How Does a Septic Tank Work?

Wednesday, 25 March 2020

How Does a Septic Tank Work?

how does septic tank work


Today on guardianconstructors.com i am going to be talking a lot about septic tanks. I will be discussing what this word means because i have seen a lot of people design septic tanks in the name of soak away, i have also seen people design these wrongly without considering several factors.


Septic tank africa
Approach View of a Sandcrete Septic Tank still Under construction
PhotoCredits MrPinner


Now lets Understand what it means to have a septic tank.

See Also: How To Calculate The Number Of Blocks A Fence Project


What is a Septic Tank?


A Septic tank is a special liquid waste management structure constructed to help collect domestic solid waste, separate the sludge which settles at the bottom, the Effluent which is a clear water and located at the middle of the compartment and then lastly the scum which comprises of oils, floating solids that settles at the top of the effluent

A Septic tank is usually made with Sandcrete Blocks (Common in Africa) or sometimes with concrete depending on what the water table of the area is like.

There also exists Precast concrete septic tanks which are commonly found in other parts of the world like Unites states, United Kingdom, Germany, etc.


Types Of Septic Tanks In Nigeria 
(Based On Material Used For Construction)

Concrete Septic tanks are usually common in the riverine areas of Nigeria especially areas where the water table is so close to the surface.

Sandcrete Septic Tanks are common in areas where the water table is located at a considerable depth. This is common in the uplands, Northern part Of Nigeria, Eastern Nigeria and other parts with less water bodies. 

Please Note: Sandcrete means Blocks

How Does A Septic Work?


For a septic tank, there always exists a pH Balance as well as a bacterial activity which breaks down solid wastes. The septic is always built separate from the soak away system.

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The thing is that the septic tank collects all forms of wastes from the home. These includes liquid wastes from the kitchen, bathroom. When these gets into the septic tank, they gradually settle into different layers within the septic tank.



Layers Of Effluents On Septic Tanks


Now lets consider the layers these wastes divide into the very moment they get into a septic tank but to do this, we must bring in the cross section of a septic tank as it would help us have a better understanding of what is talked about here.

Diagram of septic tank


Based on what we can see from the cross section of a septic tank above, Effluents in the septic tanks divides into:

Scum Layer: Now can you see the scum layer? The scum layer is where anything that couldn’t settle below the water finds itself. They gradually float on top of the main liquid. The scum layer is the very first layer you'll see if ever you open the septic tank for maintenance of to empty its content.

I Have actually attached a video link for anyone that would love to get a better idea on how septic tanks work. It is a video course created by WWMSOS and titled A Guide to Septic System Maintenance

Also See: The Roles Of A Site Engineer

Sludge Layer: The sludge layer is where all heavy materials settle. These materials are heavier than water and thus the bottom of the tank is their resting place. 

Hope you can see the sludge layer at the very bottom? On complete removal of all liquid from the septic tank, the sludge is what would be left. The sludge is usually thick in nature.

Effluent: Water is usually found below the scum layer. This is the middle layer in the septic tank. Effluent section of the septic tank is usually characterized by fowl smelling water and contain a lot of bacteria as well as chemicals such as phosphorus and nitrogen which are very necessary for the degradation of the sludge


From the Outlet Baffle, a part of the effluent is disposed by being flushed into the drain fields where they are sent to the ground by perforated drain pipes. On sending these effluents to the soil, soil bacteria acts and converts the wastes to useful nutrients such as ammonia, nitrogen which is then utilized by plants in the field


The chemical content of the water contained in a septic tank is often the main reason why the water is usually used as fertilizer.

Now you have learnt a few about the septic tank, what if you share this with others to also widen their scope about septic tanks?


Yes you can share by using any of the social media Icons below or besides this page

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