Method for simultaneous removal of heavy metals and organic matters from wastewater

Abstract

The present invention relates to a method for simultaneous removal of heavy metals and organic matters from wastewater, including four steps: anoxic reaction, incubation reaction, aerobic reaction and sedimentation reaction, to solve tricky problems and shortcomings of current treatment technologies for industrial wastewater containing both heavy metals and organic substances. Compared with current technologies, in the present invention, by regulating and controlling heavy metal ions in wastewater, catalysts with function of activating molecular oxygen are in-situ generated, catalyzing dioxygen to produce strong oxidative species, thereby realizing catalytic oxidation of organic pollutants and crystallization and precipitation removal of heavy metals, which creatively treats waste using waste to achieve green oxidation, shortened treatment process, improvement of treating efficiency, reduction of economic cost and promotion of technology for industrial application.

Claims

1. A method for simultaneous removal of heavy metals and organic matters from wastewater, comprising: (1) anoxic reaction: adding ferrous species into an industrial wastewater containing heavy metal ions and organic matters, afterward adding the industrial wastewater to an anoxic tank, controlling a concentration of dissolved oxygen in the industrial wastewater to less than 1.0 mg/L, adjusting pH value to 7.0, and reacting for 10-30 minutes to in situ produce FeM catalyst; (2) incubation reaction: after anoxic reaction, the anoxic tank contains a supernatant and a sludge containing FeM catalyst, the supernatant enters an aerobic tank; the sludge enters an incubation pool, followed by addition of sodium dithionite, and the FeM catalyst is stabilized via aging by stirring for 60 minutes; (3) aerobic reaction: the stabilized catalyst enters into the aerobic tank and reacts for 30-120 min, with 2-5 L/(min.Math.L wastewater) aeration, the stabilized catalyst generated in the incubation pool activates molecular oxygen in water, subsequently producing hydroxyl radical to oxidize the organic matter in wastewater; (4) sedimentation reaction: after completion of the aerobic reaction, wastewater of the aerobic tank enters a secondary sedimentation tank, and pH of the wastewater is adjusted to above 8.0, after settling for 30-60 minutes, heavy metal ions are removed from wastewater.

2. The method of claim 1, wherein the industrial wastewater contains one or more heavy metal ions of Cu, Ag, Co, Ni, Pd, Cr, and Mn.

3. The method of claim 1, wherein the ferrous species includes one or more selected from the group consisting of FeSO.sub.4.7H.sub.2O, FeSO.sub.4, and FeCl.sub.2.

4. The method of claim 1, wherein a ratio of molar concentration of Fe in ferrous species to that of all metal ions in wastewater is more than 2:1.

5. The method of claim 1, wherein a ratio of mass concentration of Fe in ferrous species to that of chemical oxygen demand (COD) in wastewater is more than 3:1.

6. The method of claim 1, wherein a dosage of sodium dithionite is 10-100 mg/L.

7. The method of claim 1, wherein a proportion of the sludge in the secondary sedimentation tank is refluxed to the anoxic tank, by which the catalyst is enriched and the formation of the catalyst is induced.

8. The method of claim 7, wherein the proportion is 2-5%.

9. A method for simultaneous removal of heavy metals and organic matters from wastewater, comprising: (1) anoxic reaction: adding a ferrous species into industrial wastewater containing heavy metal ion and organic matter; afterward adding the industrial wastewater to an anoxic tank, controlling the concentration of dissolved oxygen in the industrial wastewater to less than 1.0 mg/L, adjusting pH value to 7.0; according to the concentration of CO.sub.3.sup.2− in the industrial wastewater, adding 2 mol/L Na.sub.2CO.sub.3 solution to make the CO.sub.3.sup.2− concentration in the industrial wastewater greater than 500 mg/L; adding 2 g/L Fe.sub.3O.sub.4 nanoparticles as magnetic species; and reacting for 10-30 minutes to in situ produce a FeM catalyst; (2) incubation reaction: after anoxic reaction, the anoxic tank contains a supernatant and a sludge containing FeM catalyst; the supernatant enters an aerobic tank; the sludge containing the FeM catalyst enters an incubation pool, followed by addition of sodium dithionite, and the FeM catalyst is stabilized via aging by stirring for 60 minutes; (3) aerobic reaction: the stabilized catalyst enters into the aerobic tank and react for 30-120 min, with 2-5 L/(min.Math.L wastewater) aeration, the stabilized catalyst activates molecular oxygen in water, subsequently producing hydroxyl radicals to oxidize organic matter in the supernatant; (4) magnetic separation reaction: after completion of the aerobic reaction, entering wastewater of the aerobic tank to a magnetic separation reactor, adjusting the pH of the wastewater to above 8.0, and controlling a magnetic field strength to be 500-2000 G to achieve solid-liquid separation and remove heavy metal ions in the water; returning a portion of the sludge to the anoxic tank; and separating and reusing the magnetic species.

Description

ATTACHED FIGURE FOR ILLUSTRATION

(1) FIG. 1 represents the process flow chart of this invention.

(2) In this figure, 1-primary sedimentation tank, 2-adjusting tank, 3-anoxic reactor, 4-aerobic reactor, 5-secondary sedimentation tank, 6-incubation pool.

SPECIFIC IMPLEMENTING OPERATION

(3) The present invention is described in detail below combined with specific examples. The following practical examples will help those skilled in the art to further understand this invention, but will not restrict this invention in any form. It should be pointed out that for common technicians in the art, a certain amount of variations and modifications can be made under prerequisite of not departing from the concept of this invention, which belongs to the scope of protection of this invention.

PRACTICAL EXAMPLE 1

(4) Sampling a certain electroplating wastewater, pH=6.3, initial concentration and removal efficiency of pollutants in water sample are shown in Table 1.

(5) (1) Anoxic reaction: Sampling 1 L of the industrial wastewater, adding 2.78 g FeSO.sub.4.7H.sub.2O, leading to Fe molar concentration=10 mmol/L. The sum of molar concentration of heavy metal ions(M) in wastewater is 4.0 mmol/L, which makes molar ratio of Fe to M equal to 2.5:1, consistent with the technical characteristic of above 2:1. Wastewater COD is 120 mg/L, then the ratio of Fe mass concentration to COD equals to 4.7:1, consistent with the technical characteristic of above 3:1. Adding adjusted wastewater into anoxic reactor, with dissolved oxygen concentration controlled at less than 1.0 mg/L, pH adjusted to 7.0, reaction time kept for 10 min, to in-situ generate highly active FeM catalysts.

(6) (2) Incubation reaction: The supernatant enters the aerobic reaction pool after the end of anoxic reaction, while the sludge containing FeM catalysts enters into incubator, followed by the addition of 30 mg/L sodium dithionite, mixed slowly for 60 minutes to stabilize the aging of catalysts.

(7) (3) Aerobic Reaction: The stabilized catalysts enter aerobic tank, in which the catalysts react for 120 min with aeration of 2 L/(min.Math.L wastewater). The highly active catalysts produced in incubator are utilized to activate molecular oxygen in wastewater, producing strong oxidizing species, hydroxyl radicals, to oxidize and remove organic matters.

(8) (4) Sedimentation reaction: Wastewater enters secondary sedimentation tank after aerobic reaction, with pH adjusted to above 8.0, static settling for 30 min. Partial sludge from secondary sedimentation tank is refluxed to anoxic reactor, with reflux ratio of 5%, thereby realizing the enrichment of catalysts and inducing the formation of catalysts in anoxic reactor. Heavy metals concentration and COD in the effluent of secondary sedimentation tank are analyzed.

(9) TABLE-US-00001 TABLE 1 Removal efficiency of heavy metals and organic matters by FeM catalysts Pollutants Ag Cu Pb COD Initial Conc.(mg/L) 5.23 238 32 120 Removal rate(%) 100 100 100 75

PRACTICAL EXAMPLE 2

(10) Sampling a certain electroplating wastewater, pH=2.1, initial concentration and removal efficiency of pollutants in water sample are shown in Table 2.

(11) (1) Anoxic reaction: Sampling 1 L of the industrial wastewater, adding 3.34 g FeSO.sub.4.7H.sub.2O, leading to Fe molar concentration=12 mmol/L. The sum of molar concentration of heavy metal ions(M) in wastewater is 4.7 mmol/L, which makes molar ratio of Fe to M equal to 2.5:1, consistent with the technical characteristic of above 2:1. Wastewater COD is 60 mg/L, then the ratio of Fe mass concentration to COD equals to 11.2:1, consistent with the technical characteristic of above 3:1. Adding adjusted wastewater into anoxic reactor, with dissolved oxygen concentration controlled at less than 1.0 mg/L, pH adjusted to 7.0, reaction time kept for 20 min, to in-situ generate highly active FeM catalysts.

(12) (2) Incubation reaction: The supernatant enters the aerobic reaction pool after the end of anoxic reaction, while the sludge containing FeM catalysts enters into incubator, followed by the addition of 20 mg/L sodium dithionite, mixed slowly for 60 minutes to stabilize the aging of catalysts.

(13) (3) Aerobic Reaction: The stabilized catalysts enter aerobic tank, in which the catalysts react for 120 min with aeration of 2 L/(min.Math.L wastewater). The highly active catalysts produced in incubator are utilized to activate molecular oxygen in wastewater, producing strong oxidizing species, hydroxyl radicals, to oxidize and remove organic matters.

(14) (4) Sedimentation reaction: Wastewater enters secondary sedimentation tank after aerobic reaction, with pH adjusted to above 8.0, static settling for 30 min. Partial sludge from secondary sedimentation tank is refluxed to anoxic reactor, with reflux ratio of 5%, thereby realizing the enrichment of catalysts and inducing the formation of catalysts in anoxic reactor. Heavy metals concentration and COD in the effluent of secondary sedimentation tank are analyzed.

(15) TABLE-US-00002 TABLE 2 Removal efficiency of heavy metals and organic matters by FeM catalysts Pollutants Cu Cr Pd Ni COD Initial concentration(mg/L) 192 5.7 10.5 88 60 Removal rate(%) 99 98 100 99 85

PRACTICAL EXAMPLE 3

(16) Sampling a certain wastewater from titanium dioxide production, pH=1.2, initial concentration and removal efficiency of pollutants in water sample are shown in Table 3.

(17) (1) Anoxic reaction: Sampling 1 L of the industrial wastewater, on accounting that Fe mass concentration in wastewater is 3148 mg/L, which makes Fe molar concentration 12 mmol/L. The sum of molar concentration of heavy metal ions(M) in wastewater is 2.1 mmol/L, which makes molar ratio of Fe to M equal to 26.2:1, consistent with the technical characteristic of above 2:1. Wastewater COD is 447 mg/L, then the ratio of Fe mass concentration to COD equals to 7.0:1, consistent with the technical characteristic of above 3:1. Thus no more external ferrous is added into wastewater. Adding adjusted wastewater into anoxic reactor, with dissolved oxygen concentration controlled at less than 1.0 mg/L, pH adjusted to 7.0, reaction time kept for 30 min, to in-situ generate highly active FeM catalysts.

(18) (2) Incubation reaction: The supernatant enters the aerobic reaction pool after the end of anoxic reaction, while the sludge containing FeM catalysts enters into incubator, followed by the addition of 80 mg/L sodium dithionite, mixed slowly for 60 minutes to stabilize the aging of catalysts.

(19) (3) Aerobic Reaction: The stabilized catalysts enter aerobic tank, in which the catalysts react for 30 min with aeration of 3 L/(min.Math.L wastewater). The highly active catalysts produced in incubator are utilized to activate molecular oxygen in wastewater, producing strong oxidizing species, hydroxyl radicals, to oxidize and remove organic matters.

(20) (4) Sedimentation reaction: Wastewater enters secondary sedimentation tank after aerobic reaction, with pH adjusted to above 8.0, static settling for 60 min. Partial sludge from secondary sedimentation tank is refluxed to anoxic reactor, with reflux ratio of 2%, thereby realizing the enrichment of catalysts and inducing the formation of catalysts in anoxic reactor. Heavy metals concentration and COD in the effluent of secondary sedimentation tank are analyzed.

(21) TABLE-US-00003 TABLE 3 Removal efficiency of heavy metals and organic matters by FeM catalysts Pollutants Fe Mn Cr Ni COD Initial concentration(mg/L) 3148 115 2.43 0.42 447 Removal rate(%) 94 64 100 100 67

PRACTICAL EXAMPLE 4

(22) Sampling a certain plating wastewater, pH=3.0, initial concentration and removal efficiency of pollutants in water sample are shown in Table 4.

(23) (1) Anoxic reaction: Sampling 1 L of the industrial wastewater, adding 12.51 g FeSO.sub.4.7H.sub.2O, leading to Fe molar concentration=45 mmol/L. The sum of molar concentration of heavy metal ions(M) in wastewater is 18.6 mmol/L, which makes a molar ratio of Fe to M equal to 2.4:1, consistent with the technical characteristic of above 2:1. Wastewater COD is 824 mg/L, then the ratio of Fe mass concentration to COD equals to 3.1:1, consistent with the technical characteristic of above 3:1. Adding adjusted wastewater into anoxic reactor, with dissolved oxygen concentration controlled at less than 1.0 mg/L, pH adjusted to 7.0, reaction time kept for 30 min, to in-situ generate a highly active FeM catalyst.

(24) (2) Incubation reaction: The supernatant enters the aerobic reaction pool after the end of anoxic reaction, while the sludge containing FeM catalyst enters into incubator, followed by the addition of 100 mg/L sodium dithionite, mixed slowly for 60 minutes to stabilize the aging of catalysts.

(25) (3) Aerobic Reaction: The stabilized catalysts enter aerobic tank, in which the catalysts react for 60 min with aeration of 5 L/(min.Math.L wastewater). The highly active catalysts produced in incubator are utilized to activate molecular oxygen in wastewater, producing strong oxidizing species, hydroxyl radicals, to oxidize and remove organic matters.

(26) (4) Sedimentation reaction: Wastewater enters secondary sedimentation tank after aerobic reaction, with pH adjusted to above 8.0, static settling for 60 min. Partial sludge from secondary sedimentation tank is refluxed to anoxic reactor, with reflux ratio of 4%, thereby realizing the enrichment of catalysts and inducing the formation of catalysts in anoxic reactor. Heavy metals concentration and COD in the effluent of secondary sedimentation tank are analyzed.

(27) TABLE-US-00004 TABLE 4 Removal efficiency of heavy metals and organic matters by FeM catalysts Pollutants Cu Co Ni COD Initial concentration(mg/L) 433 4.20 692 824 Removal rate(%) 99 100 85 56

PRACTICAL EXAMPLE 5

(28) Sampling a certain metallurgical Wastewater, pH=2.3, initial concentration and removal efficiency of pollutants in water sample are shown in Table 5.

(29) (1) Anoxic reaction: Sampling 1 L of the industrial wastewater, adding 13.90 g FeSO.sub.4.7H.sub.2O, leading to Fe molar concentration=50 mmol/L. The sum of molar concentration of heavy metal ions(M) in wastewater is 22.4 mmol/L, which makes molar ratio of Fe to M equal to 2.2:1, consistent with the technical characteristic of above 2:1. Wastewater COD is 102 mg/L, then the ratio of Fe mass concentration to COD equals to 27.5:1, consistent with the technical characteristic of above 3:1. Adding adjusted wastewater into anoxic reactor, with dissolved oxygen concentration controlled at less than 1.0 mg/L, pH adjusted to 7.0, reaction time kept for 30 min, to in-situ generate highly active FeM catalysts.

(30) (2) Incubation reaction: The supernatant enters the aerobic reaction pool after the end of anoxic reaction, while the sludge containing FeM catalysts enters into incubator, followed by the addition of 100 mg/L sodium dithionite, mixed slowly for 60 minutes to stabilize the aging of catalysts.

(31) (3) Aerobic Reaction: The stabilized catalysts enter aerobic tank, in which the catalysts react for 60 min with aeration of 4 L/(min.Math.L wastewater). The highly active catalysts produced in incubator are utilized to activate molecular oxygen in wastewater, producing strong oxidizing species, hydroxyl radicals, to oxidize and remove organic matters.

(32) (4) Sedimentation reaction: Wastewater enters secondary sedimentation tank after aerobic reaction, with pH adjusted to above 8.0, static settling for 60 min. Partial sludge from secondary sedimentation tank is refluxed to anoxic reactor, with reflux ratio of 3%, thereby realizing the enrichment of catalysts and inducing the formation of catalysts in anoxic reactor. Heavy metals concentration and COD in the effluent of secondary sedimentation tank are analyzed.

(33) TABLE-US-00005 TABLE 5 Removal efficiency of heavy metals and organic matters by FeM catalysts Pollutants Cu Co Ni COD Initial concentration(mg/L) 227 1106 1.88 102 Removal rate(%) 100 82 100 83

PRACTICAL EXAMPLE 6

(34) A method for simultaneous removal of heavy metals and organic matters from wastewater, whose process is described in FIG. 1. The following steps are adopted:

(35) (1) Anoxic reaction: Industrial wastewater containing heavy metals like Cu, Ag, Co and organic matters enters primary sedimentation tank 1 for preliminary precipitation, and then enters into regulating pool 2. Adding FeSO.sub.4.7H.sub.2O into the above-mentioned wastewater, making a ratio of Fe molar concentration to that of all heavy metal ions(M) in wastewater equal to 3:1, ratio of Fe mass concentration to COD equals to 4:1. Afterwards the wastewater enters into anoxic reactor 3, with dissolved oxygen concentration controlled at less than 1.0 mg/L, pH adjusted to 7.0, reaction time kept for 10 min, to in-situ generate highly active FeM catalysts.

(36) (2) Incubation reaction: The supernatant enters the aerobic reaction pool 4 after the end of reaction in anoxic reactor 3, while the sludge containing FeM catalysts enters into incubator 6, followed by the addition of 10 mg/L sodium dithionite, mixed slowly for 60 minutes to stabilize the aging of catalysts.

(37) (3) Aerobic Reaction: The stabilized catalysts enter aerobic tank 4, in which the catalysts react for 120 min with aeration of 2 L/(min.Math.L wastewater). The highly active catalysts produced in incubator are utilized to activate molecular oxygen in wastewater, producing strong oxidizing species, hydroxyl radicals, to oxidize and remove organic matters. Air is utilized for aeration.

(38) (4) Sedimentation reaction: Wastewater enters secondary sedimentation tank 5 after the end of reaction in aerobic reactor 4, with pH adjusted to above 9.0, static settling for 30 min. Partial sludge from secondary sedimentation tank is refluxed to anoxic reactor, with reflux ratio of 2% and discharge of excess sludge, thereby realizing the enrichment of catalysts and inducing the formation of catalysts in anoxic reactor. Heavy metals concentration and COD in the effluent of secondary sedimentation tank 5 are analyzed.

PRACTICAL EXAMPLE 7

(39) A method for simultaneous removal of heavy metals and organic matters from wastewater, with following steps adopted:

(40) (1) Anoxic reaction: Adding FeCl.sub.2 into industrial wastewater containing heavy metals like Pd, Cr and organic matters, making a ratio of Fe molar concentration to that of all heavy metal ions(M) in wastewater equal to 4:1, ratio of Fe mass concentration to COD equals to 5:1. Afterwards the wastewater enters into anoxic reactor, with dissolved oxygen concentration controlled at less than 1.0 mg/L, pH adjusted to 7.0, reaction time kept for 30 min, to in-situ generate highly active FeM catalysts.

(41) (2) Incubation reaction: The supernatant enters the aerobic reaction pool after the end of reaction in anoxic reactor, while the sludge containing FeM catalysts enters into incubator, followed by the addition of 100 mg/L sodium dithionite, mixed slowly for 60 minutes to stabilize the aging of catalysts.

(42) (3) Aerobic Reaction: The stabilized catalysts enter aerobic tank, in which the catalysts react for 30 min with aeration of 5 L/(min.Math.L wastewater). The highly active catalysts produced in incubator are utilized to activate molecular oxygen in wastewater, producing strong oxidizing species, hydroxyl radicals, to oxidize and remove organic matters. Pure oxygen is utilized for aeration.

(43) (4) Sedimentation reaction: Wastewater enters secondary sedimentation tank after the end of reaction in aerobic reactor, with pH adjusted to above 10.0, static settling for 60 min. Partial sludge from secondary sedimentation tank is refluxed to anoxic reactor, with reflux ratio of 5%, thereby realizing the enrichment of catalysts and inducing the formation of catalysts in anoxic reactor. Heavy metals concentration and COD in the effluent of secondary sedimentation tank are analyzed.

(44) The specific examples of this invention are described above. It should be understood that this invention is not limited to these specific examples, and skilled technicians in the art are allowed to make variations or modifications under the scope of claims, without affecting the essence of this invention.