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

  • April 29, 2021 By Edward
DIGESTATE

Digestate is a fertilizer obtained from anaerobic digestion processes where microorganisms break down organic materials in the absence of oxygen. Digestate contains all crop nutrients including nitrogen, phosphorus and potassium. Since no nutrients are lost during anaerobic digestion, farmers can close the nutrient cycle and reuse the minerals. 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. The percentage of readily available nitrogen is higher in digestate compared to the same organic material in its raw form, thereby increasing its fertilizing value. 

The anaerobic digestion consist in a series of biological processes in which the microorganisms break down the biodegradable material in absence of oxygen. The main end products is the biogas, which is combusted to generate electricity and heat, or can be processed into renewable natural gas and fuels.

Examples for digestate products available on the NUTRIMAN Farmer Platform:

Some digestates selected in the NUTRIMAN project are available in Southern Europe.

The pelletized digestate from mixture of pig manure, poultry manure and straw by "MIX-FERTILIZER" process (ID:267) is made starting from digestate of pig manure, chicken manure from poultry farm, and straw (residual vegetal biomass), urea. This digestate fraction contains: 10% N (dm); 4% P2O5 (dm); - 4 % K2O (dm).

The digestate from the co-digestion of vegetable oils waste and pig manure by "VALUVOIL" process (ID:268 ) is made starting from organic wastes such as vegetable oils waste and pig manure, and it contains about: 0.09 N% (fw); 0.2% P2O5 (fw).

Typical nutrient content and availability for plants:

The pelletized digestates usually contains 2.4-10% N (d.m.) and 3-5.5% P2O5  (d.m.) depending on the input materials and on the percentage of humidity (often around 3-10%).

The liquid digestates usually contains 0.05-1% N (d.m.) and 0.2-1% P2O5  (d.m.) depending on the input materials and on the percentage of humidity (often around 70-80%).

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

These digestates are used at 0.2-1 t/ha (pelletized digestate ID:267) or at 40-80 m3/ha (liquid digestate ID:268) according to soil quality, season and crop uptake. They could be used to improve the production of a lot of cereal and horticulture crops.

Benefits for farmers

By using digestates the nutrients (N, P and others) can be more easily taken up by plants. This  implies  that  digestate and derived products can  be  more  suitable  as  fertilisers  than the raw resources from which they originated (such as sludges, slurries, biowastes, etc.).

Treating the bio-wastes in biodigestion anaerobic conditions it is possible to:

  • Produce renewable energy.
  • Reduce odors.
  • Stabilize the manure and co-substrates: the demolition of the carbonaceous organic load resulting from the anaerobic digestion gives the manure a sufficient stability in subsequent periods of storage; it causes a slowdown of the degradation and fermentation processes.
  • Reduce the pathogens content of the input materials: the anaerobic digestion in mesophilic environment (40 °C) can partially reduce the pathogenic charge in the manure. By operating in thermophilic conditions (55 °C) it is possible,  instead,  to  get  the  full  hygienization  of  the  sewage  with  the  total  destruction  of  the pathogens.

These are new fertilizers which contribute to increase the yields of the crops. They contribute to improve the quality of the soil. The soil after cultivation has higher proportion of organic matter. The controlled release of nitrogen reduces leachate losses (aquifer contamination). The GHG emissions are also lower. Furthermore, when producing ID 267-268 not only there is a recovery of waste in the form of nitrogen and phosphate fertilizer but renewable energy is also produced.

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