In the two-year project, waste water heat was studied up to the discharge of treated waste water from the property producing waste water.
The review took into account, for example, the flow of Wastewater and the heat stored in it into the network in different uses, the change in the temperature of the wastewater in the sewer network, the effects on biological nitrogen removal at wastewater treatment plants, and the effects on the centralized heat recovery implemented after the wastewater treatment plant.
In addition, the project examined the heat recovery of the hot water supplied to the properties.
The main leader of the project was HSY and its project partners were Turku region treatment plant, Turku Water Supply, Turku Region Water, Helen, Fortum and Turku Energy.
The starting point in the reviews was that wastewater treatment plants cannot, at the expense of heat recovery, begin to weaken nitrogen removal from wastewater. The project examined different scenarios in which the location and intensity of heat recovery varied.
The final results determined, among other things, the energy balance of heat recovery on the scale of the entire city and the scale of expansion investments required for wastewater treatment.
The temperature of the waste water affects the cleaning result
“Treatment plants are designed to operate in a certain wastewater temperature range. If heat is recovered from the wastewater before the wastewater treatment plant, this may require large investments in the capacity of the treatment plant. In that case, the operation of the treatment plant should also be adapted to the new situation, and not all the effects are known yet”, says the head of the wastewater treatment department Christian Sahlstedt about HSY in the bulletin.
In the project, it was discovered that there is potential in the heat recovery and cooling of domestic water, which can be exploited without harm to the various parties, because based on the network simulations of the case studies, the water reaches the consumers in a long network in any case at a temperature that is close to the temperature of the soil.