N₂ Fixation in Sugar Cane: the Role of Acetobacter Diazotrophicus

Abstract

Almost 4 million cars in Brazil are fueled by hydrated (95%) ethanol produced from sugar cane and the remaining 6 to 8 million light vehicles run on gasohol (gasoline mixed with 15 to 22% ethanol). The bio-ethanol programme has great environmental advantages: Not only does the addition of ethanol to gasoline obviate the need for tetra-ethyl lead, but engines running on hydrated alcohol produce less carbon monoxide, nitrogen oxides and hydrocarbon in the exhaust gases than conventional gasoline engines (Boddey, 1993). Furthermore, unlike gasoline or other fossil fuels, the combustion of this biofuel makes no net contribution to global CO₂ emissions as the carbon was fixed from the atmosphere by the sugar cane crop. However, when considering the CO₂ emission budget, the amount of fossil fuel used to grow the crop must be taken into account. This includes diesel fuel for agricultural machinery and transport of cane to the mill, as well as the energy used to process the cane and distill the ethanol. As sugar cane in Brazil is still largely harvested manually, and the energy to power the mills and distilleries is all provided from burning bagasse, this ratio of energy value of the ethanol to fossil fuel used in its production (the energy balance) is very favourable (approximately 4.5).