JP2601441B2 - Wastewater treatment method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wastewater treatment method,
More specifically, SS, oil, COD, BOD, turbid component,
In the treatment method of wastewater containing coloring substances, organic chlorine compounds, pesticides and other harmful substances, the purification degree of the finally obtained treated water is high and the sedimentation speed of the generated sludge, the solid content concentration and the dehydration property are high, The present invention relates to a wastewater treatment method that facilitates final treatment of sludge.

[0002]

2. Description of the Related Art Conventionally, industrial wastewater, domestic wastewater for domestic use, etc.
Various wastewaters such as leachate of industrial waste landfill, night soil, molasses wastewater, fermentation industrial wastewater, wastewater in livestock industry, etc. are generated in large quantities. These wastewaters are, for example, SS, oil, C
OD, BOD, turbid components, coloring substances, organochlorine compounds,
It contains a large amount of pesticides and other harmful substances, and it is extremely important to remove these harmful substances and return them to the natural environment as clean water after environmental protection. Among the various wastewater treatment methods described above, examples of a method for removing organic substances include an activated sludge method, a solid-liquid separation method using a coagulant or a separation membrane, and the like.
BACKGROUND ART As an advanced treatment method for wastewater containing an organic substance that is difficult to decompose and contains OD and chromaticity components, an oxidation treatment method proposed by the present applicant is widely used. In any of these methods, a large amount of sludge is generated based on the metal hydroxide used as the flocculant.

[0003]

Problems to be Solved by the Invention The treatment of sludge generated in any of the above-mentioned conventional methods remains a major problem. That is, in the activated sludge method of the prior art, the BOD component in the wastewater is decomposed and removed, but other COD
It is difficult to remove biologically hard-to-decompose organic pollutants such as colorants and chromaticity components, and a large amount of sludge is generated. Further, in the solid-liquid separation method using a flocculant or a membrane, the flocculation of floc by the flocculant has a poor sedimentation property in a sedimentation basin or the like. In addition, there is a problem similar to the above activated sludge method,
Furthermore, the sludge separated by settling not only has a high water content, but also has a poor dewatering property, and the sludge to be finally disposed of after the dehydration treatment has a very high viscosity and a high water content. There is a problem that processing is very expensive.

[0004] Further, in the method in which secondary treatment water treated by the activated sludge method, coagulation method, or membrane separation method is further treated with an oxidizing agent or a metal salt coagulant, etc., highly purified water is obtained, In addition, there is a problem that a large amount of sludge mainly composed of a metal hydroxide based on a metal salt used as a flocculant is generated, and a problem of treating the sludge is generated separately. Accordingly, an object of the present invention is to provide a wastewater treatment method in which the degree of purification of the finally obtained treated water is high, the sedimentation speed, solid content and dehydration of the generated sludge are high, and the final treatment of the sludge is easy. That is.

[0005]

The above object is achieved by the present invention described below. That is, the present invention provides a wastewater treatment in which raw water containing organic contaminants is introduced into a reaction tank to adjust pH, a metal salt is added as a coagulant to coagulate solids in the raw water, and the treated water is subjected to solid-liquid separation. In the method, a part of the separated sludge is converted into a metal salt (as a metal atom) added as a flocculant.
The method is based on a wastewater treatment method characterized by repeating or continuously performing the step of returning to the reaction tank an amount containing the metal atom in an amount of 2 to 50 times the amount of the metal atom .

[0006]

In the method of coagulating and sedimenting wastewater, a part of the sludge generated in the solid-liquid separation device is returned to the raw water to be treated and circulated, whereby the purification degree of the finally obtained treated water is high and generated. It is possible to provide a wastewater treatment method in which sludge settling speed, solid content concentration and dehydration are high, and final treatment of sludge is extremely easy.

[0007]

Preferred embodiments will now be described with reference to the drawings. The basic principle of the present invention is a wastewater treatment in which raw water containing organic contaminants is introduced into a reaction tank to adjust pH, a metal salt is added as a coagulant to coagulate solids in the raw water, and the treated water is subjected to solid-liquid separation. The method is characterized in that the step of returning a part of the separated sludge to the reaction tank is repeatedly or continuously performed. In the present invention, “pH
The term "adjustment" means that the water to be treated is adjusted to a desired pH by adding an acid or an alkali,
If the water to be treated is in a desired pH range in advance, no acid or alkali is added, but this case is also referred to as “pH adjustment”.

The embodiment shown in FIG. 1 is a preferred embodiment of the present invention. First, raw water, which is waste water to be treated, is introduced into a first reaction tank at an appropriate flow rate, and is finally passed through a second reaction tank. Sludge is separated from the solid-liquid separation device, a part of the separated sludge is returned to the raw water side, and purified water is discharged. In the first reaction tank, an agitator is operated, preferably while performing aeration, while considering the pH of the sludge returned from the solid-liquid separation device, an alkali or an acid (a normal metal salt or a flocculant is acidic. (Usually alkali addition)
Make adjustments. At this time, a third reaction tank was provided as shown in the figure,
Here, the pH can be adjusted and the sludge can be returned to the first reaction tank. If the metal salt is, for example, a ferric salt, the pH in the first reaction vessel is in the range of 3.0 to 5.5, if the metal salt is a ferrous salt, the pH is 7 to 9, and the aluminum salt is In the case of p
The alkali is injected in conjunction with the pH meter so that H is maintained at 6 to 9. The pH adjustment in the first reaction tank may be performed by using an alkali added to the third reaction tank. In this case, the addition of the alkali in the first reaction tank may be omitted. Further, primary aggregation is performed by adding a metal salt such as iron or aluminum as a primary aggregation agent so that the concentration becomes 5 to 5,000 mg / liter (as metal ions).

The temperature of the processing solution in the first reaction tank may be room temperature or may be somewhat increased. The residence time of the treatment liquid in the first reaction tank is usually about 5 to 60 minutes. At this time, by adding an oxidizing agent such as hydrogen peroxide to the first reaction tank, particularly dissolved COD in the water to be treated,
The BOD and chromaticity components are oxidatively decomposed by the Fenton reaction to reduce organic matter in wastewater, thereby further improving the quality of treated water. In the present invention, all the steps can be performed at normal temperature. However, in the case of performing the above oxidation treatment, the oxidation can be performed more advantageously by heating the water to be treated to a temperature of about 40 to 90 ° C. And at the same time, the sedimentation and dewatering properties of the sludge, which are the objects of the present invention, can be further improved. When hydrogen peroxide is used as the oxidizing agent, it is preferable to use an iron compound as the primary flocculant and also to serve as an oxidation catalyst. Further, in the first reaction tank, aeration with air or the like and supply of oxygen to the treated water can further improve the sludge settling property, dehydration property, and the like, which are objects of the present invention.

In the second reaction tank, a polymer flocculant (for example, a polyacrylamide-based weak anion) is used as a secondary flocculant while operating a stirrer so as to have an appropriate concentration, for example, 0.2 to 10 mg / liter. Flocculant, etc.) is added, and the flocculated floc that has been flocculated in the first reaction tank is further flocculated to improve sedimentability as a large floc and sent to the next solid-liquid separator. The above-mentioned polymer flocculant is necessary when the solid-liquid separation device is a sedimentation system, and is unnecessary when the solid-liquid separation device is a membrane separation system or the like. Therefore,
In this case, the second reaction tank is not essential in the present invention. Hereinafter, a case where a sedimentation system such as a sedimentation tank is adopted as a solid-liquid separation device will be described as a representative. The temperature of the processing solution in the second reaction tank may be room temperature or may be slightly heated. The residence time of the treatment liquid in the second reaction tank is usually 5
About 60 minutes. In the solid-liquid separation device (precipitation tank),
Agglomerated flocs settled in the second reaction tank settle, the settled sludge is extracted, and the pH of the supernatant is adjusted if necessary and discharged. The residence time in this solid-liquid separation device is:
Although it varies greatly depending on the type of solid-liquid separation device, for example,
In the case of a precipitation tank, it is usually about 1 to 6 hours.

In the present invention, when the sludge settled out of the solid-liquid separator is extracted, a part of the sludge extracted from the bottom of the solid-liquid separator (the metal atom injected in the first reaction tank).
Sludge containing about 2 to 50 times by weight, preferably 10 to 25 times by weight of metal atoms) is led to the third reaction tank, where the sludge is added to the sludge while stirring, thereby converting the sludge from slightly alkaline to alkaline, for example, When an iron salt is used as the metal salt, the pH is 4 or more, when an aluminum salt is used, the pH is 8 or more, and when a zinc salt is used, the pH is 9.0 or more.
After making the H5 to 13, preferably 7 to 12, the sludge is returned to the first reaction tank. By this operation, the object of the present invention is mainly achieved. The temperature of the processing solution in the third reaction tank may be room temperature or may be slightly heated.
The residence time of the processing solution in the third reaction tank is usually 2-3
It takes about 0 minutes. By the above treatment, particularly the treatment in the first and second reaction tanks, the added metal salt and the metal in the sludge are, for example, FeO (OH) in the case of iron and AlO (OH) in the case of aluminum. The sedimentation and dewatering properties of the sludge are extremely improved by circulating through the treatment step as described above.

When the above operations are performed and the conditions such as pH, coagulant, and returned sludge in all the processes are in a steady state,
Part of the sludge withdrawn from the bottom of the solid-liquid separator is continuously returned to the first reaction tank via the third reaction tank, and most of the remaining sludge is allowed to stand still, centrifuged, or separated by membrane. The dewatering and concentration treatment is performed by an appropriate means such as the above, and the final disposal. At this time, the dewatering property of the sludge is very good, and the solid content of the dewatered sludge when the present invention is not applied is usually about 12 to 25% by weight, whereas in the present invention the dewatering property is very low. The subsequent solid content can be easily reduced to about 40 to 60% by weight, and the final sludge treatment such as landfill, incineration, and recovery of valuable resources is significantly economical. On the other hand, the purified treated water shows a very high purification rate, and is subjected to pH treatment as required and discharged.

The embodiment shown in FIG. 2 is a modification of the embodiment shown in FIG. 1. The first reaction tank in the example of FIG. 1 is divided into two parts, and the first reaction tank in FIG. A metal salt is added, and if necessary, an acid or alkali is injected to adjust the pH, and the pH is adjusted by an alkali in the next second reaction tank, and the metal salt acts as a primary flocculant. Therefore, the returned sludge treated in the fourth reaction tank is returned to the second reaction tank. In the embodiment shown in FIG. 2, since the first reaction tank is in an acidic state, for example, pH 3.5 or less, preferably 2.5 to 3.0, the first reaction tank is oxidized with an oxidizing agent such as hydrogen peroxide. It is suitable for oxidative decomposition of dissolved COD, BOD and organic components such as chromaticity components in the raw water to be treated. Further, the metal salt coagulant is ionized with organic substances such as BOD, COD and chromaticity components in the wastewater. There is an advantage that the metal salt coagulant can improve the coagulation effect and the adsorption effect of the organic substance by the metal salt coagulant. In this example, the pH adjustment in the second reaction tank may be performed by an alkali agent added to the fourth reaction tank. In this case, the alkali addition in the second reaction tank may be omitted. Also, by aerating the second reaction tank and supplying oxygen, it is possible to improve the sedimentation and dewatering properties of sludge, which is the object of the present invention, as in the case of FIG.

The embodiment shown in FIG. 3 is an example in which the embodiment of FIG. 1 and the modification of the embodiment of FIG. 2 are combined, and a fifth reaction tank corresponding to the second reaction tank of FIG. A sixth reaction tank is provided between the third reaction tank and the seventh reaction tank. Using ferrous iron as a metal salt coagulant in the fourth reaction tank,
In addition, when an oxidizing agent such as hydrogen peroxide is used, most of the iron becomes ferric, and some ferrous iron may remain. In this case, first, the pH of the fifth reaction tank is adjusted to 3.0 to 5.5 and aeration is performed to remove all iron from FeO (OH).
It can be. This reaction is carried out using iron in sludge returned from the eighth reaction tank as one type of catalyst. The ferrous iron in the treated water sent to the sixth reaction tank becomes FeO (OH) by aeration at pH 6-9. Also in this case, iron from the first reaction tank serves as a catalyst. As a result, the sludge in each tank is significantly improved in sedimentation and dewatering properties.

In the first half of this embodiment, the same treatment as shown in FIG. 1 is performed, and the treated water discharged from the first solid-liquid separation device is treated in the same treatment step as shown in FIG. The advantages of the example shown in FIG. 1 and the advantages of the example shown in FIG. 2 are both obtained. The conditions of each step in this embodiment are the same as those in the embodiment shown in FIGS.
Part of the extracted sludge in the latter half of the process (shown by dotted lines)
May be returned to the first reaction tank in the first half of the processing step. In this embodiment, the purification rate of the treated water is further improved, the sludge treatment is further facilitated, and even if the injection amount of the metal salt coagulant injected into the first reaction tank is reduced, COD, BOD
In addition, since a high treatment effect on organic substances such as chromaticity components can be obtained, there is an advantage that the amount of sludge generated due to the metal salt coagulant can be further reduced.

The embodiment shown in FIG. 4 is an embodiment in which the third reaction tank and the eighth reaction tank in the embodiment shown in FIG. 3 are omitted, and the same process as shown in FIG. In this case, part of the sludge extracted by the first solid-liquid separation device is directly returned to the first reaction tank. The treated water discharged from the first solid-liquid separator is the same as the embodiment shown in FIG. 3 except that the eighth reaction tank is omitted, and a part of the sludge extracted by the second solid-liquid separator is first, It is returned to the fourth and / or fifth reaction tank. In this embodiment, since the third reaction tank and the eighth reaction tank of the embodiment shown in FIG. 3 are omitted, pH adjustment in the first reaction tank and the fourth or fifth reaction tank is important. Also in this embodiment, the same operation and effect as shown in FIG. 3 are exerted, and the use amount of the metal salt as the first flocculant can be reduced without lowering the degree of purification of the final purified water. The amount of sludge generated in the plant can also be reduced.

The wastewater to be treated in the present invention may be any one of industrial wastewater, domestic wastewater such as domestic use, leachate from an industrial waste landfill, human waste, molasses wastewater, fermentation industrial wastewater, and wastewater in the livestock industry. Alternatively, the method of the present invention is extremely useful for further advanced treatment of the secondary treated water obtained by treating the wastewater. Also, various drugs used in the above examples,
It is the same as a conventionally known chemical in wastewater treatment. For example, metal salts such as iron, aluminum, aluminate, copper, zinc, manganese, and cobalt are used as the metal salt as the primary coagulant, and iron and aluminum are particularly preferable.
Further, when the oxidation treatment is performed in combination with hydrogen peroxide, it is preferable to use an iron salt because iron also acts as an oxidation catalyst. The alkali or acid is not particularly limited, for example,
Caustic soda, sodium carbonate, slaked lime, magnesium hydroxide, sulfuric acid and the like are optionally used. As the secondary flocculant, for example, a commonly used anionic, cationic or nonionic polymer flocculant such as a polyacrylamide derivative, a polyacrylic acid derivative or chitosan is used. The solid-liquid separator may be any of a precipitation method, a pressurized or reduced pressure flotation method, a centrifugal separation method, an ultrafiltration method and a microfiltration method. The law is used.

[0018]

Next, the present invention will be described more specifically with reference to examples and comparative examples. Example 1 The process shown in FIG. 1 was performed. The raw water to be treated is secondary treated water obtained by treating public sewage by activated sludge treatment, and contains the following components as pollutants. BOD: 3 mg / liter COD: 12 mg / liter Total phosphorus: 4 mg / liter pH: 7.8

The processing equipment for the test is as follows. First reactor: 10 liter capacity Attached equipment: rapid stirrer, pH meter and aeration 2 liter / m
in. Second reactor: 10 liters Auxiliary equipment: slow stirrer Solid-liquid separator (precipitation tank): 180 liters Third reactor: 0.8 liters auxiliary equipment: rapid stirrer and pH meter

First, the raw water is introduced into the first reaction tank at a rate of 60 liters / Hr, and the retention amounts of the first and second reaction tanks are each set to 8 liters. It was set to be released. In the first reaction tank, the pH of the slaked lime milk is maintained in the range of 6 to 7 while operating the stirrer and considering the pH of the sludge returned from the third reaction tank. And a polyaluminum chloride as a primary coagulant is added so that the concentration becomes 10 mg / liter (as Al ³⁺ ). Was added as a secondary coagulant (polyacrylamide-based weakly anionic polymer coagulant) so that the concentration became 1 mg / liter.
Further, sludge is withdrawn from the bottom of the solid-liquid separator (precipitation tank), and a part thereof (sludge containing 20 times the amount of Al ³⁺ aluminum atoms injected in the first reaction tank) is led to the third reaction tank. While operating the stirrer, 15% by weight slaked lime milk was injected in conjunction with a pH meter so that the pH of the reaction tank was maintained in the range of 9 to 10, and the sludge was returned to the first reaction tank. .

At the time when all the above processes are in a steady state,
The sludge pulled out from the bottom of the solid-liquid separation device was collected in a 1-liter graduated cylinder and allowed to stand for sedimentation. After the lapse of time shown in Table 1 below, the supernatant was removed by decantation.
The concentration of the remaining settled sludge was measured, and the results shown in Table 1 below were obtained. Comparative Example 1 The same operation as in the above example was repeated except that sludge was not returned and slaked lime milk was injected into the first reaction tank to adjust the pH in the first reaction tank to 7, and the same evaluation was performed. The results are shown in Table 1.

[0022]

[Table 1] Sedimentation of sludge As is clear from the results in Table 1 above, according to the method of the present invention in which a part of the sludge is alkali-treated and returned to the first reaction tank, compared with the comparative example, about 5 hours at a standing time of 0 hour. The solid concentration of the sludge was doubled, and the tendency became more remarkable with the passage of time. After 24 hours, the solid concentration of the sludge was increased about 10 times.

Example 2 The process shown in FIG. 2 was performed. The raw water to be treated is treated water that has been treated by low-dilution two-step activated sludge treatment of human waste, and contains the following components as pollutants. BOD: 8 mg / L COD: 45 mg / L Total phosphorus: 77 mg / L Total nitrogen: 13 mg / L Chromaticity: 210 degrees pH: 8.1

The test processing equipment is as follows. First reaction tank: capacity 10 liters Attached equipment: rapid stirrer, pH meter and air exposure 2 liters / m
in. Second reactor: 10 liter capacity Auxiliary equipment: rapid stirrer and pH meter Third reactor: 10 liter capacity, used as circulating water tank for ultrafiltration membrane Auxiliary equipment: rapid agitator solid-liquid separator (ultrafiltration membrane) ): Internal pressure type 11 mmφ tubular, operating pressure 5 kg / cmG, water flow rate 15 liter / min. Per membrane. , Polyolefin membrane, molecular weight cut off 100,000, membrane area 0.8 m ² , ball washing once every 30 minutes 4th reactor: 0.8 liter capacity Attached equipment: rapid stirrer and pH meter

First, the raw water is introduced into the first reaction tank at a rate of 60 liters / Hr, and the retention amounts of the first to third reaction tanks are each set to 8 liters. Finally, treated water is discharged from the solid-liquid separation device. It was set to be done. While operating the stirrer, sulfuric acid is injected into the first reaction tank in conjunction with a pH meter so that the pH in the first reaction tank is maintained in the range of 2.5 to 3.0, and the concentration is further increased. Is adjusted to 300 mg / liter (as Fe ³⁺ ), and while the stirrer is operated in the second reaction tank, while considering the pH of the sludge returned from the fourth reaction tank, Caustic soda solution was added to maintain the pH in the range of 4-5. Further, the sludge is drawn out from the solid-liquid separation device, and a part thereof (the amount of sludge containing 20 times the amount of Fe ³⁺ iron atoms injected as the metal salt) is led to the fourth reaction tank. While operating the stirrer, 25% by weight of caustic soda was injected in conjunction with a pH meter so that the pH of the reaction tank was maintained in the range of 7 to 8, and the sludge was returned to the second reaction tank.

When all of the above steps have reached a steady state,
The sludge pulled out from the bottom of the solid-liquid separator is collected in a 1-liter graduated cylinder and allowed to stand for sedimentation. After a lapse of time shown in Table 2 below, the supernatant is removed by decantation, and the concentration of the remaining settled sludge is measured. The results in Table 2 below were obtained. Comparative Example 2 The same operation as in the above example was repeated except that the sludge was not returned and the pH of the second reaction tank was adjusted by injecting a caustic soda solution into the second reaction tank, and the same evaluation was performed. 2 is shown.

[0027]

[Table 2] Sedimentation of sludge As is clear from the results in Table 2 above, according to the method of the present invention in which a part of the sludge is alkali-treated and returned to the second reaction tank, a significant difference is recognized at 0 hours as compared with the comparative example. However, the improvement of the sludge solid concentration became remarkable with the passage of time, and after 24 hours, the sludge solid concentration was about eight times as high.

In Example 2 above, when only the pH in the first reaction tank was changed, the concentration of the extracted sludge after standing for 30 minutes and the quality of the final treated water were examined. The results in Table 3 below were obtained. Obtained.

[Table 3] pH and sludge concentration of the first reactor and treated water quality

From the results shown in Table 3 above, in the method of Example 2, the pH in the first reaction tank has a great influence on the concentration of sludge and the quality of treated water, and the ferric salt is used as the metal salt. In this case, the effect of the present invention is clear when the pH is 3.5 or less, but it is uneconomical to increase the injection amount of the acid. Therefore, the pH in the first reaction tank is 2.5 to 3.0.
A range of 0 is preferred. Furthermore, in Example 2 above, the sludge concentration of the extracted sludge after standing for 30 minutes when only the pH in the second reaction tank was changed, and the dewatered cake concentration when the sludge was subjected to vacuum dehydration in a leaf test for this sludge As a result of examining the change in water quality of the final treated water, the results shown in Table 4 below were obtained. The leaf test was performed with a filtration area of 60 cm ² , a filtration suction time of 1 minute, and a dehydration suction time of 1 minute.

[0030]

[Table 4] pH, sludge concentration and treated water quality of the second reaction tank

From the results in Table 4 above, in the method of Example 2 above, when a ferric salt was used as the primary flocculant, the pH in the second reaction tank had a great relationship with the sludge concentration, The effect of the present invention is remarkable in the pH range of 3.0 to 4.5. The concentration of the dehydrated cake also shows a very high concentration of about 50% by weight in the range of pH 3.0 to 5.5, and the effect of the present invention is clear. However, pH 2.5-
In the range of 3.0, since the ferric ions remained in the treated water, deterioration of the treated water quality was recognized. This can be avoided by providing a pH adjusting tank (not shown) after the second reaction tank to adjust the pH to 4 or more, and then performing solid-liquid separation.

Example 3 An experiment was performed according to the process shown in FIG. The raw water to be treated is the coagulated sedimentation treated water of the plating factory wastewater, and contains the following components as pollutants. BOD: 49 mg / liter COD: 55 mg / liter pH: 8.1 The processing equipment for the test is as follows. First reaction tank: capacity 10 liters Attached equipment: rapid stirrer and pH meter Second reaction tank: capacity 10 liters Auxiliary equipment: quick stirrer, pH meter and aeration 2 liter / m
in. Third reaction tank: 10 liter capacity Auxiliary equipment: slow stirrer Solid-liquid separator (precipitation tank): 180 liter capacity Fourth reaction tank: 0.8 liter capacity Auxiliary equipment: rapid stirrer and pH meter

First, the raw water is introduced into the first reaction tank at a rate of 60 liters / Hr, and the retention amounts of the first to third reaction tanks are each set to 8 liters. Finally, the treated water is discharged from the solid-liquid separator. It was set to be done. While operating the stirrer, sulfuric acid was injected into the first reaction tank in conjunction with the pH meter so that the pH of the first reaction tank was maintained at about 2.8, and the concentration was further increased to 20%.
0 mg / liter (as Fe ²⁺ ), ferrous chloride and hydrogen peroxide are added so that the oxygen concentration becomes 50 mg / liter in terms of available oxygen, and COD and B in the water to be treated are added.
OD and chromaticity components were oxidatively decomposed by Fenton oxidation. In the second reaction tank, the sludge was returned from the fourth reaction tank while operating the stirrer. In the third reaction tank, the concentration was 1 mg /
The polymer flocculant was added to make up liters. Further, the sludge is drawn out from the solid-liquid separation device, and a part of the sludge (the amount of the sludge which is 10 times the amount of iron (Fe ²⁺ ) added in the first reaction tank) is led to the fourth reaction tank. 25% by weight while operating the stirrer
The sodium hydroxide aqueous solution was injected in conjunction with a pH meter so that the pH of the second reaction tank was maintained in the range of 4 to 5, and the sludge was returned to the second reaction tank.

At the time when all the above processes are in a steady state,
The sludge pulled out from the bottom of the solid-liquid separator is collected in a 1-liter graduated cylinder and allowed to stand for sedimentation. After a lapse of time shown in Table 5 below, the supernatant is removed by decantation, and the concentration of the remaining settled sludge is measured. Then, the results shown in Table 5 below were obtained. Comparative Example 3 The same operation as in the above example was repeated except that the sludge was not returned and the pH of the second reaction tank was adjusted by injecting a caustic soda solution into the second reaction tank, and the same evaluation was performed. 5 is shown.

[0035]

[Table 5] Sedimentation of sludge As is clear from the results of Table 2 above, according to the method of the present invention in which a part of the sludge is alkali-treated and returned to the second reaction tank, the sludge is treated for 0 to 24 hours as compared with the comparative example. A remarkable improvement in the sludge solids concentration was observed. In Example 3, as a result of examining the sludge concentration after leaving the extracted sludge for 30 minutes and the quality of the final treated water when the pH in the first reaction tank was changed, the results in Table 6 below were obtained.

[0036]

[Table 6] pH and sludge concentration of the first reaction tank and treated water quality From the results in Table 6 above, also in the method of Example 3, the pH in the first reaction tank has a great influence on the sludge concentration and the quality of the treated water, and the ferrous iron added as the oxidation catalyst is hydrogen peroxide. Example 2
Similarly, when the pH is 3.5 or less, the effect of the present invention is clear. Further, since the preferred pH of the Fenton reaction itself is around 3, the pH in the first reaction tank is also 2.5 in water quality.
The range of -3.0 is preferable.

Further, in Example 3, 30% of the extracted sludge when only the pH in the second reaction tank was changed.
After examining the sludge concentration after standing for a minute and the change in the dewatered cake concentration and the water quality of the final treated water when the sludge was subjected to vacuum dehydration in a leaf test, the results shown in Table 7 below were obtained. The leaf test was performed with a filtration area of 60 cm ² , a filtration suction time of 1 minute, and a dehydration suction time of 1 minute.

[0038]

[Table 7] pH, sludge concentration and treated water quality of the second reaction tank From the results in Table 7, in the method of Example 3 described above, the pH in the second reaction tank has a great relationship with the sludge concentrating property, and the pH in the range of 3.0 to 5.5 is the same as in Example 2. The effect of the present invention is remarkable. The concentration of the dehydrated cake is also pH
In the range of 3.0 to 5.5, the concentration is as high as about 60% by weight, and the effect of the present invention is clear. However, a pH in the range of 2.5 to 3.0 is not preferable because ferric ions remain in the treated water. Moreover, pH 3.0-5.
In 5, the treated water cannot be discharged directly to the public waters, so that a pH adjusting tank is preferably provided after the second reaction tank or after the solid-liquid separation device. This is the same in the first and second embodiments.

Example 4 This was performed in the process shown in FIG. The raw water to be treated is treated water by the anaerobic aerobic circulation type activated sludge method of the leaching wastewater discharged from a waste landfill, and contains the following components as pollutants. BOD: 11 mg / liter COD: 280 mg / liter Total nitrogen: 22 mg / liter pH: 7.6 Chromaticity: 530 degrees

The processing equipment for the test is as follows. First reaction tank: 10 liter capacity Auxiliary equipment: rapid stirrer, pH meter and aeration (decarboxylation) Second reaction tank: 10 liter capacity Auxiliary equipment: slow stirrer First solid-liquid separator (precipitation tank): 180 liter capacity Third reaction tank: 0.8 liter capacity Auxiliary equipment: rapid stirrer and pH meter Fourth reaction tank: 10 liter capacity Auxiliary equipment: rapid stirrer and pH meter Fifth reaction tank: 10 liter capacity Auxiliary equipment: Rapid stirrer, pH meter and aeration 2 liter / m
in. Sixth reaction tank: 10 liter capacity Attached equipment: rapid stirrer, pH meter and aeration (Fe ²⁺ oxidation) Seventh reaction tank: 10 liter capacity Attached equipment: slow stirrer Second solid-liquid separator (precipitation) Tank): 180 liter capacity Eighth reaction tank: 0.8 liter capacity Attached equipment: rapid stirrer and pH meter

First, the raw water was introduced into the first reaction tank at a rate of 60 liters / Hr, and the retention amounts of the first, second, fourth, fifth, sixth and seventh reaction tanks were each set to 8 liters. It was set so that the treated water was finally discharged from the second solid-liquid separation device. While operating the stirrer, ferric chloride was added to the first reaction tank so that the concentration became 200 mg / liter (as Fe ³⁺ ), and the pH of the sludge returned from the third reaction tank was taken into consideration. , Sulfuric acid or slaked lime milk with a pH of 4 in the first reaction tank.
Injection is carried out in conjunction with a pH meter so that the concentration is maintained in the range of 0 to 4.5.
The polymer flocculant was added so as to be mg / liter. Further, sludge is withdrawn from the bottom of the first solid-liquid separator, and a portion of the sludge containing iron in an amount of 10 times the amount of iron (Fe ²⁺ ) added in the first reaction tank is led to the third reaction tank. While operating the stirrer, slaked lime milk having a concentration of 15% by weight
The sludge was injected in conjunction with the pH meter so that H was maintained in the range of 7 to 8, and the sludge was returned to the first reaction tank.

The treated water from the first solid-liquid separation device is led to a fourth reaction tank. In the fourth reaction tank, the concentration is adjusted to 200 mg / liter (as Fe ²⁺ ) while operating a stirrer. Oxygen concentration of 40mg in terms of ferrous solution and available oxygen
Per liter of hydrogen peroxide, and add
Sulfuric acid was injected while interlocking with a pH meter so that H was maintained at around 2.8, and COD, BOD and chromaticity components in the treated water were oxidatively decomposed by the Fenton reaction. In the fifth reaction tank, the pH of the fifth reaction tank is adjusted to 4 to 5 by controlling the amount of 10% by weight slaked lime milk to be injected into the eighth reaction tank with the pH meter of the fifth reaction tank.
Was adjusted. In the sixth reaction tank, air was fed into the reactor while stirring to oxidize Fe ²⁺ ions into Fe ³⁺ ions, and while controlling with a pH meter, 10% by weight slaked lime milk was added to control the pH to 7 to 8; In the reaction tank, the concentration was 1 while operating the stirrer.
The polymer flocculant was added so as to be mg / liter. Further, the sludge is drawn out from the bottom of the second solid-liquid separator, and a part of the sludge is guided to the eighth reaction tank in an amount 20 times as much as the added iron (Fe ⁺² ) in the fourth reaction tank. While operating the stirrer, slaked lime milk having a concentration of 10 wt%
The sludge is injected in conjunction with the pH meter of the fifth reaction tank so that the sludge is maintained in the range of ~ 5, 50% by weight of the sludge is returned to the fifth reaction tank, and the remaining 50% by weight is transferred to the sixth reaction tank. I put it back.

When all of the above steps have reached a steady state,
The sludge pulled out from the bottoms of the first and second solid-liquid separators is collected in a 1-liter graduated cylinder, and allowed to stand for sedimentation. After a lapse of time shown in Table 8 below, the supernatant liquid is removed by decantation and the remaining settled sludge is removed. Was measured to obtain the results shown in Table 8 below. Comparative Example 4 Sludge return (1) and (2) were not performed,
Inject 10% by weight slaked lime milk into the fifth and sixth reaction tanks.
The same operation as described above was repeated except that the H adjustment was performed, and the same evaluation was performed. The results are shown in Table 8.

[0044]

[Table 8] Sedimentation of sludge

Example 5 The procedure shown in FIG. 4 was performed. The raw water to be treated is treated water by the anaerobic aerobic circulation type activated sludge method of the leaching wastewater discharged from a waste landfill, and contains the following components as pollutants. BOD: 15 mg / liter COD: 310 mg / liter Total nitrogen: 18 mg / liter pH: 7.7 Chromaticity: 590 ° The processing equipment for the test is as follows. First reaction tank: capacity 10 liters Attached equipment: rapid stirrer, pH meter and air exposure 2 liters / m
in. (Decarbonation) Second reaction tank: 10 liter capacity Auxiliary equipment: slow stirrer First solid-liquid separator (precipitation tank): 180 liter capacity

Third reaction tank: 10 liter capacity Auxiliary equipment: rapid stirrer and pH meter Fourth reaction tank: 10 liter capacity Auxiliary equipment: rapid stirrer and pH meter, air exposure 2 liter / m
in. Fifth reaction tank: capacity 10 liters Attached equipment: rapid stirrer and pH meter, air exposure 2 liters / m
in. Sixth reaction tank: 10 liter capacity Auxiliary equipment: slow stirrer Second solid-liquid separator (precipitation tank): 180 liter capacity

First, the raw water was introduced into the first reaction tank at a rate of 60 liters / Hr, and the retention amounts in the first, second, third, fourth, fifth, and sixth reaction tanks were each set to 8 liters. It was set so that the treated water was finally discharged from the second solid-liquid separation device. While the stirrer and the aeration were operated, ferric chloride was added to the first reaction tank so that the concentration became 100 mg / liter (as Fe ³⁺ ), and 25% by weight of caustic soda was added to the first reaction tank to adjust the pH of the first reaction tank. Injection is carried out in conjunction with a pH meter so as to be maintained in the range of 4.0 to 4.5. In the second reaction tank, while operating the stirrer, the nonionic polymer aggregation is performed so that the concentration becomes 1 mg / liter. The agent was added. Furthermore, sludge is drawn out from the bottom of the first solid-liquid separation device, and a part thereof is returned sludge (1).
Of iron (Fe ³⁺ ) added in the first reactor as
Sludge containing twice the amount of iron is led to the first reaction tank. In the first reaction tank, the pH in the first reaction tank is maintained in the range of 4.0 to 4.5 while operating the stirrer and the aeration.

The treated water from the first solid-liquid separation device is guided to the third reaction tank. In the third reaction tank, while the stirrer is operated, the concentration of the water is adjusted to 200 mg / liter (as Fe ²⁺ ). Oxygen concentration is 40m in terms of ferrous solution and available oxygen
g / liter, add hydrogen peroxide and inject sulfuric acid in conjunction with a pH meter so that the pH of the reaction tank is maintained at around 2.8. It was oxidatively decomposed by the reaction. In the fourth reaction tank, 25% by weight of caustic soda was added while stirring and aerating to adjust the pH.
Is controlled to 4 to 5 and the air aeration is 2 liter / min. Oxidized ferrous to ferric. In the fifth reactor, the pH was adjusted to 7 to 8 by adding caustic soda having a concentration of 25% by weight while operating a stirrer and aeration. In the sixth reaction tank, a weak anionic polymer flocculant was added so that the concentration became 1 mg / liter while operating the stirrer. Further, the sludge is drawn out from the bottom of the second solid-liquid separation device, and a part of the sludge is returned as sludge (2), and the iron (F) added in the third reaction tank is removed.
e ^{2 +} ) to the fourth reactor,
And sludge containing the same amount of iron as iron added to the first reaction tank as returned sludge (3) is led to the first reaction tank, and the pH of the first reaction tank is adjusted.
Is kept in the range of 4.0 to 4.5.

When all of the above steps have reached a steady state,
The sludges (1) and (2) drawn out from the bottoms of the first and second solid-liquid separators, respectively, were placed in a 1-liter graduated cylinder and allowed to stand for sedimentation, and after a lapse of time shown in Table 9 below, the supernatant was decanted. The concentration of the remaining settled sludge was measured and the results shown in Table 9 below were obtained. Comparative Example 5 The same operation as in Example 5 was repeated, except that the pH was adjusted with an alkaline agent in the first and fifth reaction tanks without returning the sludge (1), (2) and (3). , Evaluate similarly,
Table 9 shows the results.

[0050]

[Table 9] Sedimentation of sludge Example 6 The same processing as in Example 5 was performed except that only the sludge return (3) was not performed. The sludge concentration after settling for 0.5 hour in the same manner as in Example 5 and the water quality obtained from the first solid-liquid separator and the second solid-liquid separator were determined by the following 10 along with Example 5 and Comparative Example 5. It is shown in the table.

[0051]

[Table 10] Sedimentation of sludge and water quality

Example 7 In Example 5, the pH values of the first, third and fifth reaction tanks were changed independently (that is, only one pH was changed in the treatment operation in Example 5). The relationship between the pH in the case where the pH was changed and the other conditions and the other conditions were the same as in Example 5) and the sludge concentration when the extracted sludge was allowed to settle in a 1-liter graduated cylinder for 0.5 hour. 5 is shown. FIG. 5 shows the relation between the first reaction tank and the sludge of the first solid-liquid separation device, and the relation between the third reaction tank, the fourth reaction tank, the fifth reaction tank, and the sludge of the second solid-liquid separation device. Indicated.

As shown in FIG. 5, the first and fourth reaction tanks show high sludge concentrating properties in the pH range of 3.0 to 5.5, and the third reaction tank shows high sludge concentrating properties in the pH range of 3.5 or less. was gotten. In the fifth reaction tank, a high sludge thickening property was obtained at pH 4 or more. These results show that the objective of the present invention is optimally achieved when the pH value of the fifth reactor is the same as or higher than the pH of the fourth reactor, and the fifth reactor adjusts the pH of the final treated water. It is installed only for the purpose of adjusting to the discharge reference value, and is not an important component in the present invention. When ferric chloride was used instead of ferrous chloride injected into the third reaction tank in Example 5, the COD and chromaticity values of the final treated water were slightly deteriorated. The optimum pH for the four reactors was similar to that for ferrous iron.

[0054]

According to the present invention as described above, in the method for coagulating and sedimenting wastewater, a part of the generated sludge is returned to the raw water to be treated and circulated, thereby increasing the degree of purification of the finally obtained treated water. It is possible to provide a wastewater treatment method which is high and has high sedimentation speed, concentration and dewatering property of generated sludge, and can easily perform final treatment of sludge.

[0055]

[Brief description of the drawings]

FIG. 1 is a diagram schematically illustrating a method of the present invention.

FIG. 2 is a diagram schematically illustrating the method of the present invention.

FIG. 3 is a diagram schematically illustrating the method of the present invention.

FIG. 4 is a diagram schematically illustrating the method of the present invention.

FIG. 5 shows the relationship between the first reactor and the sludge of the first solid-liquid separator, and the relationship between the third reactor, the fourth reactor, the fifth reactor, and the sludge of the second solid-liquid separator. FIG.

Continuation of the front page (72) Inventor Yoshinari Sugaya 1-5-7 Kaji-cho, Chiyoda-ku, Tokyo Environmental Engineering Co., Ltd. (56) References JP-A-57-4287 (JP, A) JP-A-53-84355 ( JP, A) JP-A-60-94197 (JP, A) JP-A-60-488189 (JP, A)

Claims (6)

(57) [Claims] 1. A wastewater treatment method in which raw water containing an organic pollutant is introduced into a reaction tank to adjust pH, a metal salt is added as a coagulant to coagulate solids in the raw water, and the treated water is subjected to solid-liquid separation. A part of the separated sludge is added as a flocculant
2 to 50 times the amount of the metal salt (as a metal atom)
A method for treating wastewater , comprising repeating or continuously performing the step of returning the amount of a metal atom to the reaction tank. 2. A raw water containing organic contaminants is introduced into a first reaction tank to adjust pH, and a metal salt is added as a primary flocculant to coagulate solids in the raw water. A polymer coagulant is added as a coagulant to further coagulate the solids, and in a wastewater treatment method for solid-liquid separation of the treated water, after adjusting the pH of a part of the separated sludge in the third reaction tank, A metal salt (gold) added with the sludge as a flocculant
An amount containing the metal atom in an amount of 2 to 50 times the amount of the metal atom) .
A wastewater treatment method, wherein the step of returning to the first reaction tank is repeatedly or continuously performed. 3. An organic contaminant-containing raw water is introduced into a first reaction tank, a metal salt is added as a primary coagulant, and the pH is adjusted.
In the second reaction tank, the pH is adjusted to aggregate the solids in the raw water using the metal salt as a primary flocculant, and then in the third reaction tank, a polymer flocculant is added as a secondary flocculant to further aggregate the solids. In the wastewater treatment method for solid-liquid separation of the treated water, after the pH of a part of the separated sludge was adjusted in the fourth reaction tank, the sludge was added as a flocculant.
2 to 50 times the amount of the metal salt (as a metal atom)
The amount, waste water treatment method, which comprises carrying out steps repeatedly or continuously returned to the second reaction vessel containing. 4. A wastewater treatment method, wherein the treatment step according to claim 2 is performed on the treated water treated in claim 1. 5. A waste water treatment method according to claim 1 wherein the oxidizing any contaminants with an oxidizing agent added to the reaction vessel. 6. A waste water treatment method for raw water according to claim 1 is a process water secondarily treated with the active sludge method.