Sorbents for Nutrient Removal from Water

Abstract

A sorbent for nutrient removal, preferably nitrate and phosphate removal, or PFAS removal comprising: a porous carbon structure, and a metal doped into the structure, so the metal cannot be removed from the carbon structure by water. The porous carbon structure may comprise an inexpensive carbon source. The metal may be iron, magnesium, zirconium, or aluminum. Preferably, the sorbent comprises 0.1-20% metal compound by weight. Also, a method for nutrient or PFAS removal from water, the steps comprising: providing a sorbent comprising a porous carbon structure, comprising a metal doped into the structure; flowing a polluted water over the sorbent; and, selectively adsorbing a contaminant from the polluted water with the sorbent.

Claims

1. A sorbent for nutrient removal from water, comprising: a) a porous activated carbon structure having a surface area greater than 100 m.sup.2/g; and, b) a metal ion or a mixture of metal ions incorporated into the porous carbon structure; wherein, the metal ion or the mixture of metal ions cannot be removed from the porous carbon structure by water; wherein, the sorbent comprises 0.2-24 atom % metal as measured by XPS, wherein, the sorbent selectively removes at least one nutrient from water.

2. The sorbent as in claim 1, wherein the at least one nutrient is selected from the group consisting: nitrate and phosphate.

3. The sorbent as in claim 1, wherein the porous activated carbon structure may be derived from sugar, cornstarch, coconut shells, coal or wood, as well as other similar inexpensive carbon sources.

4. The sorbent as in claim 1, wherein the metal ion or the mixture of metal ions comprises at least one metal from the group consisting: iron, zinc, magnesium, zirconium, and aluminum.

5. The sorbent as in claim 4, wherein the metal ion or the mixture of metal ions comprises iron, zirconium, or aluminum, or zinc.

6. The sorbent as in claim 4, wherein the metal ion or the mixture of metal ions derive from a metal compound or a mixture of metal compounds, and wherein the sorbent comprises 0.1-20% metal compound or mixture of metal compounds by weight.

7. The sorbent as in claim 6, wherein the sorbent comprises 3-10% metal compound or mixture of metal compounds by weight.

8. The sorbent as in claim 7, wherein the sorbent comprises 4.5-5.5% metal compound or mixture of metal compounds by weight.

9. The sorbent as in claim 6, wherein the metal compound or the mixture of metal compounds is selected from the following: ferric chloride, ferrous chloride, ferrous sulfate, ferric sulfate, iron oxide, iron hydroxide, aluminum chloride, aluminum oxide, aluminum hydroxide, zirconium chloride, zirconium oxide, zirconium hydroxide, zinc oxide, zinc hydroxide, magnesium oxide, magnesium hydroxide.

10. A method for contaminant removal from water, the steps comprising: a) providing a sorbent comprising a porous carbon structure with a metal compound or a mixture of metal compounds incorporated into the porous carbon structure, wherein the metal or the mixture of metals cannot be removed from the porous carbon structure with water, and wherein the porous carbon structure has a surface area greater than 100 m.sup.2/g; b) flowing a polluted water over the sorbent; and, c) selectively adsorbing a contaminant from the polluted water with the sorbent.

11. The method as in claim 10, wherein the contaminant is nitrate or nitrogen.

12. The method as in claim 10, wherein the contaminant is phosphate or phosphorus.

13. The method as in claim 10, wherein the contaminant is PFAS.

14. The method as in claim 9, wherein the metal ion or mixture of metal ions comprises at least one metal ion selected from the group consisting: iron, zinc, magnesium, zirconium, and aluminum.

15. The method as in claim 9, wherein the polluted water is 40 ml of polluted water, and wherein step c) comprises reducing 10 ppm inorganic nitrogen by at least 45%, reducing 50 ppm total nitrogen by at least 20%, and reducing 30 ppm phosphorus by at least 35%.

16. The method as in claim 15, wherein step c) comprises reducing 10 ppm inorganic nitrogen by at least 80%, reducing 50 ppm total nitrogen by at least 20%, and reducing 30 ppm phosphorus by at least 40%.

17. A sorbent for nutrient removal from water, comprising: a) a carbon content of at least 80 weight percent; b) a metal ion content of at least 1 weight percent; c) a chlorine content of at least 0.5 weight percent; and, d) a BET surface area of at least 100 m.sup.2/g.

18. The sorbent as in claim 17, wherein the sorbent comprises a BET surface area of at least 800 m.sup.2/g.

19. The sorbent as in claim 17, wherein the sorbent selectively removes at least nitrates or phosphates from water.

20. The sorbent as in claim 17, wherein the metal ion derives from one of the following: ferric chloride, ferrous chloride, ferrous sulfate, ferric sulfate, iron oxide, iron hydroxide, aluminum chloride, aluminum oxide, aluminum hydroxide, zirconium chloride, zirconium oxide, zirconium hydroxide, zinc oxide, zinc hydroxide, magnesium oxide, magnesium hydroxide.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0022] FIG. 1: Breakthrough curves for PFAS compounds.

DETAILED DESCRIPTION OF THE INVENTION

[0023] In the detailed description and throughout the claims, all terms are given their technical meaning unless defined otherwise.

[0024] Although the present disclosure has been described in considerable detail with reference to certain preferred versions thereof, other versions are possible. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred versions contained herein, except where required by 35 U.S.C. 112, i 6 or 35 U.S.C. 112(f).

[0025] All the features in this specification (including any accompanying claims, abstract, and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed in one example only of a generic series of equivalent of similar features. Any element in a claim that does not explicitly state means for performing a specified function, or step for performing a specific function, is not to be interpreted as a means or step clause as specified in 35 U.S.C. 112, i 6 or 35 U.S.C. 112(f). Any element in a claim that does explicitly state means for performing a specified function, or step for performing a specific function, is to be interpreted as a means or step clause as specified in 35 U.S.C. 112, i 6 or 35 U.S.C. 112(f).

[0026] The present disclosure provides inexpensive alternatives to current water decontamination methods (ion exchange, reverse osmosis, and distillation). We provide activated carbon sorbents doped with metal (i.e., iron, aluminum, zirconium) that overcome the deficiencies in the prior art (inexpensive, efficient, comply with EPA standards) and removes nitrates and phosphates from water. Activated carbon, a versatile adsorbent, is derived from various carbonaceous precursors through processes like carbonization and activation. Common precursors include lignocellulosic biomass, agricultural waste, and other carbon-rich materials. These precursors can be obtained from various sources, including sugar, cornstarch, peet, coconut shell, wood and coal.

[0027] To further improve the removal of nitrates and phosphates, the activated carbons may be doped with metals such as iron, magnesium, aluminum, zirconium, zinc and the like. The metal doped samples may be prepared in the form of metal halides, oxides, sulfates, and hydroxides on highly porous carbons (surface area >100 m.sup.2/g, preferably >800 m.sup.2/g, optionally >935 m.sup.2/g or >1000 m.sup.2/g). Examples are provided herein of carbons impregnated with iron (II), iron (III), aluminum, zirconium containing compounds, and mixtures of metals. The sample formulations for examples in this disclosure are provided in Table 1. The BET surface areas (SA) and pore volumes for the sample formulations are shown in Table 2 (TPV=total pore volume MPV=micropore volume). The carbon sorbents of the present disclosure efficiently remove nitrate, phosphate, PFAS, and other anionic contaminants from water via adsorption by Lewis acid-base functional groups incorporated into the porous carbon structure.

TABLE-US-00001 TABLE 1 Sorbent formulations. Lot Carbon Metal Sample# # Source Additive 1 Ref Calgon OVC none 2 1605-89C Calgon OVC 3.4% Al.sub.2O.sub.3 3 90624 Calgon OVC 3.5% FeCl.sub.3 4 Ref Calgon F400 none 5 1605-50D-1 Calgon F400 1% Al.sub.2O.sub.3 6 1605-83B Calgon F400 5% Al.sub.2O.sub.3 7 1605-50A-1 Calgon F400 2% ZrO.sub.2 8 1605-84 Calgon F400 3.5% ZrO.sub.2 9 1545-25D Calgon F400 2.3% FeCl.sub.3 10 1545-26B Norit Row 5% FeSO.sub.4 11 1545-27B Norit Row 5% FeCl.sub.2 12 1545-27D Norit Row 5% Fe.sub.2(SO.sub.4).sub.3 13 1605-50C-1 Norit Row 3.5% Al.sub.2O.sub.3 14 061924 Norit Row 3.3% FeCl.sub.2 15 6101-12B Calgon F400 9.6% MgAl(OH).sub.x 16 6101-13B Calgon F400 10% ZnAl(OH).sub.x

TABLE-US-00002 TABLE 2 Surface areas and pore volumes of sorbents. BET t-plot Lot SA TPV MPV Sample # (m.sup.2/g) (cc/g) (cc/g) 1 Ref 935 0.51 0.41 2 1605-89C 1019 0.51 0.43 3 90624 858 0.47 0.38 4 Ref 873 0.59 0.31 6 1605-83B 936 0.57 0.31 8 1605-84 1012 0.60 0.33 9 1545-25D 817 0.55 0.30 10 1545-26B 1446 0.81 0.46 11 1545-27B 1279 0.72 0.39 12 1545-27D 1231 0.69 0.41 13 1605-50C-1 1138 0.64 0.40 14 061924 1318 0.74 0.44 15 6101-12B 853 0.55 0.30 16 6101-13B 852 0.59 0.28

[0028] The samples were tested for nitrate and phosphate removal, and results in Table 3 show that the metal-doped carbon sorbent presented herein consistently provide superior performance over commercial, non-doped sorbents. In each case, a carbon sample (1.0 g) was contacted with a mixture of 50 ppm of nitrate and 30 ppm of phosphate in 40 ml of tap water for 24 hours. Adding metal compounds for iron, aluminum, zirconium, and mixed metals to porous carbon structures resulted in high nitrate and phosphate removal from water. This demonstrates that modifying the surface of the carbons with Lewis acid-base functional groups efficiently removes anionic contaminants such as nitrate and phosphate from water through electrostatic interactions, hydrophobic interactions, and ion exchange. Other metals or transition metals may be doped into the porous carbon, and other carbon structures may be used. The composition may be effective for removing phosphate and nitrate selectively over other waterborne contaminants that are likely to be in stormwater, which would compete or interfere with nitrate or phosphate adsorption. The composition may be effective at removing nitrates, phosphates, PFAS, and other anionic contaminants.

TABLE-US-00003 TABLE 3 Sorbents tested for nitrate and phosphate removal. Sample % Nitrate Removal % Phosphate Removal 1 72 0 2 100 81 3 89 88 4 81 0 5 88 78 6 95 96 7 79 79 8 68 96 9 100 84 10 90 69 11 82 66 12 90 96 13 84 96 14 100 79 15 72 84 16 88 92

[0029] The present carbon sorbents are also effective in removing PFAS from water. Batch screening tests at realistic concentrations found at contaminated sites were done using a total of 12 ppb of PFAS in tap water, with a liquid to sorbent ratio of 1000:1 and stirred 4 hours at room temperature. Table 4 shows results from batch tests for PFAS removal from drinking water, split into equal amounts of perfluorooctanoic acid (PFOA), perfluorooctanesulfonic acid (PFOS), perfluorononanoic acid (PFNA), hexafluoropropylene oxide dimer acid (HFPO-DA, commonly known as GenX), perfluorohexane sulfonic acid (PFHxS), and perfluorobutane sulfonic acid (PFBS). The present metal doped carbons enhance the PFAS removal efficiency of commercial Calgon carbon (Filtrasorb series F400) (Sample 1) through electrostatic, ion exchange and Lewis acid-base interactions between the carboxylic and sulfonic acid functional groups on the PFAS molecules and the metal additive. Filtrasorb 400 is a granular activated carbon for the removal of dissolved organic compounds from water and wastewater as well as industrial and food processing streamsthe carbons are produced by stream activation of selected grades of bituminous coal that have first been pulverized then agglomerated. These results show that the present metal functionalized carbons are superior to currently used filter media for PFAS removal.

TABLE-US-00004 TABLE 4 Batch tests for PFAS removal from drinking water. Metal % PFOA % PFNA % PFBS % PFHxS % HFPO-DA % PFOS Sample Additive Removal Removal Removal Removal Removal Removal 1 None 83 76 86 82 79 78 6 5% Al.sub.2O.sub.3 95 96 96 96 92 99 7 2% ZrO.sub.2 94 94 95 96 89 95 9 5% FeCl.sub.3 86 82 84 90 86 86

[0030] This disclosure also details the doping of carbons with metal solutions (i.e., FeCl.sub.3, AlCl.sub.3). The resulting material can be used for stormwater remediation, and specifically phosphate and nitrate adsorption. The present carbon-based sorbents are selective for nitrate, phosphate, and/or PFAS removal from water. The metal compound loading on carbon is preferably 0.1-20 wt. %, where the metal may be iron, zirconium, magnesium, zinc or aluminum.

[0031] The typical procedure for iron-doped carbons is as follows: The ferric chloride (FeCl.sub.3) solution is a 2.5% by weight solution. The mass ratio of solution to carbon is 2:1. The carbon is soaked in glass (or plastic) trays, and the trays are heated to 100-150 C. in a convection oven to evaporate the water. A nominal batch includes: 1400 g DI H.sub.2O, 35 g FeCl.sub.3, and 700 g carbon. After drying, excess FeCl.sub.3 is removed from the carbon by washing with tap water until the filtrate is colorless. The product is then dried at 100-150 C. in a convection oven.

[0032] The typical procedure for metal oxide (i.e., alumina, zirconia, mixed) is as follows: The activated carbon is impregnated with an aqueous solution of 5% AlCl.sub.3, then dried at 100 C. for 6 hours in the air. In the next step AlCl.sub.3/AC was treated with an excess of 1N NaOH or KOH to form nanoparticles of aluminum hydroxide as a precipitate on the AC surface and pores, followed by the was with DI water until final pH was neutral. The sorbent was then dried at 100 C. for 6 hours.

[0033] Characterization of the carbons was done via X-Ray Photoelectron Spectroscopy (XPS). To determine the elemental composition on the surface of the carbons, they were analyzed by XPS for carbon, nitrogen, oxygen, chlorine, iron, and aluminum, results are shown in Table 5. As expected, the unmodified carbons (samples 1 and 4) showed no iron or aluminum. The metal doped carbons showed the respective metals ranging from 0.2 to 24.1 atom %. Higher metal content is correlated with lower measured carbon content and may be due to metal residing on the outer surface of the carbon rather than in the porous inner part. Preferably, the metal is well dispersed throughout the pores like in sample 9, where the measured iron content is lower because XPS is only capable of detecting elements on the surface of the sample. This was confirmed by comparing the total amount of iron in the sample by elemental analysis (Table 8) with XPS and the results were comparable, 0.804 wt. % for elemental analysis vs. 0.9 wt % for XPS (after converting 0.2 atom % to weight %).

TABLE-US-00005 TABLE 5 Relative elemental composition of sample surfaces as determined by XPS. C N O Cl Fe Al Sample (Atom %) (Atom %) (Atom %) (Atom %) (Atom %) (Atom %) 1 88.8 8.0 0.2 2 76.2 0.4 17.6 1.5 1.2 3 24.0 0.6 44.9 4.7 24.1 4 90.7 7.9 0.2 6 81.6 0.3 13.4 0.8 3.4 9 87.1 0.5 10.4 0.2 0.2

[0034] The most probable peak assignments for the C species are listed in Table 6. The samples have a peak present that is labeled .fwdarw.*. This represents the presence of graphite like C as this transition only occurs when there is sufficient -bond conjugation to allow for the and * orbitals to form in a large area. This peak was not observed for sample 3, which suggests that other elements present on the surface may have disrupted any -bound conjugation.

TABLE-US-00006 TABLE 6 Relative compositions and most probable peak assignments for carbon species on sample surfaces as determined by XPS, C 1 s region. Carbon CC, CH, CO, CN CO, NC OCO, NCO .fwdarw.* Sample (Atom %) (Atom %) (Atom %) (Atom %) (Atom %) 2 66.3 12.5 6.7 3.6 10.9 3 54.9 28.1 10.3 6.7 6 65.9 11.2 6.5 2.4 14.0 9 64.4 12.4 7.5 2.7 13.0

[0035] The most probable peak assignments for the O species are listed in Table 7. All samples show a mixture of carbon to oxygen single and double bonds. Samples 2 and 6 show single bonding between the aluminum and oxygen atoms. Sample 3 shows single bonds between the oxygen and iron atoms as well as single bonding between oxygen and chlorine. The iron and chlorine content for sample 9 were too low to detect oxygen bonding.

TABLE-US-00007 TABLE 7 Relative compositions and most probable peak assignments for oxygen species on sample surfaces as determined by XPS, O 1 s region. Carbon OC OC Sample (Atom %) (Atom %) OFe OCl OAl 2 37.5 44.3 18.2 3 42.6 18.0 36.0 3.5 6 26.4 64.3 9.3 9 12.8 43.6

[0036] The elemental composition of selected sorbents were determined by elemental microanalysis and Inductively coupled plasma-optical emission spectroscopy (ICP-OES) and compared to the base carbons (Samples 1 and 4) (Table 8). The carbon content is greater than 80% and metal content, Al or Fe depending on the sample is greater than that found for the base materials.

TABLE-US-00008 TABLE 8 Elemental analysis of sorbents. C H N Cl O Fe Al Ash S Sample (wt. %) (wt. %) (wt. %) (wt. %) (wt. %) (wt. %) (wt. %) (wt. %) (wt. %) 1 92.6 0.45 0.18 0.458 4.76 0.006 0.005 1.88 0.129 2 89.6 0.43 0.15 1.17 5.65 0.073 1.34 4.17 0.004 3 82.9 0.39 0.18 1.26 8.07 1.31 0.825 8.32 0.137 4 86.8 0.36 0.44 0.134 3.65 0.183 1.08 8.04 0.711 6 82.7 0.50 0.15 1.17 5.65 0.162 2.31 10.7 0.655 9 86.3 0.33 0.51 0.987 3.71 0.804 1.10 8.47 0.684

Example: PFAS Removal Testing

[0037] Embodiments of the present sorbents were tested in a fixed bed flow system under realistic flow rates and PFAS concentrations. For example, a 2.8% Al.sub.2O.sub.3/Calgon F400 sorbent was heated at 100 C. overnight to drive off adsorbed gases and water and stored in a desiccator. The sorbent was packed into a stainless steel HPLC column. The sorbent was sieved in the size range of 100-325 mesh (44-149 m) and a 1 mL volume was measured out in a small, graduated cylinder and weighed (0.4432 g). The sorbent powder was packed into a stainless steel HPLC column, 0.46 cm ID, 10 cm long. The dead space in the column was packed with glass beads (0.5 mm diameter), and glass wool at both ends. The packed bed volume was measured (0.789 mL).

[0038] Six PFAS compounds (PFOS, PFOA, PFNA, PFBS, PFHxS, HFPO-DA, 2 ppb for each compound) were tested. A HPLC pump was used to pump the feed solution through the column. Deionized water was first flushed through the column in an up-flow configuration to drive out air bubbles and thoroughly wet the sorbent for 16 hours. The adsorption tests were performed in a down-flow configuration.

[0039] The total test ran for 20,000 bed volumes and the average flow rate for the tests was 0.79 mL/min. Sample solutions were collected and shipped to Eurofins for analysis via LC/MS/MS using EPA Method 537 (modified). The breakthrough curve is shown as a function of bed volumes of PFAS solution treated (FIG. 1). Initially, all the PFAS compounds were removed to nondetectable levels (well below EPA MCLs). HFPA-DA broke through first at about 6,000 bed volume, followed by the PFBS at 7,000 bed volumes (lower molecular weight PFAS compounds are the most difficult to remove). The higher molecular weight compounds showed breakthrough times in the range of 14,000-17,000 bed volumes, showing the success of the present sorbents.