Septic Tanks

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Septic Tank

Septic tank or polyethylene septic tank, is the most basic section of purification and pre-treatment of the sewage. Due to it’s internal shape, the septic tank separates the solids from the waste-water and performs a process called anaerobic digestion on them. This process, reduces a substantial amount of pollution of the waste-water. The Rothengaran Parseh Company, as the greatest producer of assembled and non-assembled septic tanks, is proud to give advise for design and purchase these tanks. This product can be manufactured in different dimension and volume.

Ability of septic tank

The septic tank can be named as the best and least expensive method for sewage disposal in various units such as  residential, commercial, industrial, and etc.

The size of septic tank: Depending on the volume of the waste-water and sewage from different units, and also the location of the septic tank, it can be designed and manufactured in standard and custom made sizes.

The outlet of septic tank: The septic tank outlet can be directed to absorption wells or the urban sewage system.

The location of septic tank: It should be determined according to the location of the project and the purpose of use.

According to the project location and the type of use of the unit, the location of the septic tank is determined.

The components of septic tank

  • The inlet system of sewage in the polyethylene septic tank: This section contains a pipe and inlet baffle.
  • Primary pool of septic tank: This section contains more than half of septic tank. The separation of solids happens in this section.
  • The baffle: This wall prevents the entry of sludge and floating greases into the clarification section of the septic tank.
  • Clarification pool of septic tank: The volume of this section is about 1/3 of the total volume. This section is the Place of accumulation of floating and sedimentable materials.
  • Ventilation system of septic tank: This system removes gases produced during anaerobic processes, which are mostly methane, from the septic tank.
  • The outlet system of sewage in the polyethylene septic tank: This section contains a pipe and outlet baffle.

How does a polyethylene septic tank work?

At the beginning of the process, the sewage enters into the first pool of septic tank from the inlet pipe. The first section of the tank gets separated with a baffle. After the sewage enters into the second section, the floating materials in the waste-water settle to the bottom of the tank due to their heavier weight than the waste-water. And the greases and oily materials, float on the surface of the waste-water due to their lighter weight. Also a mass of sludge forms in the bottom of the tank which is a suitable place for the growth and multiplication of bacteria and microorganisms. During the growth and multiplication of these bacteria, a series of biological and chemical reactions take place, which cause the decomposition of pollutants and waste-water treatment. These chemical reactions, reduces the volume of the sludge by converting them to biogas.

Calculation of the volume of the septic tank

Calculation and estimation of the volume of septic tank is done through the following formula and based on the number of people in a unit.

C = (180*P) +2000

C = capacity in liters

P = number of people

Attention: Using this calculation method alone cannot always be reliable. The use of different units should also be considered. For example; the outlet volume of a commercial unit that is open limited hours of the day can be different than a residential unit or accommodation and recreation unit, that are being used 24 hours of the day. You can speak with the experienced consultant team at Rothengaran Parseh to reach the best decision to buy the septic tank you need.

Estimation of septic tank volume for houses:

The maximum volume of septic tank

Cubic meter Number of people
1.9 4
2.3 6
2.9 8
3.8 10
4.1 12
4.6 14
5.7 16

Location and installation of septic tanks

A lot of important factors should be considered before preparation of the location and installation of septic tanks. The structure of the septic tanks manufactured in Rothengaran Parseh has been designed in such a way, that they can be located and installed in three forms of surface, burial, and air. In all three forms, there are principles and standards that if not followed, the septic tank will not function properly and can not be useful. The specialized and experienced team of Rothengaran Parseh can give you advice in the field of septic tank installation.

Minimum distance required to locate the septic tank

Minimum distance of septic tank from different places

Place or Unit Distance in meter
water resources 15
Residential building foundation 7/6
Exterior edge of residential building floor 4/5
Lake and pond 15
Water creek and waterway 30
Fountain 30
River 15
Swimming pool 4/5
Non-residential buildings and structures 3
Water Well 15
The main water pipeline 15

Warranty and after-sales service of septic tank

The septic tank of Rothengaran Parseh, has international standards certificate and It is produced and supplied with warranty and after-sales service.

Septic tank

The septic tank provides an environment for the first stage of waste-water treatment for the internal or decentralized sewage system.

A septic tank is a rectangular or cylindrical tank made of concrete, fiberglass or polyethylene that is buried in the ground and the waste-water of the entire complex is discharged inside it. The heavy material and solids settle at the bottom of this tank, and the lighter material such as greases remain on the surface, leaving a clear effluent in between.

Although the liquid in the middle zone is not purified, but, it’s much clearer comparatively to the incoming waste-water. Another important function of this tank is storing the settled solids. The waste-water leaves the septic tank, to the next stage of treatment or gets discharged into the absorption well.

Baffle or effluent screen near the outlet is designed to prevent entering the floating solids or soluble solids into the exiting effluent. The flow and turbulence in the septic tank will complicate the separation process, so the volume of the tank, and the size and shape of the baffle are designed to minimize turbulence.

Price of septic tank

The components such as body material, capacity, and installation conditions of the septic tank will affect the pricing.

Contact us to receive the latest price of septic tank.

The history of septic tank

The septic tank was first installed in the United States. However, it was patented in 1876 by Louis Mouras in France. In 1905, baffle was added as a flow regulator for greater efficiency. The first baffles were made of wood. In 1920, the use of septic tanks became common.


  • The septic tank system needs to be inspected every year or two and it should be drained every 3 to 5 years, depending on the volume of the tank and amount of entering effluent
  • In order to reduce the water entering the system, water consumption must be managed.
  • Coffee grounds, pet litter, diapers, paper towels, cigarette filters, floss and etc. should be prevented from entering the septic tank system.
  • By the entering of strong detergents and antibacterials into the septic tank, the system will malfunction.
  • The leaking valves and plumbing should be repaired because over time, they can inject hundreds of gallons of extra water into the septic tank.
  • The burial and installation location should be away from ponds and other groundwater and has a minimum passage of heavy vehicles.

Biological and chemical processes

Biological processes and anaerobic bacteria in the septic environment, provide partial digestion of some components of waste-water in the absence of oxygen. This process will be slow, incomplete and odor producing.

The activity of anaerobic bacteria produces gas (hydrogen sulfide, methane, carbon dioxide, etc.) in the septic tank, which may cause a risk to personnel. The bubble of these gases can cause the solids to float again and increase the total solids concentration (TSS) in the cleared zone, which will eventually remove more floating solids from the system with the effluent. Therefore, an exit for these gases has been designed to prevent this problem.

The function

  1. All waste-water transfers into the septic tank.
  2. Most of the septic tank fills with the effluent. Anaerobic bacteria begin to decompose the organic materials in the effluent.
  3. A sludge layer settles at the bottom of the tank. This layer contains mineral solids and by-products of digestion of anaerobic bacteria.
  4. A foam layer composed of greases and fat float in the upper part of the septic tank.

The septic tank acts like a settling pool, heavy solids settle at the bottom, and the grease floats on top. The effluent enters the drainage section or waste-water treatment system. If the effluent gets discharged into the drainage system, aerobic bacteria in the sand and soil will completely decompose the material in the effluent and the clean water will flow to the aquifers. In fact, it can prevent groundwater pollution.

If the septic tank is properly designed and constructed, it only occasionally needs to be pumped to drain the sludge and sewage from the tank.

Concrete septic tank

As the name implies, this type of septic tank is made of concrete, which can have one to three tanks. The number of sections depends on the volume of the sewage and the intensity of the discharge, so it is calculated separately for each project.

The triple-chamber septic tank is suitable for high-volume waste-water. The role of the first chamber is to receive and maintain waste-water. The solids settle at this part and the effluent separates from them, then, the anaerobic bacteria break down solids as much as possible. The lower part of the first chamber is completely made of concrete therefore, it prevents the sewage and contaminated water from entering the ground. The volume of the first chamber should be at least half of the whole system.

The second chamber is called drainage and is intended for further treatment of effluent. An additional filter made of a mixture of sand and stone, can be installed to help this process. The bottom of the second chamber is also concreted with care. To improve the quality of treatment, the second tank is often equipped with an aeration system.

The final treatment of the effluent is done in the third chamber which happens according to the treatment system through the sand section.

Double-chamber septic tank

It is the most common type of treatment plant for personal use which has a structure consisting of two concrete tanks with a height of 90 cm and a diameter of 70cm to 200 cm. The duty of the first chamber is reception, calming and separation of waste-water. The fluid left from this part, immediately goes to the second chamber. From there, it goes to the ground through a sand filter. The overflow of water between the tanks is done through a nozzle which is located at a certain height, and the water starts to overflow into the second tank when it reaches a certain level.

Single-chamber septic tank

It is a storage tank which the waste-water treatment does not happen in it, and the waste-water discharges with the help of drainage equipment. The function of this septic tank can be improved by installing a baffle in it.

Advantages and disadvantages

The popularity of concrete septic tank is due to the availability of materials and it’s simple design, and also, it does not require special equipment for installation. It has high mechanical strength and because of the high weight of concrete septic tank, the groundwater cannot move it.

One of the main disadvantages of concrete septic tanks is the need for accurate sealing of connections between tanks. Due to the high weight of concrete septic tanks, heavy equipment and machinery are needed for transportation and installation. It is impossible to use these septic tanks in irrigation areas, and also there is a possibility of spreading an unpleasant odor.

Components of septic tank

The main components of septic tank are, Inlet system of sewage including a pipe and a baffle, The primary tank which contains most of the volume of the septic tank which is usually about %70 of it, The clarification tank that contains about 30% of the total volume of the septic tank and in which the waste-water is free of sedimentable materials.

  1. Sewage inlet system: contains the Tee pipe
  2. Primary tank: this section contains about %70 of the total volume of the septic tank. The main sedimentation and separation of waste-water is done in this part
  3. Middle baffle: this wall divides the septic tank into two sections, and it prevents the grease from entering the second section
  4. Secondary tank (clarification area): it contains 30% of the total volume of the septic tank and is the collection point of treated effluent from the primary tank, and it provides more opportunities for better treatment of effluent.
  5. Air vent: it is a valve to release the gases produced by anaerobic bacteria during the decomposition process.
  6. Inspecting hatch: with enough diameter so one person can go through it (usually 600 mm), are installed to give access into the septic tank for periodic inspection.
  7. Sewage outlet: contains the outlet pipe which lets the effluent with the least solid particles exits the septic tank and enters the waste-water treatment system or absorption well for further treatment.


The septic tank is usually being used in villages and cottages which are not connected to the urban sewage system. But its better to use these tanks in all residential units, commercial units, industrial units, Cultural complexes, recreational complexes, and etc. to pretreat the waste-water, settle the solids in the waste-water, remove grease, and prevent clogging of pipes and the waste-water collection system.

Septic tank and the environment


The entry of polluted sewage into the environment can threaten the health of plants and animals, and its unpleasant odor would be disturbing. By using the septic tank system, the sewage gets pretreated and sent to the environment with much less pollution, and there is no need to be worried about contaminating underground water basins with waste-water. In addition, the polyethylene septic tanks (HDPE) can last up to 50 years and they are recyclable.

Polyethylene Septic Tank

The polyethylene septic tank is made of high density polyethylene resin (HDPE) which is an integrated and durable tank that is resistant to corrosion, rust, impact, and etc. This tank is resistant against the chemicals and gases that may be inside the soil and the sewage. The anti-UV material used in the structure of this tank, makes it suitable to be installed outdoors if needed because, the sunlight does not have an adverse effect on it. The polyethylene septic tank is light in weight and can be installed easier compared to concrete and fiberglass ones. One of its most important advantages is the ability to customize it depending on customer needs.

The polyethylene septic tanks are completely sealed and are safe from any leakage and intrusion. They contain inlet and outlet, middle baffle, air vent, and an inspection hatch for inspection and access to the septic tank. These tanks are a simple and reliable solution for waste-water and effluent management.

Fiberglass septic tank

FRP or fiberglass septic tank has eliminated all the shortcomings of traditional septic tanks due to its low weight, high strength, anti-corrosion properties, non-leakage, and easy installation. And it has become one of the most desirable options for waste-water collection.

Various design by the request of customer, high resistance against pressure, space saving, and quick in production, are other advantages of fiberglass septic tanks.

Dimension and volume of septic tank

Septic tank can be manufactured in various dimensions and volumes. The standard dimensions of the polyethylene septic tank are as follows:

Model Volume(m3) D(mm) L(mm)
Polyethylene septic tank 3 1200 2650
Polyethylene septic tank 4 1400 2650
Polyethylene septic tank 5 1400 3250
Polyethylene septic tank 8 1600 4000
Polyethylene septic tank 10 1600 5000
Polyethylene septic tank 12 1600 6000
Polyethylene septic tank 15 1800 5900
Polyethylene septic tank 18 2000 5750
Polyethylene septic tank 20 2000 6370
Polyethylene septic tank 25 2500 5100
Polyethylene septic tank 30 2500 6100
Polyethylene septic tank 40 2500 8150
Polyethylene septic tank 50 2500 10200
Polyethylene septic tank 60 2500 12500
Polyethylene septic tank 65 2500 13250
Polyethylene septic tank 70 2500 14300
Polyethylene septic tank 80 3000 11330
Polyethylene septic tank 85 3000 12000
Polyethylene septic tank 95 3000 13600

 The advantages of polyethylene septic tank

  • High resistance against impact and fracture
  • Very quick in production and installation
  • Resistant to chemicals and the pressure of the soil due to the presence of carbon and hydrogen atoms in the structure of this tank
  • Contains anti-UV material
  • Ability to be manufactured in various dimensions in accordance with the available space
  • No need for mechanical equipment
  • Complete sealing of the body due to the use of extrusion welding
  • Lifespan of at least 50 years. in other words, a guarantee of erosion and corrosion for 50 years
  • High flexibility for transportation and usage on uneven surfaces
  • Ease of installation and transportation
  • It does not occupy the space of the site of the employer because it gets buried
  • Easy operation with no need for operator
  • Prevents clogging of sewage pipes and absorption wells due to removal of solids, fats and oils in sewage

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