User:
Septic tank
Storyboard 
A septic tank is an on-site wastewater treatment system used in areas without centralized sewer systems. It consists of a buried container made of concrete, fiberglass, or plastic, designed to receive, treat, and partially treat household wastewater. The tank operates as a two-chamber system, separating solids and scum from the wastewater. In the first chamber, larger solids settle to the bottom, forming sludge, while lighter materials float to the top as scum. The first chamber functions as an anaerobic zone, breaking down organic matter. The partially treated effluent then flows to the second chamber for further settling and biological treatment. This process helps remove more solids and pathogens, improving the quality of the effluent before it leaves the septic tank.
ID:(80, 0)
Working Principle of Septic Tank
Description
A septic tank is a common on-site wastewater treatment system used in areas without access to a centralized sewer system. It is a buried, watertight container made of concrete, fiberglass, or plastic, designed to receive, treat, and partially treat household wastewater. The septic tank is an essential component of the septic system, which also includes pipes, drain fields, and the surrounding soil.
The septic tank operates as a two-chamber system, allowing for the separation of solids and scum from the wastewater. In the first chamber, the wastewater undergoes primary treatment. Larger solids settle to the bottom, forming a layer of sludge, while lighter materials like grease and oils float to the top, creating a scum layer. This separation process reduces the organic load in the effluent, making it easier for the next chamber to further treat the wastewater.
To prevent the scum and settled sludge from directly moving into the second chamber, a dividing wall (baffle) is in place. This ensures that the partially treated effluent from the first chamber flows into the second chamber for further treatment.
The first chamber acts as an anaerobic zone where the solids decompose in the absence of oxygen. The anaerobic digestion process breaks down organic matter into simpler compounds, reducing the overall pollutant load in the wastewater.
In the second chamber, further settling and biological treatment occur. The settled effluent from the first chamber flows through the baffle into the second chamber, where additional microbial action takes place. This secondary treatment stage helps remove more suspended solids and pathogens, thus improving the quality of the effluent before it eventually leaves the septic tank.
ID:(555, 0)
Water supply
Equation
To size the septic tank, the first step is to calculate the amount of wastewater to be treated. This depends on various daily consumption activities, such as:
| Activity | Symbol | Daily quantity (liters) |
| Cook | $V_{cc}$ | 16 |
| Toilet | $V_{cb}$ | 18 |
| Bath and shower | $V_{cw}$ | 50 |
| Laundry | $V_{cl}$ | 15 |
| Others | $V_{co}$ | 6 |
The first three activities are linked to the number of people, while the last two are relatively constant. Adding up these values gives the total daily water consumption:
 $V_{DWS} = n ( V_{cc} + V_{cb} + V_{cw} ) + V_{cl} + V_{co} $ |
liters per day.
For the calculation, you can utilize the sewer system design application (Sewer Application) in the section provided:
ID:(557, 0)
Wastewater volume
Equation
The wastewater generated in a household can be lost in part due to evaporation, drainage system leaks, or adherence to objects. Therefore, it's necessary to multiply the total daily flow by a factor $f_n$ that is less than one, in order to obtain a reduced volume:
| $V_{DF} = f_n V_{DWS}$ |
This factor can be adjusted in the sewer system design application:
ID:(556, 0)