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Aerobic Septic Systems Final Treatment Stage InspectAPedia®  -     This article discusses the final treatment stage for aerobic septic systems, also called aeration septic systems. Here are designs and products for aerobic septic treatment units (ATUs) for onsite waste disposal, also called fine bubble aeration systems. We address aerobic septic system design, features, inspection, repair, and maintenance. Product sources are also listed.

Post Processing or Final Treatment of Aerobic or Aeration Septic System Effluent

Septic effluent, after having been processed through the aerobic treatment unit (ATU), may require further polishing, such as by a private wetland or greenhouse system, and may also require disinfection such as by chlorination or UV light. Other common final ATU effluent treatment systems include sand bed filters, raised bed septic fields, drip irrigation systems, evaporation/transpiration effluent disposal systems, or even a conventional septic drainfield.

When all of this processing has been completed, the effluent may be sufficiently sanitary to permit discharge into a nearby body of water or directly onto the ground surface. In other circumstances the effluent is discharged into a subsurface system such as a drainfield. In this last case, the drainfield or soil absorption system will not need to meet the same treatment requirements as a conventional septic drain field, because of the pre-processing and sanitizing that have already taken place.

Aerobic or aeration septic systems should have a second settlement chamber at or past the septic tank

Because the treatment tank is continually agitated the level of suspended solids remains high.

Therefore an aerobic treatment unit will also include a second settling chamber to make sure that solids are not being sent out to the soil absorption system. Some designs may include a filter at the tank outlet for added protection of the absorption system. Sludge from the settling chamber is returned to the primary tank for further treatment.

Chlorine or Calcium Hypochlorite Disinfection for Aerobic or Aeration Septic Systems

Disinfection methods for treated effluent include chlorination or UV light treatment. Where chlorine tablets are used it is essential that the proper type of tablets are placed into the system (see the two links below about chlorine tablets, swimming pool chlorine tablets, and calcium hypochlorite tablets (the proper stuff to use).

OPINION DF: Although they may be approved for this application, I have never been completely confident in UV-light disinfection systems for several reasons:

• The "install and forget it" image of a UV light treatment system means that owners may never notice that the system has stopped working
• Sludge and debris may coat the UV light treatment bulb, shortening its effective life
• Any UV light water or wastewater treatment system is limited by the flow-rate of water past the light. If water flows faster than the design point, treatment will be ineffective. Many systems I've seen installed had no method for limiting or even monitoring the flow rate past the light.

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SEPTIC SYSTEMS HOME
HOME BUYERS GUIDE to SEPTIC SYSTEMS
SEPTIC SYSTEMS ONLINE BOOK
SEPTIC SYSTEM DESIGN BASICS
SEPTIC DESIGN ALTERNATIVES
  Wastewater Treatment Levels
  Wastewater Dispersal Methods
  Master List of Septic System Types
  AEROBIC SEPTIC SYSTEMS
    ATU Tank Sizes
    ATU Final Treatment
    ATU Certifications
    ATU Problems
    ATU Failure Rates, Costs
    ATU Maintenance Procedures
    Aerobic Septic Disinfectants- Calcium Hypochlorite
    Aerobic Septic Disinfectants-Pool Chlorine
    ATU Suppliers
    Continuous Flow, Suspended Growth Aerobics
  CESSPOOLS
  DRYWELLS
  SEPTIC EFFLUENT DISINFECTION SYSTEMS
  EVAPORATION-TRANSPIRATION SEPTIC SYSTEMS
  FIXED-FILM PROCESS SEPTIC SYSTEMS
  GRAVELLESS SEPTIC SYSTEMS
  LAGOON SEPTIC SYSTEMS
  PRESSURE DOSING SEPTIC SYSTEMS
  MEDIA FILTER SEPTIC SYSTEMS
  SEPTIC & GREYWATER FILTERS
  SEQUENCING BATCH SEPTIC SYSTEMS
  MOUND SEPTIC SYSTEMS
  RAISED BED SEPTIC SYSTEMS
  SAND BED SEPTIC SYSTEMS
  SEWAGE TREATMENT SYSTEMS
  TOILET ALTERNATIVES

  ALTERNATIVE SEPTIC DESIGNERS
  ALTERNATIVE SEPTIC PRODUCTS

• More Reading on Disinfection Tablets for Aerobic or Aeration Septic Systems:
  Chlorine Tablets - NO - Disinfection of Septic Effluent Discharged from Aerobic Septic Systems - use of Swimming Pool Chemical
  Calcium Hypochlorite - YES - Aerobic Septic Systems: Calcium Hypochlorite for Disinfections In Onsite Aerobic Waste Treatment Septic Systems

More Information on Building Diagnostic Inspections and Repairs

• Aerobic Septic System Disinfection with Calcium Hypochlorite - Use of calcium hypochlorite tablets for aerobic septic systems
• Aerobic Septic System Disinfection with Chlorine Tablets - US EPA declares use of swimming pool chlorine tablets illegal for septic system disinfection
• The Septic System Information Website home page for this topic
• Septic Systems Inspection, Testing, & Maintenance- online textbook. Detailed how to inspect, maintain, repair information
• The Home Buyer's Guide to Septic Systems
• Septic Tank Pumping Guide: When, Why, How to pump the septic tank
• Home & Outdoor Living Water Requirements
• Septic Tank Capacity vs Usage in Daily Gallons of Wastewater Flow, calculating required septic tank size, calculating septic tank volume from size measurements
• How Big Should the Leach Field Be? - table of soil percolation rate vs. field size
• Septic System Drainfield Absorption System Biomat Formation - what leads to drain field clogging and expensive drainfield repairs
• Table of Required Septic & Well Clearances: Distances Between Septic System & Wells, Streams, Trees, etc.

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