Pioneering, sustainable technology 'riothermal' will heat apartments in DOK+ from next summer

The Keerdok site in Mechelen is under development as a new, sustainable urban district with residential, office and commercial units. Currently, the necessary infrastructure is being installed to sustainably heat the buildings without using fossil energy. Sewerage, or heat from sewage water, plays the main role in this and is supplemented by geothermal, or heat from the ground. The combination of both technologies on this scale is unique in Europe.

Once the buildings of the two projects currently under construction (D'Île Malines and DOK+) are in use, the energy required for heating will be obtained from sewage water. In total, we are talking about a heat demand for 358 homes, office and hospitality spaces, as the Keerdokpark project, which is yet to be developed, may also connect at a later date.

Residual heat from showers, among other things

Riothermie is an innovative technique that is not yet widely used in Flanders. For sewage treatment company Aquafin, it is the third application, after its own office in Aartselaar and the new swimming pool in Sint-Niklaas. Mechelen does have the first for the application in a project that also includes residential units.

"With riothermal, we use the heat in the sewage water from showers, washing machines, dishwashers, etc. as an energy source to feed a local heat network," explained Maarten Raemdonck, manager of Innovation at Aquafin. "We place a heat exchanger in the sewer pipe to extract heat from the sewage water and bring a conductor fluid to the desired temperature. The heat conductor fluid is then offered to a heat pump in the building."

Geothermal energy as support

As a primary heat source for the buildings on the Keerdok site, sewage heat is a sustainable, easily deployable and financially attractive choice. It is also a stable heat source because wastewater is always flowing through the collector. In order to be able to meet the heat demand even when snow is melting, for example, when the temperature in the sewage system takes a dive, the combination is made here with geothermal energy. Under the Red Cross Square and under the new construction projects, geothermal boreholes were drilled for this purpose to extract heat from the ground. The geothermal energy also allows passive cooling to be supplied to residents during the warmer summer months, thus reheating the soil. The synergy of the two heat sources effectively creates an underground heat battery and allows the site to be supplied with 100% green heat all year round.

"Noven wants to provide sustainable heating and cooling to as many buildings in Belgium as possible and to relieve customers of as much of the burden as possible in doing so," said Jeroen Rabaey, CEO of Noven. "We are very grateful for the confidence of Aquafin, the city and the project partners Global Estate Group, DCA, Kairos-Montréal, Vanderstraeten, ION and NEW. We need projects like this a lot more."

Mechelen fossil-free

Alderman for Public Works Patrick Princen said, "The combination of sewage heat and geothermal energy on this scale is unique in Europe. The project also fits completely within the city's heating strategy to heat Mechelen fossil-free by 2050. This spring, Aquafin and about 25 other stakeholders co-signed the Charter of the Mechelen Heat Coalition. With this project, Aquafin illustrates perfectly how, thanks to collaboration between the city and various sectors, we can make great strides locally toward a fossil-free future. An example for the many organizations, companies and countries that are currently discussing a climate agreement in Baku."

"The scale at which we are combining sewage heat with geothermal on the Keerdok is a first and puts our city on the map as a pioneer in sustainable urban development. The technology we are deploying here shows how renewable energy sources can be optimally utilized. It is impressive how a relatively unknown energy source like sewage water has so much potential to heat an entire neighborhood. This project shows that in Mechelen we are not afraid to push the boundaries of urban development. This makes the Keerdok site more than a residential area, it is a blueprint for the cities of tomorrow," said Greet Geypen, alderman for Urban Development.

Collector prior renovated

Before Aquafin could install the heat exchanger in its collector on Winketkaai, it first had to renovate it. That was done very recently by means of a so-called relining technique in which a resin-impregnated stocking is pulled through the pipe. Through circulation with hot water, the stocking then hardens and closes closely against the inner wall of the pipe. This procedure significantly extends the service life of the sewage system so that the continuity of heat supply from sewage heat is ensured for years to come. Since the pipe was renovated from the inside, this did not require any excavation or breaking work and significantly shortened the execution time.

Construction work at the Keerdok site is proceeding on schedule. In the fall of 2025, the buildings can be put into use.