Energy and water resources share an important interdependency. Large quantities of energy are required to move, purify, heat, and pressurize water, while large volumes of water are necessary to extract primary energy, refine fuels, and generate electricity. This relationship, commonly referred to as the energy-water nexus, can introduce vulnerabilities to energy and water services when insufficient access to either resource inhibits access to the other. It also creates areas of opportunity, since water conservation can lead to energy conservation and energy conservation can reduce water demand. This dissertation analyzes both sides of the energy-water nexus by (1) quantifying the extent of the relationship between these two resources and (2) identifying strategies for synergistic conservation. It is organized into two prevailing themes: the energy consumed for water services and the water used in the power sector. In Chapter 2, a national assessment of United States' energy consumption for water services is described. This assessment is the first to quantify energy embedded in water at the national scale with a methodology that differentiates consistently between primary and secondary uses of energy for water. The analysis indicates that energy use in the residential, commercial, industrial, and power sectors for direct water and steam services was approximately 12.3 quadrillion BTU or 12.6% of 2010 annual primary energy consumption in the United States. Additional energy was used to generate steam for indirect process heating, space heating, and electricity generation. Chapter 3 explores the potential energy and emissions reductions that might follow regional shifts in residential water heating technologies. Results suggest that the scale of energy and emissions benefits derived from shifts in water heating technologies depends on regional characteristics such as climate, electricity generation mix, water use trends, and population demographics. The largest opportunities for energy and emissions reductions through changes in water heating approaches are in locations with carbon dioxide intensive electricity mixes; however, these are generally areas that are least likely to shift toward more environmentally advantageous devices. In Chapter 4, water withdrawal and consumption rates for 310 electric generation units in Texas are incorporated into a unit commitment and dispatch model of ERCOT to simulate water use at the grid scale for a baseline 2011 case. Then, the potential for water conservation in the power generation sector is explored. Results suggest that the power sector might be a viable target for cost-effective reductions in water withdrawals, but reductions in water consumption are more difficult and more expensive to target. / text

Treating water in order to reduce human and environmental risks requires the use of electricity and chemicals, the generation of which creates emissions of air pollutants such as NOx, SO2, PM2.5, and CO2. Emissions of air pollutants establishes a health and environmental risk tradeoff between air and water pollution. Addressing air-water tradeoffs by adopting a one environment framework requires new methods for quantifying these tradeoffs, new technologies to minimize air-water tradeoffs, and new tools for decision makers to incorporate these tradeoffs into compliance decisions. In my thesis, I develop methods for quantifying damages from air emissions associated with water treatment; assess the feasibility of forward osmosis (FO), a technology which holds the promise to avoid air-water tradeoffs; and create a tool to holistically assess compliance with air and water emission standards for coal-fired power plants (CFPPs). I start my thesis by creating a method to quantify the damages caused by the air emissions that resulting from the treatment of drinking water (Chapter 2), municipal wastewater (Chapter 3), and flue gas desulfurization (FGD) wastewater (Chapter 4). These studies use life-cycle models of energy and chemical consumption for individual water treatment unit processes in order to estimate embedded emissions of criteria air pollutants and greenhouse gasses per cubic meter of treated water. Damages from these additional air emissions are assessed and incorporated into benefit-cost analyses. I find that for drinking water rules, the net benefit of currently implemented rules remains positive but the promises of net benefits for some proposed rules are conditional on the compliance technology that is selected. For municipal wastewater, I find that while there are ~$240 million (in 2012 USD) benefits in air emission reduction from installing biogas-fueled electricity generation nationwide, there are several states where biogas-fueled electricity creates more air emissions than it displaces. For FGD wastewater treatment, I find that complying with the effluent limitation guidelines has an expected ratio of benefits to cost of1.7-1.8, with damages concentrated in regions with large chemical manufacturing industries or electricity grids that are heavily reliant on coal. In the next part of the thesis, I assess the techno-economic feasibility of power plant waste heat driven FO to reduce the air emissions associated with FGD wastewater treatment. In Chapter 5, I assess the quantity, quality and the spatial and temporal availability of waste heat from US coal, nuclear, and natural gas power plants. I find that while 18.9 billion GJ of potentially recoverable waste heat is discharged into the environment, only 900 million GJ of that heat is from the flue gas and is at a temperature high enough to drive water purification using forward osmosis (FO). In Chapter 6, I build a model of FO to assess its thermal energy consumption and find that the 900 million GJ of waste heat produced at coal and natural gas power plants is sufficient to meet their boiler feedwater and FGD wastewater treatment needs. In Chapter 7, I incorporate cost into the energy consumption model of FO, and conclude that treatment of FGD and gasification wastewater using waste heat driven FO is economically competitive with mechanical vapor recompression. In Chapter 8, I create an energy-balance model of a CFPP and nine environmental control technologies for compliance with FGD wastewater and carbon capture regulations. I use this model to maximize plant revenue at the National Energy Technology Laboratory’s 550 MW model CFPP without carbon capture. I find that revenue is maximized by using residual heat for water treatment or carbon capture. If both carbon capture and zero liquid discharge water treatment regulatory standards are in place, I conclude that the plant maximizes revenue by allocating residual heat and steam to amine-based carbon capture and electricity to mechanical vapor recompression for FGD wastewater treatment.

More water utilities are adopting Aquifer Storage and Recovery (ASR) to balance long-term water supply and demand. Due to large implementation and operation costs, ASR projects need to be optimized, particularly for energy use, which is a major operating expense. This study examines the relationships among energy use, recharge, and recovery at two ASR projects in the western United States. The major finding is an economy of scale for recovery processes, but not for gravity-fed recharge processes. The economy of scale found is as follows: the energy intensity recovered decreases with volume. This suggests it is more energy-efficient to recover large volumes of water in one interval instead of recovering smaller volumes at more frequent intervals. The H2Oaks recovery process experienced a 78% decrease in energy intensity from 0 to 50,000 m^3 recovered, while the Sand Hollow site experienced a 43% decrease in energy intensity from 0 to 50,000 m^3 recovered. Statistical analyses of the recovery process showed p values lower than 0.0001, R^2 values between 0.43 and 0.57, and a RMSE value between 0.55 and 2.1, indicating the presence of a moderate correlation between energy and volume. This economy of scale has been observed in multiple instances in water and wastewater treatment. This finding not only has applications to ASR but also all recovery or recharge wells, whether or not they are paired with each other. Furthermore, this study confirms the need for more reliable and accessible energy data to fully understand the implications of the energy–water nexus.

Horizontal drilling and hydraulic fracture stimulation have enabled the economic development of unconventional resource plays. An average horizontal well in the Barnett Shale requires 3 to 4 million gallons of fresh water, 90% of which is used for hydraulic fracture stimulation. While the water consumption of Barnett Shale operations is less than 1% of total Region C consumption, extended drought conditions and competing demands for water resources are placing pressure on operators to reduce terminal water consumption. Strategies which reduce water requirements associated hydraulic fracture stimulation without compromising the efficiency and cost of energy production are essential in developing a comprehensive policy on energy-water management. Recycling and reuse technologies were evaluated on the basis of performance, cost, and capacity to treat reclaimed flowback water and oilfield brine. Recycling flowback fluids for future hydraulic fracture applications is the most practical repurposing of oilfield waste. The low TDS content of flowback derived from water-based fracs permits multiple treatment options. Mobile thermal distillation technology has emerged as the prevailing technique for recycling flowback water, yielding maximum water savings and reduced operating costs. The estimated cost of recycling flowback water by thermal distillation is $3.35/bbl. Compared to the current cost of disposal, recycling provides an opportunity to minimize waste and reduce the fresh water requirements of hydraulic fracture stimulation at an incremental cost. The stewardship role of the Texas Legislature is to protect the water resources of the state and to facilitate the Regional Water Planning Process, ensuring future water needs are met. The support and participation of the Legislature and other planning entities is critical in advancing the energy-water nexus. As operators pursue innovative water management practices to reduce terminal water consumption in the oilfield, the Barnett Shale positions itself as a model for sustainable water use in the development of unconventional shale resources. The cost of recycling and reuse technology limits the participation of small and mid-size operators who possess the greatest market share of the Barnett Shale. Funding for research and implementation of water-conscious strategies such as shared recycling facilities, CO2 capture and storage, and pipeline infrastructure would create multi-user opportunities to promote conservation and reduce net consumption of fresh water supplies. Through the integration of technology and policy, terminal water consumption in the Barnett Shale can be greatly diminished. / text

京都大学 / 0048 / 新制・課程博士 / 博士(エネルギー科学) / 甲第19087号 / エネ博第311号 / 新制||エネ||64(附属図書館) / 32038 / 京都大学大学院エネルギー科学研究科エネルギー社会・環境科学専攻 / (主査)教授 手塚 哲央, 教授 宇根﨑 博信, 准教授 MCLELLAN Benjamin / 学位規則第4条第1項該当 / Doctor of Energy Science / Kyoto University / DFAM

As reliance on energy and water resources grow, so do the concerns regarding their security, especially in terms of availability. A projected rise in population, accompanied by the relentless pursuit of economic growth and increasing climate change, indicate that greater stress will be placed on these same resources. Biofuels are considered to be a viable alternative to fossil fuels and sugarcane-based ethanol has become an important source for energy security in Brazil, its main producer. At the same time, water scarcity issues have prompted the Brazilian government to compose its first National Plan for Water Security. Research shows that change in land use, a prevalent factor in the production of biofuels, can greatly impact water resources through evapotranspiration, suggesting the possibility of the existence of a link between the two events. This study aimed to investigate this phenomenon by assessing how Brazil’s push for energy security through the production of sugarcane-based ethanol could be affecting its water security. The state of Sao Paulo and the lower Cerrado, including the states of Goias, Minas Gerais and Mato Grosso do Sul, were selected as units of analysis since they comprise the largest production area in the country and are located within the La Plata Basin, where water issues have been experienced in the recent past. Results showed impressive increases over the past four decades in the amount of sugarcane and ethanol produced, as well as in the expansion of land used to cultivate sugarcane in both cases. Furthermore, the results disclosed an increasing trend in precipitation deficit for both regions. The discussion revealed that the direct land use change engendered by the expansion of sugarcane cultivation for ethanol cannot be linked to the decrease in availability of rainwater since it did not negatively impact moisture recycling. Indirect deforestation caused by the displacement of pastureland was, however, determined to have contributed to reduced rates of evapotranspiration, negatively impacting continental moisture recycling, which is imperative for levels of rainfall in the La Plata Basin. The study concludes that the increased production of sugarcane-based ethanol in Sao Paulo and in the lower Cerrado, aimed to ensure energy security for Brazil, is negatively affecting its water security through reduced rates of precipitation associated with indirect land use change. More generally, this conclusion provides insights into the energy-water nexus and a better understanding of critical tradeoffs and potentially irreversible risks that can come with isolated solutions to issues pertaining to larger, complex systems. Finally, it stresses the importance of a nexus approach for sustainable development.

Developing nations face insurmountable challenges to reliably and sustainably provide energy and water to the population. These resources are intricately entwined such that decisions on the use of one affects the other (energy-water nexus). Inadequate and ageing infrastructure, increased population and connectivity, urbanization, improved standards of living and spatially uneven rainfall are some of the reasons causing this insecurity. Expanding and developing new supply infrastructure is not sustainable due to sky high costs and negative environmental impact such as increased greenhouse gas emissions and over extraction of surface water. The exponentially increasing demand, way above the capacity of supply infrastructure in most developing countries, requires urgent mitigation strategies through demand side management (DSM). The DSM strategies seek to increase efficiency of use of available resources and reducing demand from utilities in the short, medium and long term. Renewable energy, rooftop rain water harvesting, pump-storage scheme and grey water recycling are some alternatives being used to curb the insecurity. However, renewable energy and rooftop water harvesting are spasmodic in nature hampering their adoption as the sole supply options for energy and water respectively. The built environment is one of the largest energy and water consuming sectors in the world presenting a huge potential towards conserving and increasing efficiency of these resources. For this reason, coupled with the 1970s energy challenges, the concept of green buildings seeking to, among other factors, reduce the consumption of energy and water sprung up. Conventionally, policy makers, industry players and researchers have made decisions on either resource independently, with little knowledge on the effect it would have on the other. It is therefore imperative that optimal integration of alternative sources and resource efficient technologies are implemented and analysed jointly in order to achieve maximum benefits. This is a step closer to achieving green buildings while also improving energy and water security. A multifaceted approach to save energy and water should integrate appropriate resource efficient technology, alternative source and an advanced and reliable control system to coordinate their operation. In a typical South African urban residential house, water heating is one of the most energy and water intensive end uses while lawn irrigation is the highest water intensive end use occasioned by low rainfall and high evaporation. Therefore, seamless integration of these alternative supply and most resource intensive end uses provides the highest potential towards resource conservation. This thesis introduces the first practical and economical attempt to integrate various alternative energy and water supply options with efficient devices. The multifaceted approach used in this research has proven that optimal control strategy can significantly reduce the cost of these resources, bring in revenue through renewable energy sales, reuse waste water and reduce the demand for grid energy, water and waste water services. This thesis is generally divided into cold and hot water categories; both of which energy-water nexus DSM is carried out. Open-loop optimal and closed-loop model predictive (MPC) control strategies that minimize the objective while meeting present technical and operational constraints are designed. In cold water systems, open-loop optimal and MPC strategies are designed to improve water reliability through a pump storage system. Energy efficiency (EE) of the pump is achieved through optimally shifting the load to off-peak period of the time-of-use (TOU) tariff in South Africa. Thereafter, an open-loop optimal control strategy is developed for rooftop rain water harvesting for lawn irrigation. The controller ensures water is conserved by using the stored rain water and ensuring only the required amount of water is used for irrigation. Further, EE is achieved through load shifting of the pump subject to the TOU tariff. The two control strategies are then developed to operate a grey water recycling system that is useful in meeting non-potable water demand such as toilet flushing and lawn irrigation and EE is achieved through shifting of pump's load. Finally, the two control strategies are designed for an integrated rain and grey water recycling for a residential house, whose life cycle cost (LCC) analysis is carried out. The hot water category is more energy intensive, and therefore, the open-loop optimal control strategy is developed to control a heat pump water heater (HPWH) and an instantaneous shower, both powered by grid-tied renewable energy systems. Solar and wind energy are used due to their abundance in South Africa. Thereafter, the MPC strategy is developed to power same devices with renewable energy systems. In both strategies, energy is saved through the use of renewable energy sources, that also bring in revenue through sale of excess power back to the grid. In addition, water is conserved through heating the cold water in the pipes using the instantaneous shower rather than running it down the drain while waiting for hot water to arrive. LCC analysis is also carried out for this strategy. Each of the two control strategies has its strengths. The open loop optimal control is easier and cheaper to implement but is only suitable in cases where uncertainties and disturbances affecting the system do not alter the demand pattern for water in a major way. Conversely, the closed-loop MPC strategy is more complicated and costly to implement due to additional components like sensors, but comes with great robustness against uncertainties and disturbances. Both strategies are beneficial in ensuring security and reliability of energy and water is achieved. Importantly, technology alone cannot have sustainable DSM impact. Public education and awareness on importance of energy and water savings, improved efficiency and effect on supply infrastructure and greenhouse gas emissions are essential. Awareness is also important in enabling the acceptance of these technological advancements by the society. / Thesis (PhD)--University of Pretoria, 2017. / National Hub for Energy Efficiency and Demand Side Management (EEDSM) / University of Pretoria / Electrical, Electronic and Computer Engineering / PhD / Unrestricted

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<p>The Food-Energy-Water (FEW) nexus conceptualizes the interactions and tension between production and consumption of food, energy, and water. With increasing uncertainties due to climate change, there is a need to address these tensions within the nexus and better comprehend the existing interdependencies and tradeoffs. Water integrity – considering both water availability and quality – is of critical concern within the FEW nexus. Thus, it is important to develop robust decision-making strategies using a FEW nexus lens. This study focuses on addressing water integrity concerns through FEW nexus assessment using an agricultural watershed in northeastern Indiana, with predominantly corn-soybean rotations, as a pilot site. Historical and futuristic climate and hydrological data were used for hydrological modeling using SWAT to quantify water quantity, quality, and crop production. Scientific literature values for farm machinery fuel requirements and their carbon emissions were implemented to obtain values based on the implemented agronomic practices. Results of this study provide methodologies and information that can be implemented to evaluate water resources management, as well as inform policymaking for more sustainable agricultural management practices.</p>