OverviewProject background

Bench scale pilot / bioreactor setup

Results to date

Continued Efforts

BackgroundLocated in La Crosse CountyRapidly GrowingMedian Resident Age

Holmen: 34 yearsWisconsin Avg: 44 years

Estimated 2011 MHIHolmen: $59,326Wisconsin Average: $50,395

2013 Estimate: 9,3182033 Estimate: 12,806

BackgroundAverage Influent Wastewater

Characteristics:0.50 MGD average daily flow330 mg/L BOD323 mg/L TSS38 mg/L NH350 mg/L SO4

The Village must have some significant high strength industrial dischargers, right?

BackgroundWrong!

Very Little Infiltration and InflowTight sewers (a lot of new construction)Sandy soilsNot many areas of high groundwater

Facility PlanningWWTF is nearing organic capacityLots of growthFuture P limit of 0.075 mg/L

Compliance OptionsOxidation Ditch A/S with Tertiary FiltrationMembrane BioReactorsRegional treatment at La Crosse WWTF (via

Onalaska)

Facility PlanningTreatment

Capital: $15.8 M Annual O&M: $243,000

RegionalizationCapital: $9.3 MAnnual O&M: $162,000

Regionalization was recommended

Facility PlanningRegionalization Assumptions

New regional pump station at location of WWTF

4.8 Miles of 16” Forcemain to OnalaskaChemical 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

Facility PlanningRegionalization 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

Facility PlanningHydrogen Sulfide (H2S) forms when:

Conditions are anaerobic (no free oxygen)Food (BOD) is availableSulfate Reducing Bacteria (SRBs) are present

Rotten egg smell

Reported Odor Thresholds VaryIn Air: 0.005 – 0.3 ppm (Ruth 1986, Guidotti

1994) In Water: 0.000029 ppm (O’Neil 2001)

Facility PlanningShould 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

Facility PlanningConditions of Regionalization Recommendation:

Condition 1Equitable agreements with Onalaska and La

Crosse would be reached

Condition 2Control of odors at the discharge in Onalaska

would be feasible and cost effective

Pilot TestGoal 1: Construct bench-scale bioreactors to

mimic forcemain conditionsGoal 2: Document and assess sulfide

generation potential of Holmen’s wastewaterGoal 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

Pilot Test BioReactors

4” Clear PVCPressure GaugesFill & Draw PortsBall ValvesRack

Pilot Test – Reactor Conditioning

Condition Reactors to establish anaerobic biofilm

Bioreactors were filled and emptied every 24 hours

Biofilm was visible after roughly 2 weeksH2S Odor was noticeable when emptying

reactors

Pilot Test – Reactor Conditioning

Influent and Effluent Sampling to Confirm Biological ActivitySulfate (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

Pilot Testing – Sample Analysis

Certified lab was used for sulfide and sulfate during bioreactor conditioningSignificant expenseLong turnaround time = disadvantage

Colorimetric tests to measure dissolved sulfideUse for routine monitoring of bioreactor

influent & effluent; instantaneousSend some samples to certified lab to verifySave costs

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 ? )

Pilot Testing – Original PlanWeek 1

Feed R1 at 3x theoretical dosageFeed R2 at 2x theoretical dosageUse 24 hour HRT for simplicity

Fill & Draw (no dose) over the weekendWeek 2

Feed R1 at 1x theoretical dosageFeed R2 at 0.5x theoretical dosage

Document reduction in sulfide generation

Pilot Testing – Initial Results Large discrepancy between certified lab and

colorimetric test resultsColorimetric typically 5% - 20% of certified lab

resultBelieved to be interference with TSS

Sulfide generation actually increased Over fed the SRBs with nitrateArtificially created a population boomTests were too short to re-achieve equilibrium

Pilot Testing – Revised PlanRe-establish natural steady-state for biofilm

Fill & Draw reactors daily; no calcium nitrate addition

Try a new colorimetric test to see if interferences are eliminatedHACH 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…

Pilot Testing – March 2014

Operate at HRTs of ~ 6-8 hours and ~ 15-17 hours

Operate one reactor as a control throughout testsNo calcium nitrate additionOperate the other reactor as the test caseBegin dosing calcium nitrate one week in advance of

trying to quantify resultsEstablish steady state of biomass and acclimate the

SRBsWeek 1: Dose at 1.5 x theoreticalWeek 2: Dose at 2.0 x theoretical

Pilot Testing – March 2014

Results are promisingTrends are visibleShorter HRTs result in lower sulfide levelsAmbient temperature influences

Cold influent takes a while to ‘warm up’ in the reactor

Likely delays the conversion of sulfate by SRBs in the biofilm

Pilot Testing – March 2014

Further Work

Continue pilot testingLong-term data should increase overall

consistencyCharacterize temperature impacts

Summertime operation will be criticalCompare modeled vs actual sulfide

production in untreated reactorTo date, observed sulfide concentrations are

much lower than modeledBegin splitting samples with certified lab