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Phosphorus Removal in a Membrane Reactor System—
A Demonstration Study
Wayne Lorenz, P.E. and Matthew J. GavinWright Water Engineers, Inc.
and
Newell Wright, P.E.Arapahoe County Water and Wastewater Authority
PROCESS SCHEMATIC
LONE TREE CREEK WASTEWATER TREATMENT FACILITY
SAMPLE POINT 1INFLUENT
SAMPLE POINT 2MBR
INFLUENT
FERRIC CHLORIDE
INFLUENT PUMP
STATION
MECHANICALLY CLEANED BAR
SCREENSOLIDS
RECYCLE
ANOXIC BASIN
AEROBIC BASIN MEMBRANES
MEMBRANE BIOREACTOR (MBR)
SAMPLE POINT 3PERMEATE
MEMBRANE VACUUM/PERMEATE
PUMPS
UV
DISINFECT DISCHARGE
SOLIDS
RECYCLE
ANOXIC BASIN
AEROBIC BASIN
MEMBRANES
MEMBRANE BIOREACTOR (MBR)
ZeeWeed® Membrane Membrane
Inner reinforcing structurecovered with a composite
polymer outer layer
Pore Size0.085 micron (nominal)0.1 micron (absolute)
Immersible, Ultra Low Pressure, Oxidant Resistant, High Strength
Operates at -2 psi to -6 psi whenfiltering and 3 psi on backpulse
Filtered Water
Process Tank(Influent)
X-Section
Membrane Layer
Inner Reinforcing Structure
Diameter Outer = 1.9 mm
Inner = 0.9 mm
FePO4(S)
Fe(OH)3(S)
Al(OH)3(S)
AlPO4(S)
Fe
(PO
4)(X
-3)/
3 (O
H) X
(S)
Al(
PO
4)(X
-3)/
3 (O
H) X
(S)
pH Value pH Value
— 7
— 6
— 5
— 4
— 3
— 7
—6
— 5
— 4
— 3
2 4 6 8 3 5 7 9
Lo
g M
ola
r S
olu
ble
P
ho
sph
oru
s
FERRIC CHLORIDE
Fe+3 + HnPO4n-3 FePO4 + nH+
FeCl3 + 3H2O Fe(OH)3 + 3H+ + 3Cl-
SODIUM ALUMINATE
Al+3 + HnPO4n-3 AlPO4 + nH+
Na2Al2O4 + 4 H2O 2 Na+ + Al2(OH)4 + 4 (OH-)
Note: Samples filtered through a 0.45-micron filter.
Jar TestingPhosphorus Vs. Ferric Chloride Dosage
Initial pH = 7.83 Intial Dissolved Phosphorus Concentration = 3.7 mg/L
0
0.01
0.02
0.03
0.04
0.05
0.06
75 100 125 150 175
Ferric Chloride Dosage (mg/L as FeCl3)
Ph
osp
ho
rus
(mg
/L a
s P
)
pH = 6.87
pH = 6.65
pH = 6.42
pH = 6.45
pH = 6.28
Jar TestingPhosphorus Vs. Sodium Aluminate Dosage @ pH = 6.5
Initial pH = 7.94, Initial Dissolved Phosphorus Concentration = 3.82
0
0.01
0.02
0.03
0.04
0.05
0.06
100 150 200
Sodium Aluminate Dosage (mg/L as Na2Al2O4)
Ph
osp
ho
rus
(mg
/L a
s P
)
Notes: 1. Samples filtered through 0.45 micron filter.2. pH adjusted to 6.5 using sulfuric acid.
Phase 1 Conditions
• Conducted over 15 weeks—December through March
• Average Daily Inflow = 0.98 mgd
• Membrane Filtration Area - 96,000 ft2
• Average Filtration Rate = 10.2 gpd/ft2
• Ferric Chloride Dosage 80 to 100 mg/L
• No pH Adjustment
Note: Phosphorus analyses performed by Chadwick Ecological Consultants.
Effluent Total Phosphorus Vs. Date
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
10/21/00 11/10/00 11/30/00 12/20/00 1/9/01 1/29/01 2/18/01 3/10/01 3/30/01
Date
Eff
lue
nt
To
tal P
ho
sp
ho
rus
(m
g/L
)
Average Effluent Total Phosphorus Vs. Ferric Chloride Dosage
0
0.01
0.02
0.03
0.04
0.05
0.06
60 70 80 90 100 110 120
Ferric Chloride Dosage (mg/L)
Eff
luen
t T
ota
l Ph
osp
ho
rus
(mg
/L)
Influent Alkalinity Vs. Date
180
200
220
240
260
280
300
320
11/30/00 12/20/00 1/9/01 1/29/01 2/18/01 3/10/01 3/30/01
Date
Infl
ue
nt
Alk
alin
ity
(m
g/L
as
Ca
CO
3)
Permeate Alkalinity Vs. Date
0
20
40
60
80
100
120
140
160
180
200
11/30/00 12/20/00 1/9/01 1/29/01 2/18/01 3/10/01 3/30/01
Date
Pe
rme
ate
Alk
alin
ity
(m
g/L
as
Ca
CO
3)
MBR Average Effluent Quality
Total Phosphorus 0.035 mg/L
BOD5 2.8 mg/L
Ammonia 1.3 mg/L
Nitrate 5.8 mg/L
pH 7.0
CONCLUSIONS
• Phosphorus Goal of 0.05 mg/L was met using ferric chloride at a dosage of 80 to 100 mg/L
• Average Phosphorus Concentration was 0.035 mg/L
• Phosphorus removed to 0.05 mg/L regardless of temperature
CONCLUSIONS
• Addition of chemical to precipitate Phosphorus impacts pH and alkalinity
• pH conditions are key in optimizing Phosphorus removal
• Activated sludge was not affected by dosages in study
Phase 2 Testing
• Demonstrate 0.02 mg/L P removal, or less
• Different chemicals
• Limit of biomass viability
• Membrane maintenance