Wastewater-based algae fertiliser in Europe

September 16, 2025

European researchers are pioneering bio-based fertilisers that reduce pollution, save energy, and could help cut the continent’s dependence on Russian imports. One of the most promising solutions comes from an unexpected source: algae grown on wastewater.

Turning wastewater into plant food

In western France, farmers are testing an algae-based powder fertiliser produced from wastewater effluents. The early results are striking—when combined with mineral fertilisers, the algae-based product reduces chemical fertiliser use by up to 25% without lowering crop yields.

“We grew unicellular algae on dairy effluents from a food processing plant,” explained Orhan Grignon, agriculture and environment advisor at the Chamber of Agriculture in Charente-Maritime.
“The algae feed on organic matter in the wastewater, transforming it into plant biomass. We dehydrate that biomass and spread it on fields as a nitrogen-rich fertiliser.”

Field trials on wheat plots showed that algae powder alone cannot yet match the performance of mineral fertilisers. But when used as a supplement, it offers equal yields while reducing reliance on synthetic inputs.

Benefits and challenges of algae-based fertilisers

Unlike chemical fertilisers, which provide instant nitrogen release, algae fertilisers release nutrients more slowly, requiring farmers to plan and manage application more carefully.

Still, the advantages are clear:

• Lower chemical use while maintaining productivity.
• Easier transport compared to sewage sludge, thanks to dehydration.
• Potential for use in regions where spreading sludge is restricted.

This innovation is part of WALNUT, a European initiative focused on giving wastewater a second life by recovering nutrients and reducing pollution.

Wastewater nutrient recovery in Spain

One standout example is in Ourense, northern Spain, home to one of Europe’s most advanced water treatment plants. Covering nearly 30,000 square meters, the facility processes over 600 litres of wastewater per second.

Instead of simply removing harmful compounds, researchers are recovering valuable nutrients like nitrogen and phosphorus for agricultural use.

Cecilia Lores Fernández, a researcher at CETAQUA, explains:

“Residual streams from sludge treatment are very rich in nitrogen, an essential nutrient for plants. We capture this nitrogen using zeolite beds, extract it with sodium hydroxide, and transform it into ammonium sulphate for farming.”

This method provides a low-carbon alternative to conventional nitrogen production, which consumes vast amounts of energy and releases greenhouse gases.

Building resilient and sustainable food systems

Traditionally, Europe has relied heavily on energy-intensive synthetic fertilisers. By recovering nutrients from wastewater and scaling algae-based solutions, the continent could:

• Cut fertiliser imports and increase self-sufficiency.
• Lower greenhouse gas emissions linked to fertiliser production.
• Reduce water pollution by recycling nutrients that would otherwise be lost.

While more research is needed to optimise these bio-fertilisers, the progress is promising. From algae grown on dairy effluents in France to nitrogen recovery in Spain, these innovations demonstrate how Europe could close the loop between waste and food production.