Ammonia Removal and pH Adjustment in Aerated Lagoons...Ammonia Removal and pH Adjustment in Aerated...
Transcript of Ammonia Removal and pH Adjustment in Aerated Lagoons...Ammonia Removal and pH Adjustment in Aerated...
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Ammonia Removal and pH Adjustment in Aerated Lagoons
Ammonia Removal and pH Adjustment in Aerated Lagoons
WWOA 45th
Annual Conference
Thursday, October 6th, 2011, 8:50 AM
Presented by:
Jeremiah Wendt, PE –
SEH
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OverviewOverview
•
Ammonia–
Background
–
Chemistry–
Toxicity
–
Reducing Ammonia Toxicity
•
Grantsburg WWTP
•
Madeline Island WWTP
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Ammonia NitrogenAmmonia Nitrogen
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Chemical Compound–
NH3 (unionized)–
NH4+ (ionized -
ammonium)
•
Used by plants to form amino acids
•
Amino acids digested by animals, excreted as urea
•
Urea converted to ammonia by microorganisms
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Manmade substances
•
Ammonia in WWTP influent
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Ammonia/AmmoniumAmmonia/Ammonium
•
Relationship between NH3
and NH4+
is based on pH.–
Lower pH means more H+
ions available, thus more NH4
+.–
pH < 6.75 –
100% NH4+
–
pH = 9.25 –
50% NH4+
–
pH > 11.75 –
100% NH3
•
Relationship between NH3
and NH4+
is based on temperature.–
Lower temperature means more NH4
+.
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Ammonia Toxicity/LimitsAmmonia Toxicity/Limits
•
Ammonia is toxic to plants and animals above certain concentrations.
•
NH3
is approximately 100 times more toxic than NH4+,
so NH3
will almost always be our concern.
•
Effluent limits are based on total ammonia, but are usually relaxed or nonexistent for low temperature and/or pH.
•
Effluent limits vary by stream classification because toxicity varies by species.–
NH3
acute toxicity for fish is as low as 2 mg/L–
NH3
chronic toxicity for fish may be as low as ~0.05 mg/L–
NH3
can also cause DO depletion as nitrification occurs.
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Reducing Ammonia ToxicityReducing Ammonia Toxicity•
pH Adjustment
•
Temperature “Adjustment”
•
Breakpoint Chlorination
•
Biological Ammonia Removal (Nitrification)
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NitrificationNitrification•
Chemical process of converting ammonia to nitrite and nitrate–
NH3
+ CO2
+ 1.5 O2
+ AOB → NO2-
+ H2
O + H+
–
NO2-
+ CO2
+ 0.5 O2
+ NOB → NO3-
•
Necessary components–
Air (oxygen, carbon dioxide)
–
Bacteria (AOB-nitrosomonas, NOB-nitrobacter)–
Temperature (40-45 degrees Fahrenheit)
–
Alkalinity (~7 grams per gram Ammonia-N)–
Absence of toxic compounds
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Grantsburg, WIGrantsburg, WI
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Proposed effluent limit of 17 mg/L daily maximum for ammonia–
Based on assumed maximum effluent pH of 8.0
–
Average effluent pH of 7.7–
If maximum effluent pH was 7.5, no effluent ammonia limit would be required.
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Grantsburg, WIGrantsburg, WI
•
Alternatives Considered:–
Fill and Draw Operation
–
Breakpoint Chlorination•
224 gpd
sodium hypochlorite
–
pH Adjustment•
Carbon Dioxide Injection
•
2.8 gpd
sulfuric acid
•
Acid addition satisfies permit and involves minimal capital/operational cost.–
Additional operator attention
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Madeline IslandMadeline Island
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Madeline Sanitary District WWTPMadeline Sanitary District WWTP
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Population and FlowsPopulation and Flows
•
Year-round population of approximately 250
•
Summer population of approximately 4,000
•
Flows vary from:–
25,000 gpd
during winter months
–
65,000 gpd
during summer months
•
Approximately 15% of flow is hauled waste from holding tanks located outside of the sewered
downtown LaPointe
area.
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Effluent Ammonia LimitEffluent Ammonia Limit
•
DNR requirements based on:–
Temperature–
pH–
Water body classification–
Effluent discharge rates–
Available dilution–
Presence of early life stage aquatic species
•
Daily limit of 16 mg/L for November through April
•
Variable limit based on effluent pH
Effluent pH Ammonia Limit (mg/L)7.1 >40
7.2 39
7.3 35
7.4 31
7.5 27
7.6 23
7.7 19
7.8 16
7.9 14
8.0 11
8.1 9.3
8.2 7.6
8.3 6.3
8.4 5.2
8.5 4.3
8.6 3.5
8.7 2.9
8.8 2.5
8.9 2.1
9.0 1.8
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Ammonia Removal OptionsAmmonia Removal Options
•
Mechanical WWTP
•
Mechanical addition to aerated lagoon WWTP
•
Treatment in existing lagoons–
Aeration upgrades
–
Media for attached growth of nitrifying bacteria–
Insulated cover for heat retention
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Aeration UpgradesAeration Upgrades
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Attached Growth MediaAttached Growth Media
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Insulated Floating CoverInsulated Floating Cover
•
R-20 insulation value
•
5-inch thick polystyrene encased in HDPE
•
Modular, removable
•
Access panels for diffuser removal
•
Prevents algae blooms, retains heat
•
Installed Fall/Winter 2009
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Insulated Floating CoverInsulated Floating Cover
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Ammonia Effluent ResultsAmmonia Effluent Results
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pH Effluent ResultspH Effluent Results
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Why are we losing nitrification in the summer?
Why are we losing nitrification in the summer?
•
Low pH can inhibit nitrification, but the data doesn’t show this correlation.
•
Temperature can inhibit nitrification, but the high ammonia is during the summer. –
Checked detention time of lagoons: in case of true plug flow, what is discharged in summer may come in during winter months.
–
3 month detention time doesn’t explain it.–
Entire lagoon contents are heated during the summer, so nitrification should pick up anyway.
•
Toxic Compounds?–
Quaternary Ammonia Compounds
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ConclusionsConclusions
•
Ammonia toxicity is variable, and can be addressed in a variety of ways.
•
Cold weather lagoon nitrification is possible, but lagoon nitrification in general can be touchy –
have a backup plan.
•
Know who is discharging what to your collection system.
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Questions?Questions?