The Science Behind It
When methanogens become stressed they lose the ability to produce methane, which leads to a buildup of volatiles acids. That build up reduces the pH which causes the digester to be acidic (sour) and leads to poor digester performance. Generally, a digester is considered sour if the pH in the digester is too low to allow for the production of significant amounts of methane. Generally this occurs below pH 6. If a digester is already sour, the pH should be adjusted before any other treatment is attempted. Sour digesters have a buildup of methanogen substrate which means the food supplement may actually make the problem worse. After a neutral pH has been reestablished, the food supplement can be used to improve pH stability.
Anaerobic digesters contain a variety of facultative bacteria, strict anaerobic bacteria, and archaea (such as methanogens) which allow a digester to break down volatile solids. Volatile solids are converted to soluble compounds by hydrolysis and then to short chain fatty acids by the acid generating bacteria. Once short chain volatile acids are present in an anaerobic system, the methane generators use the acids to produce biogas (primarily methane and carbon dioxide). Methane generating archaea are much more susceptible to adverse conditions than acid generating bacteria (acetogens) and this is why anaerobic food supplement is so helpful. Anaerobic food supplement supplies methanogens with the COD and micronutrients they need so their populations can build during periods of low nutrient loading.