Life cycle assessment of pipes and piping process in drinking water distribution networks to reduce environmental impact
Introduction
As stated by the United Nations Educational Scientific and Cultural Organization (UNESCO), water is undoubtedly one of the most vital needs humans (UNESCO, 2012). Today’s global water crisis is the result of different factors that include over-exploitation (Tilman, Cassman, Matson, Naylor, & Polasky, 2002), population growth, and climate change (Hanjra & Qureshi, 2010). On the other hand, water demand depends on many factors such as population and urban activities (Daghighi, Nahvi, & Kim, 2017; UNESCO, 2012). The world population has been predicted to increase from 7349 million in 2015 to 8501 million in 2030 (United Nations, 2015). Noticeably, this growth is predicted to happen more in areas more struggling with drought (United Nations, 2015). Accordingly, the water demand is increasing and, as a result, the requirement for water infrastructure is also enhanced. In addition to construction of water infrastructures, since renewal and maintenance of obsolete infrastructures seem essential, it is necessary to consider the different environmental and economic aspects of DWDNs in the production, transportation, installation, and maintenance phases.
The value of the environment must be considered in macro-planning of infrastructure projects, and disregarding the importance of the environment has produced many types of environmental pollution and increased toxic gas emissions (Daghighi, 2017; Hardoy, Mitlin, & Satterthwaite, 1992). Consequently, engineers' attentions have been devoted to investigating the environmental impact of infrastructure projects such as Urban Water Systems (UWSs). As shown in Fig. 1, an UWS consists of several components, including a Water Supply System (WSS), a Water Treatment Plant (WTP), a Drinking Water Distribution Network (DWDN), a Waste Water Collection Network (WWCN), and a Waste Water Treatment Plant (WWTP). DWDNs, one of the most fundamental parts of UWSs, play a key role in providing public service (Johnson, 2009).
During the past years, while most DWDN studies have focused on hydraulic, qualitative, and economical aspects of projects, recent increases in environmental pollution makes it necessary to consider their environmental impact (Hajibabaei, Nazif, & Vahedizade, 2017). In this study, the environmental impact of a DWDN is investigated using Life Cycle Assessment (LCA). According to the International Organization for Standardization (ISO), LCA is a standardized method (ISO, 2006) that assesses the environmental performance of a product, service, or activity during their lifetimes (Loubet, Roux, Loiseau, & Bellon-Maurel, 2014). LCA has demonstrated its worth, and has been employed to evaluate the environmental impact of water systems for more than 20 years (Loubet et al., 2014).
Using LCA, some studies have focused on the specific components of an UWS. For example, some researchers investigated WWTPs (Pasqualino, Meneses, Abella, & Castells, 2009; Renou, Thomas, Aoustin, & Pons, 2008; Tidaker, Kärrman, Baky, & Jönsson, 2006) and wastewater sludge treatment processes (Suh & Rousseaux, 2002). Some of these studies considered WTPs and WWTPs (Remy & Jekel, 2011), and WTPs, WWTPs and WWCNs (Barjoveanu, Comandaru, Rodriguez-Garcia, Hospido, & Teodosiu, 2014). There are also some studies that analyzed entire UWSs (Amores, Meneses, Pasqualino, Antón, & Castells, 2013; Lassaux, Renzoni, & Germain, 2007; Muñoz, Milà-I-Canals, & Fernández-Alba, 2010; Qi & Chang, 2011; Schulz, Short, & Peters, 2012; Slagstad & Brattebø, 2014). Also, since both domestic and industrial users could influence environmental impact, other researches, considered water users (domestic and industrial) as parts of the system along with the UWS (Arpke & Hutzler, 2006; Fagan, Reuter, & Langford, 2010; Godskesen, Hauschild, Rygaard, Zambrano, & Albrechtsen, 2013).
Venkatesh and Brattebø (2011) evaluated energy and cost consumption and environmental impact of the UWS during its exploitation and maintenance phases in the period 2000-2006. Their results showed that 88% of the aggregated environmental impact was related to the WWTP, while only 5% of impact was related to the WTP. In another study, Loubet, Roux, Guérin-Schneider, and Bellon-Maurel, (2016), showed that the highest environmental impact of the UWS in Paris suburban area was attributed to its WWTP. Amores et al. (2013), based on the Global Warming Potential (GWP) impact category, indicated that DWDN is the most impactful component of the UWS because of the high energy consumption of DWDN.
LCA has been used in different studies to determine environmental impact of different components of UWSs in phases of construction, transportation, installation, operation, and maintenance. For example, Stokes and Horvath (2006) assessed the energy cycle of a WSS, a WTP, and a DWDN, and concluded that 60–91% of the environmental impact was associated with the operation phase (including water pumping) and 5%–36% of the environmental impact was associated with the maintenance phase. Based on these results, the construction phase contributes only 4%–5% of the environmental impact. An examination of available literature in this regard shows that since the contribution of each phase of a system to environmental impact was mainly dependent on the case study’s characteristics, the results are local and should not be utilized in other regions with different specifications.
Different pipe materials have been considered in investigating the environmental effects of DWDNs, and a summary of the studies investigating the environmental impact of different pipe materials is given in Table 1.
Using the LCA method, Sanjuan-delmás et al. (2014) compared the environmental impact of DWDN pipes of the 90 and 200 mm diameters commonly used in small to medium cities. The results showed that 90 mm PVC, HDPE, and LDPE pipes had similar environmental impact, but in 200 mm pipes, DI and GFRP had greater negative environmental impact than HDPE and PVC pipes. In another study, Piratla, Asce, Ariaratnam, Asce, and Cohen, (2012) indicated that PVC-O pipes had the lowest environmental impact compared with 200 mm PVC, HDPE, and DI pipes, based on equivalent CO2. In the installation phase of the study, unlike in most studies, HDD was considered to be the drilling method.
In previous studies, in LCA analysis of pipes, less attention was paid to trench materials used during the installation phase, although Petit-Boix et al. (2014) considered four types of trenches when evaluating the environmental impact of sewer construction. The results showed that HDPE pipes were the worst options in terms of environmental impact, and it was also concluded that approximately 80% of the impact was related to the WWCN installation phase. In a similar study, Vahidi, Jin, Das, Singh, and Zhao, (2016) demonstrated that, among six pipe materials, DI pipes were the worst options with respect to environmental impact. In the installation phase, they considered the environmental impact of trench excavations, while the effects of the equipment and materials used for trenching were neglected. Du, Woods, Kang, Lansey, and Arnold, (2012), in comparing six commonly-used types of water and wastewater pipe materials, indicated that DI had the most GWP for pipe diameters ≤61 cm (24 in.), and among all pipe sizes, concrete pipes had the lowest GWP.
In previous studies on DWDN, the environmental impact of fibrocement and steel pipes were also not assessed, and the impacts of different trenches were not taken into account. In the present study, in addition to considering the environmental impact of fibrocement and steel pipes, the effects of PVC, HDPE and DI pipes are also evaluated. Moreover, to compare the environmental impact of different trenches, a specific trench type was considered for each pipe. 200 and 500 mm diameters have been chosen for comparing the environmental impact of different pipes in production, transportation, and installation phases. To illustrate the potentials of environmental impact reduction in a real case, a part of the Tehran DWDN was selected as the study area, and a trenchless method (pipe bursting) was employed in addition to the traditional methods of digging trenches to show the importance of installation methods with respect to environmental impact in the case study. The results of this paper can be used as a guide for estimating the environmental impact of different DWDNs in urban areas. Besides, a second point would be that designers and operators can use the results of this research to select pipes and trenches with the least environmental impact. This would be beneficial because pipe materials and piping processes could have a significant effect on the environmental impact of DWDNs.
Section snippets
Materials and methods
This research employs LCA for analyzing the environmental impact of different pipe materials in DWDNs.
In the LCA method, the environmental effects of a product, service, or process during their lives are evaluated, assessed, and calculated (Finnveden et al., 2009). The LCA framework consists of four important stages (ISO, 2006):
- 1
Goal and Scope Definition
- 2
Life Cycle Inventory
- 3
Life Cycle Impact Assessment
- 4
Interpretation
Comparison of the environmental impacts of production phase
The environmental impacts of the production phase have been assessed using the midpoint impact categories of CML2 method. The values of midpoint impact in the production phase are indicated in Table 4. Moreover, Fig. 4 shows a comparison of the environmental impact of 200 mm diameter pipes during the production phase. As indicated in Table 4, PVC pipes produce the least midpoint impact in most categories. HDPE and PVC pipes produce similar impact, but the midpoint impacts of HDPE are slightly
Conclusion
This paper employs the LCA method to evaluate the environmental impact of five commonly-used pipe materials in DWDNs, including polyvinyl chloride (PVC), high-density polyethylene (HDPE), ductile iron (DI), fibrocement, and steel. The system boundaries encompass the processes and activities carried out in the three phases of production, transportation, and installation. In this study, a part of the Tehran DWDN has been considered as the case study. The results show that 128 kg CO2 eq is
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