Aeration basin

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(CC) Photo: Charles E. Tharp
Aeration basin using a submerged grid of air diffusers.

An aeration basin (also called an aeration lagoon) is a holding and/or treatment pond provided with artificial aeration to promote the biochemical oxidation of wastewaters.[1][2][3] There are many other biological processes for treatment of wastewaters, for example the activated sludge process, trickling filters (also called biofilters) and rotating biological contactors. They all have in common the use of oxygen (or air) and microbial action to biotreat the pollutants in wastewaters.

Types of aerated basins

There are many methods for aerating a lagoon or basin:

  • Motor-driven floating surface aerators
  • Motor-driven submerged aerators
  • Motor-driven fixed-in-place surface aerators
  • Injection of compressed air through submerged diffusers

Floating surface aerators

A Typical Surface-Aerated Basing (using motor-driven floating aerators)

Ponds or basins using floating surface aerators achieve 80 to 90% removal of BOD with retention times of 1 to 10 days.[4] The ponds or basins may range in depth from 1.5 to 5.0 metres.[4]

In a surface-aerated system, the aerators provide two functions: they transfer air into the basins required by the biological oxidation reactions, and they provide the mixing required for dispersing the air and for contacting the reactants (that is, oxygen, wastewater and microbes). Typically, the floating surface aerators are rated to deliver the amount of air equivalent to 1.8 to 2.7 kg O2/kWh. However, they do not provide as good mixing as is normally achieved in activated sludge processes and therefore aerated basins do not achieve the same performance level as activated sludge units.[4]

Biochemical oxidation processes are sensitive to temperature and, between 0 °C and 40 °C, the rate of biological reactions increases with temperature. Most surface aerated vessels operate at a temperature of between 4 °C and 32 °C.[4]

References

  1. Middlebrooks, E.J., et al. (1982). Wastewater Stabilization Lagoon Design, Performance and Upgrading. McMillan Publishing. ISBN 0-02-949500-8. 
  2. Tchobanoglous, G., Burton, F.L., and Stensel, H.D. (2003). Wastewater Engineering (Treatment Disposal Reuse) / Metcalf & Eddy, Inc., 4th. McGraw-Hill Book Company. ISBN 0-07-041878-0. 
  3. Beychok, Milton R. (1967). Aqueous Wastes from Petroleum and Petrochemical Plants, 1st. John Wiley & Sons. LCCN 67019834. 
  4. 4.0 4.1 4.2 4.3 Beychok, M.R. (1971). "Performance of surface-aerated basins". Chemical Engineering Progress Symposium Series 67 (107): 322–339. Available at CSA Illumina website