Comparative exergy assessment of vinasse disposal alternatives: Concentration, anaerobic digestion and fertirrigation

The ethanol distillation produces large quantities of vinasse, a wastewater with high concentrations of organic and inorganic substances that may cause environmental damages if incorrectly disposed. In this way, different alternatives are proposed to enhance the efficiency of vinasse disposal, such as the anaerobic digestion and concentration processes. However, the evaluation of the thermodynamic performance of those systems and their possible energy integration was seldom investigated. Thus, an exergy assessment and comparison of five different scenarios of vinasse disposal, including the vinasse fertirrigation, concentration and anaerobic digestion processes, is presented in this paper. The results indicate that, among the disposal alternatives, the highest exergy efficiency (20.1%) is attained by a system combining anaerobic digestion and vinasse concentration in series. In this case, the wastewater treatment plant produces the maximum amount of biogas, while the vinasse concentration still recovers water and reduce diesel consumption. Furthermore, the heat integration between the biogas power plant and vinasse concentration is able to increase the exergy efficiency of these processes (10-51%) and reduce 9-11% of steam consumption. In general, the major sources of exergy destruction in vinasse disposal alternatives are related with the exergy loss of organic substances in fertirrigation and irreversibilities in steam generation. (C) 2019 Elsevier Ltd. All rights reserved.