Plastic vs concrete wastewater treatment systems: compliance and key differences

This article outlines the pros and cons of plastic and concrete wastewater treatment systems. It also explains the EN certification process (EN12566), which is carried out by accredited organisations such as PIA GmbH.

All prefabricated on-site wastewater treatment systems must undergo EN12566 testing to obtain CE marking — a requirement for selling these systems within Europe.

The standard is divided into the following parts:

• EN 12566-1: Prefabricated septic tanks
• EN 12566-3: Prefabricated secondary wastewater treatment systems
• EN 12566-7: Prefabricated tertiary wastewater treatment units

Each product is tested for 7 to 38 weeks to assess structural stability, water tightness, and long-term durability. Once testing is successfully completed, the system is granted EN12566 certification, meaning it can be legally placed on the market.

In Ireland, treatment systems must also comply with the EPA Code of Practice 2021, S.R. 66:2015, and Building Regulations Technical Guidance Document H. Purchasers are advised to confirm certification by requesting supplier documentation or consulting the PIA GmbH website.

Both plastic and concrete systems are effective at treating domestic and commercial wastewater, but they offer different benefits depending on the project's needs.

• Manufactured from tough polypropylene
• Lightweight, making them easier to handle and install
• Lower transport and labour costs
• Well-suited to confined or hard-to-access locations
• Often produced using 100% recycled materials

That said, plastic systems must be installed carefully, particularly in areas with a high water table. Backfilling with pea gravel is usually recommended to help stabilise the unit. In some scenarios, a lean mix concrete backfill may be required to secure the tank in place.

• Constructed from precast concrete
• Highly robust and built for long-term use
• Heavier, resulting in higher transport and installation costs
• Requires heavy machinery, which may affect certain sites
• Generally costs at least €1,000 more than a comparable plastic system (excluding septic tanks)

Plastic systems often represent a more cost-effective option, especially for sites without challenging ground conditions. They also commonly include a 15-year structural warranty. In comparison, concrete systems usually come with a 10-year warranty.

The success of any wastewater treatment system depends heavily on correct installation — more so than the material used. While plastic and concrete systems follow similar installation principles, there are some key differences to consider.

Plastic tanks are lightweight, making them easier to transport and handle, especially on sites with limited access or soft ground. They typically require smaller machinery and less manual labour, which can help reduce installation time and cost.

In contrast, concrete systems are significantly heavier and usually require larger lifting equipment and more site preparation. This may limit their suitability in hard-to-reach areas or on restricted sites.

Regardless of the material, correct siting, backfilling, and pipe connections are crucial to system performance. Always follow the manufacturer’s installation guidelines and work with an experienced contractor.

While it’s natural to focus on whether a tank is plastic or concrete, the most important factor in long-term success is how the system is sized, installed, and maintained. A high-quality plastic system, properly installed, will often outperform a poorly placed concrete one — and vice versa. Always work with an experienced installer and choose a certified product that fits your site’s needs.

Both plastic and concrete systems require periodic servicing to operate efficiently. This includes regular desludging, ensuring ventilation is clear, and checking that pumps and components are functioning correctly (if applicable). Most systems need an annual service, and failure to maintain them can affect performance and potentially void warranties. Always refer to your system’s O&M (Operation & Maintenance) manual for exact intervals and checks.

For locations with limited access, soft terrain, or budget considerations, a plastic system is often the most practical choice. Where weight, ground stability, or long-term infrastructure investment is a priority, concrete systems provide excellent durability. Both types of systems undergo the same stringent EN12566 testing, ensuring performance and compliance regardless of the material.

Ultimately, your decision will depend on site-specific factors, your budget, and personal preference. Both plastic and concrete systems can offer reliable, compliant wastewater treatment solutions. You can view the full list of EN12566-certified wastewater treatment systems in Ireland on the PIA Website.

Ask your supplier for a detailed installation guide specific to your system. This helps ensure your contractor follows the correct procedure and keeps your warranty valid. Not sure which system suits your site? Request a free percolation test review from our team and get expert advice.