Life-Cycle Energy Assessment of Alternative Water Supply Systems In California

Publication Number: CEC-500-2005-101
Publication Date: month 2005
PIER Program Area: Energy-Related Environmental Research

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Executive Summary

Introduction

Currently, water available for urban use is insufficient to meet increasing demand, due to scarce alternative sources, competition between regions, inefficient use, and pollution. A report from the U.S. Department of Interior indicates that a water supply crisis is somewhat or highly likely for many urban coastal areas of California by 2025; and the California Department of Water resources has stated that there will be statewide water shortages by 2020. This research evaluated potential alternative water sources in California, including importing, recycling, and desalinating water, to determine the life-cycle energy and environmental effects of those systems.

A strong connection exists between water provision and energy consumption. According to the California Energy Commission, one-third of electricity in California is used by industry, agriculture, and water and wastewater utilities. In the United States, approximately 3% of national electricity consumption was consumed for water and wastewater services. The energy requirements are expected to grow by 33% in the next 20 years. As readily available water sources are depleted, future supply options will likely have higher energy requirements. The environmental effects of electricity production should be considered in water supply decisions.

In addition, the U.S. water supply infrastructure is aging. The U.S. Environmental Protection Agency estimated that hundreds of billions of dollars will be spent nationwide to provide drinking water between 2000 and 2019. The energy and materials consumed and the construction activities needed to install this infrastructure will increase the life-cycle environmental effects of these systems.

Properly planning for the water supply choices while considering the energy and emissions implications requires life-cycle assessment (LCA) of water supply systems facing these choices. LCA helps target energy reduction efforts, identify air emission sources, and assist in water supply planning.

Purpose

The purpose of this study was to develop standard methods and tools to evaluate and quantify the economic, energy, and environmental impacts of alternative water delivery systems for California, and to apply those methods and tools on two case studies, to promote more sustainable water supply planning decisions.

Project Objectives

This project's objective was to conduct an LCA of two municipal water districts, specifically focusing on the economic implications, energy requirements, and air emissions attributable to the energy consumption required for importing, recycling, and desalinating water in California. To ensure that the LCA results represented a comprehensive analysis, researchers conducted the following tasks:

1. Compared economic implications, energy requirements, and air emissions attributable to energy consumption for importing, recycling, and desalinating water, including the energy implications of material consumption and its supply chain.


2. Evaluated the environmental effects, including relative energy consumption and related air emissions, of the different phases of the water supply system (supply, treatment, and distribution), life-cycle phases (construction, operation, maintenance), and specified activities (material production, material delivery, equipment use, and energy production).


3. Evaluated the economic, environmental, and energy implications of separate distribution systems for potable and non-potable water.


4. Conducted a sensitivity analysis to determine parameters and processes in the water supply system that contribute most to energy use and related environmental emissions.

Project Outcomes

To conduct the LCA for two case studies, the authors created a model that quantifies material and energy inputs into water systems, as well as the environmental outputs from those systems. The model has been developed into a computer-based decision-support tool - the Water-Energy Sustainability Tool (WEST) - that assesses the environmental effects of water systems for water utilities considering or currently using these water alternatives. WEST can be used by individual utilities, statewide planners, and policy makers to evaluate the environmental effects of their water supply decisions and incorporate those into the planning process. This analysis also included the energy implications of material consumption and its supply chain, but decommissioning was not included, because of a lack of information.

Using WEST, researchers determined the economic, energy, and air emission effects for the water supplied by two case studies - the Marin Municipal Water District (MMWD), and the City of Oceanside Water Department (OWD). In doing so, they addressed the tasks listed above.

Conclusions

Based on this study, researchers reached the following conclusions:

Imported Water

• The effects of imported water are highly site-specific, depending greatly on the amount of pumping necessary to transport the water from the source to the treatment facility. In the case study systems, most environmental effects occur in the supply phase.


• Treatment of imported water is not a significant contributor to energy demand and resulting emissions for either case study, especially for the MMWD, which uses a simpler treatment process.


• For imported water, the effects of construction and maintenance are smaller for the OWD case study, due to economies of scale: the supply system provides water to the entire region and the effects are widely distributed.

Desalinated Water

• The desalination system air emission factors are the largest for all analyzed substances as well as for energy use, on account of the reverse osmosis (RO) systems in place in the case study utilities.


• Treatment is the largest contributor to the desalination emissions in both MMWD and OWD, because of the energy intensity of RO systems.


• Most of the environmental effects from desalination are due to electricity production, but material production is also important.


• Seawater desalination creates more environmental burden than desalinating brackish groundwater, primarily due to the higher level of energy consumption required.


• The maintenance phase most affects the desalination systems, because the treatment process (e.g., RO membranes, cartridge filters) includes more components that must be replaced regularly.

Recycled Water

• Distribution was the largest global warming potential contributor to both of the recycled water systems studied. The water treatment plants are located near the wastewater treatment plants that supply their water, minimizing the supply phase impacts.


• Treatment was not a significant contributor to environmental effects. Both systems have relatively simple treatment processes (i.e., filtration and disinfection at the MMWD and filtration only at the OWD).


• Because wastewater treatment plants tend to be located at lower elevations, to minimize the energy necessary to collect sewage, distributing recycled water to customers tends to require significant pumping.


• Environmental emissions caused by recycled water system construction and maintenance in the OWD case study are smaller than for the MMWD system. The OWD recycling system is simpler and requires fewer routine inputs.


• The emissions per 100 acre-feet of water production and per length of pipeline for the recycled water distribution systems are higher than for the imported and recycled water distribution systems, due to the scale of the systems. Recycled water systems are typically at least an order of magnitude smaller than potable water systems in terms of both water produced and geographic scale. As a result, when environmental emissions are reported in terms of these parameters, recycled water results are higher.


• Due to the low emissions from the supply and treatment systems, recycled water remains an environmentally competitive and preferable source of water over desalinated water and, in some cases, imported water.

WEST

• The WEST, in its current form, has certain limitations. It does not assess all environmental emissions, account for ecological effects, or quantify environmental impacts such as human toxicity. In addition, it does not allow for analyses of alternative infrastructure choices or energy mixes.


• Generally, utilities and water planners are not aware that it is possible to assess the environmental effects of their systems using LCA; as a result, the analysis is not included in decision-making.

General

• For the MMWD case study, a significant portion of the water supplied to the utility comes from rainfall via reservoirs. Only the considered sources (imported, desalinated, and recycled water) were included in the analysis.


• Two case studies do not provide enough data to obtain complete and detailed understanding of the environmental effects of water supply systems. More case studies are needed for better understanding.


• The case study water costs indicate that desalination is consistently more expensive than importing water. In the MMWD system, recycled water is the most expensive water source; recycled water costs were not available for the OWD system.


• Potable water distribution emission factors varied significantly between the two case studies, because the OWD distribution system is designed to distribute water by gravity, whereas the MMWD must rely on significant pumping.


• For all case studies and alternatives, the operation life-cycle phase uses the most energy and creates the most emissions. The maintenance phase is also important. Construction effects are considerably less significant.


• In all case studies and alternatives, the energy produced for use in water systems creates the most air emissions for all the considered activities. Material production is also a significant contributor. Material delivery and equipment use are negligible in all cases.


• Both parameters of the sensitivity analyses had significant effects on the results. For the change in material service life, the effects were in the construction and maintenance phase. For the energy mix, the effects were primarily in the operation phase.


• The selection of an energy mix can greatly influence the results, according to the sensitivity analysis. The WEST tool should also be improved to allow the comparison of customized energy mixes.


• The results are affected by data quality. Two factors contributed to the difficulties in data collection and potentially to data quality issues: (1) security concerns that prevented full disclosure, and (2) lack of data collection by utilities. Security concerns primarily affected the detail of information about supply and distribution systems. Lack of data collection by utilities was a more significant limitation. For example, in some cases electricity consumption data were available only on a systemwide basis. Assumptions were made to allocate energy use by the systems' components.


• Results for similar California water systems considering the same alternatives may be different. The outcome will be affected by site-specific issues such as topography, process design, location, distance to water sources, climate, scale, and other factors.

Recommendations

The following recommendations can be made based on this research:

Imported Water

• Based on energy considerations, in the case study systems, water importation should be encouraged if supply pumping can be minimized. However, for imported water systems, the environmental effects of withdrawing water from the ecosystem are not captured by the current WEST model. These effects may be significant and should be included in the decision process along with the WEST results.

Desalinated Water

• If desalination is to be pursued in earnest as a water supply alternative in California, efforts should be made to advance desalination technologies so the process is more energy-efficient and the materials are longer lasting.


• Given current process requirements, projects that desalinate brackish groundwater should be encouraged above those that desalinate seawater. However, if seawater intrusion is occurring, pumping water will exacerbate the problem and should not be encouraged.

Recycled Water

• The results of this analysis indicate that the needs of water end-users in California should be evaluated in the planning process. Water should not always be treated to the potable water standard when a lower-grade product can meet the consumer's needed.


• Standards for most non-potable applications requires little treatment (and therefore energy use) beyond what is required for discharge from the wastewater treatment plant. Recycled water should be encouraged in areas where it can be provided at a reasonable cost and where consumers for non-potable water exist. However, efforts should be made to minimize distribution system pumping.


• The increasing popularity of indirect reuse (e.g., when recycled water is used to recharge aquifers which are used for potable supply) in California ensures that applications for recycled water exist within most utility service areas.


• Future analyses should evaluate the effects of putting separate piping systems in new construction, so that recycled water can be used for toilet-flushing, landscaping, and similar uses. Such information would help attract and prioritize potential recycled water customers.

WEST

• This assessment of the environmental effects of water systems should be improved and extended in the future to include assessment of other emissions (e.g., emissions to land and water) and impact assessments (e.g., human or environmental toxicity) and to include alternative infrastructure choices. WEST should be improved in the future to better capture service life variability, to allow the comparison of possible energy mixes, and to assess the environmental effects of water supply which are not due to infrastructure.


• An effort should be made to share the capabilities of WEST with utility directors and other water supply planners, so they can incorporate its results into their future water decisions.


• A simplified form of the tool should be made available so that it can be used to make "back of the envelope" estimates of the environmental burden of water supply alternatives.

General

• Results for similar California water systems considering the same alternatives may be different. The outcome will be affected by site-specific issues including topography, process design, location, distance to water sources, climate, scale, and other factors.


• Similar studies should be conducted for additional utilities to provide further information about the environmental effects of water systems. For instance, additional case studies could evaluate elements of the systems that are affected by siting and scale.


• Future research should emphasize the areas that create the greatest energy and environmental burden (e.g., desalination, system operation, electricity production, material production).


• Efforts should be made to obtain higher-quality, specific data for use in future analyses. Utilities should be encouraged to collect data that can be used for this and similar research.

Benefits to California

Water supply decisions are based on several factors, including economic, political, and reliability concerns. Heretofore, the comprehensive and systemwide life-cycle environmental effects of the water infrastructure have not been a factor in these decisions. The conceptual model and associated decision-support tool developed in this research will allow utilities and other planners to incorporate these effects and externalities into their decision processes, and with more informed analyses, strive for sustainable solutions. The methodology developed for this research, and the knowledge gained from it, can be applied to other aspects of water and wastewater systems, to further reduce future energy use and environmental emissions in California.

This research provides groundwork for future research on the use of energy by water and wastewater systems by identifying the processes that are most energy and pollution intensive in the entire water supply life-cycle. California will benefit from this research and from the development of WEST through a better understanding of water systems, and by encouraging the sustainability of the infrastructure and the systems designed to provide water.

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Abstract

In California, traditional water sources for urban use are increasingly insufficient to meet demand. Alternative water sources have higher energy and resource requirements, so the environmental implications should be incorporated into planning decisions, to develop a more environmentally responsible water supply system.

Accounting for energy and environmental effects in water planning requires life-cycle assessment (LCA), a systematic methodology that accounts for energy consumption and environmental emissions caused by extracting raw materials, manufacturing, constructing, operating, maintaining, and decommissioning the water supply infrastructure. In this research, LCA was used to compare three supply alternatives: (1) importing, (2) recycling, and (3) desalinating water. Energy use and environmental emissions were reported for the water supply alternatives, life-cycle phases, and water supply functions. A decision-support tool was developed to evaluate planning decisions with a life-cycle perspective. The tool was used to evaluate the systems of two California water utilities: (1) the Marin Municipal Water District, and (2) the City of Oceanside Water Department.

The results showed that, for both utilities, desalination was the most environmentally detrimental, because that treatment process is energy intensive. The recycled and imported water results were dependent on distance to water source, topography, treatment process, and other issues. For all alternatives, energy consumed by system operation dominated the results. Results can inform future water planning, and the tool can be used to evaluate the environmental implications of water supply decisions.

KEYWORDS: life-cycle assessment, water supply, energy end-use, desalination, recycled water

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Table of Contents

Preface ii

Abstract v

Executive Summary 1

1. Introduction 7

1.1 Background and Overview 7

1.2 Project Objectives 11

1.3 Report Organization 11

2. Project Approach 12

3. Discussion 30

4. Conclusions and Recommendations 38

5. References 45

Glossary 50

Appendix A. Publications and Presentations A-1

Appendix B. The Water–Energy Sustainability Tool B-1

Appendix C. Case Studies C-1

Appendix D. Data D-1


List of Figures

Figure 1. LCA inventory analysis framework 12

Figure 2. Example water supply system process flow diagram 14

Figure 3. WEST structure 16

Figure 4. Sample results worksheet 18

Figure 5. Global warming potential of water supply alternatives by water supply phase 31

Figure 6. Global warming potential of water supply alternatives by life-cycle phase 32

Figure 7. Global warming potential of water supply alternatives by activity 33


List of Tables

Table 1. Current and Prior Research Summary 9

Table 2. LCA System Boundaries 14

Table 3. Economic, energy, and environmental results 19

Table 4. Data Quality Criteria 27

Table 5. Energy use and GWP factors for life-cycle and water supply phase 32

Table 6. MMWD data quality assessment 35

Table 7. OWD data quality assessment 36