The acid/alkalinity ratio during good digestion should be less than which value?

• A. 0.05
• B. 0.15
• C. 0.20
• D. 0.25

Answer: (D)

In digestion, the acid/alkalinity ratio shows how much acid is being produced relative to the system’s buffering capacity. Alkalinity acts as a buffer to neutralize acids, helping keep pH in a range where methane-producing microbes stay active. When the ratio is low, buffering is sufficient and digestion stays stable. If acid production rises or buffering drops, the ratio climbs and the pH can fall, risking digester upset and inhibition of methanogens. To maintain stable digestion, this ratio should stay under about 0.25. Keeping it below this threshold helps ensure the pH remains near neutral to slightly alkaline, supporting steady methane production. If the ratio approaches 0.25 or higher, you’d typically adjust loading or add alkalinity to restore buffering and stability.