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

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

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  g/L. The final phosphorus concentration will be independent from the concentration of metallic salts at high metallic salts concentrations. Metallic salts conc. Phosphorus Conc.

Setup

Setup Flow Rate: – 450 mL/min Reagents: – Phosphorus solution: 200 mg/L KH 2 PO 4 – Alum solution: 400 mg/L Al 2 (SO 4 ) 3 o 14H 2 O – Ferric Chloride: 200 mg/L FeCl 3

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) Al 2 (SO 4 ) 3­ o 14H 2 O + 2PO 4 3-  2AlPO 4 + 3SO H 2 O FeCl 3 + PO 4 3-  FePO 4 + 3Cl -

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

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.

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.

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

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

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

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.

In the future we would… Test higher concentrations of alum Try mixing alum and FeCl 3 Adjust the pH to be in the optimum range of the coagulants (4.5-5 for FeCl 3, for Alum) – Our pH was between 8.3 and 8.4

THE END Have a great summer!