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In September 2020, the BPDA published a new report which demonstrated why the carbon footprint of concrete pipeline products is significantly lower than HDPE alternatives. However, that study did not look at HDPE pipes made of recycled HDPE. In this very lengthy blog, we raise questions about the likely carbon footprint of pipes made of recycled HDPE and explain why 100% recycled content would not necessarily mean a carbon footprint of ZERO kg CO2e.

Understanding recycled HDPE

Recycled plastic resin has been in use in plastic pipes production since the 2000s. In 2018, the main standard for plastic gravity sewer pipes, EN 13476, was revised to allow for more use of some non-virgin plastics, including polyethylene. However, EN 13476 still have restrictions on the use of recycled polyethylene sourced from outside the plastic pipeline industry. Exemptions only include processed plastic from rotational moulding processes with an agreed specification. Even for such exempt products, there is a 5% limit to recycled content. This explains why some HDPE pipeline products with 100% recycled content in the UK do not refer to EN 13476 in their specification.

Sources of recycled HDPE pellets/ resin

There is very little information about the current source of recycled HDPE pellets for pipes manufactured in the UK. It is understood that sources are likely to include local waste handlers/ recyclers such as Biffa and Veolia. However, as the UK is a net importer of recycled HDPE resin, it is reasonable to assume that some (if not most) recycled HDPE is sourced from international suppliers in Europe and Asia.

A third viable source is manufacturers’ own processing waste and off-cuts or waste and off- cuts sourced from manufacturers of similar products.

Would the carbon footprint of recycled HDPE pipes be significantly lower than concrete pipes or virgin HDPE equivalents?

There is every reason for a 100% recycled content pipe to have a significantly low carbon footprint on a “kg of CO 2 e per tonne” basis. A study by the European Commission’s JRC found significant reductions in using Recycled HDPE, reaching 28% for some products. But environmental impact is assessed based on a functional unit, not tonnes of product. Reductions in the embodied carbon of recycled content HDPE pipe seem to come at the expense of other characteristics such as the pipe’s likely stiffness class, weight per linear metre, bedding requirements and expected ‘Design Life’:

  • The Design Life is unlikely to exceed 50 years due to lack of any standard or specification support. This will directly affect the number of replacements throughout an asset service life if the rules in EN 15978, clause 9.3.3, are followed.
  • The amount of bedding granular is unlikely to be anything less than a Class S (full surround). This will add significant impact as the embodied carbon of granular, and transport to site for that granular aggregate, will need to be added.
  • A higher stiffness class, such as SN6 or SN8 means that the weight of product per linear metre is likely to be significantly higher than a lighter SN2 pipe, adding 20-30% to the embodied carbon of the recycled HDPE pipe.
  • Collection of waste HDPE for recycling and sourcing of recycled HDPE from multiple locations is likely to have a significant hidden impact which can lead to substantial increase in the carbon footprint of such pipes and undermine their case.
  • End of Life prospects are likely to change too. The PE100+ Association notes that PE reclaimed after use in a pipe application is unlikely to have the required characteristics for reuse in the same application. However, for E-o-L impacts calculated in accordance to EN 15804, there will only be a different value for Module D. The product is likely to have the same Module C impacts as for one made of virgin HDPE (e.g. abandonment, recycling, incineration, landfill).

The carbon footprint of the pipe material itself (kg CO 2 e/t) makes less than 50% of the whole- life carbon footprint when other elements such as Design Life, bedding and likely E-o-L come into play.

Last year, we carried out an assessment for a HDPE pipe with 100% recycled content, using as much information as possible from the manufacturers’ websites and videos. We used the assumptions above to build a list of ingredients for the product (recycled HDPE sourced from own process, from local suppliers and from abroad). We employed a model identical to the one developed by Circular Ecology with modifications to allow for recycled HDPE material, higher weights and stiffness classes (such as SN6 and SN8). We also followed all EN 15978 rules on Design Life and overall assets service life and followed PAS 2080 rules on Whole Life carbon assessment and its recommended assessment period of 120 years. The final result reveals very little difference between a 100% recycled content pipe and some equivalent sizes of virgin HDPE pipes. Indeed, a lighter SN2 HDPE pipe of equivalent size has almost an identical performance. British concrete pipes again performed significantly better in terms of Whole-life carbon emissions. On a cradle-to-construction assessment, concrete pipe installations had a slightly lower carbon footprint to 100% recycled HDPE pipes. Figure 1 (below) shows the main result of that assessment.

Recycled HDPE carbon blog

Figure 1. BPDA assessment of recycled HDPE pipes Whole Life carbon compared to equivalent concrete pipes.

The main lesson learnt from this blog is that developers should focus on the carbon footprint of the overall pipeline solution/ system instead of the embodied carbon of products that only make part of the system. The embodied carbon values for a 100% recycled content HDPE pipe looked very impressive for our researchers first. However, as soon as the above functionality elements and R-HDPE waste management and transport factors were added, it became apparent that much of the product’s embodied carbon advantage was being negated by its shortcomings.

It should be noted that there are limitations to our assessment as we do not know the true composition of recycled HDPE pipe brands in the UK or the nature of their supply chains. We had to make assumptions. But we should also warn that our small-scale study is not the first to find very little carbon benefit in products made of recycled HDPE. The European Commission’s recent report on plastics LCA also found an unexpectedly small carbon advantage in manufacturing chairs using mould-injected recycled-HDPE instead of virgin- HDPE, around 28% only. Recycled-HDPE was even found to have significant emissions associated with Ozone Depletion compared to virgin HDPE (Figure 2).

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Figure 2. Ozone depletion related emissions associated with chairs made of HDPE, recycled HDPE (R-HDPE) and other types of plastic.

It is important for all manufacturers, specifiers, developers, and asset operators to think about how their products are used in a “Functional Unit”. It is also important for manufacturers who want to invest in innovative products/ solutions to ensure that their plans are backed with 3 rd party verified and credible carbon footprints and EPDs (certified to EN 15804) prior to committing funds to such investments.

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