How To Disine A Septic Tank? (Question)

  • Design of Septic tank is to calculate its dimensions (length, depth and width) using daily flow used by the individuals. There are different methods used for designing of septic tanks such as British Method

How is septic tank design calculated?

Septic Tank Size Calculation based Per User Consumption

  1. Cooking – 5 Liters.
  2. Bathing & Toilet – 85 Liters/Person, So for 5 person – 425 liters/Day.
  3. Washing cloths & Utensils – 30 Liters.
  4. Cleaning House – 10 Liters.
  5. Other – 5 Litres.

What are the factors to consider in septic tank design?

Design of Septic Tanks: 7 Considerations | Waste Management

  • Sewage Flow:
  • Detention Period:
  • Tank Capacity:
  • Dimensions of Septic Tank:
  • Sludge Withdrawal and Disposal:
  • Construction Details:
  • Disposal of Septic Tank Effluent:

What is a septic design plan?

The purpose of a septic design is to provide an accurate reference tool for use throughout the permitting and installation process. An effective design will reflect the best choices in layout, system functionality and cost. The design is the cornerstone of the septic planning process.

How deep should a septic tank be?

Septic tanks are typically rectangular in shape and measure approximately 5 feet by 8 feet. In most cases, septic tank components including the lid, are buried between 4 inches and 4 feet underground.

What is the standard depth of a septic tank?

How deep in the ground is a septic tank? You can typically find your septic system buried between four inches and four feet underground.

How many chambers should a septic tank have?

New tanks must have two chambers, while older tanks may have only one. The tank is often made from concrete, but other materials are also used. The tank works by settling and microbial digestion of waste.

How often does a 1000 gallon septic tank need to be pumped?

For example, a 1,000 gallon septic tank, which is used by two people, should be pumped every 5.9 years. If there are eight people using a 1,000-gallon septic tank, it should be pumped every year.

Can you have a septic tank without a leach field?

The waste from most septic tanks flows to a soakaway system or a drainage field. If your septic tank doesn’t have a drainage field or soakaway system, the waste water will instead flow through a sealed pipe and empty straight into a ditch or a local water course.

What size pipe is used for septic?

A three-inch pipe is what’s used in homes to pipe toilets. The four-inch pipe is used as the building drain under floors or in crawlspaces to transport all the wastewater from a home out to the septic tank or sewer. The four-inch pipe may also be used in a home if it’s capturing two or more bathrooms.

What is the size of septic tank for 25 users?

Septic tank size for 25 users:- For 25 users, minimum/ standard size of septic tank could be 3.6m × 1.4m × 1.3m (12ft × 4.5ft × 4.25ft) in respect to their Length, breadth and depth.

Who designs septic systems?

Specialist #2: Septic System Designer Second, a design is completed by either a registered sanitarian or professional engineer, which is based on the information gathered during the site evaluation. Some designers are also site evaluators.

How long does it take to design a septic system?

If the land is not ideal, it may take extra time to excavate or get the soil suitable for leaching. The permitting process could delay progress, or even weather can be a factor. However, on average, it takes about 7 days for a knowledgeable team to get your system set up.

Can you design your own septic system?

To save homeowners the cost of hiring a professional septic designer and excavator, you can build a septic tank system yourself. The installation of new septic systems is expensive even if you build your own DIY septic tank and drainage systems by hand.

Septic Tank – Components and Design of Septic Tank Based on Population

Several more topics related to the home and garden

What is Septic tank?

In terms of classification, a septic tank is a main sedimentation tank with a long detention duration (12 to 36hrs against a period of 2hrs in an ordinary sedimentation tank). Septic tanks are an excellent option for disposing of night soil in rural and urban locations that are not serviced by sewers. However, there should be enough water accessible since water is essential for the movement of the night soil from the latrine to the septic tank as well as for the effective operation of the septic tank.

The size of the septic tank is such that the sewage is A soak pit is often used to dispose of septic tank waste when there is no municipal drainage system in the region.

In the event that a municipal drainage system is in the vicinity, the effluent is released to the drain.

Figure 1: The Septic Tank in Action

Design of Septic Tank

The capacity of a septic tank is determined by the number of users and the frequency with which sludge is removed. Normal sludge removal should take place every two years. The liquid volume of the tank is estimated to be between 130 and 70 liters per head. For a limited number of users, 130 liters per person is required. A septic tank is often surrounded by a brick wall that is thick with cement mortar, and the foundation floor is made of cement concrete 1:2:4 in proportion. Both the inner and exterior faces of the wall, as well as the top of the floor, are plastered with a minimum thickness of 12mm (one-half inch) thick cementmortar 1:3 mix, with a maximum thickness of 24mm (one-half inch).

Water proofing chemicals, such as Impermo, Cem-seal, or Accoproof, among others, are added to the mortar at a rate of 2 percent of the cement weight, according to the manufacturer.

The floor of the septic tank is sloped from 1:10 to 120 degrees towards the input side in order to provide adequate ease in the collection and evacuation of sludge. As a result, the floor on the outlet side will be higher in elevation than the level on the inlet side of the building.

Dimensions of Septic Tank Components

The width is 750mm (min) Length = 2 to 4 times the width width Min below water level is between 1000 and 1300mm, and the free board is between 300 and 450mm. The maximum depth is 1800mm plus 450mm of freeboard. Capacity = 1 cubic meter (10 cubic feet) at the very least.

ii)Detention period

Septic tank design takes into account a detention time of 24 hours (for the most part). The rate of flow of effluent must be the same as the rate of flow of influent to be considered equal.

iii)Inlet and outlet pipes

Septic tank design takes into account the detention time of 24 hours (for the most part). There must be an equal and opposite relationship between the rates of flow of effluent and the flows of influent.

iv)Baffle Walls of Septic Tank

Septic tank design takes into account a detention time of 24 hours (in most cases). The rate of flow of effluent and the rate of flow of influent must be equal.

v)Roofing Slab of Septic Tank

Septic tanks are covered with an RCC slab that ranges in thickness from 75mm to 100mm, depending on the size of the tank being covered. Inspection and desludging are carried out through circular manholes with a clear diameter of 500mm. Clear size is maintained at 600x450mm in the case of a rectangular aperture.

vi)Ventilation Pipe

A cast iron or asbestos pipe with a diameter of 50-100mm is supplied for the discharge of bad gases and ventilation purposes, and it should extend 2m (minutes) above ground level. The top of the ventilation pipe is protected by a mosquito-proof wire tangle, which is also called a cowl. Sectional plan ZZ depicts the usual arrangement of a septic tank (see illustration). The Cross-Sectional Detail of a Septic Tank is depicted in Section XX.

Example – Design of Septic Tank for 20 Users

When you have 120 liters per person, 0.12 x 20 is 2.4 cum Assume that the liquid depth is 1.3 meters. As a result, the floor area of the tank is equal to 24/1.3 = 1.85m 2.Taking the duration of the breath as 2.5 times the breath L X B=1.85 2.5B X B = 1.85 B = Sqrt(1.85/2.5) = 0.86, or 0.9m This results in a tank with a 22.5″ by 9″ overall size.

Suitable Sizes of Septic Tank Based on Number of Persons

The following chart lists the appropriate sizes of septic tanks for households with 5, 10, 15, 20, and 50 people.

No of users Length L in m Breath B in m Liquid Depth in m Liquid Capacity to be provided in m 3 Free Board in m Sludge to be removed(m 3) Interval Cleaning
5 1.5 0.75 1.0 1.05 1.12 1.18 0.3 0.3 0.36 0.72 1 year 2 year
10 2.0 0.9 1.0 1.4 1.8 2.0 0.3 0.3 0.72 1.44 1 year 2 year
15 2.0 0.9 1.3 2.0 2.3 3.6 0.3 0.3 1.08 2.16 1 year 2 year
20 2.3 1.1 1.3 1.8 3.3 4.6 0.3 0.3 1.44 2.88 1 year 2 year
50 4.0 1.4 1.3 2.0 7.3 11.2 0.3 0.3 3.60 7.20 1 year 2 year


In the first stage of wastewater treatment, a septic tank is a chamber constructed of concrete, fiberglass, PVC, or plastic, through which residential wastewater (sewage) travels. The anaerobic bacterial environment that develops in the tank and which decomposes or mineralizes the waste that is released into the tank is referred to as the septic system. The tanks must be designed to hold sewage for a period of 24 hours. During which a certain amount of biological degradation occurs as a result of the action of anaerobic bacteria.

Design Process

This is mostly determined by the amount of individuals who use the tank as well as the frequency with which sludge is removed from the tank. The sludge must be removed every two years, although the frequency is determined by the users. Concrete blocks containing cement mortar are used in the construction of the tank, and the foundation floor is composed of cement concrete in a 1:2:4 ratio.

Septic tanks have a slope of 1:10 to 120 in the direction of the intake side, which helps them gather and eliminate dirt when they are operating. Thus, the floor on the outlet side will be elevated above the floor on the intake side, as shown in the diagram.

i) Length, Width and Depth of Septic Tank

Before beginning the project, it is important to be aware of the numerous components. The width is 750mm (min) Length is equal to 2 to 4 times the breadth. Depth ranges from 1000 to 1300mm. plus 300 to 450mm of free board (minimum depth below sea level) The maximum depth is 1800mm plus 450mm of freeboard. Capacity = 1 cubic meter (10 cubic feet) at the very least.

ii)Detention period

Septic tank design takes into account a detention time of 24 hours (for the most part). The rate of flow of effluent must be the same as the rate of flow of influent to be considered equal.

iii)Inlet and outlet pipes

Inlet pipes are made of an elbow or T pipe with a diameter of 100 mm and are buried between 250 and 600 mm below the liquid level. Whereas for the exit pipe, an elbow or T type of 100 mm diameter should be used for a depth between 250 and 500 mm below liquid level. Pipes may be made of stoneware or asbestos and may or may not be immersed in water.

iv)Baffle Walls of Septic Tank

The use of RCC hanging style scum baffle walls in septic tanks is recommended for smaller tanks. Near the intake, baffle barriers are installed for protection. It is only required near the outlet. The inlet baffle wall is spaced at a distance of L/5 from the inlet baffle wall, where L is the length of the wall. The baffle wall will be raised 150mm above the scum level and 400-700mm below it, depending on the situation. Because scum is light, it tends to float near the surface of the water in the tank.

The lowest section of the big tanks is punctured to allow for the passage of sludge.

v)Roofing Slab of Septic Tank

The top of the septic tank is covered with an RCC slab with a thickness ranging from 75 to 100mm. The thickness of the RCC slab should be determined by the size of the tank. Inspection and desludging are carried out through circular manholes with a clear diameter of 500mm. The rectangular opening is 600 by 450mm in unobstructed space.

vi)Ventilation Pipe

Cast iron or asbestos pipe with a diameter of 50-100mm is provided for the discharge of bad gases and for ventilation purposes. It should be 2 meters (minutes) above the ground level. The top of the ventilation pipe is protected by a mosquito-proof wire tangle, which is also called a cowl. Septic Tanks of Appropriate Sizes Depending on the Number of People

No of users Length L in m Breath B in m Liquid Depth in m Liquid Capacity to be provided in m 3 Free Board in m Sludge to be removed(m 3) Interval Cleaning
5 1.5 0.75 1.01.05 1.121.18 0.30.3 0.360.72 1 year2 year
10 2.0 0.9 1.01.4 1.82.0 0.30.3 0.721.44 1 year2 year
15 2.0 0.9 1.32.0 2.33.6 0.30.3 1.082.16 1 year2 year
20 2.3 1.1 1.31.8 3.34.6 0.30.3 1.442.88 1 year2 year
50 4.0 1.4 1.32.0 7.311.2 0.30.3 3.607.20 1 year2 year

More details may be found in the following story published on GambetaNews.

Septic Tank Design

It is essentially an underground building constructed of concrete, fiberglass, or plasticthought in which residential sewagewater is kept for first treatment before it is discharged into the environment. The right design of a septic tank is critical to the efficient operation of this subsurface system. Aseptic tanks, also known as sewage collecting systems, are used to treat sewage on a local scale and are widespread in rural regions where there is no connection to municipal sewerage systems.

  • It is estimated that around 25 percent of the population in North America is reliant on septic systems.
  • In European countries, rural regions are the only places where people are dependent on others.
  • In some cases, adding extra decomposing bacterialagents to the tank will help to speed up the digestion of materials in the tank.
  • The septic tank is where the wastewater from the residence is diverted.
  • This solid waste has been partially digested by the microorganisms found in sludge.

A baffled wall system is installed at the tank’s intake and exit to aid in the prevention of scum and particles from escaping. Find out more about what is skirting, the many types of skirting, how it is used in construction, what it means, and how to design a skirting wall.

Septic Tank Design

It is essentially an underground building constructed of concrete, fiberglass, or plasticthought in which residential sewagewater is kept for first treatment before being discharged. For this subsurface system to function properly, a properly designed septic tank is required. Known by the name “sewage collection system,” an aseptic tank processes wastewater on a local scale and is commonly seen in places without access to main sewerage lines. The design of a septic tank system is one sort of onsite sewage disposal system.

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Suburbs, small towns, and rural regions can all be included in this approach.

Anaerobic bacterial conditions that exist in the tank and which breakdown or mineralize the waste released into the tank are described by the term “septic.” When extra decompose bacterialagents are introduced to the tank, the digestion of the particles in the tank can be accelerated significantly.

  1. The septic tank is where the wastewater from the residence is disposed of.
  2. In part, this solid waste was digested by the microorganisms found in sludge.
  3. It is fitted at the tank’s intake and exit with a baffleswall system to assist prevent the egress of scum and solids.
  4. There are 12 types of skirting.
  5. Skirting has a meaning.
  • Cooking uses 10 liters
  • Bathing uses 90 liters/person, or 450 liters/day for a family of five
  • Washing clothing and utensils uses 35 liters
  • And cleaning uses 10 liters. 15 liters for cleaning the house
  • 10 liters for other uses.

Cooking uses 10 liters; bathing uses 90 liters per person per day, or 450 liters per day for a family of five; washing clothing and utensils uses 35 liters; and cleaning uses 10 liters per person per day. The following amounts are recommended: 15 liters for cleaning the house; 10 liters for other purposes

Septic Tank Design 3 Chambers | 2 Tank Septic System Design

It is provided in accordance with the septic tank design formula and calculates the wastewater flow through a septic tank according to the British standard C=A plus P (rq plus ns) Where, C — Capacity expressed in liters P – Number of Individuals A – 2000 Litres per day as a baseline R – Detention Period of Sewage in Days Q – Sewage Flow in liters per day N – Number of Years R – Detention Period of Sewage in Days Sludge buildup measured in litres per person per year (rq + ns) = 180 Litres is a simplified formula.

We are able to Rewrite the formula to make it more accurate.

Septic TankConstruction Details

According to the Septic Tank Design Formula and Calculation of Wastewater Flow for a Septic Tank, the British Standard is provided. The equation C=A + P (rq + ns) is as follows: Where, C – liters of storage capacity Number of individuals (P) A continuous volume of 2000 Litres In this equation, R is the retention duration in days, Q denotes the sewage flow in liters per day, and N denotes the number of years the wastewater will be retained.

S — Sludge buildup measured in litres per person per year (per capita). (rq + ns) = 180 Litres is a simplification. We have the ability to do so Revise and resubmit the equation In this equation, C=A + 180 PC = 2000 + (180 5) = 2900 Litres (Septic tank design capacity)

  • First and foremost, wastewater from the home is let to enter the tank through an intake line, enabling particles to settle and scum to float in the water. During the detention time, solid settle down is digested by an anaerobic process, resulting in a reduction in the amount of solids. It is then routed into the second chamber, where more settling takes place with the excess liquid that is discharged in a relatively clean state onto the drainfield or seepage field. This relatively clean water is now transported to a distribution chamber, where the wastewater is directed via one or more perforated pipes embedded in a layer of gravel. As water slowly infiltrates (seeps) into the underlying soil, this method is considered effective. These include the bacterial components and waste products of this water that have been trapped by soil particles or degraded by microorganisms. In most cases, the septic tank treatment eliminates disease-causing organisms as well as organic debris and most nutrients (with the exception of nitrogen and certain minerals). When the wastewater has been somewhat cleansed, it either travels into the groundwater or evaporates from the land.

Septic TankCleaning

Regular and periodic cleaning of the septic tank treatment system are required to prevent the build-up of sludge and the ultimate escape of the effluent into the drainage field. If this occurs, it may choke the leach field plumbing, necessitating the need for costly repairs. The periodic time interval between tank emptyings in the septictank cleaning process is determined by the capacity of the tank in relation to the solids intake, the quantity of indigestible solids present, and the ambient temperature.

When cleaning the septic tank, it is important to remember that only a tiny amount of sludge should be left in the tank.

A well – constructed and thoroughly maintained septic tank system produces no odors at all.

If an aseptictank is well-maintained, it should last around 50 years in concrete, fiberglass, or plastic.

Septic Tanks Potential Problems

Excessive waste of cooking oils and grease can cause the upper section of the septic tank to become clogged and the intake drains to become clogged as well. Oil and grease are notoriously tough to decompose, and they can result in odor concerns as well as difficulty with frequent emptying of grease traps. Non-biodegradable hygiene supplies such as sanitary towels, cotton buds, and other similar items may quickly fill and clog a septic tank, therefore these materials should not be disposed of in this manner.

Septic tank system damage caused by chemical interaction with pesticides, herbicides, products containing high concentrations of bleach, or any other inorganic compounds such as paints, solvents, and other similar substances Bacterial function is inhibited by such compounds.

An excessive amount of water in the septic tank as a result of a plumbing leak may cause an overflow of the septic tank system.


The overflowing of cooking oils and grease can cause the upper section of the septic tank to overflow and the inflow drains to become clogged at times. Oil and grease are notoriously tough to decompose, and they can result in odor concerns as well as difficulty with frequent emptying of waste containers. Septic tanks may quickly fill with non-biodegradable hygiene materials such as sanitary towels, cotton buds, and other similar items, and these things should not be disposed of in this manner.

Pesticides, herbicides, items containing high concentrations of bleach, or any other inorganic compounds such as paints, solvents, and so on might cause harm to a septic tank system.

Branches and roots of a tree growing above the tank and shrubs or in the drainfield may clog and/or rupture them. Because of a plumbing leak, there may be too much water in the septic tank, which might overflow the septic tank system and cause it to overburden.

What are the disadvantages of a septic tank?

Disadvantages of using a septic system One problem that can occur with excessive squandering of cooking oils and grease is that it can fill up the upper region of the septic tank and cause the intake drains to become partially or completely clogged. 2. When some individuals use a waste grinder to dispose of their waste food, the mechanism becomes overloaded quickly, resulting in an early failure. 3. The roots of a tree growing above the tank and shrubs, as well as the drain field, may block and/or rupture the tank and drain field.

An excessive amount of water in the septic tank as a result of a plumbing leak may cause the septic tank system to become overloaded.

How often should you empty your septic tank?

Overall, septic tank systems require no more than once-yearly cleaning, and many users may decrease emptying to once every three to five years by using good management practices. When cleaning the septic tank, it is important to remember that only a little amount of sludge should be left in the tank once the process is completed.

Septic Tank Meaning

A septic tank is a subterranean building constructed of concrete, fiberglass, or plastic material in which residential sewagewater is held for first treatment.

Septic tank construction

Septic tanks are used in situations when there is no adequate drainage infrastructure. Septic tanks are developed and designed in order to keep waste or sewage for a period of 10 to 30 days in order to prevent flooding. This tank is typically installed between 1.5m and 1.8m below the surface of the earth.

Septic tank design for home

It is critical that a septic tank has the appropriate capacity, otherwise effluent would backflow into the home. The septic tank design should take into account potential increases in wastewater output and should result in a septic tank with sufficient capacity to survive for many years.

Watch Video: Septic Tank Design Calculations

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Types of Septic Systems

Septic system design and size can differ significantly from one neighborhood to the next, as well as throughout the country, due to a variety of variables. Household size, soil type, slope of the site, lot size, closeness to sensitive water bodies, weather conditions, and even municipal ordinances are all considerations to take into consideration. The following are 10 of the most often encountered septic system configurations. It should be noted that this is not an exhaustive list; there are several additional types of septic systems.

  • Septic Tank, Conventional System, Chamber System, Drip Distribution System, Aerobic Treatment Unit, Mound Systems, Recirculating Sand Filter System, Evapotranspiration System, Constructed Wetland System, Cluster / Community System, etc.

Septic Tank

Septic Tank; Conventional System; Chamber System; Drip Distribution System; Aerobic Treatment Unit; Mound Systems; Recirculating Sand Filter System; Evapotranspiration System; Constructed Wetland System; Cluster / Community System; Septic Tank.

Conventional System

Septic tanks and trench or bed subsurface wastewater infiltration systems are two types of decentralized wastewater treatment systems (drainfield). When it comes to single-family homes and small businesses, a traditional septic system is the most common type of system. For decades, people have used a gravel/stone drainfield as a method of water drainage. The term is derived from the process of constructing the drainfield. A short underground trench made of stone or gravel collects wastewater from the septic tank in this configuration, which is commonly used.

Effluent filters through the stone and is further cleaned by microorganisms once it reaches the soil below the gravel/stone trench, which is located below the trench.

In terms of total footprint, gravel and stone systems are very substantial, and therefore may not be appropriate for all residential sites or situations.

Chamber System

Gravelless drainfields have been regularly utilized in various states for more than 30 years and have evolved into a standard technology that has mostly replaced gravel systems. Various configurations are possible, including open-bottom chambers, pipe that has been clothed, and synthetic materials such as expanded polystyrene media. Gravelless systems can be constructed entirely of recycled materials, resulting in considerable reductions in carbon dioxide emissions during their lifetime. The chamber system is a type of gravelless system that can be used as an example.

  1. The key advantage of the chamber system is the enhanced simplicity with which it can be delivered and built.
  2. This sort of system is made up of a number of chambers that are connected to one another.
  3. Wastewater is transported from the septic tank to the chambers through pipes.
  4. The wastewater is treated by microbes that live on or near the soil.

Drip Distribution System

An effluent dispersal system such as the drip distribution system may be employed in a variety of drainfield configurations and is very versatile. In comparison to other distribution systems, the drip distribution system does not require a vast mound of dirt because the drip laterals are only placed into the top 6 to 12 inches of soil. In addition to requiring a big dosage tank after the sewage treatment plant to handle scheduled dose delivery of wastewater to drip absorption areas, the drip distribution system has one major disadvantage: it is more expensive.

Aerobic Treatment Unit

Aerobic Treatment Units (ATUs) are small-scale wastewater treatment facilities that employ many of the same procedures as a municipal sewage plant. An aerobic system adds oxygen to the treatment tank using a pump. When there is an increase in oxygen in the system, there is an increase in natural bacterial activity, which then offers extra treatment for nutrients in the effluent. It is possible that certain aerobic systems may additionally include a pretreatment tank as well as a final treatment tank that will include disinfection in order to further lower pathogen levels.

ATUs should be maintained on a regular basis during their service life.

Mound Systems

Using mound systems in regions with short soil depth, high groundwater levels, or shallow bedrock might be a good alternative. A drainfield trench has been dug through the sand mound that was erected. The effluent from the septic tank runs into a pump chamber, where it is pumped to the mound in the amounts recommended. During its release to the trench, the effluent filters through the sand and is dispersed into the native soil, where it continues to be treated. However, while mound systems can be an effective solution for some soil conditions, they demand a significant amount of land and require regular care.

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Recirculating Sand Filter System

Sand filter systems can be built either above or below ground, depending on the use. The effluent is discharged from the septic tank into a pump compartment. Afterwards, it is pushed into the sand filter. The sand filter is often made of PVC or a concrete box that is filled with a sand-like substance. The effluent is pushed through the pipes at the top of the filter under low pressure to the drain. As the effluent exits the pipelines, it is treated as it passes through the sand filtering system.

However, sand filters are more costly than a standard septic system because they provide a higher level of nutrient treatment and are thus better suited for areas with high water tables or that are adjacent to bodies of water.

Evapotranspiration System

Evaporative cooling systems feature drainfields that are one-of-a-kind. It is necessary to line the drainfield at the base of the evapotranspiration system with a waterproof material. Following the entry of the effluent into the drainfield, it evaporates into the atmosphere. At the same time, the sewage never filters into the soil and never enters groundwater, unlike other septic system designs. It is only in particular climatic circumstances that evapotranspiration systems are effective. The environment must be desert, with plenty of heat and sunshine, and no precipitation.

Constructed Wetland System

Construction of a manufactured wetland is intended to simulate the treatment processes that occur in natural wetland areas. Wastewater goes from the septic tank and into the wetland cell, where it is treated. Afterwards, the wastewater goes into the media, where it is cleaned by microorganisms, plants, and other media that eliminate pathogens and nutrients. Typically, a wetland cell is constructed with an impermeable liner, gravel and sand fill, and the necessary wetland plants, all of which must be capable of withstanding the constant saturation of the surrounding environment.

The operation of a wetland system can be accomplished by either gravity flow or pressure distribution. As wastewater travels through the wetland, it may escape the wetland and flow onto a drainfield, where it will undergo more wastewater treatment before being absorbed into the soil by bacteria.

Cluster / Community System

In certain cases, a decentralized wastewater treatment system is owned by a group of people and is responsible for collecting wastewater from two or more residences or buildings and transporting it to a treatment and dispersal system placed on a suitable location near the dwellings or buildings. Cluster systems are widespread in settings like rural subdivisions, where they may be found in large numbers.

How To Design A Septic System

Installing septic systems is becoming increasingly popular among homeowners, who consider it to be a superior alternative to municipal sewer systems. In general, they are more environmentally friendly since they use on naturally existing bacteria to dispose of waste instead of chemical waste disposal systems. Other homeowners reside in places that aren’t served by a centralized public wastewater treatment system, such as rural or suburban settings. Septic systems are used by around 20% of all households in the United States.

Due to the fact that your measurements must be correct, it is a meticulous process.

Local Laws and Regulations

Whenever you embark on a large project, such as septic system installation, you must be certain that your project adheres to all applicable rules and regulations in your area. In most cases, the regulations that govern septic systems are determined by where you live and the size of your project. In Pennsylvania, for example, local communities and townships will be liable for septic tanks that hold less than 10,000 gallons of water. Anything containing more than 10,000 gallons will be subject to the supervision of the State Department of Environmental Protection.

You can find yourself halfway through a project and having to start again because you weren’t aware of a legal requirement that you were required to follow.

Soil Tests

The ability of the septic system to function properly is highly dependent on the condition of the soil. The kind of soil, even down to the type of soil grain, can have an impact on how well your septic system performs in terms of efficiency. Soils with flat grains are more prone to compacting. Leaching systems become a concern when this type of soil is utilized as fill because of its high water table. There are hundreds of different types of soils on the planet. These soils are not isolated from one another.

This results in an unlimited number of possible soil combinations, which can make creating a soil report difficult.

Your best bet is to engage a civil engineer to develop a soil study for your property.

You may then refer back to the rules in your region to determine what sort of septic system you require once you have determined your soil type and composition.

Types of Septic Systems

Some health regulations will inform you what sort of septic system you require based on the type of soil in your yard. Septic systems are available in a variety of configurations. One of the most frequent types of septic systems is one that includes both a septic tank and a drain field. The drain field collects wastewater from the residence and dumps it in the soil, where it is cleaned. In this phase, you’ll need to think about the size of your septic tank. Most people will be OK with a 1500-gallon storage tank for their household needs.

Size of the Septic Field

Following the identification of your septic system, you may begin planning the layout of your septic field. Once again, you must consult the local legislation to ensure that your field complies with the requirements. In certain cases, they may be able to influence how far away your field is from your home, property borders, and waterways. Now you must consider the size of your home as well as the type of soil on which it will be built. A bigger home with poorly draining soil will necessitate the installation of a larger septic field.

The definition of a bedroom is one of the more fascinating aspects of this.

This must be taken into consideration in your calculations.

Plan the Pipes

The layout of your septic field may begin once the kind of septic system has been established. In this case, you must consult the local rules to ensure that your field is in compliance. Depending on where your field is located in relation to your home, property lines, and waterways, they may have an influence. Now you must consider the size of your house as well as the type of soil on which it will be built. It will be necessary to install a larger septic field if your home is larger and your soil is poor at draining.

The notion of a bedroom is particularly significant in this context.

Take that into consideration while making your estimates.

List the Required Materials

While you’re completing your plans, you’ll want to establish a list of the supplies you’ll need for your septic system and budget for them. You’ll need to know how long the pipes are and how wide they are. You’ll also need to account for the gravel that will be used to fill in the gaps, as well as pipe connections and joints.

Get Your Plans Approved

Before you can move forward with your project, you’ll need to get your designs authorized by the appropriate authorities in your town or county first. Depending on where you live, you may have to visit a different person. Depending on the situation, the country or state may be held liable. You want to make absolutely certain that your plans adhere to all applicable rules and regulations in your location. The people who provide their approval to these ideas bear a greater responsibility. It may seem like a little annoyance to you and your project, but if your septic system isn’t functioning correctly, it might have serious consequences for you and your project.

Other ramifications include the contamination of nearby groundwater, lakes, and streams. It’s possible that bacteria from your system has made its way into public rivers. It is possible for those individuals to get illnesses and infections as a result of this.

Hire an Engineer for Your Project

The process of designing a septic tank is not very complicated. Precision in your measurements is required throughout the procedure, which makes it a difficult task to complete. A slight error in one’s calculations might cause the entire enterprise to come crashing down around him. Hiring a professional engineer with extensive knowledge in septic system design and who can design the most appropriate system for your house or project is an option to developing the system yourself. Is it your intention to hire an expert to assist you with the design of your sewage treatment system?

Septic Tank Design and Construction

Aseptic tank design must be thoroughly thought out and constructed such that it will not fracture and will not pollute ground water. Septic tank design and construction are discussed in this section, and building blueprints for a standard-sized tank are provided as well. We will cover the characteristics of the tank, the necessity to estimate effluent levels, the tank intake and exit pipes, the transfer pipe between internal chambers, vent pipes, and the design of access manholes in order for the tank to be maintained and cleaned out.

  • In order to avoid cracking and polluting ground water, the aseptic tank design must be thoroughly thought out and built. Septic tank design and construction are discussed in this section, and building blueprints for a standard-sized tank are provided as an additional resource. We will cover the tank’s characteristics, the necessity to estimate effluent levels, the tank’s input and exit pipes, the transfer pipe between internal chambers, vent pipes, and the construction of access manholes in order for the tank to be maintained and cleaned out properly. Refer to this page for further information.

Septic Tank Design

Please go to the preceding page at if you need a refresher on how septic tanks function before continuing.

A Septic tank needs to be strong enough

Before we begin, you might want to review the preceding article on septic tanks to refresh your memory on how they function.

How big a septic tank?

The first thing we need to figure out is how big the tank should be in terms of volume. There are various ways to figure this out, but using the charts at will help you to determine the size you will need to purchase. Let us assume that we require a tank with a capacity of 2.9 cubic metres (the quantity of effluent that the tank will contain), which is normal for a two-bedroom house with two bathrooms and four people living in it. A typical domestic septic tank, with a capacity of 2.88 cubic meters, is seen in the construction sketch below.

How many chambers?

A septic tank should contain at least two chambers; three chambers are preferable, but two chambers are sufficient. The size of the second chamber can be approximately half that of the first chamber. The first chamber of this tank has a liquid capacity of 1.92 cubic metres and is 1.2m x 1.0m x 1.6m deep. The second chamber has dimensions of 0.6m x 1.0m x 1.6m deep, with a capacity of 0.96 cu m, for a total capacity of 2.88 cubic metres. It is important to note that the depth of the effluent in the tank is 1.6 metres.

To view and download the complete drawing, please click on the picture.

The reinforcing steel is a mesh of 8 mm diameter reinforcing bars that are placed 15 cm (6 inches) apart and formed into a mesh box to provide structural support.

Septic Tank Construction

When casting the concrete, plywood formwork (shuttering) is put around the steel to form a box-shaped mould, which is then ready to be filled with concrete and cast around the steel. This should be set to ensure that the walls are 4 inches thick and that, when the concrete is poured, there will be a good thick coating of concrete on both sides of the steel mesh to prevent the steel from rusting, and that the steel mesh will be covered with a good thick layer of concrete. Additionally, a layer of sand should be placed beneath the concrete floor of the tank to allow for some movement when the tank settles and moves in the earth.

The tank’s 15cm (4 inch) diameter PVC inlet, transfer, and outlet pipes must be fitted before the concrete is poured in order for it to function properly.

Too much water should not be added (a slump of 7 is recommended) in order to produce a good firm concrete, and the concrete should be vibrated with a vibrator throughout the pouring process to ensure that it is correctly compacted and free of cavities or air holes.

See also:  Who Pays For The Septic Tank To Be Cleaned? (Solution)

However, while it may appear tough, following these simple recommendations will ensure that you have a tank that is properly constructed and will not leak or break in the near future.

Levels are very important

When creating the septic tank, it is important to pay particular attention to the levels of the tank. Ideally, the effluent pipe from your toilet to the tank should be 15 cms in diameter with a slope of at least 2 percent (i.e., a fall of 2cms per meter) over the whole length of the pipe from your toilet to the tank. The tank must be built deep enough to accommodate this, and it should be meticulously designed before construction begins. The septic tank’s entrance line should be routed directly into the tank.

These manholes are a major source of clogs and foul odors throughout the city.

Inlet, Outlet and Transfer pipes

The plumbing is presently being installed. Take note of the relative placements of the inlet, outlet, and transfer pipes within the tank; the inlet pipe is slightly higher than the outlet pipe, and the transfer pipe is somewhat lower than both. These differences in relative heights are significant. There are 15cm (4 inch) tee pieces on both the inlet and outlet pipes as well as on both ends of the transfer pipe that connects the chambers in this tank design. These tee pieces help to keep the pipes clear of scum that forms on the surface of the effluent while it is being digested by the bacteria.

We want the water to flow through the tank as gently as possible.

This is done to ensure that liquid entering the pipe is drawn from the center level of the tank, which is below any turbulence and high enough to avoid being clogged by deposits at the bottom of the tank, rather than the sides or bottom of the tank.

In the end, an open 7.5cm (3 inch) diameter pipe is inserted between the two chambers above the level of the water and scum to relieve any pressure that may have built up and to enable free movement of gases between the two chambers

Manholes and Vent Pipe

The top of the tank may now be installed; once again, a reinforced concrete slab measuring 15cm (4inches) thick will be employed. The top is equipped with a galvanized steel vent pipe with a diameter of 2 inches. As a result of this design, the pipe is more than 2 metres high, allowing any gases to be dispersed freely in the wind. It’s important to remember that a septic tank should not smell while it’s running correctly. There are also two manholes in the top of the structure. Normally, grout will be used to seal them, ensuring that they are gas tight.

  1. Aside from that, the manholes provide access for pumping out the tank, which you may need to do once every five years or so, depending on your circumstances.
  2. In these situations, it is not feasible to gain access to the tank in order to repair or unblock it if the need arises.
  3. It is possible that certain contractors will make the manhole and its cover fit together with a tapered connection in select locations.
  4. Flat surfaces are far superior to rounded ones.
  5. Likewise, see:
  • Bacterial Action in a Septic Tank
  • Septic Tank Size and Capacity
  • Septic System Maintenance
  • Septic System Cleaning
  • Toilets and drains that are clogged

Phil Wilson is the owner of the copyright. The month of October 2014 This article, or any part of it, may not be duplicated or reproduced without the express consent of the author or owner of the copyright.

Design of Septic Tank with Design Example on British Method

A septic tank is a system in which a tank made of a suitable material such as concrete, fiberglass, brick masonry, or other similar material is placed in the ground to collect waste and treat it. Most countries of the globe currently employ septic tanks extensively, and people are attempting to embrace this way of eliminating ejected waste from the environment. In a nutshell, the working principle of a septic tank is quite simple: the larger particles that come with the waste water settle down at the bottom of the tank and form sludge, the greasy particles settle at the top of the tank and form a layer that floats there and is known as scum, and the water portions remain in between the two layers as shown in the illustration above.

It is recommended to provide a particular longitudinal slope to the tank so that the sludge may be transferred to the other side of the septic tank when it begins to accumulate at the entrance of the septic tank.

This will prevent the septic tank from malfunctioning. Manholes, ventilation, and inspection are also given for the purpose of septic tank maintenance and gas escape. This allows the septic tank to work better overall.

Design of Septic Tank -Example01

The design of a septic tank involves calculating the tank’s dimensions (length, depth, and breadth) based on the daily flow rate that is utilized by the individuals. Septic tank design may be accomplished by a variety of approaches, including the following:

British Method

In this section, we will go over a design example utilizing the British technique. METHOD OF DESIGNING A SEPTIC TANK IN THE BRITISH STYLE

Number of Persons P = 7 No
Daily Discharge Q = 150 Ld-1 p-1
Free Board FB = 0.3 m
Length / Width L/W = 2
Depth of Tank Assumed D Total = 1.5 m
Volume of sptic tank V = 3260 L
Volume of sptic tank V = 3.26 m 3

It is necessary to create a septic tank with a capacity of 3.26 cubic meters.

Length of Interior of Septic tank L = 2.35 m
Width of interior of Septic tank W = 1.175 m
Depth of Liquid in Septic tank D = 1.2 m

Please share your thoughts on the principles presented in this post in the comments section!

How to Design a Septic Tank Drain Field

In every septic system, the aseptic drain field is an integral aspect of the system. A drain field that is not correctly built will do nothing except cause major difficulties across the whole system. Several considerations should be taken into consideration while designing your drain field.

Step 1 – Determine the Size

It is dependent on a few things as to what size drain field you will require. First, the soil should be analyzed to determine its percolation rate. Performing the percolation test on your own is an option, as is hiring a professional to do it. The field will need to be drilled multiple times in order for you to complete this task on your own. For this project, you will need to drill holes that are at least 3 inches in diameter and 3 feet deep. This needs to be done in a random manner throughout the planned drain field’s region of operation.

The size of the field will be determined by the size of the house and the rate at which the water percolates.

Another factor to consider is the zoning rules in your area.

Step 2 – Map Out the Piping

Perforated pipes placed in gravel trenches across the drain field are required for a properly functioning drain field. It is preferable if the trenches have a little slope, often less than 1/8th inch each foot. The pipes will need to be buried in gravel and then covered with additional gravel to complete the installation. When planning the pipe layout, make sure to draw a schematic that appropriately depicts the depth of the field. Using this information, you can calculate how much dirt will be beneath the gravel, how much gravel will be under the soil, how much space will be required for the pipe, and how much gravel will be required for a cover.

Step 3 – Plan for Materials

Now that you have a rough draft of your map, you can begin to gather the materials you will need for the project. The perforated pipes must be at least 4 inches in diameter in the majority of circumstances. Purchase enough pipe to connect the septic system to the field and to be laid out on the field in the manner depicted in your drawing. Calculate the amount of gravel you will require and arrange for it to be delivered to a location near enough to the trenches that you can easily transfer it with a wheelbarrow or front end loader.

Also necessary is determining how much backfill will be required for the project. While you will have a lot of this from digging the trenches, you may find yourself in need of additional soil to fill in the gaps as well.

Septic Tank and its Design, Maintenance

Septic Tank is the name given to the tank that holds waste water from a house or a structure. Septic tanks are used in situations when there is no adequate drainage infrastructure. In order to keep the waste or sewage for a period of 10-30 days, A septic tank is built, and a design for the tank is created. This tank is typically installed between 1.5m and 1.8m below the surface of the earth. Septic tanks are used to collect waste water that is discharged from the house’s sewage pipes. In the illustration, wastewater enters the tank at one end and exits the tank at the other end, indicating a continuous flow.

  • The municipal department is in charge of removing the waste from the septic tank.
  • The waste water is combined with the fresh water sump as a result of seepage from the septic tank.
  • All waste water from the bath, toilet, and kitchen is channeled into the tank for treatment.
  • In waste water, there is an abundance of anaerobic microorganisms.
  • Generally speaking, if the density of solids is more than the density of water, the solids settle to the bottom of the tank, and if the density of solids is less than the density of water, the solids float.

Septic Tank Maintenance:-

Remove the sludge when it reaches a height of 3 inches below the suck out the pipe and is clogging the pipe. Because of the presence of waste gases, there is a possibility that a foul stench will emanate from the pit. To keep the stench at bay, periodic additions of wastewater are made to the septic tank.

The design of Septic Tank:-

a septic tank is comprised of a top slab, a bottom slab with a PCC bed, shear walls around the tank, and a top cover (with an opening) to allow for the monitoring of waste water levels The calculations for septic tank design are listed below.

How to design Septic System?

For the sake of clarity, we’re going to build a septic tank for 8 people in a house that will be filled in 10 days. The average amount of garbage created by each person every day, including kitchen waste, ranges from 95 to 150 liters.

The average waste generated from each human includes
  • Here is an example of a septic tank that will serve 8 people in a residence and will be filled in 10 days, for your convenience. For each person per day, including kitchen garbage, an average amount of 95 to 150 liters is created in waste.

The values may vary depending on the location and the surrounding environment. Calculation:-Total number of people in the residence = 8. (Assume) The total amount of waste generated by the house is 8 x 130 = 1040 liters each day. The total garbage created by the house in ten days is equal to ten times ten hundred forty (ten thousand forty) liters. Keep in mind that 1m 3 equals 1000 litres (Standard) As a result, for 10,400 lts =10.4 m 3,

How to find Septic tank Size:

If you want to determine the Septic tank size, you must first understand the usual length and breadth ratio of a Septic tank. It is 4:1 or 2:4 in length to breadth for a septic tank. 1.5m to 1.8m in depth or height, depending on the model, is the depth or height of a septic tank. As a result, the area of the septic tank is 10.4 1.8 = 5.78m2.

2Taking into consideration the length to breadth ratio of 4:1 The length of the septic tank is equal to (4/5) x 5.78 = 4.62m. 1/5 x 5.78 = 1.15m for the width or breadth of the Septic tank (Approx 10.4 m 3) Septic tank dimensions are 4.6m in length, 1.15m in width, and 1.8m in depth.

Automatic Calculator For Septic Tank Size Calculation:-

You can also read the following:-

  • There are ten different types of footings or foundations that we use in construction. Various slab kinds used in building
  • Various column types used in construction
  • And more.

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About The Author

I am the founder and administrator of, and I work as a civil engineer at Ultratech Cement Ltd. I made this blog in order to share important information with other civil engineers that have a strong understanding of the topic matter I am writing about. Please also consider becoming a fan on Facebook and Twitter by clicking on the links below.

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