There can be many warning signs to anaerobic digestion process instability. Your digester will often start to show typical symptoms of poor performance in many different ways. It is the job of the operator to spot these signs through physical checks and also biological tests. Once the problem has been identified, an appropriate solution can be made.
What is Anaerobic Digestion Process Instability?
Instability can occur at any moment in the process. There will be more trigger points when loading the digester or changing one of the variables slightly. On the whole, process instability is when the digester becomes unstable in such a way that it starts to have an impact on the performance of the system as a whole.
What Are the Main Indicators?
There can be many indicators as to why a digester is becoming unstable, but there are a few common signs:
- Low methane concentration (poor biogas quality)
- High Hydrogen Sulphide (H2S) concentration in biogas
- Reduced biogas/methane production
- Foaming (More on foaming)
- Digester acidification
- Highly sensitive against acid production
The Effects of Anaerobic Digestion Process Instability
Process instability can cause havoc in your digester. In some cases it can mean the digester has to be emptied and the whole process has to start from the beginning. This can be damaging to the environment and also your profits.
If the digester is performing sub-optimally then we can get poor electricity generation from the CHP unit, and low-quality biogas/methane to inject back into the grid, depending on the type of the system being used.
The worst effects of instability typically come from an overloading of the digester. This can either be the OLR being too high for how the digester has been designed. This causes a shock to the digester and makes the biology become unstable. Another example is irregular feeds into the digester. If the feeds are not regulated then it can mean the process variables are spiking and dropping quite quickly in short spaces of time. Whereas, if regular feeds into the digester are introduced then it can allow the digester to avoid spiking.
Reference – Roots Organics Ltd
