Skip to content

Finding the best domestic Sewage Treatment Plant for you with this buyer’s guide. Free no-obligation quotes are available.

With the upcoming 2020 legislation changes and continued environmentally focused regulation, Septic Tanks are a thing of the past. Sewage Treatment Plants are the future. Call us on 0800 3101092 to arrange a FREE quote or contact us here.  


Sewage Treatment Plant

A guide to buying the right Sewage Treatment Plant for you

Get in contact with us on 0800 3101092  or via our Contact Page

As you probably know from the 1st of January 2020 it will be illegal to discharge a Septic Tank directly into surface water. If you wish to continue to do so you will need to upgrade to a Sewage Treatment Plant. A Sewage Treatment Plant is different from a Septic Tank. If you are unsure of the difference please read the following. Should I install a septic tank or a sewage treatment plant?

Should I install a septic tank or a sewage treatment plant?

The 2020 rule change is part of a larger set of legislation changes bought in by the Environment Agency. This set of legislation is known as the General Binding Rules, it came into law on the 1st of January 2015. Some of the key elements will be addressed in this guide but please also read our summary.

Summary of the General Binding Rules for Septic Tanks and Sewage treatment plants

Okay, last bit before you are good to go and watch the videos and read the guide elements below. It will also be beneficial to read our guide on how big a tank you need. Again this is touched upon in the video but please familiarise yourself. 

What sewage treatment plant size for my house?

Please now watch our guide videos and read the rest of the guide. If you have any questions please feel free to get in contact. We also have produced the following blog post if you prefer What sewage treatment plant size for my house?

Choosing the best sewage treatment plant /tank guide part1

Choosing the best sewage treatment tank part 1


What legislation, rules, and regulations need to be considered for a sewage treatment system?

Here starts our guide to buying a sewage treatment plant. As mentioned before please see our guide to the General Binding Rules. These are very important and every potential owner should have a basic understanding. The legislation came into force in 2015. If your system complies then you will not need a permit to discharge from the Environment Agency.

If you currently have a Septic Tank which discharges to a river, stream, or drainage ditch, then you have an illegal discharge. National legislation changed in January 2020 rendering all septic tanks unfit for discharging into a watercourse. You will need to either install a drainage field in compliance with BS 6297:2007. Or replace it with a Sewage Treatment Plant. This has resulted in many properties requiring support from retrofit systems or complete replacement with a small sewerage treatment plant

If you have a Septic Tank that discharges to the ground then you need to understand its construction. If it is a drainage field constructed in accordance with BS 6297:2007 then you are okay. Please see our drainage file article for specifications. If it is not designed in this way you have two options. Apply to the Environment Agency for a permit to discharge. Or have your discharge upgraded. It is likely that if you have a Septic Tank the discharge will not comply.

Some of the key rules set out in the General Bing Rules:

  • Discharge is to ground and is of 2 cubic meters per day or less. (the equivalent of a 9-person occupancy.)
  • Sewage is only domestic.
  • The sewage system is maintained in accordance with the manufacturer’s instructions and you keep a record of all maintenance. In the case of septic tanks, this includes annual emptying records.
  • The discharge does not cause pollution of surface water or groundwater.

Your treatment system must meet the right standards (As stated on the GOV.UK website)

Your treatment system must meet the relevant British Standard which was in force at the time of installation. The standards currently in force for new systems are:

BS EN 12566 for small sewage treatment plants

BS 6297:2007 for drainage fields

Your treatment plant met the British Standards in place at the time of installation if:

  • it has a CE mark
  • the manual or other documentation that came with your tank or treatment plant has a certificate of compliance with a British Standard
  • it’s on British Water’s list of approved equipment

Guide to the best sewage treatment plant part 2

Guide to the best sewage treatment plant part 2

How does a sewage treatment plant work and how it is different from a Septic Tank?

  • A sewage treatment plant produces clean, non-polluting effluent. This effluent can be discharged directly to a stream, ditch or to a soakaway for dispersal into the soil.
  • A septic tank produces a very polluting effluent. This must be discharged only to a soakaway for further treatment of the pollutants by the natural aerobic soil bacteria.
  • Sewage treatment plants have mechanical components, which means that they need a permanent electrical supply to operate. There are no such components in a septic tank, and so it operates without a power supply.
  • The typical septic tank has two ‘zones’, whereas a sewage treatment plant typically has three.
  • A sewage treatment plant provides treatment of the waste, whereas a septic tank simply separates it. This means that the wastewater that leaves a sewage treatment plant is cleaner than what leaves a septic tank. You still might not want to take a shower with it, but it’s certainly a lot more environmentally friendly.

What are the benefits?

A sewerage treatment plant produces cleaner wastewater which can be discharged straight to a local watercourse. Many properties in the UK currently still have a septic tank that discharges to a local watercourse. This is opposed to a drainage field or soakaway. As of January 1st, 2020, this is no longer legal.

What does this mean to you?

If you own a property with this drainage system, you must upgrade it by that date. If you are selling a property with this system in place before 2020, you must upgrade it before selling. In the event, you are buying a property with a septic tank discharging to a watercourse make sure this is discussed! Until an agreement has been made about upgrading the system then don’t commit to purchasing. Call our team on 08003101092 about our pre-purchase surveys so that you’ll know exactly what you’re taking on. 

The Inner workings of a sewage Treatment Plant

How a sewage Treatment Plant

The Inner Workings of a Septic Tank

Septic Tank How it works

What size sewage treatment plant will I need?

Your treatment system must be installed properly and have enough capacity (As stated on the GOV.UK website). 

Your treatment system must be large enough to handle the maximum amount of sewage it will need to treat. If you install a new small sewage treatment plant you must check with the installer that it meets the sizing requirements in British Water’s Flows and Loads 4 guidance.

If the amount of sewage the system needs to treat increases (for example, because you’ve extended your property or connected an additional property) you must make sure the treatment system is still big enough. You must also recalculate the maximum daily volume of your discharge and apply for a permit if it is more than 5 cubic meters (5,000 litres) a day.

Your treatment system must be installed in line with the manufacturer’s specifications (the instruction manual or technical set of requirements that comes with the equipment).

Sewerage treatment plants come in all sizes. From small domestic systems for 4 people, right up to commercial sewerage treatment plants for 100s and 1000s of people.

There are a lot of variables to be considered when choosing what size sewerage treatment plant you need. The best way is to use the recently produced code of practice from British Water. This is called “Flows and Loads – 3”. 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.

How much electricity does a septic tank or sewage treatment plant and its system use?

Sewerage treatment plants use electricity to operate 24 hours a day, 365 days a year. You may be interested to know roughly how much owning one will cost you to run. Well, this varies from manufacturer to manufacturer however this simple formula gives you a rough idea.

Watts (of the system) × 24 (hours) × 365 (days) ÷ 100000 × price per kilowatt

For example, a Graf One2clean uses 36Kwh per person per year, so for a 4-person house c.£20 per year.

We cannot give you an exact figure as to the cost of running each and every system. This will depend on certain factors. You should check the price (per kilowatt) with your own electricity provider. How much your sewage treatment system will cost to run will depend on how much you pay for your electricity.

Which is the best domestic Sewage Treatment Plant?

As you can imagine this is a highly subjective question. We have our own opinion based on the quality of the tank, warranty, effluent quality, environmental credentials, and how the tank works.

In short, we like the Graf One2clean series for small domestic installations. Check out the brochure here 

The Graf tanks are single-chambered injection molded systems set up to be ultra-environmentally conscious from production through to the output. They are also designed with no moving parts or mechanical elements making them reliable, less costly, and easier to maintain. The tank comes with a 15-year warranty and 2 yr warranty on the technology.

  • Sustainability starts with manufacturing, this type of tank tech normally requires 2.7 kWh per kg of plastic to produce, and Graf has it down to between 0.38 and 0.5 kWh. Further, all heat generated by the process is recovered and used to heat the company’s logistics buildings. All the materials used are 100% recyclable
  • Electric usage is kept to a minimum, 36kWh per person per year for the One2Clean and 43kWh for the advanced, a 9w energy-saving bulb uses 78kWh, and normal sludge-activated systems use 217kWh.
  • Both of the Graf systems only require one pumping process compared to three in normal systems, extending the life of the core air compressor and delivering the energy savings.
  • The unique way the system treats the waste minimises the level of sludge produced and generates market-leading odourless effluent quality. Graf claims this leads to a carbon footprint of 25% compared to conventional wastewater treatment systems.

What is the next best domestic sewage treatment plant?

The disadvantage of the Graf Tank is that a low-profile version is not available. This means in areas of high groundwater we prefer to install a different tank.

In these circumstances, we use the Marsh Ensign Low Profile tank. Please see here for more details. 

  • Tested to BSEN12566:3 and CE-marked to ensure compliance with the latest environmental and Building Regulations requirements.
  • Class-leading effluent quality of 11.5:19.2:8.4 (BOD:SS: NH4) ensures discharges well within national consent standards
  • Three chamber system correctly sized for separation and retention of solids improves final effluent quality
  • Low-energy compressors ensure minimal running, maintenance, and servicing costs
  • High-specification bio-media (310m3 per m2) and membrane diffusers ensure even circulation to eliminate ‘dead spots’
  • Internal recirculation (from final to primary chamber) continues the treatment process to provide higher effluent quality whilst balancing flow over 24-hour period or periods of intermittent use.
  • 50-year design life.
  • 25-year structural guarantee.

What to look for when choosing the best sewage treatment plant for you.

Okay, so you want to work out for yourself what type of tank is best for you and your project. We have put together a classic top 10 elements to look out for.

Top 10 things to consider when replacing or buying a Sewage Treatment Plant

Construction of tank

Look for a tank that does not have any mechanical seals. Seals rot and perish and unless you want to dig the tank up again to replace avoid it. Many tanks are manufactured in two parts but are plastic welded together, this is okay. The same applies to inlets and outlets. Ideally, look for a tank that is constructed using injection molding techniques.

The material the tank is made of.

This is more for your information but still important to know and consider. There are two main types of material that a Sewage treatment plant is made of Fiberglass and Composite plastic materials (High-Density polyethylene. Generally, the composite tanks are stronger.     

Warranty of Tank.

It goes without saying that you want a warranty on the structural integrity of the tank. If the tank collapses, leaks, or splits then as you can imagine it’s going to be expensive and messy. You should look for at least a 10yr structural guarantee. If the manufacturer doesn’t feel comfortable offering this length of warranty then you don’t want it, simple.

Warranty of components.

In this world, the main warranty only covers the tank. This differs from the normal domestic guarantees you get. First of all, check that the internal parts have a warranty. I feel that every tank should operate trouble-free for at least a year. The Graf tanks offer a 2-year guarantee on the internal parts which I think is fair.

Electrical Consumption.

The less electricity you use the cheaper it is to run your system and this can make a big difference over a sustained period. The basic Graf One2clean uses 36Kwh per person per year compared to aeration models that use c.217 kWh a running cost difference of over £100 per annum based on a 4-person household.

No internal working parts.

Avoid tanks with complex internal moving parts be it valves, motors, discs, gearboxes, and sensors, minimalism is the way forward. Many of these parts are internalised in the tank are metal and sewage are corrosive, this equals big bills. A prime example is tanks with discs (we are not allowed to say the brand).  So, avoid lots of internal moving metal parts.

Air Blower position

Make sure the air blower is housed outside of the tank in a weatherproof unit. If the air blower is located in the tank it will fail due to the wet conditions.

Compressor running time

Look for a tank where the compressor is not constantly on. This reduces electrical costs and also significantly extends the life of the compressor.

Can the tank work when underloaded?

The way tanks are sized to pass building control rules is based on the number of bedrooms your property has. However, the process of the tank is based on the number of people in the house. If there is a large disparity between the number of people in the property or if it is a second home or holiday home then the tank will not work properly. At best this can mean poor effluent quality, which may lead to an illegal discharge. Worst case the tank may malfunction. The Graf Advanced tank comes with underload detection as standard. If you fall into the underuse category, look for a tank system with an underload program.

Servicing & Emptying intervals and costs.

Okay, let’s start by separating this out. All Sewage treatment Plants require annual servicing, this needs to be documented and certified. Failure to do this will result in potential fines if your plant’s discharge quality is below acceptable levels. Further solicitors are increasingly asking for service evidence when it comes to selling your home.

What you want to look for is the desludging or emptying frequency. An empty generally costs between £140 and £200. Personally, I think you should get it emptied annually anyway.

Treatment Performance 

This varies a great deal from one plant to another. This WTE guide is very informative. Generally, try to get as good an effluent quality as you can. This is not just to make the environment nicer and reduce any smell it also has an economic driver.  If your tank only scrapes through the effluent tests when it is brand new then as soon as it degrades it would become illegal. This will mean you will have to install a new system or face constant high servicing charges. If the quality is higher you have more wiggle room.

For Graf, the unique way the system treats the waste minimises the level of sewage sludge left over and generates market-leading odorless effluent quality. Graf claims this leads to a carbon footprint of 25% of conventional wastewater treatment systems.

The effluent quality is outstanding, up to 99%; the maximum levels of the following as set out in BS EN 12566-3 are allowable in mg/l; BOD5 (biochemical oxygen demand), 20,  SS suspended solids, 30, and NH4-N, 20. The Graf One2Clean results are 7, 14 & 0.5, the popular and very expensive (both to run and buy) One of the best-selling brands (we can’t say their name (but you can look on the WTE link)  has advertised results of 10,15 & 3.8.


New Forest Philosophy

Homeseptic is based in the New Forest in between the cities of Southampton, Salisbury and Bournemouth. We are a group of friends who grew up together in the area and grew tired of the way other Drainage firms are run. We want to actually put the customer first and turn up to do a good job we can be proud of. Unfortunately this is not the case in the market, with most companies pressuring their workers to sell unnecessary works on a visit. We are honest hardworking professionals, which we hope you will agree with. With we will not turn up in flash sales vehicles and give you a load of chat and then do a terrible job. We will come with the job in mind and to give you the best value we can in order to facilitate a quality installation. 

We cover all of Hampshire, West Sussex, Dorset, Somerset and Wiltshire. Please get in touch and see what you think.

Homeseptic Ltd. is rated 4.8 out of 5 based on 28

Our reviews on Google
Google Reviews
A Guide to Buying a Sewage treatment Plant
Article Name
A Guide to Buying a Sewage treatment Plant
This guide offers a great starting point for anyone who is looking to buy a Sewage Treatment Plant. There are two very good videos and easy to view 10 things to consider tables.
Call Homeseptic