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DP Seals puts the
bubbles back into
anaerobic digestion

DP Seals has developed a long life bubble bar component for C & C Green Energy's anaerobic digestion system.

Anaerobic digestion is the natural breakdown of organic materials into methane, carbon dioxide and a liquid fertiliser. The GALAD™ system, based on the innovative approach developed by Christopher Maltin and his team at Organic Power, uses specially shaped tanks incorporating an inverted V section aeration device with no moving parts that produces a gas curtain to stir the material being digested.

Gas at slightly above atmospheric pressure is pumped into the bubble bar at a variable flow rate; slits in the bar release the pressure as a bubble curtain that completely mixes the organic waste by setting up a controlled circulation pattern within the low energy shaped tank.

The GALAD System can treat a wide diversity of waste materials: domestic and industrial organic wastes, food processing residues, agricultural slurries and energy crops - even abattoir offal waste. DP Seals' challenge was to find a material that would survive such an extremely aggressive environment inside the tank and provide the right sized bubbles for the mixing action.

"Typically, when we select materials for a custom moulding, we know the key parameters of the surrounding environment. But this is probably the nastiest single environment we have come across."
Andrew Piper, Technical Director

After examining several alternatives, DP Seals suggested soft, high-strength silicone. Silicon is one of the few rubber polymers resistant to such a diverse range of potential waste materials; selecting a soft variant ensured the slits in the moulding would open momentarily at the right time to produce good-sized bubbles capable of stirring the effluent. Extensive live trials carried out on a test rig installed at DP Seals proved the mouldings met C & C Green Energy’s requirements.

“The tests clearly showed the new bubble bar moulding produced a better bubble flow and survived the environment significantly longer than other materials. DP Seals' input to this project has been significant."
Graeme Morpeth, Project Leader, C & C Green Energy

Each bubble bar moulding incorporates a large number gas-bubble generating slits and is locked into a recyclable plastic extrusion. The overall design ensures solids agitated by the mixing action cannot collect on the bubble bar.