As a digester approaches "sour" conditions, what happens?

As a digester approaches "sour" conditions, there are significant changes in the biochemical processes occurring within it. "Sour" conditions typically indicate an imbalance in the digestion process, often linked to increased levels of volatile fatty acids and a decline in alkalinity.

When a digester becomes sour, the concentration of volatile acids increases. This accumulation is often due to the incomplete breakdown of organic matter, leading to an overproduction of acids while the microorganisms that convert these acids into methane are either inhibited or not functioning effectively.

Simultaneously, the alkalinity of the solids within the digester decreases. Alkalinity acts as a buffering capacity, helping to neutralize the acids produced during digestion. Thus, as volatile acids accumulate and the process becomes less stable, this buffering capacity diminishes, leading to a further decline in pH levels which can exacerbate the sour conditions.

Additionally, as the biochemistry shifts towards higher acid concentrations, the amount of methane production decreases. This is due to the inhibition of methanogenic bacteria, which are essential for converting these volatile acids into methane. If these bacteria cannot thrive or function optimally in the increasingly acidic environment, the overall methane production drops severely.

Therefore, recognizing that all these factors — the increase in