Anaerobic digesters are not the easiest place to measure level. It is a demanding process within a sealed vessel, with changing surface conditions, gas production, foam formation, restricted access and, in many cases, critical pipework and valves mounted up to 30m high.
For wastewater treatment sites, foam in a digester is more than a process nuisance. If it rises too high, it can enter the gas line, restrict flow, contaminate valves and create a chain reaction of maintenance, downtime and compliance headaches.
And once gas handling is involved, venting or releasing gas is not a simple option. Some permitted sites operate under Environment Agency emissions requirements, with MCERTS providing the quality framework for emissions monitoring to comply with the Industrial Emissions Directive (IED). Reliable measurement and proactive foam management can therefore play an important role in both operational efficiency and regulatory compliance.
A water company in the UK has relied on VEGA radar level measurement to help manage these challenges. Sludge level and changing surface conditions can be monitored continuously and without contact, helping the site identify developing foam conditions and respond before they become a more serious operational problem.
Why foam control matters on digesters
Foam-over events on anaerobic digesters can have significant consequences.
If foam rises too high and enters the biogas collection line, it can cause blockages and create problems elsewhere in the process. Where emissions and gas handling are tightly controlled, this can become more than simply a process housekeeping issue.
There is also a practical maintenance consideration. Valves mounted on top of the digester are vulnerable to fouling and contamination from foam carry-over. Accessing them can require crane hire and may mean taking the vessel out of service, resulting in a costly and time-consuming intervention.
Preventing those conditions from developing in the first place is therefore considerably more desirable than dealing with the consequences afterwards.
Looking beyond the level
The non-contact radar is mounted on the digester roof and provides continuous level measurement of the sludge surface.
For this application, however, the requirement was not simply to know the level inside the digester. The site also needed greater visibility of changing surface conditions and the potential development of foam.
Radar measurement can provide valuable information about what is happening within the process beyond the primary level value. With the right application knowledge and configuration, changes in measurement conditions can be used to help identify developing foam before it reaches critical pipework or gas-handling equipment.
This gives operators the opportunity to respond earlier, while continuing to reliably monitor the sludge level itself.
From early indication to action
Identifying changing process conditions is only part of the challenge. The next consideration is what happens once those conditions are detected.
Depending on the application and the site’s existing control philosophy, the measurement system can be configured to provide an early indication to operators or to support an automated response.
For this particular wastewater application, VEGA worked with the site to use the available measurement information to help manage foam proactively rather than waiting for a foam-over event to occur.
This helps protect gas lines and valves from foam carry-over, reduces the potential for unplanned maintenance and gives operators greater visibility of what is happening inside a vessel that is otherwise difficult to access.
The response can also be integrated into the plant’s wider control strategy, helping move foam management away from reactive intervention towards a more controlled process.
Every digester is different
There is no single configuration that will suit every anaerobic digester.
Vessel geometry, process conditions, existing instrumentation, control requirements and the behaviour of the product surface can all affect the measurement approach.
That makes understanding the application as important as selecting the instrument itself.
VEGA’s water industry specialists work with wastewater operators to look at the individual process conditions and determine how radar level measurement and the information available from it can be used most effectively.
Are foam conditions causing problems on your digesters?
If foam carry-over, difficult-to-access instrumentation or unreliable level measurement is creating operational problems on your anaerobic digesters, speak to VEGA.
There may be more information available from your level measurement than you realise.
Our UK water industry team and local sales engineers can review your application and discuss how non-contact radar measurement could provide greater visibility of changing process conditions, helping you identify and respond to problems before they lead to blocked gas lines, contaminated valves, unplanned maintenance or downtime.
Talk to our water industry specialists about your application.
