Aerobic vs An-Aerobic Systems


Anaerobic (without air): Conventional septic systems are the overwhelming majority of residential septic systems in this country and they have all been based on anaerobic bacteria decomposition. Because of the overall low cost and passive ease of use, residential anaerobic septic treatment has been a wholly accepted standard for a long time. But because anaerobic decomposition is slower, less clean and less efficient, there is very limited municipal treatment use.

Aerobic (requiring air): Historically, because aerobic treatment for residential applications compared to anaerobic is a little more costly and sightly more complex, it’s residential application has been minimal until recently. On the other hand, aerobic bacteria decomposition has been utilized in virtually every major municipal wastewater sewage treatment system in the U.S. Because Aerobic treatment is faster, cleaner and more efficient, it is universally accepted on a massive scale for the municipal treatment of household waste.


Anaerobic: There are four main problems with anaerobic residental septic treatment. First, the treated effluent from an anaerobic septic tank is only about 40-65% clean, therefore its dependent on a secondary treatment phase, where naturally occuring aerobic bacteria in the soil of the leachfield finishes reducing the effluent pathogens. It is critical that a conventional anaerobic leachfield be designed large enough and deep enough to thoroughly allow for this second phase of effluent treatment  to occur. Secondly, when the effluent is discharged into the field, it accumulates as a sludge and builds up in the leach field,  forming a “bio-mat”, and eventually  leads to system failure. Third, the anaerobic biological breakdown process is slow and inefficient compaired to aerobic treatment. And lastly, anaerobic bacteria breakdown produces noxious gases such as methane and leaves offensive odors.

Aerobic: What makes Aerobic systems increasingly attractive to the public is that aerobic treatment systems produce septic effluent that is 98% clean right out of the treatment tank. This allows for a much smaller and shallower leach field. Aerobic systems are essentially a one phase process and unlike anaerobic, they are not dependent on bacterial breakdown in the field. Secondly, because the effluent is 98% clean when its discharged into the leach field there are is no “bio-mat” problems and a leach field will last indefinitely. Third, the aerobic bacteria treatment process is significantly more efficient, accelerated and thorough.  Lastly, aerobic treatment generally produces safe and odorless gas.


  • No Oxygen
  • Effluent quality: 40%-65% clean out the tank
  • Speed/Time: slow
  • Bio-mat: #1 cause of failure
  • Treatment Phases: two(2) – the tank and the field
  • Odor: noxious gasses generally odorless
  • Cost: generally, the least costly
  • Size: large field, and deep trenches 3′-8′ deep
  • Life of system: 10-40 years (average 25)
  • Example: Conventional systems
  • Requiring Oxygen
  • Effluent quality: 98% clean out the tank
  • Speed/Time: fast
  • Bio-mat: failures are not an issue
  • Treatment Phases:    One (1) –  the treatment tank
  • Odor: generally odorless
  • Cost: generally more costly
  • Size: small field and shallow trenches 8″-10″ deep
  • Life of system: indefinite when maintained
  • Examples:  Clearstream or Hydro-Action or Advantex..

Historical use: residential septic municipal sewage treatment








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