Water & Wastewater Treatment

the carbon footprint of sewer pipe installations. British Precast found that deviation from generic carbon footprint values (secondary data) to specific carbon footprint values (primary data) for sewer pipe installations can be as high as 85% for plastic pipes and 53% for concrete pipes for a single factor. Where multiple deviations apply the figure could be higher still, which implies that the carbon footprint of large diameter sewerage pipeline systems could be significantly under-or over- estimated. The importance of the type of raw materials used in the manufacture, and location from where they were originally sourced, also becomes apparent in the modelling. Attention to the recipe of the mix is particularly important when using data sourced from European databases, because pipes are not manufactured to the same concrete mix throughout Europe. Switching from the baseline concrete pipe, which incorporates a proportion of cement replacement, to a pipe without any cement replacement had a carbon footprint value 32% higher for 450mm diameter pipe. This shows the carbon savings achieved by the use of cement substitutes. In the case of HDPE pipes, switching from the baseline pipe, which does not incorporate recycled content, to one that incorporates 5% recycled HDPE content shows only a 3-8% reduction in the carbon footprint. Depending on where materials are sourced, the carbon contributed by transport and the carbon intensity of the local electricity grid should be factored into an installation's carbon footprint. Electricity is a major element in the manufacture of thermoplastic resins. As a consequence resins sourced from countries such as Saudi Arabia, India or China, all of which have electricity grids with carbon intensities higher than that of the UK, will all result in a material having a higher level of embodied carbon. The implication of British Precast's research is that if decisions are based on unadjusted generic carbon footprint values, the water industry could be making the wrong design and procurement decisions for specific installations. The water industry's Five factors that can alter the carbon footprint of concrete or plastic pipe installations assets are currently estimated at 2.32M tonnes of embodied carbon emissions. However, if the uncorrected or incorrect carbon footprint values have been used, this figure could be significantly different. Although the carbon footprint of materials used to construct a wastewater pipeline installation are only part of a scheme's environmental impact, this study serves to highlight to clients, designers and contractors who are making decisions based on embodied carbon, why they should examine the generic data to ensure it accurately reflects products and materials used for a particular application. This is the key reason why new guidance by BRE on product environmental profiles stresses the need to use appropriate factors for imported materials and products based on their countries of origin. 1 The class of pipe bedding used 2 The amount of recycled material used in the pipe's construction 3 The type of emission used in the calculation (carbon dioxide only, or all greenhouse gases). 4 Transport distance between factory and installation 5 Power use patterns in the products' country of origin The full research paper is available at : www.concretepipes.co.uk. www.wwtonline.co.uk | WWT | JULY 2015 | 35

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