Abstract
Sugarcane vinasse is one of the most polluting residues produced by Brazilian ethanol industries, mainly because of its harmful effects on the environmental, such as high organic matter load and acidity. Anaerobic digestion is a highly efficient wastewater treatment method that could potentially be used to treat sugarcane vinasse. This study examined the anaerobic biodigestion of sugarcane vinasse in mesophilic conditions (30 - 45°C) by varying the inoculum concentration (0.5 to 5.5%) and pH (6 - 8). Changes of Chemical Oxygen Demand (COD), total solids content, and yield and composition of biogas after the biodigestion of the vinasse were assessed. The vinasse was efficiently digested under mesophilic anaerobic conditions over a 23-day Hydraulic Retention Time (HRT) and a 5-day acidogenic phase with a consequent reduction of COD (54 - 83%) and total solids (52 - 87%). Statistical analyses at a confidence level of 95% suggested that temperature, pH and inoculum concentration did not influence on the anaerobic biodigestion of the vinasse. The optimal operating parameters were found to be temperatures of 30 - 35°C, inoculum concentration of 0.5% and pH of 6 - 7. The results emphasize the promising use of the treated sugarcane vinasse as a biofertilizer for agriculture, indicating that the anaerobic digestion process is an excellent alternative for Brazilian ethanol industries.
Highlights
The growing public concern over the preservation of the environment has stimulated a worldwide search for more sustainable agricultural procedures and alternative sources of energy
Characterization of sugarcane vinasse and Hydraulic Retention Time (HRT) of experiments The physicochemical characterization of the “in nature” sugarcane vinasse is reported in Similar HRT values have been reported in the literature, but with regard to the biodigestion of other residues, for example vegetable waste (20 days) (Bouallagui et al, 2003), and semi-solid organic waste (22.5 – 33.7 days) (Lastella et al, 2002)
Amaral et al (2004) reported that a HRT of 40 days reduced the total solid content of bovine manure that underwent anaerobic biodigestion, but that it decreased the relative production of biogas which was inferior to that obtained with a HRT of 20 days
Summary
The growing public concern over the preservation of the environment has stimulated a worldwide search for more sustainable agricultural procedures and alternative sources of energy. Only a few countries have a plenitude of natural resources to produce large amounts of energy crops without jeopardizing their food production capacity. For example, has developed a very modern sugarcane industry for ethanol production over the last 30 years. The country has a territory of 851 million hectares with climate conditions highly suitable to the production of massive amounts of sugarcane with minimal need for irrigation (Leite et al, 2009). Sugarcane is cultivated in more than 100 countries around the world. 80% of sugarcane production is concentrated in 10 countries, among which Brazil is the leader in terms of cultivated area and ethanol industry scale (Doll and Foresti, 2010). The annual production of ethanol in Brazil is 28 million m3 (UDOP, 2014) which, when combined with the corn ethanol production of the United States, comprises about 70 – 80% of worldwide ethanol production (Vian, 2015)
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