This document discusses a pilot project to test odor control in a proposed wastewater force main between Holmen, WI and Onalaska, WI. Bench-scale bioreactors were set up to mimic force main conditions and test calcium nitrate dosing. Initial results showed discrepancies between lab tests and colorimetric tests for sulfides. The testing plan was revised to better establish biofilm conditions before continuing dosage tests, which have shown promising trends so far in reducing sulfides. Further long-term testing is needed, especially in summer.
3. Background
Located in La Crosse County
Rapidly Growing
Median Resident Age
Holmen: 34 years
Wisconsin Avg: 44 years
Estimated 2011 MHI
Holmen: $59,326
Wisconsin Average: $50,395
5. Background
Average Influent Wastewater
Characteristics:
0.50 MGD average daily flow
330 mg/L BOD
323 mg/L TSS
38 mg/L NH3
50 mg/L SO4
The Village must have some
significant high strength
industrial dischargers, right?
6. Background
Wrong!
Very Little Infiltration and Inflow
Tight sewers (a lot of new construction)
Sandy soils
Not many areas of high groundwater
8. Facility Planning
WWTF is nearing organic capacity
Lots of growth
Future P limit of 0.075 mg/L
Compliance Options
Oxidation Ditch A/S with Tertiary Filtration
Membrane BioReactors
Regional treatment at La Crosse WWTF (via Onalaska)
9. Facility Planning
Treatment
Capital: $15.8 M
Annual O&M: $243,000
Regionalization
Capital: $9.3 M
Annual O&M: $162,000
Regionalization was
recommended
10. Facility Planning
Regionalization Assumptions
New regional pump station at location of WWTF
4.8 Miles of 16” Forcemain to Onalaska
Chemical addition at the regional pump station to
control odors (hydrogen sulfide)
Intermediate chemical feed building ~2 miles away
included in cost, but hopefully not necessary
Goal: feed chemical at regional pump station only
11. Facility Planning
Regionalization Assumptions, Continued
Estimated aqueous hydrogen sulfide generation of 16.8
mg/L or 70.5 lbs/day at startup flow (summer temps)
Calcium Nitrate dosage of 1.3 gallons per pound of
sulfide
Roughly 33,000 gallons of calcium nitrate @ $4.25/gallon
Estimated annual chemical cost of ~ $140,000
12. Facility Planning
Hydrogen Sulfide (H2S) forms when:
Conditions are anaerobic (no free oxygen)
Food (BOD) is available
Sulfate Reducing Bacteria (SRBs) are present
Rotten egg smell
Reported Odor Thresholds Vary
In Air: 0.005 – 0.3 ppm (Ruth 1986, Guidotti 1994)
In Water: 0.000029 ppm (O’Neil 2001)
13. Facility Planning
Should we worry about odors in this case?
Odors are common in forcemains, especially when:
Strong wastewater (Holmen BOD = 330 mg/L)
Plenty of Sulfates (Holmen SO4 = 50 mg/L)
Significant forcemain hydraulic retention times
Holmen HRT = 13 hours at startup flow
Holmen HRT = 8 hours at design flow
Plan for odor control
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15. Facility Planning
Conditions of Regionalization Recommendation:
Condition 1
Equitable agreements with Onalaska and La Crosse
would be reached
Condition 2
Control of odors at the discharge in Onalaska would be
feasible and cost effective
16. Pilot Test
Goal 1: Construct bench-scale bioreactors to mimic
forcemain conditions
Goal 2: Document and assess sulfide generation
potential of Holmen’s wastewater
Goal 3: Treat reactors with calcium nitrate under and
document inhibition of sulfide generation
Goal 4: Determine necessary dosage and compare
projected O&M costs to facility plan estimates
22. Pilot Test – Reactor Conditioning
Condition Reactors to establish anaerobic biofilm
Bioreactors were filled and emptied every 24 hours
Biofilm was visible after roughly 2 weeks
H2S Odor was noticeable when emptying reactors
23. Pilot Test – Reactor Conditioning
Influent and Effluent Sampling to Confirm Biological
Activity
Sulfate (influent should be higher than effluent)
Sulfide (influent should be lower than effluent)
sBOD (influent should be higher than effluent)
H2S Odor was noticeable when emptying reactors
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27. Pilot Testing – Sample Analysis
Certified lab was used for sulfide and sulfate during
bioreactor conditioning
Significant expense
Long turnaround time = disadvantage
Colorimetric tests to measure dissolved sulfide
Use for routine monitoring of bioreactor influent &
effluent; instantaneous
Send some samples to certified lab to verify
Save costs
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30. Pilot Testing – Products
Hawkins HSX AquaHawk (Calcium Nitrate)
Provided product as a courtesy
Other manufacturers’ products would be tested later
as time permitted
Bioxide (Siemens/Evoqua)
CS41 (Hydrite)
Other chemicals (Ferric Chloride? H2O2 ? )
31. Pilot Testing – Original Plan
Week 1
Feed R1 at 3x theoretical dosage
Feed R2 at 2x theoretical dosage
Use 24 hour HRT for simplicity
Fill & Draw (no dose) over the weekend
Week 2
Feed R1 at 1x theoretical dosage
Feed R2 at 0.5x theoretical dosage
Document reduction in sulfide generation
32. Pilot Testing – Initial Results
Large discrepancy between certified lab and
colorimetric test results
Colorimetric typically 5% - 20% of certified lab result
Believed to be interference with TSS
Sulfide generation actually increased
Over fed the SRBs with nitrate
Artificially created a population boom
Tests were too short to re-achieve equilibrium
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38. Pilot Testing – Revised Plan
Re-establish natural steady-state for biofilm
Fill & Draw reactors daily; no calcium nitrate addition
Try a new colorimetric test to see if interferences are
eliminated
HACH Model HS-C
Establish consistent results
Then start splitting samples with certified lab
Wait for extreme cold weather to end…
Keep busy by thawing some frozen laterals…
39. Pilot Testing – March 2014
Operate at HRTs of ~ 6-8 hours and ~ 15-17 hours
Operate one reactor as a control throughout tests
No calcium nitrate addition
Operate the other reactor as the test case
Begin dosing calcium nitrate one week in advance of
trying to quantify results
Establish steady state of biomass and acclimate the SRBs
Week 1: Dose at 1.5 x theoretical
Week 2: Dose at 2.0 x theoretical
40. Pilot Testing – March 2014
Results are promising
Trends are visible
Shorter HRTs result in lower sulfide levels
Ambient temperature influences
Cold influent takes a while to ‘warm up’ in the reactor
Likely delays the conversion of sulfate by SRBs in the
biofilm
44. Further Work
Continue pilot testing
Long-term data should increase overall consistency
Characterize temperature impacts
Summertime operation will be critical
Compare modeled vs actual sulfide production in
untreated reactor
To date, observed sulfide concentrations are much
lower than modeled
Begin splitting samples with certified lab