Concerns about global warming emissions and their impact on climatic conditions have placed great pressure on the search for energy solutions based on renewable sources. The urban planning of cities often focuses on creating efficient alternatives to ensure the well-being of its citizens. However, waste management and recycling of materials are often overlooked aspects of urban planning and are relegated to areas outside the city limits. Waste can be reintroduced into the economic cycles, but achieving this goal is not an easy task given the nuisance such activities may cause to the local population when carried out close to the generation point. The present study analyzes the feasibility of transforming conventional wastewater treatment plants (WWTP) into biorefineries dedicated to processing urban waste. The possibility of using gasification units to convert sludge, pruning, and garden waste into energy was explored. The energy recovery potential of this approach was studied and compared with the performance of a single centralized unit when adding energy crops grown in the city’s surrounding areas. Excessive energy is required to valorize sewage sludge when using thermal technologies due to the high demand for the drying stage. A great extension of land and water resources is necessary to obtain extra energy from this integrated process, which is not always available in many city configurations. However, an increase in energy production can be obtained that is more than double that of the single gasification of sludge.