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Denitrification with Carbonaceous Trickling Filters

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Title: Denitrification with Carbonaceous Trickling Filters


1
Denitrification with Carbonaceous Trickling
Filters

Presented by Sidney Biesterfeld, Greg Farmer,
Linda Figueroa, Denny Parker and Phil Russell
RMWEA / RMSAWWA Joint Annual Conference September
15-18, 2002Steamboat Springs, Colorado
RTW Professional Engineers and Consultants, Inc.
2
Introduction
  • Facilities facing stricter nitrate limits.
  • Eutrophication.
  • Drinking Water Standards.
  • Downstream Uses.
  • Existing facilities must upgrade to denitrify.
  • Biological conversion of NO3-N to N2.
  • Requires carbon source and no D.O.

Conflicts with Nitrifier Requirements.
3
Denitrification Options
  • Increase Aeration Basin Volume.
  • Site Constraints.
  • Expensive.
  • Tertiary Denitrification Processes.
  • Require Carbon Source.
  • Flammable and Costly.
  • Special Handling Requirements.
  • Risk of permit violation for BOD.

4
Another Option for WWTPs with Trickling Filters
  • Recycle nitrified effluent back to TF.
  • Oxygen penetrates upper 100-200 mm.
  • Anoxic and anaerobic layers below.
  • Denitrification can take place.

5
Advantages to Recycling
  • Delay or Avoid Facility Expansion.
  • No New Unit Processes.
  • No Chemical Addition.
  • Up to 50 removal at 100 Recycle.
  • Up to 67 removal at 200 Recycle.
  • Possible Odor Control Benefit.

6
L/E WWTP Case Study
  • Facing unknown nitrate limit.
  • Pending Outcome of TMDL Study.
  • May only need 10 to 20
    reduction.
  • Consulting engineer proposed recycle alternative
    based on previous observations.
  • Full-scale pilot successful, But..

7
Limitations of Full-Scale Pilot
  • Hydraulic constraints limited total flow.
  • High influent flow, low effluent return.
  • TF removed 100 of applied nitrate.
  • Low influent flow, high effluent return.
  • TF became COD limited.

8
Bench Scale Testing
  • Unable to determine potential capacity.
  • How much nitrate could be removed?
  • Bench-scale testing under controlled conditions
    was necessary.
  • Collected Biofilms from Full-Scale TF.
  • Monitored Denitrification Rates in Bench-Scale
    Reactors.

9
Objectives
  • To determine maximum denitrification potential of
    TF biofilms
  • Under non-rate limiting conditions.
  • In the presence of dissolved oxygen.
  • To determine if denitrification potential was
    uniform over the entire TF volume.
  • To verify potential for odor control benefits
    absence of sulfate reduction.

10
Experimental Design
11
Littleton/Englewood WWTP
  • Two filters in parallel.
  • 16 feet media depth.
  • 37 sf/cf cross flow media.
  • 105 feet diameter.
  • Three sampling ports.
  • HLR 1.6 gpm/sft.
  • Inf. COD 105 21 mg/L

12
Biofilm Sampling Device
  • Six groups of slides per sampler.
  • Each slide group contains five slides.
  • Sampling device placed in TF sample ports for
    twenty-nine days.

13
Bench-Scale Reactors
  • Contained 600 mls of sterilized primary clarifier
    effluent.
  • Aerated continuously and stirred.
  • D.O. kept at 2 - 4 mg/L
  • Nitrate-N 16 mg/L
  • Three reactors per sampling port.

14
Bench-Scale Reactors
  • Reactors run for 5 hours.
  • Three per sampling port plus three control
    reactors.
  • Samples collected at start and every 30 minutes.
  • Dissolved Oxygen.
  • pH.
  • Nitrate.
  • Nitrate reduction rates in g N/m2day calculated
    based on slide surface area.
  • Experiment repeated on three different days.

15
Bench-Scale Reactors
  • Initial and final inorganic nitrogen species
    (NH3, NO2, and NO3), sulfate, COD, SCOD,
    alkalinity, and Total Suspended Solids (TSS)
    were monitored.

16
Bench-Scale Reactors
  • Initial and final inorganic nitrogen species
    (NH3, NO2, and NO3), sulfate, COD, SCOD,
    alkalinity, and Total Suspended Solids (TSS)
    were monitored.

17
Dry Weight Biomass Measurements
  • Accumulated biomass was quantified as dry weight
    biomass in mg/slide.
  • Prior to placement in the TF, each slide was
    engraved with a serial number and weighed to the
    nearest 0.0001 grams.
  • After reactor runs, slides were dried at 103oC
    for at least two hours and re-weighed.
  • Some reports that biomass accumulation correlates
    to denitrification rates.

18
Results
19
  • First Campaign

20
  • Second Campaign

21
  • Third Campaign

22
  • Results are reproducible.
  • No lag period observed for denitrification to
    begin.
  • Capacity is inherent in biofilm.
  • Consistent with observations of activated sludge
    systems with on/off aeration.
  • Denitrification occurred in the presence of
    dissolved oxygen (2 4 mg/L).

23
Denitrification Rates
TOP MIDDLE BOTTOM
First 4.71 5.10 5.10 4.67 5.23 4.88 4.10 3.88 4.75
Second 4.64 4.02 4.49 4.33 4.49 4.64 4.38 4.33 3.09
Third 5.13 4.30 4.61 4.77 5.29 4.82 5.55 4.87 5.44
Rates are given in g-NO3-N/m2day.
Avg 4.65 0.52
24
Denitrification Rates
  • Rates obtained are for conditions evaluated here
  • NO3-N gt 5 mg/L, lt 20 mg/L.
  • D.O. between 2 and 4 mg/L.
  • COD/SCOD present in excess.
  • Conditions chosen to mimic full-scale TF.
  • Rates may be applied to other TFs.

25
Denitrification Rates
  • No significant difference in rates
  • Between Sampling Events.
  • Between Sampling Locations.
  • Denitrification potential is uniform over entire
    volume of TF.
  • Higher than previous findings of 1.2 (MBBR), 2.1
    (Fluidized Bed), and 3.6 (Slag TF) g-N/m2d
    under similar conditions.

26
Biomass versus Rate
  • No correlation between dry weight biomass
    accumulation and removal rates.
  • Contrasts with previous findings.
  • May be due to low nitrate relative to accumulated
    biomass.

27
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28
Additional Parameters
  • 3.91 grams SCOD per gram NO3-N
  • Consistent with previous findings of 3.61 and
    2.86 g/g
  • 9.95 grams COD per gram NO3-N
  • Higher than literature values.
  • Reflects oxygen based metabolism of outer layers
    of biofilm.

29
Additional Parameters
  • 3.16 grams alkalinity produced per gram NO3-N
    reduced.
  • Consistent with literature value of 3.57 g/g
  • Sulfate concentrations constant over length of
    experiment.
  • Nitrate preferentially reduced.
  • Implied odor control benefit.

30
Implications for WWTP Operation
  • Free Denitrification.
  • Avoid or Delay Facility Expansion.
  • No chemical addition.
  • 50 Removal at 100 Recycle.
  • Odor Control Benefit.
  • Beware of downstream hydraulic constraints.

31
Implications for WWTP Operation
  • Rates may be extrapolated to other facilities.
  • Allows for reliable estimate of denitrification
    potential.
  • Methanol may be used to supplement TF influent to
    maximize removal.
  • Approach works for any TF facility that nitrifies
    downstream.

32
Conclusions
  • Denitrification is due to Biofilm Activity.
  • There is no lag time for denitrification capacity
    to develop.
  • Nitrate reduction occurs in the presence of
    oxygen up to 5 mg/L in the bulk aqueous phase.

33
Conclusions
  • The rate of nitrate reduction is independent of
    slide incubation location.
  • Entire TF volume is capable of nitrate reduction
    when COD and SCOD are not rate limiting.
  • Removal rates reported are applicable to any
    plastic media trickling filter.

34
Conclusions
  • Recycling nitrate may increase TF capacity for
    COD and SCOD removal.
  • Recycling nitrate could also provide odor control
    benefits by minimizing H2S production.

35
This work was supported by a grant from the
National Science Foundation (BES-9753086) and the
Littleton/Englewood Wastewater Treatment Plant
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