Presentation on theme: "Chemical Precipitation of Phosphorous in Wastewater Geochemistry December 3, 2008 Presented by Shravan Avadhuta & Corey Bjornberg."— Presentation transcript:
Chemical Precipitation of Phosphorous in Wastewater Geochemistry December 3, 2008 Presented by Shravan Avadhuta & Corey Bjornberg
Presentation Outline Background Information Journal Article Review Impact of Environmental Conditions Seeding Conditions Conclusions
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
Background Information: Environmental Impacts Problem: Fertilizer Runoff and Product Waste Result: Eutrophication-Water body receives excess nutrients that stimulate primary production (algae, nuisance plants) Negative Effects Health (Algae releases neurotoxins) Depletes Dissolved Oxygen Fish Kills Drinking Water Economical Costs s/eutrophication.gif
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
Journal Article Review: Crystallization of Calcium phosphate Two different calcites are used as seeds in this study. (1) Juraperleneand (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.
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. ΔSI = SI o – SI s SI o = SI of solution in the initial state SI s = SI of solution after seed ‘s Positive ΔSI value indicates precipitation
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 ΔSI of HAP at different temperatures Table 1. shows the calculation at 5 different
Impact of Environmental Conditions: 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 Temperature o CΔSI of HAP
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.
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…. N 2 gas is introduced into the waters, to increase the pH (YARIV COHEN and HOLGER KIRCHMANN, 2004).
Impact of Environmental Conditions: pH effects Table below shows the pH of the waste waters before and after the N 2 introduction. Results clearly indicate that, little change in the pH would effect ΔSI, which represents the precipitation of phosphate Temperature With Nitrogen pH ΔSI (HAP) Without Nitrogen pH ΔSI (HAP) 25 o C
Seeding Conditions: Dosing Requirements Journal Article: No Seed Juraperle (CaCO 3 ) 2 g/L and 10 g/L Coccolith (CaCO 3 ) 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: 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)
Seeding Conditions: Anhydrite Seed Journal Article: Only Tried Two Seeds (CaCO 3 ) Question: Would anhydrite (CaSO 4 ) serve as a better seed? Want to maximize phosphorous precipitation
Seeding Conditions: Dolomite Seed Journal Article: Only Tried Two Seeds (CaCO 3 ) Question: Would dolomite (CaMg(CO 3 ) 2 )serve as a better seed? Want to maximize phosphorous precipitation
Seeding Conditions: Comparing Seeds Note that surface characteristics are also a significant factor in the crystallization of phosphate
Seeding Conditions: Coprecipitation of Calcite/Dolomite Both Calcite and Dolomite Show the least amount of precipitation from solution Potential Sales of precipitated phosphate: Desire as pure as product as possible requires limiting precipitation of other minerals
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
Chemical Precipitation of Phosphorous in Wastewater Questions???