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Your How-To Guide to Sewage Treatment Plants

In one of our previous blogs we outlined the basics for installing underground drainage for your home or property, however if you live in an area where there is no mains drainage system in place you may need to invest in a sewage treatment facility. Luckily, there are a range of sewage treatment facilities to choose from including septic tanks and sewage treatment plants.

If you have decided to install a septic tank then make sure you read our “Septic Tank Maintenance” blog for tips and advice, however if you are planning on using a sewage treatment plant this blog provides everything you need to know:

Septic Tanks vs. Sewage Treatment Plants

Whether you need a septic tank or sewage treatment plant depends on how clean you require the discharged effluent to be. Both sewage treatment products are designed for areas where a mains drainage system is not present and therefore waste water needs to be treated at source.

Sewage treatment plants are more effective than septic tanks as in most cases they are able to treat water to a point where it can be legally released into a water course. However, if you are unsure as to whether your sewage treatment plant is able to release grey water into land drainage systems make sure you contact the Environment Agency.

How Sewage Treatment Plants Work

Sewage treatment plants process sewage in three steps in order to convert waste water into water that can safely be discharged into a water course. These steps consist of:

Primary Treatment – During the primary treatment stage waste is temporarily held in a basin to allow for liquid and solids to separate. Any floating or settled materials are stored in the primary settlement chamber, whilst the liquid is moved to the secondary treatment stage.

Secondary Treatment – Once the liquid has passed into the secondary treatment stage the dissolved bacteria is subjected to filtering which removes them from the water. Certain sewage treatment plants use aerobic digestion processes which contain oxygen-based microorganisms that are environmentally friendly. The secondary treatment stage can require a certain amount of time to ensure that all dissolved biological matter is removed from the water before it can enter the final settlement treatment stage.

Final Treatment – To ensure that the water in the sewage treatment plant is safe to be released into the water course or used for agricultural purposes it is usually subjected to a final treatment stage ensuring any remaining solids are settled before discharge. This can consist of a number of processes, such as further filtration or adding chemicals to disinfect the water. It is of the utmost importance that the water is of an acceptable quality before being released otherwise it could cause environmental damage.

How to Install a Sewage Treatment Plant

Before installing a sewage treatment plant the first thing you need to do is calculate the capacity you require. At Drain Depot we offer sewage treatment plants with enough capacity for up to 6, 9, 12 or 18 people, many of which come with the option of either gravity or pumped outlets. However, we are also able to supply any sized plant required and have supplied tanks suitable for up to 300 people previously.

Once you have chosen your required sewage treatment plant capacity you can then arrange installation. It’s important that you remember your sewage treatment plant must be a minimum of 3 metres away from the property boundary as well as any trees or vegetation that have significant root systems. When possible many local authorities will insist on a minimum distance of 15 metres away from any habitable building. The discharge point (outlet) must be a minimum of 5 metres away from any building. It is important that when siting the plant that you remember that it will require routine maintenance, therefore we recommend that it is sited within 30 metres of a hardstanding that is suitable for a vacuum tanker.

We recommend that the sewage treatment tank is feed by gravity only, as most treatment plants are designed to work with a gradual input and will not cope with a pumped input feed.

Prior to installation check the tank for damage and always handle with care, avoiding heavy impact or contact with sharp objects. When lifting the plant into position we recommend that you thread straps underneath and only use the eyelets on the top when levelling. On no account should the maximum invert level of the plant be exceeded. Treatment plants must be installed level and the location must not be prone to flooding.

You should never fill a free standing plant with water or backfill an empty plant. Always fill the plant with water at the same time as backfilling to equalize the pressure, this will minimise the risk of flotation and prevent the plant from imploding during installation. Manufacturers will always assume that the plant is going to be install in a traffic free area, if this is not the case we recommend contacting a structural engineer.

A qualified electrician should carry out all electrical work.

What sewage treatment plant is right for me?

As previously mentioned, one of the first things you need to decide when it comes to investing in a sewage treatment plant is the capacity you require, however there are also other factors you need to keep in mind. For example, you need to determine whether you require a pumped or gravity flow sewage treatment plant; the former is essential if the tank’s outlet point is lower than the water course or soakaway that it is discharging to, however pumped sewage treatment plants will require electrical equipment which means increased running costs.

Sewage Treatment Plant 6 Population Pumped Outlet Clearwater E1


Sewage Treatment Plant 6 Population Pumped Outlet Clearwater E1





Sewage Treatment Plant 6 Population Gravity Outlet Clearwater E1


Sewage Treatment Plant 6 Population Gravity Outlet Clearwater E1





Another thing to keep in mind is that not all sewage treatment plants use microorganisms to break down dissolved biological matter, instead the waste water is filtered using an integral lift. If you don’t require the treated water to be released into the main water course, a filter may be all that is required however it’s important that you check with your local authority.


Klargester Gravity Outlet BA BioDisc 450mm Invert


Klargester Gravity Outlet BA BioDisc 450mm Invert





Maintaining your Sewage Treatment Plant

As with any form of drainage it’s important that you regularly maintain your sewage treatment plant to ensure that it does not become blocked. As a rule of thumb most sewage treatment plants are serviced once a year where checks are made to the pipes between the property and the plant as well as the septic tank.

If you have a sewage treatment plant that uses microorganisms during the secondary treatment stage you may also have to replace the organisms (live bacteria) if they are no longer filtering the water to optimum levels. To ensure that their sewage treatment plants remain operational at all times some people choose to install specialist alarms which alert you when there is a fault and advise what repairs need to be carried out.

Sewage treatment plants manage waste water in an efficient and environmentally-friendly manner in areas where you are unable to dispose of your waste water via the mains drainage system. If you would like to know more about sewage treatment plants make sure you browse Drain Depot’s range of products which are suitable for a range of property sizes.

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