Icom2008 osmbr
- 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
- 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