‘Screenings’ is the collective name for the material that is first filtered out of the influent stream at wastewater treatment plants. This material is currently transported to waste incineration plants where it is burned. But these screenings contain a number of (re)usable materials which are lost in the current procedure. The need to circularly reuse residuals is attracting more and more attention. AquaMinerals is working with BlueRoof and five Water Authorities* on a pilot to demonstrate the feasibility of developing a substrate for green roofs from this residual stream.
A substrate fulfils numerous functions in supporting the plants and their growth. It provides a base in which the plants can take root and resist weather conditions. It is also the layer from which plants draw the water and nutrients they need. Moreover, this substrate is of course applied to green roofs, which contribute to the water storage needed for climate adaptation. In the winter a green roof provides added insulation, while it actually contributes to cooling in the summer. This form of cooling is an especially welcome and sustainable (partial) solution in cities during the hot summers. In this way, a unique and circular solution is offered for the screenings generated by the Water Authorities’ operations. After all, water-storing, green roofs support the Water Authorities’ ambition to work on water storage with businesses and residents, and thereby combat both flooding and drought.
The pilot is currently in its first phase. This involves verifying on a large scale all the results achieved on a small scale. This is being done using as many test modules as possible, so as to measure the various properties of the material, such as its water-retention capacity, the runoff delay, but also the leaching or the passage of fertilisers. So far, the results look really good!
The partnership with BlueRoof is a component of the recent collaboration established between AquaMinerals and the Energy and Raw Materials Factory, the network organisation of all the Water Authorities, which is stimulating the transition from wastewater treatment to raw material recovery.
*Waterschap Hollands Noorderkwartier, Hoogheemraadschap van Rijnland, Waterschap Amstel, Gooi en Vecht, Waterschap Aa en Maas en Hoogheemraadschap van Schieland en de Krimpenerwaard