TWI424965B - Method of heavy metals removal from municipal wastewater - Google Patents

Description

Method for removing heavy metal from urban wastewater Cross-references to related applications

This application is part of the continuation application of US Serial No. 11/516,843 filed on September 7, 2006. The subject matter contained in U.S. Serial No. 11/516,843 is incorporated herein by reference.

The present invention relates to a method of removing heavy metals from municipal wastewater via the use of submerged ultrafiltration or microfiltration membrane systems.

Due to stringent environmental regulations and/or lack of water resources, some cities must remove heavy metals from wastewater before they are discharged or reused. The European Water Framework Directive (2000/60/EC) states that future emissions will preferentially reduce substances such as heavy metals. This regulation is based primarily on the primary significance of the maximum allowable risk, and compounds discharged to the environment should not or have negligible environmental or human risks. The Dutch interpretation of this European regulation is described in the national regulation entitled "4e nota Waterhuishuiding". This regulation specifically describes the metal limits for future surface water discharge. The examples from this regulation have the following possible soluble metal discharge requirements: cadmium: 0.4 ppb, copper: 1.5 ppb, nickel: 5.1 ppb, lead: 11 ppb, zinc: 9.4 ppb, chromium: 8.7 ppb and arsenic: 25 ppb . Most of the heavy metal-containing wastewater is now treated with commercial DTC/TTC chemicals or special polymeric DTC compounds, and the precipitated metal is then separated in a settling tank. In recent years, ultrafiltration (UF) or microfiltration (MF) membranes have been increasingly used to replace settling tanks for solid liquid separation because the UF/MF membrane process is more compact and produces better than settling tanks. Quality water, especially almost no suspended solids and negligible turbidity. The UF or MF permeate can be reused and with or without any further treatment for repeated use purposes. Thus, municipal wastewater, when treated with a polymeric chelating agent and subsequently filtered through a UF or MF membrane, produces high metal removal and also produces higher membrane flux than those treated with commercial DTC/TTC/TMT chemicals.

Although cross-flow UF or MF methods have been used in this application, these methods typically have high operating costs due to the need for high cross-flow energy to reduce film fouling. In the last decade or so, submerged UF and MF membranes have been successfully used in high suspended solids separation applications, such as in membrane bioreactors (MBR); or low suspended solids applications, such as raw water treatment and tertiary treatment. In these applications, the immersion film operates at low throughput (10-60 LMH) because the film becomes dirty at higher throughputs. To reduce film fouling, aeration is used to wash the film surface continuously (e.g., in MBR) or intermittently (e.g., in MBR, raw water, and tertiary treatment). Therefore, it is of interest to employ these relatively low operating cost submerged membrane systems for other applications, such as heavy metal removal, and to combine with polymeric chelating agents that act as metal complexing agents and membrane flux promoters. The use of a polymeric chelating agent in a filtration system is discussed in U.S. Patent Nos. 5,346,627 and 6,258,277, the disclosures of each of each of each

The present invention provides a method for removing one or more heavy metals from municipal wastewater using a membrane separation process comprising the steps of: (a) collecting heavy metal-containing municipal wastewater in a storage tank suitable for containing the municipal wastewater; (b) Adjusting the pH of the system to achieve precipitation of hydroxides of heavy metals in the municipal wastewater; (c) adding an effective amount of dichloroethane ammonia polymer soluble in water having a molecular weight of from about 500 to about 10,000 auricular, It comprises from about 5 to about 50 mole percent of the dithiocarbamate group to react with the heavy metal in the municipal wastewater system; (d) to selectively purify the treated wastewater from step c; (e) The treated municipal wastewater is passed through a submerged membrane wherein the submerged membrane is an ultrafiltration membrane or microfiltration membrane; and (f) the membrane is backwashed as needed to remove solids from the surface of the membrane.

Noun definition:

"UF" means ultrafiltration.

"MF" means microfiltration.

"DTC" means dimethyl dithiocarbamate.

"TTC" means trisulfide carbonate.

"TMT" means three bases three .

"TMP" means transmembrane pressure.

"LMH" means the number of liters per square meter per hour.

"Flow" means the amount of water that is filtered through the membrane per unit of membrane area per unit time.

"Urban wastewater" means wastewater from a centralized or decentralized municipal wastewater treatment plant. Centralized water treatment plants include wastewater from households and factories. Dispersed water treatment plants include wastewater from conglomerates, hotels, resorts and the like that treat their own wastewater.

"Terrant scavenger" means a compound that is capable of intermingling with a chelating agent. These scavengers are typically, but not limited to, salt forms.

"Submerged film" means a film that is completely submerged under the body of the liquid to be filtered.

"Polymerizing chelating agent" means a polymeric molecule that reacts with and/or misaligns with heavy metals.

"Amphoteric polymer" means a polymer derived from both cationic monomers and anionic monomers and possibly other nonionic monomers. Amphoteric polymers can have a net positive or negative charge. Amphoteric polymers can also be derived from zwitterionic monomers and cationic or anionic monomers and possibly nonionic monomers. This amphoteric polymer is soluble in water.

"Cationic polymer" means a polymer having an overall positive charge. The cationic polymer of the present invention is obtained by polymerizing one or more cationic monomers, by copolymerizing one or more nonionic monomers with one or more cationic monomers, by condensing epichlorohydrin with a diamine or a polyamine or condensing It is prepared by reacting vinyl chloride with ammonia or formaldehyde and amine salts. This cationic polymer is soluble in water.

"Zwitterionic polymer" means a polymer composed of a zwitterionic monomer and possibly other nonionic monomers. In zwitterionic polymers, all polymer chains and fragments within the chain are positively neutralized. Thus, zwitterionic polymers represent a group of amphoteric polymers that must maintain charge neutrality throughout the entire polymer chain and fragment because both anionic and cationic charges are introduced within the same zwitterionic monomer. This zwitterionic polymer is soluble in water.

"Anionic polymer" means a polymer having an overall negative charge. The anionic polymers of the present invention are prepared by polymerizing one or more anionic monomers or by copolymerizing one or more nonionic monomers with one or more anionic monomers. This anionic polymer is soluble in water.

Preferred specific examples :

As described above, the present invention provides a method of removing one or more heavy metals from municipal wastewater using a submerged microfiltration membrane or a submerged ultrafiltration membrane.

If a chelating agent is present in the municipal wastewater, the pH needs to be adjusted to misalign the metal in the municipal wastewater with the chelating agent, and it is necessary to subsequently or simultaneously add one or more chelating agent scavengers. When the pH is less than 4, the chelating agent will generally be misaligned with the metal, and it is preferred to adjust the pH from about 3 to about 4.

In one embodiment, the chelating agent scavenger comprises Ca or Mg or Al or Fe.

In another embodiment, the Fe-containing chelating agent scavenger is selected from the group consisting of ferrous chloride, ferrous sulfate, ferric chloride, ferric sulfate, or combinations thereof.

Various types and amounts of acids and bases can be used to adjust the pH of the municipal wastewater.

In one embodiment, the base can be selected from the group consisting of magnesium and calcium salts, such as chlorides and hydroxides.

In another embodiment, the base is selected from the group consisting of hydroxides of sodium, potassium, ammonium, and the like.

A variety of iron compounds and dosages can be used to further treat pH-adjusted municipal wastewater. In still another embodiment, the dosage of the iron compound used may range from about 1 ppm to about 10,000 ppm depending on the amount of chelating agent present in the municipal wastewater.

A step of removing heavy metals from an urban wastewater system is the step of adjusting the pH of the system to achieve precipitation of heavy metal hydroxides in municipal wastewater. Hydroxoxide precipitation occurs when the pH of the wastewater gives the metal hydroxide minimal solubility.

In a preferred embodiment, the pH of the municipal wastewater is raised to a pH of from about 7 to about 10. The pH of the municipal wastewater is adjusted depending on the metal present. Any base that can adjust the pH to the desired range has been contemplated. For example, the base selected for pH adjustment is selected from the group consisting of hydroxides of sodium, potassium, magnesium, calcium, ammonium, and the like.

In another embodiment, the heavy metal to be removed from the municipal wastewater is selected from the group consisting of Pb, Cu, Zn, Cd, Ni, Hg, Ag, Co, Pd, Sn, Sb, Ba, Be. And their combinations.

The dichloroethane ammonia polymer is prepared by the reaction of dichloroethane with ammonia. The starting dichloroethane ammonia polymer typically has a molecular weight in the range of from 500 to 100,000. In a preferred embodiment, the molecular weight is from 1,500 to 10,000 and the most preferred molecular weight range is from 1,500 to 5,000. A typical reaction for the manufacture of these polymers is described in U.S. Patent No. 5,346,627, which is incorporated herein by reference. Polymers are also commercially available from Nalco Corporation, 1601 West Diehl Road, Naperville, IL.

The dichloroethane ammonia polymer can be added in varying amounts.

In one embodiment, the effective amount of the water-soluble dichloroethane ammonia polymer added to the municipal wastewater is from 1 ppm to about 10,000 ppm active solids.

In another embodiment, the water-soluble dichloroethane ammonia polymer added to the municipal wastewater has a molecular weight of from about 2,000 to about 2,000,000 ampoules.

In another embodiment, the treated municipal wastewater is subjected to a positive or negative pressure through the driving force of the submerged membrane.

In another embodiment, the treated municipal wastewater passing through the submerged microfiltration membrane or ultrafiltration membrane can be further processed by one or more membranes.

In still further embodiments, the other film is a reverse osmosis membrane or a nanofiltration membrane.

Immersion films used to treat municipal wastewater containing heavy metals can have a variety of physical and chemical parameters.

Regarding the physical parameters, in one embodiment, the ultrafiltration membrane has a pore size ranging from 0.003 to 0.1 micron.

In another embodiment, the microfiltration membrane has a pore size ranging from 0.1 to 10 microns.

In another embodiment, the submerged film has a configuration selected from the group consisting of: a hollow fiber configuration, a slab configuration, or a combination thereof.

In another embodiment, the film has a spiral configuration.

In another embodiment, the submerged membrane has a capillary configuration.

Regarding the chemical parameters, in one embodiment, the submerged film is a polymer.

In another embodiment, the film is an inorganic material.

In yet another embodiment, the film is stainless steel.

Other physical and chemical film parameters can be performed on the claimed invention.

After treating municipal wastewater with a water-soluble dichloroethane ammonia polymer, the wastewater can be further treated with one or more water-soluble polymers to further increase particle size and increase membrane flux.

In one embodiment, the water soluble polymer is selected from the group consisting of amphoteric polymers, cationic polymers, anionic polymers, zwitterionic polymers, and combinations thereof.

In another embodiment, the water soluble polymer has a molecular weight of from 10,000 to about 2,000,000 auricular.

In another embodiment, the amphoteric polymer is selected from the group consisting of dimethylaminoethyl acrylate chloromethane quaternary salt (DMAEA.MCQ)/acrylic acid copolymer, vaporized diallyl propylene Methylammonium/acrylic acid copolymer, dimethylaminoethyl acrylate methyl chloride/N,N-dimethyl-N-methylpropenylpropyl-N-(3-sulfopropyl)-ammonium Betaine Copolymer, Acrylic Acid/N,N-Dimethyl-N-Methylacrylamidopropyl-N-(3-sulfopropyl)-ammonium Betaine Copolymer, and DMAEA.MCQ/Acrylic/N , N-Dimethyl-N-methylpropenylguanidinylpropyl-N-(3-sulfopropyl)-ammonium betaine terpolymer.

In another embodiment, the amphoteric polymer is dosed from about 1 ppm to about 2000 ppm active solids.

In another embodiment, the amphoteric polymer has a molecular weight of from about 5,000 to about 2,000,000 orthodontic.

In another embodiment, the amphoteric polymer has a ratio of cationic charge equivalent to anionic molar charge equivalent of from about 3.0:7.0 to about 9.8:0.2.

In another embodiment, the cationic polymer is selected from the group consisting of polychlorinated diallyldimethylammonium (polyDADMAC), polyethyleneimine, polyepiamine, and ammonia. Or polyethylenediamine crosslinked polyepiamine, dichloroethylene and ammonia polycondensate, triethanolamine and tall oil fatty acid polycondensate, poly(dimethylaminoethyl methacrylate sulfate) and poly( Dimethylaminoethyl acrylate chloromethane quaternary salt).

In another embodiment, the cationic polymer is a copolymer of acrylamide (AcAm) and one or more cationic monomers selected from the group consisting of: diallyldimethylammonium chloride, two Methylaminoethyl acrylate chloromethane quaternary salt, dimethylaminoethyl methacrylate chloromethane quaternary salt, and dimethylaminoethyl acrylate benzyl chloride quaternary salt (DMAEA. BCQ).

In another embodiment, the cationic polymer is present in an amount from about 0.1 ppm to about 1000 ppm active solids.

In another embodiment, the cationic polymer has a cationic charge of at least 2 mole percent.

In another embodiment, the cationic polymer has a cationic charge of 100 mole percent.

In another embodiment, the cationic polymer has a molecular weight of from about 2,000 to about 10,000,000 ampoules.

In another embodiment, the cationic polymer has a molecular weight of from about 20,000 to about 2,000,000 ampoules.

In another embodiment, the zwitterionic polymer is from about 1 to about 99 mole percent of N,N-dimethyl-N-methylpropenylpropylamino-N-(3-sulfopropyl) Ammonium betaine and one or more nonionic monomers having a percentage of from about 99 to about 1 mole.

The treated wastewater from step c can be selectively purified.

A variety of types of membrane separation methods can be used.

In one embodiment, the membrane separation method is selected from the group consisting of: a cross-flow membrane separation method, that is, washing the membrane by continuous aeration; a semi-endpoint flow membrane separation method, that is, washing the membrane by intermittent aeration; And an end-stream thin film separation method, that is, no ventilation to wash the film.

A possible urban wastewater treatment plan is shown in Figure 2.

Referring to Figure 1, the heavy metal-containing municipal wastewater is collected in a storage tank (1), wherein an acid or a base is added via line (3) to adjust the pH to 3-4. A chelating agent scavenger such as an iron compound is then added via line (3A). This water is then allowed to flow to the storage tank (2) where the pH is adjusted to 8-10 by adding alkali to the storage tank (2) via in-line (4) or directly (5). The water is then allowed to flow from the reservoir (2) to a reservoir (8) that has been immersed in the ultrafiltration or microfiltration membrane (10). Ventilation can be applied to the ultrafiltration or microfiltration membrane. A polymeric chelating agent such as a dichloroethane ammonia polymer can be added to the film tank (8) either on line (6) or directly (9). After the addition of the dichloroethane ammonia polymer, one or more water-soluble polymers may be selectively added to the line (7) before the water flows into the film tank (8). The permeate (11) from the immersed ultrafiltration or microfiltration membrane process can be selectively treated by allowing the permeate to pass through other membranes (12), and the discard (concentrate) (13) can be sent to further water removal or abandon.

The following examples are not intended to limit the scope of the claimed invention.

Example

The secondary treated wastewater is obtained after the low-load nitrification/denitrification activated mud process of the raw wastewater and the subsequent purification of the raw wastewater. The secondary treated wastewater from the local city contains 17 ppb Zn, 3.1 ppb Cu and 1.99 ppb Ni. This wastewater was treated with 10-20 ppm dichloroethane ammonia (EDC-NH ₃ ) polymer, precipitated in a settling tank, and then the purified water was filtered through a submerged hollow fiber UF film. This method is illustrated by Figure 2. The EDC-NH ₃ polymer treatment of municipal wastewater after UF then resulted in a significant improvement in metal removal compared to UF alone.

1. . . Storage tank

2. . . Storage tank

3. . . Pipeline

3A. . . Pipeline

4. . . Alkali addition

5. . . Alkali addition

6. . . Addition of polymeric chelating agents

7. . . Addition of polymer

8. . . Storage tank

9. . . Addition of polymeric chelating agents

10. . . Microfiltration membrane

11. . . Permeate

12. . . film

13. . . Concentrate

Figure 1 illustrates a general process scheme for treating municipal wastewater containing heavy metals, including submerged microfiltration membranes/ultrafiltration membranes and other membranes for further processing permeate from submerged microfiltration membranes/ultrafiltration membranes.

Figure 2 illustrates the general process of wastewater treatment with 10-20 ppm dichloroethane ammonia (EDC-NH ₃ ) polymer, precipitation in a settling tank and filtration of purified water through a submerged hollow fiber UF membrane. .

1. . . Storage tank

2. . . Storage tank

3. . . Pipeline

3A. . . Pipeline

4. . . Alkali addition

5. . . Alkali addition

6. . . Addition of polymeric chelating agents

7. . . Addition of polymer

8. . . Storage tank

9. . . Addition of polymeric chelating agents

10. . . Microfiltration membrane

11. . . Permeate

12. . . film

13. . . Concentrate

Claims (16)

A method of removing one or more heavy metals from municipal wastewater using a membrane separation process comprising the steps of: a. collecting heavy metal-containing municipal wastewater in a storage tank suitable for containing municipal wastewater; b. adjusting the pH of the system to Precipitating the hydroxide of the heavy metal in the municipal wastewater; c. adding an effective amount of a water-soluble dichloroethane ammonia polymer having a molecular weight of from about 2,000 to about 2,000,000 amps, comprising about 5 to About 50 mole percent of the dithiocarbamate group to react with the heavy metal in the municipal wastewater system; d. selectively purify the treated wastewater from step c; e. let the treated municipal wastewater By immersion film, wherein the immersion film is an ultrafiltration membrane or microfiltration membrane; and f. backwashing the membrane as needed to remove solids from the surface of the membrane. The method of claim 1, wherein the water-soluble dichloroethane ammonia polymer is present in an amount from 1 ppm to about 10,000 ppm. The method of claim 1, further comprising the steps of: adjusting the pH of the municipal wastewater system after step a and before step b to cause the metal and the chelating agent (if present) to be misplaced in the wastewater system One or more chelating agent scavengers are added subsequently or simultaneously. The method of claim 1, wherein the treated urban wastewater is subjected to a positive or negative pressure by a driving force of the immersed film. For example, the method of claim 1 of the patent scope further includes after step c and Municipal wastewater is treated with one or more water soluble polymers prior to passing through the immersion film. The method of claim 5, wherein the water-soluble polymer is selected from the group consisting of an amphoteric polymer, a cationic polymer, a zwitterionic polymer, an anionic polymer, and combinations thereof. The method of claim 1, wherein the immersed membrane separation method is selected from the group consisting of a cross-flow membrane separation method, a semi-terminal flow membrane separation method, and an endpoint flow membrane separation method. The method of claim 1, further comprising passing the filtrate from the film through another film. The method of claim 8, wherein the other film is a reverse osmosis membrane. The method of claim 8, wherein the other film is a nanofiltration membrane. The method of claim 1, wherein the submerged film has a configuration selected from the group consisting of a hollow fiber configuration, a plate configuration, or a combination thereof. The method of claim 5, wherein the water-soluble polymer has a molecular weight of from 10,000 to about 2,000,000 ampoules. The method of claim 1, wherein the heavy metal in the municipal wastewater is selected from the group consisting of Pb, Cu, Zn, Cd, Ni, Hg, Ag, Co, Pd, Sn, Sb, Ba, Be or a combination thereof. The method of claim 3, wherein the pH is adjusted to less than 4 after step a and before step b. The method of claim 3, wherein the chelating agent scavenger comprises Ca or Mg or Al or Fe. The method of claim 15, wherein the Fe-containing chelating agent scavenger is selected from the group consisting of ferrous chloride, ferrous sulfate, ferric chloride, iron sulfate, or a combination thereof.