Biodegradation and toxicity of waste from anaerobic fermentation of stillage

Several studies have been carried out to produce biofuels by anaerobic digestion of stillage from ethanol fermentation. This type of process, known as ABE Fermentation, generates by-products such as acetone, butanol and ethanol. This fermentation can use pure or mixed cultures of anaerobic bacteria, mainly of the genus Clostridium. In this context, there is the need for deeper studies for proper disposal of the residue resulting from Anaerobic Fermentation of ethanolic stillage, hereinafter referred to as AF stillage (stillage from Anaerobic Fermentation), obtained after this fermentation. Thus, the aim of this study was to evaluate the biodegradation and toxicity of stillage from Anaerobic Fermentation. The biodegradation of AF stillage in soil samples in the presence and absence of commercial inoculum was evaluated using a respirometric method described by Bartha & Pramer, according to the standard NBR 14283 (ABNT, 1999). The production of CO2 was evaluated for 57 days. Additionally, quantification of microorganisms was carried out at the beginning and end of the experiment. Toxicity tests were performed with the microcrustacean Daphnia similis using raw AF stillage and leachate from the respirometry test, according to the standard NBR 12713 (ABNT, 2009). The results of the respirometry test showed that, after 13 days of incubation, the biodegradation efficiency of all samples was above 30%. Using the Friedman statistical test, results showed  that adding the inoculum caused no statistically significant difference in the biodegradation of AF stillage. The acute toxicity tests were performed on raw AF stillage and on the leachates showed that toxicity was removed after biodegradation in soil at all concentrations used. Thus, discharge of AF stillage into soil is an alternative viable disposal. Key words: Biodegradation, stillage, anaerobic fermentation, toxicity.