ACTIVATED CARBON FOR REMOVAL OF TASTE AND ODOR COMPOUNDS FROM WATER
20230107676 · 2023-04-06
Inventors
- SRIKANTH PILLA (CLEMSON, SC, US)
- JAMES SCOTT STERNBERG (CLEMSON, SC, US)
- TANJU KARANFIL (CLEMSON, SC, US)
- ESAT ARITURK (CLEMSON, SC, US)
Cpc classification
B01J20/3078
PERFORMING OPERATIONS; TRANSPORTING
B01J20/28064
PERFORMING OPERATIONS; TRANSPORTING
International classification
B01J20/20
PERFORMING OPERATIONS; TRANSPORTING
B01J20/28
PERFORMING OPERATIONS; TRANSPORTING
Abstract
In general, the present disclosure is directed to a soyhull-based activated carbon. The soyhull-based activated carbon comprises a Brunauer-Emmett-Teller (BET) surface area of from about 750 m.sup.2/g to about 2900 m.sup.2/g and a micropore volume of from about 0.50 cm.sup.3/g to about 1.2 cm.sup.3/g.
Claims
1. A soyhull-based activated carbon, comprising a Brunauer-Emmett-Teller (BET) surface area of from about 750 m.sup.2/g to about 2900 m.sup.2/g and a micropore volume of from about 0.50 cm.sup.3/g to about 1.2 cm.sup.3/g.
2. The soyhull-based activated carbon of claim 1, further comprising an overall positive surface charge as measured by the pH of point of zero charges (pH.sub.PZC) of at least about 7.0.
3. The soyhull-based activated carbon of claim 1, further comprising an overall positive charge as measured by the pH.sub.PZC of from about 8.5 to about 10.4.
4. The soyhull-based activated carbon of claim 1, wherein the Brunauer-Emmett-Teller (BET) surface area is from about 1790 m.sup.2/g to about 2850 m.sup.2/g.
5. The soyhull-based activated carbon of claim 1, wherein the micropore volume is from about 0.80 cm.sup.3/g to about 1.1 cm.sup.3/g.
6. The soyhull-based activated carbon of claim 1, wherein the mesopore volume is from about 0.20 cm.sup.3/g to about 0.40 cm.sup.3/g.
7. The soyhull-based activated carbon of claim 1, wherein the total pore volume is from about 0.90 cm.sup.3/g to about 1.50 cm.sup.3/g.
8. A method of removing a contaminant from an aqueous medium post-chlorination, the method comprising: contacting the aqueous medium comprising one or more contaminants with a soyhull-based activated carbon; adsorbing the one or more contaminants by the soyhull-based activated carbon, wherein the one or contaminants are adsorbed by the soyhull-based activated carbon at an adsorption rate of greater than about 75% in about 90 minutes in the aqueous medium comprising at least about 5 mg/L of total organic carbon.
9. The method of claim 8, wherein the contaminant comprises a cyanobacteria-derived metabolite.
10. The method of claim 8, wherein the contaminant comprises a small molecule.
11. The method of claim 8, wherein the aqueous medium is selected from distilled, deionized, or natural waters.
12. The method of claim 8, wherein the contaminant comprises a molecular weight of less than about 500 g/mol.
13. The method of claim 8, wherein the cyanobacteria-derived metabolite comprises 2-Methylisoborneol (MIB), geosmin, or a combination thereof.
14. The method of claim 10, wherein the small molecule comprises a molecular weight of from about 100 g/mol to about 500 g/mol.
15. A method for forming an activated carbon comprising: carbonizing a soyhull in the absence of oxygen; activating the carbonized soyhull according to physical or chemical activation process, wherein the activation process comprises pyrolyzing the carbonized soyhull at a temperature of about 800° C. or less.
16. The method of claim 15, wherein the method of activating the carbonized soyhull comprises: incubating the carbonized soyhull with a chemical activating agent; and drying the carbonized soyhull mixed with the hydroxide activating agent at a temperature of about 105° C. or greater prior to the step of pyrolyzing the carbonized soyhull, wherein the chemical activating agent and carbonized soyhull are incubated at a weight ratio of from about 1:1 to about 6:1.
17. The method of claim 16, wherein the chemical activating agent is a hydroxide activating agent.
18. The method of claim 17, wherein the hydroxide activating agent comprises potassium hydroxide, lithium hydroxide, sodium hydroxide, cesium hydroxide, rubidium hydroxide, or a combination thereof.
19. The method of claim 16, wherein incubating the soyhull with a chemical activating agent is carried out for about 6 hours or greater.
20. The method of claim 15, wherein the carbonized soyhull is pyrolyzed at a temperature of from about 700° C. to about 900° C.
21. The method of claim 15, wherein the carbonization is carried out for a time period of about one hour or more in the absence of oxygen.
22. The method of claim 15, wherein the carbonized soyhull is pyrolyzed in the presence of steam.
23. The method of claim 15, further comprising incubating and carbonizing the soyhull in a one-step process.
Description
BRIEF DESCRIPTION OF THE FIGURES
[0010] A full and enabling disclosure of the present subject matter, including the best mode thereof to one of ordinary skill in the art, is set forth more particularly in the remainder of the specification, including reference to the accompanying figures in which:
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DETAILED DESCRIPTION
[0072] Repeat use of reference characters in the present specification and drawings is intended to represent the same or analogous features or elements of the present disclosure.
[0073] Reference will now be made in detail to various embodiments of the disclosed subject matter, one or more examples of which are set forth below. Each embodiment is provided by way of explanation of the subject matter, not limitation thereof. In fact, it will be apparent to those skilled in the art that various modifications and variations may be made in the present disclosure without departing from the scope or spirit of the subject matter. For instance, features illustrated or described as part of one embodiment may be used in another embodiment to yield a still further embodiment.
[0074] In general, the present disclosure is directed to materials and methods for forming activated carbons through the low temperature activation of soyhull for the removal of contaminants from an aqueous medium and activated carbons formed according to the methods. Previously, it was believed that mesopore volume was pivotal to increase adsorption kinetics as they provide diffusion pathways to micropores. It was understood that without sufficient mesopore volume, diffusion into the micropores would be slow. Surprisingly, activated carbons disclosed herein have a high proportion of microporosity on the surface of the activated carbons and exhibit faster adsorption kinetics of T&O compounds compared to commercial powdered activated carbons. Without wishing to be bound to any particular theory, it is believed that the high proportion of total pores combined with the large concentration of micropores near the surface of the activated carbons provides the unexpected and improved adsorption kinetics of disclosed materials. In particular, it is understood that pore width of activated carbon affects the organic compound adsorption, and that the adsorption strength increases with decreasing pore width as contact points between the organic compound and activated carbon surface area increase.
[0075] According to the present disclosure, raw soyhulls may be utilized herein to form the activated carbon. Beneficially, in some embodiments, the raw soyhulls utilized herein need not be subjected to any washing and/or pretreatment prior to carbonization. However, in some embodiments, the raw soyhulls may be granulated prior to carbonization. For instance, the raw soyhulls may be pulverized and/or crushed to a desired particle size of less than about 10 millimeters (mm). Beneficially, disclosed formation methods do not require the addition of a binder to the granulated starting materials, and upon any desired sizing of the starting materials, the materials can be directly carbonized and activated.
[0076] Following any granulation, the starting materials can be carbonized. The term “carbonization” or “carbonizing” generally refers to heat treatment of an organic substance in an oxygen deprived atmosphere to form a carbon char. This heat treatment may occur under an atmosphere of, but not limited to, argon, nitrogen, helium, hydrogen, steam, or any combination thereof that can generally flow over the materials during processing to remove a considerable portion of oxygen surface functionalities on the materials. In one embodiment, the raw soyhulls may undergo carbonization in an argon atmosphere tube furnace at about 500° C. using a 10° C./min ramp-up rate for about 1 hour. Argon gas flow may be utilized to remove a considerable portion of oxygen surface functionalities on the carbon-based material and decrease the surface acidity.
[0077] Heat treatment may also lead to structural changes in the carbon-based starting materials. For example, heat treatment may lead to decreases in surface area and pore volume as well as changes to the pore size distribution. Such structural changes may be observed following heat treatment of the soyhull-based starting carbon materials.
[0078] According to the present disclosure, the carbonized materials may be activated utilizing a physical or chemical activation. For instance, the carbonized soyhulls may be physically activated (e.g., thermal activation) using steam and/or carbon dioxide. The carbonized material may be contacted with steam at a pyrolysis temperature of from about 700° C. to about 900° C., such as from about 750° C. to about 850° C., or any range therebetween.
[0079] In one embodiment, the carbonized soyhulls may be activated according to a chemical activation approach. In such an embodiment, the carbonized materials may be mixed with a chemical activating agent. The chemical activating agent may include, but is not limited to, a hydroxide activating agent such as potassium hydroxide (KOH), lithium hydroxide, sodium hydroxide, cesium hydroxide, rubidium hydroxide, or a combination thereof. In another embodiment, the chemical activating agent may include, but is not limited to, potassium carbonate (K.sub.2CO.sub.3). In yet another embodiment, phosphoric acid (H.sub.3PO.sub.4) can be added to the organic material and carbonized/activated in a one-step thermal process.
[0080] Regardless of the chemical activating agent utilized, the mixture can include a larger amount of the chemical activation agent by weight than the weight of the carbonized soyhull. For instance, the weight ratio of chemical activating agent to carbonized soyhulls can be from about 1:1 to about 6:1, such as 2:1 to about 4:1, or any range therebetween. The carbonized soyhulls and chemical activating agent mixture can be incubated at room temperature for about 6 hours. In some embodiments, following the incubation period, the carbonized soyhulls and chemical activating agent mixture can be dried overnight in a box furnace at 105° C. prior to activation.
[0081] The carbonized mixture may be heated up to a pyrolysis temperature for carbon activation. While the pyrolysis temperature is traditionally about 950° C. or greater, the pyrolysis temperature disclosed herein can be lower. For instance, the carbonized mixture may be heated to a pyrolysis temperature of from about 700° C. to about 900° C., such as from about 750° C. to about 850° C., such as from about 700° C. to about 800° C., or any range therebetween. The produced activated carbon of soyhulls with a chemical activating agent may be washed with water or a dilute acid to remove undesired materials, e.g., potassium salts or the like.
[0082] Combination of a thermal activation and a chemical activation approach may optionally be utilized. The activated carbon product may be a powdered activated carbon (PAC) or a granular activated carbon (GAC). For instance, the activated carbon product may be sieved to obtain a particle size from about 50 .Math.m to about 80 .Math.m, such as from about 55 .Math.m to about 75 .Math.m, or any range therebetween.
[0083] Independent of the activation method, the activated carbon formed according to methods disclosed herein may be utilized, in one embodiment, to remove contaminants from an aqueous medium.
[0084] The pore structure of the activated carbon produced herein may be divided into micropores (<20 Å), mesopores (20-500 Å), and macropores (>500 Å).
[0085] As utilized herein, the term “microporosity” refers to that portion of the surface area of an activated carbon distributed in pores, each having an average cross-sectional dimension of less than ABOUT 20 Å. In one embodiment, an activated carbon, as disclosed herein, may have a microporosity of from about 0.7 cm.sup.3/g to about 1.5 cm.sup.3/g, such as from about 0.8 cm.sup.3/g to about 1.25 cm.sup.3/g, such as from about 0.9 cm.sup.3/g to about 1.1 cm.sup.3/g, or any range therebetween.
[0086] As utilized herein, the term “mesoporosity” refers to that portion of the surface area of an activated carbon that is distributed in pores each having an average cross-sectional dimension of from about 20 Å to about 500 Å. In one embodiment, an activated carbon disclosed herein may have a mesoporosity of from about 0.20 cm.sup.3/g to about 0.40 cm.sup.3/g, such as from about 0.25 cm.sup.3/g to about 0.35 cm.sup.3/g, or any range therebetween.
[0087] In one embodiment, the activated carbon may be characterized by its BET surface area. The term “BET surface area” refers to the Brunauer-Emmett-Teller (BET) equation used to calculate surface area based on the analysis of a nitrogen adsorption isotherm at 77.5 K. In one embodiment, the activated carbon disclosed herein may be characterized by a BET surface area of from about 1750 m.sup.2/g to about 3000 m.sup.2/g, or any range therebetween.
[0088] In one embodiment, the activated carbon may be characterized by its pore size distribution based on the analysis of a nitrogen adsorption isotherm at 77.5 K. For example, Density Functional Theory (DFT) may be applied to determine the pore size distribution of PAC from the nitrogen isotherms. The distribution of pores may be determined by associating pore widths less than 20 Å as micropores, pores in the range of 20 Å - 500 Å as mesopores, and those at 500 Å or larger as macropores.
[0089] In one embodiment, the activated carbon may be characterized by its total pore volume. The total pore volume may be calculated from the adsorbed volume of gas near the saturation point (P/P.sub.0 = 0.98). In one embodiment, the total pore volume of an activated carbon may be calculated from the adsorbed volume of nitrogen near the saturation point (P/P.sub.0 = 0.98). Micropore volume may be calculated using Dubinin-Radushkevich (DR) equation in the relative pressure range of 10.sup.-5 to 10.sup.-1. By subtracting micropore volume from the total volume, total meso- and macropore volume (Vmes + Vmac) can be determined. Reproducibility of measurements can be determined from triplicate data of randomly selected samples. In one embodiment, the activated carbon may have a total pore volume of from about 0.90 cm.sup.3/g to about 1.50 cm.sup.3/g, such as from about 0.95 cm.sup.3/g to about 1.45 cm.sup.3/g, such as from about 1.0 cm.sup.3/g to about 1.30 cm.sup.3/g, or any range therebetween.
[0090] Activated carbons produced from soyhulls, as disclosed herein, may be utilized in one embodiment in removal of contaminants from an aqueous medium. In one embodiment, an aqueous medium may be characterized as a water source comprising natural waters. The term “natural organic matter” (NOM) refers to organic compounds that are ubiquitous in various water sources (e.g., surface or ground waters) that result from decomposition of litter materials, leaves, or other organics, as well as algal (e.g., lysis, extra- and intracellular) activities. Water sources may be compared based on their differences in NOM characteristics as indicated by their SUVA.sub.254 (UV.sub.254/DOC) values. Water sources may include, but are not limited to, raw waters collected from a lake and a river intake (which serve as water sources of drinking water treatment plants) and treated water (e.g., after chlorination, coagulation, flocculation, and sedimentation).
[0091] Contaminants that are resistant to commonly used oxidants may be present in water sources’ post-conventional clarification processes. In one embodiment, such a contaminant may be removed from a water source using an activated carbon, as disclosed. The expression “T&O compounds” refers to compounds of natural or anthropogenic origin that may result in taste and order problems in water. In one embodiment, the contaminant comprises a cyanobacteria-derived metabolite characterized as a T&O compound. Cyanobacteria refers to oxygen-producing photosynthetic microorganisms. Nearly 3-3.5 billion years ago, cyanobacteria started to produce oxygen as a byproduct. They have had a significant impact on transforming the Earth’s atmosphere and climate by releasing oxygen. Cyanobacteria have adapted to almost every environment on the planet, including marine and freshwater sources. Nutrients (nitrogen and phosphorus) typically enhance the growth and abundance of cyanobacteria in water bodies, and due to the overuse of fertilizers, inadequate wastewater treatment, etc., lakes and rivers are rich in such nutrients. Global warming, as well as the associated reduced water quality, cause an increase in cyanobacteria growth as high temperatures favor cyanobacterial growth. For example, many bloom-forming cyanobacteria reach their maximal growth at high temperatures (i.e., often above 25° C.). Therefore, cyanobacteria can become abundant in an aquatic environment resulting in blooms during warmer months. T&O compounds, MIB, and geosmin are synthesized during cyanobacteria’s growth phase and released during the biological decomposition. Moreover, cyanobacteria can release T&O compounds even though they do not form blooms. Accordingly, a water source may contain a cyanobacteria-derived metabolite post-chlorination that is characterized by having a molecular weight of about 150 g/mol to about 185 g/mol, such as from about 160 g/mol to about 175 g/mol, or any range therebetween. For example, a cyanobacteria-derived metabolite to be removed from water according to disclosed methods may be MIB (168.3 g/mol) or geosmin (182.3 g/mol).
[0092] In one embodiment, activated carbons disclosed herein can successfully remove a contaminant, such as a small molecule, from a water source. “Small molecule” as used herein is characterized by having a molecular weight from about 100 g/mol to about 500 g/mol, such as from about 150 g/mol to about 400 g/mol, such as from about 250 g/mol to about 350 g/mol, or any range therebetween. In one embodiment, a water source may contain a small molecule present post-chlorination having a molecular weight of from about 160 g/mol to about 185 g/mol.
[0093] According to one embodiment of the present disclosure, activated carbons disclosed herein exhibit improved affinity for T&O compounds. One aspect of the disclosure is directed to methods for developing the beneficial combination of physical and chemical characteristics in activated carbon materials so as to improve the adsorption characteristics of the activated carbon for T&O compounds. In particular, improved adsorption of activated carbon may be attained through the development and formation of activated carbons produced from soyhulls, as disclosed herein.
[0094] In one embodiment, the PAC can exhibit a porosity that can provide an affinity of the activated carbon for T&O compounds. For instance, the activated carbon can exhibit a microporosity, mesoporosity, total porosity, and combinations thereof, which can provide a high affinity for T&O compounds.
[0095] In one embodiment, the T&O compounds may be adsorbed by the soyhull-based activated carbon at an adsorption rate of greater than about 75% in about 90 minutes in the aqueous medium comprising at least about 5 mg/L of total organic carbon, such as greater than about 80% in about 90 minutes, such as greater than about 85% in about 90 minutes, or any range therebetween.
[0096] Depending on the water source and compound being adsorbed, activated soyhull-based carbons disclosed herein have an adsorbance capacity of from about 0.5 ng/mL to about 45 ng/mL, such as from about 2 ng/mL to about 35 ng/mL, such as from about 5 ng/mL to about 30 ng/mL, such as from about 10 ng/mL to about 25 ng/mL, or any range therebetween in the presence of a natural organic matter (NOM).
[0097] The present disclosure may be better understood with reference to the Examples set forth below.
EXAMPLES
Materials and Methods
Activated Carbons
[0098] Raw soyhulls were provided from Archer Daniel Midland Company and used without washing or pretreatment. After crushing to a particle size of a few millimeters, raw materials were initially carbonized for one hour at 500° C. (OTF 1500X from MTI) in the absence of oxygen under 100 standard cubic centimeters per minute (sccm) of argon gas flow. Carbonization was followed by chemical impregnation with KOH (4:1 by mass) in 20 mL of DDW for six hours and drying overnight in a furnace at 105° C. Then, the dried mixture was activated at 750° C. for one hour. According to the results obtained during the research period, modifications were made to the method applied, and four different batches of activated carbons were produced. They are denoted as SH1, SH2, SH3, and SH4 throughout the study. Specifically, SH4 had a longer cooling time which resulted in the best characteristics among the soyhull-based and studied PACs in terms of BET surface area and micropore volume, after activation in the furnace. Four commercially available activated carbons, Calgon Carbon™ WPL® (bituminous coal-based), Calgon Carbon™ FILTRASORB® (FILTRASORB®) (bituminous coal-based), Westvaco™ AquaNuchar® (wood-based), and NORIT® 20B (bituminous coal-based) were also used for comparison with the activated soyhull-based activated carbons.
[0099] Since the products and commercial PACs have various particles sizes, larger particles were crushed, and ground PACs were sieved with a Micro Sieve Shaker kit to obtain a 50-70 .Math.m particle size range. Then, the PACs were rinsed in a glass container with DDW, dried in an oven at 105° C. for 24 hours, cooled to room temperature, and stored in a desiccator until characterization and adsorption tests. Nitrogen adsorption at 77.5 K was performed with a physisorption analyzer (Micromeritics® ASAP® 2020) to determine BET surface area, pore volume, and pore size distributions of PACs. DFT model was used to determine the pore size distribution of PAC from the nitrogen isotherms. PAC surface chemistry was characterized with the pH of point of zero charges (pH.sub.PZC) determination based on a pH equilibrium method. For pH.sub.PZC test, 20 mL solutions were prepared using 0.1 M NaCl, and HCI or NaOH was added to reach different initial pH values (2, 4, 6, 8, 10, and 12). To obtain 5 g-PAC contents in one liter, 100 mg PACs were added to the solutions. After 24 hours, pH.sub.PZC of PAC was determined by measuring the final pH of each solution.
[0100] Scanning electron microscopy (SEM) imaging analyses were performed to obtain the surface morphology, topography, and microstructure analysis of adsorbents. SEM images were obtained using Hitachi™ SU9000 ultra-high resolution scanning electron microscope. Hitachi™ SU9000 has a resolution of 0.4 nm at 30 kV, and it is currently considered one of the highest resolution SEMs available in the market. SEM sample preparation was performed by mounting specimen on 4 mm x 10 mm mounts using double-sided adhesive carbon tape. The surfaces of the specimen were cleaned for 10 minutes using a vacuum UV cleaner before imaging to remove surface contaminants. Despite the Hitachi™ SU9000 being a high vacuum Field Emission (FE)-SEM, no specimen precoating of conducting layer was applied to image sample surfaces, leaving them in as-is condition. The microscope was operated at an acceleration voltage of 15 kV and a filament emission current of 10 mA. Images were captured using a secondary electron in a lens detector at x100,000, x500,000, x1000,000, and x2,000,000 magnification. (
MIB and Geosmin Analyses
[0101] MIB and geosmin were purchased from FUJIFILM™ Wako Pure Chemicals USA Corporation in powder form. Each primary dilution solution with 4 mg L-1 concentration was prepared separately by mixing a pre-determined amount of powders with DDW (resistivity ≥ 18 mΩ cm). The primary dilution solution was kept in the refrigerator at 4° C. MIB and geosmin were analyzed by using headspace solid-phase microextraction gas chromatography/mass spectrometry (SPME-GC/MS/MS). An Agilent™ 7890B Gas Chromatograph coupled to an Agilent™ 7000C Triple Quadrupole Mass Spectrometer was used for MIB and geosmin quantification analysis. All extractions were performed using a PAL automated SPME system with a 50/30 .Math.m Divinylbenzene/Carboxen®/Polydimethylsiloxane (DVB/CAR/PDMA) fiber assembly (Supelco®). The minimum reporting levels for MIB and geosmin were 1 ng L.sup.-1. (
Surface Water Samples
[0102] Based on the difference in NOM characteristics as indicated by their SUVA.sub.254 (UV.sub.254/DOC) values, three types of waters were used for tests: 1) raw water collected from a lake; 2) raw water collected from a river intake (e.g., both of which serve as water sources of drinking water treatment); and 3) treated water (e.g., after coagulation, flocculation, and sedimentation) from the same water treatment plant stated above. After collection, samples were filtered with Whatman® Polycap TC Filters (0.2 .Math.m pore size) and stored at 4° C. in the dark to minimize biological activity. DOC concentrations were measured using a Shimadzu™ TOC-VCSH high-temperature combustion analyzer with minimum reporting levels of 0.1 mg L.sup.-1. UV absorbance at 254 nm measurement was performed using a Varian Cary® 50 spectrophotometer with a 1-cm path length quartz cell. To test the effect of NOM size (different SUVA.sub.254 values [1.3 to 4.0 L mg-m.sup.-.sup.1]), waters were diluted as needed to obtain comparable initial DOC content (2.5±0.5 mg L.sup.-1). Selected characteristics of the surface waters used in the experiments are shown in Table 1.
TABLE-US-00001 Parameters Units Treated River Water (diluted) Raw River Water (diluted) Raw Surface Water pH - 7.3 7.2 6.9 Dissolved Organic Carbon (mg L.sup.-1) 2.75 2.10 2.00 UV.sub.254 (cm.sup.-1) 0.049 0.084 0.026 SUVA.sub.254 L (mg-m).sup.-1 1.80 4.00 1.30
Adsorption Kinetics Tests
[0103] MIB and geosmin adsorption kinetics experiments were conducted in DDW and selected natural waters. For DDW tests, amber glass bottles of 60 mL containing 1.2 mg (equivalent to 20 mg L.sup.-1) PAC were filled slowly with DDW (pH = 7.0±0.1) containing 100 ng L.sup.-1 MIB and geosmin each. After filling, bottles (headspace free) were shaken for various contact times for 5, 15, 30, 60, 90, 120, and 240 minutes on an orbital shaker at room temperature, and no buffer was used. At the end of each contact time, samples were filtered through a pre-washed Supor® 0.45 .Math.m polyethersulfone polymer membrane filter and collected in 40 mL amber bottles with headspace free and extracted immediately and analyzed for MIB and geosmin as indicated before. In addition to DDW tests, following the same methodology, similar adsorption kinetic tests were conducted in different water sources (i.e., two surface waters and one treated water as stated above). Adsorption Isotherm Tests
[0104] Adsorption isotherm experiments were conducted to compare the adsorption equilibrium capacities of PACs in both DDW and natural waters. The initial MIB and geosmin concentrations each were adjusted for each water sample and various PAC dosages were tested from 1 mg-PAC L.sup.-1 to 50 mg-PAC L.sup.-1. (
[0105] The isotherms results were modeled using the Freundlich isotherm equation:
in which, [0106] q.sub.e is equilibrium solid phase concentration (ng mg.sup.-1), [0107] Ce is liquid-phase concentrations (ng L.sup.-1), [0108] K.sub.f is Freundlich isotherm constant ng mg.sup.-1, which is an indicator of adsorption [0109] capacity, and [0110] n is empirical constant, L ng.sup.-1, n.sup.-1 a measure of the intensity of adsorption.
Example 1
Characterizations of Activated Carbons
[0111] The BET surface area, micropore, mesopore, and total pore volume, DFT pore volume distribution, pH.sub.PZC, and source material of the PACs are provided in Table 2. The BET surface areas of soyhull-based PACs were higher than the commercial PACs. For instance, the BET surface area of SH4 was 2,844 m.sup.2 g.sup.-1, while Calgon Carbon™ WPL®, Calgon Carbon™ FILTRASORB®, and NORIT® 20B had similar surface areas around 1,000 m.sup.2 g.sup.-1. The AquaNuchar®, with 1,703 m.sup.2 g.sup.-1, had the highest surface area among the commercial PACs tested.
[0112] The micropore volumes (width (w) < 20 Å) of the soyhull PACs were in the range of 0.71 to 1.09 cm.sup.3 g.sup.-1, whereas the micropore volumes of commercial PACs were around 0.30 cm.sup.3 g.sup.-1. The micropore volume can play a significant role in removing MIB and geosmin. Adsorption increases with decreasing pore width because adsorption potentials between pore walls and target molecules start to overlay when the pore width is close to the molecular diameters of target compounds. However, in addition to micropore volume, the distribution of pores is also important. For instance, any micropore volume smaller than 6 Å will generally not be accessible to T&O compounds because the molecular diameters of MIB and geosmin are around 6 Å. (
[0113] The mesopore and total pore volumes are also listed in Table 2. The mesopore volume can enable rapid access to adsorption sites. The soyhull-based PACs had very similar mesopore volumes for SH1, SH2, and SH3, (~0.2 cm.sup.3 g.sup.-1), except for the largest surface area sample (SH4: 0.36 cm.sup.3 g.sup.-1). NORIT® 20B and Calgon Carbon™ FILTRASORB® had a very small amount of mesopores (<0.1 cm.sup.3 g.sup.-1), whereas AquaNuchar® had the highest mesopore volume (0.95 cm.sup.3 g.sup.-1) among all studied PACs. In addition, characterization results of commercial PACs were compared with the values reported for the same PACs in literature.
TABLE-US-00002 BET m.sup.2 g-1 DFT V.sub.micro (cm.sup.3 g.sup.-1) DFT V.sub.meso +macro (cm.sup.3 g.sup.-1) V.sub.total (cm.sup.3 g.sup.-1) (P Po.sup.-1=0.98) pH.sub.PZC Material Type SH1 1,796 0.72 0.20 0.96 8.5 Soyhull SH2 2,121 0.78 0.23 1.06 9.0 Soyhull SH3 1,835 0.72 0.21 0.93 10.3 Soyhull SH4 2,844 1.09 0.36 1.46 10.4 Soyhull Calgon Carbon™ WPL® 964 0.35 0.36 0.71 5.6 Bituminous Coal AquaNuchar® 1,703 0.32 0.95 1.48 6.5 Wood Calgon Carbon™ FILTRASORB® 1,070 0.29 0.07 0.54 7.8 Bituminous Coal NORIT® 20B 918 0.31 0.06 0.45 9.5 Bituminous Coal Brunauer-Emmett-Teller surface area, Density Functional Theory model
TABLE-US-00003 DFT pore volume cm.sup.3 g.sup.-1 <7 Å >7-10 Å >10-14 Å >14-20 Å >10-20 Å >20-50 Å >50 Å SH1 0.24 0.11 0.26 0.11 0.37 0.12 0.08 SH2 0.11 0.09 0.38 0.21 0.59 0.17 0.06 SH3 0.17 0.08 0.30 0.17 0.47 0.16 0.05 SH4 0.25 0.11 0.45 0.28 0.73 0.30 0.05 Calgon Carbon™ WPL 0.12 0.04 0.13 0.06 0.19 0.11 0.25 AquaNuchar® 0.08 0.00 0.19 0.04 0.23 0.56 0.39 Calgon Carbon™ FILTRASORB® 0.00 0.13 0.07 0.08 0.15 0.04 0.02 NORIT® 20B 0.04 0.15 0.06 0.05 0.11 0.01 0.05
[0114] For further examination of the pore structure and surface morphology of the PACs, FE-SEM pictures were obtained (
[0115] The results of PAC pH.sub.PZC experiments showed that soyhull-based PACs have a more basic surface (pH.sub.PZC: 8.5-10.4) than commercial PACs, except NORIT® 20B (
[0116] Overall, the results indicate that because of the chemical activation of the soyhull with KOH, basic carbons (pH.sub.PZC > 9.0) could be produced with relatively high BETs (>2000 m.sup.2 g.sup.-1), both micropores (>0.75 cm.sup.3 g.sup.-1) and mesopores (>0.3 cm.sup.3 g.sup.-1) present together in abundance on the structure.
Example 2
Adsorption Kinetics Tests
[0117] The adsorption kinetics of MIB and geosmin by the commercial and soyhull-based PACs in DDW are presented in
[0118] MIB and geosmin adsorption by Calgon Carbon™ WPL® and AquaNuchar® were considerably faster among the other commercial PACs (for 90-min contact time, ~90% of MIB and ~95% of geosmin were removed by Calgon Carbon™ WPL® and AquaNuchar®) (
[0119] Two commercial activated carbons from DDW experiments showing the fastest removal rates (AquaNuchar® and Calgon Carbon™ WPL®) were selected for comparison with soyhull-based PACs in natural water experiments. (
[0120] For relatively less NOM (DOC = 2.1 mg L.sup.-1) and high SUVA.sub.254 (4.0 L (mg-m).sup.-1) water (diluted river water), the effect of NOM presence on the adsorption of both MIB and geosmin was negligible compared to DDW tests (
[0121] Adsorption kinetics experiments with the raw river water at higher NOM concentration (i.e., 5 mg L.sup.-1 TOC) and high SUVA.sub.254 (i.e., 4.0 L (mg-m).sup.-1) were further conducted. (
[0122] In addition, surface water with a lower SUVA.sub.254 (1.3 L (mg-m).sup.-1) and low NOM content (DOC: 2.00 mg L.sup.-1) was also used in the adsorption kinetics tests. These characteristics did not appear to make a significant difference in the adsorption of both MIB and geosmin by commercial- and soyhull-based PACs. (
[0123] DOC and UV.sub.254 analyses were also conducted before and after adsorption during the kinetic tests to examine adsorption of NOM. (
[0124] Overall, these results suggest two different impacts exerted by NOM molecules according to their size (i.e., low, or high molecular weight). High molecular weight NOM molecules decreased the removal efficiency by pore blockage or hindrance mechanism since PACs did not adsorb considerable amounts of NOM (raw water;
Example 3
Adsorption Isotherm Tests
[0125]
Example 4
Correlation Between Adsorption Capacity and Pore Size Distribution
[0126] Different pore size regions have been reported as effective to remove MIB and geosmin. For instance, the adsorption capacity of MIB may be related to the micropore volume in the range of 10 to 12 Å in both DDW and surface water. However, a correlation between adsorption capacities of MIB and geosmin and micropore volume in the 10-12 Å pore size region has not been observed. It was concluded that total micropore volume might be a better parameter representing the adsorption capacity for MIB and geosmin. (
TABLE-US-00004 MIB Geosmin K.sub.f n.sup.-1 K.sub.f n.sup.-1 DDW SH4 0.58 1.55 44.35 0.84 SH2 1.01 1.36 34.55 0.69 SH1 0.70 1.34 NR NR FILTRASORB® 6.41 0.55 7.82 0.52 AquaNuchar® 4.58 0.87 25.58 0.81 NORIT® 20B 7.43 0.66 21.44 0.49 Treated Water SH4 31.47 0.31 NR NR SH2 0.87 0.88 NR NR SH1 5.98 0.4 NR NR FILTRASORB® 2.67 0.43 NR NR AquaNuchar® 0.32 0.76 NR NR NORIT® 20B 2.77 0.42 NR NR Calgon Carbon™WPL® 0.001 1.86 NR NR Raw River Water SH2 2.71 0.81 8.53 0.79 SH1 2.47 0.73 4.16 0.83 FILTRASORB® 0.41 0.98 3.84 0.61 AquaNuchar® 0.63 0.79 9.32 0.53 NORIT® 20B 1.96 0.68 3.90 0.67 Calgon Carbon™WPL® 0.15 1.19 9.61 0.64 Surface Water SH4 12.64 0.51 38.99 0.55 SH3 11.17 0.51 19.49 0.63 SH2 1.03 0.98 13.94 0.77 SH1 1.20 0.84 9.68 0.73 FILTRASORB® 1.29 0.7 4.87 0.72 AquaNuchar® 1.96 0.53 19.52 0.52 NORIT® 20B 1.79 0.61 11.64 0.46 Calgon Carbon™WPL® 0.99 0.71 15.64 0.6
where, K.sub.f is Freundlich isotherm constant ng mg.sup.-1, which is an indicator of adsorption capacity, and n is empirical constant, L ng.sup.-1, n.sup.-1 a measure of the intensity of adsorption.
[0127] In this study, different pore size ranges (i.e., 6-12 Å, 9-12 Å, 10-20 Å, 6-50 Å, 10-50 Å, and 10-100 Å) were compared for their adsorption capacities at different equilibrium concentrations. (
TABLE-US-00005 Ce: 50 ng L.sup.-1 MIB-R.sup.2 Geosmin-R.sup.2 Pore width (Å) DDW Treated Water Raw River Water Surface Water DDW Treated Water Raw River Water Surface Water 6-12 0.81 0.79 0.71 0.72 0.85 NR 0.59 0.82 9-12 0.82 0.76 0.54 0.73 0.92 NR 0.66 0.91 10-20 0.82 0.90 0.78 0.76 0.88 NR 0.80 0.94 6-50 0.78 0.66 0.31 0.55 0.86 NR 0.44 0.80 10-50 0.73 0.49 0.15 0.44 0.83 NR 0.36 0.74 10-100 0.59 0.33 0.05 0.30 0.70 NR 0.20 0.57
TABLE-US-00006 Ce: 100 ng L.sup.-1 MIB-R.sup.2 Geosmin-R.sup.2 Pore width (Å) DDW Treated Water Raw River Water Surface Water DDW Treated Water Raw River Water Surface Water 6-12 0.93 0.75 0.65 0.78 0.87 NR 0.64 0.78 9-12 0.93 0.72 0.55 0.80 0.94 NR 0.69 0.87 10-20 0.96 0.79 0.81 0.86 0.84 NR 0.85 0.93 6-50 0.86 0.65 0.30 0.58 0.92 NR 0.43 0.73 10-50 0.75 0.50 0.15 0.47 0.90 NR 0.33 0.67 10-100 0.58 0.35 0.04 0.31 0.79 NR 0.17 0.49
TABLE-US-00007 Ce: 200 ng L.sup.-1 MIB-R.sup.2 Geosmin-R.sup.2 Pore width (Å) DDW Treated Water Raw River Water Surface Water DDW Treated Water Raw River Water Surface Water 6-12 0.93 0.80 0.56 0.77 0.81 NR 0.68 0.70 9-12 0.93 0.79 0.52 0.79 0.87 NR 0.70 0.79 10-20 0.97 0.90 0.81 0.89 0.74 NR 0.88 0.87 6-50 0.84 0.69 0.26 0.57 0.90 NR 0.42 0.63 10-50 0.71 0.54 0.13 0.45 0.88 NR 0.31 0.57 10-100 0.54 0.37 0.03 0.28 0.80 NR 0.16 0.41 Ce is liquid-phase concentrations (ng L.sup.-1)
[0128] In the presence of NOM, correlations have also been examined between the MIB and geosmin adsorption capacity of PACs and their pore volumes in different pore size regions. (
[0129] While certain embodiments of the disclosed subject matter have been described using specific terms, such description is for illustrative purposes only, and it is to be understood that changes and variations may be made without departing from the spirit or scope of the subject matter.