Sewage Treatment Plant Selection - How sewage treatment plants compare?

Comparision of EN12566-3 Test Results for Sewage Treatment Plants

Below is a comparison list of sewage treatment plant Performance Results during the EN12566-3 Test -  Taken from the EN12566-3 PIA Test Centre website.

The figures are the average of the 38 weeks testing - the lower the figures, the better the result. It is probably better to avoid plants which have figures in red that are at, or close to, the limits, as they must have exceeded the limits on some test occasions and you are not allowed to exceed the limits at all.

Problems with the EN Test Certificate

• It is not possible to test a plant with the same strength of sewage as that coming from a domestic house. Sewage plants are tested with wastewater, as it comes, from the city where the Test Centre is situated. This wastewater is always diluted with rainwater, as many older gutters and drains are still conected to the sewage drains.
  The manufacturer must make all efforts to ensure that the sewage their plants are tested with is as concentrated as possible.
  Domestic house sewage has a BOD concentration of over 400mg/L, but many plants are tested using sewage which contains less than 250mg/L and the effluent quality may well be much poorer in normal household use situations.
  This concentration can be calculated by dividing the 'Nominal Organic Daily Load' by the 'Nominal Hydraulic Daily Load', both of which are declared on the CE Certificate, and multiplying by 1000. This gives the concentration in mg/L that the plant was tested with.

• Some manufacturers only had their sewage treatment 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 0.6M3/day, as with some plants.Some manufacturers have the EN test done with too little organic material (BOD) for the number of people they are testing for. In the UK, each person produces 60gms of BOD/Day, so for a 6 person plant, it needs to be tested with 360gms BOD/Day, for a realistic test. Some 6 person plants have only been tested with 230gms/day. It is a cheating world, unfortunately.

• Many manufacturers choose to test their plants for 38 weeks during the warmer months, missing out December, January and February, in order to get better EN Test results. This is because bacteria don't work very well in cold temperatures. However, it is not really a fair test as your plant has to work during the winter as well. If the plant has been tested this way, then the average test results are biased.

• Some manufacturers claim extended emptying intervals that are not really honest. The wording of the claim is very clever, e.g. "Up to 3 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 for sewage treatment plants is a flawed test.

• Some manufacturers opt out of the EN12566-3 Wet Pit Test which is optional. If the tank has not had this test, then you have no idea how it will cope with high groundwater. Make sure that it has the Wet Pit Certificate if your site has a high winter water table.

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™  or QUANTUM sewage treatment plants. Click here for How the VORTEX and QUANTUM  sewage treatment plant systems have such low energy consumption.

WTE Ltd. technical staff can help you with your sewage treatment options.

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 can actually do the job. Most large plants needed for a large house will not work properly if there are only 1 or 2 people living there, as they only work well if they are 50% or more loaded. This means that a 6 person sewage treatment plant has to have at least 3 people using it.

Our VORTEX and QUANTUM systems will work down to 10% and have the certification to prove it.

For flood plain sites, there is only one option for wastewater treatment.

There is also our non-electric FilterPod sewage treatment plant that will work at even lower occupation.

Regulations for Sewage Treatment Plants

All sewage treatment plants must have the EN-12566-3 certification.

They must also comply with the General Binding Rules.

 See also Wastewater Legislation.

Questions to ask the sewage treatment plant manufacturers

Does it require electricity?

Most plants apart from the FilterPod 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 £25,000/year, depending on how it works.

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 FilterPod has a 1 to 3 year emptying interval.

Some sewage treatment plants, made by the leading names, have only just scraped through the EN12566-3 test. They might not pass the UK Environment Agency standards which you have to adhere to, when they test the effluent. This is because the plant may be underloaded, has been subject to a power cut, had no loading because you have been on holiday, or you have had additional people using it for a while - Christmas, parties, visitors, etc..

The EN-12566-3 testing includes all these scenarios and the results of the 'Stress Tests' are on the EN-12566-3 Report Results, but not on the CE certificate, which is just an average of all the results.This is why many manufacturers will only offer the Test Certificate and not the test report!

If they WON'T give you the Test Report, DON'T buy the plant!

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 large, 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. Compare the table at the top of this page.

Servicing costs for sewage equipment also varies enormously, from £150.00 to over £400.00 per service, depending the complexity of the unit. Some sewage treatment 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 25 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 when it fails.

All sewage treatment plants that have the EN 12566-3 Certificate should be suitable for direct discharge to a ditch or watercourse, subject to compliance with the Environment Agency General Binding Rules. 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.

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