Sewage treatment is the removal of contaminants from wastewater and sewage. The vast majority of the UK’s population relies on the mains sewage system to discharge wastewater from their homes. But around 5% of properties need an off-mains alternative, due to their rural location.
For these homes, a domestic sewage treatment system (or sewage treatment plant) can and should be used.
The Government guidance (known as the general binding rules) states that: You must use a small sewage treatment plant to treat the sewage if you’re discharging to a watercourse such as a river or stream. A sewage treatment plant, also known as a package treatment plant, treats sewage to a higher standard than a septic tank.
If you need to replace an existing septic tank or if you are installing a sewage system at home for the first time, it makes sense to use a sewage treatment system rather than a septic tank. This will also significantly increase the value of your house.
Domestic sewage treatment plants might appear costly at the outset, but their running costs are cheaper than septic tanks. Importantly, they meet environmental regulations because they actually treat and clean the wastewater, meaning it can safely be discharged into the environment as water which is around 95% clean and safe for wildlife, fish and plants. They only produce a very small quantity of sludge, due to the treatment process itself, and only need to be emptied on average once a year.
A septic tank doesn’t clean the water and legally it can’t be discharged into the environment, meaning it has to be emptied more regularly.
What are the rules around domestic sewage treatment?
There are several regulations to be aware of when looking to install any type of sewage treatment facility, as it is likely that you will need some level of consent before you proceed. In the UK, all wastewater treatment plants must be EN 12566-3 2005 certified. It is your responsibility to ensure this is the case, whether you have bought a property that already includes a domestic sewage treatment plant, or you are planning to install a new one.
You will also need to ensure you have the necessary planning permission to carry out an installation. If the plant is part of a new build, it is possible it will already be covered. But other permits may be needed, so it is always worth checking with your local authority.
Some owners of sewage treatment plants may need a consent to discharge from the Environment Agency – a licence to say the water is now clean enough not to damage local wildlife.
You only need to apply for a consent to discharge if you are:
- Not using a sewage treatment plant
- Discharging over 5,000 litres a day
- Discharging to a chalk river
- Discharging in a site of scientific special interest
The general binding rules ensure systems are correctly installed and maintained. They also guarantee that a household’s sewage doesn’t contaminate the environment.
The rules apply to both sewage treatment plants and septic tanks. They differ depending on when a system was installed. It is important to look at them closely to apply them to your own individual situation. But generally, you will always meet the binding rules with a sewage treatment plant, but not always with a septic tank.
It is important to always check the binding rules on gov.uk before making any changes to your system or buying a new system. Failure to comply with them risks a £100,000 fine.
How do sewage treatment plants work?
Sewage treatment plants clean water across three main treatment stages. This begins with sedimentation in the first chamber of the plant, which is where gravity is used, so liquid waste floats to the top and is then separated from the solid waste by clarification machines.
The remaining sludge (the industry word generally used to describe solid waste) is then stored until the treatment plant is professionally serviced and the solids are taken away for disposal, while the liquids are moved along to the plant’s aeration chambers.
The aeration stage involves compressed air being fed into the chamber via an electricity-powered pump, which lifts the oxygen content level of the liquid waste. This encourages the growth of useful bacteria, which work to disinfect the liquid waste. Once the wastewater is decontaminated and the bacteria has settled, the bacteria is moved to the first chamber for later removal, while the treated water is ready for discharge into either a local natural water source, such as a river or stream, or an installed soakaway system.
What is domestic wastewater?
Domestic wastewater is water from toilets, showers, sinks, baths, dishwashers and washing machines at home. But you can also have ‘domestic’ water in a business, such as an office, hotel, pub, restaurant or hospital.
Wastewater would be considered domestic if it was used, for example, for washing dishes, pots and pans in a pub kitchen. But if the food was being processed and packaged for sale off-site, that wouldn’t be considered domestic. Likewise, a high street launderette or centralised laundry for a hotel chain wouldn’t be considered domestic, as it is significantly different from a normal home.
Places like hospitals and schools may have both domestic and trade wastewater.
Wastewater not classed as domestic, according to the Environment Agency, includes effluent from chemical toilets, water from launderettes, municipal or commercial swimming pools or commercial cooking facilities. If your wastewater isn’t classed as domestic sewage, you must apply for a permit from the Environment Agency.
What size of sewage treatment system do you need?
When installing a sewage treatment plant, it is important that you install the right size. If in doubt, go bigger rather than smaller, and always size for the potential occupation of the house, rather than how many people actually live there.
When calculating the size of your sewage treatment plant, you should always round the numbers up. Rounding the numbers down could result in blockages in your system.
For a three-bedroom house, a sewage treatment plant should be sized for five people. You should then add an extra person for each additional bedroom – so six people for a four-bedroom house, seven people for a five-bedroom house etc. This is called the minimum population.
It is possible or likely that the sewage treatment plant will be shared by more than one house. Follow the same calculation for up to two houses.
For larger groups of 12 to 25 people, multiply the number of occupants or users by 0.9 to find the minimum population. This is because there is likely to be slightly less water used per person in larger households – water saved on washing up or cleaning, for example.
So, 4 x 3-bedroom houses will be: 5 (people) x 4 (No. of houses) = 20 (total population)
20 x 0.9 = 18
For groups of 26 to 50 people, multiply the total number by 0.8 to find the minimum population.
Here at Tanks for Everything, we stock domestic sewage treatment plants suitable for up to 50 people.
Sewage treatment plants require an electricity supply to work. If you are sharing the treatment plant with several households, you will need a shared electricity supply with a separate meter to ensure one of you doesn’t end up footing the bill for everyone!
As mentioned above, domestic wastewater can include water used for domestic purposes at a business. For facilities like offices or factories, the size of the treatment system should be based on around a third of the workforce size – because people aren’t there 24 hours a day and they are unlikely to be doing things like showering or cooking and washing up on the premises.
For facilities like hospitals or hotels, where people are on the premises all the time, seek the advice of your supplier or manufacturer to ensure you are getting the right size of plant before going ahead and making a purchase.
Use it properly!
Domestic sewage treatment plants are designed to deal only with domestic wastewater and what it should be expected to contain. They aren’t designed to deal with items which are incorrectly and carelessly flushed away, such as baby wipes or sanitary towels, or food waste washed down a sink. These items can cause a blockage and prevent the treatment system from working correctly.
Users should avoid antibacterial cleaning products because they will upset the balance of bacteria in the sewage treatment plant and affect how well it treats the waste before it is discharged.
You should also avoid getting rainwater into the system, as it can flood the system and flush out the helpful bacteria.
Domestic sewage treatment can and should be used for all homes which aren’t connected to the domestic mains sewer. They can also be used by businesses for their domestic wastewater.
There are various types of domestic sewage treatment plants available in the UK, but they all work on the same principle, which is the same as that used for mains sewage treatment works for towns and cities, but on a much smaller scale.
Domestic sewage treatment plants should only be installed by experienced professionals, because any installation mistakes have the potential to cause harm to residents, properties, wildlife and the environment.
If you are unsure about the best domestic treatment plant model for your requirements, please don't hesitate to contact us at Tanks for Everything. One of our qualified team members will be happy to assist you to find the best sewage system solution for you and to answer any questions.
