Water And Wastewater Treatment Energy Savings Guide

Water and WastewaterTreatmentEnergy Savings GuideOregon water and wastewater treatment plants face challenges of growing hydraulicdemand, rising operating costs, increased regulatory requirements and outdatedequipment and facilities. Throughout the state, treatment plants continually look for ways tocontrol costs, while improving effluent quality and meeting temperature standards. Becausetreatment plants require a significant energy input, energy efficiency offers an expandingopportunity to trim operating costs.Energy Trust of Oregon is dedicated to helping you identify options for improving yourfacility’s energy efficiency over time. We can help you identify the best opportunities forenergy savings within your treatment plants and help you understand where to focus yourefforts. We’ve also compiled a list of “next steps” for you to review. Talk with your ProgramDelivery Contractor (PDC) about which of these steps could have the biggest impact onenergy savings at your plant.

OXYGEN TRANSFER EFFICIENCYOF SELECTED AERATIONTECHNOLOGIESLEFT: Typical range of oxygen transfer efficiency for selected aeration technologies, usinga metric of kilograms of oxygen dissolved in water per kilowatt hour of electrical energyconsumed. Technologies that maximize the efficiency of oxygen transfer reduce energyexpenditure and operating cost per unit of oxygen dissolved.Standard Aeration Efficiency(kgO2/kWh)76The Oregon Department of Energy reports that a city’s electrical power cost forwastewater treatment can consume 25 percent or more of the entire city’s electrical bill.Nationwide, that’s more than 4 billion annually. According to EPA’s ENERGY STAR program, municipalities can reduce energy costs for water and wastewater treatment byas much as 10 percent through cost-effective changes to their operations.54321Fine BubbleAerationCoarse BubbleAerationHigh Speed SplashAerationSlow Speed SurfaceAerationSurface AerationRotors0TYPICAL WASTEWATER TREATMENT ENERGY USE DISTRIBUTION53% AERATION14% WASTEWATER PUMPINGData Source: Environmental Dynamics, Technical Bullet 12714% ANAEROBIC DIGESTION8% LIGHTING & BUILDINGSVFDs AND THE AFFINITY LAWSFlowPercent of Full-LoadFlow and Power1004% SOLIDS HANDLING4% CLARIFIERSPower3% OTHER806040200020406080100Percent of Full-Load SpeedABOVE: Variable frequency drives improvepump and fan efficiency by reducing motorshaft speed to the minimum revolutionsper minute (rpm) necessary to satisfy flowrequirements. A graph of the affinity lawsshows that the flow produced by a pump orfan is directly proportional to shaft speed,while the power requirement for that flowis proportional to shaft speed cubed. Forexample, at 80 percent of full-load flow,a pump or fan operates at 80 percent offull-load rpm, but uses only 51 percent offull-load power, yielding a steady stateenergy cost reduction of49 percent. At 50 percent of full-loadflow, the pump or fan operates at50 percent of full-load rpm, but uses only13 percent of full-load power, yielding anenergy cost savings of 87 percent.TYPICAL WATER TREATMENT ENERGY USE DISTRIBUTION59.5% FINISHED WATER PUMPING11.3% NONPROCESS LOADS9.6% DISSOLVED AIR FLOTATION7.8% RAW SURFACE WATER PUMPING4.5% ONSITE CHLORINEGENERATION FOR DISINFECTION3.4% UV DISINFECTION1.7% RAPID MIXING0.7% BACKWASH WATER PUMPS0.5% FLOCCULATION0.5% SEDIMENTATION0.4% CHEMICAL FEED SYSTEMS0.2% RESIDUALS PUMPING

AERATION SYSTEMCould operations and maintenance improvements reduce energyuse in aeration basins? Making simple Operations & Maintenance(O&M) adjustments to existing aeration equipment can pay backquickly in reduced energy costs.Are there opportunities to improve the efficiency of blowersystems by implementing O&M measures? Making adjustmentsto blower system controls can yield substantial energy savings atlittle cost.Optimize the dissolved oxygen (DO) set point to reduce theamount of blower energy. It’s not uncommon for systems tooperate with DO levels that exceed what is required.Adjust controls to optimize blower staging.Adjust the position of DO sensors to provide a more accurateassessment of DO levels.Find and reduce obstructions to blower airflow to decreasethe pressure in the blower system, with accompanying energysavings.Adjust control systems to optimize mechanical mixing andbubble diffusion.Implement the most-open-valve strategy in which theaeration zone with the highest oxygen demand is opened fullyto reduce pressure at the blowers. DO levels in remainingaeration zones are controlled by valves that maintain theproper DO set point for each zone.Adjust the placement of mechanical mixers for more efficientoxygen transfer.Consider upgrading your existing aeration basin technology.Aeration uses between 40 and 60 percent of the energyconsumed in a typical treatment plant. Improving oxygen transferefficiency can significantly impact total energy consumption inyour facility.Upgrade from coarse bubble diffusion to fine bubble diffusionto increase the efficiency of oxygen transfer and reduce blowerload while maintaining proper DO control.Install automated DO controls to reduce aeration energy by upto 40 percent compared to control systems that use manualsampling. Systems that rely on manual DO sampling oftenoperate at levels that are much higher than necessary. Installinga DO sensor with integrated aeration control allows levels to bemaintained within a narrower band, thereby reducing blower load.Add DO probes to different zones of the aeration basin toprovide more accurate DO readings and optimize aeration foreach zone.Upgrade systems that use mechanical mixing by installing controlsthat cycle on and off in response to process control parameters.Retrofit mechanical mixers with variable frequency drives(VFDs) which adjust the speed of the mixer motors to matchthe process needs in real-time. Typical simple payback of two toseven years.Optimize DO set points to allow for blower system flowreduction.Could capital improvements to your blower system lead tosubstantial energy savings? Up to 75 percent of the lifecycle costof a blower system is attributable to energy use. When replacingan existing blower system, select a blower appropriate for theapplication. Your PDC can work with you to determine the blowertechnology that best fits your needs now and in the future.Install controls that allow staging of systems that have multipleblowers. Control systems optimize blower staging based onsystem requirements.Upgrade to a high-efficiency turbo blower system, whichuses very high-speed motors and air-bearing technology toefficiently produce airflow. Turbo blower systems are typicallyVFD-equipped, and are capable of providing a range of airflowbased on DO sensor feedback. Typical simple payback oftwo-and-a-half to seven years.Add VFDs with sensor control to existing centrifugal blowersystems to adjust the speed of the blower to system demand,thereby reducing energy use when oxygen demand is lower.Typical simple payback of two to six years.Identify oversized blowers and investigate using Energy Trustincentives toward the purchase of more appropriately sizedblowers.

PUMPINGLIGHTINGCould O&M improvements improve pumping system efficiency?Low-cost adjustments to existing pumping systems could boostenergy efficiency, often delivering a simple payback of less thanone year.Could plant lighting be improved for better function and energyefficiency? Modern lighting technologies offer better performanceand efficiency compared to older technologies. An upgrade tolighting systems is likely to have a quick payback, while increasingthe comfort of those working in the space.Determine pump system efficiency over the range of pumpingrequirements and stage pumps for optimum energy use.Adjust basin fluid levels to decrease pump head and reducepump load. Wet-well levels can be raised in pumping stationsto reduce pump head.Identify and adjust poorly calibrated valves that decrease pumpefficiency.Can energy be saved through capital improvements to pumpingsystems Pumping accounts for as much as 67 percent of theenergy used to maintain a typical municipal treatment facility.Improvements in pumping technology have the opportunity tosubstantially reduce facility energy use.Install VFDs on pumps that move varying volumes of fluid toadjust speed to match pumping demand in real-time. Whenless pump flow or pressure is required, pump speed andaccompanying energy use will be reduced.Replace worn or inefficient pumps with new, high-efficiencypumps that use less energy and operate with less maintenanceand downtime.Oversized pumps that operate at constant flow are goodcandidates for impeller trims. Trimming the impeller is frequentlya lower-cost alternative to making larger capital investments inpumps, motors or control technology.Install different sized pumps in new plants or during plantexpansion. As seasonal flows change, controls can bring differentpump combinations online to match pumping need.Improve piping and valves to decrease friction losses.Use occupancy sensors or timers to turn off lamps inunoccupied spaces. Equip occupancy sensors with a time delayto turn off lamps after a set period after workers leave seldomoccupied pumping stations or other isolated areas.Consider installing LED lighting as an energy-efficientreplacement for other less-efficient technologies. LEDscombine ultra-high efficiency with excellent performance andlong life in an increasingly affordable package. The long servicelife of LEDs reduces maintenance and production disruptiondue to light failure. LEDs also produce very little heat, whichdecreases the plant’s cooling load.Add photo sensors on indoor and outdoor lighting systems todim or switch off lamps when natural light levels are sufficient.ANAEROBIC DIGESTIONCould the efficiency of digester mixing be improved?Anaerobic digestion accounts for about 14 percent of the energyused at a typical activated sludge wastewater treatment plant.O&M and capital improvements applied to digesters can increasethe efficiency of digester mixing, while often improving digestergas yields.Adjust existing digester mixing systems to use the minimumnumber of mixers possible for adequate mixing of influent anda high volume of gas.Optimize mixer speed in systems with VFD-controlled motorsto reduce energy use while maintaining a high output ofdigester gas.Replace mixing systems that are not functioning correctly oroperating inefficiently with higher efficiency systems.Upgrade existing systems such as gas lance or draft tubesystems to a linear motion mixing system.