Comparative Life Cycle Assessment of four alternatives for using by-products of cane sugar production

Cane sugar production by-products can be considered either as waste, affecting the environment, or as a resource when an appropriate valorization technology is implemented. This study is made with the objective of identifying and quantifying the aspects which have the largest environmental impact of four alternatives for using by-products and wastes from the cane sugar process and suggest improvements in the systems. For this analysis a cane sugar mill was chosen in Cuba and four alternatives were designed for the by-product valorization. The first alternative represents the conventional sugar production; its main characteristics are the use of synthetic fertilizers, pesticides, the bagasse combustion and the usage of molasses and agricultural wastes as animal food. Other wastes constitute emissions to the environment. Alternatives 11, if and IV incorporate more use of by-products and wastes. Alternative 11 considers the use of wastewater, filter cake and ashes for the substitution of synthetic fertilizers. In Alternative 111, the filter cake and wastewater are used for biogas production and Alternative IV integrates alcohol and biogas production into the sugar production process. The assessment is done by means of Life Cycle Assessment, according to the ISO 14040 series by using the SimaPro 6.0 LCA software, Ecoinvent database and the Eco-indicator 99 methodology. As a functional unit the daily sugar production of the mill was defined (216 t/d). The sugar was selected as main product and all the by-products were assumed to substitute other products on the market avoided products. For the four alternatives, the agricultural stage shows the greatest impact due to land use, fuel and agrochemicals consumption. In the industrial stage, the electricity cogeneration with bagasse has the highest impact as to respiratory effects due to the emission of tiny particle material into the atmosphere. The major difference between the alternatives is found in the resource impact category. The advantage of producing alcohol, biogas, animal food and fertilizers from the by-products is made obvious through the comparative study for resource savings. (C) 2008 Elsevier Ltd. All rights reserved.