system for decontaminating well water for drinking
DESCRIPTION
:. System for Decontaminating Well Water for Drinking. Arsenic - Health and Remediation Applications, Session III Webinar April 15, 2013. TDA Research, Inc. Girish Srinivas, Ph.D., M.B.A. 303-940-2321 [email protected] Shawn Sapp, Ph.D. Steve Gebhard, Ph.D., P.E. Steve Dietz, Ph.D. - PowerPoint PPT PresentationTRANSCRIPT
:System for Decontaminating Well Water for Drinking
TDA Research, Inc.
Girish Srinivas, Ph.D., M.B.A.303-940-2321
Shawn Sapp, Ph.D.Steve Gebhard, Ph.D., P.E.
Steve Dietz, Ph.D.Will Spalding
Rachelle CobbDrew Galloway
Arsenic - Health and Remediation Applications,Session III Webinar
April 15, 2013
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TDAR e s e a r c hTDAR e s e a r c hTDAR e s e a r c h
About TDA
• Began operations in 1987• Privately held – 8 employee partners
• 88 employees
• 28 Ph.D.'s in Chemistry and Engineering
• $15 million in annual revenue
• Facilities• Combined 50,000 ft2 in Wheat Ridge and
Golden, CO
• Synthetic Chemistry
• Materials Processing & Testing
• Process Development
• Business Model• Identify opportunities with industry
• Perform R&D, primarily under government contract
• Secure intellectual property
• Commercializes technology by licensing, joint ventures, internal business units
Wheat Ridge Facility
Golden Facility
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Outline
• Introduction/Background • Well Water Contamination & Drinking Water
• Conventional Purification Technologies (IX, RO, sorbents/other)
• Capacitive Deionization (CDI)
• Flat CDI Cell Testing• TDA’s Activated Carbons
• Electrochemical Testing & Optimization
• Bench-Scale Prototypes, Testing, & Results
• Spiral CDI Cell Testing• Early Results
• Dual Cell Configuration
• Pre-prototype Units
• Commercialization and Partnerships• Competitive Advantages
• Market Landscape & Strategic Partnerships
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Executive Summary
• TDA has developed a capacitive deionization (CDI) process based on• Proprietary carbon electrodes
• Spiral wound capacitive deionization cells
• Less expensive to manufacture
• TDA has demonstrated• Arsenic removal to below drinking water standards
• 83 ppb to < 5 ppb
• Single pass flat cell
• Currently refining the design and manufacturing method for spiral cells • Well water testing (spiked with arsenic)
• Real arsenic contaminated waters
• TDA partnering with ITN Energy Systems• Develop and market PV-CDI systems
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Ground & Surface Water Contamination
• Approximately 45 million people in the U.S. (~15% of the population) get their drinking water from wells, cisterns, or springs
• These ground and surface waters can be contaminated by local geology or human activities
• Priority inorganic contaminants include arsenic, lead, perchlorate, nitrate/nitrite, fluoride, etc.
• Secondary concerns include softening hard water and desalination of briny water
• Rural and remote population sites (especially foreign)
• Some of the worst well-water quality
• Conventional treatment may be
• Unavailable
• Cost-prohibitive
• Impractical
Arsenic in Groundwater Worldwide
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International Groundwater Resources Assessment Centrehttp://www.un-igrac.org/publications/148
• Arsenic is a common, widespread contaminant
• Some areas have very high (in red) concentrations
Arsenic in Groundwater in the U.S.
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• Areas with especially high arsenic concentrations (50 g/L) are found in almost every state
Chemical Forms of Aqueous Arsenic
• Many naturally occurring and anthropogenic sources of arsenic in the environment
• Sulfur is present because Eh-pH diagram is for waters in contact with As rich gold ores used to make As2O3
• CDI removes all ionic species, which includes many arsenic species
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S. Wang, C.N. Mulligan, Occurrence of arsenic contamination in Canada:3127 sources, behavior and distribution, Sci. Total Environ. 366 (2006)701–721.
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Conventional Arsenic Removal Technologies
• Ion Exchange• Removes ions by replacing cations with H+ and anions with OH-
(forming H2O)
• Requires frequent resin bed replacement (expensive) or regeneration (time consuming)
• Can increase sodium content (e.g. home water softeners where cations are replaced by Na+ and anions by Cl-)
• Reverse Osmosis (RO)• Requires pumping the water to high pressures (the more TDS the higher
the pressure)
• Produces water at low flow rates (poor yields)
• RO membrane modules are easily contaminated
• Module replacement is expensive and time consuming
• Sorbents/Other• Can be low cost (e.g. activated carbon)
• Require disposal as hazardous waste or regenerated
Ion Exchange
• Removes ions by replacing cations with H+ and anions with OH- (forming H2O)
• Requires frequent resin bed replacement (expensive) or regeneration (time consuming)
• Some anions (e.g. perchlorate) require specialized resins
• Expensive
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http://www.tdsmeter.com/what-is?id=0015
Reverse Osmosis – TDS Reduction
• Reverse Osmosis (RO)
• Requires pumping the water to high pressures (the higher the pressure the greater the water recovery)
• Requires high power even with relatively clean feeds
• Produces water at low flow rates (at low feed pressure)
• RO membrane modules are easily contaminated
• Module replacement is expensive.
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Sorbents
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Arsenic removal from water/wastewater using adsorbents—A critical reviewDinesh Mohan and Charles U. Pittman Jr.Journal of Hazardous Materials 142 (2007) 1–53
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Capacitive Deionization (CDI)
• CDI for Decontaminating Drinking Water• Eliminates difficult to remove ions such as arsenic (III),
perchlorate, nitrate, and other toxic inorganics
• Removes both cations and anions
• Removes charged particles
• Units small and portable
• Requires no consumables (resins, sorbents, etc.)
• Can use any DC power source (batteries, solar panels, generators, etc.)
• Low voltage 1.2 VDC (safe); current scales with total dissolved solids (TDS)
• Low power at typically low TDS concentrations in drinking water
• Can deliver potable water from many sources (wells, lakes, streams, etc.)
Capacitive Deionization – Ion Removal
• CDI electrostatically removes dissolved cations and anions from contaminated water
• TDA CDI unit
• Stack (or spiral wound) high surface area carbon electrodes
• Electrodes are porous and electrically conductive
• Ions are removed when DC voltage is applied
• V 1.2 volts to prevent electrolysis of water
• Ions adsorb and are held in the electric double layers on the electrodes
Deionization Cycle• Cations migrate to negative electrode
• Anions migrate to positive electrode
• The required current rapidly decays as ions are removed so it is inherently efficient and low-power
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Ions are Held in the Electrical Double Layer
• Ions in CDI adsorb on (are held to) the charged electrode surfaces by electrostatic forces (no chemical bonding)
• IHP = Inner Helmholtz plane is where the ions are in direct contact with the electrode
• OHP = Outer Helmholtz plane is where there is closest approach and the ions still carry their complement of solvating water molecules
• Diffuse layer is transition to bulk solution
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http://www.andrew.cmu.edu/course/39-801/theory/Electrical%20Double%20Layer.png
Ele
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Capacitive Deionization – Regeneration
• Electrodes are shorted or polarity briefly reversed to force desorption
• Flush in reverse direction with product water
• Efficient because captured salt concentration is highest at the inlet
• Use of product water during flush is minimal and resulting effluent can be sent to the drain
• Can briefly reverse polarity to speed up desorption
• Flush countercurrent with clean product water
• Stored capacitance can be re-captured during discharge to improve efficiency (more relevant when treating brackish water)
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Advantages of CDI
• Does not require high pressures
• Equipment and operational costs are reduced
• Low voltages
• Safe
• Low power (low energy cost)
• Small units can be used in remote locations and run by solar panels
• Some of the energy can be recovered by utilizing stored energy (CDI is a capacitor)
Comparison of several water purification
technologies
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TDA’s Carbon CDI Electrodes
• TDA’s carbon electrodes
• Made using proprietary method
• Chemically pure
• Controllable pore size distribution
• Controllable surface area
• Can add surface functionality
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Testing TDA’s Carbon CDI Electrodes
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• Cyclic voltammetry (CV)
• Used to determine carbon electrode capacity for adsorbing ions
• Small static test cells
• Current response as a function of a linearly ramped voltage
• Shape of the CV trace gives the resistance & capacitance properties of the cell
• Electrode capacitance is calculated from the current and scan rate
• Varying the voltage scan rate enables kinetic measurements
• Both rate and capacitance must be optimized for ideal cell performance
Optimum Electrode Thickness 6 mil
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• Cyclic voltammetry between ±1.2 V at very slow and very fast scan rates
• Peak capacitance vs. scan rate plots allow for comparison between carbon materials
• Plot shows the data for optimizing the thickness of our carbon electrodes
• Data show that 6 mil (0.006” ~ 0.15 mm) is optimal
TDA Carbon Electrodes are Redox Inactive
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• Platinum electrode exhibits reduction-oxidation (redox) chemistry with 100 ppm lead, Pb2+ from Pb(NO3)2
• No current transients present using TDA carbon electrode indicating good chemical stability
• Ions can be removed without chemical reactions occurring using TDA’s carbon CDI electrodes
Long Term Stability of TDA’s Carbon CDI Electrodes
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• Cyclic voltammetry used to measure long term stability by subjecting electrodes to thousands of cycles
• Hard water, 394 mg/L as Ca(CO3)2
• Slow, 25 mV/s scan rate to simulate slow rate of charge and discharge during CDI
• TDA carbon CDI electrodes exhibit an initial break-in period followed by gradually improving performance
• Performance still slowly improving even after 6,000 cycles
• Same test done with well water contaminated with 100 ppm Pb2+ which is 6,700 times EPA drinking water limit
• Very small decrease in capacitance was observed (less than 0.04% drop, per 100,000 cycles, per ppb of lead)
Approaching Steady-State(continued
improvement)
Break-In(rapid cell
improvement)
Early Testing with Flat/Stacked Plate CDI Cells
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Typical Flat Cell Construction
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Flow Paths in Early Flat Cell Designs
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Serpentine Flow Cell
Parallel Flow Cell
Side-View of Stack Layers
Hybrid Flat Cell Design
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Hybrid (Parallel/Serpentine) Flow Cell
Typical Flat Cell PerformanceHard Well Water
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• A real-world, sample of very hard water, 394 mg/L as Ca(CO3)2 , was used to demonstrate basic CDI performance
• Data show the results of a single-pass through a parallel flow, flat plate cell with water analysis before and after treatment
• A standard break-in period of 6-8 cycles is typical for this type of cell, so the data are displayed for inlet the 14th cycle
Contaminated Well Water Testing
• Hard well water contaminated with
• 54 ppb perchlorate (ClO4
-)
• 66 ppm nitrate (NO3-)
• 25 ppb lead (Pb2+)
• 83 ppb arsenic (III) (AsO2
-)
• Concentration of all contaminates reduce to levels well below EPA drinking water standards
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Hybrid Flat Cell
Hybrid Flat Cell: Contaminated Well Water Performance
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Much better than low pressure RO which is typically ~10% efficient
TDA Spiral Wound CDI Module Technology
• Flat electrodes
• Satisfactory for testing the effects of
• Thickness
• Pore size distribution
• Surface area
• Too expensive to manufacture
• All current CDI systems use flat electrodes
• There are no spiral wound CDI modules currently in use
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TDA Spiral Wound Design – Early Prototype
• Spiral wound CDI cells have been fabricated with a factor of 4x improvement in surface/volume ratio over “plate-type” cells
• 1st Generation of spiral wound cell has typical removal efficiency of ~80% with simple saline feeds (500 ppm NaCl)
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Spiral Wound Design – Stacked Modules
• Two Pyrex glass “spool piece” bodies (4”dia x 4” long)
• Electrodes, spacers, current collectors, insulators rolled into a cylinder and inserted into the glass
• Units are then sealed and top/bottom clamped in place
• Electrical connections made to metal tabs
• Can be used individually or stacked (as shown)
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Single vs. Stacked Modules
• As expected, stacking the two cell modules improves performance
• Simulates using several spiral wound modules in series
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Carbon #1 single
Carbon #2 single
Carbon #2 two stacked
Pre-Prototype Units
• Electrodes 11 inches wide (instead of 4 in)
• Cells still 4 inch diameter
• Both Pyrex glass and PVC housings tested
• Easier to see leaks and other problems with glass unit
• Designing 1 gal/hr prototype units
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Spiral Cell Electrode Winding Machine
• Previously used hand winding to roll spiral cells
• Winding machine recently built in-house at TDA
• Greater tension
• Improves alignment at ends
• Better reproducibility
• Better scalability
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Strategic Partnerships – ITN
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• ITN Power Systems, Inc. (ITN, Littleton, CO) develops green energy and storage technology for today’s and tomorrow’s needs. Areas of core competency include:
• Energy generation & storage devices
• Sensors & actuators
• Separation membranes
• Flexible, thin film electronic device structures
• Nanotechnology
• In 2005, ITN spun off Ascent Solar who manufactures cutting-edge solar technology (CIGS & thin film PV) that easily integrates into a wide range of products and applications. Areas of core competency include:
• Custom turnkey PV systems
• Building-integrated PV
• Flexible CIGS modules
Ascent Solar flexible PV panels
Portability & Low Power
• Some domestic and many foreign population centers
• Need water decontamination systems
• Less likely to have a well developed power or water treatment infrastructure
• Portability and low power are essential requirements
• CDI modules are inherently compact; spiral wound cells reduce size by at least a factor of four and are cheaper to manufacture
• No consumables, sorbents, chemicals
• Power requirements are well below existing portable RO systems (ITN)
• PV-battery powered systems practical
• TDA has partnered with ITN to develop PV/battery powered CDI modules
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500 gal/day, field-portable, PV-powered, RO module built & tested by ITN
ITN- Partnership
• Work with ITN to build a PV unit and interface it with TDA’s prototype CDI system
• PV-CDI system will be tested on
• Well water spiked with contaminants
• Actual arsenic contaminated waters
• ITN has strategic partnerships in Asia
• ITN proposes to license (non-exclusive) TDA’s spiral wound CDI cell technology worldwide
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Competitive Advantages
• TDA’s carbons are cost competitive with Kuraray & MeadWestvaco activated carbons (≤ $10/kg)
• TDA electrodes long lasting, which reduces overall carbon cost per 1000 gal of water treated
• TDA electrodes are chemically pure carbon (no contaminants from the carbon)
• TDA electrode carbons can be optimized for improved performance
• Electrode production is easily scaled up (continuous process)
• TDA carbon CDI electrodes are compatible with spiral wound cell designs which dramatically decreases manufacturing costs
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Business Environment
• Drinking water market driven by:• Low cost for water treatment
• Health regulations
• Portability (especially military field use)
• Remote applications (powered using solar cells)
• Competing technologies (ion exchange and reverse osmosis) • Reverse Osmosis is power intensive (pumping water to
high pressure)
• Ion exchange requires expensive (and logistically inconvenient) media replacement or refill reagents
• CDI is low power and has no expendables
Conclusions
• TDA has developed a capacitive deionization process based on• Proprietary carbons
• Spiral CDI cells
• Less expensive to manufacture
• TDA has demonstrated• Arsenic removal to below drinking water standards
• 83 ppb to < 5 ppb
• Single pass flat cell
• Currently refining the design and manufacturing method for spiral cells • Well water testing (arsenic spiked)
• Real arsenic contaminated waters
• TDA partnering ITN Energy Systems• Develop and market PV-CDI systems
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Acknowledgments
• National Institute of Environmental Health Sciences (NIEHS)
• U.S. Department of Energy (DOE)
• ITN Energy Systems
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