Evaluation of Passive Nitrogen Removal Systems

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Evaluation of Passive Nitrogen Removal Systems

• Daniel P. Smith, PhD, P.E.
• Applied Environmental Technology
• Tampa, FL 33592-2250

AET
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Acknowledgements

• Florida Department of Health
• Elke Ursin, Eberhard Roeder, Paul Booher
• Dick Otis
• Mark Flint
• Damain Anderson
• Hillsborough County, Florida

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Florida Passive Nitrogen Removal Study

• Objective evaluate enhanced nitrogen removal
  from on-site wastewater using passive systems
• Influent septic tank effluent
• Goal reduce total nitrogen

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Florida Passive Nitrogen Removal Study Tasks

• Literature review and database
• Experimental evaluation
• Feasibility
• Economic analysis

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Passive Definition

• A type of onsite sewage treatment and disposal
  system that excludes the use of aerator pumps and
  includes no more than one effluent dosing pump in
  mechanical and moving parts and uses a reactive
  media to assist in nitrogen removal

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Technology Constraints

• No aerators unsaturated filter for Stage 1
• One pump otherwise gravity flow
• where to place?
• Reactive media
• electron donor for denitrification
• alkalinity
• ion exchange

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Two Stage Processfor TN Reduction

• Stage 1 unsaturated filter
• aerobic Organic N and ammonia
• produce low effluent TKN
• Stage 2 saturated
• anoxic oxidized N
• electron donor for denitrification produce
  low effluent NOx

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Pump Before Stage 1 Filter

• Allows timed dosing
• Nitrification performance of Stage 1 filter
• Potential for Stage 1 recycle
• Flow equalization to entire treatment train
• Gravity flow through second stage filter to
  dispersal field

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Media Evaluation System
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Passive Nitrogen Removal StudyApplied
Environmental Technology
Stage 1 (unsaturated)
Stage 2 (saturated)
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Media Selection Factors Stage 1 Aerobic
Unsaturated

• Particle size
• Specific surface area
• External porosity
• Air filled porosity
• Water retention capacity
• Cation Exchange Capacity (CEC)

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Stage 1 Media (nitrification)
Expanded clay
Zeo-Pure clinoptilolite
Tire crumb
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Media Selection Factors Stage 2 Anoxic
Saturated

• Reactivity electron donor release rate
• Longevity
• Alkalinity supply
• Anion Exchange Capacity (AEC)

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Stage 2 Media (denitrification)
Expanded shale
Elemental sulfur
Oyster shell
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Autotrophic Nitrogen Reduction
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Filter Media
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Expanded shale/oyster shell/elemental sulfur
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Test Site Flatwoods Park, Hillsborough County,
Florida
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Test Site Flatwoods Park, Hillsborough County,
Florida
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Operating Features (one pass)
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Nitrogen Loading
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Feed Septic Tank Effluent
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2 Stage System Effluent TN
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Nitrogen Average (n5)
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Two Stage Removal Efficiency
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Total NitrogenRemoval Efficiency
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Stage 2 Effluent LDO and pH Probes
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Results Field Parameters
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Stage 1 Removal Efficiency
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Example System

• Stage 1 Aerobic
• 100 ft2 x 24 in. expanded clay
• Stage 2 Anoxic
• Sulfur/oyster/shale 60/20/20 volume Vanoxic
  1/4 Vaerobic
• Media cost Stage 1 700 / Stage 2 825

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Theoretical Longevity of Electron Donor4 persons
_at_ 13 gram N/capita-day

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Conclusions

• Proof of Two Stage Filter concept for Passive N
  Removal
• Single pass at 3 gal./ft2-day
• Total N removal of 97
• Total N reduced from 77 to 2 mg/L
• Longer term operation needed

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Conclusions

• Stage 1 aerobic 99 NH4 reduction with
  clinoptilolite and expanded clay
• Stage 2 anoxic NOxlt0.5 mg/L and 99 reduction
  with sulfur-based denitrification
• Need to verify longevity of performance and media

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Biochemical Transformations

• Organic N NH4 NO2- NO3-
  N2

Nitrification (Aerobic)
Denitrification (Anoxic)
Ammonification
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Results Stage 1 Effluent NH4
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Stage 1 TN Removal Efficiency
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Florida Passive Nitrogen Removal Study Tasks

• Literature review and database
• Experimental evaluation
• Feasibility
• Economic analysis

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Obligatory Biochemical Sequence for TN Reduction

• Aerobic Organic N ? NH4
• NH4 ? NO3
• Anoxic NO3 ? N2

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Example On-Site Configuration
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Media Selection Factors Stage 1 Aerobic
Unsaturated

• Particle size
• Specific surface area
• External porosity
• Air filled porosity
• Water retention capacity
• Cation Exchange Capacity (CEC)

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Total Inorganic Nitrogen Removal Efficiency