If your home isn’t connected to the mains sewage network, or you are thinking of buying a home which isn’t connected to the mains sewage system, you need to treat your wastewater at home. This is all the water from your sinks, shower, bath, toilets, washing machine and dishwasher.
The two main ways of treating wastewater at home are using either a septic tank or a sewage treatment plant.
But what is the difference between the two, and which is the best choice for you?
Sewage treatment plants and septic tanks serve the same purpose, in that they both provide buildings with a way to process wastewater, but there are several differences between them.
Septic tanks are the most common way to treat wastewater at home. They are underground, watertight tanks, which separate liquid waste from solid waste.
The liquid waste from a septic tank flows out of the tank into an area known as a soakaway or drainage field (which will generally be part of your garden!), where naturally occurring bacteria break down any remaining waste.
The solid waste sinks to the bottom of the tank, forming a sludge. While some is broken down by bacteria, the remaining solid waste will need to be pumped out by a registered contractor on a regular basis.
A sewage treatment plant is sometimes seen as the modern upgrade to a septic tank. It is also a tank buried underground, but it does far more to treat your wastewater than a septic tank, making it significantly cleaner and less harmful to the environment.
The waste liquid flows into the sewage treatment plant, initially in the same way as it does in a septic tank, and gravity separates solids and liquids. In a second chamber, oxygen is introduced through an air pump, which encourages the growth of bacteria, which break down the sewage into a cleaner effluent.
The clean effluent is then discharged into a third chamber, before being discharged safely into the environment. The remaining solid waste is then removed periodically by a registered contractor.
Pros and cons of septic tanks and sewage treatment plants
Cost
The initial cost of a septic tank is significantly less than a sewage treatment plant, but a septic tank will need emptying more regularly, pushing up the running cost.
And while a sewage treatment plant will need emptying less often, it will need servicing more regularly than a septic tank (about once a year) to ensure it keeps running effectively. This will add to the overall cost of a sewage treatment plant.
A sewage treatment plant requires electricity to run, which will increase the running costs slightly. Costs will vary depending on the size of the tank and the exact technology it uses, but expect to pay something in the low three figures every year for electricity.
The law
In some instances, you will have no choice but to install a sewage treatment plant rather than a septic tank. It is important to check the latest regulations before installing a septic tank, with the Environment Agency in England, SEPA in Scotland, NRW in Wales or DAERA in Northern Island.
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A septic tank cannot discharge directly into a watercourse eg river, stream, ditch or lake.
- You cannot install a septic tank in Zone 1 of a Groundwater Source Protection Zone.
- A septic tank can only discharge into a soakaway/ drainage field which complies with Building Regulations or BS6297. This means it must be not too close to any buildings, boundaries or watercourses; away from electrical cables and pipework; not part of a road, driveway or other areas where vehicles drive; it has passed a series of tests to ensure the soil is suitable for drainage and there’s no risk of contamination of watercourses.
Is this reflective of the 2020 septic tank regulation changes?
Understanding the difference between a septic tank and a sewage treatment system is more important than ever—particularly in light of environmental legislation that continues to impact what’s permitted. Since the introduction of stricter regulations in 2020, systems that discharge directly into watercourses (like rivers, streams, or ditches) are no longer compliant, and properties with older septic tanks may need significant upgrades. If you're purchasing a property with its own wastewater system, it's vital to know whether it has a septic tank or a modern treatment system—this could save you from unexpected costs associated with non-compliance or required upgrades. Additionally, drainage fields must now meet specific construction and environmental standards, which can influence both feasibility and cost.
Size
Whether you are buying a septic tank or a sewage treatment plant, you need to be sure it has a big enough capacity to deal with the wastewater of the full potential occupancy of a home, development or business.
Generally, septic tanks are more suitable for single households or small development sites, which have enough space to develop a soakaway system. Sewage treatment plants are a better choice for bigger developments or commercial premises.
The environment
A sewage treatment plant is by far the most environmentally friendly option, as it discharges much cleaner effluent into the environment than a septic tank.
When considering whether a septic tank or sewage treatment is best, it really depends on a number of factors, including cost and any site restrictions. The most important thing is to ensure you comply with the laws around wastewater treatment. If you have any doubt at all whether a septic tank would be legal, it is important to speak to an expert.
Here at Tanks for Everything, we can give clear advice on the right choice for your own individual circumstances, to make sure you invest in wastewater treatment for your home or business which is legal, effective and suits your individual needs.
Considerations for business use
Whether you need a septic tank or a sewage treatment plant completely depends on the size of your home or business and how much waste you produce. A septic tank is usually used for homes or very small businesses that don’t produce large quantities of wastewater. However, sewage treatment plants are better for scenarios where large quantities of wastewater or contaminants are being produced and need to be dealt with on a bigger scale. Often, the decision on which tank to use will depend on how the final effluent is being discharged.
Commercial systems usually have a much more technical and intense process to deal with the larger volume of waste they must process. They also have much stricter rules and regulations due to the higher risk of environmental contamination.
Purity
A sewage treatment system provides treatment of the wastewater, whereas a septic tank simply separates it. For that reason, a septic tank produces a highly polluting effluent which must be discharged into a drainage field to receive further treatment by the natural aerobic soil bacteria. On the other hand, a sewage treatment system produces a far cleaner, non-polluting effluent which can be safely discharged directly into a local watercourse. A sewage treatment plant is therefore considered the more environmentally friendly option.
Mechanisms
Septic tanks do not require a power supply for the treatment process. Whereas sewage treatment plants have mechanical components, which means they require a continuous electricity supply to operate. The amount of electricity required varies between systems, so it is worth doing some research before you buy.
Maintenance
Under current regulations, septic tanks do not require servicing, whereas sewage treatment plants require a regular service. It is also worth noting that septic tanks need emptying at least once a year, while sewage treatment systems only need emptying every 3 to 60 months, depending on the type of plant you have.
Final thoughts
When considering whether a septic tank or sewage treatment is best, it depends on several factors, including cost and any site restrictions. The most important thing is to ensure you comply with the laws around wastewater treatment. If you have any doubt at all whether a septic tank would be legal, it is important to speak to an expert.
Here at Tanks for Everything, we can give clear advice on the right choice for your circumstances, to make sure you invest in wastewater treatment for your home or business, which is legal, effective and suits your individual needs.
You can also explore our comprehensive range of septic tanks and sewage treatment solutions from trusted providers such as Marsh Industries, Clearwater, and Klargester to find the best fit for your requirements.
