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septic tank

The septic tank is one of the basic units of the wastewater treatment process after its production, which is the most important function of creating suitable conditions for settling and collecting suspended solids downwards and floating oily materials and foam towards the surface of the wastewater. Depending on the type of wastewater and the amount of treatment allowed, septic tanks have different capacities and different components. Therefore, the units in this tank can include sedimentation, flotation, anaerobic treatment, aerobic treatment, digestion and sludge collection.

According to the following figure, the septic tank consists of the following components:

1- Sewage inlet system: includes pipe and inlet baffle.
2. The initial tank of the septic tank: which has the largest volume of the septic tank and usually the total volume of the septic tank is related to this section.
3- Separating wall: which prevents sludge, grease and floating oils from entering the clarification tank.
4. Clarification tank: This tank component contains almost the entire volume of the septic tank and accumulates wastewater free of sediment and floating materials.
5. Biogas outlet (ventilation): Through this duct, the gases produced due to anaerobic wastewater treatment processes, which are mainly methane, are released from these tanks.
6- Sewage outlet system: includes baffle and septic tank outlet pipe.

سپتیک تانک

Product details

The primary goal in designing and determining the capacity of a septic tank is to provide suitable conditions for the removal of suspended solids and floating materials such as oil and foam. In this regard, in proportion to the inflow and per capita flow of wastewater production, having a smooth flow and wastewater retention time between 6 to 24 hours, are important parameters in designing the capacity of this type of reservoirs. According to the existing standards, two methods can be used to determine the capacity of the septic tank.

Determining the capacity by using the number of rooms in the complex, which is suitable for wastewater production per capita up to 6 cubic meters per day, and according to the table below is obtained.

( EPA, Design manual )

Number of rooms

Tank capacity (cubic meters)

1

3

2

3

3

4

4

5

5

6

6

6

7

7

8

8

This method is suitable for capacities higher than 6 cubic meters per day. In this method, according to BS6297 standard, the capacity of this type of tanks is obtained from the following formula.

V = 2000 + (P × C)

In this regard, V is the capacity of the tank in liters, C is the per capita wastewater production per day in terms of liters, and P is the number of people in the complex.

The table below shows the per capita wastewater production for different locations.

Row

Location

the unit

Range

Normal amount

  

Liters per day

  

1

Urban housing units

person

150-250

200

  

2

Recreational villas

person

120-400

300

  

3

Office buildings

8-hour staff

35-75

55

  

24-hour staff

70-100

90

  

4

Factories and industrial workshops

8-hour worker

40-80

75

  

8-hour worker with bath

100-150

120

  
  

5

Construction workshops

8-hour staff

40-80

60

  

24-hour staff

80-120

100

  

6

Public Restroom

People (without flash tank)

5-12

7

  

People (with flash tank

12-20

15

  

Removal of contaminants in wastewater, especially harmful organic matter, suspended solids and oil and floating foam on it, including the use of septic tanks for a proper pre-treatment before final treatment and transfer to the main treatment site. Among the important wastewater pollution parameters are BOD5, COD, TKN and TSS, the table below shows the removal rate of each of them.

row

Parameter

Inlet concentration to septic tank

Outlet concentration from septic tank

  
  

(mg/lit)

(mg/lit)

  

1

BOD5

165-296

135-227

  

2

COD

550-700

257-335

  

3

TSS

165-370

50-150

  

4

TKN

35-98

35-70

  

5

Oil&Grease

70-105

35-40

  

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