Nutrient Removal Project: Chemical Phosphorus Removal

1. Nutrient Removal Project: Chemical Phosphorus Removal Jill Crispell, Stephanie Wedekind, Sarah Rosenbaum

2. Objectives • Reduce the concentration of phosphorus in the effluent of the wastewater treatment plant by precipitating the phosphorus with varying concentrations of metallic salts • Total phosphates should not exceed a concentration of 50ug/L in a stream entering a lake or reservoir

3. Hypothesis • As the concentration of a metallic salt added increases, the concentration of phosphorus in the effluent should decrease from 4 mg/L to a value less than 50 mg/L. • The final phosphorus concentration will be independent from the concentration of metallic salts at high metallic salts concentrations. Phosphorus Conc. Metallic salts conc.

4. Setup

5. Setup • Flow Rate: • 450 mL/min • Reagents: • Phosphorus solution: 200 mg/L KH2PO4 • Alum solution: 400 mg/L Al2(SO4)3 o 14H2O • Ferric Chloride: 200 mg/L FeCl3

6. Methods • First experiment: Effect of flocs • In each cycle, phosphorus and water added to bring concentration to 4 mg/L • Only in first cycle alum (12.5 mg/L) or ferric chloride (6.8 mg/L) Al2(SO4)3­ o 14H2O + 2PO43- 2AlPO4 + 3SO42- +14H2O FeCl3 + PO43- FePO4 + 3Cl-

7. Results: First experiment • Alum was more effective than ferric chloride in removing phosphorus. • Discovered original influent water contained ferric chloride • Flocs remaining in tank continued to react with the phosphorus added

8. Results: First experiment cont.

9. Results: First experiment cont.

10. Results: First experiment cont. • Solutions to our Discoveries: • Decided to pump tap water into the plant from a large jug. • Completely drain the tank. • Added two new states, rinse and rinse effluent, to clean out the tank of all flocs.

11. Second experiment: Increasing concentration of alum • Different concentrations, 10 mg/L, 12.5 mg/L, 15 mg/L and 25 mg/L, of alum were used to determine which concentration removes phosphorus most efficiently • All samples were analyzed using the spectrophotometer to determine the amount of phosphorus remaining in the effluent.

12. Results: Second experiment • As alum concentration in the plant increased, phosphorus concentration decreased and percent removal increased based on samples with 10 mg/L, 12.5 mg/L, 15 mg/L and 25 mg/L of alum respectively

13. Results: Second experiment cont.

14. Results: Second experiment cont. • Although we did not meet our goal of 50 g/L, our high percent removal indicates that the alum is effective • Generally, the trend appears to be decreasing

15. Results: Second experiment cont. • More testing is necessary to determine if the phosphorus reaches a minimum concentration • There cannot be 100% removal (and thus a linear solution) because there is a saturation level in which additional alum no longer effects phosphorus removal

16. Results: Second experiment cont. • According to the stoichiometry of the equations, we should have only needed to use a concentration of 12.5 mg/L of alum to completely react with the 4 mg/L of phosphorus, but much more is needed. • Reasons: other reactants in water, more mixing time.

17. In the future we would… • Test higher concentrations of alum • Try mixing alum and FeCl3 • Adjust the pH to be in the optimum range of the coagulants (4.5-5 for FeCl3, 5.5-6.5 for Alum) • Our pH was between 8.3 and 8.4

18. THE ENDHave a great summer!