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Aerobic Septic Systems with Drip or Spray Distribution

Aerobic treatment units (ATUs), sometimes called nonstandard systems, are used in most new construction. They treat wastewater to a higher level than a conventional tank, which makes them a fit for properties where soil or space is limited.

Overview

Aerobic systems (drip & spray)

01How an aerobic system works

Aerobic systems use many of the same processes as a municipal sewage plant, on a much smaller scale. The system injects oxygen into the treatment tank. The extra oxygen increases natural bacterial activity, which provides additional treatment of the wastewater. Some systems also include a pretreatment tank and a final treatment stage before the water is dispersed.

02Drip distribution

A drip distribution system spreads treated water through drip lines placed in the top 6 to 12 inches of soil. Its main advantage is that no large mound of soil is needed, and the soil itself provides further treatment. Drip distribution can be used in many types of drainfields.

03Spray distribution

Spray systems work like a sprinkler system, using treated water to irrigate the lawn. A chlorination disinfection unit is typically installed to kill microbes and bacteria before the water is sprayed.

04Is an aerobic system right for you?

  • New construction where the permit calls for an aerobic system
  • Poor soil, a high water table or limited space for a conventional drainfield
  • Commercial properties with higher treatment needs

05Maintenance

Aerobic systems have mechanical parts and need regular maintenance, and Texas rules require a maintenance agreement for most of them. We explain what applies to your system when we design it.

Technical detail

The engineering behind it

Treatment performance
Aerobic units remove 85 to 98 percent of organic matter and solids (Texas A&M AgriLife Extension)
Certification
Class I aerobic units can be used with spray distribution; TCEQ maintains the list of approved units
Components
Pretreatment tank, aeration chamber, settling chamber, final treatment and dispersal
Drip lines
About 1/2-inch tubing with emitters in the wall, run at roughly 15 to 20 psi and laid in the top 6 to 12 inches of soil
Show diagrams and process detail
Inside an aerobic treatment unit (ATU)
Components of an aerobic treatment unitWastewater flows through a pretreatment tank, an aeration chamber with an air pump and diffuser, a settling chamber with sludge return, and a final pump chamber.air pumpdiffuserwastewaterinsettled material returned to aerationto drip or spray field1234

Schematic of the four components of the aerobic treatment process, per Texas A&M AgriLife Extension publication L-5302. Actual units vary by manufacturer.

  1. 1

    Pretreatment ("trash") tank

    Removes plastics and other solids that bacteria cannot break down, protecting the equipment downstream.

  2. 2

    Aeration chamber

    An air pump and diffuser supply oxygen. Aerobic microbes consume the waste, and rising bubbles keep the water mixed.

  3. 3

    Settling chamber (clarifier)

    Microbes that have done their work settle out. The settled material is returned to the aeration chamber.

  4. 4

    Final treatment and dispersal

    Treated water collects in a pump chamber and is sent to the drip or spray field. Spray systems add disinfection first.

Subsurface drip distribution: plan view
Plan view of a subsurface drip systemA pump tank sends water through a filter to a supply manifold, then through parallel drip lines with emitters to a return manifold, with a flush line back to the treatment unit.dispersal field area (soil does the final treatment)pump tankfilteremitter spacing set by designvacuum breakerflush line back to the treatment unit1234

Schematic plan view of a subsurface drip system, per Texas A&M AgriLife Extension publication L-5237. Line spacing and layout are set by the engineered design.

  1. 1

    Treatment unit and pump tank

    Water is treated first (an aerobic unit is common), then stored in a pump tank until the field is ready for a dose.

  2. 2

    Filter

    A sand, disk or screen filter removes larger particles that could clog the emitters. Some systems use an automatic cleaning filter.

  3. 3

    Drip lines and emitters

    About 1/2-inch tubing with an emitter in the tube wall, run at roughly 15 to 20 psi inside the tube. Water leaves the emitter at 0 psi.

  4. 4

    Return manifold and flush line

    The return manifold connects back to the treatment unit so solids collecting in the tubing can be flushed out. A vacuum breaker protects the lines.

Aerobic system with spray distribution
Aerobic treatment with spray distributionAn aerobic treatment unit sends water through a chlorinator to a pump tank, which feeds spray heads over a lawn.Cl1234

Schematic elevation, per Texas A&M AgriLife Extension publication L-5302. Spray area size and head layout are set by the engineered design.

  1. 1

    Aerobic treatment unit

    Class I aerobic units treat wastewater well enough to be used with spray distribution.

  2. 2

    Disinfection

    A chlorinator kills disease-causing microorganisms before the water is sprayed.

  3. 3

    Pump tank

    Stores treated water and doses it out to the spray heads on a controlled schedule.

  4. 4

    Spray heads

    Heads spread the treated water across the lawn like a sprinkler system, where grass and soil use it.

Free guides (PDF)

FAQs

Aerobic systems (drip & spray): common questions

What is the difference between drip and spray septic systems?

Both follow an aerobic treatment unit. Drip systems release water slowly below the surface through drip lines. Spray systems disinfect the treated water and spray it over the lawn like a sprinkler.

Why are aerobic systems used in new construction?

They treat wastewater to a higher level and work on sites where a conventional drainfield will not, so they are commonly required or recommended for new builds.

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