Technical Bulletin #178: Selecting Lagoon Aeration Systems 

Surface Aeration or Diffused Aeration 

When designing lagoon aeration systems selection of optimum aeration components is critical to maximum performance, long-term operation and easy maintenance.  Lagoon aeration is generally broken down into two major categories surface aeration and diffused aeration.

Surface Aeration 

Lagoon aeration systems dating back to 1960’s were almost all surface aerators.  Surface aerators are still used today, but in fewer applications.  Diffuser technology has matured and offers many processes, or energy benefits vs. surface aerators for MOST applications.  A comparison of diffusers vs surface aerators is shown in table I enclosed.  Surface aerators are still vital for special applications; however, diffused lagoon aeration systems are usually the optimum choice for lagoon aeration technology.   

Lagoon-Diffused Aeration Technology 

Diffused aeration technology for lagoons offers many benefits and features when properly applied.  Proper lagoon diffused aeration design does involve implementation of several engineering decisions for optimum results.  The decisions include: 

 

Fine Bubble or Coarse Bubble? 

 

Floating Lateral or Floor Mounted Diffuser Systems? 

Clearly, any of the diffuser types can be successfully applied to most lagoon aeration applications.  While all these systems are functional, there are key design benefits from an engineering analysis and selection of optimum lagoon aeration technologies or systems.   

 

Fine Bubble or Coarse Bubble Diffusers? 

The selection of fine vs coarse bubble aeration requires a recognition of benefits or liabilities of each. Generally, the following items are driving factors in coarse/fine selection: 

Maintenance – Coarse bubble diffusers generally win this comparison.  Coarse bubble includes static tubes and coarse bubble diffuser units like MaxAir™ units.   

MixingFine Bubble diffusers are superior mixers vs coarse bubble in lagoons or any reactor pumping less than 3% solids.  Coarse bubbles are better mixers when very thixotropic mixtures (3% solids or more) or when energy savings of fine bubble reduces mixing energy in the basins.  Fine bubble at same energy levels pumps more water than coarse bubble at the same energy input, when operating at ½ energy savings with fine bubble, coarse bubble probably has treater pumpage (mixing). 

Energy - Fine bubble truly dominates this variable with oxygenation energy savings of 40-50% vs coarse bubble.  This aeration process energy savings is so significant that most systems today are designed with fine bubble to reduce operating costs; even with the knowledge there may be some maintenance required.  

Since most lagoon aeration systems choose to employ high efficiency diffusers (Fine Pore) technology, we can address how to best deploy Fine Bubble Diffusers.  

Floor Mounted Diffusers 

The first diffusers, coarse or fine, were all designed with piping on the floor and diffusers floor mounted.  Typical floor mounted diffusers are shown in Table 2.  Fine bubble lagoon diffusers were developed by EDI in early 1980’s and were very successful reducing energy and allowing patented access to each unit (hose plus float & rope to allow access).  While these floor mounted systems were major improvements the floor mount had limitations: 

  1. Level floor required to level unit and allow uniform air distribution. 
  2. Sludge deposits were a problem in leveling. 
  3. Sludge deposits could foul diffuser operation. 
  4. Hard to lift unit for maintenance then replace into lagoon at original or proper location. 
  5. Required maximum ballast to hold air pipes and diffusers under water. 
  6. Piping not serviceable without draining the basin.  

Floor mounted units were successful but had limitations from the floor mount that had to be recognized and engineered.  Lagoon technology continued to progress, and floating air supply laterals were introduced for EDI systems in early 1990’s. (See examples on Table 3)With this innovation, major benefits were available: 

  1. Laterals float on lagoon so no ballast to hold pipe under water. 
  2. All piping and the diffuser components available to service without shutdown or draining lagoon. 
  3. Diffuser units hang ABOVE floor. 
  4. Floor elevation not critical as units register from water surface. 
  5. Units suspended above sludge. 
  6. Units always go back into proper location under the air lateral. 
  7. No damage to liners. 
  8. Allows major water level variation with units always at constant design pressure (constant submergence below floating laterals). 
  9. Allows easy application of side slope mixing.  
  10. Suitable for use with floating lagoon covers.  
  11. Lower aerating pressure as lower losses since no need to overcome floor variations. 
  12. Allows application of Bio-Sweep™ technology. 
  13. Allows easiest deployment with wet installation and no need to dewater basin. 

Most lagoon aeration systems will probably continue to take advantage of the benefits outlined above and employ latest floating lateral lagoon aeration technology.   

For more information, contact your local EDI Representatives or contact EDI directly at here.

Table 1

EDI HIGH EFFICIENCY DIFFUSERS  SURFACE AERATORS 

Superior mixing 

  1. Full depth mixing any depth.
  2. Full basin utilization with large number of energy points and full basin distribution.
  3. Act as hydraulic baffles to eliminate short circuiting.
  4. Mixing side-to side and full length on any basin.

 

  1. Limited mixing below 12 ft depth.
  2. Limited energy locations-poor mixing/oxygen distribution.
  3. Limited energy points channelize flow and lose basin utilization.
  4. Not capable of full basin length mixing

Major energy savings 

  1. Approx. 40% energy savings vs. splash type.
  2. Approx. 70% savings vs. induced draft type.
  3.  Low demand charge. 
  1. High energy cost approx. 50% more Kw.
  2. High demand charge.

Maximum process flexibility 

  1. Turn down or throttle entire system.
  2. Throttle individual air laterals.
  3. Generally 50% to 100% spare blower capacity.
  1. Loss of oxygen when units turned off.
  2. No throttling.
  3. No spare capacity.

Reduced electrical 

  1. Lower kilowatt and smaller switch gear.
  2. Only one to three blowers for most systems for reduced switch gear.
  3. No electrical cables in basin.
  1. Large kilowatt load.
  2. Large number of starters. 
  3. Cables to each unit hazardous and costly.

Capital cost 

  1. Deep basins - very economical.
  2. Shallow basins - competitive.
  3. Present worth analysis of 5 years or more - Diffusers always win.
  1. Deep basins - more costly.
  2. Shallow  basins - competitive.
  3. Present worth analysis of 5 years or more - more costly.

Other benefits 

Excellent for cold weather operation. 

Reduced basin cooling maximizes biological efficiency. 

Reduced foaming. 

Reduced maintenance with no moving parts in aeration basin. 

Can be installed in earthen basins; no floor protection required. 

No protection required for basin liners. 

System life over 20 years 

No aerosols 

Freezing during winter may require removal. 

Spray cooling loses biological efficiency. 

Can generates major foam 

Major maintenance of mechanical items in aeration basins. 

Floor protection or erosion control required. 

Liners vulnerable to aerator vortex. 

System life approximately 10 years.  

Aerosols observed over 1 mile from plant 

Table 2: Typical Floor Mounted Diffusers

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Table 3: EDI Floating Lateral Systems 

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EDI Floating Lateral at -25 degrees F

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