NEW EUROPEAN UNION STANDARD WILL HELP BUILDERS SPECIFY THE BEST WASTEWATER TREATMENT SYSTEMS by Alison Anderson - process manager for leading sewage solutions provider Klargester and member of the team developing the standard

Tougher building regulations and a growing public awareness of the need to protect the planet by adopting a "greener" style of living have generated a high demand for environmentally friendly building products in recent years.

This change has been particularly noticeable in the off-mains drainage sector where septic tanks, which were once the universal solution for properties unable to access the main sewer, are rapidly being replaced by wastewater treatment systems.

Although wastewater treatment systems offer a far more environmentally friendly option than septic tanks, they are more difficult for purchasers to understand, since different systems achieve their results in different ways.

The absence of any clear guidelines or universal standards governing the performance of wastewater treatment systems has made it difficult for builders and other purchasers to compare models and to be confident they have made the right choice.

It has also made it difficult for manufacturers to trade across the European Union, since they have been required to test their products to different standards for different countries.

In response to this, a new European standard has been developed to define the minimum product requirements for small wastewater treatment systems. The standard also details a long-term performance test, which will see the key performance indicators of each product clearly stated on the CE (Communauté Européenne) marking label, which allows approved manufacturers to trade across the European Union.

The European standard is EN12566 Part 3: Small Wastewater Treatment Systems and covers up to 50 population equivalents Package and/or Site Assembled Domestic Wastewater Treatment plants. It has been prepared by the Technical Committee CEN/TC 165 "Wastewater Engineering" under a mandate provided by the European Commission and the European Free Trade Association, and supports key EU directives.

The minimum requirements state that products must be structurally durable, watertight and corrosion resistant. They must also be fitted with an alarm to indicate an operational problem, such as an electrical, mechanical, or hydraulic failure.

Plants may be constructed from concrete, steel, PVC-U, Polythene (PE), Polypropylene (PP) and Glass Reinforced Polyester (GRP), and the standard lays down the individual requirements for each type of material.

It also states that the hydraulic design of the plant, internal pipework and connections, must ensure no back-flows, blockage or surcharging occur during normal operation. There are minimum inlet and outlet pipework dimensions.

The plant must be designed to prevent unauthorised entry, but should allow easy access for routine maintenance, sampling, sludge removal and cleaning. The plant must resist the loads and stresses resulting from handling, installation and use, including desludging and maintenance, for its entire life.

Depending on the end use, safety factors given by national regulations, or codes of practice valid in the country of use, will determine the loads for which the plants are designed. Calculations will be based on the methods accepted in the place of use and they may take into account backfill load, hydrostatic load and pedestrian load.

The Treatment Efficiency Declaration & Treatment Testing Procedure proves that products meet the key requirements. The tests focus on watertightness (Annex A), treatment efficiency (Annex B) and structure (Annex C). The largest plants within a manufacturer's range are tested according to Annexes A and C and the smallest ones are tested under Annex B. These size choices were made as they would provide the most onerous testing.

Manufacturers must provide details of the design parameters used to size each system. These are usually based on total population loading, minimum and maximum daily organic load and/or hydraulic volume.

All plants must be assessed against the following core parameters - total chemical oxygen demand (COD), biochemical oxygen demand (BOD), suspended solids (SS), power consumption, daily hydraulic flow and temperature.

Treatment efficiency ratios for BOD and SS are mandatory. However, other treatment efficiencies may also be declared to provide added reassurance for purchasers. These may include levels of ammonia phosphate, sludge production, pH etc.

Performance tests are currently taking place in approved laboratories in Germany and Belgium. Klargester completed the testing in June 2005, with its BioDisc sewage treatment plant passing with flying colours. The company believes that it is the first manufacturer in the UK to complete the performance testing successfully.

The 38-week tests are conducted by independent researchers, who base their assessments on information provided by the manufacturer regarding the nominal hydraulic flow expressed in cubic metres per day or the nominal organic daily load expressed in kg of BOD5 or BOD7 per day.

The influent sewage quality used must fall within defined parameters to present the required loading. The test laboratory carries out checks to ensure this. Each system submitted is tested at the maximum daily flows and loads that the manufacturer says the system is capable of handling.

At the start of the test, extra time is allowed for the unit to develop its working biomass. Once the micro-organisms have developed, the 38-week test period officially begins.

During this period, a controlled volume of influent is delivered to the unit according to the defined hydraulic flow pattern. The flow pattern simulates the daily variations that a small treatment plant would receive.

Composite samples are collected and tested according to a pre-determined programme. The tests are mostly conducted under "normal" (i.e. nominal flow) usage conditions, which are defined as intermittent flows during a 24-hour period. The performance of the product in the event of a problem, such as a power failure, underloading or overloading, is also assessed.

Composite samples of the discharged effluent are taken both at the pre-defined intervals and after each stress event. All the results are included in the final report, which indicates not only how well the plant functioned during nominal flow but also how well the plant recovered from the problem.

A single treatment efficiency ratio is calculated for each parameter declared by adding up all the nominal flow test data. Twenty ratios are averaged to give a single treatment efficiency ratio for the nominal flow condition. The treatment efficiency ratio can be used to indicate the expected final effluent quality from a system.

Following the successful completion of the tests, the product's key statistics, including its daily hydraulic load, treatment efficiency and electrical consumption, will be clearly recorded in documentation. Other tested performance indicators, such as the nitrogen parameters and total phosphorus, may also be included. In addition, the manufacturer's name and address will also be clearly identified, and a label indicating the product's test status may be supplied.

Other significant information highlighted in the test report includes how much maintenance was required during the testing, how easy it was to access the components and how much power was required to operate the unit.

The new standard will come into effect in 2008. Manufacturers who do not test their products to the standard will not be able to export them for use in other European Union countries, unless they can prove to regulators by some other means that their goods will perform and are of a sufficiently high quality. Furthermore, it is understood that the UK environmental regulators will recommend the installation of CE marked products.

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