How did you come up with the idea of researching algae for agricultural use?
IA handful of farmers in the Paderborn District first had the idea. They brought the concept of using algae grown in wastewater to the Algae Biotechnology and Bioenergy Department at Bielefeld University, wondering if there could be potential to use it as an organic fertiliser. We decided to set up a partnership with experts at the Jülich Research Centre, who have extensive experience in algae growing systems. Cycling nutrients from your own wastewater to use as fertilser is exciting, not least because of the scarcity and expense of manufactured product.
How do you grow algae?
You need sun, carbon dioxide from the air, a production facility water can flow over, and a temperature of around 25˚C. At the production plant, small shovel plates ensure that a flow of water runs over a slightly slanted plate at 90 second intervals. This helps to optimise flow, allowing the protozoa to absorb nitrogen and phosphate. Success is achieved when a biofilm forms on the water’s surface. This is microalgae. As it grows, it absorbs nutrients, cleaning the water of nitrate and phosphate.
Algae isn’t too fond of wastewater containing pig manure. But it grows well in water from sewage treatment plants.Prof. Dr. Olaf Kruse
Is there anything algae doesn’t like?
Algae doesn’t tolerate heavily polluted wastewater, for example from pigs. So in partnership with a rural municipal utility, we connected an algae production plant to a sewage treatment plant. The algae grow wonderfully there, and we harvest it once a week. Then we dry it and use it to fertilise grain crops.
Is the effort worth it – what is the yield?
At the sewage treatment plant, we produce around 3 kg of dry fertiliser from 1,000,000 liters of water. This contains 115g of organically bound nitrogen and 40g of phosphorus, which is a relatively small amount due to current limitations of the production facility. However, we plan to significantly increase the output of nutrient absorption by optimising the plant. Going forward, we expect to see a three-fold increase.
When will we see green fertilizer used in our fields?
We’ve been working on this project since spring 2020 and plan a follow-up project with the Federal Ministry of Food and Agriculture (BMEL). The aim is to produce algae at larger plants which are part of the sewage treatment facility near the city of Bielefeld. There, we will examine the nutrient components of the algae, and how suited they are as agricultural fertilizer.
How economical can algae fertilizer be?
At our current test facility, we have an area of 8 m2 in operation. Including electricity, materials and personnel costs, one kilogram of dried organic fertilizer from algae is unaffordable at €272/kg. Expand the area to 1,760 m2, and modify the system slightly, and 1kg would cost €2.22. Which is comparable to organic fertiliser prices. In partnership with the Jülich Research Centre, we plan to investigate algae fertiliser efficiency on a test plot.