When an anaerobic digester is upset, what is the first sign observed?

In the context of anaerobic digestion, when an upset occurs, the first sign typically observed is a decrease in alkalinity coupled with an increase in volatile acid concentration. This occurrence is particularly important because it reflects a shift in the microbial balance within the digester.

When the digestion process is functioning normally, a balance is maintained between the production of volatile fatty acids (which are produced from the breakdown of organic matter) and the alkalinity that is generated by the buffering capacity of the system. An upset can be triggered by various factors such as excessive loading, toxicity, or issues with temperature, which can disrupt this balance.

As volatile acids accumulate, they can lead to a state of acidification, which is detrimental to the methanogenic bacteria responsible for producing methane. The increased concentration of these acids, coupled with a reduction in alkalinity, indicates that the digester is becoming more acidic and is at risk of failing to function properly if corrective measures are not taken promptly. This is significant for operators because recognizing these symptoms early allows for the implementation of interventions to restore balance in the anaerobic digestion process.

Therefore, the increase in volatile acid concentration and the corresponding decrease in alkalinity serve as critical indicators of an upset condition in an anaerobic dig