Transforming infrastructures towards sustainability – lessons learnt from using waste heat from wastewater in pilot plants in Cologne

Transforming infrastructures towards sustainability – lessons learnt from using waste heat from wastewater in pilot plants in Cologne

Martin Hirschnitz-Garbers1, Katharina Hölscher2, Alfred Olfert3

1Ecologic Institute, Germany; 2Dutch Research Institute for Transitions DRIFT, The Netherlands; 3Leibniz Institute of Ecological Urban and Regional Development

Consuming almost 75% of global energy and materials, cities are a focal point for efforts to foster sustainability transitions. Urbanization trends and urban lifestyles require investigating and testing approaches to provide public services in robust, affordable, and resource efficient ways. In this context, a German research project analyzes options for physically or organizationally coupling infrastructures that contribute to delivering public services more sustainably. One such option is to use waste-heat from sewerage systems for heat supply.

Against this background, the City of Cologne tested heat supply options through installing pilot plants for wastewater heat use. Based on literature review and expert interviews, we identified factors affecting both the implementation of the pilot plants and the potential to scale up the use of this technology across other cities.

In general, the technology is well established and has been implemented in various places in Germany and other countries. However, the specific technical requirements necessitate a detailed matching of available waste-heat potential in the sewage systems with buildings where technology for wastewater heat use can be installed. The greater the distance of the building to the sewers, the higher the upfront investment costs for laying pipes. This urges utilities to increase heat prices to ensure pay-back of investments, which may reduce acceptance of this technology among users – alongside concerns of smell from sewage water used for heating. Furthermore, different actors are responsible for sewer systems and for heat supply. Thus, using wastewater heat also requires new coordination processes and contracts.

While cooperation between different actors in Cologne allowed for installing three pilot plants, problems with economic efficiency of this technology call for political will to accept lower return on investments as well as for political support through providing co-financing and legal frameworks that foster technology scale-up, e.g. policies on renewable energy use.