Primary Clarifier Odor Control –
Replacing Nitrates with D.O.
Kevin Jacobs, P.E.
ECO Oxygen Technologies
Presentation Outline
• Primary Clarifier Odor Challenges
• Odor Treatment Options
• Case Study – Anson-Madison Sanitary
District
• Conclusions
Primary Clarifier Odor
Challenges
Quiescent by Design
Flow is slowed to allow for solids settling
• Provides for little to no re-aeration
Major Odor Source
The effluent weirs from a primary clarifier are
a major source of odor
H2S Flux
Odor
Release
H2S Flux
Sludge Blanket
Root Cause of Odor
Electron Acceptors (Order of Preference):
Oxygen
Nitrate
Sulfate
U.S. EPA (1985) Odor and Corrosion Control in Sanitary Sewerage Systems and Treatment
Plants Design Manual; EPA/625/1-85/018; Cincinnati, Ohio.
Root Cause of Odor
Under Anaerobic Conditions:
• Bacteria consumes BOD
• Strips Sulfate of O2
• Converts Sulfate to Sulfide
Sulfide
SO4 & BOD
H2S
No D.O.
Factors That Affect H2S Formation
•
•
•
•
•
•
Limited solubility of oxygen in water
High BOD
Favorable pH levels
Warm temperatures
Unlimited supply of sulfates
Long retention times
Odor Leads to Corrosion
Rate of Corrosion
100%
50%
0
5
500
H2S Concentration (ppm)
1000
Corrosion
Common Solutions
Allow H2S to Form and Treat
• Cover and Scrub
• Wet scrubbers
• Carbon units
• Biofilters
• Biotrickling Filters
• Chemical Addition
• Nitrate
• Iron
Prevent H2S Formation
•
Oxygen addition
Form and Treat Solutions
Form and Treat Solutions
Chemical Addition
Preventive Solution
D.O. Addition
• No bubbles = No impact on settling
• Add enough D.O. to satisfy HRT
• Consume BOD ahead of aeration
Aerobic “Cap”
H2S Flux
H2S Flux
Sludge Blanket
SuperOxygenation as a
Preventive Solution
40 mg/L at 1 ATM
- Increasing pressure increases the saturation point
- Use of pure oxygen versus air
SuperOxygenation
Technology Overview
Side Stream
Pump
ECO2 Cone
90-95% O2
Absorption
Efficiency
Pure Oxygen
Gas
Unscreened Raw
Wastewater
Conveyance
Pipeline
SuperOxygenated
Raw Water
Case Study – Anson Madison
Sanitary District – Madison, ME
• Operated by Woodward and Curran
• 4 MGD Flow
– 3.5 MGD from UPMMadison Paper
– 0.5 MGD from local
community
Case Study – Anson Madison
Sanitary District – Madison, ME
Plant is located in close proximity to neighbors
• Frequent odor complaints
Case Study – Anson Madison
Sanitary District – Madison, ME
Physical Characteristics
• Diameter – 90 ft
• Depth – 12 ft
• Volume – 0.57 MG
• Normal HRT –
3.5 – 5 hours
Case Study – Anson Madison
Sanitary District – Madison, ME
Wastewater Characteristics
• Temperature – 28-30 ℃
• BOD – 500-600 mg/L
• Oxygen Uptake Rate (OUR) – 5-10 mg/L/hr
PC Flow (MGD)
HRT (hrs)
OUR (mg/L/hr)
3.9
3.1
5.36
1.9
6.3
10.47
2.6
4.6
8.86
2.8
4.3
5.65
Primary Clarifier Odor – No
Treatment
Use of Nitrates
Original Design
• 200 gpd = ~750 lbs O2
– @ $2.50/gal = $183,000
• not working!
Actual required dosage
• 400 gpd = 1,500 lbs O2
– @ 2.50/gal = $325,000
Design Calculations
Low Flow Scenario:
• 2.7 MGD Flow results in 5 hour HRT
• 5 hr * 10 mg/L/hr * 8.34 * 2.7 MGD = 1,125 lbs O2/day
Average Flow Scenario:
• 4 MGD Flow results in 3.5 hour HRT
• 3.5 hr * 10 mg/L/hr * 8.34 * 4 MGD = 1,168 lbs O2/day
Peak Flow Scenario:
• 6 MGD Flow results in 2.3 hour HRT
• 2.3 hr * 10 mg/L/hr * 8.34 * 6 MGD = 1,151 lbs O2/day
SuperOxygenation System
Design Considerations
• Available primary influent pump head capacity
– All influent pumped through cone
• Pump TDH at 25’
• Cone located at grade
• Resulting system capable of adding 1,680 lbs
O2/day
• Up to 62 mg/L D.O. achieved
SuperOxygenation System
Placement
System capitalizes on PC pump head and available
static head
Primary Clarifier Pumps
Oxygen Generators
(2) 200 lpm (840 lbs/day) units generate oxygen
at 93% purity
Economics
ECO2
Chemical Cost
Oxygen Cost
Nitrates
$325,000
$27,250
254 kWhr/day per generator at
$0.147/kwHr
Annual Savings
$297,750
Equipment Capital Cost
$310,000
ECO2 System, (2) O2
Generators
Installation Cost
$270,000
Engineering, piping,
instrumentation, generator
building, etc.
Payback
<2 years
Oxygen cost reflects full operation of both generators
D.O. at Cone Discharge
H2S Level at Weir
D.O. Level at Weir
Measurement Location
Treatment Benefits Achieved
• H2S control is consistent
• Odor complaints eliminated
• BOD reduction across clarifier increased
– Prior to oxygen addition 15% removal
– Adding 1,000 lbs O2/day has increased BOD
removal to 20%
• Additional 600-1,000 lbs BOD/day removed
• Less oxygen required in aeration
– $25,000-$40,000 additional annual savings
Revised Economics
ECO2
Chemical Cost
Oxygen Cost
$325,000
$20,500
193 kWhr/day per generator at
$0.147/kwHr
Aeration Savings
$25,000
Annual Savings
$329,500
Equipment Capital Cost
$310,000
ECO2 System, (2) O2
Generators
Installation Cost
$270,000
Engineering, piping,
instrumentation, generator
building, etc.
Payback
Nitrates
1.76 years
Conclusions
• Operationally Compatible
– No impact to settling
• Efficient
– 90-95% oxygen absorption efficiency
– Oxygen is added to meet flow demand
• Economical
– Oxygen is inexpensive in comparison to alternatives
– District saves ~$300,000 per year over nitrates
– Reduced aeration requirements
• Effective
– H2S levels typically near non-detect
Acknowledgements
• Dale Clark, AMSD Plant Manager,
Woodward and Curran
Questions?
Kevin Jacobs
(317) 706-6487
[email protected]