What is a septic tank?
The term septic tank is one I know you are probably familiar with, and if you aren’t, I am sure you are using one without knowing. It is that usually invisible container where all the waste you generate in your building goes. While you conveniently wash your plates in the sink, use the toilet and bathe any time of the day, the septic tank collects all the dirt.
A Septic tank is a large volume buried rectangular or cylindrical watertight tank made of concrete, fibreglass, or polyethylene, which provides initial treatment of the household or office wastewater by intercepting solids and settle able organic matter before releasing the wastewater (effluent) to the drain field.
Function of the Septic Tank
A well working septic tank eliminates bacteria and nitrogen from domestic water, which may pollute the surrounding environment and transmit disease. It is a self-contained, underground wastewater treatment system which is highly efficient and self-contained. While relatively simple in terms of construction and operation, the septic tank undertakes a number of essential functions through a very complex interaction of physical and biological processes. The septic tank’s primary functions are as follows:
- Receive all water wastewater from the building.
- Separate solids from the wastewater flow.
- Ensure reduction and decomposition of accumulated solids and provide storage for
the separated solids (sludge and scum), as well as discharge the clarified
wastewater (effluent) out to the drain field for final treatment and disposal.
Here is a simple step-by-step process of how your Septic Tank work using a residential building as an example:
● Water from your kitchen, bathroom etc., runs through one main drainage pipe leading to your septic tank.
● Underground septic tank starts the process of holding the wastewater. It helps hold this long enough so the solids settle down to the bottom, while oil and grease float to the top.
● After this process, the liquid wastewater (effluent) will then be able to exit the tank into the drain field.
● This wastewater is discharged through pipes onto porous surfaces. These allow the wastewater to filter through the soil.
● The soil accepts, treats, and disperses the wastewater as it percolates through the soil, ultimately discharging to groundwater.
● Finally, the wastewater percolates into the soil, naturally removing harmful viruses, coliform bacteria and nutrients.
● Septic tanks work by allowing the wastewater to sit and undergo a settling process.
● Solid matter and sediments sink to the bottom of the septic system, separating from the water.
● Over time, bacteria eat away all this sludge, in the process, break it down into more manageable materials – this also releases scum, like Oil, fats, and greases, to float to the surface of the water.
● After the solids are filtered, the filtered liquid wastewater, also called “effluent,” is sent out through perforated pipes – these outlet pipes lead the water to what’s known as the leach field.
● The effluent slowly releases into the leach field or drain field, and, over time, soil and gravel filter it, slowly removing impurities.
Finally, the wastewater percolates into our soil to eliminate any harmful or bad stuff in it. This includes potentially dangerous pathogens, like coliform bacteria that are found in human waste.
Talking about wastewater. This is a relatively quiescent body of water the septic tank provides; it is retained long enough to let the solids in it separate by both settling and floatation. This process is called primary treatment and it results in three products namely, the scum, sludge, and effluent(wastewater), which I will briefly define, but before that, Look at this animated, interactive model of how a household septic system works by Guadalupe-Blanco River Authority.
Let’s look at the definition of these three products from the primary treatment of the septic tank.
Scum: Substances lighter than water e.g. Oil, grease, fats etc. floats to the top, where they form a layer called the scum layer. This layer floats on top of the surface of the septic tank where aerobic bacteria work at digesting the floating solids in there.
Sludge: Here are the “sinkable solids e.g. soil, grit, bones and unconsumed food particles that sink to the bottom of the tank to settle to form a sludge layer.
The sludge is usually denser than water and fluid in nature, so it easily forms a flat layer along the tank bottom. The underwater anaerobic bacteria then consume these organic materials in the sludge, giving off gasses in the process and, as they die off, they also become part of the sludge.
Effluent: The effluent is the clarified wastewater left over after the scum has floated to the top of the septic tank and the sludge has settled to the bottom of it. It is the clarified liquid between the scum and the sludge. It flows through the septic tank outlet into the drain field or leach field.
Types of septic tanks
Having understood how this septic tank works, let’s look at the several types of the septic tank. Septic system design and size can vary widely, from within a specific neighbourhood to across the country, due to a combination of factors.
These factors include the soil type, household size, site slope, proximity to sensitive water bodies, weather conditions, or even government regulations. Below are few of the most common types of septic systems you will find around.
Concrete septic tanks:
Concrete tanks are inherently watertight, they are the most popular tank and known for their strength, durability, and weight. They have a long life expectancy and can last for several decades but will need to be replaced in the future. The natural water tightness of concrete reduces the risk of leaks during the tank’s life. They rarely get damaged during installation and may only become susceptible to
cracking under extreme circumstances, such as exposure to heavy-duty corrosive chemicals.
Fibreglass Septic tanks:
Fibreglass Septic tanks, just as the name implies, fibreglass septic tanks are made with fibreglass, they do not bend, and they won’t crack like concrete septic tanks or rust like steel, but they undergo an extra process to hold water.
Steel septic tanks:
Steel septic tanks have the tendency to become too weak to support the weight of the ground. It lasts no more than 25 years before it starts getting rusty. To save cost, the cover of a steel tank could be replaced if the rest of the unit is structurally sound. Generally, steel septic tanks are the least durable and least popular tank options.
Plastic septic tanks:
Plastic septic tanks are durable, lightweight and relatively inexpensive. They don’t rust and are less susceptible to cracking than concrete septic tanks. These tanks are very light, which makes them quite easy to install. However, their lightness means they are prone to damage during installation, which might bring about having a new plastic tank to avoid leakage as they are not durable like concrete septic tanks. Plastic septic tanks can float to the surface if they aren’t installed correctly.
Aerobic septic tanks:
Aerobic septic tanks require little space, unlike other tanks requiring other tanks requiring a lot of space. An aerobic septic system breaks down solid wastes faster, and as a result of that, the waste does not accumulate to alarming levels. These tanks require more frequent maintenance, but they generally last for many years in as much as the system is proper, and it’s always advisable to install an aerobic septic tank as this helps to avoid water pollution.
Difference between the septic tank and soak away
Unlike septic tanks, soak away doesn’t need any tank. It’s a compromised hole dug in the ground and filled with coarse stones and rubble. Soak away can be used as a stand-alone method of wastewater control or in conjunction with other systems, such as a septic tank.
If a septic tank is being used in an area that doesn’t have the required vegetation to allow the septic tank to dispose of the wastewater in a drain field, a soak away can assist in removing the waste safely. Soak-aways are sometimes placed away from flooding areas and connected by a pipe that forms a gutter or drains.
A surface water soakaway simply allows excess rain and surface water to drain away, but a sewage soakaway not only allows liquid from the septic tank to disperse into the ground but it also uses natural aerobic bacteria to treat effluent to remove any solids suspended within the liquid, together with bacteria and viruses.
Soakaways and septic tanks are both very good methods of dealing with excess wastewater. The two, however, have very different purposes and as such often used together to provide the best wastewater solution.
How often do you empty your septic tank?
Having the right system in place with your septic tank, you don’t even need to empty your septic tank at all; I mean, for the next 30 years or more, you won’t have a cause to, even if your building is an area below water level.
Here is a proposal to restore an underground concrete tank for a septic tank system for a client in Victoria Island, Lagos, Nigeria.
How can we achieve this, you may want to ask?
PICS: Leach Field
We use a unique approach – the drain field system added to your existing septic tank. The drain field is the layer of clarified liquid, i.e. effluent flows from the septic tank to the drain field or to a distribution device, which helps to distribute the wastewater in the drain field uniformly.
A conventional drain field (also known as a leach field, disposal field, or soil absorption system) consists of a series of trenches or a bed coated with gravel or coarse sand and sunk one to three feet below ground. To disperse wastewater, perforated pipes or drain tiles pass through the trenches. The wastewater is treated in the drain field by allowing it to flow gently from the pipes into the gravel and down into the soil. In this system, the gravel and soil serve as biological filters.
Without this drain field system in place with your septic tank, you might need to inspect and maintain your septic tank regularly
Regular maintenance and inspections are needed to keep your system healthy; this means routine septic tank pumping and inspections of the septic field. If a septic tank is regularly cleaned (within twelve months for smaller tanks), antibacterial substances and toxins build up, killing the vital bacteria that break down the waste.
Every one to three years, you should have your septic tank emptied and cleaned by a professional. The frequency with which you should have your septic tank pumped is also determined by the size of the tank, the volume of wastewater, and the amount of particles that enter it.
Constant foul odour, slow drains, and drains that back up are all telltale signs that your septic tank needs pumping, and when in doubt, call in a septic pro like us.
Inspect your system for appropriate care on a regular basis, and arrange your system’s records.
Regularly pump out your septic tank. The general guideline is that your septic tank should be pumped every one to three years to ensure that sediments are adequately broken down and do not clog the drain field.
Routine pumping can assist avoid system failure and extend the life of your system.
Conserve water and keep track of how much you use. If you put more water into the system than it can handle, it will back up, which is not a good thing.
Use no more than necessary of any home chemicals. Normal quantities of home detergents, bleaches, drain cleaners, and other household chemicals can be used without interfering with the bacterial activities in the septic tank. However, do not flush cleaning water from latex paint brushes and cans into the home sewer.
Do not flush coffee grounds, cooking grease, wet-strength towels (paper towels that do not disintegrate quickly, such as heavy-duty ones), disposable diapers, face tissues, cigarette butts, or other non-decomposable items down the toilet. These items will not only disintegrate the septic tank but will clog the system and will fill it up.
Avoid Draining Oil along with Wastewater – Oil or grease that goes with wastewater can cause clogs along the drain pipes. The scum layer that floats above the wastewater should not be very thick for the tank to work properly. For better septic tank care, separate the disposal of grease and wastewater. Too much Oil will only plug the system because it does not dissolve with wastewater.
Many household cleansers cause sludge and solid waste to accumulate in the septic tank and drain field pipes. This causes a septic system failure, in which solid waste clogs the system and spills into the watercourse or through the access grating.
Failure of the septic system is not only costly but also an invitation to waterborne infections; it also stinks! People must grasp the need for septic tank cleaning based on the degree and extent of the damage to the complete septic system.
Failure symptoms in a Septic Tank
A foul odour is not always the first sign of a malfunctioning septic system. Call a septic professional if you notice any of the following:
● Wastewater backing up into household drains.
● Bright green, spongy grass on the drain field, especially during dry weather.
● Pooling water or muddy soil around your septic system or in your basement.
● A strong odour around the septic tank and drain field.
What is the best option to have with Septic Tank?
Don’t just build a septic tank; build a leach field system alongside it. With this, you are assured of longevity and no evacuation worries anytime soon. The leach-field system is designed in such a way it takes care of all the factors that usually arise and require a need for evacuation. Maybe in thirty years or even a hundred, you won’t need to evacuate your septic tank even if you live in areas below sea level.
We have a few professionals who understand how this works and have the expertise, and we at Sustainable Procurement Services are on top of that list. We have years of experience doing this with a good number of clients who can testify to the effectiveness of our leach-field system.