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Sewage Treatment Systems

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Which Sewage Treatment Plant is the right one for you?

You’ve probably realised that choosing a sewage treatment plant can be more akin to a minefield rather than a drainage field since there are so many choices – how do you know which one is right for your needs? 

Here are some important factors you will want to consider:

Is the treatment plant EN 12566-3 2005 certified?

Firstly bear in mind that without the EN 12566-3 2005, the unit will not be legal in the UK. Secondly, even if the treatment plant you have in mind is certified, the Environment Agency will not let you install it unless its ‘percentage of reduction of pollutants’ reaches certain minimum levels, as follows:

  • BOD of 93% or more (wastewater from sewage treatment plants contains organic materials that are decomposed by microorganisms, which make use of oxygen in the process – the amount of oxygen consumed by these organisms in breaking down the waste is known as the ‘biochemical oxygen demand’ or BOD).
  • Suspended solids of 88% or more.
  • Ammoniacal Nitrogen reduction of 50% or more.

At UK Septic Tanks all our sewage treatment plants are EN 12566-3 2005 certified and achieve the required percentage of reduction of pollutants described above - if you would like to see the certification for any of our plants, then please call 0800 0850640.


What type of treatment plant is good for my property?

Should I go for an Electric or Non Electric system?

Currently the there are only a few sewage treatment plants that do not require electricity

Most electric sewage treatment plants use very little electricity, for example the Tricel sewage plant only requires a small 60 watt feed. It is important to bear this in mind because if for example you go for a Biorock but need electricity to pump the outfall, you could end up using more electricity than you would with a gravity fed Tricel plant.

How often will it need to be emptied?

Emptying the tank is about the most expensive part of the maintenance, so if the unit is serving a large property this is something to think carefully about.

Most treatment plants like the Tricel need emptying annually or maybe two to three years dependent on usage, but a retro fit treatment plant like the Biorock, Jewel or the Tricel retro require less frequent emptying because of the larger holding tank, so typically every 4 years.

Does it rely on internal moving parts?

It’s the moving parts that are more prone to wear and tear, so with treatment plants like the Klargester Biodisc, there are a number of moving parts so potentially this can be more costly to repair, and is another factor to be borne in mind.

What will the sewage treatment plant look like when it’s installed?

Some plants don't look very pretty once installed – they have protruding lids, large kiosks etc. So look carefully at the design, especially if you are looking to install somewhere visible in your picturesque garden or grounds!

We hope this information has proved useful - if you have any other queries or problems regarding Sewage Treatment Plants  or are just looking for some advice please feel free to call us on 01296 326111 and we will do our best to help.


Types of treatment plants available for domestic properties:

Non- Electric


Podtank is one of the only sewage treatment plants that operates without mechanical components and electricity.

The Podtank series units are packaged domestic waste water treatment plants, providing a consistently high quality effluent that meets the highest standards. The biological purification technique requires no electricity or moving parts.  This means that maintenance and operational costs are particularly low, and reliability is maximized. The units are assembled in durable HDPE tanks with lightweight, low profile, access covers. The plants are supplied as a complete package for simple installation.



Tricel units, as the name suggests use three chambers to treat the effluent, producing very high quality discharge.

This is achieved through the following stages (it’s a bit detailed so bear with us!):

Stage 1: Primary Settlement Chamber

Anaerobic breakdown takes place in the primary settlement chamber where the wastewater is introduced into the system. The large volume of this chamber reduces the velocity of the wastewater. Combined with the long flow path, this allows the wastewater to have maximum time in the first chamber resulting in a higher settlement rate. Settlement occurs when the heavier solids drop out of the wastewater and settle to the bottom of the tank to create a sludge, or when lighter solids, like fats or oils, float to the top of the water to create a scum. Up to 70% of the solids are removed in Primary settlement zone. Anaerobic breakdown begins to occur and improves the water quality. A baffling system (are you still following this?) holds the sludge and scum in the primary settlement zone and ensures that water from the centre of the chamber moves into the aeration zone. The large sludge storage volume increases the de-sludging intervals.

Stage 2: Aeration (Treatment) Chamber

Stage 2 takes place in the aeration chamber where Submerged Aeration combines the principles of the bio film and activated sludge processes. Masses of naturally occurring bacteria inhabit a specially designed plastic filter media. The filter media has large surface area, and is supported within the aeration zone. As the liquid flows slowly through the filter media, the bacteria feed on the waste - so removing them from the liquid.

These bacteria are sustained with air, which is continuously supplied from a purpose built low pressure, high volume air compressor in the top section of the unit. The air is delivered through a diffused aeration system, which breaks the air into bubbles as they are dispersed through the aeration zone. The continuous circulation of the wastewater within the aeration zone means that the wastewater is repeatedly passed through the filter media, thus ensuring very high treatment efficiency. The purified liquid is then passed into the final settlement zone.


Stage 3: Final Settlement Chamber

As the liquid flows from the aeration zone into the final settlement zone, small quantities of bacteria may be carried with the liquid. Before discharge from the system, these solids must be separated from the liquid. With the velocity of the liquid once again slowed down and the flow path maximised the bacteria is encouraged to settle to the bottom of the tank, like sludge, through the up flow nature of the zone. A sludge return system pumps this sludge back to the primary settlement zone. The remaining treated liquid now meets the required standard to be safely passed out of the Tricel Unit.

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