CE marking on a wastewater treatment plant shows that the manufacturer has tested the product to the European standard EN 12566-3 and takes responsibility for the declared performance. Before you buy a plant for a house, villa or guest house, ask for the Declaration of Performance, check that the capacity in population equivalent (PE) matches your property and confirm that treatment efficiency was measured in a laboratory, not just promised in a brochure. Below we explain what the marking means and how to read the documents.
What EN 12566-3 is
EN 12566 is a series of European standards for small wastewater systems. Part 3 covers packaged and site-assembled domestic wastewater treatment plants of up to 50 PE. It sets out how plants are tested and which characteristics the manufacturer must declare.
The standard covers four main groups of requirements:
- Treatment efficiency: how much organic pollution and suspended solids the plant removes under real loading during a test lasting many weeks.
- Watertightness: the tank must not leak wastewater into the soil or let groundwater in.
- Structural strength: the tank must withstand soil pressure and, where declared, groundwater.
- Durability: materials must suit the aggressive environment of domestic wastewater.
Above 50 PE the standard does not apply. Plants for hotels, holiday villages and small settlements are designed individually and assessed according to the specific project.
What CE marking on a treatment plant guarantees
CE marking is not a quality seal in the advertising sense. It is the manufacturer's declaration that the product complies with the applicable harmonised standard and that the stated performance was established in the prescribed way. For treatment plants, efficiency is tested by an independent notified laboratory, not by the manufacturer itself.
In practice the marking gives you three things:
- Assurance that the model has been tested under conditions close to real use, including periods of reduced and increased inflow.
- Concrete, comparable figures you can hand to your designer and to the authorities.
- Clear accountability: if the plant does not reach the declared performance when installed and serviced correctly, you have a document to rely on.
The marking does not guarantee that the plant is right for your particular site. Choosing the correct capacity, the discharge point and the quality of installation remain the responsibility of the owner and the contractor.
The Declaration of Performance: what to read
The Declaration of Performance (DoP) is the key document to request. It is short but contains everything that matters. Check these fields:
- Product identification: the exact trade name and model. Make sure it matches the model in the quotation.
- Nominal capacity: in PE and in cubic metres per day. A declaration for 5 PE does not cover a 6 PE model.
- Treatment efficiency: usually stated for BOD5, COD and suspended solids. Some manufacturers also declare nitrogen and phosphorus.
- Watertightness and strength: the test result and the installation conditions it applies to, for example whether the tank was tested for installation in groundwater.
- Notified body: the name and number of the laboratory that tested efficiency.
If a seller cannot provide the declaration, or only sends a leaflet with percentages, look for another supplier.
How to compare two CE-marked plants
Two CE-marked plants are not necessarily equally good. The standard defines the test method, but each model achieves its own results. This is what we compare when advising a client:
| Criterion | What to look for | Why it matters |
|---|---|---|
| BOD5 and COD efficiency | Concrete values in the declaration | Determines effluent quality |
| Capacity in PE and m³/day | Match with the real number of occupants | An overloaded plant treats poorly |
| Groundwater testing | Installation conditions in the declaration | With a high water table the tank can deform or float |
| Technology | Continuous flow or SBR | Affects behaviour under uneven loading |
| Power consumption | Blower rating and operating mode | The plant runs around the clock for years |
| Service and spare parts | Availability in Bulgaria | Without service even the best plant stops |
If you are weighing up technologies, see our comparison of continuous flow and SBR treatment plants.
Red flags when buying
We regularly see situations where a buyer finds out too late that the plant lacks the necessary documents:
- The seller claims the plant is "certified" but only shows a certificate for the tank material, not a treatment test.
- The document is in a foreign language and refers to a different model or capacity.
- No notified laboratory is named.
- Impressive percentages are quoted without saying which parameter or what load they refer to.
- The plant is assembled on site from separate tanks with no test of the system as a whole.
Home-made systems built from several tanks may look cheaper, but their efficiency is unproven. That can become a problem during an inspection or when the property is sold.
Is CE marking needed for permits?
Requirements for building a plant and discharging treated water depend on the location, the receiving water body and the type of property. Decisions are made by the municipality and the River Basin Directorate, and in most cases a design approved by a qualified designer is required. So we cannot say that any single document is always sufficient.
From experience, designers and authorities expect to see the Declaration of Performance, because it shows the effluent quality the plant will achieve. Without it, the designer has a hard time justifying the solution. Before buying, check the requirements with your municipality or ask an ERMAX BG engineer which documents your case will need.
ERMAX BG BIO plants
For single-family houses and villas we offer the BIO-6 treatment plant with a capacity of 6 PE and 0.9 m³ per day. For larger households, guest houses and small hotels, the BIO 6–25 series covers 6 to 25 PE. Every delivery comes with the plant's documentation so the designer can use it directly.
If you are still deciding which system you need, read our article on the most common mistakes when choosing a treatment plant for a house.
Frequently asked questions
What does CE marking on a treatment plant mean?
It means the manufacturer declares compliance with EN 12566-3 and that treatment efficiency was tested by a notified laboratory. The results are set out in the Declaration of Performance.
Does EN 12566-3 apply to plants above 50 PE?
No. The standard covers small plants up to 50 PE. Larger systems for hotels, complexes and settlements are designed individually for the specific site.
How can I check that the documents are genuine?
Compare the model and capacity in the declaration with the quotation and check the name and number of the notified laboratory. If in doubt, ask for the full test report or consult a designer.
If the plant is CE marked, do I still need a design?
CE marking applies to the product; the design applies to your property: where the plant goes and where the water is discharged. Requirements are set by the municipality and the River Basin Directorate, so check them in advance.
If you want to be sure you are choosing a plant with the right documents and capacity, get in touch with the ERMAX BG team. One of our engineers will review your site and send you a technical offer together with the Declaration of Performance for the proposed model.