Green recycling of resources in wastewater

Untreated greywater contains nutrients such as nitrogen and phosphorous. This must be removed before the wastewater is released into circulation again to avoid eutrophication and disruption to watercourse and marine ecosystems. One way to do this is to employ nature’s own mechanisms by letting microalgae do the work for us.

In the GRAALrecovery project, NIBIO and other institutions are studying the treatment of wastewater based on a patented system using algae granules. This results in more effective purification of greywater, costs are reduced, and resources are recycled.

“We initially identified the best algae for taking up nitrogen and phosphorous from greywater. We are now focusing on recycling bioresidue products, i.e. the other constituents of the biomass produced by microalgae and which are retrieved from the greywater,” explains Michal Sposób.

Sposób and colleague Ikumi Umetani have experimented with a number of different microalgae in various standardised wastewater samples and under different living and environmental conditions. They have also tested various concentrations and take ups of nutrients such as nitrogen and phosphorous, and looked at the composition of lipids, carbohydrates and proteins measured in the biomass.

Up to now the researchers have discovered two species of microalgae in particular that produce a lot of proteins in greywater. Over 70 per cent of the cells in these are proteins.

“Microalgae can produce chemical compounds that can be used in medicine, fertiliser and food products. At the moment using products created from greywater is prohibited, but in future the algae could become a source of protein, carbohydrates and lipids,” says Sposób.