Water Resources Center
OSTP

The Water Resources Center is affiliated with the College of Food, Agricultural and Natural Resource Sciences and University of Minnesota Extension.

Alternative Septic Systems


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Traditional septic systems are typically thought of as an on- site sewage treatment system serving one household with a drainfield or mound. These are probably still the best way to treat sewage when space and good soil conditions exist. When properly designed, installed, operated and maintained, they treat sewage as well as or better than municipal treatment systems.

When space is limited or soil conditions are poor (wet or close to the water table), homeowners may need to consider a modified treatment system. Because a typical septic system does not remove all of the nitrates from sewage, additional treatment steps may be used to reduce or eliminate them. These options may be considered for individual homes or multiple household units.

Typically, alternative treatments provide "pre-treatment" of septic tank effluent before it enters the soil of a drainfield or mound. These pre-treatment systems include containers using sand, peat or gravel as a medium where filtration and biological degradation of fine solids, pathogens and nutrients occur. The containers may be manufactured or assembled on the site.

The effluent in a pre-treatment system usually passes through the system one time, but some systems collect and re-circulate the effluent several times. These systems often require more space than a traditional drainfield or mound. Research has still to determine if the size or the separation distance of the drainfield receiving the pre-treated water will be able to be reduced. These same considerations are being made when aerobic septic tanks are used to pre-treat wastewater.

Alternative methods of dispersing septic tank effluent into the soil are also being tested. These include drip irrigation over a large soil area, particularly appropriate in shallow bedrock and high water table situations. Spray irrigation onto the soil surface is another option, but presents special health risks with potential human contact. Uses of the water for watering lawns and golf courses also offer opportunities to recycle the water.

Separation technology is another concept in alternative treatment for individual homes. The idea of separating the solid wastes from the toilet and delivering them to a composting unit reduces household water use up to 40 percent and removes many of the pathogens and nutrients from the system. Some systems use worms, while others use bacteria and aeration to accomplish the composting process. Homeowners are sometimes reluctant to have a bin of composting wastes and even worms in their basements. The composted materials must be removed periodically.

Alternative treatment systems will always require increased attention to operation and maintenance. As the treatment becomes more sophisticated and technical, the need for monitoring of its performance increases. Multi-household installations must have a functional management plan.

Most alternative treatment systems require special permits for their design, installation and operation. Any system discharging to the surface must have a State Disposal System permit and any system discharging 10,000 gallons per day must have a National Pollutant Discharge Elimination System permit. Both require on-going monitoring. Information about permits is available from local planning and zoning or environmental service offices.