CircBrief: Nutrient recycling is an essential part of a sustainable food system

materiaalitkiertoon.fi @circwaste

Nutrient self sufficiency and security of supply can both be promoted by recycling domestic biomasses effectively, turning them into recycled fertilizer products and using them in farming.

Nutrient recycling is an essential part of a sustainable food system year, approx. 18 million tonnes of biomass suitable for nutrient recycling is • Each produced in Finland, such as livestock manure and municipal and industrial waste side streams.

applied evenly onto Finland’s arable lands, this biomass could cover • Ifaround 90% of the phosphorus needs of crops. recycle nutrients and carbon more efficiently, the processing • To rate of biomasses, especially manure, should be increased. have proven that the efficiency of biogas production and nutrient • Studies use on farms could be improved by sedimentation of slurry. farming techniques enable better • Precision use of recycled nutrients.

• CircBrief – best practices of circular economy • April 2023 •

Recycled fertiliser products from different biomasses Nutrient recycling enables the returning of nutrients and organic matter, contained in agricultural, urban and industrial biomasses, back to food production. Recycling reduces dependence on mineral fertilisers, increases nutrient self-sufficiency and security of supply in food production, and reduces the environmental impact. As a part of the Baltic Sea Action Plan and Governmental Programme objectives, Finland has committed to improve nutrient recycling to reduce nutrient load to water bodies.

Recycled fertiliser products can be manufactured from different biomasses, around 18 million tonnes of which are in Finland annually. These biodegradable materials, manures and waste streams from municipalities and the food industry contain around 20,000 tonnes of phosphorus, which covers 90% of the phosphorus needs of crops.

Fluctuation in fertiliser prices has increased interest in recycled fertilisers. There are already many recycled fertiliser products available on the market for different uses. For the features and application practices of these products, see Natural Resources Institute Finland’s guide on recycled fertilisers: https://jukuri.luke.fi/handle/10024/544071 (in Finnish)

Biomasses, especially manure, should be processed more efficiently At the moment, approx. 80% of nutrient-rich biomasses that can be recycled end up being used in agriculture. Most of this is manure, of which only 7% is processed. Manure is mainly used in the vicinity of livestock farms, which means that regional nutrient surpluses cannot be evened out. By processing, the nutrients can be concentrated into a form in which they can be transported more efficiently to areas where fertilisers are needed. The processing rate of biomasses should consequently be increased to improve the recycling of nutrients and organic matter.

Recyclable biomasses annually 13 Mt

Recycled fertiliser products can be produced from different biomasses, around 18 million tonnes of which are produced annually.

4,40 Mt 0,67 Mt

Nitrogen (N) Phosphorus (P)

0,42 Mt

0,40 Mt

Livestock manure

Grass

Municipal sewage sludge

Municipal biowaste

Food industry side streams

72 000 t 15 100 t

4 600 t 600 t

7 300 t 4 000 t

3 000 t 500 t

7 200 t 800 t

Gravitational settling of pig slurry improves the efficiency of biogas production and fertilisation Gravitational settling of pig slurry can promote energy production in a biogas plant and the recycling of nutrients. Compared to unseparated raw slurry, the settled solids of slurry sediment have a high energy density and phosphorus content, whereas the low-phosphorus supernatant (liquid above the settled solids) is a suitable nitrogen fertiliser for phosphorus-rich fields. The method was tested and demonstrated in the Circwaste project.

For slurries with a low dry matter content (1% to 2%), adequate settling time can be less than 24 hours per metre of slurry depth. Settling thicker (5% to 9% dry matter) slurries requires considerably longer settling times: a vast majority of methane producing organic matter can be settled in ca. 25 days, but efficient phosphorus separation may require ca. 60 days per metre of slurry depth.

• CircBrief • Nutrient recycling is an essential part of a sustainable food system • April 2023 •

After settling, if top 3/4 of the “slurry column” in a tank is removed as supernatant, the remaining settled solids at the bottom of the tank may have ca. 100% higher dry matter content and methane production potential per tonne of wet weight than unseparated slurry. Therefore, it is more profitable to use the energy-rich solids as biogas plant feedstock, rather than the unseparated slurry. If the slurry to be settled has a high dry matter content, the settled solids might not be suitable for anaerobic digestion on their own due to high contents of organic matter and nitrogen, and therefore more dilute complementary feedstocks may be needed.

If the slurry to be settled has an average dry matter content (7%), the methane production potential of the lower half of the slurry column is more than 50% higher than that of unseparated slurry. If the top half is removed as supernatant and used as nitrogen fertiliser on fields, 160% more soluble nitrogen per hectare could be applied within the phosphorus restrictions than when using unseparated slurry. Phosphorus content of the supernatant is lowest at the surface of the slurry column. Digestate produced by the biogas plant can also be separated by settling or by other, more efficient methods.

Farm 1

3/4 supernatant: soluble N/P 4.4 Field A

1/4 sediment: 328 kWh/t

Farm 2

1/2 supernatant: soluble N/P 7.3 Field B

1/2 sediment: 263 kWh/t

Farm 3

Slurry 171 kWh/t, soluble N/P 2.8

Digestate Biogas plant

Separation

Liquid fraction

Field C

Solid fraction

A concept in which unseparated slurry is delivered to a biogas plant from nearby farms and the bottom sediment of settled slurry is transported to from further away. The soluble nitrogen and total phosphorus ratio (soluble N/P) determines how much soluble nitrogen can be applied to a field within the phosphorus limit. In the Figure, the methane production potential is given as kWh/t per wet ton.

Making the most of recycled nutrients with precision farming techniques Recycled fertiliser products often contain one to two main nutrients. This enables the use of recycled nutrients for making different nutrient combinations for fertilisation in precision combined seed-drilling, together with or separately from traditional multinutrient fertilisers. The current granular recycled fertilisers are equally suitable for tractor-seeder units as conventional fertilisers. However, some recycled nutrient products, such as ammonium sulphate, are only available as liquids.

Liquid recycled fertilisers for seed-drilling Fertiliser tanks, controls and equipment for liquid fertilisers can be added to existing combined seed-driller units with little need for structural modifications. Liquid fertiliser tanks can be placed in front of, behind or even on top of the seed-driller unit shaft. Precision application of liquid fertilisers then takes place using hydraulic technology, and the fertilisers are fed through a hose system into the seeder discs together with granular fertilisers.

Efficiency and usability from machine automation Location-specific application of different types of fertilisers from separate fertiliser tanks can be managed automatically using the ISOBUS technology of agricultural machinery. The user-friendly control devices for different fertiliser grades in the system are managed as a single automation unit and with one set of controls. Manufacturers of agricultural machinery and equipment have the capacity to produce such machinery combinations if there is demand for them.

Accuracy also for top-up fertilisation Liquid recycled fertiliser products, such as ammonium sulphate, can also be applied as top dressing fertilisation for the crop. With a precision spray boom, top dressing fertilisation can be applied in specific locations as needed by the crop.

These methods have been studied and tested in the Circwaste project.

• CircBrief • Nutrient recycling is an essential part of a sustainable food system • April 2023 •

Combined information on biomasses, nutrients and recycled fertiliser products To improve the efficiency of nutrient recycling, more combined information on materials suitable for nutrient recycling, their locations, nutrient concentrations and processing possibilities is needed. For example, information on the availability of different biomasses can be used to plan local investments in the production of recycled fertilising products and raw material procurements. Regional information is needed to support not only planning but also the monitoring and steering of nutrient recycling.

Biomass Atlas – biomass resources on the map Information on the generation and locations of biomasses has been compiled in Natural Resources Institute Finland’s Biomass Atlas tool. The tool provides spatial data concerning different biomasses at a single location, as well as information on land use, forest resources, logging side streams, arable crop production and its side streams, manures, and biodegradable industrial and municipal waste and sludges.

Read more about the tool: https://projects.luke.fi/biomassa-atlas/en/ Nutrient recycling indicator The Nutrient recycling indicator published by Natural Resources Institute Finland describes the potential for nutrient recycling of different biomasses and shows the current situation of nutrient recycling. The indicator examines biomass volumes regionally and analyses the total amount of organic matter, nitrogen and phosphorus they contain. Read more about the indicator: https://www.luke.fi/fi/tilastot/ indikaattorit/ravinteiden-kierratyksen-indikaattori (in Finnish) Recycled fertiliser production on the map Information on the production of recycled fertiliser products in Finland has been compiled in both the nutrient recycling indicator and ProAgria’s, Recycled fertiliser producers on the map, tool. These services provide information on operators’ locations, quantities of nutrients produced, and any on-going projects in the sector. Read more about the tool: http:// map.karttapalvelut.fi/proagria (in Finnish)

CircBrief – best practices of circular economy:

Nutrient recycling is an essential part of a sustainable food system April 2023 Writers:

Liisa Pesonen, Ville Pyykkönen, Ari-Matti Seppänen ja Elina Tampio / Luonnonvarakeskus Luke Sari Piippo, Hanna Savolahti ja Tuuli Myllymaa / Suomen ympäristökeskus (Syke) References: Luke 2022. Ravinteiden kierrätyksen indikaattori. https://www.luke. fi/fi/tilastot/indikaattorit/kiertotalous-luonnonvaraaloilla Biomassa Atlas. Biomassatiedot yhdessä verkkopalvelussa. https:// projects.luke.fi/biomassa-atlas/ Lemola, R., Uusitalo, E., Luostarinen, S., Tampio, E., Laakso, J., Lehtonen, E., Skyttä, A., Turtola, E. 2023. Fosforin kierrätyksen tarve ja potentiaali kasvintuotannossa. Synteesiraportti.

Luonnonvara- ja biotalouden tutkimus 10/2023. Luonnonvarakeskus, Helsinki. http://urn.fi/URN:ISBN:978-952-380-612-2 Pyykkönen, V., Laakso, J., Lehtonen, E., Blasco, L. Sian lietelannan laskeutus ja biokaasuprosessointi. Circwaste-hankkeen raportti.

Julkaistaan keväällä 2023.

Seppänen, A., Luostarinen, S., Pesonen, L. 2019.

Kierrätyslannoitus - Suunnittelu, käytännön ja mahdollisuudet tulevaisuudessa. Luonnonvarakeskus, Helsinki. http://urn.fi/ URN:ISBN:978-952-326-759-6 Vainio, E. (toim.). 2022. Maatalouden typpihaaste – vaihtoehtoja ja ratkaisuja. Synteesiraportti. Luonnonvara- ja biotalouden tutkimus 53/2022. Luonnonvarakeskus, Helsinki. http://urn.fi/ URN:ISBN:978-952-380-458-6 Tehoa biokaasun tuotantoon ja ravinteiden kierrätykseen (verkkosivu) https://www.materiaalitkiertoon.fi/fi-FI/Circwaste/ Osahankkeet_alueittain/LounaisSuomi/Tehoa_biokaasun_ tuotantoon_ja_ravinteide(48167) Communications specialist: Hannele Ahponen, Syke Graphic design: Satu Turtiainen, Syke Layout and illustrations: Anna Polkutie Cover photo: Liisa Pesonen Helsinki 10/2023 ISBN 978-952-11-5600-7 (pdf) ISBN 978-952-11-5601-4 (print)

LIFE15 IPE FI 004 Circwaste-project receives financial support from EU for the production of its materials.

The views reflected within the contents are entirely the project’s own and the EU commission is not responsible for any use of them.