Renewable Natural Gas

Before entering the digester, organic feedstock must be conditioned to optimize biogas yield and protect digester biology:

• pH adjustment: Injection of acids or bases to maintain optimal pH (6.8–7.2) for methanogenic bacteria
• Nutrient supplementation: Dosing of trace elements (iron, cobalt, nickel, selenium) to sustain microbial activity
• Defoaming: Injection of anti-foaming agents to prevent digester overflow
• Substrate dilution: Water and recirculated digestate mixing to achieve target dry solids content

Inside the digester, microorganisms break down organic matter in four sequential stages 

hydrolysis → acidogenesis → acetogenesis → methanogenesis

to produce raw biogas. Chemical dosing during digestion includes:

• pH control: Continuous acid/base injection to maintain the narrow pH window required for methane production
• Iron salt injection: FeCl₃ or FeSO₄ dosing to precipitate dissolved hydrogen sulfide (H₂S), protecting downstream equipment and improving biogas quality
• Alkalinity management: Sodium bicarbonate or lime injection to buffer volatile fatty acid (VFA) accumulation

Raw biogas must be upgraded to pipeline quality through one or more technologies:

• Pressure swing adsorption (PSA)
• Water scrubbing
• Chemical scrubbing (amine wash)
• Membrane separation
• Cryogenic separation

Chemical dosing requirements during upgrading include:

• Amine solution makeup and conditioning (for chemical scrubbing)
• Activated carbon regeneration chemicals
• pH correction in water scrubbing circuits
• Anti-scaling agents for membrane protection

Before injection into the gas grid, upgraded biomethane must meet strict quality specifications for:

• Methane content (>95%)
• Wobbe index
• Moisture content
• Odorant level (THT or mercaptans)

Milton Roy's ODOROY odorization system — developed in partnership with YZ Systems — ensures compliant odorant injection at ultra-low flow rates with full automation, validated by European gas network operators.