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 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.
Setup
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
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-
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
phosphorus concentration (mg/L)
Results: First experiment cont.
5
4.5
4
3.5
3
2.5
2
1.5
1
0.5
0
0
1
2
3
alum sample
4
5
6
phosphorus concentration (mg/L)
Results: First experiment cont.
4
3.5
3
2.5
2
1.5
1
0.5
0
0
1
2
3
4
ferric chloride sample
5
6
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
alum concentration
average effluent
(mg/L)
phosphorus conc. (mg/L)
10
1.27
12.5
1.10
15
1.03
25
0.70
percent
removal
68.17
72.42
74.20
82.57
concentration of
phosphorus in effluent
(mg/L)
Results: Second experiment
cont.
1.60
1.40
1.20
1.00
0.80
0.60
0.40
0.20
0.00
8
10
12
14
16
18
20
concentration alum added (mg/L)
22
24
26
Results: Second experiment
cont.

Although we did not meet our goal of 50
mg/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 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
THE END
Have a great summer!