EP3826745A1 - Faradic porosity cell - Google Patents
Faradic porosity cellInfo
- Publication number
- EP3826745A1 EP3826745A1 EP19840364.4A EP19840364A EP3826745A1 EP 3826745 A1 EP3826745 A1 EP 3826745A1 EP 19840364 A EP19840364 A EP 19840364A EP 3826745 A1 EP3826745 A1 EP 3826745A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- voltage
- anode
- cathode
- fpc
- water
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Pending
Links
Classifications
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/46—Treatment of water, waste water, or sewage by electrochemical methods
- C02F1/469—Treatment of water, waste water, or sewage by electrochemical methods by electrochemical separation, e.g. by electro-osmosis, electrodialysis, electrophoresis
- C02F1/4691—Capacitive deionisation
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/46—Treatment of water, waste water, or sewage by electrochemical methods
- C02F1/461—Treatment of water, waste water, or sewage by electrochemical methods by electrolysis
- C02F1/467—Treatment of water, waste water, or sewage by electrochemical methods by electrolysis by electrochemical disinfection; by electrooxydation or by electroreduction
- C02F1/4672—Treatment of water, waste water, or sewage by electrochemical methods by electrolysis by electrochemical disinfection; by electrooxydation or by electroreduction by electrooxydation
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/46—Treatment of water, waste water, or sewage by electrochemical methods
- C02F1/461—Treatment of water, waste water, or sewage by electrochemical methods by electrolysis
- C02F1/467—Treatment of water, waste water, or sewage by electrochemical methods by electrolysis by electrochemical disinfection; by electrooxydation or by electroreduction
- C02F1/4676—Treatment of water, waste water, or sewage by electrochemical methods by electrolysis by electrochemical disinfection; by electrooxydation or by electroreduction by electroreduction
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/46—Treatment of water, waste water, or sewage by electrochemical methods
- C02F1/461—Treatment of water, waste water, or sewage by electrochemical methods by electrolysis
- C02F1/46104—Devices therefor; Their operating or servicing
- C02F1/46109—Electrodes
- C02F2001/46152—Electrodes characterised by the shape or form
- C02F2001/46157—Perforated or foraminous electrodes
- C02F2001/46161—Porous electrodes
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F2201/00—Apparatus for treatment of water, waste water or sewage
- C02F2201/46—Apparatus for electrochemical processes
- C02F2201/461—Electrolysis apparatus
- C02F2201/46105—Details relating to the electrolytic devices
- C02F2201/4612—Controlling or monitoring
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F2201/00—Apparatus for treatment of water, waste water or sewage
- C02F2201/46—Apparatus for electrochemical processes
- C02F2201/461—Electrolysis apparatus
- C02F2201/46105—Details relating to the electrolytic devices
- C02F2201/4612—Controlling or monitoring
- C02F2201/46125—Electrical variables
- C02F2201/46135—Voltage
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F2201/00—Apparatus for treatment of water, waste water or sewage
- C02F2201/46—Apparatus for electrochemical processes
- C02F2201/461—Electrolysis apparatus
- C02F2201/46105—Details relating to the electrolytic devices
- C02F2201/4616—Power supply
- C02F2201/4617—DC only
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F2209/00—Controlling or monitoring parameters in water treatment
- C02F2209/06—Controlling or monitoring parameters in water treatment pH
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F2303/00—Specific treatment goals
- C02F2303/22—Eliminating or preventing deposits, scale removal, scale prevention
Definitions
- the field of the invention is removal of metal ions, halide ions, derivatives of metals and halides, and ionic particulates from solutions, e.g., the removal of lead from water, by pairing selected faradic reactions with carbon electrode pore mouth diameter profiling.
- Adsorption means attracting ions in an input stream to and retaining those ions on an electrode surface.
- Alignment means removing metal ions, halide ions, derivatives of metals or halides, or particulate metal from an input stream to a cell by one or more of the following: (i) physical adsorption; (ii) capacitive adsorption; (iii) electrochemical pH modulation & metal immobilization; (iv) electrochemical peroxide (H2O2) generation & metal oxidation; (v) electrodeposition or electroplating; (vi) electrochemical oxidation or reduction; (vii) precipitation; (viii) pore mouth diameter profde, (ix) electrode treatment, (x) electrode spacing, and (xi) flow-by vs. flow-through vs. carbon block cell design.
- “Charging potential” means a voltage applied to a cell to perform work.
- Conductivity means the electrical conductivity of an input stream, through stream, output stream, or a waste stream. Conductivity is a surrogate measurement for the molarity of ions in an input stream, output stream, or waste stream. Conductivity is directly proportional to molarity of ions in such streams.
- CX means carbon xerogel.
- CX electrodes possess a mesoporous structure with a nominal surface area of -200 m 2 /g.
- “Cycle” means a cycle of operation in which a sequence of positive then negative, or negative then positive, potential has been applied to an FPC electrode.
- E means a voltage, aka electrical potential; if a direct current, E has a constant polarity (positive or negative).
- Electrode means a material, typically porous carbon, which is electrically conductive.
- ‘EDC” means an electro-dehalidation cell disclosed in this Application.
- An EDC is a species of water purification cell within the genus of FPCs.
- EDC Parameter means a user-selected FPC Parameter in an EDC.
- ‘EDX” means Energy Dispersive X-Ray Analysis.
- Eo is the potential vs. a reference electrode when the electrodes are short-circuited (i.e., E 0 is the potential during a short-circuit condition).
- EPZC or“potential of zero charge”, means the potential of an electrode at which there is a minimum in ion adsorption at the surface.
- EPZC can be intentionally shifted by surface modification of a carbon electrode, or inherently relocated as a result of oxidation of an electrode surface by extended applied potential or voltage.
- the EPZC of a pristine carbon a electrode is typically between -0.1 V and +0.1 V. Shifting the Epzc of an electrode through surface modifications is disclosed in detail in ETSAPP 62/702286 incorporated herein.
- FPC electrode EPZCS for a given target species vary by water chemistry and are empirically determined.
- “Faradic immobilization” means electron transfer to a target species in the electrolyte, or electron transfer to a species in the electrolyte, followed by a homogeneous reaction in solution with the target species of interest, after which the reaction product is adsorbed on an electrode.
- Flow-by cell design means the through stream in an FPC flows across the surface of the electrodes in an FPC, rather than through the electrodes.
- Flow-by cell design can provide the following advantages compared to a flow-through cell design: lower pressure drop, higher flow rate, equal degradation of carbon electrodes, equivalent pH regions generated for each electrode pair.
- Flow rate means the flow rate, typically in L/hr, ml/min, etc., of an input, throughput, output, or waste stream.
- “FPC” or“faradic porosity cell” or“FPC device” means a purification cell that uses agglutination to remove metal ions, halide ions, derivatives (e.g., other species) of target metals or target halides, or particulate metal from a liquid (typically aqueous) input stream and produce an output stream with a decreased metal, halide, or particulate content.
- Different species of FPC can be used in series or in parallel to remove target species from an aqueous influent to a purification system.
- An“FPC system” means a water purification system that contains one or more FPCs and optionally other types of purification cells (see definition of“hybrid system”), such as capacitive deionization (“CDI”) cells, membrane CDI cells (“MCDI”), inverted CDI (“i-CDI”) cells, and non-electrochemical cells and filters.
- CDI capacitive deionization
- MCDI membrane CDI cells
- i-CDI inverted CDI
- non-electrochemical cells and filters non-electrochemical cells and filters.
- CDI capacitive deionization
- MCDI membrane CDI cells
- i-CDI inverted CDI
- non-electrochemical cells and filters non-electrochemical cells and filters.
- CCCs and EDCs are species of FPCs.
- ‘FPC Parameter” means a user-selected value in an FPC of (i) physical adsorption; (ii) capacitive adsorption; (iii) electrochemical pH modulation; (iv) electrochemical peroxide (H2O2) generation & oxidation of target species; (v) electrodeposition (e.g., electroplating, electrophoretic deposition); (vi) electrochemical oxidation or reduction; (vii) precipitation; (viii) pore mouth diameter profile, (ix) electrode treatment, (x) electrode spacing, and (xi) flow-by vs. flow-through vs. carbon block cell design.
- One or more FPC Parameters are selected, or“tuned”, to remove a target species from a through stream, based on empirical data for a given input water chemistry.
- Halide derivative means a molecule or compound that contains a halide.
- HE means a high-efficiency mesoporous carbon. Electrodes made with HE carbon possess a predominately mesoporous structure with a nominal surface area of -380 m 2 /g. HE has a formulation of >98% mesoporous carbon with the balance being macroporous carbon. HE is formulated using the pore mouth diameter profile method disclosed in USAPP 62/702286 incorporated herein.
- “Hybrid system” means a water purification system that contains at least one FPC (CCC or EDC) and at least one other type of water purification cell, e.g., a peroxidation cell, CDI, MCDI, i-CDI, or non electrochemical cell or filter.
- FPC FPC
- EDC electrochemical cell or filter
- “Immobilization” means adsorption of a target species on an FPC electrode without later desorption into a purified output stream.
- KN means a microporous carbon marketed as Kynol® available from American Kynol, Inc (Pleasantville, NY). Electrodes made with KN carbon possess a microporous structure with a nominal surface area of -1800 m 2 /g.
- Metal means a metal, metal ion, metal complex, metal particle, or toxin for which a Pourbaix diagram exists and containing a metal selected from the group comprising As, Se, Pb, Ni, Zn, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, La, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.
- a metal selected from the group comprising As, Se, Pb, Ni, Zn, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, La, Hf, Ta, W, Re, Os, Ir, Pt, Au
- Metal derivative means a molecule or compound that contains a metal or metalloid.
- ‘Metal speciation” means the different chemical forms (“species”) of a metal in a given milieu. For instance, As(III) and As(V) are species of arsenic that can coexist in an aqueous solution at a given pH.
- “Output stream” means a liquid that has passed through an FPC and contains a lower molarity of target species than in the input stream.
- “Physical adsorption” means physical entrapment of a target species in an electrode pore.
- “Point of entry” or“POE” means the location where a water supply feeds a water distribution system in a residence, commercial/industrial building, or other structure.
- “Point of use” or“POU” means the location where water is dispensed from a water distribution system to a consumer, beverage dispenser, kitchen appliance, or other end use.
- “Polarity” means the polarity of a DC voltage, either positive or negative.
- “ Series system architecture” means FPCs (and optionally, other types of cells and filters) connected in series, i.e., the outlet of a first FPC feeds the inlet and a second FPC, the outlet of the second FPC feeds the inlet and a third FPC, and so on.
- a series system architecture can be fixed, or can comprise multiple FPCs (and optionally, other types of cells and filters), a process controller, sensors, interconnecting feed lines, and valves disposed in feed lines between the outlet of one FPC and the inlet of a second FPC.
- “ Series-parallel system architecture” means a system in which FPCs (and optionally, other types of cells and filters) can be connected in series or in parallel.
- a series-parallel system architecture can be fixed, or can comprise multiple FPCs (and optionally, other types of cells and filters), a process controller, interconnecting feed lines, sensors, and valves disposed in feed lines between the outlet of one FPC and the inlet of a second FPC, which valves are actuated by the process controller.
- the typical series-parallel system architecture comprises multiple ranks of a given series of cells, thereby treating the through stream in the same way, but with higher throughput provided by multiple serial paths.
- “Species” means a molecule, compound, or particulate in an aqueous stream or adsorbed on a cell electrode.
- “Speciation” means the distribution of an element among defined chemical species in a system or within an FPC. For instance, an uncharged metal particle, a metal ion, and a metal complex of a given metal may coexist in solution or suspension at a given pH, which distribution may change as pH changes.
- “Stacked cell design” means an FCP cell design in which separate pieces of separator and porous carbon-based electrode materials are stacked layer-by-layer to create a cylinder with multiple, predominantly flow-by, through stream paths through and/or by the porous carbon electrode.
- Current collectors are attached to the anode and the cathode, usually in multiple locations to reduce electrical losses.
- Figure 23 shows a stacked cell design.
- Surface-charge enhanced surface means an electrode surface that has been imparted with surface charge through chemical or electrochemical methods.
- “Target species” means a molecule, compound, or particulate to be removed using an FPC. “Target species” includes not only the molecule, compound, or particulate as found (aka“identified as a species in a Pourbaix diagram”) in the input stream to an FPC, but one or more intermediate and final reactive products created in an FPC that include that molecule, compound, or particulate.
- “Through stream” means the liquid stream being treated within a cell; stated differently, the through stream means the stream within a cell and between the inlet to the cell and the outlet from the cell.
- “Treat” means to feed an input stream into an operating FPC or system containing FPCs and to recover the purified output stream.
- Treated electrode means an electrode with an electrode surface modification disclosed herein.
- TDS means total dissolved solids.
- the general operational definition is that the solids must be small enough to survive filtration through a filter with two-micrometer pores.
- “Untreated electrode” means an electrode without an electrode surface modification disclosed herein, i.e., a pristine carbon electrode.
- Voltage and“potential” are synonymous herein. Voltage is direct current (“DC”) unless otherwise specified.
- a system that contains deionization cells that periodically desorb molecules will have (i) a purified output stream from deionization cells operating in an adsorption state that is combined with FPC output streams, and (ii) a waste stream from deionization cells operating in a desorption state.
- Toxic metals, esp. lead, in drinking water and crop irrigation water are a major, worldwide health problem.
- the problem, and health impacts, are largely unreported until a crisis occurs, as when the water in a municipal water system becomes toxic from lead contamination.
- At least 18 million Americans were at risk of drinking lead-contaminated water last year.
- More than 5,000 community water systems violated a federal lead rule.
- Elevated blood lead levels in children cause irreversible neurological and behavioral disorders, and even low levels have been linked to decreased IQ and lifetime achievement.
- the U.S. Environmental Protection Agency (“EPA”) emphasizes that there is no safe level of lead exposure.
- Figure 1 shows U.S. locations with dangerously high levels of lead in municipal drinking water and the incidence of elevated blood lead levels in young children in the U.S., exposing them to a risk of permanent brain damage, seizures, coma, and even death from lead poisoning.
- the U.S. Natural Resources Defense Council (“NRDC”) recently found 5,363 community water systems in violation of the EPA’s lead and copper rule (https://www.epa.gov/dwreginfo/lead-and-copper-rule), a federal requirement for monitoring of lead and copper levels in water.
- the NRDC report also found 1,110 water systems that exceed the action level for lead (15 ppb in at least 10 percent of homes tested). These systems collectively serve nearly 4 million people.
- Chlorine and/or chloramines are routinely added to the US drinking water supply as disinfectants to control microbial growth. While the removal of microbes is beneficial for human consumption, chlorine and/or chloramine contributes to tap water’s unpleasant taste and odor. Therefore, removing chlorine and chloramines before end use is desirable. Chlorine is more volatile than chloramine and easier to remove with a typical consumer’s filter pitcher; however, to remove chloramine, specially formulated filters containing activated carbon (catalytic carbon) are required. The presence of chlorine and/or chloramines is also detrimental for water purification processes that rely on polymer membranes, such as reverse osmosis (RO).
- RO reverse osmosis
- Process water Drinking water and other water for use in heat and power plants and other industrial processes (“process water”) must have chlorine, chloramines, and other halides (esp., bromine and iodine) and halide derivatives removed to reduce corrosion and fouling of process systems.
- a solution for the technical problem of removing both chlorine and chloramines from water sources without damaging RO membranes and with reduced use of activated carbon filters would not only reduce water purification costs, but improve drinking water and process water quality. Oxidation of water-borne contaminants, as a water purification process, is normally done with hydrogen peroxide or ozone. Oxidation of certain water-borne contaminants facilitates further degradation and ultimate destruction of the contaminants without further intervention.
- the technical problem to be solved is to provide (i) a more efficient, less expensive, purification device to produce purified water, especially a device that removes soluble and insoluble lead to below 15 ppb in potable water, which purification device is (ii) easily scalable for residential, municipal, commercial, and industrial use.
- Applicant has developed a faradic porosity cell (“FPC”) that solves the technical problem by agglutination of target species.
- FPC faradic porosity cell
- FPC Two genera of the FPC are disclosed herein: a first genus that uses a novel electro-dehalidation technology to remove chlorine, other halides, chloramine disinfectants, and other halide derivatives from water - called herein the electro-dehalidation cell (“EDC”); and a second genus that uses a novel capacitive coagulation technology to remove metals, metal derivatives, and particulate metal - called herein the capacitive coagulation cell (“CCC”).
- Applicant’s faradic porosity technology is significantly more effective in water purification than commonly used processes such as chemical coagulation, ion-exchange, and adsorbents.
- the EDC solves the technical problem of reducing the cost, and improving the efficiency, of removing chlorine, chloramines, and other halides and halide derivatives from drinking water and from process water.
- the CCC solves the technical problem of reducing the cost, and improving the efficiency, of removing metal, metal derivatives, and particulate metal from drinking water and from process water.
- Figure 1 A map the National Resources Defense Council produced of counties with water systems in violation of the EPA’s Lead and Copper Rule ⁇ left), and number of cases of children with elevated blood lead levels in 2012 ⁇ right).
- FIG. 3 Lead removal comparison of Applicant’s CCC device to commercially available prior art POU devices. Applicant’s CCC, denoted as“PTW” in Figure 2, was tested with different municipal water chemistries that had lead content above the EPA action level. Applicant’s CCC outperformed all prior art devices.
- Figure 4 Pourbaix diagram of lead (Pb) in a carbonate solution showing the Pourbaix operating regions for lead species removal at the intersection of E applied to anode and cathode and resultant pH near each electrode.
- FIG. Agglutination mechanisms for lead (Pb) removal showing lead speciation and pathways for immobilization of Pb species.
- FIG. Pourbaix diagram for hypochlorite. (Debiemme-Chouvy, Catherine & Hua, Y & Hui, F & Duval, Jean-Luc & Cachet, H. (2014). Corrigendum to“Electrochemical treatments using tin oxide anode to prevent biofouling” [Electrochimica Acta 56/28 (2011) 10364-10370] Electrochimica Acta. 121. 461. l0.l0l6/j .electacta.20l4.01.l30.)
- FIG. 8 Pourbaix diagram for mono chloramine (NFbCl). (www.sedimentaryores.net).
- Figure 10 Potential distribution for Kynol electrodes in a 4-electrode set-up in 4.3 mM NaCl, where pristine Kynol was the anode and cathode, Pt was the counter-electrode, and a standard calomel electrode (SCE) was the reference. The voltage was applied in 0.2 V increments from 1.6 V down to 0.8 V and back up to 1.6 V. Eo,avg represents the open circuit voltage of the system.
- FIG. 8a-e show cyclic voltammograms (CV) at a scan rate of 0.5 mV/s in 4.3 mM
- mesoporous CX and mesoporous HE follow the same trend observed for CG in Fig. 8c, but HE exhibits more area within the CV plot at 3 h and 6 h compared with CX due to a higher electrochemically active surface area, which provides a larger current response.
- the pore size of CX is 10X larger than HE, which is related to stability of the electrode and ultimate lifetime; the larger pore size of CX, however, provides much less surface area than HE.
- Figure 12 Bench-scale capacitive coagulation device.
- Figure 21 Pourbaix diagram for Al. (https://corrosion-doctors.org/Corrosion- Thermodynamics/Potenti al-pH-diagram-aluminum.htm)
- FIG 23 Schematic of an EDC device with stacked cell design.
- the feed influent, or input stream
- flows in the bottom of the device proceeds through an annular space near the wall of the cell housing, then flows centripetally over the electrode surfaces to the axial channel, and is then discharged (effluent or output stream) through the axial channel to the FPC outlet.
- Feed spacers are optional; a feed spacer (shown in Figures 23 and 29) is an additional layer of material between anode and cathode that can optionally be added to create a larger flow channel for the through stream.
- FIG. 24 Applied voltage and current transients as a function of volume treated at a flow rate of 300-500 ml/min for EDC experiments conducted with Calgon as both electrodes. Current spikes at -1500 and -1600 gallons are due to noise (inadvertent physical movement of the electrical leads) and can be neglected. At -1800 gallons, operation was switched from applying a constant voltage to applying a constant current of -0.2 A, observed as a straight line. The voltage decay (voltage is reading as negative, but the total cell voltage is increasing with constant current) seen at this condition is a consequence of applying a constant current. The subsequent switching also occurred at constant current, but the voltage reached the cutoff value quickly and the system essentially behaved as though at constant voltage.
- Figure 27 (a) Carbon cloth with white precipitates and (b) scanning electron microscopy (SEM) micrographs of the cloth showing a Pb crystal.
- FIG. 28 EDX mapping of a Pb crystal from Figure 27 confirming that the crystal is lead oxide by the presence of both lead and oxygen. Carbon (C), lead (Pb), and oxygen (O) are mapped in the three panels to the right, represented by the lightest contrast in each corresponding gray scale image. Color photograph of EDX mapping is available.
- Figure 29 Schematic of a rolled cell design in which continuous separator and porous carbon-based electrode materials are physically rolled into a spiral to create a cylinder with multiple, predominantly flow-by, through stream paths through the porous carbon electrode.
- FIG. 30 EDC experiments conducted with Kynol as both electrodes. Concentration of total chlorine in the feed and product streams, and applied voltage, as a function of volume treated at a flow rate of 500 ml/min is shown.
- FIG. 31 EDC experiments conducted with Kynol as both electrodes. Concentration of free chlorine in the feed and product streams, and applied voltage, as a function of volume treated at a flow rate of 500 ml/min is shown.
- FIG. 32 EDC experiments conducted with Kynol as both electrodes. Concentration of chloramine in the feed and product streams, and applied voltage, as a function of volume treated at a flow rate of 500 ml/min is shown.
- FIG. 33 EDC experiments conducted with Kynol as both electrodes. Percent removal of total chlorine, free chlorine, chloramine, and peroxide after treatment of tap water with the EDC, and applied voltage, as a function of volume treated at a flow rate of 500 ml/min is shown.
- FIG. 34 EDC experiments conducted with oxidized Kynol as one electrode and Fuel Cell Earth as the other. Concentration of total chlorine in the feed and product stream, and applied voltage, as a function of volume treated at a flow rate of 300-500 ml/min.
- Figure 35 EDC experiments conducted with oxidized Kynol as one electrode and Fuel Cell Earth as the other. Concentration of free chlorine in the feed and product stream, and applied voltage, as a function of volume treated at a flow rate of 300-500 ml/min.
- Figure 36 EDC experiments conducted with oxidized Kynol as one electrode and Fuel Cell Earth as the other. Concentration of chloramine in the feed and product stream, and applied voltage, as a function of volume treated at a flow rate of 300-500 ml/min.
- FIG. 37 EDC experiments conducted with oxidized Kynol as one electrode and Fuel Cell Earth as the other. Percent removal of total chlorine, free chlorine, chloramine, and peroxide after treatment of tap water with the EDC, and applied voltage, as a function of volume treated.
- FIG. 38 EDC experiments conducted with Calgon as both electrodes. Concentration of total chlorine in the feed and product stream, and applied voltage, as a function of volume treated at a flow rate of 300-500 ml/min.
- FIG. 39 EDC experiments conducted with Calgon as both electrodes. Concentration of free chlorine in the feed and product stream, and applied voltage, as a function of volume treated at a flow rate of 300-500 ml/min.
- Figure 40 EDC experiments conducted with Calgon as both electrodes. Concentration of chloramine in the feed and product stream, and applied voltage, as a function of volume treated at a flow rate of 300-500 ml/min.
- Electrode spacing is typically less than 1 mm, and is preferably as close as possible without causing a short circuit of anode and cathode or causing an unacceptable pressure drop (the corollary of which is increased residence time and decreased flow rate) within the FPC.
- Preferable electrode spacing is less 1 mm, preferably less than 200 microns, more preferably less than 50 microns, and most preferably less than 20 microns.
- immobilization by plating on an electrode can occur at potentials ranging from ⁇ 0.3 V to -0.4 V vs. NHE for pH regions from 0 to 14.
- precipitation can occur in the form of copper hydroxide (Cu(OH) 2 ) at the anode at potentials above 0 V vs. NHE and pH values higher than 4 (see Figure 17).
- Total cell potentials of approximately 0.4 V are desired for the removal of copper in a faradic porosity cell.
- target species can be removed under similar mechanisms but under different voltage regions.
- lead precipitation can occur from the pH and potentials that are generated on the electrode surfaces. At potentials more negative than—0.4 V vs. NHE and pH regions from 0 to 14, lead can be plated as a solid at the cathode. Precipitation at the anode can also occur as Pb0 2 if the pH is kept >1.5 and potentials >0.5 V vs. NHE are used ( Figure 16). Finally, oxidation from H 2 0 2 generated at the cathode can also result in precipitation of target species.
- DO dissolved oxygen
- a faradic porosity cell comprises a series of porous carbon anodes and cathodes, typically consisting of reduced cathodes (negative EPZC and positive surface charge) and pristine anodes (although anodes experience a positive EPZC shift ((negative surface charge)) during use), and operated by applying a small voltage, e.g., 1.2 V, across the electrodes.
- a small voltage e.g., 1.2 V
- the FPC invention combines adsorption (physical and capacitive) of target species (e.g., lead, iron, manganese, cadmium, chromium, chlorine, chloramine, etc.) and immobilization (aka coagulation) of the adsorbed target species by optimizing electrode porosity, applied E, and Pourbaix operating region.
- target species e.g., lead, iron, manganese, cadmium, chromium, chlorine, chloramine, etc.
- immobilization aka coagulation
- the EDC Parameters are“tuned” to remove other non-metal target species, e.g., chlorine, chloramines, and other halides and halide derivatives, from the EDC influent.“Tuning” an EDC primarily means selecting (i) a voltage applied between EDC anodes and cathodes based on (ii) analyzing and selecting an operating region in the target species’ Pourbaix diagram, and (iii) selecting a pore mouth diameter profile of the EDC carbon electrodes that maximizes removal of a target species.
- the effluent from an EDC can be used without further processing or can be routed to one or more EDCs, CCCs, or prior art water purification cells for further removal of other target species. Tuning can optionally be further optimized through electrode treatment. Device features and benefits are listed below and in Table 2 and Table 3 in the Drawings.
- An EDC or CCC optionally uses treated anodes and cathodes made of carbon in which the one or both electrodes’ Epzc has been shifted compared to a pristine electrode Epzc. Shifting the Epzc of an electrode can change the kinetics of reactions occurring (either positively or negatively). Whether to shift only anodes, or only cathodes, or both types of electrode, and how much Epzc shift to use, depends upon input water chemistry and the target species.
- Carbon electrodes are superior to metal electrodes in avoiding or reducing electrolysis, or water splitting, when potentials as high as 3 V are applied to an electrode.
- An applied potential of more than 1.23 V (“overpotential”) can cause electrolysis of water, which produces dangerous hydrogen gas.
- Metal electrodes can cause hydrogen gas production at ⁇ 2 V; in contrast, carbon electrodes can sustain higher applied voltages while avoiding substantive water electrolysis.
- the inventive steps of an EDC are: (i) decreased power consumption required for reduction of chlorine and chloramines (responsible for taste and odor) through specific carbon electrodes and applied voltage, (ii) can be used on-demand or as continuous treatment, (iii) very scalable, simple design that provides significantly lower cost POU/POE devices as well as lower cost municipal, commercial, and industrial large-scale systems, (iv) similar performance to traditional carbon blocks (such as activated carbon/activated charcoal) but with significantly less carbon needed, (v) similar removal performance of free chlorine with a much shorter residence time, (vi) the use of less carbon, (vii) longer electrode life, especially for the removal of chlorine and chloramine, (viii) finer control over specific removal amounts and output water quality, (ix) better control over balancing rate of target species removal vs. electrode life, and (x) FPC cost/benefit can be adjusted by choice of carbon for FPC electrodes.
- Activated carbon is a form of carbon processed to have numerous small, low-volume pores that increase the surface area available for adsorption or chemical reactions.
- An FPC can be used to purify wastewater, cooling water, laundry wastewater, water to be purified for human consumption, water to be purified for agriculture, water to be purified for horticulture, water to be purified for use in food, water to be softened, sea water to be purified for human consumption, water to be purified for laboratory use, brackish water to be purified for human consumption or agriculture use, and water to be purified for medical use.
- the pore mouth becomes“roofed” and/or the pore channel becomes“closed”, decreasing the surface area of the carbon (esp., the pore channel diameter and length) so that the pore no longer functions effectively.
- A“roofed” pore mouth blocks access to the interior of the pore.
- Pore mouth roofing and pore channel collapse cause a decrease in electrode performance and eventual failure of prior art cells.
- a target species if ionized, bearing an electrical charge, or bearing a partial charge due to the asymmetric distribution of electrons in chemical bonds, can be attracted to the carbon electrode due to the applied potential, which produces a driving force to move the target species close to (or in contact with) the carbon electrode.
- Non-ions and non-charged species of a target species can collide with an electrode surface. Once in contact with the electrode surface, numerous pathways to immobilization of the target species can occur. Local and large pH swings can be controlled to electrochemically produce an alkaline environment, which will produce, e.g., insoluble metal oxides, that precipitate near or on the electrodes and are entrapped in electrode pores. Faradic reactions, such as oxygen reduction reactions at the cathode, can produce hydrogen peroxide which can diffuse away from the electrode and oxidize target metal molecules that are within close proximity: hydrogen peroxide performs indiscriminate oxidation. When target species closer to the electrode are in a localized higher concentration, the statistical chance for hydrogen peroxide to oxidize the target species is greater.
- the carbon electrode can (1) transfer an electron(s) from the electrode to the target species and reduce it so that it is deposited onto the electrode or (2) transfer an electron(s) from the target species to the carbon electrode and oxidize the target species into either an insoluble oxide or hydroxide, or into a more reactive species that can be immobilized through additional electron transfer reactions or pH adjustments. Precipitated species and electrically attracted species are entrapped in electrode pores.
- pores in activated carbon depend upon the shape, tortuosity (which is usually associated with changes in pore diameter), and channel length of a given pore. Based on micrographs of activated charcoal, and depending on the activation and/or synthesis procedures, some pores in activated carbon can be tubular channels, polygonal channels, spheroid chambers, surface slits, etc. Channels and chambers can be“dead end” or“through” (i.e., a channel or chamber with two surface appearances, aka“pore mouths”, with channel continuity between the two pore mouths).
- the diameter of a pore mouth i.e., the opening of a pore to electrolyte, has a major, and in small pore mouth diameters, predominant, impact on the utilization of that pore for adsorption and on multi-cycle performance in capacitive coagulation.
- a larger pore mouth diameter (and therefore, pore mouth surface area) will provide significant contact area between the pore channel and the electrolyte.
- a small pore mouth diameter will have more limited contact area (i.e.,“pore mouth surface area”).
- Pore mouth diameters are defined by IETPAC as microporous, mesoporous, and macroporous with pore mouth diameters of ⁇ 2 nm, 2-50 nm, and >50 nm, respectively.
- the lifetime of an adsorption medium has a direct correlation to the pore mouth diameter present on the surface of the material.
- the concept and ramifications of“pore mouth roofing”, aka pore mouth closure, after repeated cycles of adsorption and desorption using an activated carbon electrode, is explained below.
- Applicant’s device incorporating capacitive coagulation technology removed soluble (dissolved) and insoluble (particulate) lead species from tap water to well below the EPA action level in samples spiked with concentrations up to -300 ppb lead. Efficient lead removal was even demonstrated with concentrations of lead as low 5 ppb in input streams, well below the action level.
- the prototype device achieved > 90%, and frequently >99%, specificity for lead removal over other constituents commonly found in tap water, such as calcium (Ca 2+ ).
- Applicant’s capacitive coagulation invention was able to achieve this performance in hard, alkaline water where lead species tend to form complexation species that are difficult to remove by commercial off-the-shelf products.
- a CCC is also unexpectedly capable of removing both soluble (dissolved) and insoluble (particulate) lead, arsenic, nickel, and copper species.
- Applicant’s capacitive coagulation invention provides in one embodiment for lead removal a POU/POE water purification device capable of meeting NSF/ANSI 53 and 61 certifications at a minimum flow rate of 1 gallon per minute (gpm) regardless of input water source conditions: hardness, pH, alkalinity, and types of disinfection. Additionally, the device is (i) highly specific for target metals, e.g., arsenic, lead, nickel, copper, cadmium, lead, manganese, mercury, and radioactive metals, (ii) more reliable, (iii) more efficient, and (iv) lasts longer than state-of-the-art solutions.
- target metals e.g., arsenic, lead, nickel, copper, cadmium, lead, manganese, mercury, and radioactive metals
- capacitive coagulation cells provide a more efficient, less expensive, and very scalable water purification device that removes soluble and insoluble lead to below 15 ppb and is suitable for residential as well as scale-up to higher-throughput systems.
- CCC parameters permit“tuning” of a CCC to remove any other metal or metal derivative for which a Pourbaix diagram exists, such as arsenic, cadmium, manganese, and mercury, as well as Se, Ni, Zn, Al, Sc, Ti, V, Cr, Fe, Co, Ni, Cu, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, La, Hf, Ta, W, Re, Os, Ir, Pt, Au, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.
- Applicant’s CCC outperformed commercially available POU/POE water purification devices, such as the Brita ® LonglastTM and Brita ® PUR filters and the Calgon GAC filter material.
- the Brita ® LonglastTM pitcher filter had drastically different performance when tested on two different days based on the change in water chemistry being supplied by the municipal water system in Lexington, Kentucky. This differing performance emphasizes the need for a more reliable device that performs well in varying water chemistries that occur from day- to-day.
- Applicant’s invention outperformed the Brita ® LonglastTM device in both instances.
- Soluble lead ions adsorb onto the carbon electrodes by physical and/or chemical adsorption, a process that is well documented (J. Chem. Technol. Biotechnol. 2002, 77, 458-464, Shekinah, P.; Kadirvelu, K.; Kanmani, P.; Senthilkumar, P.; Subburam, V. and Carbon. 2004, 42, 3057- 3069, Swiatkowski, A.; Pakula, M.; Biniak, S.; Walczyk, M.), and undergo additional electro-adsorption onto the cathode under an applied potential. Modulation of the pH can also be exploited to control lead speciation in tap water.
- Pb 2+ is in solution equilibrium in most of the white area (approximately pH 7) between the darker PbCte(s) and Pb(s) areas; however, in the solution nearest the anode and cathode, Pb 2+ becomes (i) reactive or (ii) immobilized as other Pb species.
- Figure 5 shows the reaction mechanisms by which Pb is removed from solution.
- hydrogen peroxide generated at the cathode from dissolved oxygen reduction and combined with the acidic pH emanating from the anode (pH 2 to pH 3) with an applied E of -0.4 V is a potent oxidizer. Hydrogen peroxide diffuses into the through stream, including the region near the anode where it oxidizes lead species in the intermediate reactions described above. The immobilized lead species are thereby removed from solution. Additional lead species are susceptible to immobilization through reactions with hydrogen peroxide that is generated via oxygen reduction at the cathode (“peroxidation cell”). Water Research. 2017, 120, 229-237, Tang, W.; He, D.; Zhang, C.; Kovalsky, P.; Waite, T. D. In a hybrid system, FPCs can be using in series with peroxidation cells to provide increased lead removal.
- an EDC a cascading series of chemical-electrochemical-chemical-electrochemical reactions are occurring to decompose free chlorine and chloramine.
- the pH and operating voltage are correlated through the Pourbaix diagram for a target species. Examples are given below for hypochlorite, hypobromite, and monochloramine and shown in Figure 6, Figure 7 and Figure 8, respectively.
- the target speciation can be controlled by selecting the pH and voltage to apply. This calibration process determines and controls what species are decomposed at what voltage and in a given influent water chemistry.
- the y-axis is voltage applied between the anode and cathode vs. a standard hydrogen electrode (SHE), and the x-axis is pH.
- SHE standard hydrogen electrode
- EDCs typically operate with total cell potential of ⁇ 3.0 V applied across anode and cathode; depending upon target species and input water chemistry, total cell potential of ⁇ 3.0 V applied across anode and cathode in an EDC is usually between 1.0 V to 3.0 V.
- Figure 10 shows that at a given applied voltage there will be a potential distribution between the anode and cathode in a CCC; the voltage will split between the electrodes, which may not be equal.
- the cathode may be at -0.9 V vs. SCE and the anode at +0.7 V vs. SCE ( Figure 10).
- This affects the FPC operating parameters and frequency of polarity- switching performed in each cycle of operation in an EDC.
- the active surface area, carbon material, and applied voltage affect the potential distribution.
- the Epzc of an electrode affects the distribution of applied E during the initial use of an electrode, and the potential distribution changes slightly. Balancing of faradic reaction rates at the anode and cathode ultimately stabilize potential distribution
- a bench-scale CCC system is shown in Figure 12.
- the capacitive coagulation system provides >50% lead removal selectivity vs. non-metal ions.
- lead removal can approach 100%.
- various oxygen-based surface groups are added to the electrode and lead removal below 15 ppb is achieved in all cases for ⁇ 50 ppb lead tap water input stream, at a CCC operating voltage of 1.2 V.
- a lead-removal CCC reduced the concentration of lead in the output stream to only 0.05 ppb, equating to 99.9% removal efficiency.
- CCC systems remove lead to below EPA action levels even if the input stream has various combinations of lead content, water hardness, alkalinity, disinfectants, and pH. Water chemistry will impact lead speciation (e.g., day to day variations in municipal water chemistry, the effect of which are shown in Figure 4 above).
- lead speciation e.g., day to day variations in municipal water chemistry, the effect of which are shown in Figure 4 above.
- CCCs can remove lead in all forms (species) commonly found in drinking water sources.
- Oxygen reduction and H2O2 generation Oxygen reduction at the cathode generates H2O2 that can react with lead species to facilitate the formation of lead oxides. There is a significant reduction in DO at an applied voltage of 1.2 V and measured 1.25 ppm H2O2 in the filtered water. The operating voltage is controlled to amplify this reaction for maximal lead removal. Experiments conducted at open circuit, short-circuit, and up to a voltage of 1.4 V with 0.2 V increments, and the pH, DO, and H2O2 concentrations at the outlet typically remove lead to below EPA action levels.
- the CCC lead removal technology relies on (i) physical adsorption; (ii) capacitive adsorption; (iii) electrochemical pH modulation and metal immobilization; (iv) electrochemical peroxide (H2O2) generation & metal oxidation; (v) electrodeposition (e g., electroplating, electrophoretic deposition); (vi) electrochemical oxidation; (vii) precipitation; (viii) pore mouth diameter profile, (ix) electrode treatment, (x) electrode spacing, and (xi) flow-by vs. flow-through vs. carbon block cell design.
- a combination of these factors, or a cascade of these factors, causes speciation and immobilization of target species that become trapped in the pore network of the carbon electrodes, which results in a purified effluent. It is imperative that the carbon electrodes are conductive. The more conductive the carbon material, the more uniform the current distribution was across the electrodes, which typically results in increased H2O2 generation and a more efficient lead removal process.
- the pore size and surface area are related to the adsorption capacity and tortuosity of the material. Pore size and surface area also affect H2O2 generation in an FPC device.
- a POU/POE FPC product design parameters include: (1) Residence time and size of device was identified to achieve a flow rate of 1.5 gpm; and (2) Effective lead removal, defined by a reduction in dissolved lead levels from 150 ppb to ⁇ 10 ppb and removal selectivity >90% over non-metal divalent ions, at 1.5 gpm for at least 150 gallons of water treated.
- Pressure drop The pressure drop across a FPC device is increasingly important as the flow rate increases. A pressure drop of ⁇ 20 psi is considered acceptable and is below a normal inlet water pressure for residential and municipal buildings of -45 psi.
- FPC replacement threshold ranges for various embodiments.
- a CCC is replaced when the target metal concentration in the output stream exceeds the relevant threshold level, e.g., 15 ppb for lead concentration and 1.3 ppm for copper (see the Lead and Copper Rule, a regulation published by the EPA in 1991 (https://www.epa.gov/ground-water-and-drinking-water/national-primary-drinking- water-regulations).
- the threshold level (aka sorption capacity) could be specified by a government agency, or user selected. Municipal and industrial wastewater discharge limits are different from drinking water limits; the metal concentration thresholds are typically higher. There are effluent guidelines for different industries (https://www.epa.gov/eg).
- FPC Regeneration When a FPC output stream metal concentration equals or exceeds the threshold level, rather than replacing the FPC, some types of FPCs can be regenerated (e.g., in a CCC, the adsorbed metal ions and particles desorbed (removed) from the CCC electrodes).
- CCC regeneration is by flushing acid through the cell to dissolve coagulated metals and regenerate the electrodes.
- this“acid regeneration” step the output stream is diverted to a receptacle in which the highly concentrated waste stream is collected for other processing.
- FPCs connected in series e.g., pH of the through stream and voltage applied to the cell electrodes of a given cell, of multiple cells connected in series to different FPC Parameters and EDC Parameters, as the case may be, enable each cell in a series to remove a different target species from the through stream in a single pass.
- FPC Parameters e.g., pH of the through stream and voltage applied to the cell electrodes of a given cell
- FPC Parameters and EDC Parameters as the case may be, enable each cell in a series to remove a different target species from the through stream in a single pass.
- Pourbaix diagrams which show the speciation of a target species at a given voltage and pH, best illustrate the“cell series” concept.
- Applied voltage and electrochemical pH modulation are selected to remove target species of Ni, Fe, Mn, Al, and Zn from CCC influent using the Pourbaix diagrams shown in Figures 18-22, respectively, as explained below.
- Those of skill in the art can select an applied voltage and electrochemical pH modulation to remove a given species of a target element or complex. Copper is removed by the CCC via electrodeposition, hydroxide precipitation, and/or oxidation to copper oxides.
- FPC control system FPC Parameters for a given FPC are monitored and controlled using a computer system that monitors and/or controls various sensors, interfaces, valves, and peripheral equipment, and is commonly known as a process control computer (aka processs controller), a computer generally associated with continuous or semi-continuous production operations involving materials such as chemicals and petroleum, whether in liquid, solid, or gas phases.
- process control computer enables FPC Parameters to be applied to one or more FPCs in a system and changes in through-stream routing, e.g, changes that convert a series system architecture to a series-parallel system architecture.
- a positive voltage is applied to the anodes and a negative voltage is applied to the cathodes.
- the polarity of the voltage applied to a given electrode is periodically switched (converting each anode into a cathode, and each cathode into an anode) to ensure that all electrodes degrade at the same rate and to extend the lifetime of the EDC device.
- An example is shown in Figure 24.
- the polarity-switching interval for a given EDC can be arbitrarily set (e.g., every hour) or can be set based on one or more EDC parameters, e.g., current threshold, voltage threshold, rate of current decrease at constant voltage, percentage of current decrease at constant voltage, rate of voltage decrease at constant current, percentage of voltage decrease at constant current, total volume treated, and concentration of target species in EDC effluent.
- EDC parameters e.g., current threshold, voltage threshold, rate of current decrease at constant voltage, percentage of current decrease at constant voltage, rate of voltage decrease at constant current, percentage of voltage decrease at constant current, total volume treated, and concentration of target species in EDC effluent.
- Preferred polarity-switching points are (i) a percentage decrease in current at a constant applied voltage, (ii) a percentage increase in voltage at a constant applied current, (iii) total volume treated, and (iii) concentration of target species in effluent.
- Electrode properties are shown in Table 4.
- Capacitive coagulation experiments were conducted to test Cu removal using 16 pairs of carbon electrodes (-13 g of carbon), in which the cathodes were pristine SC and the anodes were nitric acid oxidized SC.
- the FPC was operated at short-circuit (0 V).
- a 1 L feed solution of -100 ppm Cu [CU(N03)2] in direct inj ection (“DI”) FhO was treated at a flow rate of 20 ml/min.
- Samples were analyzed by inductively coupled plasma (ICP) with optical emission spectrometer (OES) and the results in Table 9 show that approximately 1/3 of the Cu was removed in a single pass.
- Capacitive coagulation experiments were conducted to test Cu removal using 12 pairs of carbon electrodes (-10 g of carbon), in which the cathodes and anodes were both pristine SC.
- the FPC was operated at an applied potential of 1.2 V on the cathode.
- a 18.5 L feed solution of -50 ppm Cu [CU(N03)2] and -50 ppm Ca (CaCh) in Dl FhO was treated at a flow rate of 20 ml/min.
- Cu plated out of solution onto the cathode shown as a grayish deposit in Figure 25a.
- Breakthrough curves were obtained for packed columns of pristine or nitric acid oxidized carbon ( ⁇ 5 g) and 1 L of -150 ppb Pb [Pb(NC>3)2 tap H2O was filtered at a flow rate of 20 mL/min (Table 34 and Table 35).
- Pb removal is occurring via physical adsorption (passive filtration) as opposed to capacitive adsorption and coagulation (active filtration) with our device.
- the initial Pb concentration decreases dramatically, but both carbons saturate quickly at -0.3 L of water treated and become ineffective.
- Pristine carbon appears to be more effective for physical adsorption of lead as compared to oxidized carbon at the conditions tested.
- a rolled cell design was used for capacitive coagulation experiments with a 1.5 L feed solution of -150 ppb Pb [Pb(NO;)>] in tap H2O, -14 g of carbon electrodes, pristine anodes and nitric acid oxidized cathodes, and flow rates of 50, 100 , and 200 mL/min, all showed Pb removal to below the federal action level of 15 ppb in a single pass (Table 41).
- the cell was operated at an applied potential of 1.2 V. Samples were taken before and after filtration with the cell and the Pb 2+ concentration measured with a handheld sensor from ANDalyze.
- MarketsandMarketsTM Report Retrieved from MarketandMarketTM database.
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