If you’re thinking about installing an aerobic septic system on your property, consider downloading Living with an Aerobic Treatment Unit and Spray Field.
Aerobic units treat wastewater for homes and small businesses using the same process as our municipal wastewater treatment system uses, only scaled down. They remove 85% to 98% of the organic matter and solids from the wastewater, producing effluent as clean as effluent that comes 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 land application system 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 (chlorinator) 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 Texas.
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 the trash tank, aeration chamber, and clarifier in one structure.
The main advantage to having the components in one structure is that the system can be delivered pre-built. The installer must dig only one hole with a level bottom, reducing preparation time for installation.
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. The systems must be installed according to manufacturer specifications and must be watertight to prevent groundwater from entering the system and overloading the treatment unit and land application area.
The aerobic treatment unit components (pre-treatment tank, aeration chamber, air pump, and settling chamber) work together to treat the water to a high quality.
In the system, wastewater first enters the pretreatment tank or trash trap, which removes plastic objects and other solids that float or settle. Then it enters an aeration chamber, where oxygen supplied by air pump allows aerobic organisms to live. Treatment in the aeration chamber is a biological process in which microbes eat the waste and their bodies transform it into non-polluting material.
The microbes change dissolved and solid pollutants into cell mass, such as non-degradable material, and gases (carbon dioxide, hydrogen, and methane). 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.
Treated wastewater moves from the aeration chamber into a settling chamber or clarifier. The clarifier allows the cell mass and non-degradable materials to settle from the water before it leaves the treatment system.
The separation of microbial cells from treated effluent is an important part of the process. Aerobic treatments 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 disease-causing organisms in the waste.
When selecting an aerobic unit, your provider will first determine the amount of daily wastewater flow from the home or small business, then choose a Class I aerobic unit that can handle the amount of flow (which is determined by the square footage and number of bedrooms). Most residential systems can treat 500 gallons a day.
This approach to choosing a system assumes that the wastewater includes an amount of organic matter common for homes; it may be inadequate for certain businesses. The size of the system for restaurants and other facilities with strong wastes is calculated by using both quantity and organic strength of the facility’s wastewater.
Aerobic treatment units, marketed in Texas as Class I aerobic treatment units, must be tested and certified according to National Sanitation Foundation International Standard 40 policies for wastewater treatment devices. Aerobic treatment units that pass the test are approved for sale as Class I units.
To remain effective, aerobic treatment unit components need regular maintenance. Poorly maintained systems may not produce water as clean as desired. For the best care for an aerobic treatment unit, follow the manufacturer’s recommendations.
Use these general guidelines as a basis for maintaining your system.
The National Sanitation Foundation Standard 40 Program provides a way for homeowners to make sure their units can be serviced. Those who cannot find a local maintenance provider can contact the manufacturing company for help in locating one. If the manufacturer does not respond, the homeowner can contact the testing and certification group that tested the unit to find a maintenance provider.
If the aerobic unit uses a spray distribution or subsurface drip distribution system, you need to keep a maintenance contract in force. The maintenance provider will report to local permitting authority on the unit’s operating condition every 4 months.
Reference: Lesikar, Bruce. Agricultural Communications, The Texas A&M University System. Aerobic Treatment unit. Publication L-5302. 26 Jul. 2000.