The Technical University of Munich is experimenting with mixtures made from construction and organic waste to reduce pollution and improve soil fertility
Urban regeneration also passes through the recycling of materials, particularly those from construction sites, to be reused in the creation of so-called artificial soils: mixtures produced by combining excavated material with a series of substances that can enhance their functions according to the intended use.
This is the focus of a project — which has already led to field tests — carried out by the Technical University of Munich (TUM). “Soil excavated from construction sites usually ends up in landfill, but it has great potential”, explain the researchers involved in the project, which has already shown that “by adjusting the mixture” — that is, combining construction-site waste with other materials — “specific properties can be adapted to each use case, such as fertile green spaces or groundwater protection”.
Excavated construction soil from building sites accounts for a quarter of waste in EU countries. And while part of this material is currently used to “enrich” soil in urban areas, for example in parks, under EU rules this practice will have to be phased out by 2050 as part of the strategy to protect extra-urban areas.
Artificial soils could therefore represent a valid alternative, according to the German researchers, who are using excavated construction soil and identifying its potential in urban planning. Specifically, samples of soil excavated from construction sites in Munich and Augsburg were collected and then mixed with compost from organic waste and with biochar, also known as “black earth”, made from organic waste products, for example from biogas production.
In the soils where these materials were used, several indicators of soil functionality increased. The soils became more fertile in terms of nitrogen content, which quadrupled, and carbon accumulation also rose. In addition, groundwater can be protected, as these materials can immobilise up to 90% of pollutants such as heavy metals.
“It is a win-win situation: we keep waste out of landfill and can create soil as a basis for different purposes in urban spaces,” explains Lauren Porter, first author of the publication presenting the results of the tests, which focused on artificially produced soils used as plant substrates in greenhouses.
The results, according to the paper, show that plants from wetland areas thrive in these soils and can withstand various stress factors, including heat, flooding and pollutants.
There is another important benefit: the mixtures can be highly customised. For example, in solutions designed to reinforce road sections, the anti-pollution properties can be increased, while in green areas the mixture can be adjusted to promote plant fertility. In short, “tailor-made” soils can be created according to the desired functions and the area of application.
“In the long term, our findings can support city and building planners,” Porter highlights. “The more knowledge we have about soils, the more they can be adapted to each use. And this is essential for closing the resource cycle for soils.”
