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Chemical Precipitation of Phosphorous in Wastewater

Chemical Precipitation of Phosphorous in Wastewater

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Chemical Precipitation of Phosphorous in Wastewater

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  1. Chemical Precipitation of Phosphorous in Wastewater Geochemistry December 3, 2008 Presented by Shravan Avadhuta & Corey Bjornberg

  2. Presentation Outline Background Information Journal Article Review Impact of Environmental Conditions Seeding Conditions Conclusions

  3. Found in all living cells (80% of Phosphorous in Bones/Teeth in People) Major Use: Fertilizer (Triple Superphosphate, Monamonium Phosphates) Background Information: Phosphorus • Other Uses: • surfactants • cleaners • metal treating • lubricants • fire retardants • tooth paste http://bioweb.wku.edu/faculty/ameier/phoscycle.gif

  4. Problem: Fertilizer Runoff and Product Waste Result: Eutrophication-Water body receives excess nutrients that stimulate primary production (algae, nuisance plants) Background Information: Environmental Impacts http://www.aplandscaping.com/images/1-23-07/IMG_0056.jpg • Negative Effects • Health (Algae releases neurotoxins) • Depletes Dissolved Oxygen • Fish Kills • Drinking Water • Economical Costs http://www.samford.edu/schools/artsci/biology/wetlands/assets/eutrophication.gif

  5. Pretreatment • Primary Treatment • Secondary Treatment • Disinfection • Advanced Wastewater Treatment • Nutrient Removal • Ammonia • Phosphorous • Biological • Chemical Background Information: Wastewater Treatment http://nsm1.nsm.iup.edu/tsimmons/Environmental%20Health%20Photolibrary/Wastewater%20Treatment%20Plant%20Photogallery/Wastewater_Treatment_Plant_Aeration_Tank_Rectangular.jpg http://ian.umces.edu/imagelibrary/albums/userpics/10001/normal_iil-ian-aj-0087.jpg

  6. 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 Journal Article Review: Crystallization of Calcium phosphate

  7. 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. Journal Article Review: Crystallization of Calcium phosphate

  8. 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. • ΔSI = SIo – SIs • SIo = SI of solution in the initial state • SIs = SI of solution after seed ‘s • Positive ΔSI value indicates precipitation Impact of Environmental Conditions: Temperature and pH effects

  9. 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 ΔSI of HAP at different temperatures • Table 1. shows the calculation at 5 different Impact of Environmental Conditions: Temperature Effects

  10. Table 1 • The graph shows, as the temperature is increasing ΔSI is decreasing reflecting the low precipitation at higher temperature and high precipitation at low temperatures Impact of Environmental Conditions:

  11. 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. Impact of Environmental Conditions: pH effects

  12. 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). Impact of Environmental Conditions: pH effects

  13. 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 ΔSI, which represents the precipitation of phosphate Impact of Environmental Conditions: pH effects

  14. 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) Seeding Conditions: Dosing Requirements

  15. 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) Seeding Conditions: Hydroxyapatite (HAP) Seed

  16. Journal Article: Only Tried Two Seeds (CaCO3) Question: Would anhydrite (CaSO4) serve as a better seed? Want to maximize phosphorous precipitation Seeding Conditions: Anhydrite Seed

  17. Journal Article: Only Tried Two Seeds (CaCO3) Question: Would dolomite (CaMg(CO3)2)serve as a better seed? Want to maximize phosphorous precipitation Seeding Conditions: Dolomite Seed

  18. Seeding Conditions: Comparing Seeds Note that surface characteristics are also a significant factor in the crystallization of phosphate

  19. Potential Sales of precipitated phosphate: Desire as pure as product as possible requires limiting precipitation of other minerals Seeding Conditions: Coprecipitation of Calcite/Dolomite Both Calcite and Dolomite Show the least amount of precipitation from solution

  20. 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 Conclusions: Suggestions for Phosphorous Precipitation

  21. Chemical Precipitation of Phosphorous in Wastewater Questions???