The main purpose of wastewater treatment plants concerns water pollution control. However, recent research has shown, that wastewater treatment plants also seem to be interesting from an energetic point of view, as they have high potentials for heat generation beyond common digester gas combustion. Focusing on a case study we intend to feed the available surplus energy of the wastewater treatment plant into public energy distribution grids to supply external consumers. Different software tools are applied to support optimised integration: a central role plays the Geographical Information System based Energy Zone Mapping to analyse existing and future energy demands of different spatial units. Process Network Synthesis is applied to perform optimisation on an economical level. With the Sustainable Process Index the ecological footprint of the regarded technologies is assessed. Besides describing the theoretical background and the practical application of the tools, the paper presents the results obtained from the case study. The investigations give clear evidence, that significant amounts of heat could be supplied to the adjacent consumers at competitive costs and with considerable ecological benefit. Consequently, the wastewater treatment plant analysed provides local energy planners with an “unexpected” and locally available renewable source of energy.