COMPOSITE AND METHOD FOR REMOVING DISSOLVED ORGANIC MATTER FROM WATER

Abstract

A process for preparing a granular composite adsorbent, that includes combining poly (diallyl dimethyl ammonium halide) and a clay mineral in water, maintaining the mixture under stirring, recovering a wet mass, forming the wet mass into granules and drying the granules to obtain the granular adsorbent having surface layer with positive zeta potential. The granular material and methods using the granular material in water treatment are also disclosed.

Claims

1. A process for preparing a granular composite adsorbent, comprising combining poly (diallyl dimethyl ammonium halide) and a clay mineral in water, maintaining the mixture under stirring, recovering a wet mass, forming the wet mass into granules and drying the granules to obtain the granular adsorbent having surface layer with positive zeta potential.

2. The process according to claim 1, wherein the clay mineral and polymer are combined in water is in the range from 5:1 to 7:1 (clay:polymer).

3. The process according to claim 1, wherein the polymer and the clay mineral are combined in a controlled manner by slowly adding an aqueous polymer solution to a suspension of the clay mineral in water.

4. The process according claim 1, wherein the clay mineral has cation exchange capacity of not less than 30 milliequivalents/100 g.

5. The process according to claim 4, wherein the clay mineral comprises montmorillonite.

6. The process according to claim 1, wherein the wet mass is recovered by separating a wet solid from the water and adjusting its moisture content in the range from 65 to 75 wt. %.

7. The process according to claim 6, comprising pressing the wet mass through a screen to form granules.

8. The process according to claim 1, wherein drying the granules is by oven drying or freeze drying.

9. The process according to claim 8, wherein the adsorbent consists of granules with an average particle size within the range from 0.3 mm to 2.5 mm.

10. A granular sorbent comprising poly (diallyl dimethyl ammonium halide) and a clay mineral, said granular sorbent having a surface layer with positive zeta potential.

11. The granular sorbent according to claim 10, comprising: from 85 to 93 wt. % of a clay mineral having cation exchange capacity of not less than 30 milliequivalents/100 g; and from 7 to 15 wt. % of poly (diallyl dimethyl ammonium halide).

12. The granular sorbent according to claim 11, comprising: from 88 to 90 wt. % of a clay mineral having cation exchange capacity of not less than 30 milliequivalents/100 g; and from 10 to 12 wt. % of poly (diallyl dimethyl ammonium halide).

13. The granular composite according to claim 10, which is binder-free.

14. A method of water treatment, comprising removing dissolved organic material from water by adsorption onto the granular sorbent defined in claim 10.

15. The method according to claim 14, wherein the adsorption is a fixed-bed adsorption.

16. The method according to claim 14, wherein the dissolved organic material possesses high aromatic content, indicated by the water having SUVA.sub.2.54 value above 2.

17. The method according to claim 14, further comprising regenerating the granular sorbent by rinsing with a salt solution.

18. A method of water treatment, comprising removing dissolved organic material from water by adsorption onto: granular activated carbon; and granular adsorbent comprising poly (diallyl dimethyl ammonium halide) and a clay mineral, said granular adsorbent having a surface positive zeta potential.

19. The method according to claim 18, wherein the adsorption is a fixed-bed adsorption, with the fixed-bed consisting of a mixed granular material in the form of homogeneous blend of GAC and GPDADAMAC-MMT, or with the fixed-bed consisting of a mixed granular material in the form of alternate layers of GAC and GPDADAMAC-MMT.

20. The method according to claim 18, comprising passing the water through an array of fixed-bed adsorption columns connected to operate in series, wherein one or more of said columns is(are) packed with granular activated carbon and one or more of the remaining columns is(are) packed with the granular adsorbent comprising poly (diallyl dimethyl ammonium halide) and a clay mineral, said granular adsorbent having a surface positive zeta potential.

21. The method according to claim 14, wherein the dissolved organic material to be removed from the water comprises anionic and/or cationic pharmaceutical compounds.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0041] FIGS. 1a and 1c show DOM removal percentages plotted against bed volume, measured in filtration experiments of Suwannee River waters through columns packed with GAC or the GPDADMAC-clay of the invention, for virgin and regenerated particles; FIG. 1b illustrates regeneration experiment.

[0042] FIGS. 2a and 2c show DOM removal percentages plotted against bed volume, measured in filtration experiments of lake Kinneret waters through columns packed with GAC or the GPDADMAC-clay of the invention, for virgin and regenerated particles; FIG. 2b illustrates regeneration experiment.

[0043] FIG. 3 is a bar diagram showing the adsorption of five different organic compounds by GAC and granular GPDADMAC-MMT of the invention.

[0044] FIG. 4 shows DOM removal percentages plotted against bed volume, measured in filtration experiments of lake Kinneret waters through columns packed with GPDADMAC-clay, GAC and their blend.

[0045] FIGS. 5a and 5b are bar diagram showing removal percentage of micropollutants (pharmaceutical compounds) from secondary effluent, measured in filtration experiments through columns packed with GAC or GPDADMAC-clay, after six hours (5a) and eighteen hours (5b).

[0046] FIG. 6 shows plots of removal rates versus SUVA, measured for GPDADMAC and GAC.

DETAILED DESCRIPTION

EXAMPLES

[0047] Materials

[0048] Wyoming Na-montmorillonite SWy-3 (MMT) was obtained from the Source Clays Repository of the Clay Mineral Society (Columbia, Mo.). Poly(diallyl dimethyl ammonium chloride) (average M.sub.w 400,000-500,000), gallic acid, humic acid, tannic acid, and octanol were purchased from Sigma Aldrich. Toluene was purchased from Gadot-Group. Suwannee River NOM (2R101N) was obtained from the International Humic Substances Society (IHSS).

[0049] Lake Kinneret waters were obtained from Tiberius filtration plant after undergoing pH adjustment, flocculation with alum and sand filtration prior to filtration by GAC. The GAC used in this study was the virgin GAC (Hydraffin 30N, purchased from Benchmark Lt.) and the regenerated GAC employed in the plant.

[0050] The pH and the conductivity of the water are 7-8 and ˜1300 μS/cm, respectively. Suwannee River water was prepared by adding the solid organic matter to distilled water with sodium chloride and sodium hydroxide to adjust the conductivity and pH to the values of Lake Kinneret.

[0051] Methods

[0052] The UV absorbance of the surface waters was measured at 200-300 nm by UV-Vis spectrophotometer (Thermo Scientific, Evolution 300, Waltham, Mass.). The UV absorption of Lake Kinneret was measured by a 10 cm quartz cuvette due to a very low absorption by a 1 cm cuvette.

[0053] DOC concentrations were determined by a total organic carbon analyzer (Shimadzu, Japan) and by laboratory total organic carbon analyzers (Sievers M5310 C, GE Analytical Instruments, USA).

[0054] Zeta potentials were measured with a Zetasizer Nano series (Malvern Instruments, UK).

[0055] The amount of PDADMAC adsorbed on the MMT was determined by an element analyzer calculated for carbon (FlashEA 1112, Thermo).

[0056] Preparing and testing NMT-PDADMAC granules

[0057] A series of experiments was conducted. The general procedure consists of combining NMT and PDADMAC in water under varying addition rates and mixing ratios, collecting the so-formed composites by filtration, drying in an oven to achieve masses with varying water content, forcing the wet masses through a screen, drying the granulate and sieving. The exact conditions are set out below and tabulated in Table 1.

[0058] PDADMAC was dissolved in distilled water to form 5 g/Liter solution. NMT was added to distilled water to form 5 g/Liter suspension. The PDADMAC solution and NMT suspension were separately stirred for 1-2 hours.

[0059] Next, a vessel equipped with a magnetic stirrer was charged with 10 liter of NMT suspension, followed by addition of the PDADMAC solution via peristaltic pump. The mixture was stirred for four hours, following which the solid was separated by filtration through 15 μm filter paper.

[0060] The wet cake was transferred to an oven (105° C.) and dried to the moisture content tabulated below. The mass was pressed through a mesh with 2.5 mm opening size. The granulate was then placed in an oven for 24 hours to achieve full dryness. The granules were sieved to collect the 0.3-2.5 mm fraction.

[0061] The granules were then tested to assess their 1) mechanical strength (by rubbing the granules between the thumb and finger), 2) stability against disintegration in water (by suspending the granules in tap water) and 3) electrostatic repulsion/attraction profile (by measuring the Zeta potential). The experimental conditions and results are tabulated below.

TABLE-US-00001 TABLE 1 Addition Mois- Mechan- Disinte- clay:polymer rate ture ical gration ζ Ex. weight ratio (ml/min) (%) strength in water potential 1   10:1 10 75 strong NO negative 2  8.3:1 9 55.3 strong NO neutral 3 6.25:1 10 56 weak YES negative 4 6.25:1 20 70 strong NO positive 5 0.83:1 10 60 strong NO positive 6 0.83:1 10 73.12 strong NO positive 7 0.83:1 12,000 70 strong NO positive

[0062] Next, granules were selected for DOM removal tests based on filtration of Lake Kinneret water through columns packed with the granular NMT-PDADMAC. The granules of Examples 1 and 3 were rejected and were not tested, due to their poor mechanical properties and negative surface charge (which is expected to cause electrostatic repulsion of the negatively charged DOM molecules).

[0063] The granules of Examples 2 and 4-7 were tested in column filtration experiments (see typical protocols in the next examples), from which the granules of Example 4 emerged superior, achieving 40-60% DOM removal rate, better than the other granules (DOM removal rates measured for the granules of Examples 2, 5, 6 and 7 were 15-30%, 20-40%, 15-40% and 10-30%, respectively).

[0064] Therefore, in the experimental work reported below, granules produced by the procedure of Example 4 were used (6.25:1 of NMT:PDADMAC mixing weight ratio; 20 ml/min addition rate of the polymer solution to the clay suspension, 70% moisture level of the mass prior to granulation, to produce mechanically strong granules with positive zeta potential around 30 mV).

[0065] Filtration of Surface Waters with High and Low SUVA Values Through GAC or GPDADMAC-MMT Packed Columns

[0066] In this study, removal of DOM from Suwannee River and Lake Kinneret waters, with high (3.6-4.2) and low (˜1) SUVA, respectively, by filtration with GAC and granular GPDADMAC-MMT columns, was investigated. Following the filtration, in-situ regeneration of the granular GPDADMAC-MMT, by passing a brine through the column, and ex-situ regeneration of GAC, by thermal reactivation, were carried out. Subsequently, the post-regeneration performance of the sorbents was demonstrated.

[0067] Experimental Protocol

[0068] DOM removal by filtration was performed at controlled room temperature 25° C. Glass columns (23 cm length, 1 cm diameter) were packed with 14 cm.sup.3 sorbents. Lake Kinneret (3 mg/L DOC) or Suwannee River waters (1.8-6.7 DOC, varied for different experiments) were pumped through the columns with a flow rate of 1.7 ml/min, equal to a velocity of 1.3 m/h and an empty bed contact time of 8 min. Every few hours the effluent was collected, filtered with 0.45 μm PTFE syringe filters (simplepure) and DOM concentrations measured as described above. Lake Kinneret filtration experiments were performed also at controlled temperatures of 6° C. (in a walk-in refrigerator) and 40° C. (in a hothouse).

[0069] Column regeneration was obtained by pumping a brine solution (2 M NaCl) through the columns (from the 25 ° C. experiments) with the same flow rate as the filtration experiments (1.7 ml/min). All of the volumes of the effluent were collected for mass balance and DOM discharged was measured by UV absorption.

[0070] Results

[0071] FIG. 1 presents the results of DOM removal from high SUVA value Suwannee River waters, adjusted to the DOC concentration of Lake Kinneret (Suwannee River DOM is commercially available in a powder form; it is added to water to form test solutions with desired DOM concentrations). In the graphs appended in FIGS. 1A and 1C, DOM removal rates measured in the filtration experiments are plotted against the pore volume.

[0072] The results in FIG. 1A indicate steadily high removal rates achieved by the granular GPDADMAC-MMT composite (marked by triangles), as opposed to sharp decrease in DOM removal percentages by the GAC column (marked by circles). The results suggest the presence of high percentage of macromolecules (mainly dissolved humic substances) among the UV.sub.254-absorbing molecules in the bulk DOM. These macromolecules cause pore-clogging in GAC, leading to the sharp drop in its performance. The advantage demonstrated by the granular GPDADMAC-MMT composite is probably due to its ability to form strong electrostatic interactions with these humic substances and remove them from the water.

[0073] Turning now to FIG. 1B, the regeneration of the composite columns by rinsing with brine solution was nearly 70% (of the adsorbed material), whereas, GAC regeneration by the brine was extremely low, ˜6% (FIG. 1B). The high desorption from the composite column, induced by an abrupt increase in the ionic stretch, supports the suggestion that the main adsorption mechanism is electrostatic, while GAC adsorbed DOM molecules thorough other chemical and physical interactions. An important result is that nearly two-thirds of the regeneration occurs within the third pore volume, which is only 0.75% of total pore volume initially passed through the column.

[0074] As shown in FIG. 1C, the performance of the GPDADMAC-MMT composite-packed column post-regeneration was very good, demonstrating high DOM removal rates, while the efficiency of thermally regenerated GAC was quite poor.

[0075] FIG. 2 presents the results of DOM removal from the low SUVA value Lake Kinneret waters.

[0076] The results are arranged in a similar manner to that discussed above: FIG. 2A (filtration through GAC and granular NMT-PDADMAC composite-packed columns), 2B (regeneration of the columns) and 2C (post-regeneration filtration).

[0077] The results shown in FIG. 2A indicate reversal of trend vis-à-vis FIG. 1A upon switching to low SUVA value waters, namely higher removal by GAC columns versus the granular GPDADMAC-MMT composite columns, suggesting that the granular composite of the invention is especially suitable for use in high SUVA waters (e.g., as for Suwannee River), rather than for low SUVA waters.

[0078] FIG. 2B shows that the despite the reversal of trend in the filtration experiments, the granular composite of the invention is of potential benefit owing to its excellent post-regeneration action. That is, efficient regeneration post-Lake Kinneret filtration with the aid of brine solution, reaching 97% discharge the regenerated composite, enables the regenerated composite of the invention to demonstrate DOM removal rates comparable to those obtained with the virgin composite (see FIGS. 2A and 2C, triangles). In contrast, thermally regenerated GAC demonstrates drop in performance (see FIGS. 2A and 2C, circles).

[0079] Affinity of GPDADMAC-MMT Granules Towards Various Organic Compounds

[0080] The adsorption of five different organic compounds (dissolved at concentration of 12.5 mg/L) by the granular GPDADMAC-MMT of the invention and GAC was tested at equilibrium (reached within 24 hours).

[0081] Experimental Protocol

[0082] The compounds selected for this study were toluene, octanol, gallic acid (GA), tannic acid (TA) and Aldrich humic acid (AHA) (pre-treated as described by Kam et al., 2001. Water Res. 35, 3557-3566)]. These compounds possess varied physicochemical properties such as size (molecular weight MW), charge (pKa), polarity (polar surface area), and aromaticity (number of rings).

[0083] The sorbents (90 mg) were added to solutions of the dissolved organic molecules (12.5 mg/l) and for GA also a sorbent concentration of 50 mg/L was measured. The samples were agitated overnight and the adsorption was calculated by measuring the concentrations in the supernatant. Gallic, tannic and humic acids were measured by UV absorption at 262, 276 and 254 nm, respectively. Toluene and octanol were measured by TOC.

[0084] Results

[0085] The results (shown in FIG. 3 in the form of a bar diagram) indicate that very low affinity is demonstrated by the granular GPDADMAC-MMT towards toluene. The adsorption to the granular GPDADMAC-MMT increases with increasing charge, polarity and molecular weight of the compounds dissolved in the solution (due to electrostatic interactions and enthalpy gain, respectively). Owing to its positively charged surface, the granular GPDADMAC-MMT is especially useful in removing compounds which dissociate in water to form negatively charged species, e.g., organic acids. In contrast, GAC tends to adsorb small, aromatic and hydrophobic molecules. Toluene, which has all three features, is completely removed by GAC.

[0086] Filtration of Surface Waters with Low SUVA Values Through Columns Packed with a Combination of GAC and GPDADAMAC-MMT

[0087] The goal of the study was to test the performance of a combination consisting of GAC and GPDADAMAC-MMT in a filtration column in terms of DOM removal from low SUVA waters. To this end, filtration columns were filled with both sorbents arranged in various configurations and Lake Kinneret water streams, with their characteristically low SUVA value, were passed through the columns.

[0088] Experimental Protocol

[0089] Glass columns (23 cm length, 1 cm diameter) were packed with a total volume 14 cm.sup.3 sorbents; bed height was 17.5 cm. Three downflow fixed bed filtration column designs were tested:

[0090] the fixed bed is made up of equally proportioned homogeneous blend of GAC/GPDADAMAC-MMT;

[0091] the fixed bed is made up of two layers of GAC and granular GPDADAMAC-MMT, the top layer consisting of GAC and each layer being 8.75 cm thick;

[0092] the fixed bed is made up of two layers of GAC and granular GPDADAMAC-MMT, the top layer consisting of granular GPDADAMAC-MMT, and each layer being 8.75 cm thick;

[0093] Lake Kinneret (3 mg/L DOC) waters were pumped through the columns with a flow rate of 1.7 ml/min, equal to a velocity of 1.3 m/h and an empty bed contact time of 8 min. Every few hours the effluent was collected, filtered with 0.45 μm PTFE syringe filters (simplepure) and DOM concentrations measured as described above. Lake Kinneret filtration experiments were performed at controlled temperatures of 6° C. (in a walk-in refrigerator), at 27° C. and 40° C. (in a hothouse).

[0094] Results

[0095] As shown in FIG. 4, the integrated columns demonstrated superior performance with 90% DOM removal (all three designs were equally good and results shown in FIG. 4 represent their average), better than removal rates measured for regenerated GAC or virgin GPDADMAC-MMT (about 75 and 40%, respectively—see also FIG. 1). The data shown in FIG. 4 is based on filtration experiments carried out at 27° C.

[0096] The effect of temperature change (6° C..fwdarw.27° C..fwdarw.40° C., simulating temperature variation throughout the year) was also investigated in this study and the results are tabulated below. It is seen that removal of Lake Kinneret DOM by the GAC column increases moderately with increasing temperature, such that the difference (Δ) between removal rates measured at 40° C. and 6° C. is less than 10% (e.g., Δ=+5-8%). In contrast, DOM filtration by the GPDADMAC-MMT column decreases with increasing temperature, such that removal rates measured at 40° C. can be significantly lower than removal rates measured at 6° C. DOM filtration by the integrated column, averaged out the changes in removal, stabilizing the filtration performance.

TABLE-US-00002 TABLE 2 DOM removal volume passed Δ (%) by (ml) 6° C. 27° C. 40° C. Removal GAC 202 88 90 96 8 2218 86 88 92 6 2923 86 89 91 5 4637 83 83 89 6 GPDADMAC- 202 54 34 13 −41 MMT 2218 51 46 37 −14 2923 54 47 38 −16 4637 52 46 39 −13 Integrated 202 92 89 92 0 column 2218 85 90 88 3 2923 87 90 85 −2 4637 82 87 83 1

[0097] Removal of Pharmaceutical Micropollutants from Secondary Wastewater Flowing Through Columns Packed with GPDADAMAC-MMT

[0098] The purpose of the study was to investigate the removal of pharmaceutically active compounds from secondary effluent generated in a municipal wastewater treatment plant, by fixed-bed adsorption to the granular composite of the invention, GPDADMAC-MMT and comparative sorbents. The pH of the secondary effluent was ˜7.5 and its COD level was ˜31 mg/liter.

[0099] Experimental Protocol

[0100] The as-received secondary effluent was filtrated using a vacuum pump through 0.45 μm filtering papers, to remove undissolved matter. The filtered secondary effluent (FSE) served as the feed solution for the micropollutant removal filtration experiments.

[0101] The FSE was charged to a glass tank and maintained under constant stirring throughout the filtration experiment, which was performed at room temperature over forty-eight hours. The experimental set-up consists of four 1.6 cm diameter glass columns, each packed with 15 cm.sup.3 of the following sorbents: [0102] GAC; [0103] regenerated GAC; [0104] GPDADMAC-MMT; and [0105] GAC/GPDADMAC-MMT blend (arranged in two layers, bottom layer: GAC top layer: GPDADMAC-MMT)

[0106] The (FSE) was simultaneously caused to flow through the four columns using four peristaltic pumps (Watson Marlow 520U) operating at a flow rate of 0.75 ml/min. Each of the columns discharged to its respective recipient. The treated effluents were sampled 6 hours and 18 hours from the beginning of the experiment, and finally, at the end of the 48 hours test period. The concentrations of the pharmaceutical compounds were measured by Liquid chromatography-mass spectrometry (LC-MS).

[0107] Results

[0108] The pharmaceutically active compounds, the removal of which was investigated, are carbamazepine (non-ionic), diclofenac (anionic; used commercially as in a salt form with sodium or potassium) and metoprolol (cationic; used commercially in a salt form with tartaric acid). The initial concentrations of the micropollutants were 0.729 ng/mL for carbamazepine, 1.231 ng/mL for diclofenac and 0.061 ng/mL for metoprolol.

[0109] The results are shown in the form of bar diagrams. The left (black) and right (green) bars correspond to the removal rate achieved with GAC-packed and GPDADMAC-MMT-packed columns, respectively.

[0110] The results shown in FIG. 5A (which pertain to removal of the pharmaceuticals compounds after six hours) indicate that the granular sorbent of the invention is equally effective to GAC in removal of adsorbates consisting of small compounds (200-500 g/mol) with varying properties, i.e., which exist in solution as neutral, negatively and positively charged species. The ability of GPDADMAC-MMT to remove metoprolol (cationic) and carbamazepine (non-ionic) is surprising, bearing in mind the fact that its outer layer is positively charged. This may be explained by sites at the clay which are not occupied by the polymer and remain available for cation exchange with the positively charged metoprolol.

[0111] Turning now to FIG. 5B, it is of note that after 18 h of filtration, removal of anionic and cationic pharmaceutical compounds by GPDADMAC-MMT is still very efficient. On the other hand, a lower removal of the non-ionic compound is noted, owing to the clay adsorption sites getting progressively saturated. Similar trends were observed at the end of the 48 hours test period (not shown).

[0112] Filtration of Surface and Treated Waste Waters with Varying SUVA Values Through GAC or GPDADMAC-MMT Packed Columns

[0113] FIG. 6 shows removal rates of DOM (C/Co initial concentration/eluting concentration (measured by UV 254 nm) at ˜70 pore volumes), achieved by GAC (marked by squares) and GPDADMAC-MMT (marked by triangles), versus SUVA values (water was collected from six locations, SUVA varying in the range from 0.9 to 3.6)

[0114] As the SUVA of source water increases, removal rate achieved by the GPDADMAC-MMT columns increases. An opposite trend is observed for GAC. These results suggest that optimal sorbent mixtures could be designed, combining GAC and GPDADMAC-MMT, to maximize DOM removal based on the water's SUVA. For example, by passing the stream through a fixed-bed consisting of a mixed granular material in the form of homogeneous blend of GAC and GPDADAMAC-MMT, or with the fixed-bed consisting of a mixed granular material in the form of alternate layers of GAC and GPDADAMAC-MMT.

[0115] While the present disclosure has been illustrated and described with respect to a particular embodiment thereof, it should be appreciated by those of ordinary skill in the art that various modifications to this may be made without departing from the spirit and scope of the present disclosure.