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.

2. Overview
 Project background
 Bench scale pilot / bioreactor setup
 Results to date
 Continued Efforts

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

4. Background
2013 Estimate: 9,318
2033 Estimate: 12,806

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

7. Background

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

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

17. Pilot Test
 BioReactors
 4” Clear PVC
 Pressure Gauges
 Fill & Draw Ports
 Ball Valves
 Rack

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

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

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

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

43. Pilot Testing – March 2014

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