Presentation Outline

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1 Presentation Outline Introduction Osmotically driven membrane processes Hybrid forward osmosis/ reverse osmosis process Project overview and objectives Experimental Work Experimental setup Chemistry Analytical methods Results Water flux and fouling Solute transport Economic feasibility Conclusions 2 1

2 Water Scarcity and Barriers to Reuse Water scarcity becoming increasingly acute in many regions of the world Water recycling and seawater desalination are utilized to augment water supplies Trace levels of organic micropollutants in reclaimed water: pharmaceuticals, endocrine disruptors, personal care products Desalination produces high quality water, but is energy intensive and requires extensive pre-treatment The current study seeks to mitigate both problems synergistically 4 2

3 Membrane Processes in Desalination Nanofiltration and reverse osmosis used for desalination Consume energy proportional to salt concentration Susceptible to organic fouling with untreated feed water and scaling at high recoveries Microfiltration and ultrafiltration generally used as pretreatment before membrane desalting (and water and wastewater treatment) Require frequent cleaning Remove suspended solids and macromolecules only 5 Osmotically Driven Processes Driving force dependent on difference in osmotic pressure Forward osmosis (FO) - water diffuses across the membrane Reverse Osmosis (RO) - hydrostatic pressure applied to reverse flow of water P Feed Brine Feed Brine Feed Brine Osmosis Reverse Osmosis 6 3

4 Osmotically Driven Processes Solute transport during forward osmosis is in both directions Water Water Solutes Solutes Solutes Freshwater Saltwater Freshwater Saltwater Forward osmosis Reverse osmosis 7 Energy Consumption & Osmotic Pressure High energy demand of reverse osmosis desalination due to high osmotic pressure of the brine Can lower osmotic pressure by dilution Additional flux Freshwater Decreasing Feed Conc. RO Flux Membrane P FO Decreased Osmotic Pressure Saltwater 8 4

5 Concentration Polarization Concentration gradient across the active layer different than between the bulk solutions Reduction in driving force across the active layer 9 FO/RO Hybrid for Enhanced Water Recovery Desalination plant in vicinity of recycled water source Forward osmosis can be utilized to dilute feed stream to RO without additional pre-treatment of the recycled water (e.g., 2,3 ) Forward osmosis added to concentrate waste for possible beneficial reuse and to dilute RO brine stream FO Stage 2 FO Stage 1 RO Drinking Water Seawater (Draw Solution) Recycled Water (feed) Ocean 10 5

6 Project Objectives Objectives of study Investigate the performance and limitations Forward osmosis process for pretreatment of impaired/reclaimed water combined FO/RO desalination hybrid system and its effects on membrane fouling and organic solute rejection Develop recommendations and cost estimates for an FO/ RO hybrid system 11 6

7 Experimental Apparatus Bench scale forward osmosis system Closed loop system 0.07m 2 Acrylic membrane cell Doses concentrated salt to maintain DS concentration SCADA control of salt dosing, temperature, and data acquisition Conc. DS DI Water Temp. Control Seawater Draw Solution FO Cell BALANCE Feed (Recycled) Water Solution 13 Bench scale FO system Experimental Apparatus 14 7

8 Experimental Apparatus Pilot Scale System Forward osmosis / reverse osmosis hybrid system Draw solution continuously reconcentrated by RO system 0.24 m 2 forward osmosis membrane surface area ~30 L/day produced Temp. Control Seawater Draw Solution FO Cell Feed (Recycled) water Waste Permeate RO Cell 15 Pilot Scale System Experimental Apparatus 16 8

9 Membranes Forward osmosis Flat sheet, cellulose triacetate membrane; Hydration Technologies Inc. Reverse osmosis Spiral wound, SW ; Dow Filmtec FO RO pilot system Three-stage array Element 3 F F C Element 2 F C Element 1 Permeate P Brine Tank P Temp. Control High Pressure Pump 17 Experimental Procedure Baseline performance test (bench) DI feed water 4 hour duration Short term fouling (bench) Secondary, nitrified, and river feed water 4 hour duration Long-term fouling/rejection (pilot) Secondary feed water Tertiary feed water 3-month duration 18 9

10 Experimental Procedure Pilot study at Denver Water Recycling Plant Integrated process performance (flux, rejection, stability) Rejection of micropollutants of concern Trace organic analysis by GC/MS SPE used to remove compounds from salty matrix 19 Solution Chemistry Feed waters Deionized water ph: 7.0 TDS < 40 mg/l Nitrified Effluent ph: 7.5 TDS: 400 mg/l TOC: 10 mg/l Ammonia: 0 mg/l NH 3 -N Nitrate: 10 mg/l NO 3 -N Secondary Effluent ph: 7.5 TDS: 400 mg/l TOC: 10 mg/l Ammonia: 5 mg/l NH 3 -N Nitrate: 5 mg/l NO 3 -N South Platte River ph: 7.5 TDS: 400 mg/l TOC: 10 mg/l Ammonia: 0.02 mg/l NH 3 -N Nitrate: 1.5 mg/l NO 3 -N 20 10

11 Solution Chemistry Draw Solution Synthetic Seawater DI + Instant Ocean synthetic sea salt Compound 35 g/l TDS, mg/l Potassium 420 Sodium 10,780 Magnesium 1,320 Calcium 400 Strontium 8.8 Barium 0.04 Carb/Bicarb 200 Chloride 19,290 Flouride 1 Sulfate 2,660 Boron 5.6 Lithium 0.3 Bromide 56 Iodide Solution Chemistry Organic Micropollutants Compounds targeted: Wide variety of properties Present in wastewater effluent Pose potential health risk Act as surrogates for other compounds Clofibric acid, dichlorprop, diclofenac, fenofibrate, gemfibrozil, ibuprofen, ketoprofen, mecoprop, naproxen, salicylic acid, TCEP 22 11

12 Bench Scale Results: Short term fouling test No flux decline seen in short term secondary effluent experiments Conditions: 19ºC 1.5 LPM ph 7.5 Feed Cond: 850 μs Draw Sol. Conc. 35 g/l SW 24 12

13 Bench Scale Results: Operating Envelope DI benchmark experiments confirm low flux and driving force Water quality has little effect on flux Seawater Conditions: 19ºC 1.5 LPM ph 7.5 Feed Cond: SE: 850 μs/cm DI: 80 μs/cm 25 Pilot Scale Results Minor and reversible fouling PC PC CC Conditions: 2.4 LPM ph g/l Seawater Feed Cond: SE: 850 μs/cm PC = Physical Cleaning CC = Chemical Cleaning 26 13

14 Pilot Scale Results FO cell inverted Allow gravity to pull solids away from membrane Temp. Control Feed (Recycled) water Seawater Draw Solution FO Cell Waste Permeate RO Cell FO Cell Waste Feed (Recycled) water 27 Pilot Scale Results Very low fouling of FO membrane oriented with feed down Secondary Effluent Conditions: 2.4 LPM ph g/l Seawater Feed Cond: SE: 850 μs/cm FO Cell Feeddown 28 14

15 Pilot Scale Results No fouling seen after 2 weeks with tertiary treated wastewater feed Conditions: 2.4 LPM ph g/l Seawater Feed Cond: TE: 850 μs/cm FO Cell Feeddown 29 15

16 Solute Transport: TDS TDS flux generally between mg/l Conditions: 1.5 LPM ph 7.5 Feed Cond: SE: 850 μs/cm DI: 80 μs/cm 31 Solute Transport: Ammonia Rejection: FO: 75%, RO: 75%, Total: 94% Conditions: 2.4 LPM ph g/l Seawater Feed Cond: SE: 850 μs/cm nd nd 32 16

17 Solute Transport: Nitrate Rejection: FO: 79%, RO: 82%, Total: 97% Conditions: 2.4 LPM ph g/l Seawater Feed Cond: SE: 850 μs/cm nd nd nd nd 33 Solute Transport: UV Rejection: FO: 86%, RO: >99.9%, Total: >99.9% nd nd nd nd nd nd nd nd Conditions: 2.4 LPM ph g/l Seawater Feed Cond: SE: 850 μs/cm 34 17

18 Solute Transport: Micropollutants Trace organic rejection Accumulation over 7-day experiment Some compounds were not detected in feed water Clofibric acid, dichlorprop, diclofenac, fenofibrate, gemfibrozil, ibuprofen, ketoprofen, mecoprop, naproxen, salicylic acid, TCEP FO partially rejected most compounds RO rejected almost all compounds 35 Solute Transport: Micropollutants Trace organic rejection Accumulation over 7-day experiment Some compounds were not detected in feed water Clofibric acid, dichlorprop, diclofenac, fenofibrate, gemfibrozil, ibuprofen, ketoprofen, mecoprop, naproxen, salicylic acid, TCEP FO partially rejected most compounds RO rejected almost all compounds 36 18

19 Solute Transport: Micropollutants Compound Bench FO Pilot FO Pilot RO Pilot Total Diclofenac >99.9% 89% >99.9% >99.9% Gemfibrozil 80% 78% 78% 97% Ibuprofen n/a 87% 64% 93% Mecoprop 95% >99.9% - >99.9% Naproxen 90% 85% 94% 98% Salicylic Acid 72% >99.9% >99.9% >99.9% TCEP n/a 31% 94% 95% 37 19

20 Economic Feasibility Simple model constructed Helps to determine the level of recovery of impaired water possible Parameter Unit Value Finished water flow rate m 3 /day 100 Impaired water flow rate m 3 /day 200 Seawater TDS concentration g/l 35 Seawater stream Forward Osmosis RO influent stream Reverse Osmosis Impaired water stream Concentrated impaired water stream Permeate (finished water) RO reject stream Impaired water TDS concentration g/l 0.5 RO recovery % 50 Energy cost $/kwh 0.31 Forward osmosis membrane cost Minimum return on investment ratio $/m Economic Feasibility Effect of changing impaired water flow rate 200 m 3 /day 200 m 3 /day 40 20

21 Economic Feasibility Effect of changing impaired water flow rate 150 m 3 /day 150 m 3 /day 41 Economic Feasibility Effect of changing impaired water flow rate 300 m 3 /day 300 m 3 /day 42 21

22 Economic Feasibility Effect of changing price of energy $0.31/kWh $0.31/kWh 43 Economic Feasibility Effect of changing price of energy $0.31/kWh $0.25/kWh $0.25/kWh $0.31/kWh 44 22

23 Economic Feasibility Effect of changing price of energy $0.35/kWh $0.35/kWh 45 Conclusions Driving force and flux are low in forward osmosis Flux unaffected by changes in water quality Minimal water flux decline No pre-treatment for FO required Orientation of membrane cell has significant effect on fouling Salt loss from draw solution cannot be ignored RO membranes protected from organic foulants Multiple barriers provide adequate rejection of trace contaminants Process feasible over a wide range of operational parameters 46 23

24 Acknowledgements AWWA Research Foundation for supporting this research (AwwaRF-4150) Russell Plakke, Denver Water Ed Beaudry, Hydration Technologies Inc. AQWATEC Nathan Hancock, Brandy Laudig Experimental assistance Dr. Eric Dickenson, Christiane Hoppe, Jennifer Teerlink, Matt Sonnenberg GC/MS analysis Dr. Dean Heil Laboratory assistance 47 24