Phosphorus Removal at Sand Creek Water Reuse Facility

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Phosphorus Removal at Sand Creek Water Reuse
Facility

• by
• Duane Bear Steib and Kathy Bill/City of Aurora
• Steve Polson/CH2M HILL

presented at the 2006 Water Reuse
Workshop Co-sponsored by RMSAWWA, RMWEA, and the
Water Reuse Association Thursday, August 10th,
2006 Colorado School of Mines Golden, Colorado
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Purpose of Study
Determine the advanced phosphorus removal
capabilities of the Sand Creek Water Reuse
Facility
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Treatment Facility

• Primary clarification
• Activated sludge
• Nutrient (N and P) removal
• Filtration
• UV disinfection
• Ferric chloride addition (available)
• Polymer addition (available)

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Primary Clarifiers
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3650 diffusion heads
Biological Nutrient Removal Basin
3 Aerobic Cells
3864 diffusers
Anoxic Cell
Anerobic Cell
Anoxic Cell
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Secondary Clarifiers
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Secondary Effluent
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Chemical Pumps Storage
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DynaSand Filters
Backwash Waste
Filtered Effluent
Upflow, Continuous Backwash Filter
Filter Media (sand)
Filtered Influent
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Trojan 3000 Ultraviolet System 864 Low Pressure
Low Intensity Bulbs
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Reuse Distribution Pumps
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Design Criteria

• Plant capacity 5.0 mgd
• Secondary effluent TP 0.5 - 1.0 mg/L
• Tertiary effluent TP 0.2 mg/L limit
  (anticipated)
• Discharge to Sand Creek
• BOD5/TSS 30 mg/L each (monthly)
• Fecal coliform 2,000 mpn/100 mL (monthly)
• Ammonia Driven by WET requirements

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Design Criteria (cont)

• Reuse quality
• BOD/TSS 5 mg/L each (monthly)
• Total coliform 2.2 org/100 mL (7-day)
• Turbidity 2 NTU (daily)
• Requirements are different now
• E. coli 126 org/100 mL
• Turbidity 3.0 NTU
• Phosphorus not currently regulated

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Why Mess With Near Perfection?

• Leading up to the study, the Sand Creek WRF
  consistently produced an effluent with a total
  phosphorus (TP) concentration of 0.10 0.20
  mg/L. These low levels were achieved utilizing a
  very efficient biological nutrient removal
  process.
• Analysis in mg/L

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Goal of Study -- Determine the Limits of Tertiary
P-Removal at the Sand Creek WRF

• Design target 0.10-0.12 mg/L (0.2 mg/L limit)

Metal salt addition followed by effluent
filtration has been used successfully to meet
monthly average effluent discharge standards of
approximately 0.20 mg P/L. (Phosphorus and
Nitrogen Removal from Municipal Wastewater --
Principles and Practice, Richard Sedlak, Editor,
1991)

• Study goal 0.05 mg/L

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BNR System Treats Nitrogen and Phosphorus
Johannesburg Process
Secondary Clarifier
BNR Reactor
MLR
PE
Anaerobic
Aerobic
Anoxic
Anoxic
SE
Denitrification
P-Release
RAS
Carbon Oxidation
Denitrification
Nitrification
Phosphorus Uptake
WAS
RAS
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Chemical-P Removal Alternatives

• Capability to add metal salts at several
  locations
• Primary clarifier influent
• Secondary clarifier influent
• Secondary clarifier effluent
• Multiple-point chemical addition add at several
  locations
• Alum or ferric chloride can be used
• Ferric used to comply with Metro Denver request

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First Steps in the AWT Process are Chemical
Addition and Flocculation

• Chemicals added at the rapid mix chamber
• Flocculation occurs in the filter influent flow
  distribution structure

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Filtration and Disinfection Follow...

• Next, the flocculated water flows through four
  DynaSand filters to remove the precipitate formed
  
• The filters are mono-media, deep bed, upflow,
  continuous backwash type
• The sand size is 1 mm and the sand depth is 80
• The filtration rate is 3.5 gal/min/ft2
• The filtered water then flows through two UV
  disinfection channels

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The Pilot Project Plan

• Determine the types of phosphorus in the
  secondary effluent
• Bench studies jar tests
• Full scale pilot test

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Analytical Method Used to Determine Types of
Phosphorus in the Secondary Effluent

• Analysis determined soluble and insoluble forms
  for total, polyphosphate and ortho phosphate
  using Hach equipment and methods
• Procedures used to ensure the validity of results
  including dedicated acid washed glassware,
  reagent blanks, standards and splits with QC
  laboratory

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Bench Studies Method Jar Tests

• Set up to simulate operations from the rapid mix
  to the filter effluent
• Chemicals used were ferric chloride and anionic
  polymers
• Analysis on secondary effluent and simulated
  filter effluent included phosphorus, alkalinity,
  pH, turbidity and iron residual

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Bench Studies Results

• 20 40 reduction in total phosphorus noted
• Little or no effect on pH and alkalinity
• Turbidity increased and iron residual present

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Full-Scale Pilot Test Method (Objectives)

• Feed chemicals at the AWT to reduce the total
  phosphorus in the plant effluent to 0.05 mg/L
• Determine the effect of chemical treatment on the
  plant effluent
• Feed chemical doses at reasonable doses that will
  not the negatively impact AWT equipment and
  filter media

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Full-Scale Pilot Test Results
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Conclusions

• Bench and full-scale pilot testing did reduce the
  total phosphorus, however in this study the
  target level of 0.05 mg/L was not reached.

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Conclusions (cont)

• Experience at Sand Creek was similar to that at
  other advanced P-removal facilities
• Achieving a reliable effluent TP less than 0.1
  mg/L was not feasible using ferric chloride and
  direct filtration
• Lower concentrations would require major process
  modifications
• Increased chemical feed
• Flocculation/sedimentation filtration
• Membranes

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