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Demonstration of Foam Sensing and Control PDF Print E-mail
Written by Martin Juleff   
Friday, 22 July 2011 09:44

Foam Sensor Control


Waste water is treated by using Anaerobic Biodigesters which are essentially very large fermenters. The effect is to reduce the volume and mass of the inflow. Flammable gases, such as methane, can be produced as part of the process creating possible safety hazards. The digesters are classified as hazardous areas and require equipment to comply with ATEX rules. The organisms usually used in this process, is prone in some cases to generate foam which can cause problems in the digester including "foam-overs" which require a lot of maintenance work to deal with.

Charis, the manufacturer of Semrad's foam sensor, has been supplying the waste water industry in the UK with sensors and controls particularly Southern Water, who have a program to fit the sensors on all their digesters. Southern Water is a privatised public utility who supply and treat water to the south of England.

The System

The system which is being used at Southern water is as follows:

Sensor: FP401/20/2100 Foam/Liquid Sensor installed in the top of the digester via a gas tight connection. Typical length 2.1m

Controller: FLCW2/Z Foam/Liquid Controller, wall mounting IP65 installed with MTL zener barriers. Outputs 4-20 ma and volt-free contacts for foam & sludge detection.

Fittings: FF10/BSP/20 adjustable gas tight fitting for 1" BSP process entry, ball valve welded to pipe flange suitable for digester.

The fitting allows the sensor position to be adjusted at commissioning to set the operating level while retaining the gas pressure. The fitting is screwed into a ball valve with a bore of <20mm diameter, this in turn is fitted to a pipe flange. The sensor can be removed and the valve closed to prevent gas leaking should it ever be necessary.

System Operation.

The sensor detects either foam or sludge. When the foam is detected the controller signals to the site SCADA system via volt-free contacts to add an anti-foam agent to the digester. The anti-foam agent is only added when required which optimises its use and also prevents over dosing.

If the digester outflow blocks or some other event causes the sludge level to rise too high the sensor then signals sludge to the SCADA via a second output and the inflow at the top of the digester is inhibited.

Watch this video to see exactly how it works;


There are several major benefits to the system for Southern Water.

Reduced anti-foam usage
Improved throughput to digester
Better overall process control
Reduced operator time in climbing to top of digester to monitor levels.

Cost saving example: Millbrook water treatment works, Southampton.

No of digesters: 3

Capacity: 2000 cu m each

Throughput: 12000 tonne /year

Anti-foam saving: $53,000 per year

Increased thru put: ~ 6%

Southern Water Sites with the System Installed:

Millbrook, Southampton

Ford, Sussex

Worthing, Sussex

Budds Farm. Portsmouth

Ashford, Kent

Snodland, Kent

Gillingham, Kent

Goddards Green, Brighton

Aylesford, Kent

Anglican Water Sites with the System Installed:

Basildon, Essex

Colchester, Essex

As you can see, this system has become a valuable asset to Southern Water. If you have the same issues as Southern Water had, then you should look into getting one of these systems from us for your own business, and you too could save a huge amount of money.

Last Updated on Friday, 20 July 2018 14:35

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