The granulation of manure and biogas digestate is a process by which these organic materials are transformed into granules or pellets, making them easier to handle, transport, and apply as fertilizer.
The granulation process
1. Collection and preparation of raw material
- Manure (ideally 20–30% dry matter) and digestate are collected from farms or biogas plants (ideally 20–30% dry matter).
- Large impurities are removed (stones, plastic pieces, etc.).
- Moisture content is adjusted by drying or by adding absorbent materials (straw, sawdust).
2. Fermentation or composting (optional)
- The material is allowed to partially decompose to reduce pathogens and unpleasant odors.
- The process can last between 5 and 30 days, depending on composting conditions.
3. Drying
- This step is required to reduce moisture content to approximately 10–15%, preventing mold formation and ensuring the stability of the final product.
4. Grinding and homogenization
- The material is finely ground to obtain a suitable texture for granulation.
5. Granulation / Pelletizing
- Granulating presses or pellet mills are used to compress the material into a dense and uniform form.
- Natural binders may be added to improve pellet cohesion.
6. Cooling and sorting
- The granules are cooled to harden them and prevent crumbling.
- Non-compliant particles (too small or too large) are removed.
7. Packaging and storage
- The product is packed in bags or in bulk, depending on market requirements.
- Stored in dry, well-ventilated areas.
Advantages of manure and biogas digestate granules
- ✅ Eliminate unpleasant odors compared to fresh manure.
- ✅ Facilitate transport and application due to their compact form.
- ✅ Improve soil fertility through the gradual release of nutrients.
- ✅ Can be used in organic farming as a natural source of fertilization.
