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Onsite Wastewater Systems: How They Work

If your home or business is not connected to a central sewer system, you will need an onsite wastewater system. All your household wastewater will be collected and treated on the spot (on site). The treated effluent will be returned to the soil, and, after soil filtration, to the groundwater. Some components are common to all onsite systems. Others depend on your site conditions.

Primary Treatment in the Septic Tank

tank cutaway

All onsite systems start with an underground septic tank that receives the wastewater from the house. There, the raw wastes naturally separate into settled solids, floating material, and liquid effluent -- a process called primary treatment.

Primary treatment is a passive and very reliable process. It provides 70% of the waste water segregation with no energy input. As long as the tank is watertight, the solids remain in the tank for years, while microorganisms slowly break them down to a fraction of their volume.

Every 5-12 years, (depending on usage) the remaining solids are pumped out of the tank by a service provider. These solids are either taken to further treatment and processing for disposal.

In contrast, the effluent remains in the tank for only a couple of days. Then exists the tank via pump or gravity to the next treatment step.

Dispersal to the Drainfield

The effluent can be returned directly to the soil by means of a drainfield. This is an array of perforated pipes is placed in trenches to disperse effluent to native soil. There, microorganisms remove the nutrients in the effluent, purifying it. Plant roots take up some of the remaining water, and the rest is further treated by the native soils before making it to groundwater. 

A drainfield requires soil with the proper permeability -- not too much, and not too little. When your house was built, an engineer or designer evaluated the soil and determined whether or not a drainfield was possible.

Three Main Types of Onsite Systems

Standard Gravity Systems: Depending on the terrain of your lot, you may be able to install an onsite system that discharges effluent to the drainfield via a gravity system. As wastewater flows into the tank at the inlet, it pushes out clear effluent at the outlet. A Biotube Effluent Filter on the outlet of your septic tank will protect the drainfield from particles that could clog and damage it.

Standard Pumping Systems: Other onsite systems discharge effluent to the drainfield using an effluent pumping system. This is necessary when the drainfield is not downhill or soils dictate pressure distribution is required. One advantage of an Orenco pumping system is that it delivers wastewater to the drainfield in small, uniform doses throughout the day. This keeps the drainfield in a uniformly moist condition favorable to the growth of treatment organisms. 

In our effluent pumping systems, the pump is protected by a Biotube Effluent Filter and operated by a control panel. The panel may activate the pump based on demand, when the effluent in the tank reaches a certain level. Or it may activate it on a timed schedule.

Advanced Treatment Systems: If your site is unsuitable for a drainfield of conventional size, or if your site has poor soils or is in an environmentally sensitive area, you may need an advanced treatment system. These systems treat household waste to very high, advanced treatment levels: 10 mg/L BOD and TSS*, or better. 
Many of the treatment organisms need oxygen to do their work. In a municipal wastewater treatment plant, and in many, less efficient advanced treatment systems, machinery or blowers continuously aerate the effluent to supply the necessary oxygen. 

However, a more stable and energy-efficient practice is to trickle the effluent over a bed of porous material, called a media filter. The filter media develops a thin coating of microorganisms. Nutrients continuously wash over them, and oxygen from the air passively permeates the thin layer of moisture. Periodically trickling effluent with a small pump uses much less electricity than continuously aerating liquid with a blower. Treatment efficiency is also considerably greater, with biosolids and management significantly reduced. The effluent that comes out of the AdvanTex Textile Treatment System is so clean and odorless that, in many cases, it can be used for drip irrigation of landscaping.  Many jurisdictions around the United States allow the use of drip irrigation for the dispersal of effluent.  Our Shallow Pressurized Dispersal Systems (SPDSs) offer a simpler, less expensive way to disperse of the highly treated effluent.

Media Filter Systems


In media filter systems, effluent trickles through a moist, porous media. Microorganisms growing in the media remove impurities from the effluent. Compared with advanced treatment systems that blow air into liquid or use membranes, packed bed systems use less electricity, require less maintenance, and are much less prone to upsets from the ups and downs of day-to-day life.

Textile Filter Technology Proven AdvanTex Technology

Our AdvanTex® Treatment Systems are based on media filter technology, a reliable, proven method for onsite secondary treatment of wastewater. In fact, in the 1980s, Orenco's engineers pioneered the use of the modern sand filter. But instead of using sand as the filtering media, the AdvanTex product line uses a synthetic textile, which has five times more surface area than the same volume of sand. That's why, with textile filters, you can treat the same amount of wastewater in a fraction of the space that a sand filter requires. And textile doesn't plug like foam filters or have to be replaced every few years, like peat filters.

AXMax SpinNozzleIn an AdvanTex system, effluent trickles through and between the textile sheets. In this moist, oxygen-rich (aerobic) environment, naturally occurring microorganisms remove impurities from the effluent.

After recirculating several times, the effluent is dosed to the dispersal area. The effluent is so clean (typically 10 mg/L BOD5 and TSS, depending on the loading rate) that it can be used for drip or subsurface irrigation or discharged to shallow, inconspicuous trenches. Reductions in drainfield size are often permitted with AdvanTex Treatment Systems. And the AdvanTex system can't spill solids into the drainfield or irrigation system.

Meets Nitrogen Reduction Standards

The AdvanTex Treatment System is a recirculating process. If local conditions require it, recirculation can be configured to favor maximum nitrogen reduction.

A Sustainable Technology

Unlike aerobic treatment units (ATUs) that constantly pump air through the effluent in the "activated sludge" process, the AdvanTex Treatment System has a pump that runs only a few minutes a day, using just a dollar or two in electricity each month. And unlike activated-sludge ATUs, AdvanTex systems don't generate extra sludge during the secondary treatment process. In normal household use, most tanks go 8-10 years between pumpings. Low energy use and low sludge generation have made AdvanTex a wastewater treatment technology of choice for developers and homeowners committed to sustainable building.

More than 20,000 AdvanTex filter units have been installed in the United States, Canada, and around the world, on all sorts of sites: single-family homes, commercial properties, community systems, and government-funded and monitored testing sites.