(218e) Evaluation of Dioxins and Their Precursors in Fly Ashes and Wastewater Generated in the WET Scrubbing of Flue Gases from Sugarcane Bagasse Boilers

Sugarcane is one of the most efficient crops in the world for the combined production of sugar, ethanol, and energy. Brazil, India, and China produce together 66% of World’s total. Despite the clear benefits to the economy and to the renewable energetic matrix of these countries, the enormous numbers of sugarcane processing also imply important impacts for the environment. The operation of boilers and cogeneration plants based on combustion of sugarcane bagasse releases great amounts of flue gases containing particulate matter (PM), which must be collected before emission to the atmosphere. Wet scrubbers are the most used technology to control PM, presenting the required efficiency to meet the emission limits to the atmosphere. Nevertheless, scrubbers demand the recirculation of large volumes of water that must be treated and represent important costs for the process. Recent studies have alerted that fly ashes conveyed in flue gases from bagasse combustion can contain dioxins, a group of highly toxic and persistent chemical compounds that are harmful to humans and other species. The absorption of dioxins in the scrubbing water could possibly contaminate the whole sugarcane process (due to water recirculation) and the environment (due to wastewater discharge in the field or in aquatic systems). The origin of the precursors of dioxins in the bagasse boilers is still unclear, but the possibility of spreading the contamination to the environment is of special concern in Brazil, where most of the ≈ 400 sugarcane industries in operation are located above the Guarani Aquifer System, one of the largest reservoirs of fresh water in the world. In this work, the collected ashes and the wastewater generated in the scrubbing process of five of the largest sugarcanes industries in Brazil were monitored along the season to detect the presence of dioxins or chlorine and organic carbon compounds, which are dioxin precursors. The metal composition of bagasse ashes was also evaluated to track possible catalysts for formation of dioxins. The results were correlated to the production processes in each industry to identify the sources of contaminants and to propose actions to prevent dioxin formation or to mitigate the environmental impacts.