METHOD OF TREATING WASTEWATER

Abstract

Provided is a method of treating wastewater, which can treat wastewater, particularly organic wastewater while saving labor and decreasing the environmental impact by improving deterioration in the purification performance due to clogging of the filter bed, which is regarded as a problem when purifying wastewater, particularly organic wastewater having high SS concentration, BOD, and COD by a constructed wetland and by decreasing increases in the area and the number of stages of wetland required due to an increase in the BOD and COD load. A method of treating wastewater provided comprises: an aggregate floc forming step of forming an aggregate floc by adding a polymer flocculant to wastewater; a solid-liquid separation step of obtaining separated water by solid-liquid separation of the aggregate floc; and a purification step of purifying the separated water by using a constructed wetland.

Claims

1. A method of treating wastewater, the method comprising: forming step of forming an aggregate floc by adding a polymer flocculant to wastewater; obtaining separated water by solid-liquid separation of the aggregate floc; and purifying the separated water with a constructed wetland.

2. The method according to claim 1, wherein suspended solids in wastewater to which a polymer flocculant is added in the aggregate floc forming step is from 6,000 to 100,000 mg/L with respect to a total amount of the wastewater.

3. The method according to claim 1, wherein a content of total phosphorus in wastewater to which a polymer flocculant is added in the aggregate floc forming step is from 10 to 10,000 mg/L with respect to a total amount of the wastewater.

4. The method according to claim 1, wherein the polymer flocculant comprises at least one polymer flocculant selected from the group consisting of an amidine-containing cationic polymer (A), an amphoteric polymer (B), and a non-amidine-based cationic polymer (C).

5. The method of according to claim 4, wherein the polymer flocculant includes comprises an amidine-based cationic polymer (A).

6. The method of according to claim 5, wherein an amount of the polymer flocculant added to the wastewater is from 100 to 3,000 ppm by mass with respect to a mass of the wastewater.

7. The method of treating wastewater according to claim 4, wherein the polymer flocculant comprises an amphoteric polymer (B).

8. The method of according to claim 7, wherein an amount of the polymer flocculant added to the wastewater is from 100 to 2,000 ppm by mass with respect to a mass of the wastewater.

9. The method according to claim 4, wherein the polymer flocculant comprises a non-amidine-based cationic polymer (C).

10. The method according to claim 9, wherein an amount of the polymer flocculant added to the wastewater is from 100 to 2,000 ppm by mass with respect to a mass of the wastewater.

11. The method according to claim 5, wherein the amidine-containing cationic polymer (A) is a polymer comprising an amidine constitutional unit of either formula (1) or formula (2): ##STR00005## wherein, R.sup.1 and R.sup.2 are each independently a hydrogen atom or a methyl group and X.sup. is an anion, ##STR00006## wherein, R.sup.1 and R.sup.2 are each independently a hydrogen atom or a methyl group and X.sup. is an anion.

12. The method according to claim 7, wherein the amphoteric polymer (B) is a polymer comprising an anionic constitutional unit, a nonionic constitutional unit, and a cationic constitutional unit of formula (3): ##STR00007## wherein, R.sup.3 is a hydrogen atom or a methyl group, R.sup.4 and R.sup.5 are each independently a hydrogen atom or an alkyl group having from 1 to 4 carbon atoms, R.sup.6 is an alkyl group having from I to 4 carbon atoms or a benzyl group, Y is an oxygen atom or NH, Z.sup. is an anion, and n is an integer from 1 to 3.

13. The method according to claim 9, wherein the non-amidine-based cationic polymer (C) is a polymer comprising a cationic constitutional unit of formula (4): ##STR00008## wherein, R.sup.3 is a hydrogen atom or a methyl group, R.sup.4 and R.sup.5 are each independently a hydrogen atom or an alkyl group having from 1 to 4 carbon atoms, R.sup.6 is an alkyl group having from 1 to 4 carbon atoms or a benzyl group, Y is an oxygen atom or NH, Z.sup. is an anion, and n is an integer from 1 to 3.

14. The method according to claim 1, wherein a colloid value in the separated water is from 2.00 to 0.50 meg/L.

15. The method according to claim 1, wherein the constructed wetland comprises at least one selected from the group consisting of a vertical flow wetland or a horizontal flow wetland.

16. The method of according to claim 1, wherein a value (COD (Mn) in wastewater/COD (Mn) at outlet of final wetland) obtained by dividing a value of COD (Mn) in the wastewater by a value of COD (Mn) in treated water at an outlet of a final wetland located at a most downstream side is from 8 to 10,000.

Description

EXAMPLES

[0148] Hereinafter, the invention will be described in detail with reference to Examples and Comparative Examples, but the invention is not limited by the following description unless it goes beyond the gist thereof Incidentally, the term % in Examples and Comparative Examples denote % by mass unless otherwise specified. The reduced viscosity of the respective polymers obtained in the following Production Examples was measured as follows. For the measurement, a powdery polymer was used.

[0149] [Measurement of Reduced Viscosity]

[0150] The reduced viscosity of a polymer solution of 0.1 g/dL in a 1 mol/L sodium chloride aqueous solution was measured by using an Ostwald type viscometer at 25 C.

[0151] The raw materials used in Examples and Comparative Examples are presented below.

[0152] [Monomer]

[0153] (i) Cationic Monomer:

[0154] (a) N,N-dimethylaminoethyl acrylate methyl chloride quaternary salt (hereinafter referred to as DME) manufactured by OSAKA ORGANIC CHEMICAL INDUSTRY LTD., aqueous solution at 80% by mass

[0155] (b) N,N-dimethylaminoethyl methacrylate methyl chloride quaternary salt (hereinafter referred to as DMC) manufactured by OSAKA ORGANIC CHEMICAL INDUSTRY LTD., aqueous solution at 80% by mass

[0156] (ii) Anionic Monomer:

[0157] (a) Acrylic acid (hereinafter referred to as AA) manufactured by Mitsubishi Chemical Corporation, aqueous solution at 50% by mass

[0158] (iii) Nonionic Monomer:

[0159] (a) Acrylamide (hereinafter referred to as AAM) manufactured by Mitsubishi Rayon Co., Ltd., aqueous solution at 50% by mass

[0160] (b) Acrylonitrile (hereinafter referred to as AN) manufactured by Mitsubishi Rayon Co., Ltd., purity of 99% by mass

[0161] (c) N-vinylformamide (hereinafter referred to as NVF) manufactured by Mitsubishi Rayon Co., Ltd., aqueous solution having purity of 91% by mass

[0162] [Initiator]

[0163] (i) 2-Hydroxy-2-methyl-1-phenylpropane-1-one (DAROCUR (registered trademark) 1173) (hereinafter referred to as D-1173) manufactured by Ciba

[0164] (ii) 2,2-Azobis(2-amidinopropane)dihydrochloride (V-50) (hereinafter referred to as V-50) manufactured by Wako Pure Chemical Industries, Ltd.

[0165] [Chain Transfer Agent]

[0166] Sodium hypophosphite (hereinafter referred to as HPA) manufactured by Wako Pure Chemical Industries, Ltd.

[0167] [Synthesis of Amidine-Based Cationic Polymer (A)]

Production Example 1

[0168] In a four-necked flask which was equipped with a stirrer, a nitrogen introducing tube, and a cooling tube and had an internal volume of 50 mL, 6 g of a mixture of AN and NVF (molar ratio=55:45) and 34 g of distilled water were put. While stirring in a nitrogen gas, the temperature of the mixture was raised to 60 C., 0.12 g of V-50 was added into the flask, and the mixture was further retained at 60 C. for 3 hours, thereby obtaining a suspension in which a polymer was precipitated in water. To the suspension, 20 g of distilled water was added, concentrated hydrochloric acid was added into the flask by one equivalent with respect to the formyl group of the polymer, and the mixture was retained at 100 C. for 4 hours, thereby obtaining a yellow highly viscous liquid. This was added to a large amount of acetone to precipitate the polymer, the polymer gel thus obtained was chopped, dried at 60 C. for 24 hours, and pulverized, thereby obtaining an amidine-based cationic polymer (A) (polymer A-1).

[0169] The polymer A-1 was dissolved in heavy water, and .sup.13C-NMR spectrum was measured by using an NMR spectrometer (manufactured by JEOL Ltd., 270 MHz). The composition of each constitutional unit was calculated from the integral value of the peak corresponding to each repeating unit in the .sup.13C-NMR spectrum. The contents of the constitutional units of the general formulas (1) and (2) were not distinguished from each other but were determined as the total amount. The results are presented in Table 1.

TABLE-US-00001 TABLE 1 Consti- Reduced tutional Composition viscosity unit (*) [% by mole] [sp/C] Production Amidine 52.0 4.5 Denatured product of Example 1 NVF 1.6 polymer composed of Polymer AN 22.4 AN/NVF = 55/45% by A-1 VAM 24.0 mole by hydrochloric acid (*) Amidine: amidine hydrochloride constitutional unit, NVF: N-vinylformamide constitutional unit, AN: acrylonitrile constitutional unit, and VAM: vinylamine hydrochloride constitutional unit

[0170] [Synthesis of Amphoteric Polymer (B)]

Production Example 2

[0171] In a brown heat-resistant bottle having an internal volume of 2000 mL, 632.9 g of DME, 100.0 g of AA, and 900.0 g of AAM were put, and 3.0 g of HPA and distilled water were added thereto, thereby preparing an aqueous monomer solution (DME: AA: AAM=26.9: 7.2: 65.9 (% by mole), monomer concentration: 50%) having a total mass of 2000 g. Furthermore, D-1173 was added to the aqueous monomer solution so as to be 150 ppm with respect to the total mass of the aqueous monomer solution, and the temperature of the aqueous monomer solution was adjusted to 20 C. while blowing nitrogen gas thereinto for 30 minutes.

[0172] Thereafter, the aqueous monomer solution was transferred to a stainless reaction container and irradiated with light at an irradiation intensity of 5 W/m.sup.2 from the top of the container by using a chemical lamp until the surface temperature reached 40 C. while spraying water at 16 C. from the bottom of the container. After the surface temperature reached 40 C., the aqueous monomer solution was irradiated with light at an irradiation intensity of 0.3 W/m.sup.2 for 30 minutes. Furthermore, in order to decrease the residual amount of monomer, the aqueous monomer solution was irradiated with light at an irradiation intensity of 50 W/m.sup.2 for 10 minutes. In this manner, a polymer in the form of a hydrogel was obtained. The polymer in the form of a hydrogel thus obtained was taken out from the container, crushed by using a small meat chopper, and then dried at a temperature of 60 C. for 16 hours. Thereafter, the dried polymer was pulverized by using a Wheelie type pulverizer, thereby obtaining an amphoteric polymer (B) (polymer B-1).

Production Example 3 and Production Example 4

[0173] Amphoteric polymers (B) (polymer B-2 and polymer B-3, respectively) were obtained by conducting the same operation as in Production Example 2 except that the amounts of the respective monomers and HPA were adjusted and the proportions thereof were changed to those presented in Table 2 in Production Example 2.

[0174] [Synthesis of Cationic Polymer (C)]

Production Example 5 to Production Example 9

[0175] Cationic polymers (C) (polymer C-1 to polymer C-5, respectively) were obtained by conducting the same operation as in Production Example 2 except that the amounts of the respective monomers and HPA were adjusted and the proportions thereof were changed to those presented in Table 2 in Production Example 2.

TABLE-US-00002 TABLE 2 Proportion of constitutional unit derived from each monomer Reduced [% by mole] HPA viscosity Polymer AAM DME DMC AA [ppm] [sp/C] Production B-1 65.9 26.9 0.0 7.2 125 3.5 Example 2 Production B-2 59.1 16.3 10.0 14.6 120 7.2 Example 3 Production B-3 65.9 26.9 0.0 7.2 25 11.5 Example 4 Production C-1 80.0 20.0 0.0 0.0 30 15.0 Example 5 Production C-2 60.0 40.0 0.0 0.0 65 9.5 Example 6 Production C-3 40.0 60.0 0.0 0.0 40 12.0 Example 7 Production C-4 12.6 78.8 8.6 0.0 40 6.8 Example 8 Production C-5 0.0 0.0 100.0 0.0 0 8.6 Example 9

[0176] [Measurement of SS Concentration in Wastewater and Separated Water]

[0177] The SS concentrations in the wastewater and the separated water were measured by the SS concentration measuring method described above.

[0178] [Measurement of BOD in Wastewater]

[0179] The BOD in the wastewater was measured by the BOD measuring method described above.

[0180] [Measurement of COD in Wastewater, Separated Water, and Treated Water]

[0181] The COD in each of the wastewater, the separated water, and the treated water was measured by the COD (Mn) measuring method described above. Incidentally, the measurement result for COD in the separated water was used as an alternative value representing BOD in the separated water.

[0182] [Measurement of Total Phosphorus in Wastewater, Separated Water, and Treated Water]

[0183] The total phosphorus in each of the wastewater, the separated water, and the treated water was measured by the total phosphorus measuring method described above.

[0184] [Measurement of VTS in Wastewater]

[0185] The VTS in the wastewater was measured by the VTS measuring method described above.

[0186] [Measurement of Colloid Value in Supernatant Water of Wastewater and Separated Water]

[0187] The colloid values in the supernatant water of the wastewater and the separated water were measured by the colloid value measuring method described above.

[0188] [Measurement of CST of Supernatant Water of Wastewater and Separated Water]

[0189] The colloid value of the supernatant water of the wastewater and the separated water were measured by the CST measuring method described above.

Examples 1 to 10

[0190] [Wastewater]

[0191] As the wastewater, organic wastewater which was generated from a disposing facility of the dairy industry and had the following properties was used. In other words, organic wastewater having a pH of the wastewater of 7.81, a SS concentration of 65000 mg/L, VTS of 52.8%/solids, a colloid value in the supernatant water of -6.50 meq/L, CST of supernatant water of 4180 seconds, BOD of 25000 mg/L, COD of 24000 mg/L, and a total phosphorus of 860 mg/L, which were measured by the analysis methods described in the JIS standard.

[0192] [Flocculation Test]

[0193] In a 1000 L open tank, 600 L of the organic wastewater was collected. Subsequently, an aqueous solution of polymer flocculant was prepared by dissolving the polymer flocculant presented in Table 1 and Table 2 in water so as to be 0.3%, this was added to the organic wastewater so as to have the concentration presented in Table 4, and the mixture was then stirred and mixed by using a medium speed stirrer under the stirring conditions of a stirring speed of 300 rpm and a stirring time of 60 seconds to form aggregate flocs. Thereafter, the organic wastewater was separated into aggregate flocs and separated water by precipitating the aggregate flocs for 5 minutes for solid-liquid separation. The evaluation results to be described later are presented in Table 4.

Comparative Example 1

[0194] The aggregate flocs were formed and the organic wastewater was separated into aggregate flocs and separated water in the same manner as in Example 1 except that the polymer flocculant used was changed as presented in Table 4. The evaluation results to be described later are presented in Table 4.

[0195] [Evaluation Method]

[0196] [Particle Size of Aggregate Floc, Filterability, and SS Concentration, CST, Colloid Value, COD, and Total Phosphorus in Separated Water]

[0197] In each Example and Comparative Example, stirring was then stopped after aggregate flocs were formed and the particle size of the aggregate flocs was visually measured. Thereafter, 300 ml of the wastewater having aggregate flocs formed was collected in a 500 ml beaker and transferred to a Nutsche which had previously been covered with a filter cloth to measure the filterability (amount of filtered and separated water for 60 seconds). In addition, separated water was collected by solid-liquid separation in a 1000 L open tank, and the SS concentration, CST, colloid value, COD, and total phosphorus in the separated water were measured.

[0198] [Effect of Purifying Separated Water by Constructed Wetland]

[0199] In Examples 1 to 10 and Comparative Example 1, separated water was collected by solid-liquid separation in a 1000 L open tank, the separated water was allowed to flow into a constructed wetland as presented in Table 3 and purified, and treated water was obtained. Thereafter, the treated water was collected and subjected to the measurement of COD and total phosphorus. The measurement results for COD and total phosphorus in the treated water are presented in Table 4.

TABLE-US-00003 TABLE 3 Constructed wetland First stage Second stage Third stage Fourth stage Fifth stage Entire facility Type of wetland Vertical flow Vertical flow Horizontal flow Vertical flow Area of wetland 22.5 22.5 40.0 22.5 107.5 [m.sup.2] Material of filter Pumice stone A Pumice stone A Pumice stone A bed(*1) Pumice stone B Pumice stone B Pumice stone B Gravel Andosol Gravel Aquatic plant Carex dispalata (*1)Particle size of pumice stone A is from 20 to 40 mm, particle size of pumice stone B is from 5 to 20 mm, particle size of gravel is from 0.2 to 2 mm, and particle size of andosol is from 0.2 to 2 mm.

TABLE-US-00004 TABLE 4 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Polymer flocculant Polymer Polymer Polymer Polymer Polymer Polymer A-1 A-1 B-1 B-1 B-2 B-3 Amount added [ppm] 1000 1500 1000 1500 1000 1000 Particle size of aggregate floc [mm] 1.5 4 4 2 3 3 Filterability [mL/60 sec] 94 170 130 124 116 98 SS concentration in separated water [mg/L] 450 180 420 460 460 420 CST of separated water [sec] 78 15 89 97 104 112 Colloid value in separated water [meq/L] 1.62 0.03 1.40 1.22 1.62 1.92 COD in separated water (Mn) [mg/L] 1700 660 1620 1500 1700 1900 Inlet of wetland COD in treated water (Mn) [mg/L] 440 114 440 436 464 482 Outlet of final wetland COD in wastewater (Mn)/COD at outlet of final wetland (Mn) 54.4 210.5 54.4 55.0 51.7 49.8 Total phosphorus in separated water [mg/L] 17.0 8.2 30.3 27.5 32.1 32.6 Inlet of wetland Total phosphorus in treated water [mg/L] 0.6 0.4 2.1 2.4 2.6 2.3 Outlet of final wetland Number of stages of wetland required(*2) 4 2 4 4 4 4 Example Comparative Example 7 Example 8 Example 9 10 Example 1 Polymer flocculant Polymer Polymer Polymer Polymer Not added C-1 C-3 C-5 C-5 Amount added [ppm] 1000 1000 1000 1500 Particle size of aggregate floc [mm] 1.5 2.5 3 1.5 Filterability [mL/60 sec] 74 100 120 54 SS concentration in separated water [mg/L] 208 470 380 890 65000(*3) CST of separated water [sec] 78 86 88 186 4180 Colloid value in separated water [meq/L] 0.56 0.80 1.80 0.20 6.50 COD in separated water (Mn) [mg/L] 1300 1650 1800 2400 24000(*3) Inlet of wetland COD in treated water (Mn) [mg/L] 470 470 464 490 Impossible to Outlet of final wetland conduct purification treatment COD in wastewater (Mn)/COD at outlet of final wetland (Mn) 51.1 51.1 51.7 49.0 Total phosphorus in separated water [mg/L] 28.2 29.1 28.4 25.6 860(*3) Inlet of wetland Total phosphorus in treated water [mg/L] 1.6 1.4 1.3 1.2 Impossible to Outlet of final wetland conduct purification treatment Number of stages of wetland required(*2) 4 4 4 4 (*2)This is the number of stages of wetland required to decrease COD in treated water to less than 500 mg/L, and denotes that COD in treated water is 500 mg/L or more. (*3)Polymer flocculant is not added and flocculation treatment is not conducted.

[0200] As presented in Table 4, in Examples 1 to 10 in which the flocculation treatment was conducted by the method of treating wastewater of the invention, the SS concentration, COD, and total phosphorus in the separated water after the flocculation treatment were greatly decreased as compared to the wastewater used. Furthermore, the COD and total phosphorus in the treated water were further decreased by purifying the separated water by a constructed wetland, and high quality treated water was obtained. In addition, in Examples 1 to 10 in which the colloid value in the separated water was 2.00 to 0.50 meq/L, the COD in the treated water was less than 500 mg/L.

[0201] As presented in Table 4, Comparative Example 1 is the results in a case in which the wastewater which was not subjected to the flocculation treatment by the method of treating wastewater of the invention was purified by a constructed wetland, the SS concentration, COD, and total phosphorus in the separated water were high, the filter bed of the constructed wetland was clogged, and it was impossible to conduct the purification treatment by the constructed wetland.

Examples 11 to 14 and Comparative Example 2

[0202] [Organic Wastewater Used]

[0203] As the wastewater, organic wastewater which was generated from a disposing facility of the swine industry and had the following properties was used. In other words, organic wastewater having a pH of the wastewater of 6.66, a SS concentration of 16500 mg/L, VTS of 76.0%/solids, a colloid value in the supernatant water of 1.80 meq/L, CST of supernatant water of 1153 seconds, BOD of 18300 mg/L, COD of 7240 mg/L, and a total phosphorus of 2420 mg/L, which were measured by the analysis methods described in the JIS standard.

[0204] [Flocculation Test]

[0205] The same flocculation test as in Example 1 was conducted except that the polymer flocculant used in the test was changed as presented in Table 6. The evaluation results in Examples 11 to 14 and Comparative Example 2 are presented in Table 6.

[0206] [Effect of Purifying Separated Water by Constructed Wetland]

[0207] In Examples 11 to 14 and Comparative Example 2, separated water was collected by solid-liquid separation in a 1000 L open tank, the separated water was allowed to flow into a constructed wetland as presented in Table 5 and purified, and treated water was obtained. Thereafter, the treated water was collected and subjected to the measurement of COD and total phosphorus. The measurement results for COD and total phosphorus in the treated water are presented in Table 6.

TABLE-US-00005 TABLE 5 Constructed wetland First stage Second stage Third stage Fourth stage Fifth stage Entire facility Type of wetland Vertical flow Vertical flow Vertical flow Horizontal flow Vertical flow Area of wetland 22.5 22.5 22.5 40.0 22.5 130.0 [m.sup.2] Material of filter Pumice stone A Pumice stone A Pumice stone A bed(*4) Pumice stone B Pumice stone B Pumice stone B Gravel Andosol Gravel Aquatic plant Carex dispalata (*4)Particle size of pumice stone A is from 20 to 40 mm, particle size of pumice stone B is from 5 to 20 mm, particle size of gravel is from 0.2 to 2 mm, and particle size of andosol is from 0.2 to 2 mm.

TABLE-US-00006 TABLE 6 Example 11 Example 12 Example 13 Example 14 Comparative Example 2 Polymer flocculant Polymer A-1 Polymer A-1 Polymer C-5 Polymer C-5 Not added Amount added [ppm] 600 1200 600 1200 Particle size of aggregate floc [mm] 2 4 2.5 2 Filterability [mL/60 sec] 120 160 118 108 SS concentration in separated water [mg/L] 340 226 380 330 16500(*6) CST of separated water [sec] 56 11 79 68 1153 Colloid value in separated water [meq/L] 0.60 0.08 0.11 0.18 1.80 COD in separated water (Mn) [mg/L] 1320 880 1480 1560 7240(*6) Inlet of wetland COD in treated water (Mn) [mg/L] 480 180 470 490 Impossible to conduct Outlet of final wetland purification treatment COD in wastewater (Mn)/COD at outlet of final wetland (Mn) 15.1 40.2 15.4 14.8 Total phosphorus in separated water [mg/L] 180 120 330 310 2420(*6) Inlet of wetland Total phosphorus in treated water [mg/L] 3.2 1.1 7.7 7.5 Impossible to conduct Outlet of final wetland purification treatment Number of stages of wetland required(*5) 5 3 5 5 (*5)This is the number of stages of wetland required to decrease COD in treated water to less than 500 mg/L, and denotes that COD in treated water is 500 mg/L or more. (*6)Polymer flocculant is not added and flocculation treatment is not conducted.

[0208] As presented in Table 6, in Examples 11 to 14 in which the flocculation treatment was conducted by the method of treating wastewater of the invention, the SS concentration, COD, and total phosphorus in the separated water after the flocculation treatment were greatly decreased as compared to the wastewater used. Furthermore, the COD and total phosphorus in the treated water were further decreased by purifying the separated water by a constructed wetland, and high quality treated water was obtained. In addition, in Examples 11 to 14 in which the colloid value in the separated water was 2.00 to 0.50 meq/L, the COD in the treated water was less than 500 mg/L.

[0209] As presented in Table 6, Comparative Example 2 is the results in a case in which the wastewater which was not subjected to the flocculation treatment by the method of treating wastewater of the invention was purified by a constructed wetland, the SS concentration, COD, and total phosphorus in the separated water were high, the filter bed of the constructed wetland was clogged, and it was impossible to conduct the purification treatment by the constructed wetland.

Examples 15 to 22 and Comparative Example 3

[0210] [Organic Wastewater Used]

[0211] As the wastewater, organic wastewater which was generated from a disposing facility of the dairy industry and had the following properties was used. In other words, organic wastewater having a pH of the wastewater of 7.94, a SS concentration of 35800 mg/L, VTS of 66.3%/solids, a colloid value in the supernatant water of 12.30 meq/L, CST of supernatant water of 3120 seconds, BOD of 7480 mg/L, COD of 12000 mg/L, and a total phosphorus of 980 mg/L, which were measured by the analysis methods described in the JIS standard.

[0212] [Flocculation Test]

[0213] The same flocculation test as in Example 1 was conducted except that the polymer flocculant used in the test was changed as presented in Table 7. The evaluation results in Examples 15 to 22 and Comparative Example 3 are presented in Table 7.

[0214] [Effect of Purifying Separated Water by Constructed Wetland]

[0215] In Examples 15 to 22 and Comparative Example 3, separated water was collected by solid-liquid separation in a 1000 L open tank, the separated water was allowed to flow into a constructed wetland as presented in Table 3 and purified, and treated water was obtained. Thereafter, the treated water was collected and subjected to the measurement of COD and total phosphorus. The measurement results for COD and total phosphorus in the treated water are presented in Table 7.

TABLE-US-00007 TABLE 7 Example Example Example Example Example Example Example Example Comparative 15 16 17 18 19 20 21 22 Example 3 Polymer flocculant Polymer Polymer Polymer Polymer Polymer Polymer Polymer Polymer Not added A-1 A-1 A-1 C-2 C-2 C-3 C-4 C-4 Amount added [ppm] 800 1200 1600 800 1200 800 800 1200 Particle size of aggregate floc [mm] 1 6 10 6 8 3 1 3 Filterability [mL/60 sec] 56 120 164 110 90 98 36 96 SS concentration in separated water 1130 420 150 960 860 930 1800 920 35800(*8) [mg/L] CST of separated water [sec] 68 22 11 36 216 116 212 238 3120 Colloid value in separated water 1.50 0.14 0.05 0.47 0.72 0.15 2.15 1.40 12.30 [meq/L] COD in separated water (Mn) [mg/L] 2100 930 780 1050 1180 1120 2350 1050 12000(*8) Inlet of wetland COD in treated water (Mn) [mg/L] 380 120 46 180 680 420 580 520 Impossible Outlet of final wetland to conduct purification treatment COD in wastewater (Mn)/COD at outlet 31.6 100.0 260.9 66.7 17.6 28.6 20.7 23.1 of final wetland (Mn) Total phosphorus in separated water 20.2 14.5 7.7 23.2 28.2 27.3 31.6 30.7 980(*8) [mg/L]Inlet of wetland Total phosphorus in treated water 2.2 0.6 0.1 1.7 9.2 3.6 9.7 9.2 Impossible [mg/L]Outlet of final wetland to conduct purification treatment Number of stages of wetland 4 3 1 3 4 required(*7) (*7)This is the number of stages of wetland required to decrease COD in treated water to less than 500 mg/L, and denotes that COD in treated water is 500 mg/L or more. (*8)Polymer flocculant is not added and flocculation treatment is not conducted.

[0216] As presented in Table 7, in Examples 15 to 22 in which the flocculation treatment was conducted by the method of treating wastewater of the invention, the SS concentration, COD, and total phosphorus in the separated water after the flocculation treatment were greatly decreased as compared to the wastewater used. Furthermore, the COD and total phosphorus in the treated water were further decreased by purifying the separated water by a constructed wetland, and high quality treated water was obtained. In addition, in Examples 15 to 18 and 20 in which the colloid value in the separated water was 2.00 to 0.50 meq/L, the COD in the treated water was less than 500 mg/L.

[0217] As presented in Table 7, Comparative Example 3 is the results in a case in which the wastewater which was not subjected to the flocculation treatment by the method of treating wastewater of the invention was purified by a constructed wetland, the SS concentration, COD, and total phosphorus in the separated water were high, the filter bed of the constructed wetland was clogged, and it was impossible to conduct the purification treatment by the constructed wetland.

Examples 23 to 25 and Comparative Example 4

[0218] [Organic Wastewater Used]

[0219] As the wastewater, organic wastewater which was generated from a disposing facility of the dairy industry and had the following properties was used. In other words, organic wastewater having a pH of the wastewater of 7.85, a SS concentration of 35000 mg/L, VTS of 66.0%/solids, a colloid value in the supernatant water of 12.40 meq/L, CST of supernatant water of 3020 seconds, BOD of 7200 mg/L, COD of 11000 mg/L, and a total phosphorus of 900 mg/L, which were measured by the analysis methods described in the JIS standard.

[0220] [Flocculation Test]

[0221] The same flocculation test as in Example 1 was conducted except that the polymer flocculant used in the test was changed as presented in Table 9. The evaluation results in Examples 23 to 25 and Comparative Example 4 are presented in Table 9.

[0222] [Effect of Purifying Separated Water by Constructed Wetland]

[0223] In Examples 23 to 25 and Comparative Example 4, separated water was collected by solid-liquid separation in a 1000 L open tank, the separated water was allowed to flow into a constructed wetland as presented in Table 8 and purified, and treated water was obtained. Thereafter, the treated water was collected and subjected to the measurement of COD and total phosphorus. The measurement results for COD and total phosphorus in the treated water are presented in Table 9.

TABLE-US-00008 TABLE 8 Constructed wetland First stage Second stage Third stage Fourth stage Fifth stage Entire facility Type of wetland Vertical flow Vertical flow Vertical flow Vertical flow Area of wetland 22.5 22.5 22.5 22.5 90 [m.sup.2] Material of filter Pumice stone A bed(*9) Pumice stone B Gravel Aquatic plant Carex dispalata (*9)Particle size of pumice stone A is from 20 to 40 mm, particle size of pumice stone B is from 5 to 20 mm, and particle size of gravel is from 0.2 to 2 mm.

TABLE-US-00009 TABLE 9 Example 23 Example 24 Example 25 Comparative Example 4 Polymer flocculant Polymer A-1 Polymer A-1 Polymer A-1 Not added Amount added [ppm] 800 1200 1600 Particle size of aggregate floc [mm] 2 5 10 Filterability [mL/60 sec] 60 125 160 SS concentration in separated water [mg/L] 1100 430 150 35000(*11) CST of separated water [sec] 65 20 13 3020 Colloid value in separated water [meq/L] 1.50 0.14 0.05 12.40 COD in separated water (Mn) [mg/L] 2200 920 760 11000(*11) Inlet of wetland COD in treated water (Mn) [mg/L] 390 130 43 Impossible to conduct Outlet of final wetland purification treatment COD in wastewater (Mn)/COD at outlet of final wetland 28.2 84.6 255.8 (Mn) Total phosphorus in separated water [mg/L] 20.0 14.0 7.3 900(*11) Inlet of wetland Total phosphorus in treated water [mg/L] 2.3 0.5 0.2 Impossible to conduct Outlet of final wetland purification treatment Number of stages of wetland required(*10) 3 3 1 (*10)This is the number of stages of wetland required to decrease COD in treated water to less than 500 mg/L, and denotes that COD in treated water is 500 mg/L or more. (*11)Polymer flocculant is not added and flocculation treatment is not conducted.

[0224] As presented in Table 9, in Examples 23 to 25 in which the flocculation treatment was conducted by the method of treating wastewater of the invention, the SS concentration, COD, and total phosphorus in the separated water after the flocculation treatment were greatly decreased as compared to the wastewater used. Furthermore, the COD and total phosphorus in the treated water were further decreased by purifying the separated water by a constructed wetland, and high quality treated water was obtained. In addition, in Examples 23 to 25 in which the colloid value in the separated water was 2.00 to 0.50 meq/L, the COD in the treated water was less than 500 mg/L.

[0225] As presented in Table 9, Comparative Example 4 is the results in a case in which the wastewater which was not subjected to the flocculation treatment by the method of treating wastewater of the invention was purified by a constructed wetland, the SS concentration, COD, and total phosphorus in the separated water were high, the filter bed of the constructed wetland was clogged, and it was impossible to conduct the purification treatment by the constructed wetland.

INDUSTRIAL APPLICABILITY

[0226] According to the invention, in the purification treatment of wastewater, particularly organic wastewater by a constructed wetland, a method of treating wastewater is provided in which the load of purification treatment by the constructed wetland is decreased without adversely affecting the microbial and bacterial flora and aquatic plants in the wetland, BOD, COD, total nitrogen, and total phosphorus in treated water are greatly decreased, and high quality treated water is obtained by adding a polymer flocculant to organic wastewater and conducting the flocculation and separation treatment in advance before the organic wastewater is allowed to flow into the constructed wetland. In addition, according to the method of treating wastewater of the invention, it is possible to expand the application range of the purification treatment of wastewater, particularly organic wastewater containing target substances which increase the values of SS, BOD, COD, and total phosphorus at high contents by a constructed wetland and to greatly cut down the treatment cost by decreases in the number of stages and the area of the constructed wetland required.