Evaluation of the biogas productivity potential of some Italian agro-industial biomasses

Batch trials were carried out to asses the biogas productivity potential of rice and barley straw, grape stalks, grape marcs, maize drying up residues, tomato skins and seeds, and whey. Trials were carried out in 2 l glass digesters kept in a thermostate controlled room at 40°C for 40 days. The most productive biomasses, in terms of specific methane yield, were the whey and the maize drying up residues. Their specific methane yields were 501 and 317 lN CH4 *kg SV-1, respectively. Barley and rice straw gave a specific methane yield of 229 and 195 lN *kg VS-1. Similar result was also obtained from tomato skins and seeds. Grape stalks and grape marcs produced lowest amounts of specific methane, respectively, 98 and 116 lN CH4 *kg SV-1. According to trial results and considering the availability of examined biomasses in Italy, it is possible to estimate their total energetic potential close to a value of 21,900 TJ*year-1. This energetic potential value is equal to that obtainable from the anaerobic digestion of about 6.5 million tons of maize silage.