Patent Application
20130299361
This invention relates to methods for treatment of wastewater to destroy organic contaminants by electrochemical advanced oxidation processes.
The recent dramatic increase in the use of hydraulic fracturing (“fracking”) and horizontal drilling in low permeability shale formations for the production of oil and natural gas (“tight oil and gas”) has caused a dramatic increase in water usage and in requirements for treating wastewater. The EPA estimates that between 1.7-3.0 million barrels (300-600 million tonnes) of water are currently used each year in the US for the fracking of ˜35,000 wells. This huge increase in water use and wastewater treatment is being driven by a combination of higher water use per well (˜50-250 thousand barrels of water per well are typical for fracking operations, which is at least an order of magnitude greater than older drilling methods) and by an increase in the number of wells. As much as 80% of the water from a drilling operation along with the fracking chemicals added to it, return to the surface and must be treated or re-injected into deep wells to avoid groundwater contamination. This water can contain a wide array of hazardous fracking chemicals, e.g. methanol, benzene, phenols, isopropyl alcohol, acrylates, and naturally-occurring organics such as napthenic acids, benzene, methane, phenols, organosulfur compounds and other hydrocarbons. Another example of this type of wastewater is the “Tailing Pond Water” generated from oilsands hydrocarbon recovering in large quantities in Alberta, Canada, which is contaminated with a significant toxic load of napthenic acids (e.g. 50-100 ppm).
Despite the high economic value of fracking, many states are reluctant to expand fracking operations due to concerns about water contamination. It is therefore vital that more effective wastewater remediation technologies be developed for fracking and for other hydrocarbon recovery processes that produce large volumes of wastewater containing organic contaminants.
It is well known in the art that chemical oxidation or electrochemical oxidation of wastewater can be used for water purification or destruction of biological and chemical contaminants, both inorganics and organics.
For chemical oxidation, oxidants such a hypochlorite or persulfate may simply be added to the wastewater. During electrochemical treatment or oxidation of wastewater, it is usually required that sodium chloride or other salts are added to the wastewater, to provide sufficient conductivity for electrolysis, and for electrochemical production of an oxidant or sterilant species, such as chlorine. See for example, U.S. Pat. No. 6,328,875 entitled “Electrolytic apparatus, methods for purification of aqueous solutions and synthesis of chemicals” and U.S. Pat. No. 6,547,947 entitled “Method and apparatus for water treatment”, which discloses electrochemical generation of hydrogen peroxide and an oxidation product such as hypochlorite or persulfate for water treatment.
It is well known that persulfuric acid (H2S2O8), or the anion of the acid, i.e. peroxodisulfate (S2O82−) or persulfate, can provide more effective chemical destruction of some organic contaminants than chlorine or hypochlorite. Persulfates can be produced efficiently by electrolysis of sulfuric acid or sulfate salts, and then added to wastewater. See for example, U.S. Pat. No. 6,503,386 entitled “Process for the production of alkali metal and ammonium peroxodisulfate”. This patent discloses the use of conductive diamond electrodes to provide longer life and better efficiencies in operating costs such as maintenance, for electrochemical production of persulfates.
While persulfate can chemically oxidize many organic molecules more effectively than hypochlorite, the process can be a very slow, resulting in a very time-consuming or expensive process. As an example, it will be apparent that a number of oxidation steps are necessary to oxidize a molecule such as phenol to small acids or carbonate. It is observed that persulfate added to wastewater oxidizes phenol and napthenic acid very slowly.
Thus, once the persulfate is produced electrochemically, activation is typically required to accelerate the oxidation reactions during wastewater treatment, both to provide more complete oxidative destruction of contaminants and to accelerate the reaction. In the past, ultraviolet radiation, application of heat and/or use of transitional metal catalysts have been primary methods of activation (Block; Philip, et al., “Novel Activation Technologies for Sodium Persulfate In Situ Chemical Oxidation”, 2004). The activation process can be very energy intensive and/or costly. It also tends to cause additional complexity in both the oxidative destruction process and in the treatment of the resultant wastes (e.g. insoluble ferric salts from the catalysts).
In considering electrochemical oxidation processes, a particular issue is that the large volumes of wastewater produced by processes for hydrocarbon recovery, such as fracking, may contain relatively low concentrations of contaminants, e.g. 10 ppm to 100 ppm or 500 ppm of contaminants such as, naphthenic acid and phenols. These contaminants can be destroyed by electrochemical oxidation, e.g. using persulfate or other oxidants activated using the methods mentioned above. However such wastewater has low conductivity, meaning that electrochemical treatment has to be carried out at a low current density, and the process is therefore slow and has low current efficiency (e.g. <10% current efficiency). Moreover, persulfate oxidants are not efficiently generated in situ from low concentrations of sulfuric acid or sulfate salts added to wastewater, i.e. requiring high energy costs per unit of contaminant for electrochemical destruction. Large quantities of salt can be added to wastewater to increase conductivity and current efficiency for electrochemical processing at higher current density, and in any case are necessary in order to increase conductivity and lower operating voltages for electrochemical treatment.
However, when there is a relatively low concentration of contaminants, the high total dissolved solids (TDS) in the treated wastewater may itself create other wastewater disposal issues, i.e. how to dispose of the salt water. Thus, it is usually desirable to avoid the need to add significant amounts of salt, so as to maintain low total dissolved solids, i.e. a low salt concentration, in treated wastewater.
Thus, there is a need for improved or alternative solutions which address one or more shortcomings of known methods and systems for wastewater treatment to destroy organic contaminants. In particular, alternative chemical or electrochemical processes for treatment of wastewater to destroy refractory organic contaminants, such as phenols and napthenic acids, are required for applications such as hydrocarbon recovery, e.g. in particular where the concentration of salts already present in the wastewater is relatively low (i.e. wastewater having low conductivity).
The present invention seeks to mitigate the above mentioned problems, or at least provide an alternative system and method for wastewater treatment to destroy organic contaminants.
Thus one aspect of the present invention provides a method for treatment of wastewater to destroy organic contaminants, comprising:
For destruction of contaminants such as phenol and napthenic acids, the peroxy oxidant species preferably comprises persulfate and/or hydrogen peroxide. In some embodiments the peroxy oxidant species may comprise alternative peroxy oxidant species such as, perborate or pyrophosphate.
The concentrated oxidant solution comprises persulfate or other peroxy oxidant species at a concentration that can provide a desired mole ratio relative to the concentration of a target organic contaminant to be oxidized when the concentrated solution is mixed with the wastewater in the prescribed ratio. For example, it may be required that the contaminant load is sufficiently reduced to a particular target level, e.g. to attain a particular Chemical Oxygen Demand (COD) level.
Preferably, step a) comprises generating the concentrated oxidant solution by electrolysis at high current density in an electrochemical cell comprising a diamond anode, from an aqueous solution containing ≧1M sulfate, e.g. >1M sulfuric acid, with salt added (0.5 to 2M) to increase conductivity and current efficiency. For example, persulfate may be generated with high current efficiency by electrolysis of sulfuric acid at high current density.
Step a) is preferably carried out at a high current density, e.g. in the range from 300 mA/cm2 to 1000 mA/cm2 or more preferably in the range from >500 mA/cm2 to 1000 mA/cm2.
The wastewater and concentrated oxidant solution are mixed in a ratio in the range from 5:1 to 25:1, for example in a ratio of about 10:1. This ratio is selected to efficiently reduce the organic contaminant load in the wastewater. For example, the amount of concentrated oxidant solution may be added in a quantity sufficient to lower the contaminant load in the final treated solution to a desired effluent level, e.g. more than a 80% reduction in COD level or preferably more than a 90% reduction in COD.
Since the conductivity of the mixed solution is low, step c) is carried out at lower current density, e.g. 60 mA/cm2 to 200 mA/cm2. However, it is observed that the majority of the peroxy oxidant species, such as persulfate, are generated in step a), and then after mixing, these oxidant species are quickly and effectively activated on the diamond electrodes in step c), even using the lower current density. As demonstrated by experimental data disclosed herein, this process sequence with electrochemical activation in step c) of the peroxy oxidant species produced in step a) results in much faster and more effective and complete destruction of organic oxidants such as phenol, compared to known processes.
The peroxy oxidant species preferably comprises persulfate or hydrogen peroxide for destruction of organic contaminants comprising one or more of naphthenic acid, phenols, methanol, benzene, isopropyl alcohol, other alcohols, ethers, acrylates, methane, organosulfur compounds, other aromatic hydrocarbons such as Poly-aromatic hydrocarbons (PAHs) and other naturally occurring and added hydrocarbons or other contaminant species subject to oxidation by peroxy compounds, such as those typically found in produced water from hydrocarbon recovery and fracking. However, the method may be unsuccessful in oxidizing some highly oxidation resistant hydrocarbon contaminants, such as synthetic organic pesticides like atrazine and organo-fluorine compounds such as perfluorooctonyl sulfonate.
The oxidative destruction of the organic contaminants may be controlled primarily by the concentration of the concentrated peroxy oxidant solution provided in step a), the original mix ratio in step b), and the current density of the electrochemical destruction step c). While the current density in step c) could be increased without a prohibitive increase in cell voltage by adding salt to increase conductivity and current efficiency, it is desirable to maintain low TDS, even though this limits the electrochemical wastewater treatment step c) to lower current density. Nevertheless, with electrochemical activation in step c) of peroxy oxidant species generated in step a) fast and effective destruction of contaminants was observed. The effectiveness of this process sequence is believed to result from the large store,or concentration of peroxy oxidants that are already available in solution in the initial mixture of wastewater and oxidant, and the relative efficiency of the electrochemical process, at the diamond electrode, for breaking the peroxy bonds to generate reactive and relatively long-lived radical species capable of oxidizing a wide variety of contaminants such as those listed above in paragraph [0021].
In summary, a multistep process sequence is provided for electrochemical treatment of wastewater to destroy organic contaminants. The use of conductive diamond electrodes enables efficient electrochemical generation of concentrated solutions of persulfates or other useful peroxy oxidants in step a). After mixing, during the electrochemical treatment, step c) diamond electrodes effectively activate the peroxy oxidants to provide effective destruction of the organic contaminants. Since the process steps for generation of peroxy species and for electrochemical oxidation and destruction of contaminants are separated, each step of the process can be separately controlled. Thus these steps can be conducted in different cells, and can be conducted separately from the treatment of wastewater with these species under very different electrochemical cell operating conditions, (e.g. cell current density, electrode gap, flow velocity, etc.).
A second aspect of the invention provides a system for treatment of wastewater to destroy organic contaminants, comprising:
Preferably, the first cell comprises a first electrochemical cell comprising a diamond anode for high current density operation for generating a concentrated oxidant solution comprising the peroxy oxidant species, e.g. concentrated persulfate solution.
The first electrochemical cell may be operable for producing a concentrated oxidant solution comprising persulfate at a concentration of about 0.5M, e.g. by electrolysis at high current density from an aqueous solution of ≧1M sulfate, with salt added (0.5 to 2M) to increase conductivity and current efficiency. The first electrochemical cell generates a concentrated oxidant solution at current density in the range from 300 mA/cm2 to 1000 mA/cm2, or more preferably at 500 mA/cm2 to 1000 mA/cm2.
The feed system provides for mixing the wastewater and concentrated oxidant solutions in a mole ratio in the range from 5:1 to 25:1, e.g. a mole ratio of about 10:1. This required mole ratio of oxidant to contaminant depends on the electron demand for oxidation of the target organic contaminant species to an environmentally more acceptable, non-toxic species, such as small acids or carbonate.
The second electrochemical cell operates at a lower current density, e.g. from 30 mA/cm2 to 200 mA/cm2, e.g. 60 mA/cm2 for electrolysing the mixture of wastewater and diluted oxidant solution, comprising activating the oxidant species in the wastewater and diluted oxidant solution for rapid and effective destruction of organic contaminants.
Preferred embodiments seek to provide one or more of: an improved rate of contaminant destruction; improved completeness of contaminant destruction for any given type of contaminant; increased range of possible contaminants that can be treated with a given oxidant decreased overall energy costs of the process; decreased the load of salt added to a wastewater in order to treat it; and decreased complexity of the processing.
Thus, a system and method for wastewater treatment are provided, which address at least some of the problems mentioned above.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description, taken in conjunction with the accompanying drawings, of preferred embodiments of the invention, which description is by way of example only.
By way of example, a system 100 for treatment of wastewater using a method according to a first embodiment of the present invention is illustrated schematically in
The first cell 110 may supply a pre-prepared, pre-mixed concentrated oxidant solution with a suitable concentration of persulfate, e.g. 0.5M. However, for treatment of large volumes of wastewater, the first cell 110 is preferably also an electrochemical cell for in situ generation of the concentrated oxidant solution electrochemically.
Thus, in a preferred embodiment, wherein the peroxy oxidant species is persulfate (peroxodisulfate), the concentrated solution of persulfate 112 is generated by electrolysis of sulfuric acid, or other aqueous sulfate solution having a concentration of at least 1M, and preferably a more concentrated solution. The solution may contain sufficient salt, i.e. Na2SO4, or H2SO4 to increase the conductivity of the solution for electrolysis at high current density. The sulfate solution is electrolyzed at high current density, e.g. 300 mA/cm2 to 1000 mA/cm2 and more preferably in the range from >500 mA/cm2 to 900 mA/cm2 to generate the peroxy oxidant species with high current efficiency. In alternative embodiments, alternative peroxy oxidant species may be used, such as hydrogen peroxide (H2O2), pyrophosphate, perborate or percarbonate, for example, or combinations thereof to achieve different reaction pathways and potentially more complete destruction of contaminants.
The concentrated oxidant solution 112 is generated comprising the persulfate, or other peroxy oxidant species at a concentration that provides a desired dilution or concentration ratio (e.g. a mole ratio) relative to the concentration of a target organic contaminant to be oxidized when the concentrated solution 112 is mixed with the wastewater 122 in the prescribed ratio. For example, produced water from hydrocarbon recovery, which may contain ˜50 ppm, ˜100 ppm or more of organic contaminants, such as phenols, benzene, naphthenic acid, alcohols, organosulfur compounds, hydrogen sulfide, hydrocarbons and other oxidizable contaminants. Thus, if the concentrated oxidant solution comprises, e.g. 0.5M persulfate solution, the treatment, the wastewater 122 and concentrated oxidant solution 112 may be mixed in a 5:1 to 25:1 mole ratio, e.g. 10:1 mole ratio as illustrated schematically in
Examples will now be described to illustrate the application of methods according to embodiments of the invention, i.e. diamond activated EAOP processes, for destruction of refractory organics including, for example: methanol, phenol, estradiol, methylene blue and napthenic acids, in an electrochemical system comprising ultrananocrystalline diamond (UNCD) electrodes for diamond activation of peroxy oxidant species.
Table I shows non-optimized diamond activated EAOP experiments with input persulfate (PS) and solar salt concentrations, cell operating conditions and calculated rates, current efficiencies and calculated operating (OPEX) and capital costs (CAPEX) for oxidative destruction of methylene blue (MB).
The oxidative destruction of methylene blue was monitored by changes in the absorbance of its 665 nm visible light absorption peak by spectrophotometry. Table 1 shows the results of various experiments for a range of concentrations of added solar salt (SS, which substantially comprises sodium chloride, NaCl), and persulfate (PS) (peroxodisulphate), concentrations at different applied cell current densities. Methylene blue destruction rates by persulfate at ambient temperature outside an electrochemical cell (i.e. not activated by the electrochemistry within the cell), without a catalyst, are at least 3 orders of magnitude slower, while solar salt does not oxidize methylene blue at all. Referring to table 1, lower current densities generally show higher current efficiency but lower destruction rates. However, the rate, current efficiency and energy costs are significantly improved by higher concentrations of solar salt added to the solution, by lower current densities and by higher concentrations of added persulfate, in that order. Given that the rate is being measured by changes in a visible absorption peak, the Cl (solar salt) concentration is likely to show a disproportionately large effect since Cl. (chlorine radicals) generated on a UNCD anode are sufficiently reactive to break the single-bonds between conjugated pi-bond absorbers in methylene blue and to separate the molecule into non-UV/Vis absorbing fragments. Other experiments conducted with sodium fluoride have demonstrated increases in oxidative destruction rates as well at a similar rate to the increase from chloride and persulfate. This suggests the possibility that fluorine radicals are being created on the doped diamond surface and are themselves agents for oxidation of the organic contaminants.
The 95% level of destruction of methylene blue was monitored by the decline in the absorbance of the 665 nm visible absorption peak of methylene blue by spectrophotometer. Reasonable assumptions for cost calculations are as listed above, e.g. a commercial electricity price of 70 per kWh, a high volume diamond price of $60,000/m2 and commercial prices of $1.00/kg for purchased persulfate and $0.04/kg for solar salt. The rows indicate candidate conditions that produced both reasonable rates of methylene blue destruction at reasonable OPEX and CAPEX with reasonable trade-offs for salt concentration and rate of destruction. Higher persulfate concentrations than were used in these experiments would have reduced the OPEX/CAPEX further. Note that the bottom entry (*) in the table showing a very low solar salt concentration (0.01M=580 mg/L, 580 ppm) with a low destruction rate and high OPEX/CAPEX, would be representative of an “as-extracted” salt concentration of a wastewater without added salt. Very low cost persulfate can be synthesized on UNCD from the oxidation of sodium sulfate or sulfuric acid (see next section) which would greatly improve current efficiency and lower OPEX and CAPEX. OPEX and CAPEX close to $1/tonne are likely with further process optimization for this type of relatively non-refractory organic
Destruction of Napthenic Acid. In this example, experimental results are provided for oxidation and destruction of phenol and napthenic acid by electrochemically activated persulfate solutions. These results show the rate of destruction of the organic contaminant with time, as evidenced by spectrophotometry, together with the electrochemical regeneration of persulfate as oxidation of the organic contaminant proceeds towards completion (e.g. see
Prior to the addition of the napthenic acid and methanol, 2 L of a 0.64M persulfate solution, (i.e. .SO4− concentration=30,500 mg/L, shown at time=0 minutes on the graph) was generated from 4M sulfuric acid in the same cell operated at 600 mA/cm2 (25.2 A and 4.1V) for 2.75 hours with a current efficiency of 49%.
The dashed line shows the concentration of monoperoxosulfate ion (.SO4−) (“persulfate”) as measured by iodometry. A UV spectrometer was also used to assess the formation of oxidative breakdown products of napthenic acid. The UV spectrum showed that a large concentration of acetic acid or other carboxylic acid species was present after the first hour. After the initial drop in persulfate concentration in the first hour, the UNCD anode recreates the persulfate from non-oxidized sulfate (SO42−) already in the solution, producing additional current efficiency and offering the possibility of reuse of the sulfate solution.
The solid line shows the total organic carbon in ppm. This is the total oxidative conversion of all the organic carbon present to carbonate ions (CO32−) and CO2. It also shows a 30-35% current efficiency destruction of the napthenic acids and methanol.
This proof-of-concept experiment on a synthetic fracking waste comprising a two-component solution of methanol (MeOH) and napthenic acid (NA) was conducted to demonstrate the potential for this activated EAOP technology. Initially, a 2 L 0.64M persulfate (PS) solution was generated by the oxidation of 4M sulfuric acid in an electrochemical cell with a UNCD anode. Subsequently, a 2 L solution of 250 ppm MeOH and 100 ppm laboratory-grade NA was added to the prepared persulfate solution to form a combined volume of 4 L. The experimental parameters and results from the subsequent NA/MeOH oxidation with persulfate in the same cell are shown in
A two-step process in which a highly concentrated oxidant solution is first prepared and then diluted to form an initial oxidant to contaminant ratio which is then activated on a diamond anode reduces the TDS level and allows the use of low current density and lower voltages appropriate for a dilute contaminant mixture which is referred to as a “Diamond Activated Electrochemical Advanced Oxidation Process” (DAEAOP). A combined CAPEX/OPEX of <$1-$2 per tonne ($0.16-$0.32/bbl) should be achievable with an appropriate selection of salt concentrations, current density and flow rates. This compares very favorably with typical fracking waste trucking costs of $18/tonne ($3/bbl1) and overall fracking waste treatment costs of $30/tonne ($5/bbl).
Further diamond activated EAOP experiments were implemented with phenols, which are one of the key refractory containments found in the waste water of oil recovery processes such as “fracking” or bitumen recovery, other enhanced oil recovery (EOR) processes or in oil refinery wastes.
Table 2 shows the results of the decomposition of a 100 ppm concentration of Phenol (molecular weight=94.1 g/mol) using 200 ml solutions of Persulfate, sodium fluoride (NaF), and Solar Salt (SS), comprised mostly of mostly of NaCl.
In the experiments with persulfate, the persulfate was generated by electrolyzing a 0.11 M concentration from 0.5 M anhydrous sodium sulfate (Na2SO4).
In table 2, the operating expense (OPEX) per tonne to decompose 100 ppm Phenol is determined assuming 70/kWh for the electricity for the electrolysis. In the experiments with solar salt, a further expense of 2¢/lb for the salt based on current industrial bulk prices for this very impure feedstock. With the persulfate being produced from sodium sulfate, the anhydrous sodium sulfate was estimated at 5¢/lb at current industrial bulk prices. The cost of electrical power (at 7¢/kWh) for UNCD synthesis of persulfate was included resulting at a cost of 56¢/kWh or 11.9¢/mole of persulfate. The cost of the sodium fluoride at the bulk prices was not obtainable but would be substantially higher than solar salt or persulfate costs.
From these experiments, solar salt is a very effective agent for the destruction of phenols although the production of chlorinated organic byproducts such as chloroform or trichloroacetic acid are possible using these chemistries. Using UNCD electrodes for the anode a 30 mA/cm2 current density provides a better than 95% decomposition or destruction of the phenols in 20 minutes with a current efficiency of 22.5%. This configuration also provides a substantially low OPEX per tonne of 100 ppm phenol of only $0.35. Higher current densities tend to increase the overall rate of destruction and therefore to reduce the capital cost of the electrodes required. However, higher current densities also tend to exhibit lower current efficiencies and therefore the operating costs tend to be higher. The overall efficiency of the persulfate only oxidation is greatly increased and the cost to destroy reduced when the persulfate is generated from sulfuric acid (see examples below).
Table 3 and
The shorter time spectra in
A further experiment is shown in
In another example, the oxidant (persulfate) in solid form, sodium persulfate, (Na2S2O8) was added at a ratio of ten parts sodium persulfate to one part phenol directly to the wastewater instead of being synthesized in a first cell. The experimental results show that electrochemical activation of the peroxy oxidant species in a wastewater mixture comprising a minimum amount of oxidant and accompanying salt can provide a similar level of activation compared to that achieved with all the extra salinity (TDS) of a “standard EAOP” (Electrochemical Advanced Oxidation Process) which is usually done with the whole process being conducted as a combined synthesis/oxidation process. By performing the process sequence disclosed herein, the amount of added persulfate and non-oxidized sulfate salt can be reduced which reduces the overall TDS increase in the wastewater solution from the addition of the oxidant mixture, the oxidation process is speeded up and the amount of power required is significantly reduced.
The graph in
In a further example, similar to example G, sodium persulfate solid was added directly to the wastewater at a mole ratio of sodium persulfate to phenol of twenty-four to one. The persulfate concentration declined during the experiment with the lower current density of 60 mA/cm2 but the effectiveness of the destruction is very high (i.e. the persulfate is being “activated” by the electrode and the even the relatively current density of 60 mA/cm2). The final spectrum at 3 hours shows the organics (absorption around 320-350 nm) greatly reduced in concentration if not completely absent. The pH was reduced to 1.6 and 30 mM of extra sulfate was added to reduce the cell voltage. The total concentration of added sulfate is therefore 30 mM, added as sulfuric acid, and 40 mM×2 added from the persulfate (persulfate has 2 moles of sulfate), for a total of 110 mM (0.11M) of net sulfate in the final solution. That is about 10 g/L of sulfate overall, or 10,000 ppm.
Iodometric Results
In a further example of the method using hydrogen peroxide as the principal oxidizing species,
Exemplary experiments have been described to demonstrate the effectiveness of the method of treating wastewater containing organic contaminants in a laboratory setting. While mixtures of wastewater and oxidant are described comprising specific mole ratios of organic contaminants and peroxy oxidants, it will be apparent that in large scale processing, the initial concentration and organic contaminant species may be uncertain or unknown, or vary from process to process or from day to day. Consequently, the prescribed ratio for mixing the concentrated oxidant solution with the wastewater would typically be determined empirically for a particular wastewater application.
For example, it may be sufficient that the wastewater is treated only to reduce its COD (chemical oxygen demand) below a certain threshold, or reduce total organic contaminants or specific organic contaminants to an acceptable level, rather than to completely destroy the contaminants. Thus the prescribed ratio for dilution of the concentrated oxidant solution may simply be estimated to provide a sufficient concentration of peroxy oxidant species for effectively meeting the required threshold or target parameter for wastewater treatment. In other applications, where the composition or concentration of contaminants is known, and a particular level of destruction is required, the prescribed ratio may be more specifically determined to provide a suitable concentration ratio or mole ratio of oxidant to organic contaminant to effect a required level of destruction of the organic contaminant within a given time frame, for example, typical initial persulfate (or alternative peroxy oxidant) concentrations would be in the range of 0.1M to 2.0M with an initial mole ratio of the peroxy species to contaminant of at least 5:1 or as much as 25:1 where the peroxy species is persulfate and the contaminant species is phenol with a molecular weight of 94 g/mole. For the example of larger molecular weight contaminants, such as napthenic acids (which often have molecular weights in the range from 200-300), higher mole ratios of persulfate oxidant are appropriate because of the larger number of carbon and hydrogen atoms that require oxidation. In general, the above-mentioned 5:1 to 25:1 mole ratios for persulfate and phenol can be translated into a similar mass ratio of persulfate oxidant to contaminant (i.e. a mass ratio between 5:1 and 25:1). Other peroxy species will preferably utilize mass ratios proportional to the difference in their molecular weights as compared to persulfate. For example, the use of hydrogen peroxide (H2O2) with a molecular weight of 34 g/mole as compared to the molecular weight of persulfate of 238 g/mole, would imply a mass ratio of between 0.7 to 3.6 instead of 5:1 to 25:1 for persulfate. For other peroxy oxidant species, the concentration ratio of oxidant to contaminants for diamond activated EAOP will need to be adjusted accordingly, keeping in mind the respective molecular weights of the selected peroxy oxidant and the contaminants to be destroyed.
Although embodiments of the invention have been described and illustrated in detail, it is to be clearly understood that the same is by way of illustration and example only and not to be taken by way of limitation, the scope of the present invention being limited only by the appended claims.
This application claims priority from U.S. provisional patent application Ser. No. 61/644392 entitled “Diamond Activated Electrochemical Advanced Oxidation Processes”, filed May 8, 2012, which is incorporated herein by reference, in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61644392 | May 2012 | US |
