Intron Study Summary

An independent leading Dutch consultancy (INTRON) was commissioned to carry out a cradle-to-grave comparative environmental Life Cycle Assessment (LCA) study for seven types of sewer pipeline systems in the UK in 1999. These included concrete, clay, solid wall PVC, twin wall PVC, ultrarib, twin wall PP, spirally wound HDPE.

The study accounted for a variety of environmental impacts arising throughout the life cycle of pipeline systems (see Figure 1); 13 different environmental impact categories were considered in the study. These included Depletion of raw materials, Eco-toxicity Sediment (also known as Marine Eco-Toxicity), Soil (or land) Eco-Toxicity, Water Eco-toxicity, Energy consumption, Human Toxicity, Chemical waste, Non-chemical waste, Acidification, Eutrophication, Summer Smog (also known as Photochemical Ozone Creation Potential), Greenhouse effect, and Depletion of Ozone Layer.

For every stage in the life cycle of sewer systems, data on products’ system inputs and outputs were collected (e.g. input of raw materials, input of energy, output emissions to air, water, and soil, output solid waste). The data was collected from across the products’ supply chains; including raw material suppliers, concrete pipe and manhole manufacturers, pipeline contractors, water companies, and many other sources of secondary information.

Figure 1. Different life cycle stages, inputs, and outputs considered in the study.

Functional Unit

In order to set the LCA study, it was necessary to establish a functional unit for the different pipeline systems included in the study. The functional unit used is 1 km of gravity sewerage system under a road in a non-aggressive soil and groundwater environment, used for the removal of mixed household water, consisting of pipes DN 300 or DN 450 and manholes DN 1200 or DN 1350, with a service life of 50 years.

The study was subject of an independent critical review from the BRE. Moreover, a sensitivity analysis was carried out to test the credibility and robustness of the study’s findings.

Study findings

The environmental impacts throughout the life cycles of the sewer systems were compared, and following conclusions were made:

• Concrete and clay sewer systems can be regarded as comparable.
• Concrete pipeline systems can be regarded as more environmentally sound than PVC, twin wall HDPE, and PP systems.
• Concrete sewer systems can be regarded as moderately better than spirally wound HDPE.

The results of the study clearly show a massive gap between concrete and other types of plastic pipe systems – the environmental performance of concrete pipeline systems had the best performance in seven categories and second best in another three:

1st Depletion of raw materials

1st Eco-toxicity Sediment (Marine Eco-toxicity)
1st Eco-toxicity Soil (Land)
1st Eco-toxicity Water

1st Energy

1st Human Toxity

1st Chemical Waste

2nd Acidification

2nd Eutrophication

2nd Summer Smog (Photochemical Ozone Creation)

There are many reasons why concrete pipeline systems perform better than plastic-based systems, INTRON notes that plastic pipes require more bedding material, therefore more earth material have to be removed during excavation. Moreover, the production process in concrete pipe manufacturing facilities consumes less energy and generates less harmful emissions than in plastic pipe factories.

These results come as no surprise, the study is one of a number of LCA and environmental comparative studies carried out throughout Europe (Netherlands, Germany, Finland, and Austria) to investigate the environmental performance of pipeline systems.

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This is not to mention calls from the Committee for the Environment, Public Health and Consumer Policy at the European Commission demanding a substation policy, starting with a rapid replacement of PVC, these calls were backed by a number of MEP. In the UK, a report published by the Select Committee on Environment, Transport and Regional Affairs in 1998 highlighted clearly a number of concerns about the UK sewerage system and recommended the use of concrete pipeline systems.

Download Environmental Assessment of UK Sewer System