How long does a sour digester typically take to recover?

• A. 30-60 days
• B. 7-14 days
• C. 90-120 days
• D. 1-2 days

Answer: (A)

Sour digesters recover as the microbial community rebalances and the chemical conditions inside the digester stabilize. When a digester goes sour, acid-producing bacteria surge and pH drops, inhibiting the methanogens that produce methane. Restoring a healthy balance requires time for the acid conditions to subside, alkalinity to rebuild, and the methanogenic population to re-establish, all while operating conditions such as temperature, loading rate, and mixing are brought back to normal. In typical wastewater treatment practice, this stabilization process takes on the order of weeks to a couple of months, with 30–60 days being the usual recovery window. Short periods like 7–14 days aren’t enough for the microbial community to rebound, while 1–2 days is unrealistically fast and 90–120 days is longer than commonly observed for standard recoveries.