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energy efficiency in wastewater facilities

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energy efficiency in wastewater facilities

  1. 1. Energy Efficiency in Wastewater Facilities Prepared by Tongyan Li
  2. 2. Treated Source Water Treatment 100-16,000kWh/MG Treated Wastewater Wastewater Collection & Treatment Water End Use Conveyance 0-14,000kWh/MG Distribution 700-1,200Wh/MG Treated wastewater discharge Energy Opportunities • Use efficient pumping systems (pumps, motors, variable frequency drives) • Capture energy from water moving downhill • Store water to avoid pumping at times of peak energy cost Energy Opportunities • Install SCADA software • Use efficient pumping systems • Install efficient disinfection equipment • Implement lighting • HAVC improvements Energy Opportunities • Use efficient pumping systems • Reduce distribution leaks • Implement automatic meter reading Energy Opportunities • Improve efficiency of aeration equipment and anaerobic digestion • Implement cogeneration and other onsite renewable power options • Implement lighting, HVAC improvements • Fix leaks • Install SCADA software • Use efficient pumping systems • Recycle water Energy Opportunities • Use efficient pumping systems • Capture energy from water moving downhill Figure 1 Energy Intensity of Each Stage in the Water Cycle [1]
  3. 3. WHY DOES ENERGY EFFCIENCY MATTER FOR WASTEWATER TREATMENT FACILITIES? Water and wastewater systems are significant energy consumers with an estimated 3%-4% of total U.S. electricity consumption used for the movement and treatment of water and wastewater [2]. A secondary treatment plant may use as much as 1500 to 1700 kilowatt hours (kWh) of electricity to treat one million gallons of sewage and manage the resulting sludge and residuals [3]. Electricity is a critical input for delivering municipal water and wastewater services. Electricity costs are usually between 5 to 30 percent of total operating costs among water and wastewater utilities (WWUs) worldwide [4]. The Oregon Department of Energy reports that a city’s electrical power cost for wastewater treatment can consume 25 percent or more of the entire city’s electrical bill. Nationwide, that’s more than $4 billion annually [5].
  4. 4. Figure 2 Process flow diagram of a typical wastewater treatment plant
  5. 5. 1.65% 8.67% 1.23% 19.24% 0.48%68.73% Tertiary treatment Sludge treatment Lighting and other Pretreatment Primary treatment Secondary treatment Figure 3 Energy consumption in different processes [6] Secondary Treatment Microorganisms break down organic material, such as sugar s, fats, and proteins, that were not removed in the primary sedimentation process. This process reduces the majority of BOD5 and suspended solids Pretreatment Remove coarse materials such as paper, rocks, plastic, and rags Tertiary Treatment Biological treatment for nitrogen or phosphorus removal, chemical precipitation for phosphorus or metals removal, air stripping for ammonia removal Disinfection Remove the remaining pathogens and bacteria Primary Treatment The remaining settleable and floatble materials are removed during primary sedimentation
  6. 6. 0 50 100 150 200 250 300 Trickling Filter Activated Sludge Physical Chemical Other Trickling Filter Activated Sludge Physical Chemical Other Figure 4 Number of treatment plants in New York State that use various forms of secondary wastewater treatment [3] Activated sludge Trickling filter Non-electric secondary filtration CONVENTIONAL SECONDARY TREATMENT PROCESSES Oxidation ponds
  7. 7. Wastewater Plants Energy Consumption Figure 5 Typical wastewater treatment energy use distribution [1] Sewage aeration at an activated sludge WWTP accounts for about 30 to 80 percent of the total plant electricity demand. At the Fort Collins, Colorado, wastewater treatment facility. In 2012, the facility upgraded the controls on its blower system, installing an automated control system with much better turndown capabilities and a blow-off valve to improve system performance. Along with other blower upgrades, the improved controls helped reduce energy consumption from the aeration system by about 30 percent. Figure 6 Typical blower efficiencies Turndown capability is an indication of the blower’s ability to meet a range of airflow requirements
  8. 8. Aeration  Aeration electric demand and energy consumption could be reduced by using fine-pore diffused-air systems and aeration process controls, or lowering the sludge age. A cross section of a typical coarse-bubble aeration tank at an activated sludge treatment plant A cross section of a typical fine-bubble aeration tank at an activated sludge treatment plant Aeration systems consist of blowers and diffusers are the most significant consumers of energy in a wastewater treatment system  Installing variable-speed drives for blowers and matching the blower output with air requirements can reduce energy use  Fine bubble diffusers coupled with variable flow compressors and energy efficient motors can reduce aeration energy consumption by 50% The Jackson, Wy., wastewater treatment plant replaced its 75 and 40 hp aerator mixers with 50 and 25 hp models, and replaced the 250 hp fixed speed blower with a high efficiency 150 hp variable speed blower. This has reduced the annual demand of 5.9 million kWh by about 1.95 million kWh and saved the plant around $85,000 a year.
  9. 9. Understanding Energy Use in Wastewater Treatment Facilities Size Category Energy Use kWh/ML (kWh/MG) <4MLD (<1MGD) 990 (3,749) 4-19MLD (1-5MGD) 403 (1,527) 19-76MLD (5-20 MGD) 394 (1,490) 76-284MLD (20-75MGD) 413 (1,562) >284MLD (>75MGD) 282 (1,067) Table 1 Comparison of Energy Use for Wastewater Treatment Magnitude of energy use and demand in different facilities Daily and seasonal load patterns/Facility size The role of energy-intensive equipment in the wastewater treatment process Type of processing Efficiency levels of the equipment Dependence of energy use on the quality of the waste stream (the level of treatment required to meet regulations, the treatment technologies used) Figure 7 Municipal Wastewater Treatment Facility Load Pattern According to EPA’s ENERGY STAR program, municipalities can reduce energy costs for water and wastewater treatment by as much as 10 percent through cost-effective changes to their operations [7].
  10. 10. CASE STUDY: NYSEDA municipal wastewater treatment plant energy evaluation Town of Tonawanda wastewater treatment plant NYSERDA: New York State Energy Research and Development Authority Figure 8 Electrical demand and usage Power metering was installed at each plant to accurately determine the energy consumption and savings of the evaluated processes. Through the use of submetering data and a thorough understaning of wastewater treatment processes, many opportunities to reduce plant energy costs while maintaining or increasing treatment and/or capacity were identified
  11. 11. Figure 9 Total plant hourly kW draw
  12. 12. Figure 10 Change in usage
  13. 13. NYSERDA Energy Saving Measures Capital Improvements  Replacement of existing sludge stabilization and dewatering facilities  Modification or replacement of UNOX mixers with more efficient mixing equipment  Replacement of existing cryogenic oxygen generation system with vacuum-assisted pressure swing adsorption technology  High pressure service water pump modifications  Replacement of constant speed standard efficiency motors with premium efficiency motors Operation modifications  Operational modifications to reduce energy usage and cost Lighting/HVAC modifications
  14. 14. GE Energy-Neutral Wastewater Treatment Replace conventional aeration process with ZeeLung Membrane Aerated Biofilm Reactor (MABR) [8] Four times more energy efficient than the conventional fine-bubble aeration systems many municipalities are currently using ZeeLung MABR Features  Simple  Low Energy  Nutrient Removal  Small Footprint The Metropolitan Water Reclamation District of Greater Chicago began a demonstration project to evaluate GE’s new ZeeLung MABR technology to increase the removal of nutrients in the existing plant footprint and reduce the energy required for biological aeration by 40%
  15. 15. U.S. EPA offers energy-efficient equipment, technology and operating strategies Step 1: BENCHMARK your energy use Step 2: Perform an energy AUDIT Step 3: IMPLEMENT audit recommendations Step 4: Share your sucesses and REPEAT, for continuous improvement Equipment and Collection System Upgrades  Install Variable-Frequency Drives  Upgrade to Energy Efficient Motors and Motor Systems  Heating, Cooling, Ventilation System Upgrades  Bright Lights Bring Energy Savings Operating Strategies  Managing your electrical load  Biosolids management  Operation and maintenance  Inflow and infiltration control Energy Efficient Technology  Cogeneration or combined heat and power  Cogeneration using landfill gas Renewable Energy  In conduit hydro-power  Solar power  Wind power Source: https://www3.epa.gov/region9/waterinfrastructure/technology.html The city of Pacifica, California, recently began operating 1,800 solar panels to supply a portion of the Calera Creek Water Recycling Plant’s electric needs. The solar panels provide 10 to 15 percent of the treatment plant’s energy needs. The facility estimates $100,000 per year in energy savings
  16. 16. California Energy Commission A multitude of energy efficient equipment, technologies and operating strategies are available to help take a bite out of the energy costs in water and wastewater facilities. • Variable frequency drives • Energy-Efficient Motors • Heating, Cooling, Ventilation Improvements • Lighting Improvements • Electrical Load Management Strategies • Cogeneration Optimization • Fuel Cells California water and wastewater agencies spend more than $500 million each year on energy costs Source: http://www.energy.ca.gov/process/water/wastewater_treatment.html
  17. 17. The role of big data in wastewater treatment plants SCADA systems Retrieve information on plant operation and other systems Predicting pipe failure Predictive weather data Managing water costs Energy management Measuring asset condition Energy monitoring can be used to help understand and quickly intervene when energy consumption at plant or component level increases. Data analytics can then be used to prevent efficiency excursions before they happen and to identify further reductions by a change of operation or equipment. Many water companies have extensive energy data at plant level, but rarely at component level, but this is improving. The water and wastewater industry is currently in transition from business-as-usual operations, employing traditional engineering solutions, to a new approach – Smarter Water Management – which uses big data and advanced analytics to create new insights that can improve operational efficiencies. IBM Research, working in partnership with a European wastewater utility, developed an end-to-end water resource recovery plant optimization that can save as much as 15 percent or more of costs associated with energy consumption, biosolids handling, and chemical usage. Using a big data approach that integrates dynamic plant simulation forecasting and mathematical optimization, activated sludge treatment processes can be significantly improved in the areas of resources recovery, cost efficiency, and regulatory compliance.
  18. 18. Programs Federal programs ENERGY STAR Water and Wastewater ENERGY STAR Green Buildings and Energy Efficiency U.S. EPA Office of Water, Energy Efficiency for Water and Wastewater Utilities U.S. EPA Combined Heat and Power (CHP) Partnership U.S. EPA Green Power Partnership U.S. EPA Wastewater Management Website U.S. EPA WaterSense Program U.S. EPA State and Local Climate and Energy Program
  19. 19. Useful Resources EPA’s Energy Use Assessment Tool is a free, downloadable, Excel‐based energy audit tool. The tool allows both water and wastewater systems to conduct a utility bill analysis, determine baseline energy consumption and cost in total and also broken down to the process‐level and equipment‐level, and identify the most energy‐intensive areas of the system. In addition, the tool highlights areas of inefficiency that users may find useful in identifying and prioritizing ECMs. The tool can be found at: http://water.epa.gov/infrastructure/sustain/energy_use.cfm. EPA’s EnergyStar Portfolio Manager is a free, online tool drinking water systems can use to develop a simple energy baseline based on utility bill data and track changes in energy use and GHG emissions over time. The tool can be found at: http://www.energystar.gov/index.cfm?c=evaluate_performance.bus_portfoliomanager. Understanding Your Electric Bill is a Wisconsin Focus on Energy Fact Sheet that can be found at: http://water.epa.gov/infrastruture/sustain/Understanding‐Your‐Electirc‐Bill.pdf Electric Power Research Institute (EPRI) Energy Audit Manual for Water /Wastewater Facilities can be found at: http://www.cee1.org/ind/mot‐sys/ww/epri‐audit.pdf. How to Hire an Energy Auditor is a California Energy Efficiency document that can be found at: http://www.energy.ca.gov/reports/efficiency_handbooks/400‐00‐001C.PDF. California Energy Commission (Process Energy-Water/Wastewater Treatment) http://www.energy.ca.gov/process/water/wastewater_treatment.html
  20. 20. Reference 1. Efficiency, E., Energy Efficiency in Water and Wastewater Facilities. 2. Daw, J., et al., Energy efficiency strategies for municipal wastewater treatment facilities. Contract, 2012. 303: p. 275-3000. 3. Pakenas, L. J. (1995). Energy Efficiency in Municipal Wastewater Treatment Plants: Technology Assessment, New York State Energy Research and Development Authority. 4. Liu, F., et al., A primer on energy efficiency for municipal water and wastewater utilities. 2012. 5. https://energytrust.org/library/GetDocument/3441 6. Tao, X. and W. Chengwen (2009). Energy consumption in wastewater treatment plants in China. IWA world congress on water, climate energy. 7. ICF International. 2008. Water and Energy: Leveraging Voluntary Programs to Save Both Water and Energy. http://water.epa.gov/scitech/wastetech/upload/Final‐Report‐Mar‐2008.pdf 8. http://www.gewater.com/products/zeelung.html

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