Subsurface Water Aeration
Subsurface water aeration seeks to release bubbles at the bottom of the water body and allow them to rise by the force of buoyancy. Diffused aeration systems utilize bubbles to aerate as well as mix the water. Water displacement from the expulsion of bubbles can cause a mixing action to occur, and the contact between the water and the bubble will result in an oxygen transfer. (1)
Air diffusion systems aerate by pumping air into water through perforated pipes, strainers, porous plates, or tubes. Aeration by diffusion is theoretically superior to water-fall aeration because a fine bubble of air rising through water is continually exposed to fresh liquid surfaces, providing maximum water surface per unit volume of air. Also, the velocity of bubbles ascending through the water is much lower than the velocity of free-falling drops of water, providing a longer contact time. Greatest efficiency is achieved when water flow is countercurrent to the rising air bubbles. (2)
Fine bubble diffused aeration is able to maximize the surface area of the bubbles and thus transfer more oxygen to the water per bubble. Additionally, smaller bubbles take more time to reach the surface so not only is the surface area maximized but so are the number of seconds each bubble spends in the water, allowing it more time to transfer oxygen to the water. As a general rule, smaller bubbles and a deeper release point will generate a greater oxygen transfer rate. (1)
However, almost all of the oxygen dissolved into the water from an air bubble occurs when the bubble is being formed. Only a negligible amount occurs during the bubbles transit to the surface of the water. This is why an aeration process that makes many small bubbles is better than one that makes fewer larger ones. The breaking up of larger bubbles into smaller ones also repeats this formation and transfer process. (1)
One of the drawbacks to fine bubble aeration is that the membranes of ceramic diffusers can sometimes clog and must be cleaned in order to keep them working at their optimum efficiency. Also, they do not possess the ability to mix as well as other aeration techniques, such as coarse bubble aeration. (1) Keeton Industries offers a non-clogging, self-cleaning and self-balancing Duraplate Diffuser that produces fine bubble aeration.
Degraded or Eutrophic ponds and lakes can be characterized by low levels of dissolved oxygen and highly stratified water; where warm, oxygen-rich water is suspended above cool, oxygen-depleted bottom water.
As anaerobic (devoid of oxygen) conditions begin to develop in deeper water, naturally occurring aerobic microbes can no longer perform beneficial tasks, such as waste digestion or water purification. With time, water quality greatly decreases leading to unsightly blooms of algae, the accumulation of organic sludge and the buildup of gases such as hydrogen sulfide, well known for its offensive odor. Low oxygen levels can also lead to fish kills.
Degraded ponds and lakes can easily be enhanced with the addition of a Subsurface Lake Bed Aeration System. This form of aeration acts to increase dissolved oxygen levels while eliminating water stratification. Aerobic microbes can then recolonize deeper water where they rapidly begin to digest accumulated organic sludge and improve water quality.
DIFFUSER AERATION CIRCULATION
- Water is pulled into the diffuser.
- The water is Oxygenated.
- Water is transported up to the surface.
- A laminar current is created.
In fluid dynamics, laminar flow (or streamline flow) occurs when a fluid flows in parallel layers, with no disruption between the layers. At low velocities, the fluid tends to flow without lateral mixing, and adjacent layers slide past one another like playing cards. There are no cross currents perpendicular to the direction of flow, nor eddies or swirls of fluids. In laminar flow, the motion of the particles of the fluid is very orderly with all particles moving in straight lines parallel to the pipe walls. Laminar flow is a flow regime characterized by high momentum diffusion and low momentum convection. (3)
*Lift Rate will vary depending on water depth.