Written by: picco20
Grease, foam, and lighter particles float to the surface and form a layer of scum. The exit baffle holds back sludge and scum while allowing a partially digested wastewater to flow out of the tank.
This picture depicts the three layers within the septic tank. Anything that floats rises to the top and forms a layer known as the scum layer. Anything heavier than water sinks to form the sludge layer. In the middle is a fairly clear water layer. This body of water contains bacteria and chemicals like nitrogen and phosphorous that act as fertilizers, but it is largely free of solids.
A properly designed and maintained septic tank removes most of the organic substances from raw wastewater. Additional removal of these materials from the septic tank effluent occurs in the soil, where removal of organic?s is accomplished by filtration (through the sand), decomposition, and the breakdown through the use of microbial.
Only a small part perhaps 10% (Wells and Septic Systems, pg. 102), of the total nitrogen in raw wastewater is removed through the extraction of sludge that accumulates at the bottom of the tank. Present in the soil are several mechanics which break down nitrogen through denitrification, absorption, plant uptake and volatilization (turning into a gas).
Some nitrogen in effluent may be removed by one or more of these mechanics before the effluent reaches groundwater. But half or more of the nitrogen is likely to travel with effluent to the groundwater
Nitrification the conversion of ammonium-nitrogen into nitrate form, occurs in the first foot or so of soil below the drain field, assuming that the water table is not present and the soil is unsaturated. Nitrate is very soluble and does not interact with soil components allowing it to travel through the soil practically untouched. Unless conditions for denitrification (conversion of nitrate to nitrogen gas) exist, nitrate will not undergo further transformation in the ground water. Therefore, dilution is the best hope of reducing concentrations of nitrite from septic systems in ground water. *Waste water leaching into surface waters contains nitrogen and phosphates that, being fertilizers, encourage the growth of algae. Excessive algae growth can block the sun and foul the water.
In contrast too then non reactive nitrate, most phosphate will react vigorously with the soil. Phosphate ions in the waste water are removed from the soil by several mechanisms including absorption, precipitation, plant uptake, and biological breakdown.
However phosphorus transport through the soil, to the water table is more likely to occur in: 1. Coarse-textured soils 2. Soils with low organic matter 3. Soils which have a shallow depth to the water table and/or bedrock
This can become a problem when wells and surface water become contaminated. Although over time phosphate removal will occur in the water table through, precipitation, absorption and dilution.
Removal of Viruses Viruses are smaller than bacteria and have a behavior in the soil environment that is different from that of bacteria. Virus removal or inactivation in the soil may be accomplished by several mechanisms, including filtration, precipitation, adsorption, biological enzyme attack, and natural die-off. The small size of viruses, and their surface properties, deriving from a protein coat that may or may not have an electrical charge, causes removal of viruses to be controlled more by absorption to soil particles than by filtration. Many of the soil properties that affect adsorption of bacteria also affect adsorption of viruses. Cation exchange properties of soils, mineralogy, texture, pH , and temperature are just a few of the soil properties that influence the survival of a virus.
As with bacteria, unsaturated flow conditions in the soil beneath a septic system, resulting in good aeration, slow travel, long travel, long residence times, good effluent-contact, and opportunity for die-off, is very important in ensuring the cleanup of viruses in effluent.
Water table fluctuations are one of the major pitfalls of the percolation test, in which the rate of water in a standard-size hole is measured in order to estimate the ability of the soil to accept effluent. The percolation test has some value in estimating the ?perk? rate of soils at a site, establishing appropriate loading rates, and predicting system performance. The test might indicate a rapid perk rate during dry times, but these figures will change during the wet season when the watertable is just below the drainage field.
To design a septic system such that the unsaturated zone will exist, the depth to the wet season water table must be estimated at the site, by examining soil color patterns, features of the soil profile, landscape position, the vegetation growing on the land, and additional information on water table fluctuations in the soil survey reports for the area.
If a grain of sand was the size of a basketball, then a piece of silt would be the size of a marble and a particle of clay would be a pinpoint. Clay particles are so small, less than one 12 500th of an inch, that an electron microscope must be used to see them.
These tiny react well with contaminates found in waste water, but the problem is that they are shaped like tiny plates of flakes. When the cationic influence of sodium is present, these flakes tend to stick together like a peanut butter sandwich.
1. Class I -- Raw Sewage on the Bathroom Floor. This is the classic failure in which raw sewage is rejected by the disposal system.
2. Class II -- Sewage in the Yard. In this class of failure the toilet and other facilities seem to function just fine, but untreated or poorly treated sewage is surfacing in the yard, in nearby ditches, in the neighbor's yard, or elsewhere in the environment. It is probably going to be obvious to someone in the neighborhood that a failure has occurred.
3. Class III -- Decline in Water Quality. In this case the household plumbing and drain field seem to be working perfectly. There is no smell in the neighborhood, and no excess wetness around the drain field. But a research team, using monitoring devices, groundwater sampling and tracers, observe that the system or systems are causing degradation of ground water and/or surface water.
4. Class IV -- Long Term, Gradual, Environmental Degradation. Here there is little if any scientific evidence that waters are being degraded at a rate likely to be a problem to this or the next generation of residents. But computer modeling and/or long term monitoring indicates that very gradual environmental degradation will happen as a result of septic system practices at a particular home site, in a neighborhood, or in a region. This is the hardest type of "failure" to prove.
Some of these causes might be: