Biofuels & Bioenergy

Maralfalfa (Pennisetum spp.) Is a Poaceae family forage grass used as livestock feedstock in Latin America, but its popularity is growing worldwide. The origin of maralfalfa grass is still unclear but it is likely to be of Pennisetum violaceum (Lam.) Rich. expers. or a hybrid (Pennisetum hybridum) Pennisetum americanum between L. and Pennisetum purpureum. Like all Pennisetum grasses, it reacts very positively to nitrogen and organic fertilization (Ramos Trejo et al. , 2012). Several cultivars have been established in Spain, associated to agroindustrial biogas plants located in Vall d´Uixó (Castellón) and Los Alcázares (Murcia), with rows of Maralfalfa of 15 m length, planted with two canes in parallel 0,10 m deep. The planting frame was 0,75 m between plants. Those plants have been fertilized with different amounts of digestates coming from the biogas plants. The doses of fertilization where adjusted to 80, 170 and 340 kg of Nitrogen per hectare and year. The average productions of dry matter per hectare have been 40, 55 and 59 t of DM of biomass, with an average content of water of the harvested material in 82,5%. It was made three harvests per year. The level of Crude Protein reached 17,2%, very much dependent on the age of each harvest. On parallel, several biogas tests have been performed, leaving yields of biogas between 520 and 600 l of biogas per kg of Volatile Solids. This positive relation between the yield of biomass generated per hectare and the use of the surplus digestates from waste management biogas plants reveals with extraordinary potential. On the energy field, the potential of methane generation reaches 18.200 Nm3 per hectare, compared to the 9.000 Nm3/ha of maize silage and 8.000 Nm3/ha of sorghum. On the sustainability and economical fields, the enormous reduction of fertilizer costs and the recycle of agrifood waste originated Nitrogen intro vegetable protein and tissue opens many areas of development of this application. Biorefinery and bioethanol projects might also benefit from this synergic relationship between biogas plants and maralfalfa plantations.