I am sure you have come across the words either “septic system” or “septic tank” at some point in your life but don’t know exactly what that is.
Don’t worry because you are not alone.
For many folks like me who grew up in rural Kenya, the primary sewage system we knew back then was a pit latrine and we would simply discard kitchen waste into the nearby gardens and earth trenches.
Words like sewage lines, manholes, effluent treatment plants were simply non-existent to us.
We didn’t know that domestic wastage from homesteads in urban / municipal areas was discharged by means of a series of interconnected pipes and manholes and taken to a treatment plant in what is known as a sewage system.
But what happens to your household waste if your home is not connected to this extensive sewage system?
This is why you need a septic system.
So, what exactly is a septic system?
I love to think of a septic system as home based waste treatment plant. It includes several components namely;
- Main sewer line from your house to the septic tank.
- The septic tank (main component).
- The outlet from the septic tank
- The septic drain field.
How does a septic system work?
The main sewer line brings in waste water from the house into the septic tank.
The waste contains grey waste water (from wash hand basins, kitchen, washing machine) and black water (from toilets).
Septic tanks
Septic tanks may be built of plastic or stones or most commonly reinforced concrete.
Inside the septic tank, the heavy solid waste sink to the bottom and this is what is called scum. This process is called sedimentation.
The fats, oils and greases will float on top of the water as they have a lesser density than water. They form the sludge.
Organic waste is dealt with by anaerobic bacteria (bacteria that don’t need air to survive).
As waste accumulates, the liquid waste devoid of solid waste now pass through the filter at the outlet pipe of the septic tank.
This outlet leads to the septic system drain field.
A septic drain field is made of a system of perforated pipes laid on loose gravel as shown below;
Through the tiny holes in the pipes, the waste water seeps into the gravel and eventually into the ground.
As the water seeps through, the aerobic bacteria (needs air to survive) breaks down the contaminants such as viruses, parasites, etc. making sure that the water reaching the water table and nearby streams is safe to consume.
What happens to the sludge and scum in the septic tank?
From time to time, you will need to call in the waste disposal trucks otherwise known as honey suckers.
They will suck the waste from the septic tank through the access hatches into their trucks.
Most trucks in Nairobi have a volume of around 20,000 ltrs of sewer and they charge about Ksh. 20,000 per trip.
Cost of a septic system
Most septic systems will cost between Ksh. 120,000 to Ksh. 180,000 to initially install / construct.
This cost covers for the main sewer line from the house, the septic tank and the drain field.
You will also need about Ksh. 10,000 per year for periodic maintenances.