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Water, Climate Change, and Sustainability. Группа авторов
Читать онлайн.Название Water, Climate Change, and Sustainability
Год выпуска 0
isbn 9781119564539
Автор произведения Группа авторов
Жанр Физика
Издательство John Wiley & Sons Limited
3.1.1. Bio‐Based Systems for Achieving the Sustainable Development Goals
One of the challenges of the twenty‐first century and beyond is the development of secure and sustainable sources of energy, and supply of clean water and food for the exponentially growing world population (Waskom et al., 2014). World primary energy consumption in 2015 was estimated as ~13.7 Billion Tons of Oil Equivalent (IEA, 2018). In addition, the world water use in the same year was estimated as ~ 4 trillion m3 (IGBP, 2015). Population growth creates shortage in energy, water and food supply. By 2050, compared to 2015, 80% more energy and 55% more water will be required to meet the increasing population demand (Waskom et al., 2014). The countries are responsible to facilitate the effective implementation of the Sustainable Development Goals (SDGs), set by the United Nations General Assembly (UNCTAD, 2014). Among the SDGs, those related to the conservation of the natural resources and environment are of high importance for reducing the risks of natural disasters and ensuring the resource security for future generations. Bio‐based systems play an important role in achieving the SDGs by: (i) sustainable management of water resources (SDG 6), (ii) sustainable development of energy resources (SDG 7), (iii) adopting the sustainable production and consumption concept (SDG 12), and (iv) developing the renewable energy sources for tackling climate change (SDG 13).
Figure 3.1 Carbon cycle of biofuels.
Substituting petroleum‐based fuels with biofuels allows the conservation of natural resources and mitigates greenhouse gas (GHG) emissions by reducing the environmental burdens associated with petroleum‐based fuels, thus contributing to the attainment of the SDGs. The supply of biofuels mitigates the environmental impacts due to the use of fossil fuels, because of carbon dioxide uptake by plants during the growing phase (Figure 3.1).
3.1.2. Interconnection of Water and Energy in Bio‐Based Systems
Water and energy are two necessary resources for human life. Energy production from bio‐based systems can reduce the environmental impacts and increase the energy security of the nations by reducing the reliance on fossil fuels. Water being a scarce source is important in biobased systems. Thus, bio‐based systems can contribute help achieve the global climate change mitigation goals, but this needs valuable resources such as water and energy in the process. Some of the other key concerns associated with the development of bio‐based systems include food security because of the use of food crops for energy supply, risks of increased emissions during biomass production and processing, and reduction in biodiversity due to land use change by expansion of bioenergy crops. External factors such as lack of economic competitiveness of biofuels with petroleum‐based fuels is also restricting the expansion of bio‐based systems for energy purposes. Development of bio‐based systems that advance the SDGs requires policies and measures to ensure sustainability of the systems (IRENA, 2019), including a rational use of energy and water throughout the entire cycle.
3.1.3. Overview of the Chapter
The goal of this chapter is to exhibit the interactions of water and energy in the development of bio‐based systems as a mean for achieving the SDGs. Accordingly, energy use and supply in bio‐based systems are explained, and water supply for bio‐based energy production as well as the role of bio‐based energy in water supply are discussed. Then, the water‐energy nexus in bio‐based systems is presented, and finally the tools and metrics for quantifying the sustainability of water‐energy nexus are explained.
3.2. WATER SUPPLY AND USE IN BIO‐BASED SYSTEMS
3.2.1. Water Availability
More than two thirds of the earth’s surface is covered with water (USGS, 2016). However, ~97.5% of that is saltwater which cannot be used for industrial, agricultural, or residential purposes. Of the remaining freshwater, ~1.75% is frozen in glaciers, and the rest is available as ground water (~0.68%) and freshwater in lakes and rivers (0.07%) (USGS, 2016). Freshwater is used for residential purposes (11%), industries (19%), and agriculture (70%) (FAO, 2016). Water is essential in all sectors, and bio‐based systems utilize large quantities of water, increasing the pressure on this already scarce resource. Water in bio‐based systems is not the most expensive input; however, unlike other resources, it has no substitutes. Water is required at different stages in bio‐based systems, from irrigation during biomass production up to recovery of the final products after biomass processing. However, water consumed during biomass production and processing have different intensities of water use. Water used for irrigation during biomass production is consumed in the process, which means no wastewater is generated. However, some of the water used during the processing may be reused by wastewater treatment and purification processes. Steam used in the process can also be reused after being condensed to water.
3.2.2. Water Use in Biomass Production
Water required to produce fossil fuel is low (1 m3/GJ), compared to the large quantities of water needed to produce biofuels (24 ‐ 146 m3/GJ) (Gerbens‐Leenes et al., 2008). In biofuel production process, biomass production uses large quantities of freshwater. In areas with enough rainfall, crops are mainly rainfed; however, irrigation supplements the insufficient supply of water due to low rainfall in dry regions. Irrigation is required at different stages of plant growth, and lack of water at the key growth stages can significantly affect the crop yield.
Crop water demand depends on the evapotranspiration (ET) rate, which is the process of evaporation of water from the soil and transpiration from plants (Schwalbe, 2017). ET is affected by the environmental conditions, such as precipitation, soil moisture, temperature, tillage practices, crop rotation practices, cover crops, types of fertilizers used, and irrigation scheduling. Only ~5% of the water received by the plant is utilized to perform biochemical reactions, transport nutrients, and maintain turgidity, and the remaining is lost through ET (Langeveld and van de Ven, 2010). Of the total water received by the plant, 0.2% to 0.4% actually contribute to the plant dry matter (Condon et al., 2004). For the purpose of sustainable development of bioenergy systems, development of bioenergy crops with low ET is more desirable. ET and water footprint of some crops, including starch, lignocellulosic, and oil containing crops, which can be used for bioenergy purposes, are presented in Table 3.1.
Bioethanol is the main biofuel produced worldwide. The two largest crops for ethanol production are corn in the US and sugarcane in Brazil. Most of the US corn is produced under rainfed conditions; however, in areas where it is irrigated, water is mainly supplied from groundwater sources, such as the Ogallala Aquifer which supplies irrigation water for ~45 million ha of land in eight states of the US (Maupin and Barber, 2005). Sugarcane is a perennial crop, with high concentration of sugar juices, which is mostly produced under rainfed conditions (Moreira, 2007). Irrigation is becoming necessary as sugarcane production is expanding to arid areas (Goldemberg et al., 2008). Irrigation needed for most of the crops grown for food, except corn, is higher than that for dedicated energy crops, such as switchgrass, miscanthus, willow, poplar, and eucalyptus (Fraiture and Berndes, 2009). Corn production in the US needs low quantities of water, because it is grown in areas with enough rainfall (Le et al., 2011; VanLoocke et al., 2012; Wu and Liu, 2012). Other types of biomass used for energy production, such as sewage sludge and