Effluent Tanks & Sewage Treatment Tanks: What’s the Difference?

In the UK, if your property does not have connection to mains sewerage then you are legally obliged to install a system for filtering and discharging waste in an environmentally conscious manner (ie. in a way that avoids pollution). Typically, this will involve the installation of either a septic tank or a wastewater treatment tank (in other words, sewage treatment). The distinction between septic tanks and sewage treatment plants lies in their functionality. In this brief edition of our blog we’ll explain that difference.

Sewage Treatment Tanks

A sewage treatment tank is, generally, a more sophisticated and advanced version of a septic tank in that it includes components which require a power supply to operate correctly. This type of tank actively treats wastewater to produce a ‘higher quality’ of effluent. In other words, the water that leaves this type of tank is cleaner than the wastewater that is discharged from a septic tank.

Whereas septic tanks rely on gravity to separate out solid and liquid waste, wastewater treatment systems use mechanical components to introduce aerobic bacteria, which break down the waste. Sewage treatment plants work by sewage and waste water entering a holding chamber where gravity separates solids from liquids. This liquid flows into a second chamber, with the solid waste left behind for later removal (by a registered waste operative). Oxygen is introduced into the system via an air pump, which encourages the growth of aerobic bacteria that works to break down the remaining sewage. The liquid then flows into a third and final chamber where the bacteria settles to the bottom (it is then recycled back into the first chamber). The clean effluent is discharged.

Some wastewater treatment systems, such as aerated treatment plants, utilize aerated technology (blowers) for the breakdown process. A big difference for property owners to consider is that sewage treatment plants can discharge into watercourses (eg. rivers and streams), whereas septic tanks cannot. This is because the effluent contained in septic tanks is of lower quality and is therefore deemed to cause an environmental pollution problem. Sewage treatment plants separate out liquid and solid waste, treat liquid waste for a higher quality effluent, are connected to a power supply with mechanical components, require less frequent emptying than septic tanks, demand more servicing and maintenance, and can be legally discharged into watercourses, subject to local environmental regulations.

Effluent Tanks

The key features of septic tanks are that they are installed underground and the way that solid and liquid waste are separated (relying on gravity). There is also a lack of treatment for liquid waste, no connection to a power supply, and they have to be emptied regularly and must not be discharged into watercourses. Since January 2020 it has been illegal to discharge the contents of a septic tank into a local watercourse. Septic tanks can also only service the sewage / wastewater of a limited number of people. For further advice on this issue, you can contact your national environment authority for advice: Environment Agency (England); SEPA (Scotland); NRW (Wales); or DAERA (Northern Ireland).

While there is no absolute need to replace a septic tank with a sewage treatment plant, property owners with a septic tank and a drainage field meeting government standards can continue using their existing system. A drainage field allows for the dispersion of liquid waste through the ground for further treatment, offering a similar filtering effect to that of a treatment plant. Septic tanks also must:

• Be away from electricals or pipework.
• Not be too close to any buildings, boundaries or watercourses.
• Not be part of a road, driveway or other traffic areas.
• Pass a series of tests to ensure no risk of contamination to watercourses.
   

At Tanks R Us we can supply all of the equipment needed to meet your sewage and wastewater treatment requirements. Simply get in touch with us and we will advise you of the correct system for your situation, and the gear required.