MBR

1. Osmotic MBR and
Pressure-Retarded Osmotic MBR
for Wastewater Treatment
Andrea Achilli
University of Nevada, Reno
Tzahi Y. Cath, PhD
Colorado School of Mines
Eric A. Marchand, PhD, PE
University of Nevada, Reno
Amy E. Childress, PhD
University of Nevada, Reno
ICOM 2008
July 15 – Honolulu, Hawaii USA

2. Presentation Overview
• Introduction
– Membrane Bioreactor (MBR)
– Osmotic MBR
– Pressure-Retarded Osmotic MBR
• Objectives
• Materials and Methods
• Results and Discussion
• Concluding Remarks

3. Introduction
• Membrane bioreactors (MBRs)
– Rapidly growing field
– Replacing conventional waste
water treatment plants
• MBR + Forward osmosis (FO)
– Wastewater treatment
– Potable water reuse
• MBR + Pressure-retarded osmosis
(PRO)
– Wastewater treatment
– Renewable energy production

4. Membrane Bioreactor
• Reduced footprint
• High solids removal from effluent
• Reduced disinfection needs
• Modular
• Removal efficiencies:
– 95% COD
– 90% nutrients

5. Membrane Bioreactor
Reject
Wastewater
Treated
water High quality
Vacuum Product water
pump
Reverse osmosis (RO)
RO membrane fouling
Final product quality
MF
membrane
Sludge
Bioreactor MF membrane fouling
MF permeate quality

6. Forward osmosis and
Pressure-Retarded Osmosis
Semi-permeable membrane
Pressure (ΔP < Δπ) Pressure (ΔP > Δπ)
Feed DS Feed DS Feed DS Feed DS
FO PRO RO
Feed = Feed solution, low salinity, high water chemical potential
DS = Draw solution, high salinity, low water chemical potential

7. Forward Osmosis and
Pressure-Retarded Osmosis
Power density (W), W/m2
Water flux (J), L/h·m2
J=A(ΔP-Δπ) J
W=-JΔP
W RO
0 ΔP
ΔP = Δπ/2 ΔP = Δπ
PRO
FO
Adapted from Lee et al., 1981

8. The Osmotic Membrane Bioreactor for
Water Reuse
Wastewater Concentrated draw solution
RO
FO
membrane
Treated
Sludge water
Diluted draw solution

9. The Pressure Retarded Osmotic
Membrane Bioreactor
Pressure
Pressurized exchanger
Wastewater vessel Booster
pump LP pump
SW in
PX
Bioreactor BW out
Net power
Turbogenerator
LP pump BW out
Sludge

10. Possible Advantages of
Osmotic Membrane Processes
• Low pressure / low energy operation
• High rejection of contaminants
– Soluble constituents
– Hormones and PPCPs
• Reduced fouling potential

11. Possible Problem Associated with
Osmotic Membrane Process
Salt accumulates inside bioreactor due to concentration
gradient between draw solution and activated sludge
Wastewater
Salt
Activated Draw
sludge solution
Water
Reverse salt transport
Reduces driving force
Hinders biological processes

12. Objective
Evaluate the feasibility of novel osmotic MBR
systems to treat wastewater for potable reuse or
for power generation
• OsMBR
– Membrane fouling
– Water quality
– Reverse salt transport
• ProMBR
– Membrane fouling
– Power output

13. Materials & Methods

14. Membranes
• Flat-sheet cellulose triacetate (CTA) membrane
(Hydration Technologies, Inc., Albany, OR)
– Semi-permeable (similar to RO membranes)
• Membrane A
• Membrane B
• Membrane C
– Only commercially available FO membranes

15. Solution Chemistries
• Reactor solution
– Doubly deionized water (DDW)
– Mixed liquor
• 5.5 g MLSS/L OsMBR
• 1.0 g MLSS/L ProMBR
• Draw solution
– 5 to 70 g NaCl/L solution
• Synthetic feed solution (OsMBR) F/M = 0.25 g COD/g MLSS*d
COD = 4.5 g/L
– Meat extract (5 g/L) HRT = 3 d
– Glucose (1 g/L) TOC = 1.3 g/L
– (NH4)2SO4 (0.6 g/L) SRT = 15 d
NH4-N = 0.065 g/L
– K2HPO4 (0.14 g/L)
– NaHCO3 (1 to 2 g/L) C:N:P = 100:5:1

16. Batch OsMBR Process
Reactor
FO Draw solution
membrane reservoir
Computer
Recirculating
Pump
Aerator
Analytical balance
Reactor solution is DDW
Draw solution concentration decreases from 70 to 30 g NaCl/L

17. Bench Scale OsMBR System
Feed
reservoir
Bioreactor RO
Module
Analytical balance
FO Draw solution
membrane reservoir Positive
Computer
Recirculating displacement
pump pump
Aerator
Sludge
Reactor solution is activated sludge
Draw solution concentration is constant at 50 g NaCl/L

18. Bench Scale ProMBR System
DDW
reservoir Recirculating
pump
Feed Membrane
Analytical balance reservoir unit HP
pump
Computer
Pressure
Draw
gauge
Solution
reservoir
HP
pump
Draw solution concentration is constant at 35 g NaCl/L
R0 module

19. OsMBR Results

20. Membrane Flux Characterization
Batch experiment
Reactor solution is DDW
20 30
Reverse NaCl Transport (g/(m *h))
18 Membrane A Membrane A
Membrane B 25 Membrane B
2
16 Membrane C Membrane C
Water Flux (L/(m *h))
14 20
2
12
10 15
8
6 10
4 5
2
0 0
0 10 20 30 40 50 60 70 0 10 20 30 40 50 60 70
DS Concentration (g NaCl/L) DS Concentration (g NaCl/L)

21. OsMBR Flux Performance
Continuous flow experiment
14 14
Salt Concentration in bioreactor (g/L)
Membrane B
CB = 5.5 g MLSS/L
CDS = 50 g NaCl/L 12 12
Pure water flux
Water Flux (L/(m h))
10 10
2
8 14d 21d 28d 8
BW BW BW
6 6
4 4
2 Water Flux 2
Salt Concentration
0 0
0 5 10 15 20 25 30
Time (days)

22. Operation Comparison
Membrane Material Pore size Flux Filtration Backwashing BW/day Net flux Ref.
time time
µm L/(m2·h) min min L/(m2·h)
Hollow fiber Polyethylene - 0.1 20 5-45 0.25-15a 24-274 15.0-18.0 2, 3, 4
Polysulfone
Tubular Polypropylene 0.2 8-22 30 0.25 48 5, 6
Flat sheet C-PVC – 0.2-0.4 17-22 3-8 1-4a 120 8.7-11.0 7, 8
Stainless steel
OsMBR CTA Semi- 9 10,080 60 0.14 9.0 This
permeable study
a
Relaxation time

23. Simplified Operation
• MBR – 15 minutes production / 1 minute backwashing and/or relaxation
• OsMBR – “smooth operation”
MBR
OsMBR
Water flux
Time

24. Water Quality
TOC and NH4-N concentrations
Feed Bioreactor Draw Solution Product
TOC (mg/L) 1,325 ± 25 140 ± 5 3 ± 0.5 2.5 ± 0.5
NH4-N (mg/L) 65 ± 5 15 ± 2 1.5 ± 0.5 0.4 ± 0.1
TOC and NH4-N removal efficiencies
% Rejection of % Removal of % Removal of
FO membrane OsMBR process overall system
(bioreactor + FO) (OsMBR + RO)
TOC 97.9 99.8 99.8
NH4-N 90.0 97.7 99.4

25. ProMBR Results

26. ProMBR Flux Performance
965 kPa (140 psi) transmembrane hydraulic pressure
12 Membrane B
Active side faces DS
10 CDS = 35 g NaCl/L
Water flux (L/m *h)
8
2
6
4
DDW feed solution
2 2.5 g NaCl/L feed solution
5.0 g NaCl/L feed solution
AS 1.0 g MLSS/L feed solution
0
0 6 12 18 24
Time (hours)

27. ProMBR Power Performance
4
Membrane B
Active side faces DS
972 kPa Transmembrane hydraulic pressure
CDS = 35 g NaCl/L
3
Power density (W/m )
2
2
DDW model
DDW experimental
2.5 g NaCL model
1 2.5 g NaCL experimental
5.0 g NaCL model
5.0 g NaCL experimental
AS 1.0 g MLSS/L experimental
0
0 1000 2000 3000
Hydraulic pressure (kPa)

28. Concluding Remarks
• OsMBR
– Long-term water flux (9 LMH) only 18% less than
pure water flux (11 LMH)
– Fewer backwash cycles than conventional MBRs due
to lower membrane fouling
– OsMBR system removal efficiencies
• TOC > 99%
• NH4-N > 99%
• ProMBR
– Activated sludge water flux (6.5 LMH) 35% less than
pure water flux (10 LMH)
– ProMBR power density 1.7 W/m2 @ 1000 kPa

29. Acknowledgements
• Department of Energy, Grant No. DE-FG02-05ER64143
• Hydration Technologies Inc.
• UNR Membrane Research Group Members

30. Andrea Achilli
aachilli@unr.edu