Ask the average city dweller to define the word septic and they might respond with infectious or diseased. Ask a country dweller the same question and they may answer that it is part of a water purification system (referring to a septic tank). Difficult as it may seem, a septic system is , indeed, an infectious container where household waste water purification begins.
Approximately 25 percent of American homes use some type of on-site waste treatment (septic) system rather than direct city sewer hookups. Residents seem largely unaware of their systems and many have learned the hard way that replacing a septic system may cost more than the room addition (or swimming pool!) they have been dreaming about. Concerns about the proper operation of septic systems have risen the level of state legislators who are now trying to regulate what you dump down your toilet. There is a vast quantity of misinformation out there. This article addresses the technical aspects of how these systems work, including what you should and should not introduce to them and why. Specifically, we will discuss the technical issues regarding the discharge of brine waste from an automatic softener into a septic system.
Misinformation has risen to the ranks of the regulator agencies, which are trying to regulate what you dump down your toilet.
What is the purpose of a septic system?
Man learned early on that it was best to bury his household waste, rather than run the risk of stepping in something ugly and tracking it back into the cave. Modern septic systems have evolved little in principle since the Stone Age: they are still basically holes in the ground into which we discharge our household waste water and sewage and then allow it to seep into the ground.
How do They work?
The anaerobic septic tank system is actually alive with both aerobic and anaerobic bacteria. Its main purpose is to separate the floaties (fats, oils, grease) from the sinkies (waste matter, food scrapes, whatever). Aerobes work on the floaties, helping to digest and breakdown fats and oils to liquids and gases. The gases are vented and the liquids
What are the different types of septic system?
Those living in rural areas, or other low-density residential regions, not connected directly to city sewer hookups, are familiar with septic systems or other on-site waste disposal systems. There are two basic types of systems: anaerobic and aerobic. The anaerobic system is older, simpler and more common.
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It consists of a septic tank (which receives household waste and gives it "primary" treatment) and a leach field or drain field (that does further treatment before allowing the liquid by products to seep back into the soil...and the groundwater table).
Aerobic systems require aeration (and therefore have moving parts) but are more compact with smaller drain fields. Aerobic systems do a better job in the digestion of the water but they require more maintenance and can be a little touchy with respect to what gets dumped into them and how fast. Both systems prefer steady state operations.
What can go wrong: and what is to blame when it does?
Septic systems are designed with a normal life expectancy of 20 to 30 years. However, if their equilibrium is upset by poor maintenance, or infrequent cleaning out of the septic tank, excess nutrient can carry over to the drainage trenches and the biomat will increase and eventually plug the drain field. The result is system failure. Failure can result in the ponding of the water at or above the ground level, backup into the house and runoff to nearby waterways creating dangerous biological pollution of beaches and rivers. Systems failure is all too common. Studies have shown that in any given area, as many as 85 percent of the systems are not properly functioning due to poor maintenance. Those responsible for paying the costs of fixing the problem often point fingers at anything that may have contributed to the failure - including the discharge of water softeners into the receiving tank. This has led to a rash of actions to ban the discharge of softener waste into these systems. But are the allegations leveled against the use of softener supported technically?
Regulatory agencies think (or have been led to believe) that high concentrations of salt have a deleterious effect on the biological functions occurring in the septic tank.
Fact: The discharge waste from softener regeneration contains high calcium and magnesium and some excess sodium salts. The optimal osmotic potential for most bacteria is between -5 and -20 bars. Many bacteria divide and grow most rapidly at -14 bars. This osmotic potential corresponds to a sodium chloride concentration of 15,000 ppm as CaCO3. Typical osmotic potential of septic tank effluents on systems without softeners is 0.36 bars. The osmotic potential on systems with softeners ranges from -0.51 to -0.10 bars. The salts added by a water softener regeneration actually reduce the stress on the bacteria by decreasing osmotic potential differences. According to this information, the softener discharge will not retard sludge digestion and may even stimulate the essential bacteria growth.
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There is considerable debate on this issue. Observations made by experts in the field have proposed that septic systems operate differently when there is a softener in the system. Nonetheless, these systems did not fail and there are tens of thousands of homeowners out there with softeners on septic systems who do not have a problem.
It is also speculated that the additional volume of waste water will overwork the septic system.
Fact: The additional volume of waster from softener regeneration is 30 to 50 gallons per cycle and it is added to the waste water stream over a period of about two hours. This is a lesser state than draining a bathtub or doing a few loads of laundry. There is no hydraulic overload.
A third area of concern is that the soil structure and drainage properties of the leach field would be adversely affected by the high sodium concentrations.
Fact: It is well known that high levels of calcium and magnesium which are preferably absorbed by the soil. This will actually help maintain drainage.
The high density of the brine from the softener regeneration will cause solids to float and damage the system by causing excess solids to flow into the drain field. Fact: This was one of the observations made by Terry Bounds, an engineer with Orenco Systems, Inc. Field tests can confirm that the heavier salt brine tends to sink deeper in the liquid portion of the septic system while lower total dissolved solids (TDS) waste water flows that are subsequently introduced tend not to penetrate it. On average, the TDS increase in a septic system brought about by softener regeneration adds less than 500ppm of TDS and a miniscule difference in density. However, there has not been sufficient research conducted to determine whether this stratification affects the long term performance of septic tanks and there is no evidence to show that it causes additional buoyancy for solids that would otherwise sink.
Salt is detrimental to the concrete tanks in septic systems.
Fact: Perhaps, but the few hundred ppm of increased TDS would not be significant, especially when it is balanced by calcium and magnesium in the waste water.
Salts in the softener system discharge are more detrimental to aerobic systems.
Fact: This was through tested and reported by NSF in 1978. Their conclusion was that water softener wastes had no adverse effect on on-site aerobic waste water treatment systems.
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