silages are grown as feedstock for the plant in nearby growers' soils. Heat is planned to be used in several ways: (i) to warm up water used in the tobacco float system nurseries, also to extend their use during the cold season to produce turfgrass sods; (ii) to pre-heat air entering into the curing chambers, in order to contain energy costs; (iii) to dehydrate and stabilize the digestate phase to 35% w/w DM. Both liquid and "solid" digestate phases are delivered to soils where silage crops are grown, as organic fertilizers. Some of the water phase (0.2% N plus K, and trace elements) is reused in the first step of the digestion or delivered to nurseries, but the largest part is applied in fertigation to crops during the dry summer season.