Annual Conference - WTP Residuals

7/30/2019 Annual Conference - WTP Residuals

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Impact of Water Treatment Plant

Residuals on Fixed Film Processes

Sidney Biesterfeld1, Mark Dane2, Richard Dingeman2,

Dan Freeman2, Paul Heppler2,

Kurt Keilbach2, Ernie Oram2, Dr. David Paterniti2,

Dan Wadas2

, and Mike Lutz1

1Integra Engineering, 2City of Boulder 75th Street WWTP


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2004 Joint Annual Conference

WTP Residuals

Water treatment plants use ferric chloride,ferric sulfate, and alum as coagulants.

Resulting residuals are sometimes dischargedto the sanitary sewer for WWTP co-disposal.

Increases inert fraction of MLSS; alsoincreases total MLSS concentration.

Adds 5-20% to WWTP solids handling costs.

Can increase metals and radionuclide levels.


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WTP residuals increase WWTPsolids handling costs

CTP Total WTPResiduals

PercentIncrease

Influent flow, mgd 156.7 0.55 0.3

Mass load, tons/day

Influent BOD 142.5 0.1 0.1

Influent TSS 178.2 22.9 12.8

Primary Sludge 106.8 20.6 19.3

Secondary Sludge 87.6 2.3 2.6

Digester Feed 196.7 25.3 12.9

Digested Sludge 118.0 22.8 19.3


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WTP Residuals have beneficialeffects on WWTP operation

Iron based residuals mitigate odors bypreventing H2S formation. Iron sulfide, an insoluble forms instead.

Minimize H2S in anaerobic digester gas.

Improve sludge settleability.

Mitigate struvite formation by precipitatingortho-phosphorus.

May aid in soluble metals and P removal.

Edwards et. al. 1997


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75th Street WWTP, Boulder, CO


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Too much of a good thing,isnt always

February 2001, the Boulder ReservoirWater Treatment Plant experimentedwith a new operational mode.

WTP residuals were held for an extendedperiod of time to build deep blankets.

New operational mode was not successful.

Excess residuals were discharged toBoulder 75th Street WWTP.


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Too much of a good thing,isnt always

Total pounds of iron delivered unknown.

Biological processes were disrupted.

Upper levels of trickling filter rocks werecoated with an orange, gelatinous material.

Still visible after nearly three years.

Final effluent quality was impacted for anextended period; nitrification, TSS, and BOD5


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75th Street Plant implementedan aggressive control plan

WTP was issued a pretreatment permitlimiting iron discharge to 400 ppd.

WTP now discharges residuals for threeminutes once every 1.5 hours to minimizeimpact on WWTP operation.

WTP switched from FeCl2 to FeSO4 forcompatibility with WWTP operations.

Control plan limited effects of residuals.


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Control strategy was effective,but wasnt science based

Total pounds of iron received prior to upsetwas unknown.

Pretreatment limit set high enough that WTPwould not be impacted.

Anecdotal evidence raised concerns thatpretreatment limit is too high.

Where should the pretreatment limit be set?


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Limits should be set to minimizeimpacts on operation.

Coating of trickling filter biofilm whichreduces oxygen transfer.

Phosphorus deficiency in biological processes

due to precipitation of P.

Iron toxicity. 1.84 mg/L Fe impacts activated sludge1

1.68 mg/L Fe drops nitrification rates by 20-34%2

High levels of Fe associated with nitriteaccumulation in activated sludge.3

Ciliated protozoa impacted at 2.0 mg/L Fe4

1. Lees et al. 2001a 2. Lees et al. 2001b3. Clarket al. 2000 4. Abraham et al. 1997


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Trickling filters may be moreresistant to toxic effects

Heavy metal toxicityin activated sludgedepends on:

Metal to biomass ratio Temperature

pH

Presence of other

metal ionsPlant specific

Jar testing required.


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Boulder 75th Street WWTP

Four filters in parallel.

8 feet media depth.

4 - 6 coarse rock media.2 @ 155 feet diameter.

2 @ 200 feet diameter.

HLR = 0.45 gpm/sft.Inf. cBOD5 = 74 + 9 mg/L


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Sampling Device providesbiofilms identical to full-scale TF

Two layers of eightslide groups.

Each slide group

contains five slides.

Intact Biofilms

Sampling device

placed on top of TF

media for fourteendays.


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Bench-Scale Reactors allow for acontrolled testing regime


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Bench-Scale Reactors allow for acontrolled testing regime

Contained 600 mls ofprimary clarifier effluent.

Aerated continuously andstirred.

Added molasses to raiseCOD to 900 mg/L.

Added varying amounts ofWTP residuals to each

reactor.

Two reactors per residualconcentration.


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Bench-Scale Reactors

Experiment repeated ontwo different days.

Reactors run for 2.5

hours.Dissolved oxygenmonitored.

Samples collected atstart and every 30minutes for COD andsoluble COD.

Total iron measured atstart and end of reactorruns.


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Iron may be partitioning intothe biomass at higher levels

# mLs START Fe, mg/L END Fe, mg/L

1 None 1.20 1.51

2 None 1.18 1.08

3 1 1.91 1.77

4 1 1.81 2.81

5 5 5.06 4.10

6 5 5.44 4.82

7 10 9.26 7.39

8 10 9.25 7.84

9 15 14.22 12.98

10 15 13.39 11.16


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Total COD concentrations didnot vary during the test

Six measurements per reactor for atotal of 60 measurements.

Total COD averaged 927 + 30 mg/L

Should not change since soluble COD is

converted into particulate COD(biomass)


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Soluble COD removal wasunaffected by Fe up to 15 mg/L


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No effect concentration was higherthan previously reported values

Iron toxicity observed at 2.0 mg/L andlower in activated sludge samples.

Researchers used raw chemicals, ferricchloride and ferric sulfate, not WTPresiduals.

Most of iron in WTP residuals is boundas ferric hydroxide; possibly less toxic.


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High iron tolerance likely relatedto properties of biofilms

Toxicity in activated sludge is a functionof metal to biomass ratio.

Biofilms have more mass per volumethan activated sludge.

Exopolymers may mitigate toxic effects

by binding to metal ions.

Biofilms known to be more robust.


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Acute iron toxicitywas not observed

Iron concentrations between 1.2 and 14.2mg/L did not impact soluble COD removal in14-day old biofilms.

Chronic effect levels are typically lower thanacute effect levels.

The 75th

Street WWTP should be able toroutinely accept influent iron up to 14.2 mg/Lwithout impacting rock TF performance.


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Current operating practices atWTP protect WWTP biology

At an influent iron concentration of 14.2 mg/Land an average daily flow of 16 mgd,ppd = 1890

Pretreatment permit limit of 400 ppd of WTPresiduals protects WWTP unit processes.

Assumes continuous, not slug loading.Conclusions apply to ferric sludge only.


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Future work

Test effects of WTPresiduals on activatedsludge.

Test effects of WTPresiduals on biofilmsat higherconcentrations.

Look at chroniceffects with longertest periods.


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F loyd Bebler, Ernie Oram

Mark Dane, Richard Dingeman,

Dan Freeman, Paul Heppler,

Kur t Keilbach, Dr. David Paterni ti,

Dan Wadas, and the rest of the

Boulder 75thStreet WWTP staff .


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Questions?


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1. Abraham, J.V., Butler, R.D., and Sigee, D.C. "Ciliate Populations and Metals in an ActivatedSludge Plant." Water Research 31.5 (1997): 1103-1111.

2. Clark, T., Burgess, J.E., Stephenson, T., and Arnold-Smith, A.K. "The Influence of IronBased Co-Precipitants on Activated Sludge Biomass." Process Safety and EnvironmentalProtection 78.5 (2000): 405-410.

3. Edwards, M., Beorn, C., Heppler, P., and Hernandez, M. Beneficial Discharge of Iron Coagulation

Sludge to Sewers.

Journal of Environmental Engineering October (1997): 1027-10324. Genschow, E., Hegemann, W., and Maschke, C. "Anaerobic Treatment of TanneryWastewater: Toxic Effects of Wastewater Constituents and Dosage of Ferric Chloride."Environmental Management and Health 8.1 (1997): 2-3.

5. Gerardi, Michael H. "Effects of Heavy Metals upon the Biological Wastewater TreatmentProcess." Public Works.June (1986): 77-80.6. Johnson, D.K., Carliell-Marquet, C.M., and Forster, C.F. "An Examination of the Treatmentof Iron-Dosed Waste Activated Sludge by Anaerobic Digestion." Environmental Technology

24.8 (2003): 937-945.7. Lees, E.J., Noble, B., Hewitt, R., and Parsons, S.A. "The Impact of Residual Coagulant onDownstream Treatment Processes." Environmental Technology 22.1 (2001): 113-122.

8. Lees, E.J., Noble, B., Hewitt, R., and Parsons, S.A.f1f1. "The Impact of Residual Coagulanton the Respiration Rate and Sludge Characteristics of an Activated Microbial Biomass."Environmental Technology 79.5 (2001): 283-290.f1

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Annual Conference - WTP Residuals

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