What Is Septic Tank?
A septic tank collects and treats wastewater in a property that isn’t linked to the mains sewer system and is, thus, most commonly used in rural areas.
The term ‘septic’ means infected with microorganisms’; the tanks contain bacteria that break down organic waste.
The inclusion of a bacterial treatment mechanism would be the difference between a septic tank and a cesspit, and such structures have both industrial and residential appliances.
Installed underground, a septic tank makes use of natural processes to treat the sewage it stores. Usually made up of two compartments or chambers, the tank receives wastewater from an inlet pipe.
If you’re in need of maintenance servicing or work on a Septic Tank, follow this link, otherwise read on to learn more about Septic Tanks, and how they may be emptied.
How Does A Septic Tank Work?
A septic tank May digest organic matter and separate float-able matter(e.g., oils and grease) and solids in the wastewater A septic tank will be connected with two pipes (for inlet and outlet).
The inlet pipe can be used to transport the water waste from the house and collect it in the septic tank. It’s kept here long enough so that the liquid and solid waste are separated from each other.
The second pipe is the outlet pipe. It can also call the drain field. This pipe moves out of the pre-processed wastewater from the septic tank and spreads it evenly from the soil and watercourses.
When waste-water was collected after a while, it will begin to separate into 3 layers. (as shown in the image above) The top layer is oils and grease and floats above all the waste.
This is commonly referred to as”scum.” The middle layer contains wastewater along with waste particles. The third and bottom layer consists of particles that are heavier than water and form a layer of sludge.
Bacteria within the tank does it is best to break down the solid waste, which then allows liquids to drain and separate away easily.
What’s left at the bottom of the tank is what needs to be periodically removed as part of general maintenance. This is one of the reasons why a septic tank is only a basic form of sewage treatment.
Septic Tank Construction
It’s best to construct a single compartment for small-capacity septic tanks. Larger capacities are the best fit for a both-compartment tank.
The wall separating the both is about two-thirds the length away from the inlet. It, therefore, performs better than the single-compartment tank. Both compartments interconnect above the sludge storage using pipes or square openings.
A plastic or concrete tank would be the best to use. The floor and side walls are made with plastered concrete to render a smooth surface. The floor has a slight slope of 10 percent towards the sludge outlet.
As a result, slung moves out more easily. The top cover of a septic tank is watertight and very thick. But a manhole of relative size is created. This allows inspection and emptying of the tanks.
Septic Tank Design based Per User Consumption
The proper capacity of a septic tank is essential otherwise wastewater backflow toward the house. The septic tank system is much designed considering a future increase in wastewater generation design proper capacity septic tank that may last long for years.
- Let take one example of House – 4 Members.
- Daily Water Usage for a House – 4 Person
- Cooking – 8 Liters
- Bathing & Toilet – 90 Liters/Person, So for 4 person – 360 liters/Day
- Washing clothes & Utensils – 28 Liters
- Cleaning House – 12 Liters
- Other – 8 Litres
Total – 416 Litres/Day Approximately
We consider detention time as 4 days. So the designed tank should have the capacity to retain household wastewater for at least 4 days.
Total wastewater in 4 days – 416 × 4 = 1664 Liters
So, we take more than that about 1800 Liters capacity minimum for a home. For the Septic tank design depth of the tank should not be less than 1.5m.
Take sludge settled down per person – 30 liters/year. So here we take sludge removal 1 year once.
Total Accumulated Sludge = 30 litres x 4 persons x 1 years = 120 Litres
Total Septic Tank Capacity = 1800+120 = 2120 Liters
We know that 1 cubic meter = 1000 Liters = 2120 /1000 = 1.92 Cum
Area required @ 1.8m depth = 1.92 / 1.5 = 1.28 Sqm
We take the Length and Width ratio of the Septic Tank as 4:1 or 2:1
Length(L): Breath(B) ratio taken as 4 : 1
So, 4 B2 = 1.28 Sq. m where B=0.565 m
(Note: Minimum width of tank should not be less than 750mm)
So that L = 4 × 0.75 = 3m
L – 3 m; B – 0.75 m ;
Depth = 1.5 + 0.3 = 1.8 m (freeboard should be provided at least 300mm)
Septic Tank capacity = 3 x 1.8 x 0.75 = 4.05 Cum
Septic Tank capacity = 4.05x 1000
Septic Tank capacity = 4050 Liters
British Standard Calculation:
British standards given the following formula calculate the wastewater flow for a septic tank.
C=A + P (r q + n s)
Where,
C = Capacity in liters
P = Number of People
A = 2000 Litres as constant
R = Detention period of Sewage in Days
Q = Sewage Flow in liters per day
N = Number of years
S = Sludge accumulation in liters per person/year
Simplification of (r q + n s) = 180 Litres
We can Rewrite this formula C=A + 180 P
C = 1800 + (180 × 4)
C = 2520 Litres
Frequently Asked Questions (FAQ) about Septic Tanks:
What is the purpose of a septic tank?
A septic tank is designed to collect and treat wastewater from properties that are not connected to the main sewer system. It utilizes natural processes to break down organic waste and separate solids from liquids, ultimately treating the sewage before it is dispersed into the soil.
How does a septic tank work?
A septic tank works by receiving wastewater from the property through an inlet pipe. Inside the tank, solid waste settles at the bottom as sludge, while oils and grease float to the top as scum. Bacteria within the tank break down the solid waste, allowing the liquids to drain away. The treated wastewater then exits the tank through an outlet pipe and is dispersed into the soil in a drain field.
What is the difference between a septic tank and a cesspit?
While both septic tanks and cesspits collect wastewater from properties not connected to the main sewer system, a septic tank includes a bacterial treatment mechanism to break down organic waste. In contrast, a cesspit simply collects and stores sewage without treating it, requiring more frequent emptying.
How often does a septic tank need to be emptied?
The frequency of septic tank emptying depends on factors such as tank size, household size, and water usage. On average, septic tanks should be emptied every 3 to 5 years to remove accumulated sludge and scum, ensuring efficient operation.
What is the optimal capacity for a septic tank?
The capacity of a septic tank should be determined based on factors such as household size, daily water usage, and detention time. Properly sized septic tanks should have enough capacity to retain wastewater for at least 3 to 5 days to allow for effective treatment.
What are the construction considerations for septic tanks?
Septic tanks can be constructed from materials such as plastic or concrete, with single or dual compartments. The design should include features like a watertight cover, inlet and outlet pipes, and proper slope for sludge removal. Additionally, the size and depth of the tank should be sufficient to accommodate the anticipated wastewater flow.
How is the capacity of a septic tank calculated?
The capacity of a septic tank can be calculated using formulas that consider factors such as household size, sewage flow rate, detention period, and sludge accumulation. British standards offer a simplified formula, while other methods take into account specific design parameters to determine the optimal tank size.
What are the maintenance requirements for a septic tank?
Regular maintenance is essential to ensure the proper functioning of a septic tank system. This includes periodic inspection, pumping out accumulated sludge and scum, and monitoring for signs of leaks or blockages. Proper disposal of household waste and avoidance of harmful chemicals can also prolong the lifespan of the septic tank.
