How Does a Septic Tank Work?

If you’re planning a septic tank installation or already own one, knowing how it works is essential to understanding how to ensure a long trouble-free lifespan.

Let’s take a look into how a septic tank works, pros, cons and some alternatives.

What is a Septic Tank?

A septic tank is a large waste water container which is set into the ground, directly plumbed to an adjacent property where no connections to the mains sewer system are possible.

It’s designed to store domestic sewage and wastewater, and partial treatment is carried out using naturally occurring bacteria.

A septic tank is generally made of concrete, GRP or HDPE.

Septic tanks are commonly found in rural settings, especially where properties cannot be connected to the mains sewage system.

They’re also used in cases when a property cannot be serviced by a sewage treatment plant which discharges into a suitable watercourse.

How Does a Septic Tank Work?

All waste will flow to the septic tank.

A septic tank will typically consist of two compartments. These will contain wastewater.

From one side, the wastewater that is generated from bathrooms and kitchens will flow.

Any heavy solids will settle to the bottom of the tank.

Here, bacteria will turn them into sludge and gas.

Sludge is made up of inorganic solids and other byproducts of bacterial digestion.

Any lighter solids which are present, such as grease, fats and oils, will end up rising to the top and a layer of scum will form.

From the second tank, the wastewater, or as it is also referred to, the effluent, will flow out into the soakaway.

This is basically a network of pipes underground which will lead this effluent to dissipate in the soil and gravel.

The drain septic field offers a large area where the bacteria can do their job.

The treated water will seep into the ground.

There will also be holes in the drain septic field pipe which will allow the effluent to seep in any surrounding gravel.

This allows water to flow in the soil and as a result, oxygen will reach the bacteria.

Here in the gravel and soil, the aerobic bacteria will be responsible for completing the decomposition of the waste.

Hence, it is the bacteria that ultimately makes the septic tank system work.

Bacteria are able to break down the waste to leave the water clean enough to then percolate safely down in the earth.

The septic tank system is essentially designed to allow these anaerobic bacteria to thrive.

It acts like a settling pond so that the greases float to the top while the heavier solids sink to the bottom.

In the tank there will be a filter which will prevent the solids from making their way into the outlet pipe.

Why Get a Septic Tank?

You will need to get a septic tank system if your property cannot be connected to the mains public sewer system.

Getting a septic tank is also necessary if your circumstances prevent you from being able to utilise a sewage treatment plant.

Types of Septic Tank

While all septic tanks process and discharge sewage and wastewater, there are different types.

These vary in terms of sizes and materials.

Concrete septic tanks are heavy. So in order to install them, heavy duty lifting equipment will be required.

On the other hand, GRP tanks are considerably lighter.

That said, these are more prone to damage while they’re being transported and installed.

The shape of the tank should also be considered.

There are spherical shaped tanks, which are sometimes referred to as onion tanks.

These have the advantage of taking up less space underground.

However they need a deeper hole.

Conversely, shallow dig, or low profile tanks do not need much depth as they take up more space horizontally.

The type of septic tank that you will need will be influenced by the site requirements and any pertinent legislation.

Thus it is not much of a personal choice, but one dictated by rules and site needs.

Septic Tanks vs Sewage Treatment Plants

Both septic tanks and sewage treatment plants use gravity in order to separate liquid waste from solid wastes.

In the case of septic tanks however, the effluent is not treated completely.

Hence it cannot be discharged into a watercourse.

Conversely, a sewage treatment plant can produce near-clean effluent.

This is because a sewage treatment plant adds an important additional stage.

As soon as the solids have been separated, the wastewater will be subjected to more oxygen through an air pump.

This increases the growth of aerobic bacteria, which in turn breaks down the remaining sewage to achieve a cleaner effluent in the tank.

As a result, the effluent can then be discharged directly in a watercourse.

Septic Tanks vs Cesspits

Cesspits are essentially storage tanks for effluent.

However, unlike septic tanks they do not treat the effluent.

Therefore, cesspits need to be emptied on a regular basis as otherwise there is a high probability of overflowing.

Septic tanks are sort of the middle option between cesspits and sewage treatment plants.

Indeed a cesspit is the most basic option as there is no discharge point or treatment of any kind being carried out.

It is literally a storage tank of a property’s waste.

Since regular emptying is a must, cesspits should only be considered if all other off-mains drainage possibilities are impossible.

How Long Do Septic Tanks Last?

A well maintained septic tank can last decades.

The key is to ensure proper and regular maintenance.

However, while pumping needs to be carried out from time to time, it’s important to know when is the best time to do it, otherwise you could damage the system.

Indeed, the lifespan of a septic tank will depend on various factors, such as the ground conditions and the material.

Generally, steel septic tanks should last between 15 and 20 years.

These are not that common anymore.

Some may still be found in old rural properties.

Plastic or GRP tanks are more common these days.

These have a life expectancy of around 30 years.

Concrete tanks are the most durable, and are expected to last at least 40 years.

Are Septic Tanks Environmentally Friendly?

When it comes to answering this question, it’s important to point out that as long as a septic tank is:

• properly designed and installed
• of a suitable size
• regularly maintained

Then it should not be harmful to the environment.

If a septic tank has not been properly designed, installed and maintained, it could easily lead to contamination of the surface as well as ground water resources.

This would be harmful to the environment, and it could even end up being hazardous to public health.

This highlights the importance of leaving the design and installation of such a system in the hands of drainage professionals, whilst also ensuring responsibility when it comes to its regular maintenance.

Do Septic Tanks Need a Soakaway?

Yes, all septic tanks need a drainage field, or as it is often referred to, a soakaway.

This is where the effluent from the tank is treated.

Septic tanks do not treat effluent sufficiently within the tank itself.

The main treatment process is carried out in the septic soakaway.

Moreover, as of January 2020, a drainage field is the only permissible discharge option, and hence it will need to be installed along with the septic tank.

This is because it’s no longer permissible for discharge to go directly in any watercourse.

In case you cannot install a drainage field for the septic tank, such as in cases where there is no space on the property, you will not be able to install such a system at all.

In such an eventuality you would need to either pump sewage and wastewater to the mains sewer that is closest to your property, or else use a sewage treatment plant.

Who’s Responsible for Septic Tank Maintenance?

It is important to note that you are responsible for the maintenance of the septic tank, including emptying it.

You need to make sure that the discharge quality is not harmful to the environment, and effective and safe disposal is carried out.

Regular pumping is important as it will remove the sludge and scum in the septic tank.

In this way the septic tank system will be able to run more smoothly.

It is better to ensure that you carry out regular maintenance by pumping, as it is much more cost effective than having the tank fail and spend a hefty sum in order to replace it.

Signs of a Failed Septic Tank

You may wish to be aware of certain signs that the septic tank may have failed.

Some of such signs to look out for include:

• fixtures may have started draining more slowly
• odours and surface sewage
• wet spots or vegetation growth in the drainfield area
• back-ups in the tank or in the general plumbing system, resulting in overflowing
• gurgling sounds coming from the pipes

If you notice any one or more of such signs it is important to act immediately.

Delays may cause serious problems, including solids flowing in the soakaway and leading to substantial damages which will most likely cause the whole system to eventually fail.

How Often Should My Septic Tank Be Emptied?

Pumping will remove the buildup of sludge and scum.

This will ultimately slow down the bacterial action in the septic tank.

So, even though it is often recommended to pump a septic tank once a year, it could be that your tank does not need pumping that often.

It ultimately depends on the amount of waste that runs through the system as well as the size of the tank.

It may be best to contact a professional drainage company regarding how often to pump your septic tank.

You may check whether it is time to call a professional to do the pumping process yourself.

As a general rule the septic tank emptying should be carried out if you notice the level of scum has reached over 3 inches in depth.

At that point, it’s time for the septic tank to be pumped.

You can measure this by dipping a 6 foot pole into the tank and move it around to check if you encounter resistance.

Upon reaching the bottom of the scum in the tank, remove the pole and check where the scum reached.

Should the level of sludge in the tank be deeper than 12 inches, it’s also time to have the tank pumped.

To check, use a pole, but this time wrap a towel around the end.

Push it down to the bottom of the tank and then remove it to measure the distance that there is between the top of the sludge and the marking made before.

When it comes to emptying a septic tank, it’s best to seek professional assistance by a qualified waste disposal company.

This is crucial since the waste will need to be discharged at a designated disposal point.

Conclusion

Now you should have a much better understanding of how septic tank systems work.

You will be better equipped to consider the various types of septic tanks available, as well as other alternatives sewage storage systems.

Hopefully, you’ll be able to make a well informed decision whether to install a septic tank, or if you already have one present on your property, to be responsible for its maintenance.