CEE 426 October 25 2010 12:05 PM UW Madison Room 1209 Engineering Hall Aeration and Energy Thomas E. Jenkins, P.E.

Aeration and Energy “An engineer is someone who can do for $5,000 what any damn fool can do for $50,000. Anonymous

Aeration and Energy Calculating Air Rates Types of Aerators and Processes Basin Geometry Blower and Pump Selection

Aeration and Energy Aeration is the Most Significant Use

Oxygen Transfer Efficiency (OTE %) Calculating Air Rates BOD Nitrification NH3  NO3 Denitrification Mixing Limitations Oxygen Transfer Efficiency (OTE %) Oxygen Transfer Rate (OTR lbO2/hp-hr) α and β Diurnal Variations and Equalization Basin Depth

Types of Processes BOD Removal Oxygen Required for metabolism Amount of O2 is proportional to Organic Load Utilization Approximately 1.1 lb. O2/lb BOD5

Types of Processes Nitrification NH3  NO3 Oxygen Required to convert Ammonia to Nitrate Amount of O2 is proportional to Ammonia Concentration Utilization 4.6 lb. O2/lb NH3 Converted Hydraulic Residence Time and SRT (Solids Retention Time) Determine if Nitrification Will Occur

Denitrification NO3  N2 and O2 Anoxic Reaction Carbon Source Required Types of Processes Denitrification NO3  N2 and O2 Anoxic Reaction Carbon Source Required Approximately 25% of O2 Used for Nitrification Can be Recovered Only if raw wastewater is used as carbon source If methanol or other carbon source is provided then no oxygen recovery

Calculating Air Rates and O2 Transfer Basic Calculations Rectangular Round

Calculating Air Rates and O2 Transfer Basic Calculations For BOD or NH3 or NO3

Calculating Air Rates and O2 Transfer Basic Calculations

Types of Aerators Mechanical Fine Pore Coarse Bubble Jet Aeration

Mechanical Aerators Horizontal Mechanical Aerator (Brush Aerator)

Mechanical Aerators Vertical Shaft and Aspirating Mechanical Aerator

Calculating O2 Transfer Typical aerator SOTR 2.0 to 4.5 lbO2/hp-hr

Calculating Air Rates and O2 Transfer Mechanical Aerators

Calculating Air Rates and O2 Transfer Mechanical Aerators Mixing Limits: 1 ft/sec velocity 0.5 hp/1,000 ft3

Mechanical Aerator Energy Proportional to Immersion Reduced Immersion < OTR and < hp Variable Weir Level Control Proportional to Speed Lower Speed < OTR and < hp Variable Frequency Drives, Two Speed Motors Proportional to Actual DO Concentration Lower is Better DO Control Significant

Diffused Aeration Coarse Bubble

Diffused Aeration Fine Pore (Fine Bubble)

Calculating OTE and O2 Transfer

Calculating Air Flow Rates

Calculating Air Flow Rates

Diffused Aeration Energy Proportional to Submergence Deeper is Better Also Requires Higher Blower Power Proportional to Air Flow per Diffuser Flux Rate (1 to 10 SCFM/ft2 Typical) Lower is better Proportional to Actual DO Concentration Lower is Better DO Control is Significant

Calculating Air Rates and OTE Typical OTEf ≈ 50% SOTE SOTE Fine Pore ≈ 2% per foot submergence SOTE Coarse Bubble ≈ ¾ % per foot submergence Mixing Limits: Fine Pore: 0.12 to 0.08 CFM/sq ft Coarse Bubble: 20 CFM/1,000 cu ft

1m3/hr = 0.58 CFM 5m3/hr = 2.94 CFM 9m3/hr = 5.30 CFM Diffused Aeration OTE Increases with Higher Submergence OTE Decreases with Higher Air Flow per Diffuser 7.6m = 25’ 6.1m = 20’ 4.6m = 15’ 3.0m = 9.8’ 1.5m = 5’ 1m3/hr = 0.58 CFM 5m3/hr = 2.94 CFM 9m3/hr = 5.30 CFM

Excess DO means significantly more aeration power. Diffused Aeration Excess DO means significantly more aeration power.

Diffused Aeration

Aeration and Energy Process Mechanism for DO Control

Types of Processes Miscellaneous Aeration Processes Aerobic Digestion Sludge Holding Post-Aeration Channel Aeration and Equalization

Basin Geometry Variations Complete Mix Plug Flow Most Common Tapered Aeration can Minimize Energy Can be Achieved with Baffles SBRs (Sequencing Biological Reactors) MBRs (Membrane Bioreactors) IFAS (Integrated Fixed Film Activated Sludge) Lagoons Usually Shallow

Basin Geometry Variations SBRs (Sequencing Biological Reactors) MIX FILL REACT FILL REACT SETTLE DECANT/SLUDGE WASTE

Basin Geometry Variations IFAS (Integrated Fixed Film Activated Sludge)

Aeration and Energy Energy use varies with time of day OTE, α, Organic Load, Hydraulic Load, All Vary with Time of Day

Aeration and Energy Equalization Can Minimize Power

Blower Selection Considerations Efficiency Control Turndown Design Parameters

Aeration and Energy Efficiency Varies with Blower Type Range is 60% to 80%

Aeration Blower Power Blower Power is a Function of Pressure and Flow Rate Efficiency Varies Flow Rate for a Given Blower Efficiency Drops as Flow is Decreased Good Turndown (>50%) is Desirable

Aeration Blower Power

Aeration Blower Power Ignoring Relative Humidity

Aeration Blower Power

Blower System Qmax:Qmin = 8:1 Specify Blower System for Turndown Aeration Blower Power Blower System Qmax:Qmin = 8:1 Specify Blower System for Turndown Four with Design Flow at 33% Max Q Two with Design Flow at 50% Max Q Plus Two with Design Flow at 25% Max Q 50% Turndown Each Blower

Aeration Blower Power Control Method Significantly Impacts Energy

Aeration Blower Power Control Method Significantly Impacts Energy

Aeration Blower Power Design Specifications Identify Worst Case Operating Conditions For Discharge Pressure Max Temperature Max Relative Humidity Max System Flow Rate and ΔP For Motor Power For Throttled Centrifugal bhp at Min Temperature For Variable Speed Centrifutal bhp at Max Temperature Evaluation Conditions do not Equal Design Conditions

Pump Selection Considerations RAS, WAS, Recycle Efficiency Control Design Parameters

Pump Selection Considerations For Aeration most Pumps Low Static Head

Pump Selection Considerations Try to Operate at BEP (Best Efficiency Point) Efficiency Varies, Typical 75% to 85%

Pump Power

Pump Design Parameters Max Q, Min Q TDH = Total Dynamic Head Inlet Losses and Lift Discharge Static Head Discharge Friction Losses Suction Head (Prevent Cavitation) Motor hp Control Influences Power VFD more Efficient than Throttling

Aeration and Energy Process Requirements Come First! Systems should be justified by payback

Aeration and Energy Over Life of Equipment Energy Cost is more Significant than Equipment, Installation, or Maintenance

Internet References http://www.sanitaire.com/3117803.asp http://www.stamfordscientific.com/ http://www.wastewater.com/ http://www.eimcowatertechnologies.com/ http://www.water.siemens.com/en/about_us/legacy_brands/Pages/envirex.aspx http://rootsblower.com/ http://pumpsystemsmatter.org/ http://water.epa.gov/scitech/wastetech/upload/Evaluation-of-Energy-Conservation-Measures-for-Wastewater-Treatment-Facilities.pdf

Aeration and Energy Questions?