Wastewater treatment plants have a relevant role within the circular economy chain of the cities. They purify contaminated waters and materials and biogas can be recovered from their processes. This article analyzes the potential integration of District Heating systems with wastewater treatment plants, using the biogas generated, in combination with natural gas, to supply heat and domestic hot water to the municipalities integrated in the wastewater network. A methodology is proposed to analyze the potential for implementation of these systems based on the evaluation of the requirements of transmission and distribution networks and cost benefit analysis. As case study this methodology was applied to 88 sewage treatment plants located in the Atlantic and Continental regions of Spain. Each wastewater treatment facility provides services to more than 50,000 equivalent users. The analysis is oriented to district heating system in cities with high/medium urban wastewater load. Analytical expressions to estimate capital expenditures as function of district heating network capacity have been obtained from data of the municipalities under analysis. The results for the analysed region show a potential for CO2 emissions savings of 1.8 Mt per year with an overall investment of 2,854 M euros. (C) 2019 Elsevier Ltd. All rights reserved.