Alkalinity Supplementation in Anaerobic Digestion (AD)

Anaerobic digestion is used for solids reduction and as a method of energy production in wastewater treatment.  Organics digesting bacteria use oxygen that is chemically bound in organic compounds such as starches, proteins, and fats.

“Acid former” bacteria break down the organic compounds into organic acids. Then “methane fermenter” bacteria converts the organic acids into biogas.  Methane fermenter bacteria will not work in a pH less than 6.6.  Acids that are being formed will lower the pH, making it important to maintain sufficient alkalinity in the digester to buffer the effect of the acids.  Alkalinity adjustment with magnesium hydroxide causes a rise in both alkalinity (in mg/l as CaCO3) and pH, due to dissociation, which increases the hydroxide content of the digest, increasing the pH.  Monitoring volatile acids and alkalinity in the digester is required for efficient digester process control because the acid/alkalinity ratio will change before the pH begins to drop.    

FloMag®H magnesium hydroxide slurry is ideal for alkalinity supplementation in digestion because:

  • higher alkalinity contribution – more pounds CaCO3 equivalent per pound of dry solids than either 50% caustic soda or 34% hydrated lime,
  • buffering characteristic does not allow pH to elevate above 9, thus the digest is not exposed to microorganism-killing basicity, and
  • non-corrosive, non-hazardous and non-toxic (when used properly) properties provide safer handling for operators.