Biogas produced by the treatment of industrial and urban waste become an important alternative to produce renewable energy. It can be used in generating thermal and electric energy and can reduce environmental impacts in production processes, increasing energy efficiency. In the present paper it was developed a model to predict the amount of savings achieved when substituting partially firewood by biogas in industrial boilers to produce electricity. Annual costs and consumption of firewood, and electricity tariffs are considered in the model. A case study in a biotechnology industry located in Maringá, Brazil, was used to test the model, in which biogas is produced from waste water organic sludge and is composed of 73.93 % of methane. Results show that, for the case studied, savings of 26 % where obtained, when compared to the consumption of firewood currently used. The potential of electricity generation is 5 % in relation to the total consumption of the industry. This model could be used for different types of wastewater treatment for biogas production and other fuel used in industrial boilers.