ABSTRACT
Concerns about the high dependence on fossil fuels and the resultant GHG emissions have highlighted the importance for sustainable and renewable energy production. Biomass-derived fuel (biofuel) is attracting attention because it is renewable and it has zero net GHG emissions. Biofuel can be produced from food crops such as corn, sugarcane, or oil palm. However, use of food crops for fuel production has been a subject of food versus fuel criticism. Recently, utilizing agricultural crop residues to produce energy has been receiving an increasing attention because the residues are non-edible, thus the criticism can be avoided. Water and land are finite resources, and the intensive use of agrochemicals to obtain high biomass yield can threaten the environment by releasing pollutants and nutrients. For this reason, water and agrochemical use of biofuel production (kg/ha and L/ha, respectively) were compared for eight first-generation feedstocks. The agrochemical use (kg/ha) was then converted into energy equivalent values (GJ/ha) to investigate the potential environmental impact of using the chemicals. Total potential energy yield (GJ/ha) produced from both crops and residues was estimated using the data from previous studies. Sugarcane, sugar beet, corn, and wheat were selected as bioethanol feedstocks, and soybean, oil palm, rapeseed, and sunflower were selected as biodiesel feedstocks. Biofuel produced from the lignocellulosic biomass such as crop residues is classified as the second-generation biofuel, which requires additional pre-treatment processes for the fuel production or can be used for electricity production through thermal conversion processes. Calorific value of each type of residue was employed to estimate the additional energy that can be produced from the residues. The results of this study showed that the sugar beet production required the least volume of water to produce a unit of energy (32.9 L/MJ). In contrast, soybean consumed the highest volume of water (270.4 L/MJ) but required the least energy input for applying agrochemicals per hectare of crop production (1.2 GJ/ha) among the eight feedstocks. Sugar beet had the highest energy input of 15.8 GJ/ha for using agrochemicals, followed by rapeseed production (11.8 GJ/ha). Sugarcane had significantly high crop and residue yield (73.4 t/ha and 14.6 t/ha, respectively) among the eight feedstocks. The energy yield produced from the main crops was in the order of sugarcane (141.5 GJ/ha) > sugar beet (136.7 GJ/ha) > corn (68.9 GJ/ha) > wheat (62.3 GJ/ha) for the bioethanol feedstocks, and oil palm (157.5 GJ/ha) > rapeseed (44.9 GJ/ha) > sunflower (25.1 GJ/ha) > soybean (16.6 GJ/ha) for the biodiesel feedstocks. Bagasse, as the sugarcane residue, showed the largest potential for producing additional energy of 266.0 GJ/ha. Oil palm (133.2 GJ/ha) and sugar beet (74.9 GJ/ha) residues also demonstrated the potential to produce considerable amount of additional energy. Overall, bioethanol production requires less water for crop cultivation than biodiesel production and produces more energy from the crops and residues, except oil palm biodiesel production. This study suggests that the second-generation bioenergy feedstocks have the potential to reduce the fossil fuel dependency by producing additional energy.
