Organic overloading of an anaerobic digester will cause the pH to do what?

• A. Rise
• B. Drop
• C. Stay the same
• D. Fluctuate

Answer: (B)

When the digester is overloaded with organic matter, acid-producing microbes (acidogenesis) churn out volatile fatty acids faster than the methanogens can convert them to methane and CO2. Those acids accumulate, driving the liquid toward more acidic conditions. The system’s buffering capacity can blunt this, but with excessive loading the buffering is overwhelmed and the pH falls. So the most likely outcome is a decrease in pH, not a rise, stable pH, or mere fluctuation.