Why is a septic tank or sewage treatment plant required?

Posted by Callum Vallance-Poole, on July 4, 2022.

When it comes to wastewater treatment systems there is always a choice to be made between septic tanks and sewage treatment plants. Here we discuss why a septic tank or sewage treatment plant may be required and how to choose the right system for your home.

Why do you need a septic tank or sewage treatment plant?

UK Building Regulations state that properties should be connected to the mains sewer wherever possible (a sewage pumping station can be used if needed) to remove household wastewater and sewage.

However, this isn’t always an option, especially for houses that are isolated or in remote locations. When this happens, it may be better to manage the disposal of waste within the boundaries of your property using a septic tank or sewage treatment plant.

You can use these systems to treat and dispose of relatively small volumes of wastewater, providing a solution if you are moving to a remote location or building a new home or extension that doesn’t enable you to connect to a mains drainage network.

Which system is better: a septic tank or sewage treatment plant?

Because the two systems operate differently and offer their own unique benefits, there is no single answer to this question. Choosing the right system for your property will depend on cost, site restrictions, property location, permit requirements and many other factors.

In general terms, septic tanks have a lower upfront cost, although this should be weighed up against the fact it will likely need to be emptied more regularly, requires more space and cannot be used to discharge into a watercourse. On the other hand, you will likely pay more to install a sewage treatment plant, but they will need less emptying and produce cleaner effluent.

Whether you opt for a septic tank or sewage treatment plant you must ensure it is fully complaint with the latest regulations. The most notable change in recent years is that septic tanks are no longer allowed to discharge into a watercourse, so if you have an existing system, you will either need to use a soakaway or change to sewage treatment plant.

To make things a little clearer, and perhaps a bit easier for you to decide, here are some of the key advantages and disadvantages of installing a septic tank or sewage treatment plant.

Septic tanks

These systems are best suited to an individual house or small development, providing the ground is porous enough to create a soakaway for drainage. 

Septic tank advantages:

  • Comparatively low installation costs
  • Generally costs less to run and maintain
  • Usually only needs to be emptied once/twice a year

Septic tank disadvantages

  • Should only be used on porous ground to support a soakaway
  • Needs professional company to empty the tank which adds to costs

To maintain high performance levels, it is recommended that treatments are regularly applied to the tank to ensure the naturally formed bacteria remains healthy.

When it comes to sizing you must be careful not to place too much pressure onto the system, as it will only be designed to service a limited number of people. For that reason, it is always advisable to ‘oversize’ your requirements, as this ensures there is always enough capacity.

Sewage treatment plants

You should consider installing a sewage treatment plant for a single house, large development or for a commercial property.

Sewage treatment plant advantages:

  • Sewage treatment ensures waste is at least 95% clean before being discharged
  • Waste can be discharged into a watercourse (provided the system meets BS12566 standard)
  • The system works to essentially recycle water for reuse again

Sewage treatment plant disadvantages:

  • Needs an electricity supply to operate
  • Requires regular maintenance to maintain performance

You will need to use a professional service engineer to check the system due to it having more mechanical parts than a septic tank, which will ensure it continues to effectively manage your waste.

How to plan the installation of your wastewater treatment system

As the owner of a septic tank or sewage treatment plant, it is important to remember that you are legally responsible for the disposal of the waste. It’s why having a clear maintenance plan is required, as it ensures you minimise the risk of pollution occurring which could lead to you being prosecuted and fined.

Before any installation takes place, a full, professional site survey should be carried out, where they can check the suitability of the ground for the proposed system. If a septic tank is being installed, they will also be able to help decide on the best location to reduce the risk of groundwater becoming contaminated by untreated effluent. They will also ensure that the tank is installed in Zone 1 of a Groundwater Source Protection Zone, which is not permitted by law.

If you opt for a sewage treatment plant that discharges into a local watercourse, you will have to first apply and register with the local environmental agency. Not everyone will require a permit, but even so there are some strict conditions that still need to be adhered to. For example, whether it’s a septic tank or sewage treatment plant, industry guidelines must be followed during the installation process. Building Regulations apply when it comes to the drainage field design (or compliance with BS 6297) and guidance provided by British Water relating to servicing and desludging also must be taken into account.

Septic tank owners do not need to register their ownership if they live in England (registration is required in Scotland, Wales and Northern Ireland) but it is still recommended that maintenance records are kept and that you inform your environment agency if the system is no longer in use.

It is always advisable to seek professional help when it comes to septic tanks or sewage treatment plants due to the possible effects it could have on the local environment. If you are unsure about your garden’s ability to safely filter wastewater, investing in a sewage treatment plant will likely be the best option for you.

Marketing Coordinator - Based at our UK HQ in Banbury, Oxfordshire, Callum is responsible for promoting Water Management Systems, Attenuation Tanks, Treatment Plants, Rainwater Harvesting Systems and more!