Water-Energy Nexus Approaches for Solar Development and Water Treatment in the Southwestern United States

Water is crucial for energy production and conversion, and energy is crucial for various water related processes including water conveyance, treatment and distribution. Sustainability of water and energy are inextricably linked with each other. Over-utilization/ degradation of these resources may occur due to limited availability of water under the changing climate scenario, growing population, and increasing pollution due to the burning of fossil fuels. The goal of the current research was to study the water-energy nexus of the Southwestern U.S. and develop approaches for solar development and treatment of drinking water. To achieve the overall objective, the work was divided into two main research tasks. Research task 1 addressed the water demands and availability issues for utility-scale solar development in six southwestern states to meet the target goals of their renewable portfolio standards (RPS) between the years of 2015-2030. Solar energy-water nexus was analyzed for the southwestern states of Arizona, California, Nevada, Colorado, New Mexico and Utah. Estimates were gathered for water withdrawal and consumption (related to plant construction, operations, and dismantling) and land use (direct and total) for solar technologies of concentrated solar power and solar photovoltaics (PV), and harmonized through review and screening of relevant literature. Next, the estimates were incorporated into a system dynamics model to analyze water availability and usage, land availability and usage, and associated reductions in carbon emissions for utility-scale solar development in the nineteen solar energy zones (SEZs) of six southwestern states based upon the RPS during 2015-2030. Results showed that solar PV was the most appropriate technology for water-limited regions. Sufficient land was available within the 19 SEZs to meet the RPS requirements. Available water was adequate to meet RPS solar carve-out water requirements for Nevada and New Mexico. Further, solar development led to tremendous reduction in carbon emissions in the region. Contributions of this study include a greater understanding of solar energy-water nexus, especially on a local scale, which is crucial for successful implementation of energy policies, by quantifying the effects of solar land and water demands on the resources of southwestern region. The generated model may be used as a screening tool for a crude assessment of future energy planning, solar project applications, and permit approvals. For future work, the generated model can be modified to analyze the performances of renewables in addition to solar. Research task 2 involved the application of water-energy nexus approach for treatment of drinking water, which is an energy-intensive process and essential for safeguarding public health. Environmental impacts of the nexus are carbon emissions, which were reduced by using distributed solar to fulfill the energy requirements of three drinking water treatment plants (DWTPs), located in southwestern United States. The three plants differed by capacity (10 MGD, 90 MGD, 300 MGD), raw water source (groundwater, river, lake), and unit processes involved for treatment of raw water (in-line filtration, conventional filtration, direct filtration). Energy consumption was determined for various energy driving units. This, along with the existing acreage of the plant and economic feasibility; the DWTP was sized for solar photovoltaics. System Advisor Model was used for the performance and economic analysis of the solar system. Associated reduction in carbon emissions was also estimated. Energy intensity was determined as 153.7, 165.4, and 508.1 Wh m-3 for the small, medium and large DWTP, respectively. Pumping operation was determined to be the largest consumer of electricity for all three plants and utilized about 98%, 95%, and 90% of the total energy consumption for the 10 MGD, 90 MGD and 300 MGD plant, respectively. The development of solar PV for the three treatment plants was found to be economically feasible with positive NPV, with and without battery-storage systems. However, standalone solar PV development was not profitable for the 300 MGD DWTP for offsetting the total energy consumption. Further, the economic assessment was sensitive to changes in governmental incentives and financial parameters. Existing landholdings of the plants were sufficient for solar development. Moreover, change in geographic location from the southwest to east coast US, identified governmental incentives to affect the economic feasibility of PV systems. Contributions of this study include a successful application of the water-energy nexus approach for sustainable treatment of drinking water, by offsetting the fossil-fuel based energy consumption of three existing DWTPs by means of solar development. The design equations and results for the energy consumption can be applied to other plants utilizing similar processes. With the aim of incorporating sustainability in DWTPs in the southwestern U.S., the study provides a roadmap for using solar PV for DWTPs, leading to reduction in carbon emissions, energy costs and achieving energy independence

Incorporating the Oceanic-Atmospheric Climate Variables to Enhance Streamflow Reconstruction Skill

Streamflow is a vital source of water supply. Information about the historic streamflow helps understand the range of climate variability and develop sustainable water management strategies for the future. The available instrumental data is usually limited and thus might be insufficient to describe the long-term hydrologic patterns of a region. Streamflow reconstruction, by increasing the length of the hydrologic data, is an important tool to understand past hydrology

Design Aspects, Energy Consumption Evaluation, and Offset for Drinking Water Treatment Operation

Drinking water treatment, wastewater treatment, and water distribution are energy-intensive processes. The goal of this study was to design the unit processes of an existing drinking water treatment plant (DWTP), evaluate the associated energy consumption, and then offset it using solar photovoltaics (PVs) to reduce carbon emissions. The selected DWTP, situated in the southwestern United States, utilizes coagulation, flocculation, sedimentation, filtration, and chlorination to treat 3.94 m3 of local river water per second. Based on the energy consumption determined for each unit process (validated using the plant’s data) and the plant’s available landholding, the DWTP was sized for solar PV (as a modeling study) using the system advisor model. Total operational energy consumption was estimated to be 56.3 MWh day−1 for the DWTP including water distribution pumps, whereas energy consumption for the DWTP excluding water distribution pumps was 2661 kWh day−1. The results showed that the largest consumers of energy—after the water distribution pumps (158.1 Wh m−3)—were the processes of coagulation (1.95 Wh m−3) and flocculation (1.93 Wh m−3). A 500 kW PV system was found to be sufficient to offset the energy consumption of the water treatment only operations, for a net present value of $0.24 million. The net reduction in carbon emissions due to the PV-based design was found to be 450 and 240 metric tons CO2-eq year−1 with and without battery storage, respectively. This methodology can be applied to other existing DWTPs for design and assessment of energy consumption and use of renewable

An Analysis of Energy Consumption and the Use of Renewables for a Small Drinking Water Treatment Plant

One of the pressing issues currently faced by the water industry is incorporating sustainability considerations into design practice and reducing the carbon emissions of energy-intensive processes. Water treatment, an indispensable step for safeguarding public health, is an energy-intensive process. The purpose of this study was to analyze the energy consumption of an existing drinking water treatment plant (DWTP), then conduct a modeling study for using photovoltaics (PVs) to offset that energy consumption, and thus reduce emissions. The selected plant, located in southwestern United States, treats 0.425 m3 of groundwater per second by utilizing the processes of coagulation, filtration, and disinfection. Based on the energy consumption individually determined for each unit process (validated using the DWTP’s data), the DWTP was sized for PVs (as a modeling study). The results showed that the dependency of a DWTP on the traditional electric grid could be greatly reduced by the use of PVs. The largest consumption of energy was associated with the pumping operations, corresponding to 150.6 Wh m−3 for the booster pumps to covey water to the storage tanks, while the energy intensity of the water treatment units was found to be 3.1 Wh m−3. A PV system with a 1.5 MW capacity with battery storage (30 MWh) was found to have a positive net present value and a levelized cost of electricity of 3.1 cents kWh−1. A net reduction in the carbon emissions was found as 950 and 570 metric tons of CO2-eq year−1 due to the PV-based design, with and without battery storage, respectively

Renewable Energy Generation and GHG Emission Reduction Potential of a Satellitewater Reuse Plant by Using Solar Photovoltaics and Anaerobic Digestion

Wastewater treatment is a very energy-intensive process. The growing population, increased demands for energy and water, and rising pollution levels caused by fossil-fuel-based energy generation, warrants the transition from fossil fuels to renewable energy. This research explored the energy consumption offset of a satellite water reuse plant (WRP) by using solar photovoltaics (PVs) and anaerobic digestion. The analysis was performed for two types of WRPs: conventional (conventional activated sludge system (CAS) bioreactor with secondary clarifiers and dual media filtration) and advanced (bioreactor with membrane filtration (MBR)) treatment satellite WRPs. The associated greenhouse gas (GHG) emissions were also evaluated. For conventional treatment, it was found that 28% and 31.1% of the WRP’s total energy consumption and for advanced treatment, 14.7% and 5.9% of the WRP’s total energy consumption could be generated by anaerobic digestion and solar PVs, respectively. When both energy-generating units are incorporated in the satellite WRPs, MBR WRPs were on average 1.86 times more energy intensive than CAS WRPs, translating to a cost savings in electricity of $7.4/1000 m and$13.3/1000 m treated, at MBR and CAS facilities, respectively. Further, it was found that solar PVs require on average 30% longer to pay back compared to anaerobic digestion. For GHG emissions, MBR WRPs without incorporating energy generating units were found to be 1.9 times more intensive than CAS WRPs and 2.9 times more intensive with energy generating units. This study successfully showed that the addition of renewable energy generating units reduced the energy consumption and carbon emissions of the WRP. 3

Design Aspects, Energy Consumption Evaluation, and Offset for Drinking Water Treatment Operation

Drinking water treatment, wastewater treatment, and water distribution are energy-intensive processes. The goal of this study was to design the unit processes of an existing drinking water treatment plant (DWTP), evaluate the associated energy consumption, and then offset it using solar photovoltaics (PVs) to reduce carbon emissions. The selected DWTP, situated in the southwestern United States, utilizes coagulation, flocculation, sedimentation, filtration, and chlorination to treat 3.94 m3 of local river water per second. Based on the energy consumption determined for each unit process (validated using the plant’s data) and the plant’s available landholding, the DWTP was sized for solar PV (as a modeling study) using the system advisor model. Total operational energy consumption was estimated to be 56.3 MWh day−1 for the DWTP including water distribution pumps, whereas energy consumption for the DWTP excluding water distribution pumps was 2661 kWh day−1. The results showed that the largest consumers of energy—after the water distribution pumps (158.1 Wh m−3)—were the processes of coagulation (1.95 Wh m−3) and flocculation (1.93 Wh m−3). A 500 kW PV system was found to be sufficient to offset the energy consumption of the water treatment only operations, for a net present value of $0.24 million. The net reduction in carbon emissions due to the PV-based design was found to be 450 and 240 metric tons CO2-eq year−1 with and without battery storage, respectively. This methodology can be applied to other existing DWTPs for design and assessment of energy consumption and use of renewables

Evaluating the Feasibility of Photovoltaic-Based Plant for Potable Water Treatment

One of the pressing issues being faced by water industry today is incorporating sustainability considerations into design practices. Water treatment, an indispensable step for safeguarding public health, is an energy-intensive process. Changing climate, carbon emissions, and rising energy costs are some of the issues that warrant exploring alternate energy sources for achieving sustainability goals of water treatment systems. The goal of the current study was to determine the feasibility of using photovoltaics (PV) as a source of energy generation for an existing drinking water treatment plant (DWTP). The selected 10 MGD plant, located in the southwestern U.S., treated groundwater by primarily using filtration and chlorination processes. Based on the energy consumption, individually determined for each unit process of the DWTP, the DWTP was sized for distributed PV and the subsequent reduction in carbon emissions was computed. Results showed that the dependency on the traditional electric grid of a DWTP can be greatly reduced by the potential use of solar PV

Renewable Energy Generation and GHG Emission Reduction Potential of a Satellite Water Reuse Plant by Using Solar Photovoltaics and Anaerobic Digestion

Wastewater treatment is a very energy-intensive process. The growing population, increased demands for energy and water, and rising pollution levels caused by fossil-fuel-based energy generation, warrants the transition from fossil fuels to renewable energy. This research explored the energy consumption offset of a satellite water reuse plant (WRP) by using solar photovoltaics (PVs) and anaerobic digestion. The analysis was performed for two types of WRPs: conventional (conventional activated sludge system (CAS) bioreactor with secondary clarifiers and dual media filtration) and advanced (bioreactor with membrane filtration (MBR)) treatment satellite WRPs. The associated greenhouse gas (GHG) emissions were also evaluated. For conventional treatment, it was found that 28% and 31.1% of the WRP’s total energy consumption and for advanced treatment, 14.7% and 5.9% of the WRP’s total energy consumption could be generated by anaerobic digestion and solar PVs, respectively. When both energy-generating units are incorporated in the satellite WRPs, MBR WRPs were on average 1.86 times more energy intensive than CAS WRPs, translating to a cost savings in electricity of $7.4/1000 m3 and$13.3/1000 m3 treated, at MBR and CAS facilities, respectively. Further, it was found that solar PVs require on average 30% longer to pay back compared to anaerobic digestion. For GHG emissions, MBR WRPs without incorporating energy generating units were found to be 1.9 times more intensive than CAS WRPs and 2.9 times more intensive with energy generating units. This study successfully showed that the addition of renewable energy generating units reduced the energy consumption and carbon emissions of the WRP

Using Distributed Solar for Treatment of Drinking Water in Developing Countries

Unsafe drinking water is a major cause of disease in developing countries. Lack of adequate water treatment and delivery infrastructure, high operational costs and poor maintenance are some of the factors contributing to the problem. Many developing countries also have large population clusters in cities and inadequate sanitation services, which increase the risk of water- borne disease outbreak. Incorporating renewable energy sources for treatment and distribution of potable water may be the key to developing sustainable water supply systems to reduce water- borne diseases in developing countries. This study focused on evaluating the potential of using distributed solar for a 4.5 million gallons per day (MGD) existing drinking water treatment plant (DWTP), located in Sindh, Pakistan. The DWTP utilized a conventional treatment train, consisting of coagulation, flocculation, sedimentation, filtration and disinfection processes to treat water obtained from the Indus River. The DWTP was sized by designing the various unit processes involved and then the energy consumption associated with each unit process was determined. The results showed that the energy consumption was largest for the flash and rapid mixers. Existing land holdings were sufficient for the deployment of solar photovoltaics (PV) which was successfully incorporated into the design of the DWTP