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Nutrient recycling speeding up

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8.7.2022

The recycling of nutrients has been studied and advanced in Finland for years, especially for environmental reasons. Now, the steep increase in the prices of inorganic nitrogen fertilisers is also shifting consumption towards recycled fertilisers.

Our beloved fertilisers have various names: mineral, artificial and synthetic fertilisers. They are produced industrially from inorganic raw materials, and their nutrient content is closely regulated. As a result, they are easy to dose as necessary. The challenge with animal manure is high animal intensity. In certain areas the application of manure has especially increased the amount of phosphorus in fields, but also in waterbodies through discharges.

However, mineral fertilisers also produce additional adverse environmental impacts. Nitrogen nutrients are made from fossil natural gas with high carbon dioxide emissions, and phosphorus and potassium are obtained from minerals – non-renewable natural resources. This is why Finnish researchers have extensively studied how plant- and animal-based nutrients could be recycled easily and profitably under control.

Recently, the record-high price of nitrogen nutrients has especially increased general interest in recycled nutrients. The higher cost of natural gas increased prices last year, and the increase continued this year when fertiliser imports from Russia came to a stop.

“By recycling nutrients, we could discontinue the use of mineral fertilisers almost completely regarding phosphorus. At the same time, we could reduce the need for mineral nitrogen if we also used nitrogen-binding methods in crop production,” says Kimmo Rasa, research manager at the Natural Resources Institute Finland (Luke).

Manure to be used at biogas plants on farms

Rasa divides the sources of recycled nutrients into two main streams, of which manure has the higher nutrient content. The other stream consists of sludge from water treatment plants, municipal biowaste, and the side streams of the food and forest industries.

What these nutrients have in common is that it is not usually profitable to transport them unprocessed over long distances to farmers or fertiliser producers. On pig or cattle farms, a biogas plants could be the solution.

Last year, Kyösti and Saara Marttila acquired a biogas plant on their farm to become self-sufficient in terms of energy. They have roughly a thousand pigs, some 200 cows and approximately 600 hectares of cereal fields and grasslands in Jalasjärvi in Kurikka.

They used to spread pig- and cattle-based sludge on their fields by mixing it with soil and to increase the range of nutrients using mineral fertilisers. Now, their biogas plant produces digestion residues from manure, still containing all the nutrients, and in a format in which they are partly easier to use.

If the phosphorus- and potassium-containing solid matter of the digestion residues were placed in a centrifuge to make it relatively dry, it could be transported to farmers for use or fertiliser producers as raw material. The nitrogen-containing liquid could be used on local fields.

“However, we need all the manure we have, and then some, on our fields. Certainly, the separation of digestion residues would also produce benefits on our fields, but each new piece of equipment produces extra costs. We believe that we obtain the most benefits if we build a pipeline and pump digestion residues unprocessed onto our fields,” Kyösti Marttila says.

A solution for all biomass

Marja-Liisa Tapio-Biström, senior adviser in the Ministry of Agriculture and Forestry, expects biogas plants to finally become clearly profitable.

“Now, recycled nutrients are valuable, and interest in biogas plants is very high,” Tapio-Biström says. She has run national trial programmes for nutrient recycling ever since the first was launched some six years ago.

“The trial programmes have developed technologies and logistics, among other things, for producing marketable recycled nutrients from various types of biomass. In recent years, we have rather talked about investments, not about trials.”

Tapio-Biström emphasises that each type of biomass requires a separate solution. For example, sludge obtained from water treatment plants must be processed to separate clean nutrients from any harmful substances.

Focusing on the quality of raw materials

In the town of Eura, it was already understood in 1974 that people need poultry manure in their home gardens, while only a few live close to a local henhouse. Biolan Oy was established next to chicken production, and it has grown into a major producer of recycled fertilisers and substrates, and also expanded its product range to greenhouse and field cultivation under the Novarbo brand.

Hannamaija Fontell, director of R&D and business development at Biolan, says that the company still primarily uses locally obtained poultry and horse manure in its fertilisers.

“We need to know precisely what our raw materials are like, how they fit our recipes and how they need to be processed. In addition, our raw materials must be in compliance with the fertiliser legislation,” Fontell says.

Despite the strict requirements, the company is constantly studying new raw materials, including different side streams of insect production. Biolan is investigating with HKScan whether the imported soy fed to chickens could be replaced by domestic broad beans that would be grown using fertilisers made from poultry manure. As a result, nutrients would be recycled as effectively as possible and completely locally.

Benefits of organic farming for everyone

On his organic farm in Orimattila, Ari Vappula uses recycled fertilisers, including pellets that contain poultry manure and meat bone meal, as well as certain minerals accepted for organic farming. In addition to fertilisation, Vappula ensures the nitrogen supply through nitrogen collector crops and crop rotation.

“It would be perfect if I also had dry poultry and horse manure to add humus to this clay soil,” Vappula says. One obstacle for the application of manure is the scarcity of livestock farms in the nearby area. The farmer’s own attitudes have presented other obstacles.

“The equipment required for application is a high-cost investment, but I simply have to understand that I don’t have to do everything myself. Contractors are top professionals who invest in their equipment.”

Vappula expects the increase in fertiliser prices to make regular farmers – something he also was no more than ten years ago – start using recycled fertilisers.

“The line between organic and regular farming has been too clear-cut. Recycled fertilisers are just as easy to use as other fertilisers, as long as you note the differences in solubility and the effectiveness rate. If I didn’t want to follow the organic criteria for some reason, my production would still be as organic as possible.”

Text: Marianna Salin