The Energy-Water Nexus Rising Energy Costs Meet Vulnerable Water Supplies
Water and wastewater treatment facilities are the largest and most energy-intensive facilities owned and operated by local governments.
According to Ted Jones, with Consortium for Energy Efficiency (CEE), and R. Neal Elliott, with the American Council for an Energy-Efficient Economy, in a 2002 paper, water and wastewater treatment facilities account for 35% of energy used in municipalities. Electricity use in water and wastewater treatment and pumping in the United States is estimated to cost $6.5 billion annually, with savings of 15% readily achievable.
Robert Goldstein, a researcher at the Electric Power Research Institute (EPRI), addressed the issue of electric power and water sustainability at a US Department of Energy (DOE) regional workshop in November 2005. He said there is a fast-growing demand for clean, fresh water and an increased demand for environmental protection and enhancement.
Furthermore, Goldstein said, all regions of the United States are experiencing vulnerability to water shortages, while water availability is impacting electricity supply and demand and electricity grid topology. The consequences of the growing electric power and water demands will require more intensive management of water resources, greater integration between water and energy planning, more watershed or regional planning, and new science and technology to meet these needs.
EPRI, in a large 2002 study, reported that no more than 4% of total energy use in the country is used to convey and treat water and wastewater, and that its growth will track population growth. It estimated 137.8 billion kWh would be used to supply and treat water and wastewater in 2005. Furthermore, up to 80% of that energy would be used to move water in both public and private systems.
The EPRI study went on to report that over the next 45 years, electricity demand associated with supplying water and its treatment is expected to double, alongside population growth. Irrigation pumping and industrial uses (excluding mining), however, are projected to triple in that same time frame.
In California, the California Energy Commission (CEC) says water agency electricity use is already growing at a faster rate than is the population, and will likely accelerate again in coming years as agencies grapple with new regulations and requirements that could roughly double urban water agency electricity use.
What’s Happening at the Micro Level?
Before the large studies began, water utilities and waste treatment plants were hearing messages about efficiency.
Starting in 1992 when Ray Ehrhard was at EPRI, he and his colleagues created a national program to encourage individual water and wastewater plants to study how they could reduce energy use.
“In the past 10 years it has changed a lot,” Ehrhard says. Most plants recognize energy is a substantial cost, just behind labor in operating costs. But 15 years ago most plant managers thought they could not control energy costs without putting water quality at risk. In the conventional approach, water is taken from the river or ground, energy is used to clean it up and treat it, it is distributed to homes and businesses, and then it is dumped in a sewer. “There’s a lot of waste” in this approach, he says.
Ehrhard, who is now deputy director of the Community Environment Center at Washington University in St. Louis, and his group there are discovering facilities across the country are taking unique approaches, defined by region, weather, and population, all guided by understanding the overall energy impacts of what is done and keeping water quality and energy use at the site in balance. “You can’t sacrifice water quality for energy efficiency. … They work together to achieve both goals,” says Ehrhard.
Also, new technologies and good studies are making a difference, Ehrhard explains. In 1992, it was easy to reduce energy use. There was a lot of low-hanging fruit, he says. By changing operations to improve water quality and reduce energy use, the plant could save between 15% and 40% of its operating costs. For example, Ehrhard and his colleagues at EPRI demonstrated that shifting some of the large energy-using equipment to nighttime operations to get the plant off high demand rates saved money. Furthermore, by looking at processes, managers could see how pumping schedules could be modified to match water levels. And they were shown more effective ways to reduce energy use by installing diffuser units to add air to water on a controlled basis, rather than adding it indiscriminately.
The new microturbine technology and escalating energy prices are introducing new opportunities at wastewater plants, Ehrhard says. In his current job, he and his staff have done energy audits at plants to demonstrate how to best use and recover energy. For example, sludge produced at a wastewater plant is transferred to a digester where methane is produced. Traditionally it has been flared, but it is becoming increasingly cost-effective to install microturbines to burn the methane gas and produce electricity. Moreover, the State of Wisconsin is now giving incentives to wastewater plants to install microturbines, Ehrhard says.
In another example, ultraviolet lighting is replacing chlorine as a water disinfectant for safety reasons, but the retrofitting should be done in the most energy-efficient and relevant way, given the process considerations, explains Ehrhard.
Energy-Efficient Motors
The Consortium for Energy Efficiency’s National Municipal Water and Wastewater Facility Initiative is encouraging suppliers of products and services to adopt energy efficiency as a standard industry practice. CEE’s Web site features case studies on illustrating the savings available to facilities.
To cite one case study, the Kennewick, WA, Wastewater Treatment Plant, among its many operations, uses large motors to aerate two high-rate treatment ponds. The annual costs for fixed aeration represent the biggest single operating cost at the plant, and increased from $152,000 in 2001 to $211,000 the following year. The plant achieved annual cost savings of $4,500 by adopting motor repair purchasing specifications designed to ensure that energy efficiency is retained when a motor is repaired.
Rewinding eight motors ranging in size from 40 horsepower to 150 horsepower is saving the facility $25,000 over the life of the motors. Efficiency loss of rewound motors could increase operating costs between $242 and $907 per motor, depending on the size, according to the case study. Kennewick plant managers also completed a plant-wide motor census and database of 95 motors, which will allow them to launch additional motor system efficiency efforts.
The View From the Macro Level
The Energy-Water Nexus is a far-ranging US Department of Energy multi-laboratory reporting effort funded to the tune of $50,000 last year by Congress to produce a report on the interdependency of energy and water focusing on the “threat to national energy production resulting from limited water supplies.” Its scope, based on the results of three regional workshops, goes well beyond that limited focus.
Sandia National Laboratories took the lead in organizing and coordinating the regional workshops and preparing the report to Congress. The report was submitted to DOE and the Office of Management and Budget in March for review. Once the review is completed, it will be posted on the Energy-Water Nexus Web site, www.sandia.gov/energy-water/.
In its overview, the Energy-Water Nexus Committee notes that the electricity industry is second only to agriculture as the largest user of water in the US, with electricity production from fossil fuels and nuclear energy accounting for 39% of all daily freshwater withdrawals in the nation. Fossil fuel generation accounted for 71% of that total. Yet energy use to distribute and treat water and wastewater by public agencies and private companies is just 4%. The Energy-Water Nexus report will cover the whole of the energy/water relationship, while this story is focusing on the 4% and its future growth.
The Energy-Water Nexus Committee observed in a synopsis on its Web site following the workshops held in the fall and winter of 2005 that the three regions displayed distinct differences and similarities between each other in their concerns about problems and needs. Eastern region participants are particularly concerned about the decay of water treatment and delivery infrastructures leading to significant energy consumption and water loss from leakage.
Central and western region participants noted significant transmission and distribution problems and constraints. Western participants were more interested in climate change and its impacts on water supplies and energy production, as well as conservation programs.
Eastern region participants generally had a more difficult time “seeing” the interactions between energy and water than their western and central counterparts and generally did not seem to view water vis-à-vis energy production as a significant long-term problem, said the committee synopsis of the workshops. The synopsis attributed this viewpoint as possibly being a result of eastern water law and relatively high precipitation rates in the region.
Similarities among the regions included common concerns with the lack of long-term or integrated resource planning, the lack of consistent and detailed data, the lack of models that can be used to address current and emerging problems at the energy-water nexus, and the lack of water-intensity considerations in current energy research, development, and demonstration programs.
Is There Enough Energy?
A major report published by EPRI in 2002, referred to earlier, is widely referenced by professionals in the field. The four-volume work, including the fourth volume Water and Sustainability: U.S. Electricity Consumption for Water Supply & Treatment—The Next Half Century, researched and written by ICF Consulting, concluded in Volume 4 that “given this relatively small portion of total electricity requirement” (4%), changes in the supply or availability of electricity are not expected to have a major impact on water production and demand.
The EPRI research was guided by the question, “Will there be sufficient electricity available to satisfy the country’s need for fresh water?” To answer this question, the study authors created a methodology to estimate and project electricity requirements to deliver and treat water and wastewater using forecast data from the Energy Information Administration, the US Census Bureau, and inventories of public water systems maintained by the US Environmental Protection Agency.
The EPRI research resorted to creating a methodology because, as others have noted, most public agencies that supply or treat water were not able to provide information on energy consumption of their facilities, even though it is probably the most costly element in freshwater treatment.
The EPRI study noted that there are more than 150,000 public water supply systems, 23,000 privately operated wastewater treatment facilities, and 16,000 publicly owned treatment works. The privately owned facilities were estimated to consume 49 billion kWh in 2005, the public supply systems consumed an estimated 31.9 billion kWh, and the publicly owned treatment facilities consumed 24.5 billion kWh.
The EPRI study projects that water use by public water agencies will increase from 31.9 billion kWh in 2005 to 45.6 billion kWh in 2050. This projection will vary up or down 2.2%, between 36 billion kWh and 55 billion kWh, based on the following factors.
As water systems age, friction in piping increases, resulting in an increase in electricity requirements for pumping. Water conservation programs could reduce the overall amount of electricity required, but this may result in an increase in unit electricity consumption as economies of scale are lost or systems operate at below optimum levels.
Furthermore, as standards and requirements for drinking-water quality increase, more rigorous treatment will be required, and increased processing will result in increased pumping energy requirements. Additional water pumping associated with advanced wastewater treatment may triple the electricity use of a conventional trickling filter system. The study suggested public supply agencies could expect to see their electricity use increase by 20% by 2005. Once major treatment approach changes are completed, another 20% increase can be expected over the next 45 years, the study said.
Factors that may decrease electricity consumption for water supply are a trend to larger systems that would provide economies of scale, and replacement of older equipment with more energy-efficient pumps, drives, and water processing equipment.
Privately owned wastewater treatment facilities are associated with industrial plants, are designed to deal with specific contaminants generated by the industrial processes, and are smaller than publicly owned wastewater treatment plants. Unit electricity consumption is presumed to be about 2,500 kWh per million gallons. The EPRI study predicts that more aggressive wastewater treatment will be required over the next 20 years and increase unit electricity consumption by perhaps 5% to 10%.
The EPRI study predicts that more privately operated wastewater treatment facilities will be constructed between now and 2025, increasing the total amount of electricity required to process industrial wastewater over the next 45 years.
One factor pushing this trend likely will be municipally owned wastewater treatment facilities reaching their treatment limits. Industrial facilities that have been releasing pretreated or untreated wastewater to the public treatment facilities may find it less expensive instead to increase pretreatment than to pay increasing public surcharges.
To correct the lack of real-world data, the American Water Works Association Research Foundation (AWWARF) is managing research funded by the California Energy Commission (CEC) and the New York State Energy Research and Development Authority. CDH Energy Corp., on behalf of AWWARF, developed, tested, and now is conducting a national survey of water and wastewater facilities.
The project is collecting data about facility usage and energy consumption. The intention is to create an index or indices to measure the results of a water or wastewater utility’s energy management strategy. The utilities will be able to measure operational performance relative to internal and external benchmarks, establish performance targets and budgets, and identify key drivers and practices that produce high performance, according to AWWARF.
The Consortium for Energy Efficiency has the survey forms on its Web site and is asking that municipal water and wastewater facilities download the forms, complete them, and send them to CDH Energy. The Web address for the surveys is www.cee1.org/ind/mot-sys/ww/ww.php3. It can also be found by going to CEE’s Web site at www.cee1.org and clicking on “Water and Wastewater” under the “Industrial” heading.
Profile of an Energy-Intensive Water System
The California Energy Commission has launched a research effort, the first of its kind in the US, to identify and manage energy use in California’s water conveyance, treatment, and end-use system. It already has produced an early report estimating energy usage for most of its water sector as part of its 2005 Integrated Energy Policy Report.
The CEC found that very little data exist for groundwater pumping in the state. Huge data gaps exist in the energy requirements for irrigation in the agriculture industry, and what few data are available is quickly outdated because of rapid changes in planting patterns in response to crop price dynamics.
Energy consumption in California in 2004 was 271,000 GWh, and grew an average of 2% over the prior two years, due to diminished voluntary consumer conservation and a shorter and milder recession. Consumption is forecast to grow between 1.2% and 1.6% annually to between 313,464 GWh and 326,452 GWh by 2016. This growth matches projected population growth.
Current electrical demand in California’s water supply, treatment, and irrigation pumping sectors is 15,610 GWh, about 5% of total energy consumption in the state.
California has developed highly sophisticated water conveyance systems to move water from northern California to its most dense urban population center in southern California. As a result, unit energy use varies in the extreme compared to other parts of the US, primarily because of the wide distances water is shipped. The actual electricity needed for conveyance of a given water shipment varies from essentially zero to more than 9,000 kWh per million gallons. The CEC staff estimates that, on average in California, about 100 kWh are needed to convey 1 million gallons from their source to the treatment plant.
To illustrate, in its report, Water-Energy Relationshipin Support of the 2005 Integrated Energy Policy Report, the CEC contrasted electricity use by two water agencies, both in northern California. Sonoma County Water Agency required nearly 2,600 kWh per million gallons to pump and treat water from the Russian River for its water supply over the period of April 2000 to September 2002. Pumping costs were constant throughout the year.
In contrast, the East Bay Municipal Utility District (EBMUD) gets 95% of its water from the Mokelumne River delivered by gravity through an aqueduct. The water is relatively high in quality at its source, requiring little treatment. The district’s treatment facilities are located high in the East Bay hills (east of San Francisco) using the elevation to help pressurize its distribution system. As a result, EBMUD’s electricity use is approximately 150 kWh per million gallons for conveyance, and 275 kWh per million gallons for treatment.
The state’s major water conveyance systems also illustrate the contrasts in energy costs. The Hetch Hetchy water system brings water from a reservoir on the Tuolumne River in Yosemite National Park 280 miles to San Francisco. Gravity moves the water 160 miles to the San Francisco Bay Area through pipes buried beneath the Central Valley floor. Pumping is needed only after the water reaches the Bay Area. Three major powerhouses located on its system deliver 1.7 GWh annually to the San Francisco area.
The Los Angeles Aqueduct’s 220-mile water system was built almost 100 years ago by the Los Angeles Department of Water and Power to bring water from the Owens Valley on the east side of the Sierra Mountains to Los Angeles. A second aqueduct added in 1970 transports water more than 137 miles from a reservoir in southern Inyo County to Los Angeles. Neither system consumes or produces electric power.
The State Water Project, the largest in the nation, and the largest energy consumer in the state’s water system, ships water south from the Feather River basin and Lake Oroville in northern California up and down mountains to users in southern California. It has a complex network of pumping plants that consume about 12,200 GWh each year and generating plants that produce about 7,600 GWh per year, for a net energy use of about 4,600 GWh.
According to the CEC, the urban agencies that are recipients of this water and water from other sources use between 100 and 5,000 kWh per million gallons for water treatment, and zero to 1,200 kWh per million gallons for distribution. Wastewater pumping varies between zero and 400 kWh per million gallons, and wastewater treatment varies between 1,000 and 3,500 kWh per million gallons.
As a comparison, the EPRI study estimated that nationally a surface-water treatment facility uses, on the average, 1,406 kWh per million gallons and a groundwater treatment unit consumes 1,824 kWh per million gallons, some 30% greater than for surface water because of the increased pumping that is required. About one-third is used for well pumping while the remainder is used for booster pumping into the distribution system. Less than 0.5% of electricity is used for chlorination of the water. Unfortunately, the authors of the EPRI study did not separate out costs for conveyance and treatment.
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In Conclusion
The EPRI study authors, in the end, offered the perspective that electricity availability is not a constraint on water supply and treatment capabilities. Rather, they said, it is electricity supply and demand that depends on water availability.
As we face the environmental impacts of climate change, drought, and population increases, especially in the western states, plus increased clean-water regulations, we will have to count on improving energy and water efficiencies as the controllers for rising costs.
Author's Bio: CA-based, Lyn Corum is a technical writer, specializing in energy topics.
September-October 2006
The Energy-Water Nexus Rising Energy Costs Meet Vulnerable Water Supplies
Water and wastewater treatment facilities are the largest and most energy-intensive facilities owned and operated by local governments.
According to Ted Jones, with Consortium for Energy Efficiency (CEE), and R. Neal Elliott, with the American Council for an Energy-Efficient Economy, in a 2002 paper, water and wastewater treatment facilities account for 35% of energy used in municipalities. Electricity use in water and wastewater treatment and pumping in the United States is estimated to cost $6.5 billion annually, with savings of 15% readily achievable.
Robert Goldstein, a researcher at the Electric Power Research Institute (EPRI), addressed the issue of electric power and water sustainability at a US Department of Energy (DOE) regional workshop in November 2005. He said there is a fast-growing demand for clean, fresh water and an increased demand for environmental protection and enhancement.
Furthermore, Goldstein said, all regions of the United States are experiencing vulnerability to water shortages, while water availability is impacting electricity supply and demand and electricity grid topology. The consequences of the growing electric power and water demands will require more intensive management of water resources, greater integration between water and energy planning, more watershed or regional planning, and new science and technology to meet these needs.
EPRI, in a large 2002 study, reported that no more than 4% of total energy use in the country is used to convey and treat water and wastewater, and that its growth will track population growth. It estimated 137.8 billion kWh would be used to supply and treat water and wastewater in 2005. Furthermore, up to 80% of that energy would be used to move water in both public and private systems.
The EPRI study went on to report that over the next 45 years, electricity demand associated with supplying water and its treatment is expected to double, alongside population growth. Irrigation pumping and industrial uses (excluding mining), however, are projected to triple in that same time frame.
In California, the California Energy Commission (CEC) says water agency electricity use is already growing at a faster rate than is the population, and will likely accelerate again in coming years as agencies grapple with new regulations and requirements that could roughly double urban water agency electricity use.
What’s Happening at the Micro Level?
Before the large studies began, water utilities and waste treatment plants were hearing messages about efficiency.
Starting in 1992 when Ray Ehrhard was at EPRI, he and his colleagues created a national program to encourage individual water and wastewater plants to study how they could reduce energy use.
“In the past 10 years it has changed a lot,” Ehrhard says. Most plants recognize energy is a substantial cost, just behind labor in operating costs. But 15 years ago most plant managers thought they could not control energy costs without putting water quality at risk. In the conventional approach, water is taken from the river or ground, energy is used to clean it up and treat it, it is distributed to homes and businesses, and then it is dumped in a sewer. “There’s a lot of waste” in this approach, he says.
Ehrhard, who is now deputy director of the Community Environment Center at Washington University in St. Louis, and his group there are discovering facilities across the country are taking unique approaches, defined by region, weather, and population, all guided by understanding the overall energy impacts of what is done and keeping water quality and energy use at the site in balance. “You can’t sacrifice water quality for energy efficiency. … They work together to achieve both goals,” says Ehrhard.
Also, new technologies and good studies are making a difference, Ehrhard explains. In 1992, it was easy to reduce energy use. There was a lot of low-hanging fruit, he says. By changing operations to improve water quality and reduce energy use, the plant could save between 15% and 40% of its operating costs. For example, Ehrhard and his colleagues at EPRI demonstrated that shifting some of the large energy-using equipment to nighttime operations to get the plant off high demand rates saved money. Furthermore, by looking at processes, managers could see how pumping schedules could be modified to match water levels. And they were shown more effective ways to reduce energy use by installing diffuser units to add air to water on a controlled basis, rather than adding it indiscriminately.
The new microturbine technology and escalating energy prices are introducing new opportunities at wastewater plants, Ehrhard says. In his current job, he and his staff have done energy audits at plants to demonstrate how to best use and recover energy. For example, sludge produced at a wastewater plant is transferred to a digester where methane is produced. Traditionally it has been flared, but it is becoming increasingly cost-effective to install microturbines to burn the methane gas and produce electricity. Moreover, the State of Wisconsin is now giving incentives to wastewater plants to install microturbines, Ehrhard says.
In another example, ultraviolet lighting is replacing chlorine as a water disinfectant for safety reasons, but the retrofitting should be done in the most energy-efficient and relevant way, given the process considerations, explains Ehrhard.
Energy-Efficient Motors
The Consortium for Energy Efficiency’s National Municipal Water and Wastewater Facility Initiative is encouraging suppliers of products and services to adopt energy efficiency as a standard industry practice. CEE’s Web site features case studies on illustrating the savings available to facilities.
To cite one case study, the Kennewick, WA, Wastewater Treatment Plant, among its many operations, uses large motors to aerate two high-rate treatment ponds. The annual costs for fixed aeration represent the biggest single operating cost at the plant, and increased from $152,000 in 2001 to $211,000 the following year. The plant achieved annual cost savings of $4,500 by adopting motor repair purchasing specifications designed to ensure that energy efficiency is retained when a motor is repaired.
Rewinding eight motors ranging in size from 40 horsepower to 150 horsepower is saving the facility $25,000 over the life of the motors. Efficiency loss of rewound motors could increase operating costs between $242 and $907 per motor, depending on the size, according to the case study. Kennewick plant managers also completed a plant-wide motor census and database of 95 motors, which will allow them to launch additional motor system efficiency efforts.
The View From the Macro Level
The Energy-Water Nexus is a far-ranging US Department of Energy multi-laboratory reporting effort funded to the tune of $50,000 last year by Congress to produce a report on the interdependency of energy and water focusing on the “threat to national energy production resulting from limited water supplies.” Its scope, based on the results of three regional workshops, goes well beyond that limited focus.
Sandia National Laboratories took the lead in organizing and coordinating the regional workshops and preparing the report to Congress. The report was submitted to DOE and the Office of Management and Budget in March for review. Once the review is completed, it will be posted on the Energy-Water Nexus Web site, www.sandia.gov/energy-water/.
In its overview, the Energy-Water Nexus Committee notes that the electricity industry is second only to agriculture as the largest user of water in the US, with electricity production from fossil fuels and nuclear energy accounting for 39% of all daily freshwater withdrawals in the nation. Fossil fuel generation accounted for 71% of that total. Yet energy use to distribute and treat water and wastewater by public agencies and private companies is just 4%. The Energy-Water Nexus report will cover the whole of the energy/water relationship, while this story is focusing on the 4% and its future growth.
The Energy-Water Nexus Committee observed in a synopsis on its Web site following the workshops held in the fall and winter of 2005 that the three regions displayed distinct differences and similarities between each other in their concerns about problems and needs. Eastern region participants are particularly concerned about the decay of water treatment and delivery infrastructures leading to significant energy consumption and water loss from leakage.
Central and western region participants noted significant transmission and distribution problems and constraints. Western participants were more interested in climate change and its impacts on water supplies and energy production, as well as conservation programs.
Eastern region participants generally had a more difficult time “seeing” the interactions between energy and water than their western and central counterparts and generally did not seem to view water vis-à-vis energy production as a significant long-term problem, said the committee synopsis of the workshops. The synopsis attributed this viewpoint as possibly being a result of eastern water law and relatively high precipitation rates in the region.
Similarities among the regions included common concerns with the lack of long-term or integrated resource planning, the lack of consistent and detailed data, the lack of models that can be used to address current and emerging problems at the energy-water nexus, and the lack of water-intensity considerations in current energy research, development, and demonstration programs.
Is There Enough Energy?
A major report published by EPRI in 2002, referred to earlier, is widely referenced by professionals in the field. The four-volume work, including the fourth volume Water and Sustainability: U.S. Electricity Consumption for Water Supply & Treatment—The Next Half Century, researched and written by ICF Consulting, concluded in Volume 4 that “given this relatively small portion of total electricity requirement” (4%), changes in the supply or availability of electricity are not expected to have a major impact on water production and demand.
The EPRI research was guided by the question, “Will there be sufficient electricity available to satisfy the country’s need for fresh water?” To answer this question, the study authors created a methodology to estimate and project electricity requirements to deliver and treat water and wastewater using forecast data from the Energy Information Administration, the US Census Bureau, and inventories of public water systems maintained by the US Environmental Protection Agency.
The EPRI research resorted to creating a methodology because, as others have noted, most public agencies that supply or treat water were not able to provide information on energy consumption of their facilities, even though it is probably the most costly element in freshwater treatment.
The EPRI study noted that there are more than 150,000 public water supply systems, 23,000 privately operated wastewater treatment facilities, and 16,000 publicly owned treatment works. The privately owned facilities were estimated to consume 49 billion kWh in 2005, the public supply systems consumed an estimated 31.9 billion kWh, and the publicly owned treatment facilities consumed 24.5 billion kWh.
The EPRI study projects that water use by public water agencies will increase from 31.9 billion kWh in 2005 to 45.6 billion kWh in 2050. This projection will vary up or down 2.2%, between 36 billion kWh and 55 billion kWh, based on the following factors.
As water systems age, friction in piping increases, resulting in an increase in electricity requirements for pumping. Water conservation programs could reduce the overall amount of electricity required, but this may result in an increase in unit electricity consumption as economies of scale are lost or systems operate at below optimum levels.
Furthermore, as standards and requirements for drinking-water quality increase, more rigorous treatment will be required, and increased processing will result in increased pumping energy requirements. Additional water pumping associated with advanced wastewater treatment may triple the electricity use of a conventional trickling filter system. The study suggested public supply agencies could expect to see their electricity use increase by 20% by 2005. Once major treatment approach changes are completed, another 20% increase can be expected over the next 45 years, the study said.
Factors that may decrease electricity consumption for water supply are a trend to larger systems that would provide economies of scale, and replacement of older equipment with more energy-efficient pumps, drives, and water processing equipment.
Privately owned wastewater treatment facilities are associated with industrial plants, are designed to deal with specific contaminants generated by the industrial processes, and are smaller than publicly owned wastewater treatment plants. Unit electricity consumption is presumed to be about 2,500 kWh per million gallons. The EPRI study predicts that more aggressive wastewater treatment will be required over the next 20 years and increase unit electricity consumption by perhaps 5% to 10%.
The EPRI study predicts that more privately operated wastewater treatment facilities will be constructed between now and 2025, increasing the total amount of electricity required to process industrial wastewater over the next 45 years.
One factor pushing this trend likely will be municipally owned wastewater treatment facilities reaching their treatment limits. Industrial facilities that have been releasing pretreated or untreated wastewater to the public treatment facilities may find it less expensive instead to increase pretreatment than to pay increasing public surcharges.
To correct the lack of real-world data, the American Water Works Association Research Foundation (AWWARF) is managing research funded by the California Energy Commission (CEC) and the New York State Energy Research and Development Authority. CDH Energy Corp., on behalf of AWWARF, developed, tested, and now is conducting a national survey of water and wastewater facilities.
The project is collecting data about facility usage and energy consumption. The intention is to create an index or indices to measure the results of a water or wastewater utility’s energy management strategy. The utilities will be able to measure operational performance relative to internal and external benchmarks, establish performance targets and budgets, and identify key drivers and practices that produce high performance, according to AWWARF.
The Consortium for Energy Efficiency has the survey forms on its Web site and is asking that municipal water and wastewater facilities download the forms, complete them, and send them to CDH Energy. The Web address for the surveys is www.cee1.org/ind/mot-sys/ww/ww.php3. It can also be found by going to CEE’s Web site at www.cee1.org and clicking on “Water and Wastewater” under the “Industrial” heading.
Profile of an Energy-Intensive Water System
The California Energy Commission has launched a research effort, the first of its kind in the US, to identify and manage energy use in California’s water conveyance, treatment, and end-use system. It already has produced an early report estimating energy usage for most of its water sector as part of its 2005 Integrated Energy Policy Report.
The CEC found that very little data exist for groundwater pumping in the state. Huge data gaps exist in the energy requirements for irrigation in the agriculture industry, and what few data are available is quickly outdated because of rapid changes in planting patterns in response to crop price dynamics.
Energy consumption in California in 2004 was 271,000 GWh, and grew an average of 2% over the prior two years, due to diminished voluntary consumer conservation and a shorter and milder recession. Consumption is forecast to grow between 1.2% and 1.6% annually to between 313,464 GWh and 326,452 GWh by 2016. This growth matches projected population growth.
Current electrical demand in California’s water supply, treatment, and irrigation pumping sectors is 15,610 GWh, about 5% of total energy consumption in the state.
California has developed highly sophisticated water conveyance systems to move water from northern California to its most dense urban population center in southern California. As a result, unit energy use varies in the extreme compared to other parts of the US, primarily because of the wide distances water is shipped. The actual electricity needed for conveyance of a given water shipment varies from essentially zero to more than 9,000 kWh per million gallons. The CEC staff estimates that, on average in California, about 100 kWh are needed to convey 1 million gallons from their source to the treatment plant.
To illustrate, in its report, Water-Energy Relationshipin Support of the 2005 Integrated Energy Policy Report, the CEC contrasted electricity use by two water agencies, both in northern California. Sonoma County Water Agency required nearly 2,600 kWh per million gallons to pump and treat water from the Russian River for its water supply over the period of April 2000 to September 2002. Pumping costs were constant throughout the year.
In contrast, the East Bay Municipal Utility District (EBMUD) gets 95% of its water from the Mokelumne River delivered by gravity through an aqueduct. The water is relatively high in quality at its source, requiring little treatment. The district’s treatment facilities are located high in the East Bay hills (east of San Francisco) using the elevation to help pressurize its distribution system. As a result, EBMUD’s electricity use is approximately 150 kWh per million gallons for conveyance, and 275 kWh per million gallons for treatment.
The state’s major water conveyance systems also illustrate the contrasts in energy costs. The Hetch Hetchy water system brings water from a reservoir on the Tuolumne River in Yosemite National Park 280 miles to San Francisco. Gravity moves the water 160 miles to the San Francisco Bay Area through pipes buried beneath the Central Valley floor. Pumping is needed only after the water reaches the Bay Area. Three major powerhouses located on its system deliver 1.7 GWh annually to the San Francisco area.
The Los Angeles Aqueduct’s 220-mile water system was built almost 100 years ago by the Los Angeles Department of Water and Power to bring water from the Owens Valley on the east side of the Sierra Mountains to Los Angeles. A second aqueduct added in 1970 transports water more than 137 miles from a reservoir in southern Inyo County to Los Angeles. Neither system consumes or produces electric power.
The State Water Project, the largest in the nation, and the largest energy consumer in the state’s water system, ships water south from the Feather River basin and Lake Oroville in northern California up and down mountains to users in southern California. It has a complex network of pumping plants that consume about 12,200 GWh each year and generating plants that produce about 7,600 GWh per year, for a net energy use of about 4,600 GWh.
According to the CEC, the urban agencies that are recipients of this water and water from other sources use between 100 and 5,000 kWh per million gallons for water treatment, and zero to 1,200 kWh per million gallons for distribution. Wastewater pumping varies between zero and 400 kWh per million gallons, and wastewater treatment varies between 1,000 and 3,500 kWh per million gallons.
As a comparison, the EPRI study estimated that nationally a surface-water treatment facility uses, on the average, 1,406 kWh per million gallons and a groundwater treatment unit consumes 1,824 kWh per million gallons, some 30% greater than for surface water because of the increased pumping that is required. About one-third is used for well pumping while the remainder is used for booster pumping into the distribution system. Less than 0.5% of electricity is used for chlorination of the water. Unfortunately, the authors of the EPRI study did not separate out costs for conveyance and treatment.
In Conclusion
The EPRI study authors, in the end, offered the perspective that electricity availability is not a constraint on water supply and treatment capabilities. Rather, they said, it is electricity supply and demand that depends on water availability.
As we face the environmental impacts of climate change, drought, and population increases, especially in the western states, plus increased clean-water regulations, we will have to count on improving energy and water efficiencies as the controllers for rising costs.