Research aim is to analyze how sustainable is the use of biosolids generated in a Wastewater Treatment Plant to energy production by fluidized bed gasification under exergy analysis. Energy production system was taken from previous studies by sustainable emergy indicators as the biosolids alternative use more sustainable in emergy terms (Cano et al., 2017). Sustainable evaluation is done by identifying stages of the production chain (from Driying to electricity generation) where it is possible to reduce useful energy losses as well as identifying valorization of waste streams within the system. Exergy destroyed is illustrated by stage and by product. Also, the efficiency in each stage of the supply chain is calculated in order to assess the effects of inefficiencies in the process sustainability. It should be clarified that, in the gasification process, biosolids are mixed with 10% carbon to favor fluidization with the purpose of achieving an improvement in the calorific value of biomass used. Biosolids mixed with coal is exergetically identified as the more sustainable stage of the process, since it presents the highest index of exergetic sustainability (0,99). In contrast to the stages of energy transformation (turbine) and gas cleaning, where efficiency is equal to 0,17 and 0,4 respectively; these stages are of interest in terms of improvements for energy recovery process, making it more efficient, applying new technologies and / or using those waste streams with high energy potentials.