Lake Aeration Diffusers
Tech Talk 94
The air diffusers used will determine the overall efficiency of a lake aeration/destratification system. The two most common styles are the synergistic airlift assembly (developed by Pentair AES) and the rubber membrane diffuser. Each was designed for different tasks. The synergistic airlift assembly (SAM) is made to lift a large volume of bottom water, thus removing stratification. The rubber membrane type (RM) was designed to aerate wastewater.
Destratification is the most economical form of lake aeration. This is only accomplished by moving large volumes of water. SAMs were developed through extensive underwater flow testing to lift the maximum amount of water from above the diffuser to the surface of the lake with a minimum amount of air (8,000 gpm/hp). This technique requires a specific spacing of the individual diffuser fingers to provide nonturbulent entrainment of the bottom water into the column of rising bubbles. For that reason, they must take on the odd shape of the ALA4GLB, 6GLB and 8GL diffuser manifolds. Each is optimized for a specific depth range.
The smaller ALA4GLB manifold is designed for shallow lakes from 4 to 8 feet in depth. These shallow depths cause short circuiting of the lifted water back to the diffuser, which limits their effectiveness. Therefore, more diffuser manifolds per surface acre of water are required than for a deeper lake of the same size.
The ALA6GLB diffuser manifolds are best used in water 8 to 40 feet deep. The deeper the water, however, the greater volume of air that needs to be used by each diffuser. This is true for all diffusers. The ALA8GLB diffuser manifold is typically used in water deeper than 30 feet.
RM diffusers are not designed to lift water for destratification, so they are not recommended for lake aeration. If used for lake aeration, many more of them must be used to achieve the same result as a single synergistic airlift assembly.
When the rubber membrane diffusers are used in salt water or waste water, they may operate for as long as one year without excessive clogging. After that, remote cleaning can be accomplished by doubling or tripling the amount of air delivered to a diffuser. This will blow up the rubber, as in a balloon, dislodging the fouling matter. Wastewater treatment plants are designed for this, but it may be impractical for lake applications where there is only one compressor.
Sometimes, RM diffusers will tear, greatly reducing their oxygen transfer ability. If detected, retrieve the diffuser and replace the rubber membrane.
The ceramic diffusers used on SAMs should be inspected every three years in most cases. Clogging can be detected by recording the air pressure when new, then annually checking the pressure to see if it has increased. Diffusers can be cleaned by pouring muriatic acid into the air lines and turning on the compressor. The original pressure will be quickly restored and the small amount of acid will be diluted with no effect on the lake.
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