Wastewater Treatment Systems: Plastic vs Concrete

There are manufacturers worldwide supplying plastic and concrete septic tanks, packaged secondary wastewater treatment systems, and tertiary wastewater treatment systems to customers in Ireland. A question that is frequently asked when we talk to customers out on-site or at trade shows is: what is the difference between plastic and concrete wastewater treatment systems?

We are going to discuss some of the advantages and disadvantages of both below as well as provide information about EN Certification (EN12566) and the testing process carried out by an accredited organisation such as PIA GmbH.

Before we get started, we would like to mention that we deal with multiple manufacturers and supply both plastic and concrete-packaged secondary wastewater treatment systems which both benefit from the same market-leading SBR (sequencing batch reactor) technology.

We have our own opinion on which material is more practical and cost-effective but if you would like to deal with us, we want to be able to give you the information you need to make your own decision.

The first thing you need to know is that every prefabricated on-site wastewater treatment system goes through the EN12566 testing process. The basis for a successful market entry in Europe is the CE marking of the product. For this purpose, the series of standards – EN 12566 – is used.

The standard EN 12566 is divided into several parts, each of which defines the basis for the respective tests:

• Part: 1 Prefabricated septic tanks.

• Part: 3 Prefabricated secondary wastewater treatment systems.

• Part: 7 Prefabricated tertiary wastewater treatment units.

Each part undergoes the same test which checks for stability, water resistance, and durability. To ensure the product meets the minimum standard of treatment efficiency and effluent quality required for each part, an accredited organisation such as PIA GmbH carries out various tests over a period of 7-38 weeks. Once the product meets the minimum standard, it receives EN12566 certification. It can now be legally sold on the market in Europe.

In Ireland, we are governed by the EPA Code of Practice 2021, S.R. 66:2015, and the Building Regulations Technical Guidance Document H. Each states that a prefabricated on-site wastewater treatment system must be certified to EN12566 to be legally sold on the market in Ireland.

If you are installing an on-site wastewater treatment system, it is worth checking that the particular system has been tested by an accredited organisation such as PIA GmbH and has received EN12566 certification. You can request a copy of this certification from your supplier or you can check the list of products in Ireland that meet the minimum standards on the PIA GmbH website.

In summary, both plastic and concrete on-site wastewater treatment systems go through the same testing process and are checked for stability, water resistance, and durability to receive EN12566 certification.

What is the difference between plastic and concrete on-site wastewater treatment systems?

Both plastic and concrete on-site wastewater treatment systems are used for domestic and commercial wastewater treatment, but they have some key differences.

Plastic on-site wastewater treatment systems are typically made of polypropylene and are durable, lightweight and easy to install. They are also relatively inexpensive compared to concrete alternatives, making them a popular choice for domestic use. They have a lower mass than concrete on-site wastewater treatment systems, which reduces transportation/installation costs and they can be installed in tight spaces or hard-to-reach areas.

Concrete on-site wastewater treatment systems are typically made of precast concrete, which is a type of concrete that is cast and cured in a controlled environment before being transported to the site for installation. They are known to be durable but also much heavier when it comes to transportation/installation costs. In some cases, depending on ground conditions or the time of the year, your garden will need to be modified due to the heavy vehicle needed to offload a concrete on-site wastewater treatment system.

If it is an existing site, a plastic on-site wastewater treatment system can be more cost-effective with minimal excavation and damage to the landscape. Some sites are not suitable or practical for heavy vehicles, but if access, ground conditions, and impact on the landscape are not an issue then a concrete on-site wastewater treatment system can be a perfect solution.

Wastewater treatment reduces contamination of the environment and promotes sustainability by reducing the environmental impact of human activities. A huge benefit of plastic on-site wastewater treatment systems is manufacturers are using 100% recycled material. Recycling plastics helps the environment by diverting-ocean bound plastics, reducing greenhouse gases, and limiting energy consumption. Combine that with an energy-free septic tank or energy-efficient SBR packaged secondary wastewater treatment system and you have one of the most sustainable on-site wastewater treatment systems available on the market today.

So that all sounds great right? but you are probably wondering what are the disadvantages of installing a plastic on-site wastewater treatment system.

When you are installing a plastic on-site wastewater treatment system it is important to know that even though polypropylene is known for its durability, they are still much lighter than a concrete alternative.

If you have good ground conditions on-site, you will need to backfill your wastewater tank with pea gravel as this helps keep everything in place when the ground settles. This is standard procedure with pipework and manholes coming from your home or commercial facility when you are installing a plastic or concrete on-site wastewater treatment system.

The main difference between plastic and concrete is clear when you have a high water table on-site. In this case, we recommend using lean mix concrete to backfill any plastic on-site wastewater treatment system. This helps secure the wastewater tank in place, protects it from groundwater, and increases the overall mass and weight. A concrete on-site wastewater treatment system does not require any additional backfill.

In general, concrete on-site wastewater treatment systems are at least €1000 more expensive than plastic alternatives (except septic tanks). If you use lean mix concrete to backfill a plastic on-site wastewater treatment system you are increasing the cost by roughly €350. There are plenty of sites that do not have a high water table which means there are considerable cost savings to be made by choosing a plastic on-site wastewater treatment system which often shares the same technology.

As discussed, plastic and concrete on-site wastewater treatment systems go through the same testing process and this ensures that they are fit for purpose. Plastic manufacturers are confident in the structural integrity of their products which is evident in the structural warranty they provide. Plastic on-site wastewater treatment systems are usually supplied with at least a 15-year structural warranty and concrete alternatives are usually supplied with a 10-year structural warranty. There are exceptions of course, but this is definitely something to take into consideration when choosing your new on-site wastewater treatment system.

It is impossible to create a durable, lightweight, inexpensive concrete on-site wastewater treatment system that reduces transportation/installation costs and can be installed in tight spaces or hard-to-reach areas. This is why plastic on-site wastewater treatment systems are growing in popularity in recent years.

There are other factors to consider when choosing an on-site wastewater treatment system such as the treatment process and efficiency (which can affect running costs and maintenance requirements) but it’s not relevant to the structural differences between plastic and concrete on-site wastewater treatment systems.

In summary, a plastic on-site wastewater treatment system is the perfect solution for any domestic or commercial project, but so is a concrete alternative if your site is suitable and the price is right for you.