Aerobic units treat wastewater for homes and small businesses using the same process, only scaled down, as our municipal wastewater treatment systems use. They remove 85 to 98 percent of the organic matter and solids from the wastewater, producing effluent as clean as that from municipal wastewater treatment plants, and cleaner than that from conventional septic tanks.

Aerobic units, which are certified as Class I aerobic systems, treat wastewater well enough to be used in conjunction with spray systems, which distribute treated wastewater over lawns. They are the most common way to treat wastewater for spray systems.

The aerobic treatment process includes four main components that work together to purify wastewater:

A pretreatment tank, generally referred to as the “trash tank” because it removes materials that microorganisms (microbes) cannot degrade.

An aeration chamber, where aerobic microbes decompose waste in the water. An aeration system consists of an air pump, piping and diffusers that force air into the aeration chamber. The air pump, located near the aerobic tank, compresses air to flow into the aeration chamber. The diffuser forces the air into the water, dividing the air into bubbles that float to the surface. The oxygen in the air bubbles goes into the water for the microbes, while the rising bubbles mix with the water.

A settling chamber, commonly called a clarifier, which provides a place for the microbes that have treated the wastewater to settle out of the water.

A land application system, which distributes the wastewater into the soil for final treatment and disposal/reuse. Aerobic treatment units usually disperse wastewater via spray distribution systems, which include a disinfection component for removing disease-causing microorganisms, a pump tank for dosing water, and spray heads for spreading the water over the ground.

Aerobic treatment units can be built from concrete or fiberglass. Both materials are durable and can be used across the state.

Concrete tanks are heavier and require larger equipment to carry them to the site, which can delay installation during wet periods. Some concrete systems incorporate the trash tank, aeration chamber, clarifier and pump tank into a single structure; others include in one structure only the trash tank, aeration chamber and clarifier.

Fiberglass tanks are light enough to be carried to the installation site by a backhoe. They generally have an aeration chamber and clarifier in one structure. A separate trash tank and pump tank accompany the aeration chamber and clarifier.

Both tank types can meet your wastewater management needs. But the systems must be installed according to manufacturer specifications. They also must be watertight to prevent groundwater from entering the system and overloading the treatment unit and land application area.

It is important to maintain an active population of microbes in the system to break down solids. A variety of aerobic microorganisms living together in a mixed state can decompose many kinds of materials. The mixed state keeps the microorganisms and the solids suspended in the wastewater.

Aerobic treatment processes greatly lower biochemical oxygen demand (BOD), a common measure of pollution, as well as reduce the suspended solids that do not settle to the bottom of the clarifier. This process also removes some of the nitrogen and reduces the number of disease-causing organisms in the waste.

To remain effective, aerobic treatment unit components need regular maintenance. Poorly maintained systems may not produce water as clean as desired. Please see our service section for a complete list of the maintenance available.

Fiberglass treatment unit | Concrete treatment unit


Conventional septic systems have traditionally been the most commonly used technology for treating wastewater. These systems use gravity to treat and distribute wastewater in the soil. They have the lowest cost and require the least amount of maintenance, which is generally limited to periodic pumping of the septic tank.

A conventional gravity flow septic system consists of a series of tanks or a compartmented tank followed by a distribution system. The septic tanks are used to settle out solids and partially treat wastewater before it reaches the distribution system. The distribution system can be one of the standard subsurface drain field options. They consist of gravel-filled trenches, plastic chambers or plastic pipe installed underground to hold the wastewater leaving the tanks until it can seep into surrounding soil.

The soil provides most of the wastewater treatment. Soil particles filter solids and organic matter from the wastewater. Microbes living in the soil break down the solids and kill the bacteria and pathogens in the wastewater.

The size of the tanks and distribution system are based on the number of bedrooms in the house and the type of soil where the distribution system is installed.

The conventional gravity flow septic system is usually the most inexpensive system to install and operate for on-site wastewater disposal.

Conventional gravity flow septic systems cannot be installed in clay soils, shallow soils, rock, soils that become saturated during wet periods of the year, or soils with a high water table.

Low Pressure Dosing

A low-pressure dosing system treats wastewater and then pumps it into the soil several times daily. Of the nonstandard drain fields, it is the least expensive to install and operate. The system generally has three components: a series of tanks or compartmented tanks used to settle out and partially treat the wastewater; a pump tank for dosing wastewater to the distribution system; and a system for distributing the wastewater to the soil.

The pump tank houses a pump that discharges wastewater to the distribution system three or four times a day. The distribution system consists of a small pipe with holes drilled in it, laid in narrow 6- to 12inch-wide trenches.

The pump discharges wastewater to the trenches. Once in the trench, the wastewater seeps into the soil.

The soil provides most of the wastewater treatment. Soil particles filter solids and organic matter from the wastewater. Microbes in the soil break down the solids and kill the bacteria and pathogens in the wastewater.

Subsurface Drip

A subsurface drip system distributes wastewater to the lawn through a system of tubing installed below the ground surface. It generally consists of four main components a treatment device, a pump tank, a filtering device and a drip distribution system.

Several treatment devices are available, including an aerobic unit, sand filter, or trickling filter. The minimum treatment required is a septic tank to settle the solids. Most drip systems require additional treatment of the wastewater before it enters the filtering system.

The pump tank stores the water until the drip field is ready for a dose of water. A high head pump delivers the water from the pump tank through the filtering device to the drip distribution system.

The filtering device can be a sand, disk or screen filter. Its main purpose is to remove larger particles from the wastewater so they do not cause problems with the drip emitters.

Depending on the waste water quality, the filter may need to be an automatic cleaning system.

The drip distribution system is made of a drip tubing approved by the manufacturer for use with wastewater. The tubing is generally 12 inch in diameter with an emitter in the tubing wall. The pressure inside the tubing is generally operated at 15 to 20 pounds per square inch (psi), with the water exiting the emitter at 0 psi.

The collection manifold for the drip system needs to be connected back to the treatment device for flushing solids collecting inside the drip tubing back to the treatment device.

The drip system has very small emitters that can become clogged with organic matter and solids if the system is improperly maintained.

Drip distribution systems require an ongoing maintenance contract to operate and maintain the drip field.


  • Liquid and tablet chlorinators
  • Chlorine tablets
  • Sprinkler heads and blocks
  • Aerators
  • Sump pumps
  • Microbes
  • Tank risers and lids
  • Full line of replacement parts

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