Fuel Quality Gates

A 2026 TEA/LCA modeled sewage sludge, manure, and food waste HTL with separate upgrading strategies for marine fuel, renewable diesel, and SAF. Marine fuel used mild hydrotreating; renewable diesel and SAF used full hydrotreating and fractionation, with SAF needing deep hydrodenitrogenation below 2 ppm nitrogen.

Implication

The project should not claim one universal fuel product. It should rank product slates by measured nitrogen, sulfur, oxygen, hydrogen demand, and fractionation yield.

Required check

Run one product-slate table for marine, renewable diesel, and SAF using the same biocrude assay and the same hydrogen/catalyst ledger.

Pilot-scale trickle-bed work on nitrogen-rich sewage-sludge biocrude found a useful mild stabilization window, but persistent nitrogen means deeper hydrodenitrogenation is still required for high-value fuels.

Implication

Mild hydrotreating can make raw biocrude safer to handle and less reactive, but it should not be presented as a drop-in diesel or SAF route.

Required check

Separate stabilization success from finished-fuel success by reporting TAN, viscosity, O, N, S, residue, and hydrogen uptake after each stage.

A 2026 food-waste HTL biocrude hydrotreating study compared Pd/C, sulfided NiMo/Al2O3, and CoMo/Al2O3, reporting meaningful differences in deoxygenation and hydrogen consumption.

Implication

Food waste or FOG co-feeds may improve oil quality, but the catalyst/hydrogen tradeoff has to be measured rather than assumed.

Required check

Add catalyst cases for Pd/C, NiMo, and CoMo only after a blended sewage-sludge plus co-feed biocrude assay is available.

ASTM D975-style diesel evaluation includes properties such as flash point, cloud point, water and sediment, ash, distillation, viscosity, sulfur, copper corrosion, cetane, aromaticity, lubricity, and conductivity.

Implication

The model needs property targets, not just elemental targets, before calling a hydrotreated fraction renewable diesel.

Required check

Add a diesel property checklist and require lab data for sulfur, viscosity, distillation, cetane index, cloud point, water/sediment, ash, and stability.

ISO 8217:2024 covers marine fuels from petroleum, synthetic, renewable, and recycled sources, including blends where permitted, and defines requirements before onboard handling such as storage, settling, centrifuging, filtration, and heating.

Implication

Marine fuel may tolerate less severe upgrading than diesel or SAF, but sludge-derived material still has to pass viscosity, stability, sulfur, ash/metals, water, sediment, and compatibility checks.

Required check

Treat marine fuel as the nearest product candidate, with explicit onboard-handling and fuel-cleaning assumptions.

ASTM describes D7566 as the global synthetic aviation turbine fuel standard, with approved annex pathways that produce blending components which can be blended and reidentified as D1655 Jet A or Jet A-1 after final requirements are met.

Implication

Sludge-derived SAF should stay a long-range option until pathway eligibility, deep nitrogen removal, distillation, freeze point, aromatics, thermal stability, and contaminants are proven.

Required check

Do not put SAF in the base case unless the product meets an approved pathway, deep HDN target, and aviation property test suite.