Steps to take when planning a new sewage treatment system

What you need to know about Sewage Treatment Systems


Installing a new sewage treatment system or upgrading your existing septic tank should be a simple procedure. 

We often hear it said "It sounds so simple what is the difficulty"  No problem, is our answer, it is simple if you get a few things straight from the start.

Two things connive to make it more difficult.  Water and Gravity.  Oh and the other thing that makes it really hard is sewage!

The following information is based on the situation in England and Wales.  If you are living in Scotland or Northern Ireland you will have to adjust it to suit the specific regulations in your country.  For other EU countries the information needs to be adjusted completely to your specific regulations.

What you need to know before you start.

  1. What size of system do I need?

  2. How deep are the existing or new drains going to be?

  3. What am I going to do with the water that comes out of the system?

  4. Where am I going to site the system?

  5. Will I need to pump water or even sewage to make it work?

  6. Do I need a discharge permit or exemption?

  7. Do I need planning permission?

  8. Do I need Building Regulations approval?

  9. Where am I going to get my power from?

  10. Who is going to look after the system once it is installed?

  11. Who is going to install the system?

It is quite surprising how many phone calls we get from people who have not even given these sort of questions a thought.

If you really don't wish to answer these questions yourself then please give us a call and we can get a qualified installer to come and see you.  They will answer the questions for you.

Here are some typical questions:

1. What size of system do I need?

It seems like a simple question.  But, there are a lot of variables that need to be considered.  The best way to answer is to use the recently produced code of practice from British Water.  Called "Flows and Loads - 3" this answers this question beautifully. Simply put, it bases the calculation on the number of bedrooms that your property has from a base of 3  i.e. if you have a 3 bedroom house you need a 5 PE system.  (This is a 5 Person Equivalent system that will treat sewage to give an effluent standard of 20 mg/l BOD, 30 mg/l SS and 20 mg/l Ammonia. For every additional bedroom you add another 1PE, so a 4 bedroom house requires a minimum 6 person plant.

Answer: You will end up with a system size expressed in PE.

2. How deep are the existing or new drains going to be?

Again, a simple question that is quite difficult to determine.  If you are building a new house then your architect ought to be able to answer this.  The reason we need to know is that sewage treatment systems can be supplied with different "Invert" levels.  This is the depth of the bottom of the inlet pipe into the system...  it varies from about 500 mm to 1000 mm and needs to be specified at the start of the ordering process.  Deeper invert levels can be accommodated but we need to know this from the beginning.

If you are putting in a replacement system your drain depth will already be determined and thus it can be quite difficult to find out what this depth is.  A small hole is often required to find the depth of the inlet into the existing septic tank if you are going to replace the septic tank completely.  If not, i.e. you are going to use the existing septic tank and add a treatment plant to the back of the septic tank then you need to know the invert level of the outlet of the septic tank.

Answer: Normally between 500 mm and 1000 mm but you need to check.

3. What am I going to do with the water that comes out of the system?

One of the reasons that people call us is that their soakaway has failed and they have septic waste spreading over the garden. Two solutions to this situation.  Firstly you can replace the soakaway with a new one.  This will work fine for a few more years until it gets blocked up and then you have the same problem once again.  Secondly you replace the soakaway with a treatment system like a Biokube to treat the septic waste and turn it into clean water...  You still have to get rid of the water. Normally this will go to a ditch / stream / river / pond or even the sea.  Another solution will be to form a new soakaway, if you have the space, just for the treated water.  Because the water is clean the soakaway does not block up in the future.

Answer: Drop it into the nearest watercourse or a new soakaway.

4. Where am I going to site the system?

A question that needs to be carefully thought about. Here are a few things that need to be looked at:

There are several considerations with regard to the positioning of a Sewage Treatment system.

 Intrusion of water

It is crucial that the plant is not flooded with surface water. The terrain must be evaluated thoroughly.

If the plant cannot be placed so the terrain is sloping, the plant must be elevated to avoid water entering the air inlet.


A well functioning sewage treatment system smells a little bit like a wet forest floor. When the system is serviced  some odour could occur. The plant should therefore be placed so working with the plant does not disturb the daily activities on the property.


A treatment system emits a vague buzzing sound and you can hear the water gurgling softly. These sounds can however be disturbing for some clients, and it is therefore a good idea not to place the plant below the bedroom window or i.e. near a terrace.

Alarm bell

The Biokube treatment system can generate several alarms. It is therefore important to place the alarm where you can hear it. Often the alarm components are placed in the household’s electrical cabinet, which gives the most central placement.

Finally you need to consider Building Regs which state that the plant should not be closer than 7m from the foundations of a habitable building and 10m from the watercourse.

Remember what I said in the introduction.  Gravity plays a bit part in positioning the system. It needs to be downhill from the house preferably.  If not then you might have to think about pumping either waste from the septic tank or worse sewage from the house.  Not a good option if it can be avoided.  The sewerage pipes need to have a gradient on then to get from the house to the sewage treatment system.  This often determines how far you need to go from the house with the system.  Finally the limiting factor might be the area of land that you have for the system.  If it is not that large then you will need to speak with your building regulations department to see what they can come up with.

Answer: Ideally, between 7 and 10 metres from the house, considering the terrain and gravity!

5. Will I need to pump water or even sewage to make it work?

Even with the best will in the world it is often necessary to incorporate pumps into the system.  The best liquid to pump is the water coming out of the outlet of the treatment system.  Next comes the waste water that comes from the septic tank or settlement tank.  This has very little solid matter in it and will normally be easily pumped by submersible pumps designed for this purpose.  The last thing you want to pump is sewage.  This requires a form of cutting or macerating pump that will need regular maintenance.  Something that is going to add costs to your system.  If you can't avoid it then purchase a pumping system with dual pumps and with a maintenance contract in place on the system to ensure that you are always able to move your sewage around.

Answer: It may be necessary if no other method is available.

6. Do I need a discharge permit?

Probably not. You must abide by the Environment Agency General Binding Rules, which covers installations of up to 13 people for plants that discharge into soakaway drainfields and up to 33 people  for surface water (ditch, stream, etc.) discharges. If you don't comply with these General Binding rules, then you will require a Permit for the discharge.

The new HIPS documentation includes sections on "Sewage and Water Services" and a lot of solicitors are now enquiring about sewage in their pre-sale enquiries.

Answer: Possibly not, but all discharges must conform with the Environment Agency General Binding Rules, no matter how old the system is.

7. Do I need planning permission?

This is another simple one.  Ask your planning department. If you are replacing an existing system with an upgraded one then it is likely that you don't. All that you will require is Building Regs approval.  If it is a completely new system then the likelihood is that you will require planning permission.

Answer:  Ask the planning department of your local authority.

8. Do I need Building Regulations approval?

This is almost certainly answered with a Yes, especially if you are going to sell the property in the future.  All such works will require signing off by the building regulations department of you local council.

Answer: Most definitely Yes.

9. Where am I going to get my power from?

Most sewage treatment systems on the market require a power source.  This is normally not a very large supply but needs to comply with electrical codes that are in use in your area.  So normally this will require a supply that is protected by an RCD and has a switching load of at least 16 amps.  Most systems will run with about 3 amps so it is normally overkill.  They will also normally need to have an armoured cable supplying the system. It is quite useful if an isolating switch can be installed outside of the house before the power enters the sewage treatment tank.  This means that the engineer can turn off the power to the tank without the householder being present and wasting a day being at the house when the annual service is done.  The power supply will normally come from the main circuit board in the house.  Please be aware that if a system is serving more than one property then a shared supply will be required with a separate meter.

Answer: Normally direct from the house main supply board.

10. Who is going to look after the system once it is installed?

One of the biggest issues with modern sewage treatment systems is maintenance.  You need to have a system that is going to be maintained on an annual basis, or whenever there are problems with the system.  Currently British Water are in the process of certifying engineers who have proved that they are able to maintain all sorts of treatment systems.  It is well worth ensuring that your system is going to be maintained either by the manufacturer or his representative or by a reputable company who is able to do such work.

Answer: Ensure that you take out a maintenance contract. Contact Sapphire Environmental Ltd Tel 01759 369582 for BioKube sewage treatment plant servicing and repairs

11.Who is going to install the system. 

 For a lot of people this is one of the last things that they think about.  We often hear "We will get the man with the local JCB down to install it!"  Yes, you can get them down.  They can dig the hole and install it if things go to plan. What happens when they don't? This is why I talk about Gravity and Water.  When you start digging around in the ground at over 2m deep both of these things start to get in the way. Gravity has a habit of bringing large lumps of the walls down into the hole and water almost invariably starts to find its way in.  We have seen many installations that go just to plan but many more that have been thwarted by our two friends Gravity and Water.

Save yourself time and effort and use a groundwork contractor who has real experience with installation of this type of system.  Not only that but also have the resources to hand when things start to go wrong.  They need large equipment so that the hole is not left open for longer than necessary. They need pumps and even side plates to enable the hole to be shored up if water is a problem.  The best installations are normally finished in a couple of days at the most.  If it takes longer than this there have to be major problems and you are going to be the one paying for it.

If you do wish to install it yourselves then by all means do so. But be warned that it might not be that simple unless you know your land and soil very well.

In any case, it will need commissioning by a Biokube trained installer, or contact White Rose Sewage Treatment Plant Installations on 01757 289555

If there is anything that you don't understand give us a call: