Thematic training material for the use of digestate in Northern Europe has been published

Digestate is a wet mixture obtained from an anaerobic digestion process where microorganisms break down organic materials in the absence of oxygen. The anaerobic digestion process converts around 15 % of the feedstock to gas and 85 % remains as organic solid/liquid material. Depending on the composition of the feedstock (biodegradable waste) that is digested, the digester type and process parameters, the composition of digestate may vary strongly. The digestate is usually separated into a solid fraction which contains most of the dry matter, and a liquid fraction which generally has a higher content of mineral N.


Examples for digestate products available on the NUTRIMAN Farmer Platform

There are two digestate products available in Northern Europe that were selected on the NUTRIMAN Farmer Platform. The liquid and solid (dried) fraction digestate from manure and energy maize by "Agrogas" process (ID:264) is produced by physically separating the raw digestate into a liquid and a solid fraction. A  ‘vegetal’  or  animal  manure  status  liquid fraction with a dry matter-content of 3,5-8,5% – issue of the digestate passing a screw press – contains 5,7 – 9,9% N (dm), 2,1 – 6,4% P2O5 (dm) and 5.4 -8.9% K2O (dm). Agrogas’ solid fraction digestate (with animal manure-status) – issue of the digestate passing a (‘sieve’ or ‘screen’) belt press – is usually dried until reaching a dry matter- content of 80-90% and contains N 2,4 – 3,1% N, 3,7 – 5,5% P2O5 (dm) and 1,5 -4,2% K2O (dm).

The high NP pelletized digestate from animal manure and organic waste digestate by "Arbio and NPirriK-project" process (ID:270) is provided by Arbio Bvba in Belgium. Firstly, the digestate of Arbio (biogas installation digesting manure and organic wastes) is separated into a liquid and a solid fraction. The liquid fraction is concentrated via Reverse Osmosis (RO). This concentrate (NK) is then backmixed into the drying of the solid fraction digestate just before drying. Finally, pelletised, this results in an easy to distribute fertiliser-pellet with an optimised and higher N/P-content: 5,9% N (dm)  of which 50% mineral N, 3% P2O5 (dm) and 2,5% K2O (dm)

Typical nutrient content and availability for plants:  The contents of nutrients and availability in digestate can vary a lot due to the variation in the composition of the feedstock (biodegradable waste), the digester type and process parameters. The typical nutrient contents of the digestate products can be N 2.4 – 9.9%, P2O5 2.1 – 6.4% and K2O 1.5 -8.9% on dry matter basis.

Fields of application in agriculture: crop, dosages, application method and practical recommendations.

The digestate product in Northern Europe is recommended to be applied in conventional low input farms. It can be used as fertilizer for cereals, fresh vegetables and strawberries, potato, sugar beet, fresh vegetables and strawberries, grapes, permanent crops (fruit trees), permanent grassland, etc. The recommended application dose range between 2-4 t/ha of solid fraction (ID:264-270) and average 30 t/ha for liquid fraction (ID:264) (depending on soil, season, crop,…). To reduce the ammonia volatilization during field application, it is recommended to incoporate the digestate into soil immidiately after spreading, or use low emission application techniques like injection.

Benefits for farmers: Digestate contains most of the nutrients and micronutrients demanded by plants, including a high content of nitrogen, phosphorus and potassium. After anaerobic digestion, the percentage of readily available nitrogen is higher in digestate compared to the same organic material in its raw form, thereby increasing its fertilising value. The recovery of nutrients from digestate as crop fertilizer can help to close the nutrient loops and contribute to a more sustainable agriculture. Additionally, organic matter in digestate can build up the humus content in the soil which is particularly crucial for arid and semi-arid lands with low carbon content.

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