NEW EUROPEAN UNION STANDARD WILL BRING MUCH NEEDED CONFORMITY TO THE SMALL WASTEWATER TREATMENT SYSTEM INDUSTRY
by Alison Anderson - process manager for leading sewage solutions provider Klargester and member of the team developing the standard

Wastewater treatment systems, which break down sewage and discharge a high quality of effluent, are rapidly replacing septic tanks as a more environmentally friendly solution for properties unable to access the main sewer.

There are many different types of sewage treatment plants on the market and they may achieve their results in different ways, using a wide variety of biological processes.

However, the absence of any clear performance guidelines governing the manufacture of sewage treatment plants has made it difficult for builders' merchants and other purchasers to compare the quality and effectiveness of these products in the past.

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.

To tackle this problem, 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.

The standard 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. Minimum inlet and outlet pipework dimensions are also specified.

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 38-week testing procedure is conducted by independent researchers. 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 test period officially begins.

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.

During the tests, 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.

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 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.

This new standard will bring much needed conformity to the wastewater treatment industry and help to increase customer understanding of these complex, yet highly effective solutions for off-mains drainage properties.

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