ELEPHANT GRASS AS A FEEDSTOCK FOR BIOENERGY PRODUCTION

The establishment of perennial grasses as energy crops has emerged as a viable option to bioenergy production mainly due to their comparative advantages over annual energy crops and attractive characteristics to the bioenergy production (Morais et al., 2009). Perennial grasses are excellent candidate feedstocks for renewable energy production in support of several rationales such as high potential of dry matter yields, fast growth, and additional potential use of inputs compared to annual crops (Samson et al., 2005). Perennial grasses that utilize the C4 photosynthetic pathway have a great potential to provide large quantities of cellulosic biomass. Among these species, elephant grass or napier grass  (Pennisetum purpureum Schum.) has a significant potential as a renewable biofuel feedstock, because is a fast-growing energy plant with annual dry matter yields often exceed 40 Mg ha-1 in tropical and subtropical areas (Singh et al., 2013).

Elephant grass is a major forage crop in the wet tropics of the world that belongs to the Poaceae family and is native from tropical Africa, with an annual precipitation demand over than 1,000 mm. This species has a high photosynthetic efficiency, which results in a great capacity to accumulate dry matter, between 20 and 45 Mg ha-1 year-1 (Quesada et al., 2004). Elephant grass is a hardy grass that can grow up in clumps up to seven meters in height and is particularly important as a forage and pasture grass, erosion inhibitor, mulch, and as a windbreak for other crops. Traditionally, this crop has been managed for forage production for dairy cattle due to its high yield and protein content. However, for bioenergy purposes, apart from high dry matter production, the plant material should suit quality parameters for reaching the optimal energetic efficiency, which means high levels of fiber and lignin, and low levels of N and ash (McKendry, 2002).

Elephant grass as a potential feedstock for bioenergy production, due the high potential to be used in biofuel production, in the form of charcoal, alcohol, methane or even for direct burning, due to the extremely high positive energy balance. Elephant grass contains 30.9% total carbohydrates, 27% protein, lipid 14.8%, total ash 18.2%, fiber 9.1% (dry weight) (Fedenko et al., 2013).

An important feature of elephant grass in use for energy production is its similarity to crushed sugarcane in high fiber content (~65%), an important characteristic for the calorific value of the biomass (Quesada et al., 2004). Biomass of elephant grass has the potential to be used in biofuel production, in the form of charcoal, alcohol, methane or even for direct burning, due to the extremely high positive energy balance (Strezov et al., 2008; Flores et al., 2012).

Developing biorefineries aimed at resource recovery is a growing trend to devise alternative systems for obtaining energy and materials in a more sustainable way. Within this concept is the use of sugarcane vinasse or other industrial residues to recover water, nutrients and energy as coproducts. In this context, besides of the use of elephant grass in processes of heat generation it can be used as a co-substrate, increasing efficiency of biogas production process.

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