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Septic tank is a key component of the septic system, a small-scale sewage treatment system common in areas that lack connection to main sewage pipes provided by local governments or private corporations. Other components, generally controlled by local governments, may include pumps, alarms, sand filters, and clarified liquid effluent disposal methods such as a septic drain field, ponds, natural stone fiber filter plants or peat moss beds.
The term "septic" refers to the anaerobicbacterial environment that develops in the tank which decomposes or mineralizes the waste discharged into the tank. Septic tanks can be coupled with other onsitewastewatertreatment units such as bio filters or aerobic systems involving artificially forced aeration.
Periodic preventivemaintenance is required to remove solids that remain and gradually fill the tank, reducing its efficiency. Maintenance requires regular pumping to remove these. According to the US Environmental Protection Agency, in the United States it is the home owners' responsibility to maintain their septic systems. Those who ignore this requirement will eventually be faced with costly repairs when solids escape the tank and clog the clarified liquid effluent disposal system. A properly maintained system will likely not need replacement during the homeowner's lifetime.
WORKING OF SEPTIC SYSTEM
The septic system is a natural method of treating and disposing liquid household waste. The first component of all septic systems is the tank. Most tanks are split into two compartments and have pipe baffles and an outlet filter to ensure the solids stay in the tank.
The biologic process begins in the tank where the effluent separates into layers and begins the process of decomposition. Bacteria, which are naturally present in all septic systems, begin to digest the solids that have settled to the bottom of the tank, transforming a large percentage of these solids into liquids and gases. When liquids within the tank rise to the level of the outflow pipe, they enter the next part of the treatment system (pre-treatment device, distribution box, pump chamber, etc, depending on the type of system). Final treatment of the effluent always occurs in the soil where additional microbes break down the waste and the “clean” water is put back into the ground thereby recharging the aquifers.
Wastewater contains several undesirable pollutants. Pathogens such as viruses or bacteria can enter drinking water supplies creating a potential health hazard. Nutrients and organic matter entering waterways can lead to tremendous growth in the quantity of aquatic microorganisms. Metabolic activity of these microbes can reduce oxygen levels in the water causing aquatic life to suffocate. Septic system regulations attempt to reduce the chance of these pollutants from having a negative impact on people and animals.
TYPES OG SEPTIC SYSTEM
There are nearly as many types and sizes of septic systems as there are cars on a new car lot. In Washington, the systems are divided up into three basic categories:
1) Standard Gravity
2) Pressure Distribution
3) Advanced Treatment
The first two types (standard gravity and pressure distribution) are relatively straightforward, non-propitiatory system types. Standard gravity systems require three feet of "good" soil under the trenches while pressure distribution systems only require two feet. Advanced Treatment systems however are a much bigger animal and can be used where there is only one foot of "good" dirt beneath the trench bottom. They come is many makes, models and sizes. Some are proprietary, name brand systems and others are not. If you would like to know a brief history of why we have so many types of systems, please see our history section above.
Most systems today include pumps, control panels, grave less infiltration chambers and effluent filters. Some systems even include textile filters, aerobic digestion and ultraviolet disinfection!
1)Standard Gravity:
As the name implies, gravity drain fields work by letting gravity drain the effluent from the septic tank into a series of underground trenches. This means the drain field area must be below the elevation of the septic tank. If this is not the case, then a pump is necessary and it is called a pump to standard gravity system.
When you send new liquid waste into the septic tank, an equal amount of liquid (called effluent) comes out the outlet side of the tank. An “outlet filter” is installed in the tank to help prevent solids from escaping the tank.
After passing through the outlet filter, the effluent flows through a distribution box (d-box) which diverts the flows to multiple pipes.
The effluent leaves the d-box under the power of gravity and flows downhill to each of the underground drainage trenches. The trenches are made up of either: perforated pipe over drain rock or grave less chambers. Each type effectively does the same thing…they allow the effluent to “perk” into the ground at the bottom of the trench. By design, Standard gravity systems are progressively failing as the effluent works it's way down the trench.
The bottom of the trench needs to be 3 feet above any restrictive layer, such as a hardpan, water table or excessively permeable soil (rock). Chemical and biological processes treat the effluent as it percolates down through the required three feet of soil. The size of the drain field depends on the estimated daily wastewater flow and the soil conditions at your site. (i.e.- how much water is used per day and how fast will the soil take it?)
Pressure distribution
Pressure distribution systems are usually required when there is less than optimal soil depth available for complete treatment of the effluent by a gravity system. A minimum of two feet of properly drained soil is required under the trenches. The tank and drain field size are normally the same as a standard gravity system, but the method by which the effluent is distributed to the soil is different.
Advanced Treatment Systems:
As mentioned above, advanced treatment systems come in MANY makes and varieties. Some are built in a factory and some are built on site. Some are proprietary and some are public domain. These systems are required when shallow soils exist on the site (12-30 inches). The basic function of these systems is to clean the wastewater prior to the final disposal into the ground. Most of the time, these treatment systems are followed by pressure distribution drain fields (trenches or drip tube).
The most common types of pre-treatment systems used in Clark County include the following:
• Sand Filters
• Sand Mounds
• Aerobic Treatment
• Textile Filters
• Glyndon Pods
• Sand Filter – After the septic tank, a pump sends pressurized effluent to a large underground box which is full of sand and drain rock. Effluent is spread evenly over the surface of the sand via a pressurized pipe network (similar to a pressure distribution system). The dirty effluent filters through the sand and collects in a sump at the bottom. A second pump sends the relatively clean effluent to the drain field where the final treatment occurs and the effluent is disposed in the soil.
• Sand Mounds – Another system suited for sites with shallow soils is a sand mound. A mound is a drain field raised above the natural soil surface with a sand fill material. Within the sand fill is a gravel bed with a network of pressurized pipes. Septic tank effluent is pumped through the pipes in controlled doses to insure uniform distribution throughout the bed. Treatment of the effluent occurs as it moves downward through the sand and directly into the natural soil beneath.
• Aerobic Treatment – Another method of treating wastewater involves an “aerobic” process by which air is injected into the effluent in a specific manner. The increased levels of oxygen in the effluent allow the microorganisms to thrive and digest the biological nutrients. A small air compressor is used to inject air into the effluent.
EGSD does not typically recommend these systems for residential projects. They do however have a place in commercial applications with high-strength waste. Although we do not recommend aerobic systems for residential projects, you may have heard about many aerobic systems being installed for residential projects in Clark County. Most of these systems are specified by designers who are also associated with selling this product.
• Textile Filter (AdvanTex) – Considered to be one of the higher quality treatment systems available, AdvanTex filters are becoming more and more popular in Washington State. Similar to a sand filter, the AdvanTex filter uses media to filter out the contaminants in the effluent. Instead of sand however, the AdvanTex uses a textile product.
The AdvanTex system has the following benefits:
• Easily replaceable media (no need to dig up the whole yard if the media gets plugged)
• Constant re-circulation of the effluent to keep all biological processes working and ensure consistent treatment
• 24/7 monitoring with an advanced control panel
• Much smaller footprint than a sand filter
• Glen don Bio filters – glen don Bilfilters are used on the really tough sites, typically where seasonal groundwater or significant rock is found at 12-18 inches below the surface. The system consists of different layers of sand and gravel placed in a watertight box built into the soil with a sand fill placed over the top of the entire area. Effluent is pumped into the bottom of the filter and allowed to wick itself up through the sand and over the rim of the box and into the soil (effluent remains under the cover sand). Typically one “pod” is used for each bedroom in the residence. After installation, grass can be planted over the mounds.
ADVANTAGES OF SEPTIC SYSTEM
Septic tanks in the long run are more cost effective, running about 3,000 dollars.
There are no water bills, and costs about 100 dollars to pump it
it needs to be pumped every three years, depending on the person
It needs little maintenance
The bacteria are aerobic, so the speed of the bacteria breaking down the waste increases immensely
An aerobic system will break down solids faster so less solids will reach the draining field and groundwater
For cement septic tanks, they last much longer and will not rise out of the ground as time passes.
They can hold a lot of septic effluent because of the size and weight, and are permitted in every state
DIS ADVANTAGES OF SEPTIC SYSTEM
The disadvantages of a septic system are the cost, electricity, maintenance, effectiveness, and law.
Cost: The cost of having a septic can be very expensive to install and maintain.
Electricity: Electricity must be used to run a septic system, which adds the extra cost of paying electricity.
Maintenance: The maintenance of a septic must be checked frequently, if it is not there is a bigger chance that things could go wrong. The contents of the septic tank should be cleaned every two or three years or when the total depth of sludge and scum exceeds 1/3 of the liquid depth of tank. If the tank does not get cleaned it can cause rapid clogging in absorption field, which causes premature failure. The cost of pumping your tank is less expensive than replacing absorption field.
Problems: Roots from trees in immediate area of absorption lines may clog system. Keep swimming pools (above or in-ground) away from absorption lines.
Effectiveness: The effectiveness of a septic system can decrease due to excessive chemicals pouring down the lines or neglect of the system.
Law: The last disadvantages of a septic system is law. The septic system is not allowed in Municipalities. The use of a septic system can only occur in certain locations.