Aqua Technique has extensive experience in engineering aeration systems to combat the effects of eutrophication. Aqua Technique’s LIMNO® and DAD systems operate by maintaining a minimum level of dissolved oxygen in the water body. This breaks the vicious circle of eutrophication, since restoring oxidising conditions in the sediments helps to curb the release of nuisance compounds. Two methods are used: destratification and aeration of the hypolimnion.
Aqua Technique has extensive experience in engineering aeration systems to combat the effects of eutrophication. Aqua Technique’s LIMNO and DAD systems operate by maintaining a minimum level of dissolved oxygen in the water body. This breaks the vicious circle of eutrophication, since restoring oxidising conditions in the sediments helps to curb the release of nuisance compounds. Two methods are used: destratification and aeration of the hypolimnion.
Destratification is used to increase oxygen levels in lakes or reservoirs 3 to 15 metres deep through top-to-bottom mixing of the water column. This is effected by means of a bubble curtain immersed in the water body, into which compressed air is fed.
The LIMNO, our hypolimnetic aeration system, is an original device which works by dissolving compressed air to raise oxygen levels in the bottom layers of water without mixing the water column. This type of device is used in lakes more than 15 metres deep.
These systems are designed following collection of a range of data on the water body concerned.
Principles of operation: Compressed air is blown through a system of perforated pipes located at the bottom of the lake. This leads to the formation of a rising plume of air bubbles which entrains the water upwards. Reoxygenation is achieved, first through direct diffusion from the air bubbles, and then through the eddies at the surface.
Aqua Technique's DAD technology is suitable for water bodies of up to 15 metres in depth or having a low degree of thermal stratification. For greater depths, the LIMNO technology is recommended.
Installation characteristics such as air flow and pipe design, depend on the size, depth, shape and water quality parameters of the lake. Aqua Technique designs custom-built pipe systems using its own software to model lake behaviour.
Air supply: Clean air is delivered into the pipes from an electrically-powered compressor in a sound-proof chamber on the bank of the lake. Oil-free air can be supplied, if required, and the air may be oxygen-enriched to improve water quality.
Implementation: The DAD system is generally implemented in conditions of high thermal stability, usually between April and October when the cold, stagnant, bottom layer of the lake is progressively deprived of its oxygen content. The system may be operated on either a part-time or permanent basis, depending on water quality and lake characteristics.
The LIMNO® aerates the deep, cold, oxygen-poor layers of the water body. It does not upset its thermal stability and thus avoids the mixing of the deeper layers with the warmer surface layers.
- Compressed air is blown into a diffuser (1) at the bottom of the LIMNO and entrains water up with it (2).
- The water is reoxygenated by contact with the air bubbles (3), then returned to the bottom where it discharges through radial outlets (4). The excess air is discharged through the vent pipe (5).
The standard system is generally used in water bodies more than 15 m deep. For shallower reservoirs and lakes, a shorter LIMNO® may be used or, alternatively, diffuse Aeration /Destratification techniques.
There are several designs of LIMNO, all manufactured in materials which are highly resistant to prolonged immersion in water. The largest model, 10 m long and 5 m in diameter is constructed of a flexible fabric and oxygenerated the hypolimnion to a distance of more than 300 m from the point of installation. The smallest model, in polyester, provides aeration at different flow rates.
Clean air (oil residual level: 0,005 ppm) is delivered by an electrically powered air compressor in an outdoor sound-proofed chamber. Where necessary, completely oil free or oxygen enriched air can be supplied.
- Operation: During the deep layer oxygen deficit period usually April through October.
- Maintenance: An annual visit to replace the filters and change the compressor oil.