By David Graff, AAU Communication and Public Affairs

Crushed concrete from the building and construction sector and iron-coated granules from drinking water plants can significantly improve the removal of contaminants in stormwater management and treatment systems in urban areas.

This is the conclusion documented by Irina Pitropova, lead author of three peer-reviewed articles that were the focal point of the PhD degree she just successfully defended at the Department the Built Environment at Aalborg University.

The research findings have pluses for several bottom lines:

• First, a stronger treatment process is key to limiting the harmful effects of nutrient discharge, such as eutrophication and oxygen depletion.
• Second, the recycling of concrete and iron-coated granules can potentially be included in the nature-based solutions that are increasingly used for treatment at drainage system outlets in urban areas.
• And third, recycling supports the widespread ambition in the country's municipalities for strengthened sustainability and circular economy.

"The research demonstrates significant potential to help solve one of society's most pressing problems, namely water pollution, by upgrading existing stormwater infrastructure with locally available residual materials rather than investing in completely new treatment technologies," says Irina Pitropova, who after defending her PhD joined VIA University College as an assistant professor.

Big pluses - and some minuses 

The results from the experiments discussed in the research articles are convincing. For example, in experiments with pilot-scale bioretention plants and column experiments, the materials removed more than 90% of the phosphorus under the conditions studied.

This represents improvements of up to 33.3% compared to the control systems.

Similar results were achieved in the experiments with crushed concrete, but there were also challenges that require further research, explains Jes Vollertsen, Professor, BUILD and the principal supervisor on Irina Pitropova's PhD project:

"Although crushed concrete has great potential as a long-lasting, sustainable and cost-effective filter media for removing phosphorus, copper and zinc, the experiments also showed an elevated pH value in the runoff water as well as significant leaching of chromium, among other things. Therefore, further research is needed that examines optimized material sourcing, targeted pre-treatment and possible applications," he explains.