As green issues continue to rise up the political agenda, the water industry is being forced to look towards more innovative solutions that play a part in reducing carbon footprints. Plastics specialist, Dr Vasilios Samaras, examines how a material traditionally thought of as being detrimental to the environment is now proving to be the ‘greener’ option.
In an era where global warming is having a significant effect on our climate and catastrophic weather events are devastating local communities, the use of innovation is of vital importance.
Historically, the use of traditional materials within the water industry has not only propagated hydraulic inefficiencies but also paid negligible attention to the environment. Independent research has demonstrated that the use of plastic pipes, contrary to traditional beliefs, sets the foundation that could position the water industry at the cutting edge of the environmental agenda.
When you consider that even a small construction site can produce approximately 0.8 tonnes of CO2 per week we begin to understand the importance of looking at the whole picture rather than identifying the areas of least pollution. The main challenge at the moment is to analyse the carbon footprint in every project and then try to reduce it as much as possible without infringing too much on budget constraints.
High-density polyethylene (HDPE) pipes have witnessed a strong growth in usage, particularly within the water industry, and research suggests they can contribute significantly towards the green objective. This will become more evident in the future as the water and construction industries begin the systematic evaluation of the carbon footprint for every individual scheme.
Delivery is one of the major areas in which the advantage of plastic pipes becomes apparent and is supported by the use of a simple carbon footprint calculator endorsed by the Environment Agency.
For example, considering the CO2 emissions on the delivery of 14 metres of 2.1 metre diameter HDPE pipe (which would be delivered on one vehicle) compared to the equivalent length of concrete pipe, which would have to be delivered over a number of vehicles, it is clear that the CO2 emissions of the plastic is just a fraction of the concrete. This is before we even take into consideration the installation time and plant requirements. This can be represented graphically as follows: (see figure1).
Due to the different mixtures and production methods for concrete pipes three different values have been used to demonstrate the best and worst case scenario. Even in the best case scenario for concrete pipes, the CO2 emissions are 50 per cent higher than the HDPE equivalent. It is also important to emphasise that there is a considerable increase in CO2 footprint of concrete pipes the further they travel from their manufacturing base due to their heavy weight.
Of course, this is still a simple calculation, however water authorities across the UK and the private consulting engineers attached to the AMP 4 programme are providing more extensive independent research that adds conclusive evidence to the debate. While the level of the results varies from project to project in every case, the outcome is firmly in favour of plastic.
On one particular flood alleviation project carried out by Asset in the last few months it was calculated that the carbon footprint of the large diameter plastic pipe was only 15 per cent of the concrete equivalent.
These statistics contradict research carried out a few years ago that was endorsed by the Department of Trade and Industry that concluded concrete pipes used in gravity sewers were environmentally sound. The work omitted vital carbon contributing factors such as speed of installation, a reduction in plant requirements and one of the major offenders, transport to site.
Figure 2 clearly illustrates the advantages of transporting plastic pipes with reference to the carbon footprint. In figure 2, 140 metres of pipes are nested inside one another and are delivered to site in a single load.
Figure 3 shows a massive pre-fabricated section of a 300m3 CSO attenuation tank with a weight of less than five tonnes that was manufactured offsite, delivered and installed in just a few hours. To construct this on site using traditional methods would have taken at least eight weeks.
The 300m3 CSO attenuation tank consisting of 3000mm diameter pipes and prefabricated sections which is illustrated in Figure 3 was installed in a very populated area. The tank was placed in the open trench in less than five hours and the total installation including excavation of the trench and back-fill took only few days. This dramatically reduced the environmental impact not only through the CO2 emissions but also through something which is almost impossible to measure, the effects of such a large scale construction on the local community (see figure 4).
The Government has set a challenging target to reduce the UK’s carbon footprint by up to 60 per cent by 2050 and it is therefore essential that the construction and water industries synchronise their efforts to ensure a significant reduction in CO2.
As the years pass we will encounter examples showing how HDPE pipes stand up to the environmental test against its competitors. Meanwhile designers and specifiers can feel confident that they are working towards a greener agenda.
Dr Vasilios Samaras is technical engineer at water management specialist, Asset International Limited.
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