In this study, a new methodology for online monitoring of second-generation ethanol production is presented. The prediction of the concentration of ethanol, substrate and cells from secondary measurements (pH, turbidity, CO2 and temperature) is compared with experimental data from the fermentation of a mixture of molasses and hydrolyzed sugarcane bagasse from the alkaline hydrogen peroxide pre-treatment at 25% and 75% of volume. The Extreme Learning Machine algorithm (ELM) provided a very good alternative to traditional Multilayer Perceptron neural networks (MLP) and the BAT optimization technique applied to ELM algorithm provided a fast parallel search for the best solution. This new methodology offered a good alternative to the standard soft- sensor approach based on MLP and fast and reliable product quality estimates for key process variables as in second-generation ethanol production. © 2014 Elsevier B.V.33 955960Dias, M.O.S., Junqueira, T.L., Cavalett, O., Pavanello, L.G., Cunha, M.P., Jesus, C.D.F., Maciel Filho, R., Bonomia, A., Biorefineries for the production of first and second generation ethanol and electricity from sugarcane (2013) Applied Energy, 109, pp. 72-78Oiveira, J.F.L., Ludermir, T.B., A Modified Artificial Fish Swarm Algorithm for the Optimization of Extreme Learning Machines (2012) Proceedings ICANN 2012. (Org.). Lecture Notes in Computer Science. 1ed.: Springer Berlin Heidelberg, 7553, pp. 66-73Salvatore, L., Souza, M.B., Junior, M.C., Campos, M.M., Design and Implementation of a Neural Network Based Soft Sensor to Infer Sulfur Content in a Brazilian Diesel Hydrotreating Unit (2009) Chemical Engineering Transactions, 17, pp. 1389-1394Rivera, E.C., Farias, F.S., Atala, D.I.P., Andrade, R.R., Costa, A.C., Maciel Filho, R., Development and implementation of an automated monitoring system for improved bioethanol production (2009) Chemical Engineering Transactions, 18, pp. 451-456Herrera, W.E., Maciel Filho, R., Development of a monitoring hybrid system for bioethanol production (2013) Chemical Engineering Transactions, 32, pp. 943-948Herrera, W.E., Development and implementation of a software sensor for monitoring online of bioprocess (2012) MSc dissertation, School of Chemical Engineering, , State University of Campinas, BrazilYang, X.-S., A New Metaheuristic Bat Inspired Algorithm (2010) Nature Inspired Cooperative Strategies for Optimization, 284, pp. 65-74Huang, G.-B., Zhu, Q.-Y., Siew, C.-K., Extreme Learning Machine: A New Learning Scheme of Feedforward Neural Networks (2009) Proceedings of International Joint Conference on Neural Networks, 2, pp. 985-990