EXTENDED AERATION/FIXED FILM SYSTEMS

Extended aeration (suspended growth) systems operate using the activated sludge process which is a process for treating sewage using air and a biological mass composed of bacteria and protozoans. The bacteria are free floating in the effluent.This process is not new to the industry. In fact, it was discovered around 1913 by two engineers in the UK.

In sewage treatment, this process is used to oxidize organic/boilogical matter and nitrogenous matter (mainly ammonium and nitrogen), remove phosphate, drive off gases (carbon dioxide, ammonia, nitrogen etc.) and generate a biologcial floc that settles easily. Used in aerobic treatment systems, this process typically generates a clear/odorless effluent.

Fixed film systems utilize a medium in which microorganisms grow. There are basically two types of fixed film systems, trickle and submerged systems. Trickle systems operate by allowing wastewater to flow over the media. Common media types are sphagnum moss, coconut husks or geotextiles. The media in a submerged system is just that, submerged. In this type of system the effluent is in continual contact with the media.

Advantages of fixed film over extended aeration:

  1. no washout of the bacteria will occur during high flows (click  here to  view video)
  2. quick recovery of the bacteria population occurs after periods of low or no use
  3. less susceptible to toxic events/chemicals
  4. no bulking of solids due to endogenous respiration (reduces sludge production)

If designed and dosed properly, a trickle system can provide better treatment than a submerged because there is a higher oxygen content available to the bacteria as the media is in a completely aerated environment. A submerged system only has as much oxygen available as can be dissolved into solution of the effluent. The amount of oxygen that can be dissolved is dependent upon alkalinity, temperature and elevation.

A submerged system, however, does not require additional equipment to continuously pump and distribute effluent over the media which is required in a trickle system to avoid the drying of the bacteria on the media. There are also no moving parts or media/diffusers to clean. The submerged media is self cleaning and does not have to be replaced as trickle system media periodically does. In addition, added nitrogen removal that is inherent and passive occurs and requires no other parts like pumps/panels, etc.

Trickle fixed film systems tend to be relatively cost prohibitive for single family residences. Several suspended growth products are available in Florida (AquaKlear, HOOT, Singulair®). These systems perform well especially in residential applications. Fixed film systems such as the MicroFAST® perform exceptionally well on residential applications whether it be single or multiple family homes. The HighStrengthFAST® is used for commercial sites such as day cares, assisted living facilities, restaurants etc.

ize organic/biological matter and nitrogenous matter (mainly ammonium and nitrogen), remove phosphate, drive off gases (carbon dioxide, ammonia, nitrogen etc.) and generate a biologcial floc that settles easily. Used in aerobic treatment systems, this process typically generates a clear/odorless effluent.

Suspended growth treatment systems freely suspend microorganisms in the wastewater (that is, they float around in the wastewater). They use biological treatment processes in which microorganisms are maintained in suspension within the liquid. In suspended growth treatment systems, microorganisms convert the organic matter or other constituents in the effluent into gases and cell tissue. The suspended growth treatment system is the most common type of aerobic treatment system

Fixed film systems utilize a medium in which microorganisms grow. There are basically two types of fixed film systems, trickle and submerged systems. Trickle systems operate by allowing wastewater to flow over the media. Common media types are sphagnum moss, coconut husks or geotextiles. The media in a submerged system is just that, submerged. In this type of system the effluent is in continual contact with the media.

Advantages of fixed film over suspended growth:

  1. no washout of the bacteria will occur during high flows
  2. quick recovery of the bacteria population occurs after periods of low or no use
  3. less susceptible to toxic events/chemicals
  4. no bulking of solids due to endogenous respiration (reduces sludge production)

If designed and dosed properly, a trickle system can provide better treatment than a submerged because there is a higher oxygen content available to the bacteria as the media is in a completely aerated environment. A submerged system only has as much oxygen available as can be dissolved into solution of the effluent. The amount of oxygen that can be dissolved is dependent upon alkalinity, temperature and elevation.

A submerged system, however, does not require additional equipment to continuously pump and distribute effluent over the media which is required in a trickle system to avoid the drying of the bacteria on the media. There are also no moving parts or media/diffusers to clean. The submerged media is self cleaning and does not have to be replaced as trickle system media periodically does. In addition, added nitrogen removal that is inherent and passive occurs and requires no other parts like pumps/panels, etc.

Fixed film systems tend to relatively cost prohibitive for single family residences. Several suspended growth products are available in Florida (AquaKlear, HOOT, Singulair®) and perform extremely well. This type of system is extremely well suited for the residential market. Fixed film systems (MicroFAST® & HighStrengthFAST®) are much better suited for commercial sites (day cares, restaurants etc.).

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