The Undiluted Cost of Energy and Water: From Rainfall to Outfall. Greg Harrington Professor and Associate Chair

Transcription

1 The Undiluted Cost of Energy and Water: From Rainfall to Outfall Greg Harrington Professor and Associate Chair

2 Acknowledgments Graduate students Todd Elliott Irene Xagoraraki Ben Zeier Joshua Bohnert Mike Danielson Yejoong Kim David Miller Nick Baniel Matt Hayes

3 Presentation Background & Objectives Drinking water utilities in Wisconsin use 1.5 to 2.3 kwh of electricity for every 1000 gallons of water produced Total amount of energy used statewide is about 370 GWh/year Wastewater utilities use 1.4 to 7.3 kwh/1000 gallons The objectives of this presentation are to: Illustrate the dominant uses of energy Highlight sources of inefficiency Describe options to consider for reducing energy consumption

4 Why We Have Municipal Water Systems Part 1 Typhoid Deaths in Wisconsin Milwaukee Cryptosporidium Outbreak March/April ,000 illnesses; 69 to 105 deaths $96.2 million community-wide * $31.7 million medical $64.6 million productivity losses Individual total costs * $7,800 for severe case $500 for moderate case $100 for mild case $89 million treatment upgrade Source: Baumeister. June Wisconsin Natural Resources * Corso et al., 2003, Emerging Infectious Diseases, vol 9, no 4

5 Why We Have Municipal Water Systems Part 2 $168 million property loss in 1871 Chicago fire (below left) $3.3 billion in Year 2013 dollars, 3 rd largest property loss in a U.S. fire 1152 deaths in 1871 Peshtigo, Wisconsin fire 3 rd largest loss of life in a U.S. fire Oshkosh 5 major fires from 1859 to aftermath (below right) Chicago & Peshtigo statistics from Madison has 8,500 fire hydrants Oshkosh has 2,800 fire hydrants

6 Average Daily Gallons Sold per Customer Water Conservation and Reducing Water Loss Milwaukee Madison Per capita water use is declining Chart on left shows use per residential customer Per capita use would be about 2.5 times smaller Water loss is 10% to 20% of water pumped Significant opportunities to reduce energy use with use at 1.5 to 2.3 kwh/1000 gallons Consequences of conservation: Increased water age and associated treatment cost Loss of revenue and need to increase cost per gallon

7 Pressure to Serve Minimum allowable pressure at tap = 35 psi Utilities often target 40 psi minimum to ensure compliance Vertical distance must be at least 92.3 feet between: Highest tap in buildings served Lowest water elevation in tank 0.29 kwh to lift 1000 gallons of water across an elevation change of 92.3 ft Assuming 100% efficiency (more on this later ) Typical water tower holds 100,000 to 1,000,000 gal 92.3 ft

8 Why So Much Pressure? If gasket ruptures under normal operating pressure, water will flow out and limit contamination. If gasket ruptures under low enough operating pressure, water could flow in and lead to contamination. fire fighting, too

9 Total Lift for Surface Water Sources Water elevation in tank fluctuates to meet hourly changes in water demand Adds elevation to minimum pressure needs Volume needed is community-specific Source water elevation varies with climate and engineered systems (locks & dams) Lake Michigan: 576 to 582 feet above sea level Lake Winnebago: 745 to 748 feet above sea level Pumping is needed to get water from lowest water elevation in source to highest water elevation in tank 92.3 ft Total Lift

10 Impact of Topography Inadequate Pressure < 92.3 ft 92.3 ft Total Lift < 40 psi

11 Impact of Topography Max Allowable Pressure 92.3 ft (40 psi) Must be 231 ft (100 psi) Total Lift

12 Impact of Topography Pressure Zones 92.3 ft 92.3 ft Total Lift to Pressure Zone 1 Total Lift to Pressure Zone 2 Pressure Zone 2 Pressure Zone 1

13 Example: Oshkosh, Wisconsin 92.3 ft 92.3 ft 172 ft 260 ft Pressure Zone ft = 0.82 kwh/1000 gal energy values still assume 100% efficiency Pressure Zone ft = 0.54 kwh/1000 gal Lake Winnebago

14 Example: Racine, Wisconsin 205 ft 286 ft 299 ft 357 ft PZ kwh/1000 gal PZ kwh/1000 gal energy values still assume 100% efficiency PZ kwh/1000 gal PZ kwh/1000 gal Lake Michigan

15 Total Lift for Groundwater Sources Water elevation in tank fluctuates to meet hourly changes in water demand Adds elevation to minimum pressure needs Volume needed is community-specific Drawdown in well varies with: Geologic formation Pumping rate Pumping is needed to get water from lowest water elevation in well to highest water elevation in tank 92.3 ft Total Lift Drawdown

16 Example: Madison, Wisconsin Wells 6 and ft 332 ft 92.3 ft 282 ft Unit Well 6 Unit Well kwh/1000 gal (47% due to drawdown) 157 ft 0.89 kwh/1000 gal (62% due to drawdown) 175 ft energy values still assume 100% efficiency

17 Example: Madison, Wisconsin Well ft 1.40 kwh/1000 gal (56% due to drawdown) 92.3 ft 1.06 kwh/1000 gal (74% due to drawdown) 336 ft Unit Well ft 249 ft energy values still assume 100% efficiency

18 Aquifers Used in Northern Wisconsin Sand & Gravel Dolomite Shale Crystalline Bedrock

19 Aquifers Used in Southern Wisconsin Sand & Gravel Dolomite Shale Crystalline Bedrock

20 Depth to Groundwater in Wisconsin

21 Depth to Groundwater and Energy Intensity

22 Can You Do Anything About This? Minimum pressure expectation at tap is fixed Can t change minimum amount of energy needed per foot of lift Source water elevation control Utilities have little to no control of surface water elevations Drawdown of groundwater can be controlled with modified operation - more on next slide Might be able to modify pressure zone boundaries Can high-volume customers or large number of mid-volume customers be moved from a higher pressure zone to a lower pressure zone? Maximum tank elevations can theoretically be managed Larger diameter storage tanks are more energy efficient than smaller diameter tanks of same volume Only recover kwh/1000 gallons for every 10 feet of lowered elevation; tough to save more than 10 feet

23 Drawdown Management Instead of operating a pump at full flow rate for short time periods, operate pump at lower flow rate for longer time periods Example: 1500 gal/min for 9 hrs/day vs 750 gal/min for 18 hrs/day Slower flow rate produces less drawdown and less total lift Need to use variable frequency drive (VFD) to slow pump s operating speed

24 VFD Example: Madison, Wisconsin Well ft 332 ft energy values still assume 100% efficiency 92.3 ft 268 ft Unit Well 6 Unit Well 6 Full Speed 2430 gal/min 1.04 kwh/1000 gal (47% due to drawdown) 157 ft 70% Speed 1250 gal/min 0.84 kwh/1000 gal (35% due to drawdown) 93 ft

25 Be Careful With Drawdown Management Do water towers or other storage tanks have sufficient capacity? Slower pumping requires more water in the tank at the start of high demand periods Can pump achieve required lift at slower speed? Reduced speed reduces both flow rate and lift capabilities Does loss in pump efficiency offset amount of drawdown?

26 Pump Efficiency Pump Efficiency Depends on Motor Speed Motor Speed (%) Unit Well 6 Unit Well 9 Unit Well 25

27 Energy (kwh) What About Throttling Flow? Single speed pump with throttled valve Same pump with variable frequency drive Flow Rate (gpm)

28 Other Hydraulic Inefficiencies Pumps typically have optimal efficiencies of 75% to 85% Some may be operated at 60% efficiency, as noted above Strive to operate near optimal Pump motors have 90% to 95% efficiencies Pipe friction Smaller pipe diameters consume more energy Corroded pipe consumes more energy

29 Water Treatment Uses Electricity Implementation of additional barriers against Cryptosporidium has increased energy use Conventional filtration techniques consume approximately 0.20 kwh per 1000 gallons above usage due to distribution system pumping Lift needed to push water through filter Mixers and pumps for chemical feed Waste stream pumping Filter backwash pumping

30 Energy Intensive Technology Implementation Processes installed since 1998 in Wisconsin Ozonation 0.3 to 0.5 kwh/1000 gal Milwaukee, Oshkosh, Green Bay Ultraviolet Irradiation 0.05 to 0.1 kwh/1000 gal North Shore, Cudahy, Neenah, Menasha, Sheboygan Membrane Filtration 0.2 to 0.5 kwh/1000 gal Kenosha, Manitowoc, Ashland, Appleton, Marinette, Two Rivers, Racine, South Milwaukee

31 Implementation of Membrane Treatment New Treatment Plant in Appleton Appleton +1.3 kwh/1000 gal Ashland +0.8 kwh/1000 gal Two Rivers +0.5 kwh/1000 gal Racine +0.4 kwh/1000 gal Manitowoc +0.3 kwh/1000 gal Kenosha -0.1 kwh/1000 gal

32 Radium Removal in Hustisford, Wisconsin Two radium treatment plants installed

33 Wastewater Collection and Treatment Lift stations in the collection system Removing substances that consume oxygen requires aeration Activated sludge Oxidation ditches Aerated lagoons Biosolids processing Anaerobic digestion Dewatering From Water and Wastewater Energy Best Practice Guidebook; Focus on Energy, SAIC (2006)

34 Activated Sludge Systems Average of 4.0 kwh/1000 gal Entire system, not just activated sludge component Depends on system size, smaller uses more Based on survey of 51 facilities in Wisconsin Benchmarks 1.7 kwh/1000 gal for systems > 1 MGD 3.1 kwh/1000 gal for systems < 1 MGD

35 Oxidation Ditch Systems Average of 6.9 kwh/1000 gal Entire system, not just oxidation ditch component Based on survey of 19 facilities in Wisconsin Benchmark 4.3 kwh/1000 gal

36 Aerated Lagoon Systems Average of 7.3 kwh/1000 gal Entire system, not just oxidation ditch component Based on survey of 15 facilities in Wisconsin Benchmark 3.5 kwh/1000 gal

37 Conclusions Water and wastewater systems are integral components in sustaining public health and welfare Water is heavy, about half of energy used in pumping is fundamentally tied to the physics of lifting water Energy used in pumping should be no more than twice the fundamental need If your system uses more than this, probably a reasonable payback with grants available to help defray the cost of an improved system Conservation is probably the most significant way of reducing energy use Must prepare for challenges in operation of treatment plants and distribution/collection systems Public education needed to help them understand why bill isn t proportional to water used Benchmark your treatment system against others

38 Head (ft) Head (ft) Example Deep Well Pumps in Madison Unit Well 6 Unit Well rpm 56% 70% 79% 83% 1620 rpm 79% 1440 rpm 62% 1260 rpm Flow (gpm) rpm 73% 81.5% 1682 rpm 1602 rpm 85% 1469 rpm 80% 1325 rpm Flow (gpm)