What are common causes of a sour digester?

A sour digester is typically characterized by a buildup of volatile fatty acids (VFAs) that leads to a decrease in pH and can produce odor issues due to anaerobic conditions. Overfeeding occurs when the amount of organic material entering the digester exceeds the operational capacity, resulting in an imbalance in the microbial population and causing stress on the digestion process. If the digester is unable to adequately deal with the excess organic material, this can lead to the fermentation of these materials into VFAs, contributing to the sour condition.

Insufficient mixing is another key factor that can exacerbate sour digester conditions. Proper mixing is essential to evenly distribute the organic matter and microbes throughout the digester, ensuring uniform digestion. Lack of mixing can cause localized areas of high solids concentration and lead to dead zones where digestion is minimal.

Low solids concentration, although not a primary cause of sour conditions on its own, can indicate an overall unhealthy environment in a digester that may struggle to process organics efficiently, potentially contributing to other operational issues.

In summary, overfeeding combined with insufficient mixing creates an environment conducive to sour conditions in a digester, as these issues directly influence the microbiology and the biochemical processes that support effective digestion.