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Aeration and Circulation

Overview

Oxygen loss can have significant consequences in a lake or water supply reservoir. Oxygen loss can increase nutrient availability via internal loading. It can eliminate critical habitat which purturbs the food-web and the "natural balance" between producers and consumers. It can result in the accumulation of anaerobic respiration products (especially Iron, Sulfide, and Manganese) and can cause serious water supply treatment problems. However, not all oxygen loss results in serious impacts, some anaerobiosis can actually be very good (e.g. Denitrification and Total Phosphorus removal by Iron in the Fall).

Although you will find dozens of "Aeration Vendors", there are only three fundemental Aeration Methods available for lakes and reservoirs:

  1. Eliminate Thermal Stratification by mixing the warm surface layer to the bottom
  2. Subsidize Oxygen Input to the cold water below the thermocline
  3. Circulate a Specific Depth Range to redistribute available oxygen and heat.

Artificial Circulation

Commonly referred to as "destratification", this method mixes the entire water column to prevent the development of a warm water layer floating on colder water. The method can be implemented using diffused air ("bubblers"), mechanical mixers, or other devices. Artificial Circulation can be very useful during specific seasons (for example to extend Spring mixing), to expand the depth of natural mixing of the surface epilimnion layer, or to control how a lake or reservoir mixes in the Fall. It is also useful to control metals accumulation in storage reservoirs. Artificial Circulation is usually not the best approach for direct supply reservoirs, or deep lakes, because it eliminates depth-selective supply withdrawal capability, significantly increases bottom temperatures, eliminates important cool water habitat, and can accelerate respiration rates (increasing oxygen demand at the sediment-water interface).

Hypolimnetic Aeration

Hypolimnetic Aeration increases delivery of dissolved oxygen to the cold water layer below the thermocline without disrupting stratification or warming the bottom. The method can be implemented using several types of hypolimnetic aeration towers (full-lift or partial-lift), oxygenation systems using liquid oxygen or on-site oxygen generators, or side-stram systems. Hypolimnetic Aeration is a very good approach in deeper lakes or reservoirs, to maintain high quality cold water for supply, restoring cold water habitat, and reducing internal nutrient loading due to hypolimnetic anoxia. In reservoirs and lakes where oxygen loss ascends above the thermocline metalimnetic (mid-depth) oxygen loss is likely to persist despite an aerobic hypolimnion.

Layer Aeration

Layer Aeration is the most recent method developed for lakes and reservoirs. This method circulates a mid-depth water layer (designed using a heat and oxygen mass budget). The natural thermocline-metalimnion zone is focused above and below the aerated layer; stratification is preserved. By designing the upper extent of the Aerated Layer above the depth where photosynthesis produces a net excess of dissolved oxygen, the method actually uses the biology of a lake to aerate deeper waters. Layer Aeration is very effective for restoring cold water habitat immediately below the epilimnion, for creating and maintaining high quality raw supply water layers (below algae and above anoxia and metals), and for reducing internal nutrient loading and transport to productive surface waters.

Variation and Oxygenation

There are many variations of these three basic Methods (DownFlow Systems, Solar Driven Systems, etc.). Ecosystem Consulting Service has over 30 years of experience with implementing, operating, and maintaining each of these aeration methods. We service what we sell, and on-and-under water that isn't always easy! No other company has experience with all of these aeration methods. A diagnostic evaluation is needed to identify which method, or integrated combination, is best for a specific reservoir, lake, and intended resource use.

Cost-effectiveness is always a primary consideration, second only to effectiveness! For example, in very large reservoirs, where air conveyance piping is a significant expense, we've developed effective approaches to driving multiple aeration units from one air feed line.

We've also invented equipment that overcomes the problem of water depth/pressure differences causing uneven distribution of diffused aeration, which means more aeration with less in-lake infrastructure.

We design Layer Aerators and Hypolimnetic Aerators that are either fully submerged, partial air-lift systems, or full-lift aerators which can be observed, monitored, and maintained from the surface.

Aeration can be driven by Electric Air Compressors, Solar Power, Wind Turbines, or even Water Power (hydro).

Independant Technical Documentation

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