The VOA/TIC analysis is a swift and cost-effective test for facility operators to determine the health of their biogas facility. However, what is behind it, what are the benefits, and where are the limitations of this type of analysis?

The VOA value (volatile organic acids) is the total of all acids contained in a sample expressed as acetic acid regardless of the various possible acids. This value does not tell what acids are there and in what concentrations. However, the process quickly shows in which direction biology is developing.

The TIC value (total inorganic carbonate buffer), also simply called buffer, is just like the FOS value - a so-called summary parameter. It includes all buffer substances (carbonate, phosphate, and ammonium compounds) and it is expressed as if all would be carbonates. The buffer allows for a certain stability of the pH-value, which is important for the well being of bacteria. These unicellular organisms thrive on stable conditions, one of which is the pH-value.

The buffer substances bind the acids and release them without a larger impact to the pH-value. The pH-value measures the free acidity level. As mentioned before, it is an important parameter for the bacteria to do their work. However, any changes of biological processes are usually shown too late. The acid spectrum (acidic acid, propionic acid, and butyric acid)

The analysis to determine the acid spectrum is more extensive than the VOA/TIC analysis. The large benefit is the greater significance it expresses. It determines the concentration and ratio of individual acids. In a healthy plant fed with renewable raw materials, the ratio of acidic acid to propionic acid should be 3 to 1 or higher.

An increased propionic acid value may indicate disruptions in the process. This may be caused by a lack of trace elements or medications or chemicals (for example in the manure).