Woody vs Manure Ag Feedstocks
Chapter contrasting woody / lignocellulosic vs manure and other high-ash agricultural feedstocks for carbon fraction, nutrients, contaminants, and eligibility. Report context: 2026-09-16.
Related notes: Feedstocks · Production · Gasification Residues · Heavy Metals and Ash · Contaminants and Quality · Biochar Nutrients and Fertilizer Chemistry · Production Hub · Key Sources
1. Why the contrast matters
Feedstock sets baseline ash, lignin, and nutrient loads that pyrolysis concentrates or transforms. Woody biomass → high-C, low-ash chars optimized for CDR mass per tonne product. Manures / sludges → lower FC, higher ash and nutrients, tighter contaminant and certification constraints (models soil GHG from biochar · DOI; EBC 10.5E §4).
2. Biomass priors (Woolf Table 1 / Phyllis2)
Mean dry-matter ash and DAF carbon for feedstock classes (Woolf open PDF Table 1; database Phyllis2):
| Feedstock class | Ash (DM) mean | C (DAF) mean | Lignin mean |
|---|---|---|---|
| Wood | 2.2% | 50.7% | 24.7% |
| Herbaceous | 7.0% | 48.9% | 11.8% |
| Wheat straw | 7.2% | 48.8% | 12.3% |
| Manure | 28.5% | 45.2% | 11.3% |
| Sewage sludge | 39.4% | 51.1% | 6.0% |
| Rice residues | 17.9% | 48.3% | 17.9% |
| Pits/shells/stones | 3.8% | 50.6% | 33.2% |
Ash is largely conserved into the solid, so high-ash feedstocks produce high-ash biochars even when organic matter carbonizes fully (Woolf eqs. 2–4).
3. Biochar carbon fraction (Woolf Table 2)
| Feedstock | Pyrolysis FC (mean) | High-T pyro FC | Gasification FC |
|---|---|---|---|
| Wood | 0.76 | 0.81 | 0.63 |
| Herbaceous | 0.64 | 0.66 | 0.38 |
| Manure | 0.39 | 0.39 | 0.14 |
| Sewage sludge | 0.37 | 0.38 | 0.10 |
| Rice residues | 0.47 | 0.48 | 0.20 |
| Pits/shells | 0.72 | 0.76 | 0.52 |
(DOI). CDR implication: one tonne of manure char stores much less organic C than one tonne of wood char at similar permanence of that C.
4. Nutrients and agronomy
EBC notes nutrient contents can reach ~one-third of biochar mass; first-year plant availability often roughly ~15% of P, ~1% of N, ~50% of K in cited ranges (EBC 10.5E §7.4). Manure chars are therefore more “fertilizer-like”; woody chars are nutrient-poor sponges that often need inoculation (Biochar Inoculation for Fertilizer). EBC encourages keeping manure-derived nutrients in agricultural cycles rather than locking them into industrial materials (EBC §4.8).
5. Certification / safety contrasts
| Topic | Woody / plant residues | Manure / animal by-products | Biosolids |
|---|---|---|---|
| EBC soil classes | Positive-list biomass; forest wood needs FSC/PEFC/etc. | Allowed except Feed; H/C_org < 0.4 required | Generally EBC-Basic only; metals often too high for Agro/Urban |
| Heavy metals | Usually low if clean biomass | Watch Cu/Zn; concentration effect | Often limiting |
| PFAS | Low unless contaminated | Variable | Elevated risk → test (PFAS) |
| Feed grade | Possible (FeedPlus plant biomass) | Not for FeedPlus | No |
(EBC 10.5E §4.7–4.9). Credit methodologies add their own feedstock eligibility—see MRV Stack / methodology notes, not duplicated here.
6. Practice takeaway
- Match feedstock to goal: CDR mass → clean woody/low-ash; nutrient recycling → manures with metals/PFAS controls.
- Always measure FC and H/C_org on high-ash chars rather than assuming wood defaults (H-Corg and O-Corg).
- Track competing uses (feed, bedding, soil OM, energy) for additionality narratives (Feedstocks).