Why is Process monitoring necessary?

Biogas plants are biological systems involving various interacting microorganisms that anaerobically degrade organic matter. The main product is biogas, a gas rich in methane (CH4) that can be used as a renewable fuel for vehicles or to generate heat or electricity for local use or for use via energy distribution grids. The degradation involves four consecutive biological processes: hydrolysis, acidogenesis, acetogenesis and methanogenesis. If one of these processes is negatively affected in any way there is an immediate influence on the other processes and the biogas plant can become unstable. Typical process failures include, among others, organic overload, hydraulic overload and ammonia inhibition.

Process monitoring can help to understand what happens in a biogas plant and help to maintain a stable process. In many cases, a strongly inhibited microorganism population or a total crash of the whole plant can have severe financial consequences for the biogas plant operator.

In general, process monitoring can help to:

• give an overall picture of the biogas process
• identify upcoming instabilities in anaerobic digesters before a crash happens
• accompany a successful start-up or re-start of a plant

The costs of basic monitoring are often much lower than the costs and lost revenue associated with re-establishing a biologically destabilised plant. For example, if a biogas plant has totally crashed it may have to be emptied and filled again with new inoculum. This, together with the necessary start-up period, means that several months can be lost during which the plant could have operated at full load. The financial consequences can be devastating for the plant operator.