Nutrient Removal Project: Oxygen RequirementsExcreta Disposal: Land ApplicationToiletsNight Soil vs. SewersConversion of Storm Sewers to “Sanitary” SewersWastewater into Streams: Enter Environmental Engineering!Evolution of Treatment GoalsNutrient Removal ProjectOxygen ProbeDissolved Oxygen Probe: TheoryDissolved Oxygen Probe: CalibrationWhat Controls Oxygen Transfer?What is ?Aeration: Initial Oxygen Deficit, No BODMeasuring the Transfer CoefficientAeration MethodsOxygen Transfer Efficiency (OTE)Oxygen Transfer Efficiency: O2 dissolved / O2 deliveredAir Supply Design QuestionsDiffuser Air Supply DesignPreparation for LabLab SetupAeration AnalysisIndirect referencing: Calculate the SlopeLookup TablesNRP Context… Can you control the oxygen concentration?A model for the oxygen transfer coefficient?ReviewData HintsMonroe L. Weber-Shirk School of Civil and Environmental EngineeringNutrient Removal Project: Oxygen RequirementsNutrient Removal Project: Oxygen RequirementsDO probeStir barAirTemperature probePressure sensorHistory of Human WasteNutrient Removal ProjectDissolved oxygen measurementsOxygen TransferExcreta Disposal:Land ApplicationExcreta Disposal:Land ApplicationWhen population densities were low excreta disposal was an individual problem. As cities grew it was no longer possible for individuals to practice “direct land application.”Before 1800 city residents placed “night soil” in buckets along streets and workers emptied the waste into “honeywagon” tanks. The waste was transported to rural areas for disposal on farm land. The honeywagon system preserved the essential feature of land application of the waste.Nutrient RecycleToiletsToiletsUntil about 1850 even the members of Congress were required to go outside and walk down Capitol Hill to privy facilities. 1850-1900: The flush toilet came into general use in the U.S. during the last half of the nineteenth century.Introduction of the toilet coincided with ______ _____. central heatNight Soil vs. SewersNight Soil vs. SewersDutch engineer Charles Liernur advocated dry disposal. He claimed underground sewers would be the source of ________ _____ giving rise to sickness and death. English engineer Baldwin Latham supported water carriage of excreta. Latham proceeded with the installation of a water carriage system for Croydon, where he was engineer of public works. The water carriage system led to an immediate decrease in the death rate in the cities that installed it. noxious gasesBut what about the cities downstream?Conversion of Storm Sewers to “Sanitary” SewersConversion of Storm Sewers to “Sanitary” SewersToilets were connected to existing storm sewersThe storm drain systems discharged directly to streams, lakes, and estuaries without treatment Treatment of wastewater only became an issue after the self-purification capacity of the receiving waters was exceeded and ________ __________ became intolerablenuisance conditionsWastewater into Streams:Enter Environmental Engineering!Wastewater into Streams:Enter Environmental Engineering!Drinking water treatment began to receive attention in the 1800s. London, and cities on the Great Lakes found themselves draining their raw sewage into the same body of water from which they took their drinking water. Chicago solved this problem by reversing the flow of the Chicago river and sending its waste through a canal to the Illinois River to the Mississippi. English engineers tackled the problem by developing treatment techniques for both wastewater and drinking water.Evolution of Treatment GoalsEvolution of Treatment GoalsSolids (sedimentation)BOD (activated sludge)Nitrification (convert ammonia to nitrate)Denitrification (convert nitrate to N2)Phosphorus (get bacteria to take up phosphorus so phosphorus can be removed with the sludge)Nutrient Removal ProjectNutrient Removal ProjectThe challenge: build an automated wastewater treatment plant that removes organic carbon and (as research projects) nitrogen or phosphorus from a synthetic feedBatch or continuous feedVarious nitrogen removal strategiesMaintain high cell concentrations using sedimentationWe need to monitor oxygen levelsWe need air (oxygen)…Oxygen ProbeOxygen Probe2 24 4 2e H O H O- ++ + �A0.8 V Voltage sourceCurrent meteranodecathodeKCl electrolyteOxygen permeable membraneO’ring330 nanoamps typical at 37°C and 1 atmosphere in air.Oxygen consumption: less than 10-7 grams of oxygen per hour (less than 0.1 µL of oxygen per hour) in air.What controls the current?Signal Conditioning circuit turns A into a voltageDissolved Oxygen Probe: TheoryDissolved Oxygen Probe: TheoryApplied 0.8 V reduces O2 to H2O at the cathode and keeps the O2 concentration very lowThe cell is separated from solution by a gas permeable membrane that allows O2 to pass throughThe rate at which oxygen diffuses through the gas permeable membrane is proportional to the difference in oxygen concentration across the membrane (proportional to the oxygen concentration in the solution)Oxygen reduction produces a current that is measured by the meter2 24 4 2e H O H O- ++ + �m mCJ DxD=-DDissolved Oxygen Probe: CalibrationDissolved Oxygen Probe: CalibrationSingle point (linear) calibration at saturationSaturation concentrationTemperature dependenceAtmospheric pressure dependenceMembrane temperature effectDiffusion through membrane is a function of temperatureLinear calibration coefficientEquation for calculating DO( )0.05( )refT Tmembranek Te-=( )0.05refT TkVCe-=( )**cal membrane calcalC k TkV=217272.105*TOC Pe� �-� �� �=atmKmg/LWhat Controls Oxygen Transfer?What Controls Oxygen Transfer?__________________________________________ ______________________________________________________________________________________________________________________Deficittransfer coefficientBubble surface areaBubble residence timeTurbulence,ˆ( * )v ldCk C Cdt= -overall volumetric oxygen transfer coefficient ,ˆv lk*C C-Bubble pressure (depth and surface tension)What is C* at the bottom of a 10 m water tank?How could you change residence time?What is ?What is ?Overall volumetric gas transfer coefficientv is for volumetric (it is based on the volume of the reactor rather than the more fundamental and illusive quantity of the interfacial area)l is for the