Public dossier The risks The digestate goes on fields
Soil
Digestate is spread as fertiliser. Digestion does not remove heavy metals, and digestate from packaged food waste can carry microplastics.
What is known
- Nitrogen. Most of the nitrogen in digestate is in mineral form: crops use it better, but more of it is also lost by leaching and to the air. When broadcast-spread, 35–60% of the nitrogen can be lost as ammonia. In nitrate-vulnerable zones manure is capped at 170 kg of nitrogen per hectare per year.
- Metals. Digestion does not remove copper and zinc, which end up in the digestate. EU organic fertilisers have limits, for example 300 mg/kg of copper and 800 mg/kg of zinc.
- Microbes and antibiotics. Category 3 animal by-products must be hygienised at 70 °C for 60 minutes. Digestion reduces, but does not eliminate, antibiotics and resistance genes; the evidence is limited.
- Microplastics. Digestate from a commercial-waste digester had 895 particles per kg; from energy-crop digesters, 0–11. Food and packaged waste are the problem.
- PFAS. PFAS have been found in sludge and digestate, but research is still limited.
In Guarda
It is not known which waste will be treated or where the digestate will go. So it is not known which contaminants could reach the fields. Part of the site is in an area at high risk of soil erosion by water.
What to ask the promoter
- Which waste will be accepted? Sewage sludge, slaughterhouse waste, packaged food waste?
- Who receives the digestate, on how many hectares and where?
- What tests will be carried out (metals, microbes, microplastics)?
- Air and odours
- Water
- Soil
- Traffic and noise
- Leaks, fires and explosions
- House values
- Health: what the evidence says
Sources on this page
- Frontiers in Sustainable Food Systems (2024): revisão sobre o uso agrícola do digerido
- Weithmann et al. (2018), Science Advances 4: eaap8060: fertilizantes orgânicos como via de entrada de microplásticos no ambiente
- Diretiva 91/676/CEE (Diretiva Nitratos)
- Regulamento (UE) 2019/1009 (produtos fertilizantes), anexo I
- Higienização de subprodutos animais para metanização (Regulamento (UE) n.º 142/2011, anexo V): ficha do Ministério da Agricultura francês
- Allegrini e Zabaloy (2024), Revista Argentina de Microbiología 56: digeridos anaeróbios em solos agrícolas e resistência a antibióticos
- Estudo de caso sueco sobre PFAS em lamas e digerido
- Ata da reunião ordinária da Câmara Municipal da Guarda de 19 de junho de 2026 (Ponto 18, Proposta VPCM n.º 10/2026)
[1] Peer-reviewed paper
Frontiers in Sustainable Food Systems (2024): revisão sobre o uso agrícola do digerido
[2] Peer-reviewed paper
Weithmann et al. (2018), Science Advances 4: eaap8060: fertilizantes orgânicos como via de entrada de microplásticos no ambiente
[3] Official document
Diretiva 91/676/CEE (Diretiva Nitratos)
[4] Official document
Regulamento (UE) 2019/1009 (produtos fertilizantes), anexo I
[5] Public body
Higienização de subprodutos animais para metanização (Regulamento (UE) n.º 142/2011, anexo V): ficha do Ministério da Agricultura francês
[6] Peer-reviewed paper
Allegrini e Zabaloy (2024), Revista Argentina de Microbiología 56: digeridos anaeróbios em solos agrícolas e resistência a antibióticos
[7] Peer-reviewed paper
Estudo de caso sueco sobre PFAS em lamas e digerido
[8] Official document