Polymer assisted forward osmosis for desalination and water reuse Xinying Wang Illinois Sustainable Technology Center
Earth s water percentage 71% Earth surface is covered by water Only 0.3% of the fresh water or 0.007% earth water can be readily accessed.
Clean water crisis By middle of this century The world population is estimated to reach 10 billion 47% of population will be living in areas suffering clean water stress
71% Earth surface is covered by water, but we are facing > salt water problem. Isn t it ironic?
Desalination
Desalination technologies Electric Thermal CO2 RO 4-8 kwh/m 3 0 kwh/m 3 MSF 3.5-5 kwh/m 3 69-83 kwh/m 3 >1.7 Kg/m 3 >9.4 Kg/m 3 MED 1.5-2.5 kwh/m 3 42-61 kwh/m 3 >7.0 Kg/m 3 T.Mezher et al. Desalination 266 263-273
What is forward osmosis? Forward Osmosis Reverse Osmosis ΔP Δπ Salty water Salty water Δπ Draw solution Feed J w = A(Δπ-ΔP)
FO process advantages Reverse Osmosis Forward Osmosis Energy Source High grade Low grade Membrane Fouling High Low Operation pressure High Low
Forward osmosis desalination Brine in Draw solution out Fresh Water Brine out Membrane Draw solution in Draw solution concentration process
Where is the challenge? Conc DS Diluted DS Conc DS Water Take diluted draw solution as final product Select appropriate draw solute, i.e. NH4HCO3, modified magnetic particles
Ammonia-CO2 draw solution NH4HCO3 heat NH3 + CO2
Magnetic particles draw solution
Our Solution-Aquapod Use polymer to extract water from diluted solution Aqueous two phase extraction Top phase: polymer, water, and tiny amount of draw solute Bottom phase: concentrated draw solution and tiny amount of polymer
Our Solution-Aquapod Polymer used: Poly ethylene glycol-poly propylene glycol (UCON TM ) Cost: $2.2/lbs Cloudy point: 60/140 ⁰C/⁰F Non-toxic Draw solution: MgSO4
Our Solution-Aquapod Polymer Diluted Draw Solution FO Concentrated Draw Solution Water Extraction Polymer Polymer Heart exchanger Polymer solution Water polishing Raw water Water-polymer Separation Water product
Forward osmosis process Polymer Diluted Draw Solution FO Concentrated Draw Solution Water Extraction Polymer Polymer Heart exchanger Polymer solution Water polishing Raw water Water-polymer Separation Water product
Forward osmosis Membrane: TFC (lab-made) and HTI (commercial) Draw solution: 20wt% MgSO4 Lab-scale forward osmosis system FO system HTI TFC
Forward osmosis TFC-PA membrane Flux(LMH) 50.0 40.0 30.0 20.0 10.0 0.0 0 5 10 15 20 25 30 Time(min) 25.0 DI feed 2000 ppm NaCL feed 10000ppm NaCL feed 20000ppm NaCl feed 30000ppm NaCl feed HTI membrane 20.0 Flux(LMH) 15.0 10.0 5.0 0.0 0 5 10 15 20 25 30 Time (min) DI 2000ppm NaCl 10000ppm NaCl 20000ppm NaCl 30000ppm NaCl
Our Solution-Aquapod Polymer Diluted Draw Solution FO Concentrated Draw Solution Water Extraction Polymer Polymer Heart exchanger Polymer solution Water polishing Raw water Water-polymer Separation Water product
A polymer extraction example Stock solution: MgSO4 20wt%, polymer 10wt%, and water 70wt% Top phase or polymer phase : MgSO4 0.02wt%, polymer 59.4wt%, and water 40.6wt% Bottom phase or salt phase: MgSO4 23.5wt%, polymer 0.018wt%, and water 76.5wt% 0.0 1.0 0.2 0.8 0.6 UCON 0.4 0.6 Water 0.4 0.8 0.2 1.0 0.0 0.0 0.2 0.4 0.6 0.8 1.0 MgSO4
Gravity separation (time) Centrifuge-assisted (energy) Centrifuge speed (G force/rpm) Water extraction Centrifuge time (min) MgSO4 Concentration UCON concentration 151/1000 603/2000 1358/3000 2410/4000 Polymer-rich phase (g/l) Salt-rich phase (g/l) Polymer-rich phase (g/l) Salt-rich phase (g/l) 5 3.70 283.08 699.66 0.23 10 2.20 282.90 696.76 0.20 20 0.85 285.09 793.00 0.20 5 0.66 286.35 702.60 0.23 10 0.46 285.89 701.16 0.21 20 0.28 288.41 707.06 0.20 5 0.37 286.55 702.65 0.20 10 0.31 286.60 746.55 0.21 20 0.26 288.42 707.06 0.20 5 0.35 285.38 743.42 0.21 10 0.23 286.64 702.65 0.20 20 0.20 287.87 749.69 0.20
Our Solution-Aquapod Polymer Diluted Draw Solution FO Concentrated Draw Solution Water Extraction Polymer Polymer Heart exchanger Polymer solution Water polishing Raw water Water-polymer Separation Water product
Water polymer separation by heat Heat can lead polymer chain reconfiguration Above cloudy point, the polymer becomes hydrophobic and precipitates out from the homogenous solution. Above cloudy point Below cloudy point
Water polymer separation by heat 0 min 0.25 min 1 min 3 min 5 min
Water polymer separation by heat Temperature Top phase (water) Bottom phase (polymer) UCON660(g/L) MgSO4 (g/l) UCON660 (g/l) MgSO4(g/L) 70⁰C 49.2 1.6 87.5 ND 80⁰C 21.6 1.3 89.7 ND 90⁰C 13.9 1.3 90.9 ND
Our Solution-Aquapod Polymer Diluted Draw Solution FO Concentrated Draw Solution Water Extraction Polymer Polymer Heart exchanger Polymer solution Water polishing Raw water Water-polymer Separation Polished water
Water polishing Water sample from polymer-water separation unit process has ~1wt% polymer ~0.5wt% MgSO4 A Nanofiltration process was evaluated for the polishing
Water polishing Flux (LMH) NF90 25 20 15 10 5 0 0.0 20.0 40.0 60.0 80.0 Permeate recovery rate (%) Membrane: NF90 2540 Pressure: 70psi Water product: Polymer ~7ppm Flux(LMH) 40 35 30 25 20 15 10 5 0 NF270 0 20 40 60 80 Permeate Recovery (%) Membrane: NF270 2540 Pressure: 70psi Water product: Polymer ~110ppm
Process integration
Summary A novel polymer-assisted FO desalination process is proposed A suitable draw solution-polymer pair is identified Four sub-processes are evaluated individually
Acknowledgement Dr Kishore Rajagopalan John Scott Vinod Patel And all other people at ISTC who helped me on this project
Thank you!