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