Project Design on Septic Tank

Table of Contents
Introduction 2
Definition: 2
Description: 2
Project Description 3
Villa requirements: 3
Villa Capacity: 4
Design Capacity: 4
Procedure 4
The capacity 5
Conversion 5
Calculations 5
Conclusion 9
References 10

A sewage tank can be defined as a system that carries the treatment of the sewage that is produced on a small basis either in the households or commercial centres or schools, colleges and factories. They are usually developed in those regions where the availability of the main sewage line is not there or is situated at a very large distance from the place where the sewage is generated. In the household areas, the handling of the sewage has to be clean and proper to ensure that it does not affect the health of the people living in it. This kind of system is developed to ensure the proper disposal of the waste that is generated (Gray, 1995).
The septic tank works on the action of the bacteria to decompose the material that enters the tank. This kind of action is known as “anaerobic bacterial environment” which is developed in the tank to provide the bacterial action that would help in the decomposition of the waste. It can also be referred to as an “On-site sewage system”.
We are going to develop a septic tank for a villa which does not have a central sewage treatment system and this would help in safe disposal of the waste and ensure the sewage lines to be handled effectively.
The septic tank that is used is usually kept individually for the villa and its design depends on the Waste Water flow and the per capita usage of the people in the villa. Many times if one septic tank is not sufficient enough for effective handling of the sewage generated, then there is a requirement of the second septic tank. During the design, the septic tank volume varies from 1500 to 2500 Gallon.
The septic tank consists of inlet in the top of the tank. In this phase, the solid substances in the sludge settle down and the scum will flow on the top. The second end is usually made as a T section pipe like the first one. This is done to avoid the damage that the material could make to the wall and the body of the septic tank. The outlet is at the same level of the inlet pipe in order to ensure that the scrum would go through it with the liquid sewage (Gray, 1995).

Project Description
Villa requirements:
The size of the septic tanks depend on the quantity of the waste water generated and the capacity of the disposal system to handle it. Considering the above points, the design of a septic tank for a villa is done and the capacity of the tank is determined for the sewage of the waste water. The number of persons that are living in the villa and are using the system are to be considered while designing the septic tank for the villa (Bounds, 1997).

Villa Capacity:
The villa that we have selected has 11 bathrooms and 4 kitchens and there are 18 people living in the villa for 24 hours daily. We will be able to determine the size of the tank will be known after calculating the rate of flow and getting the information from some tables.
Design Capacity:
This villa has 18 person living in and there is a daily consumption of 300L per capita. When the total consumption per day is compared with the tables acquired we will be able to estimate the number of tanks needed. We would also be determine the design of the septic tank through suitable calculations of the capacity of the tank and the waste water that is to be disposed in it. These calculations and its applications are discussed in the report further (Bounds, 1997).
For the designing of a septic tank we have to follow certain steps and the procedure is listed below:
Design the septic tank for a villa
Consider the villa and its location that we have taken into consideration.
Arranging a meet with the contracting company
Obtaining adequate information from the contracting company:

Name of the owner Mr. Saeed AlGhafry
Area(m) 56.6 x 21.6
Number of People 18
Number of Bathrooms 11
Number of Kitchen 4

Calculating per person or per capita usage.
Evaluate the design developed and check its feasibility and suitability for the villa that we have taken into consideration.
The capacity
Using appendix 1, the consumption rate for the single family is 300 L/Day/Person. After the calculation we will find out whether the resultant consumption per day is high or not high as per the calculation in the next page since 18 person live in this villa.
British system is the standard system used in UAE for units. There is a conflict since the criteria and standards tables are all in American system. We should convert all the units from American gallons to L and from L to m s (Cotteral & Norris, 1969).
* Villa Capacity : 18 person
*Villa Consumption rate: 300 L / day / person
*Peak Flow Q
Q = consumption x number of staff
Q = 300 x 15
Total Q = 4500 L / day
The peak flow calculated is less than the mentioned values, so we used 1 tank which drains a flow of wastewater equal to 4500 L / day.
We had to extend the values of Average Sewage wastewater flow; we took the closest value to Q which is 4987.2 L / day (Appendix 3).
Also from Appendix 3, we took the minimum size of effective capacity needed from the extension of the values as 6904 L / day.
The volume of the septic tank of the clinic:
V = 6904/1000=6.904m3
We had to convert the volume to dimensions that can fit with the formulas of septic tank design criteria as the following (Cotteral & Norris, 1969):
Ratio of Length: Depth= 4:3
Length = L
Depth = 0.75 L
Width = 0.5 L
L x 0.75 L x 0.55 L = 6.904
0.3375 L3 = 6.804
L3 = 21.16
L = 2.922m
Length= 2.922m Depth= 2.842m Width= 1.825m
Volume= 2.922×2.842×1.825
V= 6.909 m3
Converting these result to standard dimension for designing in millimeters:
Length= 2922 mm
Depth= 2842 mm
Width= 1825 mm
Layout of Septic tank

Typical Gravity Septic Tank

(Single Compartment)

(Two Compartment)

The design of the septic tank provided us with an in depth understanding of the construction process that is followed in the management of the waste water. The system that we have developed will help to estimate the design of the tank for the villa. The design that we have provided is made on the basis of calculation and conversion that we have developed during the process. The design would help the villa during the development of the septic tank.

Bounds, T. R. (1997). Design and performance of septic tanks. ” ASTM SPECIAL TECHNICAL PUBLICATION 1324, 217-234.
Cotteral, J. A., & Norris, D. P. (1969). Septic tank systems.
Government of Western Australia. (2014). Understanding Septic Tank Systems. Government of Western Australia.
Gray, N. F. (1995). The influence of sludge accumulation rate on septic tank design.”. Environmental technology, 795-800.


Posted on

March 9, 2018

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