Sewage Treatment Plants - How they Work - How to choose a Manufacturer

Which Type of Sewage Treatment System is Right for You

Choosing a sewage treatment system manufacturer can be a nightmare as there are so many on the market that you probably have no idea how to choose the right one for you?  The most important factor is that the manufacturers plant has an EN 12566-3 2005 Certificate as without it, it is no longer legal in the UK. Worse than that, the Environment Agency will not accept plants that HAVE the Certificate if their percentage reduction of influent pollutants during the 38 week EN Test is below certain levels. These are:

BOD reduction less than 93%

Suspended Solids reduction less than 88%

Ammoniacal Nitrogen reduction less than 50%

BUYER BEWARE!!!!

Some manufacturers that have got the EN 12566-3 2005 but which have failed the above reductions do not offer the Certificate and refuse to send a copy when asked. Others claim that their plants are 'Designed to' or 'Conform to' the EN 12566-3 standard. This is like saying that you are educated to 'A' level standard - it does NOT mean that you passed any!.Some still refer to the outdated BS 6297 1983 or ISO 9001 and hope that you don't know the new regulations. Some even only offer the letter from the EN Test Centre confirming delivery of the tank for testing (written in German or French to confuse the issue). These have presumably failed E.A. criteria on the test.

Some manufacturers only had their plants tested for the effluent from 4 persons during the test, but sell the plant as a 6 person. Ask how many litres/day the plant received during the EN Test - it should be 1.200M3/day for a 6 person system, not 0.8M3/day, as with some plants.

Some manufacturers claim extended emptying intervals that are not really honest. The wording of the claim is very clever, e.g. "Up to 5 year emptying intervals" - yes, if there was only 1 person living in the house and they were out at work all day! You need to ask how often it will need emptying if fully loaded and even then, you may not get an honest answer. Assume that ALL package (all-in-one tank) plants need emptying at least annually under normal use. For more information visit Why we think that the EN 12566-3 is a flawed test.

Cheap sewage treatment plants may not be the most economical option, as running and installation costs vary enormously between different types of wastewater equipment, depending on how each one works. Some are probably not even legal.  If you want a low cost system that WORKS and is certified, consider the VORTEX™ sewage treatment plant from £1420 plus VAT.

Click here for the UK list of EN 12566-3 Certified Sewage Treatment Plant Manufacturers. WTE Ltd. technical  staff can help you with your sewage treatment options.

There are 4 different types of domestic sewage treatment plants:

Differences between the sewage treatment plants available

Checklist	Traditional 3 stage Plant	Activated Sludge Plant	Non-Electric Filter Systems
Electricity required	YES (not very much)	Yes (not very much)	NO
Emptying Interval	3 to 18 months	1 year	2 to 3 years
Smelly Primary Tank	SOME (Unless Vented)	NO	NO (Vented)
Internal Moving Parts	SOME (Biodiscs)	NO	NO
Ability to perform during intermittent use (holiday lets, etc)	SOME	SOME	YES
Ability to perform if underloaded	YES	SOME	YES
Visually Intrusive	SOME	SOME	NO
Expensive Servicing	SOME	NO	NO
Warranty Period	1 to 25 years	10 Years	10 years
Effluent Standard	OK to Excellent	Excellent	5 times cleaner than UK Standard
Makes of Plants	Traditional 3 Stage	Activated Sludge	Non-Electric Filter
	Valence	VORTEX™	Biorock
	Moduline
	Klargester Biodosc
	Entec Biotec
	Falcon
	Bioclean

The new standard for private domestic sewage treatment plants in the UK is the BS EN 12566-3 2005 - not to be confused with CE marking which is not mandatory.  Trading Standards and the Environment Agency have advised us that only plants which already have this BS EN 12566-3 2005 test conformity certificate are legal for sale in the UK, as it is now a requirement for Environment Agency EPP2 Exemption or Permit registration.  Many plants, including some of the manufacturers above, do not have it, or the plant performed so badly in the test that they do not declare it.  These plants do not conform to Trading Standards or Environment Agency requirements. Before you decide on a wastewater plant, DEMAND to see the independent TEST REPORT, NOT the CERTIFICATE, and do not be surprised if they are refused!  If they are refused, DON'T BUY IT!  See also Wastewater Legislation.

Questions to ask the sewage treatment plant manufacturers

Does it require electricity?

All plants apart from Biorock sewage treatment plants and the Conder ECO require electricity to work.  Some need much more than others!  Make sure you ask what the average KW hours/year the plant uses BEFORE you buy it!  This is particularly important for the larger sewage treatment plants as the cost for a 100 person plant can be £12,000/year, depending on how it works.

How often should the sewage treatment plant be emptied?

Emptying is often the most expensive part of system running costs. Emptying intervals also depend on how it works.  All of the 3 stage package plants need emptying every 3 to 12 months, depending on the size and make of the plant, as they don't fully digest the solids, but store them as sludge in the primary tank.  The extended aeration sewage treatment plants partially digest the solids as well and have a 1 to 2 yearly emptying interval, depending on the model (not 5 years as is the claim with some). The BIOROCK has a 2 to 3 year emptying interval.

Can I have a copy of the full EN12566-3 2005 test RESULTS?

 

BEWARE as many sewage treatment plants for sale in the UK have NEVER been tested by anyone! 

Others, even some made by the leading names, which have passed the EN12566-3 2005 would NOT pass the UK Environment Agency standards which YOU have to adhere to!!  This is because the EN12566-3 2005 only tests the percentage reduction of pollutants in the final effluent, NOT the final effluent quality produced by the sewage equipment!  Yes, it is stupid as many sewage treatment plants which failed, during the test, to meet the UK Royal Commission Standard of 20BOD:30S.S.:20NH3 on a 95 percentile basis have been given the EN Certification!   This is why many manufacturers will only offer the Test Conformity Certificate and not the test report! 

If they WON'T give you the test REPORT, DON'T buy the unit!!  

It is YOU that the Environment Agency prosecutes ( see Latest News) not the sewage equipment manufacturer! 

 

Does it have a Primary Settlement Tank?

 

If it does, then it is a 3 stage wastewater treatment plant as described above. Unvented UK Primary Settlement Tanks do not tend to be odourless as gases can escape through the sewage treatment unit lid, particularly when the bath, etc. is emptied, displacing air through the lid of the plant.  It is called Primary Settlement Tank Odour.  Ask if the PST is vented as part of the works! 

 

Does it rely on internal moving parts?

 

Moving parts wear out and sewage is very corrosive.  Replacement parts - motors, gearboxes, bearings, drive shafts, etc.- and labour can be very expensive for some plants. 

 

How thick is the fibreglass/polyethylene?

 

This can vary between plants from about 3mm to 10mm, depending on the make of unit. Obviously, the thicker the better as thin-walled tanks can distort or crack under the pressure of groundwater or soil on the top.  In this business you really do get what you pay for.

 

What do you see when the sewage treatment works is installed?

Some plants are an eyesore, either because the lids are enormous and protrude well above ground level, or because there are multiple large lids on view.  Some sewage treatment units have unsightly Kiosks containing compressors and timers etc. whilst others are small and inconspicuous.

How clean is the effluent?

Sewage treatment plant vary enormously in their ability to treat sewage. The majority only treat it to a minimum standard to satisfy Environment Agency requirements, but some treat it to a far higher standard and provide a safety net when relatives stay. Again, you get what you pay for.

How much is the annual servicing cost?

Servicing costs for sewage equipment also varies enormously, from £75.00 to over £300.00 per service, depending the complexity of the unit. All extended aeration plants require 2 services per year, not one. A general rule is, the simpler the treatment system works, the cheaper the service. Ask what the service cost is per annum.

How long is the tank warranty?

This varies from 1 year to 30 years, depending on the plant manufacturer. Ask about the warranty period as, in our opinion, 12 months is far too short a warranty for a tank costing upwards of £2000.

In our experience, tanks do not tend to crack during the first 12 months. They crack as the pressure increases over time due to settlement of the ground around them. This normally takes place over 18 months to 2 years, so what use is a 12 month warranty? It is only of benefit to the manufacturer who does not have to replace the tank.

All sewage treatment plants that have the EN 12566-3 Certificate, except for the Klargester Sigma (now called Entec SuperSeptic), should be suitable for direct discharge to a ditch or watercourse, subject to Environment Agency Permit to discharge.  However, not all sewage equipment is designed for this type of disposal system.  Septic Tanks are NOT, and expensive soakaways, with a limited lifespan, must be constructed to dispose of all septic tank effluent.

You will need a PERMIT TO DISCHARGE from the Environment Agency to discharge to a watercourse.  It is not difficult to get and we will help you with the forms free of charge.

Waste Tech gives INDEPENDENT advice on all the above sewage treatment manufacturers and equipment