What are the four primary RNG feedstock categories?

Landfill gas (LFG), dairy/livestock manure, WWTP digester sludge, and food waste / source-separated organics. Each produces ~60% CH₄ biogas but with materially different H₂S/siloxane loads, lifecycle CIs, and regulatory drivers — dairy is the most economically attractive due to the CARB LCFS avoided-baseline credit (typical CI −250 to −400 gCO₂e/MJ).

What is the typical RNG project revenue stack?

Industry stacked value for California-injected dairy RNG is ~$70–80/MMBtu: gas tariff $5/MMBtu + D3 RIN $35/MMBtu (12.987 RINs/MMBtu × ~$2.75/RIN) + CARB LCFS $30/MMBtu (depends on pathway CI and credit price). Landfill/WWTP projects without the dairy avoided-methane credit typically achieve $30–50/MMBtu stacked.

Which CO₂ removal technology is best for biogas upgrading?

It depends on project scale and CI sensitivity. PSA (6-bed CMS): lowest OPEX ($0.50–1.50/MMBtu), 96–98% recovery, best for mid-scale projects. Membrane (2- or 3-stage polyimide): higher OPEX but lower CH₄ slip — preferred for CARB LCFS-critical dairy projects. Amine: highest recovery (99.5%+), best for large plants (≥10 MMscfd). Water scrubbing: common in Europe, simpler but less common in US.

RNG / Biogas Engineering Fundamentals

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Feedstock Characterization

LandGEM v3.03 / IPCC 2019 / M&E 5e

Landfill, dairy manure, WWTP digester, and food waste — methane potential, yield models, regulatory triggers.

Feedstock LandGEM

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Biogas Cleanup: H₂S, Siloxane, Moisture, VOC

GPSA §21 / Schweigkofler 2001 / Soreanu 2011

Iron-oxide scavenger sizing for H₂S, GAC adsorption for siloxanes, moisture / VOC pretreatment before upgrading.

Cleanup GPSA

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CO₂ Removal Upgrading

Yang / Ruthven / Baker 3e / GPSA §17

PSA vs membrane vs amine vs water scrubbing — methane recovery, slip, compression power, capex/opex tradeoffs.

PSA / Membrane Upgrading

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Pathway Economics: D3 RIN + CARB LCFS

40 CFR 80.1415 / 17 CCR §95488 / CA-GREET

D3 RIN + LCFS + pipeline tariff stacked revenue, 2024 avoided-methane phase-out, NPV / IRR / payback drivers.

D3 RIN LCFS