1. Nutrient Removal and Power Savings in Wastewater Treatment Systems*
07/16/96
Aero-Mod®
Wastewater Process Solutions
Nutrient Removal and Power Savings in Wastewater Treatment Systems
Todd L. Steinbach, PE *

2. Aero-Mod, Inc.*
Energy Consumption
What determines the amount of aeration required in an activated sludge plant?
It can be the organic loading (Organic Requirement)…
but it is often the amount of energy required to keep the basin(s) in suspension (Mixing Requirement).
How does an under-loaded plant operate energy-efficiently?
How does this relate to Nitrogen Removal?
Wastewater Process Solutions*
2##

3. Aero-Mod, Inc.*
Organic Requirement
Oxygen required by the bacteria to break down BOD and ammonia.
For Extended Aeration:
1 lb of BOD requires from 1.33 to 1.5 lbs of O2.
1 lb of ammonia requires 4.6 lbs of O2.
Wastewater Process Solutions*
3##

4. Organic Requirement 1.0 MGD Typical Example:
Aero-Mod, Inc.*
Organic Requirement
1.0 MGD Typical Example:
BOD: 240 mg/l, NH3-N: 35 mg/l, 1.5 lbs O2/lb BOD, 24 hr HRT, 11’ water depth, fine bubble efficiency of 2.0%/ft of subm., psi, 1,000 FASL, summer temp.
O2 for BOD would be 325 lbs/hr,
…or 1,409 scfm (1,656 icfm) of blower air.
O2 for NH3-N would be 145 lbs/hr,
…or 630 scfm (741 icfm) of blower air.
Wastewater Process Solutions*
4##

5. Organic Requirement 1.0 MGD Typical Example:
Aero-Mod, Inc.*
Organic Requirement
1.0 MGD Typical Example:
Blower Power Required, assuming pd 70% efficiency
BHP for BOD = (icfm) * (psi) / (229 * eff%)
= (1,656 icfm) * (5.5 psi) / (229 * 70%)
= 57 HP
BHP for NH3-N = (icfm) * (psi) / (229 * eff%)
= (741 icfm) * (5.5 psi) / (229 * 70%)
= 25 HP
82 HP Total (sizing program gave me 79 HP)
Wastewater Process Solutions*
5##

6. Mixing Requirement 1.0 MGD Typical Example:
Aero-Mod, Inc.*
Mixing Requirement
1.0 MGD Typical Example:
Side-roll aeration, 20 cfm/1,000 cf, 24 hr HRT, 11’ water depth, psi, 1,000 FASL, summer temp.
Air required for mixing would be:
cfm = (1 Mgal) / 7.48 cf/gal / 1,000 cf * 20 cfm
= 2,674 cfm
BHP = (2,674 cfm) * (5.5 psi) / (229 * 70%)
= 92 HP (sizing program gave me 89 HP)
Wastewater Process Solutions*
6##

7. Aero-Mod, Inc.*
Energy Consumption
What determines the amount of aeration required in an activated sludge plant?
It can be the organic loading (Organic Requirement)…
but it is often the amount of energy required to keep the basin(s) in suspension (Mixing Requirement).
How does an under-loaded plant operate energy-efficiently?
How does this relate to Nitrogen Removal?
Wastewater Process Solutions*
7##

8. Nutrient Discharge Limits*
07/16/96
Ammonia toxicity to aquatic organisms
Nitrite toxicity to aquatic organisms
Nitrate toxicity to humans
Methemoglobinemia (blue baby syndrome)
Eutrophication
Fertilization *

9. Wastewater Process Solutions*
07/16/96
Aero-Mod®
Wastewater Process Solutions
Ammonia *

10. Urea + H2O ----------> 2NH3 + CO2
Ammonia Production *
07/16/96
Hydrolysis of urea
Adds water to the molecule
Urea + H2O > 2NH3 + CO2 *

11. Ammonia Production De-amination of organic compounds*
07/16/96
De-amination of organic compounds
Organism breaks protein into amino acids
Removes NH2- group from amino acids
Amino Acid > Keto Acid (fatty acid) + NH3 *

12. Ammonia Reduction Oxidation of Ammonia*
07/16/96
Oxidation of Ammonia
Urea (CH4N2O) => NH3 => NO3-
Protein => Amino Acid => NH3 => NO3- *

13. Nitrification *
07/16/96
Nitrification is accomplished by two unrelated groups of autotrophic microorganisms
Ammonia-oxidizing bacteria such as Nitrosomonas
Nitrite-oxidizing bacteria such as Nitrobacter *

14. Nitrification Consumes 4.6 grams of O2 per gram of NH3-N oxidized*
07/16/96
Consumes 4.6 grams of O2 per gram of NH3-N oxidized
Consumes 7.1 grams of alkalinity per gram of NH3-N oxidized
Forms 0.15 grams of new cells per gram of NH3-N oxidized *

15. Nitrifying Bacteria *
07/16/96
Nitrite oxidizers cannot proliferate until the ammonia oxidizers have produced enough nitrite for the nitrite oxidizers
Different species nitrify at different D.O. levels
Clusters of ammonia oxidizers and nitrite oxidizers appear to grow close together within the floc
Nitrifiers need NH3-N, not NH4+-N *

16. Wastewater Characteristics that Impact Nitrification*
07/16/96
Wastewater Characteristics that Impact Nitrification
SRT
Temperature pH
Alkalinity
D.O. *

17. Wastewater Characteristics that Impact Nitrification*
07/16/96
Wastewater Characteristics that Impact Nitrification
SRT
Typically, at least 5 days will be required for stable nitrification *

18. Wastewater Characteristics that Impact Nitrification*
07/16/96
Wastewater Characteristics that Impact Nitrification
Temperature
Colder temperatures require an older sludge age because reproduction slows down
Colder temperatures cause more of the ammonia to be ionized (NH4+) *

19. Wastewater Characteristics that Impact Nitrification*
07/16/96
Wastewater Characteristics that Impact Nitrification pH
Nitrifiers are sensitive to changes in pH
As pH decreases, ionization increases and less NH3-N is available *

20. Wastewater Characteristics that Impact Nitrification*
07/16/96
Wastewater Characteristics that Impact Nitrification
pH vs. Alkalinity
pH is a measure of hydrogen ion concentration
Alkalinity is a measure of a water’s ability to neutralize acid
Water with high alkalinity will always have an elevated pH, but a water with elevated pH does not always have a high alkalinity
Both measurements are needed *

21. Wastewater Characteristics that Impact Nitrification*
07/16/96
Wastewater Characteristics that Impact Nitrification
Why Low Alkalinity Affects Nitrifiers pH
Alkalinity neutralizes acid
Inadequate alkalinity results in low pH
Carbon Source
Nitrifiers cannot use organic compounds for synthesis and growth
Bicarbonate/carbonate alkalinity may satisfy their need for an inorganic carbon source *

22. Wastewater Characteristics that Impact Nitrification*
07/16/96
Wastewater Characteristics that Impact Nitrification
Chemical Sources of Alkalinity
For every mg of _______ added, _______ mg of alkalinity as CaCO3 is gained
CaO Quick Lime 1.8
Ca(OH)2 Hydrated Lime 1.4
Mg(OH)2 Magnesium Hydroxide 1.4
NaOH Caustic 1.2
Na2CO3 Soda Ash 0.9 *

23. Wastewater Characteristics that Impact Nitrification*
07/16/96
Wastewater Characteristics that Impact Nitrification
Dissolved Oxygen
Nitrification is an aerobic process and elemental oxygen (O2) is required
Nitrifiers may not compete as well for oxygen as heterotrophic bacteria
If not enough oxygen is present, the heterotrophs may get most of it first *

24. Problems Caused by Nitrification*
07/16/96
Large oxygen requirement
Potential low pH (if alkalinity is low)
If pH is low, fungi can develop
Discharge of nitrogen as Nitrate
Potential for clarifier denitrification
Sludge age range where filaments can develop *

25. Wastewater Process Solutions*
07/16/96
Aero-Mod®
Wastewater Process Solutions
Nitrogen Removal *

26. Denitrification The other half of biological nitrogen removal*
07/16/96
The other half of biological nitrogen removal
Accomplished by many different kinds of facultative bacteria
Facultative bacteria can use oxygen or nitrate
Denitrifiers are facultative heterotrophs and must have an organic carbon food source
Bacteria forced to use the oxygen in Nitrate *

27. Denitrification Bacteria reuse about 60% of nitrification O2*
07/16/96
Bacteria reuse about 60% of nitrification O2
Produces 3.6 grams of alkalinity per gram of Nitrate reduced (about 50%)
Forms about 0.5 grams of new cells per gram of Nitrate reduced
Consumes about 2.9 grams of BOD per gram of Nitrate reduced *

28. Denitrification Methods*
07/16/96
Anoxic zone with nitrate recycle from aeration tank
High recycle rate of 2Q to 4Q
Sequenced aeration
Low D.O. operation
D.O. Probes & Controller
VFD Motor Drives
PLC Process Controller *

29. Denitrification Designs*
07/16/96
A2O and Bardenpho
SBR
Oxidation Ditch w/ Mixed Anoxic Zone
MBBR (Moving Bed BioReactor)
Step feed aeration
SEQUOX *

30. Denitrification Designs*
07/16/96 *

31. Denitrification Issues*
07/16/96
D.O. level too high will prevent bacteria from using NO3-
Lack of carbon source available for bacteria
Recycle rate too low will not bring back enough Nitrate
Recycle rate too high will shorten detention time of aeration basin
High peak flows in an SBR reduces allowed time for aeration on and aeration off
High fluctuations of BOD/ammonia disrupt D.O. level *

32. Aero-Mod SEQUOX Solution
2nd Stage Aeration
(Air-off)
Supernatant
Effluent
Aerobic
Digestion
Clarification
1st Stage Aeration
(Air on)
RAS
WAS
Influent
Bio-Selector
WAS
RAS
1st Stage Aeration
(Air off)
Aerobic
Digestion
Clarification
Effluent
2nd Stage Aeration
(Air on)
Supernatant

33. Aero-Mod SEQUOX Solution 2 hours later
2nd Stage Aeration
(Air on)
Supernatant
Effluent
Aerobic
Digestion
Clarification
1st Stage Aeration
(Air off)
RAS
WAS
Influent
Bio-Selector
WAS
RAS
1st Stage Aeration
(Air on)
Aerobic
Digestion
Clarification
Effluent
2nd Stage Aeration
(Air Off)
Supernatant

34. SEQUOX Nitrogen Removal Process*
07/16/96
Denitrification without mixers
Sequenced aeration with continuous clarification
Reclaim portion of oxygen & alkalinity consumed in nitrification
Concentrated settled biomass consumes D.O. quickly
Oxygen-starved biomass uses nitrates quickly when basin is re-aerated
Plug flow pattern ensures several cycles of sequenced aeration
Common-wall construction provides small footprint *

35. SEQUOX Features
SEQUOX controls:
Where we the air is placed (only 50% of basins aerated at a time)
When we aerate basins (simple timer control on typical 2-hour cycle)
How much air we provide via VFD control on the aeration blowers
How fast we allow the D.O. to rise in the Aeration Basins using a PLC-based D.O. control system to control each blower VFD

36. SEQUOX with DO2ptimizer Benefits
Aero-Mod, Inc.*
SEQUOX with DO2ptimizer Benefits
Energy Savings
a. When D.O. is below low set point, blower output increases.
(Organic Requirement)
b. When in-between low and high set points, blower output decreases to mixing requirement.
(Mixing Requirement)
c. When above high set point, blowers can be turned off.
(Rest)
2. Flexibility when organic loading is high, plant can automatically switch to SEQUOX (both 1st Stage Aeration Basins aerating) and when the organic loading subsides – go back to SEQUOX-Plus.
3. Nitrogen Removal levels to Total N of 3 mg/l achieved.
Wastewater Process Solutions*
36##

40. NEYCSA - Mt. Wolf, PA
1.70 MGD

41. Neligh, NE 210,000 gpd municipal facility
One 30 HP blower for process and aerobic digester
Blower operated with manual control of VFD for nine years
PLC-based D.O. control placed into operation in Fall of 2011
Average of 5,000 kWh reduction per month ≈ $500 savings per month
Along with the power savings, plant is also achieving TN reduction

42. Holton, Kansas
0.528 MGD Bio-P

43. Ammonia Removal - Nitrification*
07/16/96
Ammonia is oxidized by nitrifying bacteria
Bacteria use oxygen to strip carbon from alkalinity and hydrogen from ammonia
Bacteria use 7.1 mg alkalinity per mg ammonia reduced
Bacteria use 4.6 mg oxygen per mg ammonia reduced
Nitrate is reduced product – NO3- *

44. Nitrogen Removal - Denitrification*
07/16/96
Nitrate is reduced by heterotrophic bacteria
Bacteria use the oxygen from nitrate
DO must be controlled to force the bacteria to use the nitrate
Alkalinity is reclaimed – about 3.6 mg per mg of nitrate
A carbon source must be available for the bacteria to use *

45. AERO-MOD’S DO2PTIMIZER
Aero-Mod, Inc.*
Energy Consumption
What determines the amount of aeration required in an activated sludge plant?
It can be the organic loading (Organic Requirement),…
but it is often the amount of energy required to keep the basin(s) in suspension (Mixing Requirement)
How does an under-loaded plant operate energy-efficiently?
USING SEQUOX &
AERO-MOD’S DO2PTIMIZER
Wastewater Process Solutions*
45##

46. 1 SEQUOX BNR DO2ptimizer D.O. Control Sliderail Diffuser Access System
ClarAtor Clarifier
Tritan Belt Filter Press 1

47. Custom Designed Wastewater Treatment Solutions
Aero-Mod, Inc.*
Custom Designed Wastewater Treatment Solutions
Wastewater Process Solutions*