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Article

Study on Carbon Emissions from an Urban Water System Based on a Life Cycle Assessment: A Case Study of a Typical Multi-Water County in China’s River Network Plain

by
Zihan Gui
,
Heshuai Qi
and
Shiwu Wang
*
Zhejiang Institute of Hydraulics and Estuary (Zhejiang Institute of Marine Planning and Design), Hangzhou 310020, China
*
Author to whom correspondence should be addressed.
Sustainability 2024, 16(5), 1748; https://doi.org/10.3390/su16051748
Submission received: 10 January 2024 / Revised: 13 February 2024 / Accepted: 19 February 2024 / Published: 21 February 2024
Browse Figures
Figure 1
<p>Topographic map of Yiwu City.</p> "> Figure 2
<p>Three kinds of water supply systems in Yiwu City.</p> "> Figure 3
<p>Research framework for carbon footprint assessment throughout the lifecycle of urban water systems.</p> "> Figure 4
<p>Carbon emissions from the urban water system at different phases in the study area.</p> "> Figure 5
<p>The carbon emission intensity for each stage and link of the multi-source urban water system. ((<b>a</b>) Quality water subsystem; (<b>b</b>) general water subsystem; and (<b>c</b>) reclaimed water subsystem).</p> "> Figure 6
<p>Comparison of water system carbon emissions in the study area under different scenarios.</p> "> Figure 7
<p>Comparison of carbon emission intensity of different links of urban water in the study area.</p> ">
Review Reports Versions Notes

Abstract

:
Revealing the inherent relationship between urban water systems and carbon emissions has important theoretical and practical significance for promoting “water conservation and carbon reduction” in cities. This study utilizes the 2021 social water cycle statistical data of Yiwu City to quantify the carbon emissions of urban water systems. It analyzes the “water–carbon” related characteristics and carbon emission intensities under different water sources and stages and explores the carbon reduction potential of urban water systems under different scenarios. The results show that the operational phase is the main contributor to the carbon emissions of the urban water system in the research area, accounting for approximately 86% of the total carbon emissions. Over the entire process, the carbon emissions from the water supply and drainage stages are the largest, accounting for 39% and 31% of the total carbon emissions, respectively. In terms of carbon emission intensity, the carbon footprint of the water cycling process using reclaimed water as the water source is higher than that of high-quality water and conventional water sources. This is primarily due to the significantly higher carbon emission intensity in the reclaimed water phase compared with the other phases. In terms of influencing factors, the differences in the “water–carbon” correlation characteristics of different links in the water system in the research area are mainly affected by changes in urban water consumption, water treatment methods and processes, and other related factors. For the coordinated development of “water conservation and carbon reduction” in urban areas, future efforts should focus on improving the reuse rate of reclaimed water in urban life and industry, reducing the leakage rate of water distribution networks, and enhancing water treatment processes. These measures aim to increase water efficiency in urban water systems and reduce carbon emissions.

1. Introduction

Global climate change not only affects the entire ecosystem but also has certain impacts on the socio-economic system [1]. Since human society entered the industrial era, the emissions of greenhouse gases, mainly carbon dioxide (CO2), have increased rapidly [2]. The increase in carbon concentration enhances the atmosphere’s ability to trap heat, resulting in a stronger greenhouse effect and a close connection between greenhouse gas emissions and climate change. The catastrophic impacts of adverse climate change have driven global efforts to reduce carbon emissions, leading to a global consensus to mitigate climate change through carbon emission reductions. Cities are the most concentrated areas of human economic activities and the regions with the highest concentration of water and energy resource consumption. Their greenhouse gas emissions account for over 70% of the global total [3]. Urban water systems, accounting for over 50% of the total carbon emissions from urban infrastructure operations, constitute a significant source of carbon emissions that cannot be underestimated [4]. Therefore, seeking solutions for carbon reduction in cities is crucial for mitigating global climate change. With the continuous development of cities, human exploitation and utilization of water resources are also intensifying, leading to increased energy consumption and continuous growth of carbon emissions from urban water systems [5]. In this context, it is necessary to clarify the carbon emission characteristics of the entire process of urban water system operation and the carbon emission reduction potential of different links, thus revealing the internal relationship mechanism between the water cycle process and its associated energy consumption and carbon emissions in urban water systems, which will help formulate differentiated carbon emission reduction measures according to the characteristics of urban water system carbon emissions. This will provide a reference for the economical utilization of water and energy resources and the low-carbon operation of urban water systems.
In recent years, domestic and international scholars have discussed carbon emissions from urban water systems from various perspectives, which can be broadly categorized into three types. The first type is carbon emissions of national or urban water systems and various industries, such as Melbourne [6], Mexico City [7], Zhengzhou [8], and other urban water systems. The second type is the study of carbon emission from the sub-links of urban water systems, such as rainwater systems [9], seawater desalination [10], sewage treatment [11], sewage reuse [12], etc. The third type is the assessment of individual carbon emissions, such as the accounting of energy consumption and carbon emissions in each link from the perspective of the whole life cycle of large stadiums [13]. In addition, scenario simulations of carbon emissions from water systems have also become a hot research topic [14]. Some scholars have used methods such as carbon emission factor assessment [15], input–output analysis [16], material flow analysis [17], life cycle assessment [18], and system dynamics [19] to simulate and predict carbon emissions from water systems. These methods provide theoretical and practical guidance for optimizing urban water resource management and achieving low-carbon management.
In China, with the rapid economic expansion and industrialization, the energy used for water conveyance, treatment, and distribution processes is increasing significantly [20]. The shift to energy-intensive water use could have a measurable impact on future energy demand and carbon emissions and thus, it is gradually gaining public attention. However, few analyses have been performed to quantify the lifecycle and whole process of carbon emissions from urban water systems to establish benchmarks for today’s conditions. Most of the current studies focus on a certain stage or a certain link in the urban water system, and the benchmarks and accounting boundaries of each study are inconsistent, resulting in a lack of continuity and comparability. Therefore, our study takes Yiwu City as an example and calculates the carbon emissions from the urban water system throughout its lifecycle and the whole process. We compare the energy consumption and carbon emission characteristics of different water sources, links, and processes and explore the main influencing factors of the total carbon emissions and intensity changes and the potential for carbon reduction. This study provides a reference for optimizing urban water system planning, improving the ecological benefits of water system operations, effectively promoting the construction of low-carbon cities, and achieving carbon neutrality goals.

2. Overview of the Study Area

2.1. Regional Profile

Yiwu City is a county-level city located in the eastern inland region of China. It has a north–south length of 58.18 km and an east–west width of 44.41 km, covering a total area of 1105 km2. It enjoys a favorable geographical position and is situated at the geographic center of Zhejiang Province, China (Figure 1). Yiwu City is located on the edge of a basin, surrounded by mountains to the south, east, and north. The elevations of the hills and mountains within the city range mainly from 100 to 500 m, with a general trend of higher elevations in the northeast and lower elevations in the southwest. Approximately 49% of the area is covered by mountainous terrain, while plains and hills account for about 41%, and water bodies occupy nearly 10% of the total area. The main urban area of Yiwu is in the plain of the Yiwu River basin.
Yiwu City is one of the economically developed areas in Zhejiang Province, China. The city enjoys convenient transportation with a three-dimensional transportation network consisting of roads, railways, and air travel that radiates to all parts of the country. This has elevated the commercial status of Yiwu City, attracting more national and international economic and trade activities to the city and driving rapid economic growth. Yiwu City is home to China’s largest small commodity market, with a well-balanced industrial structure where the secondary and tertiary industries are developing rapidly. Preliminary calculations show that in 2020, the city’s gross domestic product reached CNY 148.56 billion, with growth rates surpassing those of the country and Zhejiang Province by 1.7 and 0.4 percentage points, respectively.
By 2020, the permanent population of Yiwu City exceeded 1.85 million. However, the per capita water resources in Yiwu City are only 433 m3, which is a quarter of the average level in Zhejiang Province. From the perspective of water resources, the current water resources in Yiwu can only support the urban development scale of a population of around 1.5 million, indicating a significant mismatch between the water resource guarantee capacity and urban development. In response to this challenge, Yiwu City has vigorously promoted the construction of a differentiated water supply system in the past decade, opening a new era of water conservation from the aspects of “increasing sources” and “reducing consumption”.

2.2. Water Supply System Overview

At present, there are three sets of water supply systems in Yiwu: a high-quality water system with reservoir water as the source, a general water system with Yiwu River as the source, and a low-quality water system with reclaimed water as the source (Figure 2). The main sources of high-quality water are domestic reservoirs and water diversion projects outside the region, and raw water is supplied to domestic and industrial users after treatment by water plants. The main water source of general water is the Yiwu River. Due to the poor water quality of the Yiwu River, general water is mainly supplied to general industrial users and ecological users through industrial water plants and recycled water plants. The main source of reclaimed water is the tailwater of the sewage treatment plant, which is supplied to general industrial users and ecological users after advanced treatment by the reclaimed water plant.

2.3. Sources of Carbon Emissions from Water Systems

The urban water system is formed by a series of water facilities connected in sequence, and thus, its entire lifecycle refers to the complete process of all water facilities in the system from the construction stage to decommissioning. The full lifecycle of the urban water system encompasses a series of activities related to the development, allocation, utilization, and protection of water resources, generally summarized as water intake, water supply, and drainage. Carbon emissions during the full lifecycle of the urban water system originate from three aspects: the consumption of materials and construction during the construction of facilities and equipment in the urban water system, the construction and transportation consumption during the decommissioning process, and various types direct or indirect energy consumption related to water during the operation process.
During the construction stage, carbon emissions mainly focus on the construction of water intake projects, water supply projects, drainage projects, and reuse projects, including reservoirs, pumping stations, water plants, water supply and drainage networks, sewage treatment plants, and recycled water treatment plants. The main sources of carbon emissions during this stage are the direct emissions of fossil fuels burned by equipment during the construction process, as well as indirect emissions from electricity consumption, building materials, and transportation.
The operation stage includes the entire process from the formal commissioning of facilities to the end of operation. The main source of carbon emissions during this stage is the emissions resulting from the consumption of electricity or thermal energy during the operation process.
During the decommissioning stage, carbon emissions are mainly related to the scrapped buildings constructed in the construction stage. Similar to the construction stage, the main sources of carbon emissions are the direct or indirect emissions of fossil fuels and electricity consumed during the demolition process of buildings or equipment engineering.

3. Methods

Based on the main sources of carbon emissions during the full lifecycle and stages of the urban water system, the carbon emissions for the construction stage, operation stage, and decommissioning stage were calculated separately and then aggregated to obtain the total carbon emissions of the urban water system in the study area. The calculation formula is as follows:
C E T = C E C o n + C E O p e + C E D e m
where C E T represents the total carbon emissions of urban water systems, kg. C E C o n represents total carbon emissions during the construction phase, kg. C E O p e represents the total carbon emissions during the operation phase, kg. C E D e m represents the total carbon emissions during the dismantling phase, kg.

3.1. Construction Phase

Based on the carbon emission sources, the carbon emissions during the construction stage mainly consist of three parts: material and equipment production, transportation processes, and construction processes. Therefore, the calculation formula for the construction stage is as follows:
C E C o n = C E m a + C E t r + C E c o
where C E m a represents the carbon emissions during the material and equipment production process, kg. C E t r represents the carbon emissions generated during the transportation of construction materials, kg. C E c o represents the carbon emissions generated during the construction phase, kg.
Due to the complexity and temporality of the data, typically only the material data inventory is relatively complete. According to the existing literature studies, material consumption is the largest proportion among the three stages, accounting for over 85% [21,22]. Therefore, when there is insufficient information on construction and transportation inventories, carbon emissions during the construction process of water engineering can be estimated using the proportion of carbon emissions from the material consumption stage. Therefore, the total carbon emissions during the construction stage in Yiwu City can be estimated using the carbon emissions from the material and equipment production process. The calculation formula is as follows:
C E m a = ∑ n C E S n · T n
where C E S n represents the carbon emission factor for the n type of construction material, kgCO2eq/t. T n represents the quantity of the n type of material used, t/d.
According to Figure 3, the urban water system in Yiwu City mainly includes hydraulic engineering and facilities such as reservoirs, water diversion projects, pumping stations, water plants, water distribution networks, sewage treatment plants, and reclaimed water treatment plants. Based on the above formula, and considering the carbon emission intensity parameters generated from the materials, transportation, and construction of different projects, along with the construction inventory of hydraulic engineering projects or facilities, the total carbon emissions during the construction stage for each hydraulic engineering project and facility can be calculated separately.
The hydraulic engineering projects and facilities within urban water systems are unique and distinct. Each hydraulic engineering project or facility has its own construction plan, materials, and service life. From a temporal perspective, the “cradle-to-grave” lifecycle of different hydraulic facilities varies. For example, according to the “Code for Rational Service Life and Durability Design of Water Conservancy and Hydropower Engineering in China,” the operational lifespan of reservoirs is approximately 50 years, while the operational lifespan of water supply facilities in water plants, sewage treatment and reclaimed water treatment facilities, and water distribution networks is around 20 years, and that of pumping station facilities is 10 years. After separately calculating each hydraulic engineering project and facility, due to the varying lengths of their service lives, the carbon emissions within each stage cannot be directly aggregated. From a spatial perspective, if only the total carbon emissions of the overall system are evaluated, the different stages will not be comparable. To compare and analyze the carbon emissions of different water sources and stages, this study averaged the total lifecycle carbon emissions of each hydraulic engineering project and facility on an annual scale more accurately. The evaluation indicator was the annual carbon emissions generated per unit of water product produced or delivered, known as the engineering carbon emission intensity, measured in kgCO2eq/m3/a. The calculation formula is as follows:
C E S s = C E C o n , s N s · Q s
where C E S s represents the carbon emission intensity of the s-th hydraulic engineering project, measured in kgCO2eq/m3/a. C E C o n , s represents the carbon emissions during the construction phase of the s-th hydraulic engineering project, measured in kg. N s represents the operational lifespan of the s-th hydraulic engineering project, measured in years. Q s represents the maximum capacity of the s-th hydraulic engineering project (e.g., water supply capacity for water source projects, water treatment capacity for water plant projects, and flow capacity for pipeline networks).
The calculation results of carbon emissions and intensity during the construction phase of Yiwu City’s urban water system are as follows (Table 1):

3.2. Operational Phase

The total carbon emissions during the operational phase of an urban water system are the sum of carbon emissions from the water intake, water supply, wastewater discharge, and reclaimed water utilization stages. This can be expressed as:
C E O p e = C E i n t a k e + C E s u p p l y + C E d r a i n a g e + C E r e u s e
where C E i n t a k e represents the total carbon emissions from the water intake link, kg. C E s u p p l y represents the total carbon emissions from the water supply link, kg. C E d r a i n a g e represents the total carbon emissions from the drainage link, kg. C E r e u s e represents the total carbon emissions from the reuse link, kg.

3.2.1. Water Intake Link

In Yiwu City, there are three main water intake methods: reservoir storage, river pumping, and external water diversion. Carbon emissions are calculated based on the energy consumption parameters associated with each water intake method.
(1)
Reservoir storage. Carbon emissions mainly come from the energy consumption of operating and maintaining the infrastructure of the reservoir, as well as the energy consumption associated with water head loss during transmission. According to reference [23], the energy intensity of the reservoir storage process generally does not vary by region. This study used a value of 0.14 kWh/m3 to calculate the energy consumption carbon emissions for Yiwu City’s reservoir storage water supply. The specific calculation formula is as follows:
C E x = W x · E F d · Q x
where C E x represents the total carbon emissions caused by reservoir water intake, kg; W x represents the energy intensity during reservoir water supply, with a value of 0.14 kWh/m3; E F d represents the regional electricity emission factor, with a value of 0.7921 kgCO2eq/kWh (obtained from “General Rules for Comprehensive Energy Consumption Calculation” (GB/T 2589-2008) [24] and “Guidelines for Provincial-level Greenhouse Gas Inventory Compilation” for the East China region; the same applies to subsequent values); and Q x represents the water intake volume from the reservoir, t.
(2)
River pumping. The pumping process mainly involves converting electrical energy into the energy needed to pump water using pumping stations. The energy consumption and resulting carbon emissions depend on the pumping height, pump efficiency, and pumping volume. Yiwu City has four pumping stations, and the carbon emissions associated with river pumping were calculated based on the parameters of each station. The calculation formula is as follows:
C S p = ∑ i = 1 n g · h i · ρ · Q i 3.6 × 10 6 η i · E F d
where C S p represents the carbon emissions generated during the river pumping water supply process, kg; h i represents the actual pumping height for the i-th group, meters; ρ represents the density of water, kg/m3, with a value of 1000 kg/m3; η i represents the efficiency of the pump unit for the i-th group; and n represents the total number of different pump units with varying efficiencies.
(3)
External water diversion. Any inter-basin water diversion project consumes energy during its construction, operation, maintenance, and water transportation phases, resulting in carbon emissions. Yiwu City has two external water diversion projects: Dongyang Reservoir Water Diversion Project and Pujiang Water Plant Water Diversion Project. The total water supply volume for both projects is 90 million cubic meters per year. Since there are no specific energy consumption data available for the water diversion projects at present, a rough estimation can be made using the reference formula from the literature [25]:
C S t = ∑ i = 1 n W t · l i + g · h i · ρ 3.6 × 10 6 η i · E F d · Q t
where C S t represents the carbon emissions generated during the water supply process of the external water diversion project, kg, and W t is the long-distance water diversion energy intensity, kWh/(m3·km). In the absence of data, a value of 9.73 × 10−6 kWh/(m3·km) can be used as a reference. l i is the transport distance for the i-th consecutive ascending segment of the long-distance water diversion project, km; g is the acceleration due to gravity, 9.8 m/s2; h i is the actual pumping height for the i-th consecutive ascending segment of the long-distance water diversion project, meters; ρ is the density of water, kg/m3, with a value of 1000 kg/m3; η i is the efficiency of the pump unit for the i-th consecutive ascending segment of the long-distance water diversion project, typically ranging from 75% to 80%; Q t and is the water supply volume for the water diversion project, m3.

3.2.2. Water Supply Link

The main carbon emissions in this process come from the energy consumption of water treatment and distribution in urban water plants. The calculation formula is as follows:
C E s u p p l y = W z + W d · E F d · Q s
where W z and W d represent the energy intensity of the water treatment and distribution processes. Due to the lack of energy consumption data of the water plant in the study area, the total water supply, water supply, and corresponding energy consumption values of the national tap water treatment were calculated by the China Urban Water Supply Association to approximate the energy intensity values of the water treatment and water distribution processes in the study area. (According to public statistics, China’s waterworks treated 667 million m3 of raw water, with a total energy consumption of 20,700 GWh, and the energy intensity of raw water treatment was 0.31 kWh/m3. The total energy consumption of water supply was 13,300 GWh, and the energy intensity of water distribution was 0.20 kWh/m3.) Q s represents the water supply volume, t.

3.2.3. Drainage Link

This stage includes the processes of sewage discharge, collection, and treatment. Since sewage discharge is generally achieved by gravity flow and does not generate energy consumption or carbon emissions, the carbon emissions in the discharge stage mainly come from the energy consumption in sewage collection and treatment processes. Based on the investigation of the sewage treatment plants in the study area, reference data such as sewage treatment processes and types of energy consumption [26] are used to calculate the energy consumption and carbon emissions of sewage treatment in the study area. The calculation formula is as follows:
C E d r a i n a g e = ∑ t W t · E F d · Q t
where W t represents the energy intensity in the collection and treatment process of sewage, kWh/m3 (the energy intensity and emissions from each sewage treatment plant in Yiwu City are shown in Table 2) and Q t represents the sewage treatment volume, t.

3.2.4. Water Reuse Link

The recycling stage involves the advanced treatment of wastewater from urban sewage treatment plants after secondary treatment or meeting the secondary treatment standards. This process aims to produce recycled water that meets the quality requirements for reuse. Carbon emissions in this stage result from the energy-intensive treatment of the effluent from the sewage treatment plant. The calculation is based on the average energy intensity of the local water recycling plants and can be expressed using the following formula:
C E r e u s e = W r · E F d · Q r
where W r represents the energy intensity during the advanced treatment of recycled water. Based on the energy consumption data from the reclaimed water plants in the study area, the value is taken as 1.14 kWh/m3. Q r represents the amount of recycled water used, t.

3.3. Demolition Phase

Currently, there is limited research on carbon emission accounting during the demolition process of urban water system-related buildings such as water treatment plants and wastewater treatment plants. Real cases and actual data are largely lacking, and most estimates are based on carbon emissions during the construction phase, expressed as percentages. In this study, the carbon emission accounting results during the demolition phase of water treatment plants, wastewater treatment plants, and reclaimed water plants were based on the existing literature research, assuming that the carbon accounting in this process was 90% of that in the construction phase [27]. Large-scale hydraulic structures such as reservoirs and water diversion projects (tunnels) have longer service lives, and the main structures are not demolished after being decommissioned. Therefore, carbon emissions from this process are not considered.

4. Results

4.1. Carbon Emission Analysis of Urban Water Systems

The annual average carbon emissions from the urban water system in the study area for its entire lifecycle is 20.48 × 104 tons. The carbon emissions during the operational phase amount to 17.53 × 104 tons, accounting for 86% of the total carbon emissions (as shown in Figure 4). The carbon emissions during the operational phase are significantly higher than those during the construction and dismantling phases. This indicates that although water projects involve a large initial investment of materials and energy during the construction phase, it is the ongoing operation and maintenance of these projects that contribute significantly to the carbon emissions in urban water systems on an annual scale. The carbon emissions during the construction phase are 1.92 × 104 tons in total, with the largest amount coming from the water intake stage. This is because the construction of reservoirs and water diversion projects requires many high-emission materials such as steel bars and cement, resulting in significant carbon emissions. The substantial carbon emissions resulting from the large-scale construction of water projects are not the primary focus of carbon reduction. Increasing the service life of water projects can indirectly achieve the goal of carbon reduction. In the operational phase, the carbon emissions from the water supply stage account for the largest portion, at 43% of the total operational emissions. This is due to the significant water supply volume in the study area and the relatively high energy intensity associated with this stage, resulting in substantial carbon emissions. The carbon emissions in the recycling stage are the lowest, as the amount of recycled water is relatively small, accounting for only 0.01‰ of the water supply volume. The carbon emissions from this stage constitute only 2% of the total carbon emissions during the operational phase. This also indicates that although the energy intensity in the recycling stage is much higher than in the water supply stage, the disparity in water consumption leads to such differences. In the future, an increase in the utilization rate of recycled water will reduce the water intake and supply volume, consequently reducing carbon emissions.

4.2. Analysis of Carbon Footprint Intensity in Multi-Source Water Supply

According to the generalized results of the urban water system in Figure 2, the carbon emission intensities of different subsystems in Yiwu City were calculated. Taking the status of the water supply target as an example, the carbon emission intensity results are shown in Figure 5. The overall carbon footprint intensity of the urban high-quality water subsystem is 0.90 kgCO2eq/m3, which means that supplying 1 m3 of high-quality water to the distribution network users (residential or industrial users) will result in the emission of 0.90 kg of CO2. The carbon emission proportions of the water intake, water supply, and wastewater discharge stages in the urban high-quality water subsystem are approximately 2:5:3. During the operational phase, the relatively high energy consumption in the water treatment process leads to a significant contribution of carbon emission intensity in the water supply stage. The overall carbon footprint intensity of the urban general water subsystem in the study area is 0.78 kgCO2eq/m3, indicating that supplying 1 m3 of general water to the distribution network users (general industrial users) will result in the emission of 0.78 kg of CO2. The operational phase accounts for the highest carbon emission intensity, constituting 86% of the overall carbon emission intensity. The carbon emission intensity in the water supply stage of the general water subsystem is reduced by 0.08 kgCO2eq/m3 compared with that of the high-quality water subsystem. This is because industrial water plants have lower water quality requirements for their supply, and the treatment processes are relatively simpler compared with those in conventional water plants. As a result, the energy consumption during the water treatment process is lower, leading to a smaller carbon emission intensity. The carbon emission intensity of the reclaimed water cycle for users such as industrial pipeline networks is 1.38 kgCO2eq/m3, meaning that supplying 1 m3 of reclaimed water to the distribution network users (general industrial users) will result in the emission of 1.38 kg of CO2. The operational phase accounts for the highest carbon emission intensity, constituting 95% of the overall carbon emission intensity. Although the carbon emission intensity of the water intake stage in the low-quality water subsystem is reduced compared with that of the high-quality water subsystem, due to the construction and operation of water intake facilities, the energy consumption during reclaimed water treatment in the water supply stage is much higher than that during conventional water treatment. This leads to a higher carbon emission intensity for the reclaimed water subsystem compared with the high-quality water subsystem. Although the carbon emission intensity in the construction and demolition stages for the reclaimed water plant is lower than that for the industrial water plant in Yiwu City, the difference in energy consumption during the water treatment process during the operational phase results in a higher carbon emission intensity for the reclaimed water subsystem.
Due to the different urban water circulation pathways, the carbon emission intensity varies for different water sources supplied to different users (domestic, industrial, agricultural, ecological, etc.). For domestic users with high water quality requirements, the carbon emission intensities for high-quality water, general water, and reclaimed water are 0.90 kgCO2eq/m3, 1.50 kg CO2eq/m3, and 1.38 CO2eq/m3, respectively. Due to the poor quality of the Yiwu River water and reclaimed water, complex treatment processes are required to meet water quality standards, resulting in higher carbon emission intensity. Additionally, since the reclaimed water subsystem lacks a water intake stage, it has a lower carbon emission intensity. For industrial users, the carbon emission intensities for high-quality water, general water, and reclaimed water are 0.90 kgCO2eq/m3, 0.78 kg CO2eq/m3, and 1.38 kgCO2eq/m3, respectively. In Yiwu City, there is an industrial water plant catering to industrial needs, with lower water quality requirements compared with domestic water. Therefore, the carbon emission intensity of the general water subsystem is lower than that for domestic users. For agricultural and ecological users, according to the system generalization results, the urban water circulation pathways only involve the water intake stage. Thus, the carbon emission intensities for high-quality water, general water, and reclaimed water are 0.15 kgCO2eq/m3, 0.12 kgCO2eq/m3, and 0.12 kgCO2eq/m3, respectively.

4.3. Analysis of Carbon Emission Reduction Potential

4.3.1. Scenario Setting

Scenario exploration is crucial for analyzing carbon emission reductions in urban water systems under different operational modes. In this study, three different water system operation scenarios were primarily set as follows:
(1)
Baseline scenario. The baseline scenario mainly predicts the carbon emissions from urban water systems in 2030 based on the development trends of water resource utilization intensity in water intake, water supply, and wastewater treatment stages under the natural operation state of the study area’s urban water system over the years. Based on the development indicators of the population, industry, agriculture, and other sectors at different levels in the study area, as well as water consumption quotas, and using statistical data on total water consumption, water supply, and water usage over the years, the water demand for each sector in 2030 is predicted (as shown in Table 3). The total urban water demand can reach 3.92 × 108 m3. If the water supply pattern in 2030 remains basically the same as the current situation. Among them, all of the domestic water supply will be provided by high-quality water sources (reservoir water and water from outside the area), 17% of the industrial water supply will come from river water, agricultural water supply will be provided by low-grade water, and the ecological water supply will be provided by reclaimed water. The expansion of urban scale and population growth in the future determines the increase in water consumption and wastewater discharge for production and daily life. Therefore, based on the proportional relationship between water supply and wastewater treatment volume in 2021, the projected wastewater treatment volume for 2030 is estimated to be 2.66 × 108 m3. The energy intensity of wastewater treatment (0.32 kWh/m3) and reclaimed water treatment (1.14 kWh/m3) is assumed to remain at the 2021 level.
(2)
Moderate low-carbon scenario. Based on the Yiwu City water resources planning document, the substitution rate of low-quality water is expected to increase for various sectors, and the utilization rate of unconventional water resources in the urban area is expected to reach 30% by 2030. Assuming that the water supply volume in Yiwu City remains unchanged according to the baseline scenario in 2030, with the upgrading of future raw water, wastewater, and reclaimed water treatment equipment and technology, the energy intensity of the water production process is expected to decrease to 0.29 kWh/m3, the energy intensity of wastewater treatment can reach the average level of cities in East China (0.22 kWh/m3) [28], and the energy intensity of reclaimed water reuse can reach the typical level of municipal water treatment in the United States (0.43 kWh/m3) [29].
(3)
Highly low-carbon scenario. This scenario is mainly set based on the moderate low-carbon scenario. It assumes that the actual water consumption in the study area in 2030 exceeds the annual total control target by 19%, and the water supply network leakage rate can reach the domestic average level (7.6%). For the wastewater treatment process, further optimization of the wastewater treatment equipment is assumed, leading to a decrease in the energy intensity of wastewater treatment to the average level of cities in South China (0.194 kWh/m3) [28].

4.3.2. Comprehensive Evaluation

According to the baseline scenario, the predicted carbon emissions of the water system in the study area in 2030 are 29.65 × 104 t, which is an increase of 9.93 × 104 t compared with 2021 (Figure 6). The main reason is the continuous expansion of urban-scale and socioeconomic development in the study area in recent years, which has led to a year-by-year increase in urban water demand. In addition, in 2023, Yiwu City was selected as one of the first batch of national typical areas for pilot projects in reclaimed water utilization, and the amount of reclaimed water reuse has been increasing year by year. The utilization of unconventional water has risen from 1.91 million cubic meters in the base year to 43.49 million cubic meters. At the same time, the energy intensity of the water supply process and reclaimed water utilization process is relatively high, leading to a year-on-year increase in carbon emissions from the urban water system. In terms of carbon emission growth rate, apart from the reclaimed water utilization process, both the water supply and wastewater sectors in Yiwu City are experiencing rapid growth. In the baseline scenario, the carbon emissions from these two systems in 2030 are approximately 1.5 times and 1.4 times higher than those in 2021, respectively. The significant increase in water supply volume and reclaimed water reuse leads to the growth in carbon emissions in these two sectors. As for the rapid growth in carbon emissions in the wastewater sector, it is mainly due to the fast annual increase in urban sewage discharge volume in Yiwu City, coupled with a continuous rise in the urban sewage treatment rate.
In 2021, the current supply of high-quality water in the study area was 2.79 × 108 m3, and according to the predicted trend in each industry sector (baseline scenario), the total urban supply is projected to reach 3.92 × 108 m3 by 2030. Furthermore, in 2023, as one of the first selected national pilot cities for reclaimed water allocation in China, the study area witnessed a gradual increase in the volume of reclaimed water reuse. In 2021, the volume of reclaimed water treatment and reuse was relatively low, reaching only 1.91 million m3. With the expansion of reclaimed water reuse initiatives, by 2030 (baseline scenario), the urban unconventional water utilization is projected to reach 43.49 million m3. At the same time, the high unit energy intensity factors in these two links together will lead to a year-by-year increase in carbon emissions from urban water systems. Furthermore, in terms of the carbon emission growth rate, the supply, drainage, and reclaimed water utilization sectors in the study area have shown a faster growth rate. The carbon emissions from these two systems in 2030 (baseline scenario) are projected to be approximately 1.5 times and 1.4 times the levels of 2021, respectively. Among them, the reclaimed water utilization sector has the fastest growth rate of carbon emissions, followed by the water supply and drainage sectors. In addition to the significant increase in water supply and reclaimed water reuse, the rapid growth of carbon emissions in the drainage sector is due to the annual increase in urban wastewater discharge and the continuous improvement of urban wastewater treatment rates.
In the future operation of urban water systems, a series of water-saving and energy-saving measures can be implemented to achieve carbon emission reduction scenarios for water systems. In 2030, the carbon emissions from urban water systems under the moderate low-carbon scenario and the highly low-carbon scenario are projected to be 23.62 × 104 tons and 18.31 × 104 tons, respectively. Moreover, the carbon emission reductions compared with the baseline scenario are 6.03 × 104 tons and 11.34 × 104 tons, respectively. The highly low-carbon scenario has greater potential for carbon emission reduction in the operation of urban water systems, with carbon emissions even lower than the total carbon emissions generated by urban water systems in 2021 (20.48 × 104 tons). By further strengthening planning and policy constraints on the development and utilization of urban water and energy resources, focusing on improving the efficiency and technological level of water and energy utilization in various stages of urban water system operation, particularly emphasizing reclaimed water treatment technology and efficiency enhancement, the carbon emission reduction effect of the water system becomes more pronounced.
Table 4 presents the carbon emission reduction and contribution in different sectors under different scenarios. From the table, it can be observed that the water supply sector has the greatest carbon emission reduction potential in Yiwu City’s water system. Compared with the baseline scenario, the moderate low-carbon scenario and highly low-carbon scenario contribute to carbon emission reductions of 41.5% and 42.0%, respectively. In the water supply link, the moderate low-carbon scenario reduces energy intensity, while the highly low-carbon scenario decreases the total water supply volume. The carbon emission reduction potential in the water withdrawal phase is the smallest, which aligns with the previous analysis results, indicating that large-scale water source projects do not significantly contribute to carbon emissions. Due to the significantly higher energy intensity in the reclaimed water treatment process compared with other phases, the carbon emissions increase as the rate of reclaimed water utilization rises. According to the table, the main reason for the significant carbon emission reduction potential of the urban water system operation mode in the highly low-carbon scenario is, on the one hand, due to the water quantity factor. Due to the implementation of water-saving measures and the promotion of reclaimed water reuse, the urban water system has significantly reduced its intake of fresh water, resulting in a decrease in water consumption in subsequent stages such as water supply from water plants and wastewater discharge from treatment plants. On the other hand, it is due to the energy consumption factor. With significant improvements in water treatment processes for water plants, wastewater treatment processes, and reclaimed water treatment processes, the energy intensity of these previously high-energy-consuming stages has decreased, resulting in a reduction in carbon emissions.

4.4. Rationality Analysis

During the operational phase of the urban water system in the study area, there are significant differences in carbon emissions intensity among different links. The ranking of carbon emission intensity from high to low is as follows: water reuse > drainage > raw water treatment > tap water distribution > water diversion > water storage > river water lifting. Among them, the energy consumption of the water reuse process is the highest, at 0.90 kgCO2eq/t, which is much higher than that of other processes (Figure 7).
Currently, there is relatively limited direct research on the “water–carbon” nexus, with more research results in China focusing on the “water–energy” relationship. Energy intensity is identified as a crucial factor influencing carbon emissions across different sections of urban water systems. In comparison with existing studies, the energy intensity values determined in this study fall within the range of values reported in previous research [30]. In a study by Yu et al. [26] that analyzed the water system of Zhengzhou City, China, in terms of “water–energy–carbon”, significant differences were noted in the water withdrawal process (attributed to most water sources in Zhengzhou City being groundwater, leading to higher energy consumption during groundwater extraction), while the energy intensity in other sections was similar to that of this study. Zhu et al. [5] investigated the overall energy consumption in the social water cycle in the Beijing–Tianjin–Hebei region, showing similarities in the energy consumption ratio between the water withdrawal and supply phases compared to this study. Xiang [23] conducted a study on the “water–energy” relationship in the existing social water cycle in China, with energy intensity values for each phase closely aligning with those in this study. He [31] researched energy consumption in the social water cycle process in Beijing, with energy intensity values in most phases similar to those in this study, except for slightly lower energy consumption in reclaimed water treatment due to advanced processes. Therefore, the energy intensity values determined in this study for the operational phases fall within a reasonable range.

5. Conclusions

Based on the perspective of the “water–carbon” nexus, this study constructs a research framework and method for carbon emission analysis of urban water systems throughout their entire lifecycle, from cradle to grave, in terms of temporal and spatial scales. Using Yiwu City as an example, the carbon footprint intensity of a multi-water source and quality supply system is compared and analyzed, evaluating the status of the carbon footprint of the urban water system. Additionally, utilizing scenario analysis, this study examines the carbon reduction potential of different operational modes and identifies factors that influence carbon emissions in urban water systems.
This research found that 39% of the carbon emissions from urban water systems are attributed to water treatment, transportation, and distribution, while 31% of the carbon emissions are attributed to sewage collection and treatment. From the perspective of the lifecycle of urban water systems, 86% of the carbon emissions originate from the operational phase, while construction activities of the water system only account for 9% of the total lifecycle carbon emissions. Additionally, there are variations in the carbon emissions generated by different water sources supplying different users. From the current water supply situation in Yiwu City, further increasing the use of recycled water can effectively alleviate urban water pressure, but it may lead to a sharp increase in carbon emissions. However, adopting low-carbon intensity treatment technologies in both the drainage and recycled water utilization phases can offset the carbon emission impact caused by the expansion of sewage treatment and recycled water utilization scale. Considering the current proportion of carbon emissions, the greatest carbon emission reduction potential lies in the water supply and drainage processes. Corresponding policies can be proposed to increase the water reuse rate in urban life and industry, reduce the leakage rate of water distribution networks, and strengthen water treatment processes.
The accounting process of urban water systems is closely related to the current water supply situation of the research object. Yiwu City is in a plain river network area with abundant surface water resources and low-lying terrain. Therefore, it mainly relies on surface water supply, and water intake from reservoirs is often in a self-flow state. If a study were to focus on mountainous or water-deficient areas, the water supply patterns would differ significantly. Hence, this research is only applicable to regions with similar topography and can serve as a reference in those areas. Analyzing the influencing factors of carbon emissions from urban water systems from the perspective of the “water–carbon” correlation is essentially exploring the factors affecting the changes in “water” and “energy” in the water system. From the perspective of “water”, it is difficult to achieve synergistic development, but from the perspective of “water–energy” synergistic development, measures for “water conservation–carbon reduction” can be proposed. Therefore, finding the balance point between “water conservation–carbon reduction” is the key to the sustainable development of urban water systems and will be a focus of future work.

Author Contributions

Conceptualization, Z.G. and S.W.; data curation, H.Q.; investigation, Z.G. and S.W.; methodology, Z.G.; resources, S.W.; writing—original draft, Z.G. and H.Q.; writing—review and editing, S.W. All authors have read and agreed to the published version of the manuscript.

Funding

This research was jointly supported by the Applied Basic Public Research Program and Natural Science Foundation of Zhejiang Province (No. LZJWY23E090009, No. LGF22E090007), the Key Research and Development Program of Zhejiang Province (No. 2023C03134), the Technology Demonstration Project of Chinese Ministry of Water Resources (No. SF202212), and the Soft Science and Technology Plan Project of Zhejiang Province (No. 2022C35022).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data that support the findings of this study are openly available at www.yw.gov.cn (accessed on 18 February 2024).

Conflicts of Interest

The authors declare no conflicts of interest.

References

  1. Wang, S.; Fang, C.; Wang, Y. Spatiotemporal variations of energy-related CO2 emissions in China and its influencing factors: An empirical analysis based on provincial panel data. Renew. Sustain. Energy Rev. 2016, 55, 505–515. [Google Scholar] [CrossRef]
  2. Clark, P.U.; Shakun, J.D.; Marcott, S.A.; Mix, A.C.; Eby, M.; Kulp, S.; Levermann, A.; Milne, G.A.; Pfister, P.L.; Santer, B.D.; et al. Consequences of twenty-first-century policy for multi-millennial climate and sea-level change. Nat. Clim. Change 2016, 6, 360–369. [Google Scholar] [CrossRef]
  3. IPCC Working Group. I Contribution to the IPCC Fifth Assessment Report, Climate Change 2013: The Physical Science Basis; Cambridge University Press: Cambridge, UK, 2013. [Google Scholar]
  4. Johnson, J.; Zakaria, F.; Nkurunziza, A.G.; Way, C.; Camargo-Valero, M.A.; Evans, B. Whole-system analysis reveals high greenhouse-gas emissions from citywide sanitation in Kampala, Uganda. Commun. Earth Environ. 2022, 3, 80. [Google Scholar] [CrossRef]
  5. Zhu, Y. Research on Evaluation Method of Energy Consumption in the Whole Process of Social Water Cycle. Master’s Thesis, China Institute of Water Resources and Hydropower Research, Beijing, China, 2017. [Google Scholar]
  6. Arora, M.; Aye, L.; Malano, H.; Ngo, T. Water-Energy-GHG emissions accounting for urban water supply: A case study on an urban redevelopment in Melbourne. Water Util. J. 2013, 6, 9–18. [Google Scholar]
  7. Valek, A.M.; Sušnik, J.; Grafakos, S. Quantification of the urban water-energy nexus in México City, México, with an assessment of water-system related carbon emissions. Sci. Total Environ. 2017, 590, 258–268. [Google Scholar] [CrossRef]
  8. Zhao, R.; Yu, J.; Xiao, L.; Sun, J.; Luo, H.; Yang, W.; Chuai, X.; Jiao, S. Carbon emissions of urban water system based on water-engry-carbon nexus. Acta Geogr. Sin. 2021, 76, 3119–3134. (In Chinese) [Google Scholar]
  9. Li, C.; Zheng, T.; Peng, K.; Cheng, W.; Xu, J.; Qiao, J.; Huang, J. Study on carbon emission from rainwater system of sponge city based on whole life cycle method. Environ. Sustain. Dev. 2019, 44, 132–137. (In Chinese) [Google Scholar]
  10. Segurado, R.; Costa, M.; Duić, N.; Carvalho, M. Integrated analysis of energy and water supply in islands. Case study of S. Vicente, Cape Verde. Energy 2015, 92, 639–648. [Google Scholar] [CrossRef]
  11. Pratima, S.; Arun, K.; Cynthia, C.-M. Energy and carbon footprints of sewage treatment methods. J. Environ. Manag. 2016, 165, 22–30. [Google Scholar]
  12. Vieira, A.S.; Ghisi, E. Water-energy nexus in low-income houses in Brazil: The influence of integrated on-site water and sewage management strategies on the energy consumption of water and sewerage services. J. Clean. Prod. 2016, 133, 145–162. [Google Scholar] [CrossRef]
  13. Lu, Y.; Wang, H.; Li, Y.; Pang, M.; Wan, D. Water-energy-carbon footprint correlation model and uncertainty analysis for large-scale sports venues. Environ. Eng. 2022, 40, 165–172. (In Chinese) [Google Scholar]
  14. Qin, H. Urban Water System and Carbon Emission; Science Press: Beijing, China, 2014. [Google Scholar]
  15. Yan, X.; Qiu, D.-Z.; Guo, D.-L.; Qi, X.-H.; Zheng, S.-K.; Cheng, K.; Sun, J.-H.; Liu, J.-W. Emission inventory of greenhouse gas from urban wastewater treatment plants and its temporal and spatial distribution in China. Huanjing Kexue 2018, 39, 1256–1263. [Google Scholar] [PubMed]
  16. Wang, Y.Q.; Zhou, Y.; Zhang, R. A review of the research methods on influencing factors of carbon emissions and carbon footprint. Environ. Eng. 2017, 35, 155–159. [Google Scholar]
  17. Kenway, S.J.; Scheidegger, R.; Larsen, T.A.; Lant, P.; Bader, H.-P. Water-related energy in households: A model designed to understand the current state and simulate possible measures. Energy Build. 2013, 58, 378–389. [Google Scholar] [CrossRef]
  18. Zawartka, P.; Burchart-Korol, D.; Blaut, A. Model of carbon footprint Assessment for the Life cycle of the System of Wastewater collection, transport and treatment. Sci. Rep. 2020, 10, 5799. [Google Scholar] [CrossRef]
  19. Chhipi-Shrestha, G.; Hewage, K.; Sadiq, R. Water–energy–carbon nexus modeling for urban water systems: System dynamics approach. J. Water Resour. Plan. Manag. 2017, 143, 4017016. [Google Scholar] [CrossRef]
  20. Han, G.; Hoff, H. Energy for water utilization in China and policy implications for integrated planning. Int. J. Water Resour. Dev. 2016, 32, 477–494. [Google Scholar]
  21. Li, J.; Zhang, X.; Li, H. Research on carbon emission accounting during sponge city construction and operation in Beijing. Water Resour. Prot. 2023, 39, 86–93. (In Chinese) [Google Scholar]
  22. Huang, Y.; Liu, Y.; Xu, W. Study on life-cycle carbon emissions of water conservancy and hydropower projects: A case study of the Quanmutang Project. J. Tsinghua Univ. (Nat. Sci. Ed.) 2012, 62, 1366–1373. (In Chinese) [Google Scholar]
  23. Xiang, X.; Jia, S. China’s water-energy nexus: Assessment of water-related energy use. Resour. Conserv. Recycl. 2019, 144, 32–38. [Google Scholar] [CrossRef]
  24. GB/T 2589-2008; General Rules for Comprehensive Energy Consumption Calculation. Chinese Standard: Beijing, China, 2008.
  25. Guo, Z.; Zhen, C.; Shui, G.; Shui, P.; Hui, X. Technical Guide for Carbon Accounting and Emission Reduction Path of Urban Water System; China Building and Construction Press: Beijing, China, 2022. [Google Scholar]
  26. Yu, J.; Zhao, R.; Xiao, L.; Zhang, L.; Wang, S.; Chuai, X.; Han, Y.; Jiao, S. Carbon emissions of urban wastewater treatment system based on the “water-energy-carbon” nexus. Resour. Sci. 2020, 42, 1052–1062. (In Chinese) [Google Scholar] [CrossRef]
  27. Zhou, L. Life Cycle Analysis of Environmental Benefits of Urban Sewage Treatment Plants. Master’s Thesis, Chongqing University, Chongqing, China, 2006. [Google Scholar]
  28. Mei, X.; Zhou, Y. Discussion on evaluation criteria of energy conservation level of municipal wastewater treatment plant. Water Supply Drain. 2011, 47, 45–49. (In Chinese) [Google Scholar]
  29. Gu, Y.; Li, Y.; Li, X.; Luo, P.; Wang, H.; Wang, X.; Wu, J.; Li, F. Energy self-sufficient wastewater treatment plants: Feasibilities and challenges. Energy Procedia 2017, 105, 3741–3751. [Google Scholar] [CrossRef]
  30. Zhao, Y.; Chen, W.; Xu, H.; Gao, W.; Cheng, C. Feasibility analysis of energy saving and emission Reduction in the Process of improving the quality and efficiency of urban sewage collection and treatment system. Water Supply Drain. 2019, 55, 42–46. (In Chinese) [Google Scholar]
  31. He, G.; Zhao, Y.; Wang, J.; Zhu, Y.; Jiang, S.; Li, H.; Wang, Q. The effects of urban water cycle on energy consumption in Beijing, China. J. Geogr. Sci. 2019, 29, 959–970. [Google Scholar] [CrossRef]
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Figure 1. Topographic map of Yiwu City.
Figure 1. Topographic map of Yiwu City.
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Figure 2. Three kinds of water supply systems in Yiwu City.
Figure 2. Three kinds of water supply systems in Yiwu City.
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Figure 3. Research framework for carbon footprint assessment throughout the lifecycle of urban water systems.
Figure 3. Research framework for carbon footprint assessment throughout the lifecycle of urban water systems.
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Figure 4. Carbon emissions from the urban water system at different phases in the study area.
Figure 4. Carbon emissions from the urban water system at different phases in the study area.
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Figure 5. The carbon emission intensity for each stage and link of the multi-source urban water system. ((a) Quality water subsystem; (b) general water subsystem; and (c) reclaimed water subsystem).
Figure 5. The carbon emission intensity for each stage and link of the multi-source urban water system. ((a) Quality water subsystem; (b) general water subsystem; and (c) reclaimed water subsystem).
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Figure 6. Comparison of water system carbon emissions in the study area under different scenarios.
Figure 6. Comparison of water system carbon emissions in the study area under different scenarios.
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Figure 7. Comparison of carbon emission intensity of different links of urban water in the study area.
Figure 7. Comparison of carbon emission intensity of different links of urban water in the study area.
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Table 1. Summary of the carbon emissions and intensity during the construction phase of Yiwu City’s urban water system.
Table 1. Summary of the carbon emissions and intensity during the construction phase of Yiwu City’s urban water system.
CategoryTotal Emissions (t)Annual Emissions(t)Emission Intensity(kg CO2eq/m3/a)
Reservoir180,855.083617.100.019
Hengjin Diversion Project90,106.891802.140.036
Pujiang Diversion Project7606.70380.340.035
Water treatment plant72,782.103639.110.014
Pumping station14,7521475.200.008
Water supply pipeline network302,851.5115,142.580.001
Drainage pipeline network279,108.2013,955.410.067
Wastewater treatment plant149,361.607468.080.036
Reclaimed water plant1942.897.140.001
Table 2. Carbon emissions from sewage treatment plants in Yiwu City in 2021.
Table 2. Carbon emissions from sewage treatment plants in Yiwu City in 2021.
NumberTreatment ProcessEmission FactorTreatment Volume
(10,000 t)		Carbon Emissions
(10,000 t)
1Oxidation ditch0.30323360.5607
2A2/O0.26753211.1253
3Oxidation ditch0.30340990.9838
4Oxidation ditch0.30313440.3226
5A2/O0.26718510.3915
6A2/O0.2676100.1290
7A2/O0.26723850.5044
8Oxidation ditch0.3035960.1430
9A/O+SBR0.6194180.2049
Total18,9614.3652
Table 3. Water demand forecast results for various departments in the study area in 2030.
Table 3. Water demand forecast results for various departments in the study area in 2030.
UserResidentIndustryAgricultureEcologyTotal
Volume (million m3)16,75513,0896395298439,223
Table 4. Carbon emission reduction and the carbon emission reduction contribution rate of the water system in Yiwu City under different scenarios.
Table 4. Carbon emission reduction and the carbon emission reduction contribution rate of the water system in Yiwu City under different scenarios.
Carbon Emission Reduction (104 t)Contribution Rate
Moderate
Low-Carbon		High Low-CarbonModerate
Low-Carbon		High Low-Carbon
Intake0.651.3810.8%12.1%
Supply2.504.7641.5%42.0%
Drainage2.113.8135.0%33.6%
Reuse0.771.3912.8%12.3%
Total6.0311.34——
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Gui, Z.; Qi, H.; Wang, S. Study on Carbon Emissions from an Urban Water System Based on a Life Cycle Assessment: A Case Study of a Typical Multi-Water County in China’s River Network Plain. Sustainability 2024, 16, 1748. https://doi.org/10.3390/su16051748

AMA Style

Gui Z, Qi H, Wang S. Study on Carbon Emissions from an Urban Water System Based on a Life Cycle Assessment: A Case Study of a Typical Multi-Water County in China’s River Network Plain. Sustainability. 2024; 16(5):1748. https://doi.org/10.3390/su16051748

Chicago/Turabian Style

Gui, Zihan, Heshuai Qi, and Shiwu Wang. 2024. "Study on Carbon Emissions from an Urban Water System Based on a Life Cycle Assessment: A Case Study of a Typical Multi-Water County in China’s River Network Plain" Sustainability 16, no. 5: 1748. https://doi.org/10.3390/su16051748

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