Water Supply Network

Table 22.3 displays the environmental impacts of the drinking water network considering constructive solutions with different pipe materials and diameters. The environmental burdens were related to a functional unit of 1 linear meter of network. High and low density polyethylene (HDPE, LDPE) and polyvinyl chloride (PVC) were compared for a pipe with a diameter of 90 mm, and HDPE, PVC, glass fiber

Table 22.3 Global warming potential (GWP) (kg of CO2 eq.) of different water supply constructive solutions for a functional unit of 1 m of pipe in a time frame of 50 years

Stage

90 mm-diameter pipes

200 mm-diameter pipes

HDPE

LDPE

PVC

HDPE

PVC

GFRP

DI

Production

4.03

6.93

3.56

13.6

12.3

49.9

131

Transport

8.73

8.94

8.70

9.83

9.71

9.73

16.2

Installation

12.5

12.5

12.5

13.3

13.3

13.3

13.3

Total

25.3

28.4

24.8

36.7

35.4

73.0

161

Table 22.4 Global warming potential (GWP) (kg of CO2 eq.) of different sewer constructive solutions with a diameter of 300 mm for a functional unit of 1 m of pipe in a time frame of 50 years

Life-cycle stage

HDPE (lifespan: 50 years)

PVC (lifespan: 50 years)

Concrete (lifespan: 100 years)

PP1

PP2

PP1

PP2

CP1

CP2

Pipe production

23.7

23.7

7.2

7.2

4.8

4.8

Transport

35.1

21.1

34.8

20.8

10.2

11.0

Installation

33.2

125

33.2

125

42.3

65.0

Demolition

0.95

1.20

0.95

1.20

0.60

0.60

Total impact

93.0

171

76.2

154

57.9

81.4

reinforced polyester (GFRP) and ductile iron (DI) for 200 mm (Sanjuan-Delmás et al. 2014). The life cycle stages included were the production, transport, and installation. The operation was excluded because it depends on the specific network. The end of use phase was also omitted since the supply network is left underground after its use.

In water supply network solutions, the installation stage contributed the most to the GWP (around 50 % for 90 mm; 10–40 % for 200 mm). Furthermore, the relevance of the installation phase was higher for smaller diameters, since the pipe required a lower amount of material and, thus, production is less impacting (15–25 % for 90 mm, 35–80 % for 200 mm). Consequently, previous studies that only analyzed the pipe instead of the whole constructive solution were omitting a significant part of the impacts. No significant differences were found between constructive solutions with different plastic pipe materials. In contrast, GFRP and DI had a much larger impact than HDPE and PVC for 200 mm constructive solutions (around two times higher for GFRP and 5 for DI) due to the higher impacts of these materials.

Sewer Network

Table 22.4 shows the environmental impact of concrete, PVC, and HDPE sewer pipes with different trench designs. Sewer pipes with a diameter of 300 mm were considered because they are widely used in medium-sized cities. The environmental burdens of sewer pipes were related to a functional unit of 1 linear meter of network for a timeframe of 50 year, considering the different lifespan of the materials (i.e., 100 years for concrete and 50 for PVC and HDPE). The sewer operation was excluded from the assessment, given that the electricity required for pumping wastewater depends on the configuration of the city.

In terms of GWP, concrete pipes scored better than plastic pipes, mainly because of their longer durability. The composition of plastic pipes (i.e., oil-based materials) derived in a larger amount of CO2 eq. emissions than in the case of concrete (i.e., mainly cement). There were also differences related to the trench designs that can be applied to each pipe material. In a first attempt to compare constructive solutions, two configurations were assigned to each pipe material: sand beddings (PP1), concrete beddings (PP2 and CP2), and mixed beddings (CP1). PP2 and CP2 resulted in greater environmental impacts because of the contribution of concrete to the GWP (>80 %). In general, the installation stage accounted for more than 70 % of the total life cycle impacts when PP2 and CP2 were applied. At the end, it was determined that concrete pipes with CP1 trenches were the most environmentally friendly alternative (Petit-Boix et al. 2014).

 
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