Reducing Energy for Urban Water and Wastewater

Prospects for China

Kate Smith, Shuming Liu

• Publisher: IWA Publishing
• Year: 2019
• eBook ISBN: 9781780409955
• Topic: Biological Sciences
• Subtopic: Applied Sciences
• Index: Biological Sciences

Cities use large amounts of costly energy to supply water and treat wastewater, especially in China, one of the world's largest providers of urban water and sanitation services. Reducing Energy for Urban Water and Wastewater shows how cities can reduce energy use, cut costs and curb greenhouse gas emissions. First, it guides the reader through water supply and wastewater treatment, explaining how energy is used at each step. Then the authors: • Outline the most effective ideas for reducing energy use in cities, using China as a case study. • Provide a decision-making framework to help cities focus their efforts. • Investigate an often-overlooked high energy user in dense cities and suggest a way to cut energy. • Assess the unintended downside of stricter wastewater standards and how to optimise the upside. • Provide suggestions for increasing water and energy recovery in water-scarce cities. The focus throughout is China, the biggest greenhouse gas emitter in the world.

© IWA Publishing 2019. Kate Smith and Shuming Liu Reducing Energy for Urban Water and Wastewater: Prospects for China DOI: 10.2166/9781780409948_0001

Chapter 1

Introduction

1.1  THE WATER–ENERGY NEXUS

Water and energy resources are inherently linked and this connection is referred to as the water–energy nexus (Smith et al., 2016b). Energy is needed to abstract, pump, treat, distribute, heat, cool and recycle water (Klein et al., 2005), and water is a critical component in the production of electricity and the extraction of oil, gas, coal and uranium. For example, for every cubic metre of water supplied to urban areas in China, about 0.3 kWh is required (Smith et al., 2016b) and, for every 1000 kWh of electricity generated in the Shanghai area, 60 m3 of water is consumed (Gu et al., 2016; Smith & Liu, 2017).

This book covers one element of the water–energy nexus – energy use for water supply and wastewater in urban areas – with a main focus on China.

Electricity use is one of the major contributors to emissions of greenhouse gases and air pollution by the water sector, especially in countries like China where the majority of electricity is coal-generated (Smith et al., 2018b). Furthermore, electricity is generally the largest cost faced by the water sector in many countries. Electricity can represent over 30% of annual operation and maintenance expenses in a typical water treatment plant (Biehl & Inman, 2010), and between 25% and 40% of operation and maintenance expenses in wastewater treatment plants (Balmér, 2000; Tsagarakis et al., 2003). For these reasons, electricity use is of increasing importance to water companies and regulators.

1.2  CHINA'S URBAN WATER SYSTEM

The quantity of water produced and wastewater treated in Chinese cities has increased significantly over the past two decades, but efforts to reduce net energy use for these processes, particularly through energy recovery during wastewater treatment, lag behind other countries (Jin et al., 2014; Smith et al., 2018b; Yang et al., 2015; Zhang et al., 2016b). Since the start of the 21st century, the proportion of the Chinese population living in cities has risen from around 36% to just under 60% (National Bureau of Statistics, 2019) and is expected to reach 60% within a couple of years (National Development and Reform Commission, 2014; Smith et al., 2018c). China's daily wastewater treatment capacity more than doubled between 2007 and 2018 and electricity use for wastewater treatment more than quadrupled over the same time (China Urban Water Association, 2018). The number of wastewater treatment plants using the most common form of energy recovery – anaerobic sludge digestion – is still fairly low (Smith et al., 2018b). Electricity consumption for potable water supply in China has more than doubled since 2000 (Zhang et al., 2016b).

The number of Chinese households living in buildings of seven or more storeys more than doubled between 2000 and 2010 (National Bureau of Statistics, 2010); this has added to the energy required for water supply (Smith et al., 2017). Floors seven and above in China require in-building pumping systems, which means that supplying water to these floors tends to require more energy than to lower floors. The country is expected to see a further 25 cities break the 1 million population mark by 2025 compared with 2012 (National Bureau of Statistics, 2013a; Woetzel et al., 2009).

Water-scarce urban areas in China are increasingly turning to alternative water sources – seawater desalination, surface water transfer and wastewater reuse – which generally require more energy to source and treat than conventional water resources (Smith et al., 2018b). Water availability is not stable in time or space in China (Smith et al., 2018a). The north has fewer surface water resources than the south and far less rainfall, most of which is concentrated over a few months of the year (National Bureau of Statistics, 2017). Demand for water, as defined by population and production, is often high in areas with limited water resources (National Bureau of Statistics, 2017). For example, Beijing can only meet 70% of water demand using local water resources despite an 84% reduction in water use per unit of Gross Domestic Product over the past 15 years (Beijing Bureau of Statistics, 2016). Alternative water sources are necessary, but use of these sources increases the cost and greenhouse gas emissions associated with water supply.

China has committed to national and international energy and emissions targets, specifically a cap on total energy consumption in the 13th Five Year Plan and an aim to peak greenhouse gas emissions by 2030 according to the 2015 Paris Agreement on climate change. In order to meet these targets, it is important to reduce energy and emissions in every sector of the economy, including the water sector.

1.3  SCOPE

The term ‘urban water supply’ is used in this book to refer to the processes of obtaining, producing and distributing water for urban areas. The book does not discuss energy for processes where the main output is not water; for instance, it does not include energy for water end use (e.g. household water heating) or energy embedded in construction materials and chemicals associated with the water system (Kyle et al., 2016). The study focuses on urban water systems, which are well represented in the literature. China's urban water system is of particular interest due to rapid urbanisation.

1.4  SUMMARY

This book presents a review of energy for water supply and wastewater treatment in urban areas of China, with comparisons to other countries (Chapters 2, 4 and 5). It includes both conventional and alternative water sources and all stages of wastewater treatment. It highlights some factors that may influence energy use for water supply (Chapter 3) and assesses the unintended downside of stricter wastewater standards and how to optimise the upside (Chapter 6). It then outlines the most effective ideas for reducing energy use in cities (Chapters 7 and 9), including water-scarce cities (Chapter 10). It highlights the significant contribution of pumping in high-rise buildings and provides steps for reducing energy use for water distribution through pressure management and building layout (Chapter 8). Finally, it provides a decision-making framework to help cities focus their efforts to save energy in the urban water system (Chapter 11).

© IWA Publishing 2019. Kate Smith and Shuming Liu Reducing Energy for Urban Water and Wastewater: Prospects for China DOI: 10.2166/9781780409948_0005

Chapter 2

Energy for water supply

2.1 ENERGY FOR WATER SUPPLY

In conventional water supply, water is transferred from ground and surface water reserves to a treatment plant where it undergoes a series of treatment stages, such as coagulation, sedimentation, filtration and disinfection. Clean water is pumped through a central water distribution system to users and may also be pumped within buildings.

Electricity use for conventional water supply to urban areas of China grew by 35% between 2001 and 2014 and the volume of water supplied during this time increased by 52% (China Urban Water Association, 2002, 2015). As a result, the electricity intensity of water supply decreased from 0.33 to 0.29 kWh/m3 (China Urban Water Association, 2002, 2015). Table 2.1 provides the main indicators for urban water supply in China.

Table 2.1 Main electricity use indicators for urban water supply and wastewater treatment in China in 2013.

Indicator	Value
Electricity intensity of water supplya	0.29 kWh/m3
Electricity per capita for water supplya	37.5 kWh/cap
Total electricity for urban water supplya	1.17 × 1010 kWh
Electricity use ...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Contents
• About the Authors
• Preface
• Chapter 1: Introduction
• Chapter 2: Energy for water supply
• Chapter 3: Factors that may influence electricity use for water supply
• Chapter 4: Comparison of electricity for water supply between water sources and countries
• Chapter 5: Energy for wastewater treatment
• Chapter 6: Evaluating the environmental benefit and energy footprint of stricter wastewater standards
• Chapter 7: Reducing net energy use for water supply
• Chapter 8: Reducing energy for water distribution through pressure management and building layout
• Chapter 9: Reducing net energy use for wastewater treatment
• Chapter 10: Reducing energy use for water in water-scarce cities
• Chapter 11: A road map for reducing energy use in urban water supply
• References
• Index