During good digestion, what is the typical alkalinity range?

• A. 100-200 mg/L
• B. 1000-5000 mg/L
• C. 5000-10000 mg/L
• D. 50-200 mg/L

Answer: (B)

Alkalinity is the buffer capacity of the digester, expressed as mg/L of CaCO3, and it’s what keeps pH from swinging downward as acids are produced during digestion. In a well-functioning anaerobic digester, you want enough buffering to ride out those acids, so the typical range is about 1000 to 5000 mg/L as CaCO3. Values much lower (around 100–200 mg/L or 50–200 mg/L) wouldn’t protect the pH well and could hamper digestion, while a range as high as 5000–10000 mg/L is higher than what’s normally required for good digestion. Maintaining this 1000–5000 mg/L level helps keep the pH in the optimal window for methane-producing microorganisms.