Chemical Precipitation of Phosphorous in Wastewater

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Chemical Precipitation of Phosphorous in
Wastewater

• Geochemistry
• December 3, 2008
• Presented by
• Shravan Avadhuta
• Corey Bjornberg

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Presentation Outline

• Background Information
• Journal Article Review
• Impact of Environmental Conditions
• Seeding Conditions
• Conclusions

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Background Information Phosphorus
Found in all living cells (80 of Phosphorous
in Bones/Teeth in People) Major Use
Fertilizer (Triple Superphosphate, Monamonium
Phosphates)

• Other Uses
• surfactants
• cleaners
• metal treating
• lubricants
• fire retardants
• tooth paste

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Background Information Environmental Impacts
Problem Fertilizer Runoff and Product
Waste Result Eutrophication-Water body receives
excess nutrients that stimulate primary
production (algae, nuisance plants)
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• Negative Effects
• Health (Algae releases neurotoxins)
• Depletes Dissolved Oxygen
• Fish Kills
• Drinking Water
• Economical Costs

http//www.samford.edu/schools/artsci/biology/wetl
ands/assets/eutrophication.gif
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Background Information Wastewater Treatment

• Pretreatment
• Primary Treatment
• Secondary Treatment
• Disinfection
• Advanced Wastewater Treatment
• Nutrient Removal
• Ammonia
• Phosphorous
• Biological
• Chemical

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Journal Article Review Crystallization of
Calcium phosphate

• Present study is to remove phosphate without
  carbonate removal and without base addition.
• Crystallization process is composed of three
  steps (1) Super saturation - Thermodynamic basis
  of the process, expressed by SI.
• (2) Nucleation - Heterogeneous with seeded and
  Homogeneous without seed
• (3) Crystal growth Growth occurs on the seed

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Journal Article Review Crystallization of
Calcium phosphate

• Two different calcites are used as seeds in this
  study.
• (1) Juraperlene and (2) Coccolith
• The study shows that the calcites are effective
  seeds for crystallization of calcium phosphate.
• carbonate is co precipitated along with
  phosphate.
• Used calcite seeds are found to be more
  efficient than the new calcite seeds.

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Impact of Environmental Conditions Temperature
and pH effects

• Waster water, usually rich in calcium phosphates
• Super saturation expressed as solubility index
  SI
• Change in the solubility index shows the
  thermodynamic force for the crystallization.
• ?SI SIo SIs
• SIo SI of solution in the initial state
• SIs SI of solution after seed s
• Positive ?SI value indicates precipitation

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Impact of Environmental Conditions Temperature
Effects

• Decrease in thermodynamic property indicates the
  greater potential to react, precipitate in this
  case.
• Phosphate is precipitated as Hydroxyapatite
  (HAP)
• Temperature effect on the crystallization is seen
  by measuring the ?SI of HAP at different
  temperatures
• Table 1. shows the calculation at 5 different

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Impact of Environmental Conditions

• Table 1
• The graph shows, as the temperature is
  increasing ?SI is decreasing reflecting the low
  precipitation at higher temperature and high
  precipitation at low temperatures

Temperature oC ?SI of HAP
0 12.45
25 12.07
50 11.61
75 11.1
100 10.56
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Impact of Environmental Conditions pH effects

• How the pH is a deciding factor for the
  precipitation of Phosphate?
• Phosphate is usually precipitated at higher pH
  conditions.
• Carbonate, a major hindrance for phosphate
  precipitation is removed at lower pH.
• Hence, to remove carbonate first and than
  phosphate, pH of the waste water is changed.

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Impact of Environmental Conditions pH effects

• Use of Calcite seeds for phosphate removal !!
• As the phosphate is precipitated from the
  solution, pH will be decreasing.
• Decrease in pH, inhibits phosphate
  precipitation.
• To maintain the pH levels of the waste water.
• N2 gas is introduced into the waters, to
  increase the pH (YARIV COHEN and HOLGER
  KIRCHMANN, 2004).

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Impact of Environmental Conditions pH effects

• Table below shows the pH of the waste waters
  before and after the N2 introduction.
• Results clearly indicate that, little change in
  the pH would effect ?SI, which represents the
  precipitation of phosphate

Temperature With Nitrogen pH ?SI (HAP) With Nitrogen pH ?SI (HAP) Without Nitrogen pH ?SI (HAP) Without Nitrogen pH ?SI (HAP)
25 oC 7.418 15.43 7.391 12.07
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Seeding Conditions Dosing Requirements
Journal Article No Seed Juraperle (CaCO3) 2
g/L and 10 g/L Coccolith (CaCO3) 2 g/L and
10 g/L Question Can we find an optimum dosing
amount??? Want to maximize phosphorous
precipitation Minimize seed (costs)
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Seeding Conditions Hydroxyapatite (HAP) Seed
Journal Article Stated that collected
precipitates were reused and showed improved
precipitation. Question Would hydroxyapatite
serve as a better seed? Want to maximize
phosphorous precipitation Minimize seed costs
(self sustaining)
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Seeding Conditions Anhydrite Seed
Journal Article Only Tried Two Seeds (CaCO3)
Question Would anhydrite (CaSO4) serve as a
better seed? Want to maximize phosphorous
precipitation
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Seeding Conditions Dolomite Seed
Journal Article Only Tried Two Seeds (CaCO3)
Question Would dolomite (CaMg(CO3)2)serve as a
better seed? Want to maximize
phosphorous precipitation
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Seeding Conditions Comparing Seeds
Note that surface characteristics are also a
significant factor in the crystallization of
phosphate
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Seeding Conditions Coprecipitation of
Calcite/Dolomite
Potential Sales of precipitated phosphate Desire
as pure as product as possible requires limiting
precipitation of other minerals
Both Calcite and Dolomite Show the least amount
of precipitation from solution
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Conclusions Suggestions for Phosphorous
Precipitation

• Environmental Conditions
• Lower temperature improves precipitation
• Maintaining pH would be beneficial for
• phosphate removal
• Seeding Conditions
• Minimal Dose
• Acts as catalyst
• Higher dose improves but costly
• CaCO3 or Dolomite
• Most phosphorous precipitation
• Least Calcite/Dolomite precipitation

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Chemical Precipitation of Phosphorous in
Wastewater

• Questions???