JPH06182365A - Method and apparatus for treating water separated from water purifying treatment sludge - Google Patents

Abstract

PURPOSE:To enable the suitable high-level treatment of purified water while avoiding the return of soluble Fe and Mn to raw water from return water by injecting chlorine dioxide into sludge separated water and subsequently applying filtration and/or contact filtration due to Mn sand to the sludge separat ed water to return the filtered water to a water prufing treatment process. CONSTITUTION:In a process returning the separated water from sludge of a water purifying treatment process to raw water, the supernatant water from a concn. tank 6 and the filtrate from dehydration treatment equipment 7 are allowed to be merged with each other to be introduced into a flocculation and sedimentation tank 9 or allowed to individually flow in the tank and subjected to flocculation and sedimentation treatment by the addition of a basic aluminum cloride to be supplied to filtering equipment 10 packed with anthracite and Mn sand through an outflow pipe (b) and the sludge-separated water consisting of the supernatant water and the filtrate is filtered to be returned to raw water. Chlorine dioxide is injected at the part of the outflow pipe (b) transferring the sludge separated water from the flocculation and sedimentation tank 9 to the filtering equipment 10.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to F in sludge separation water in an advanced treatment facility for purified water for the purpose of producing drinking water.
e, Mn treatment.

[0002]

2. Description of the Related Art Conventionally, separated water such as supernatant water in sludge concentration step or filtered water in dewatering step, which is generated by sludge treatment in water purification treatment, may be simply discharged, but some or all of it is effectively used. Due to this, it was returned to the raw water side and then sent to the water purification process. However, Fe and Mn in the raw water and the returned sludge separation water did not pose a problem in the treatment process. This is because chlorine was injected in the middle of the treatment process, such as pre-chlorine injection to the landing well and medium chlorine injection to the treatment water of the sedimentation basin in the previous water purification facility. This is because Fe and Mn in Example 2 were sufficiently oxidized and were almost removed by coagulating sedimentation, sand filtration, or the like. However, in recent years, due to changes in the water purification process, such as health problems due to organic pollution of water sources, and the development of advanced treatment that accompanies the demand for delicious water,
The problem of Fe and Mn in sludge separation water has arisen.

In advanced treatment of purified water, chromaticity, odor,
In addition to removing surfactants, etc., it also aims to remove chlorinated hydrocarbons that are carcinogens. Chlorinated hydrocarbons represented by trihalomethane, which is a carcinogen,
When chlorine is injected in a state where the amount of trace organic substances in the raw water is large, it occurs due to the reaction between the generated free chlorine and trace organic substances. For this reason, trihalomethane and the like are removed by adsorption with activated carbon or the like for health reasons, but trihalomethane or the like has a problem that breakthrough is very fast in adsorption with activated carbon. Therefore, in recent advanced treatment facilities, post-chlorine injection, in which chlorine is injected after the final filtration step after removing trace organic substances as much as possible in the first stage, is common, and pre-chlorine and medium-chlorine injection is avoided.

For this reason, suspended and dissolved Fe and Mn contained in the raw water are not treated and are reduced in the sludge treatment step, and the dissolved Fe and Mn thus eluted are sent to the raw water side for purification. It is sent to the process and causes various problems. FIG. 3 shows the coagulation sedimentation tank 1, the filtration equipment 2,
The flow of the advanced treatment process in which the activated carbon adsorption filtration equipment 3 is arranged is shown. That is, the sediment in the coagulation sedimentation tank 1 is stored in the drainage basin 4, the filtration sludge in the filtration equipment 2 and the activated carbon adsorption filtration equipment 3 is stored in the drainage basin 5, and the supernatant water thereof is stored in the return pipe b. The sludge that is returned to the treatment step is further recovered as a dehydrated cake through the steps of the concentrating tank 6 and the dehydration treatment facility 7, and the supernatant water and the filtrate thereof are returned to the raw water treatment step via the return pipe b. Is. In such a process, Fe and Mn contained in the sludge separation water (the above-mentioned supernatant water and filtrate) could not be removed and returned to the raw water treatment process, and Fe and Mn contained in the raw water were filtered along with the filtration facility 2 and activated carbon adsorption. It flows through the filtration equipment 3 and the treated water outflow pipe a into the treated water. The Fe and Mn that have flowed out impair the chromaticity of the treated water, cause a problem of pipe blockage in the treatment process, and further consume chlorine, so that the amount of post-chlorine injection increases.

FIG. 4 shows a flocculation settling tank 1 in which an ozone treatment facility 8 is arranged between the filtration facility 2 and the activated carbon adsorption filtration facility 3 in the advanced treatment process shown in FIG. 3, a filtration facility 2, and an ozone treatment facility. 8 shows the flow of the advanced treatment consisting of each step of 8 and activated carbon adsorption filtration equipment 3. The other parts of the advanced processing step of FIG. 4 are the same as those of FIG. Such a figure 4
In the process shown in, the soluble F
The e and Mn are subjected to the oxidation treatment with ozone, like the raw water. Concerning the quantitative fluctuations of the soluble Fe and Mn supplied by returning, the consumption of ozone greatly changes depending on whether or not they are supplied by returning.

Thus, in the unstable oxidation treatment,
When the injection rate of ozone is less than the consumption amount, soluble Fe and Mn flow out to the treated water side by the activated carbon filtration. In Japan,
The amount of free residual chlorine or the amount of combined residual chlorine that should be retained in the tap water indicated in the Waterworks Law Enforcement Regulations and the Ministry of Health, Labor and Welfare Ministry of Environment Notification “Enforcement of the Waterworks Law (Kansui No. 81, July 26, 1974)” The post-chlorine injection is obligatory according to the regulations. The effluent Fe and Mn cause problems such as chromaticity damage due to oxidation due to post-chlorine injection, cause of blockage of water distribution and water supply pipes, and increase of post-chlorine injection due to consumption of chlorine. Occurs.

When the injection rate of ozone is appropriate, the soluble Mn is oxidized into pentavalent Mn and converted into SS, but these SS-converted Mn are retained in the activated carbon layer.
Problems such as filtration blockage occur. Further, when the injection rate of ozone is equal to or more than the consumption amount, it becomes a state in which pentavalent SS-converted Mn and soluble 7-valent Mn are mixed. Under such a condition, the pentavalent Mn causes the above-mentioned problem of filter clogging, and the 7-valent soluble Mn becomes pentavalent due to the reducing action of the activated carbon, resulting in the problem of over-clogging and at the same time the pentavalent Mn. When reduced to pentavalent, the surface of the activated carbon is coated with Mn, which reduces the adsorption capacity of the activated carbon and further lowers the activation ability of the activated carbon. In addition, when the amount of injected ozone becomes excessively large, a phenomenon in which the 7-valent soluble Mn flows out into the treated water as it is, these 7-valent Mn becomes 5-valent Mn with the lapse of time, and the same problem as described above occurs. Occur.

In order to solve the above problems, there has been proposed a method of secondarily removing Fe and Mn during solid-liquid separation of sludge. However, for example, in flotation concentration, Fe,
Mn cannot be sufficiently oxidized, and the coagulation-sedimentation method has almost no effect on soluble Fe and Mn. As one of the coagulation-sedimentation methods, there is a method of injecting an excessive alkaline agent into sludge to obtain a high pH (usually 11 to 12 or more) and solid-liquid separation using Fe and Mn as hydroxides. Had problems such as changing the properties of sludge and pH adjustment when returning sludge-treated separated water to the raw water side.

[0009]

The present invention avoids the supply of soluble Fe and Mn from the returned water to the raw water when returning the sludge-treated separated water, and can perform suitable advanced treatment of purified water. It is an object to provide a method and a device.

[0010]

The above-mentioned problems can be solved by the method and apparatus for treating purified water treated sludge separated water according to the present invention. That is, in the step (1) of returning the sludge separation water generated in the water purification process to the raw water side, chlorine dioxide is injected into the separation water, and then filtration and / or contact filtration with Mn sand is performed to perform the water purification process. A method for treating purified water treatment sludge separated water, which is characterized by returning the water. (2) In a device for returning sludge separation water generated from a water purification facility to the raw water side, means for injecting chlorine dioxide into the separation water, and a filtering device and / or Mn for treating the separation water after injecting chlorine dioxide A treatment device for purified water treatment sludge separated water, which is configured to be returned to the purified water treatment process through a sand contact filtration device. Is.

(Structure) 1 of the structure of the water purification process of the present invention
An example is shown in FIG. However, the present invention is not limited to this specific example. The configuration of the water purification process of the present invention shown in FIG. 1 is the same as the configuration of the conventional water purification process shown in FIG. 4 except for the process of returning sludge separated water to the raw water side. Of course, the configuration of this part may be the same as the configuration of the water purification process shown in FIG. The constitution of the step of returning the sludge separated water in the water purification process of the present invention of FIG. 1 is such that the supernatant water from the concentration tank 6 and the filtrate from the dehydration treatment facility 7 are combined (or separately) to coagulate and precipitate. After flowing into the tank 9, PAC (basic aluminum chloride) was added to cause coagulation and sedimentation, and the sludge separation water composed of the supernatant water and the filtrate was filtered through the outflow pipe b with a filtration facility 10 filled with anthracite and Mn sand. In the returning step, chlorine dioxide is injected at the portion of the outflow pipe b for transferring the sludge separation water from the coagulating sedimentation tank 9 to the filtration facility 10 in the returning step. It is the essence of the structure of the water purification process.

(Function) In the present invention, it is important that chlorine dioxide is used to oxidize soluble Fe and Mn in the sludge-treated separated water. In ordinary water treatment, oxidation is performed with chlorine and sodium hypochlorite, but in a situation where there are many organic substances such as sludge separation water, by-products such as trihalomethane are produced as described above, and raw water and treated water are treated. Comes of poor quality. On the other hand, chlorine dioxide does not generate trihalomethane. Further, chlorite ion (ClCO ₂ ⁻ ) and chlorate ion (ClCO ₃ ⁻ ) generated by the reaction with the organic matter are reduced and removed by the activated carbon in the water purification step. Breakthrough of activated carbon by these ions is much slower than that of trihalomethane.

The reaction between chlorine dioxide and Fe, Mn is as follows, and the reaction product is removed by subsequent sand filtration and / or catalytic filtration with manganese sand. That, Mn (II) + MnO ( OH) 2 → MnO 2 · MnO + 2H + ...... (1) MnO 2 · MnO + 2ClO 2 + 3H 2 O → 2MnO (OH) 2 + 2ClO 2 - + 2H + ...... (2) Fe (II) _{+ ClO 2 → Fe (III)} + ClO 2 - ...... (3) (1) equation adsorption reaction to the manganese sand Mn (II) in water samples, (2) is a activation reaction by ClO ₂ manganese sand . Equation (3) is the oxidation reaction of Fe (II) to Fe (III). Fe (III) becomes Fe (OH) ₃ and is removed by filtration.

In addition, ClO _{2 is} obtained by performing coagulation and precipitation before chlorine dioxide injection to remove organic substances to some extent.
^-, ClO ₃ ^- perform a significant reduction of. Also, ClO ₂
^-, ClO ₃ ^- is used to Eat quickly by air aeration, ClO ₂ ^-, ClO ₃ ^- can also be performed by aeration as removed.

[0015]

EXAMPLES The present invention will be specifically described below with reference to examples. However, the embodiment of the present invention is not limited to this example. In each of the following examples, the Mn-removing and Fe-removing treatments were performed according to the water purification treatment flow shown in FIG.

Compared to the raw water side water purification treatment flow of the present invention shown in FIG. 1, the raw water side water purification treatment flow of FIG. The process is the same as the water purification process flow of FIG. 1 except that it includes a step of actively decomposing organic substances. However, the treatment process of sludge and sludge separation water is different. That is, in the clean water treatment flow of FIG. 2, sludge from the biological contact oxidation tank and coagulation sedimentation tank 1 is collected in the sludge basin 4, and sludge from each of the filtration equipment 2 and the activated carbon adsorption filtration equipment 4 is discharged into the drainage basin 5. This is a method of collecting and treating the separated sludge water from the drainage pond 4 and the separated sludge water from the drainage pond 5 separately.

Further, in the water purification treatment flow of FIG.
The sludge from No. 5 and the sludge from the drainage basin 5 are also treated in separate concentration / dehydration processes depending on the difference in their water content. That is, the sludge from the drainage pond 4 is concentrated in the concentration tank 11 and dehydrated by the pressure dehydrator 12 to be dehydrated sludge, and the sludge from the drainage pond 5 is concentrated in the primary concentration tank 13 and the secondary concentration tank 14. After passing through the pretreatment tank 15, it is dried on a sun drying bed to obtain dehydrated sludge. The sludge separation water containing Fe and Mn from each of the above sludge concentration / dehydration steps is shown in the diagram of the purified water treatment process in Fig. 2 ...
... is indicated by a mark. As can be seen from the figure, in this water purification process, unlike the case of FIG. 1, sludge separation water from the sludge basin 4 and sludge separation water from the drainage basin 5 from the concentrating tank and the like are separately supplied to the Mn and Fe removing tanks 16 and 17, respectively. Mn and Fe are removed from the sludge separation water by oxidation treatment with chlorine dioxide and returned to the raw water side.

(Example 1) The sample water shown below was subjected to Mn removal and Fe removal processing according to the water purification processing flow of FIG.

(Sample water) Sample water is dechlorinated tap water containing Fe and M.
n was added and used. Addition amount of Mn and Fe is 1 mg each
/ Liter. Table 1 shows the sample water quality. In addition, F
To add e and Mn, Fe (II) SO ₄ , Mn (II) S
O ₄ was used.

[0020]

[Table 1]

(ClO ₂ adjusting method and analyzing method) ClO ₂ adjusting method Sodium chlorite (5 g), citric acid (2.5 g) and kaolin (8 g) were mixed in a powder state, and the generated ClO ₂ gas was absorbed in about 200 ml of pure water. It was In this method, almost pure Cl
An O ₂ aqueous solution (about 800 to 1200 mg / liter) is obtained. Analytical method The analysis was performed using the sodium thiosulfate titration method described by Aieta et al. (*) Below. * Determination of Chlorine Dioxide, Chlorine Chl
orite and Chlorate in Water; EMAieta et al. J.AW
Volume 76 Pages 64 (1984)

(Processing test conditions) The column test conditions are as follows. Column: φ20 mm × H · 1200 mm Filler: Deferrite M (EBARA Infilco Manganese Sand 0.6 mmφ) Packing layer thickness: 600 mm Water flow method: Downflow water flow rate: 120-240 m / day (SV8.3-
16.3 h ^-1 )

(Results) Table 2 shows the results of the water flow test by the column.
Shown in.

[0024]

[Table 2]

1. Mn (II) about 1 mg / liter, Fe (I
I) Chlorine dioxide (ClO ₂ ) was injected at 4 mg / liter into the sample water quality (see Table 1) containing about 1 mg / liter, and a treatment test was conducted. As a result, Mn removal and Fe removal were good. . 2. Chlorine dioxide (ClO ₂ ) injection rate of 10 and 15 m
Even when the amount was increased to g / liter (Table 2, Cases 6 and 7), the removal of Mn and the removal of Fe were good. However, the residual ClO ₂ concentration of the treated water is high, and the chromaticity and chlorine odor are high. When the residual ClO ₂ concentration is 4 and 10 mg / liter, the chromaticity is 26 and 90 degrees, respectively. 3. Table 3 shows the residual ClO ₂ and chromaticity with the lapse of time when the treated water was allowed to stand.

[0026]

[Table 3]

Although ClO ₂ and chromaticity decrease with the passage of time, almost no increase in ClO ₂ ion is observed. The chromaticity is derived from ClO ₂ , and with time, ClO
_It can be said that ₂ is distracting. Standing in the dark (about 25 ℃)
After 5 hours, about 80% of ClO ₂ has been dispersed. Further, ClO ₂ required to remove 1 mg / liter of Mn (II) can be calculated as 1.21 mg / liter from the above equations (1) and (2). In this test, Mn (II), F
Sample water containing 1 mg / l of each e (II) was used. The required amount of ClO ₂ with respect to this sample water is 3.6 in terms of chemical equivalent.
Since the actual treatment result (Table 2), injection of 4 mg / liter of ClO ₂ gave good results, which is in agreement with the theory.

(Embodiment 2) According to the water purification treatment flow of FIG. 2, for removing dewatered drainage of sludge in a water purification facility, Mn removal,
Fe removal treatment was performed.

(Water to be treated) Drainage of non-chemical injection long-time pressure dehydrator (with compression mechanism) of water purification facility

(Results) 1. The results of water quality analysis of the filtered water are shown in Table 4.

[0031]

[Table 4]

The main items in the table are turbidity of 8 degrees and chromaticity of 100.
Degree, NH ₃ -N 14.8 mg / liter, Fe 1.8 m
g / liter and Mn 5.6 mg / liter. It is considered that the effect of Fe (ferric hydroxide) is greatly involved in the turbidity and chromaticity. Mn is almost an Mn ²⁺ ion. 2. Fig. 5 shows the breakpoint curve that examined the chlorine demand. Since NH ₃ —N in the raw water is as high as 14.8 mg / liter, the chlorine demand is about 150 in this embodiment.
It is mg / liter.

3. ClO ₂ infusion rate and the relationship between the residual ClO ₂ in FIG. 6, ClO ₂ ^- Figure 7 shows the relationship between ion. The measuring method was based on the measuring conditions of the required amount of chlorine (dark place, 1 hour reaction). The amount of ClO ₂ consumed in the treated water is 20 mg
/ Liter. All ClO ₂ consumed is ClO
_It has changed to ₂ ^- ion. The reaction between NH ₃ —N and ClO ₂ was separately tested using an aqueous solution of NH ₄ Cl dissolved in pure water. Almost no reaction between the NH ₃ -N aqueous solution and ClO ₂ was observed, and the results are shown in FIGS. 6 and 7. From this result, it can be seen that almost no reaction between the NH ₃ —N aqueous solution and ClO ₂ is observed. That is, ClO ₂
Makes Fe, M effective even in the presence of NH ₃ -N.
It can be seen that n can be oxidized.

Example 3 To remove Mn and Fe from the dehydrated filtrate, Mn sand was filtered after chlorine and chlorine dioxide were injected. The processing conditions are as follows. Column: φ20 mm × height 1000 mm Filler: Deferrite M (EBARA Infilco Manganese sand 0.6 mmφ) Packing layer thickness: 600 mm Water flow method: Downflow water flow rate: LV200 m / day

(Results) 1. The processing results are shown in Table 5.

[0036]

[Table 5]

Fe and Mn can be satisfactorily removed by adding 20 mg / liter of ClO ₂ as an oxidant or 150 mg / liter of NaClO as chlorine.
In the case of ClO ₂ treatment, chromaticity hindrance occurs due to residual ClO _2, but chromaticity can also be removed by removing ClO ₂ by aeration or the like. 2. Trihalomethane (THM) of Mn sand treated water is Cl
Almost no generation by O ₂ treatment. With NaClO treatment,
42% of THM was generated immediately after the collection and 89% of THM was generated 24 hours after the collection target water generation capacity (108 μg / liter). Although TOX is generated to some extent in the ClO ₂ treatment, it is about 15 to 30% of that in the NaClO treatment.

3. In the NaClO treatment-Mn sand filtration, a phenomenon was observed in which air bubbles were mixed in the water-filled bed.
It is presumed that this is because the NH ₃ —N concentration of the water to be treated was as high as 15 mg / liter, and denitrification occurred due to the NaClO treatment and bubbles were formed. To apply this method, N
It is desirable to take a longer residence time after mixing aClO and further perform aeration treatment. 4. The US Environmental Protection Agency (USEPA) recommends that the total amount of residual ClO ₂ , ClO ₂ ⁻ ions, and ClO ₃ ⁻ ions in tap water be 1 mg / liter or less. In this case, the amount of ClO ₂ consumed by the dehydrated filtrate is about 29 mg / liter, and most of the ClO ₂ is converted to ClO ₂ ⁻ ions. C
In order to apply the treatment method using 10 ₂ , it is preferable to perform the treatment with activated carbon in the latter stage.

[0039]

The following effects can be obtained by the processing of the present invention. Since chlorine dioxide is used, it does not produce harmful substances such as trihalomethane. Since Fe removal and Mn removal are performed in the sludge returning step, there is no load of Fe and Mn on the raw water due to the returning. Therefore, the life of activated carbon in the water purification process is extended and the usage amount is reduced. As a result, advanced treatment of purified water without pre-chlorine injection and medium-chlorine injection can be efficiently performed, and safe drinking water can be efficiently performed.

[Brief description of drawings]

FIG. 1 is a conceptual flow chart showing an example of an advanced treatment process of purified water including a treatment process of sludge separated water according to the present invention.

FIG. 2 is a flow chart showing one specific example of an advanced treatment process of purified water including a treatment process of sludge separated water according to the present invention.

[Fig. 3] Flow chart of conventional advanced water purification treatment with coagulation sedimentation and filtration equipment plus activated carbon adsorption equipment

[Figure 4] Flow chart of conventional advanced water purification treatment in which coagulation sedimentation and filtration equipment are added with ozone treatment and biological adsorption treatment with activated carbon

[Figure 5] Breakpoint curve

[Fig. 6] Relationship graph between chlorine dioxide injection rate and residual chlorine dioxide

FIG. 7: Relationship graph between chlorine dioxide injection rate and residual chlorine dioxide ion

[Explanation of symbols]

 1 Coagulation Sedimentation Tank 2 Filtration Equipment 3 Activated Carbon Adsorption Filtration Equipment 4 Drainage Pond 5 Drainage Tank 6 Concentration Tank 7 Dehydration Treatment Equipment 8 Ozone Treatment Equipment 9 Coagulation Sedimentation Tank 10 Filtration Equipment 11 Concentration Tank 12 Pressure Dehydrator 13 Primary Concentration Tank 14 Secondary concentration tank 15 Dehydration pretreatment facility 16 Mn, Fe removal tank A Landing well a Treated water outflow pipe b Outflow pipe

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hitoshi Kimura 1-6-27 Konan Minato-ku, Tokyo Ebara-in Filco Co., Ltd.

Claims (2)

[Claims] 1. In the step of returning the sludge separation water generated in the water purification treatment step to the raw water side, chlorine dioxide is injected into the separation water, and then filtration and / or contact filtration with Mn sand is applied to the water purification step. A method for treating purified water treatment sludge separated water, which is characterized by returning the water. 2. A device for returning sludge separated water generated from a water purification facility to the raw water side, means for injecting chlorine dioxide into the separated water, and a filtering device for treating the separated water after injecting chlorine dioxide, and / or Alternatively, a treatment device for purified water treatment sludge separated water configured to be returned to the purified water treatment process through a contact filtration device using Mn sand.