JP2000185289A - Waste water treatment method and apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pretreatment process for effectively removing iron and manganese contained in waste water at a low cost in a waste water treatment method for treating waste water containing org. compounds by using ozone and light. SOLUTION: Ozone supplied from an ozone generator 7 through a line L5 is injected into waste water supplied from a line L1 in an ozone treatment tank 1 to oxidize soluble metals in waste water to insolubilize them and the treated soln. is passed through a sand filter tank 3 through a line L2 to separate the insolubilized matter and the waste water from which soluble metals are removed is sent to an org. matter treatment apparatus 2 and an org. compd. is decomposed by using ozone and light.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for treating water, industrial wastewater, tap water, wastewater from treated sludge, and particularly wastewater containing soluble metals such as leachate from landfills.

[0002]

2. Description of the Related Art A treatment method is known in which ozone is added to wastewater and the organic compound is oxidatively decomposed by irradiating light such as ultraviolet rays (see Japanese Patent Application Laid-Open No. Hei 7-136668).

By the way, of wastewater containing organic compounds,
Landfill leachate often contains iron and manganese. In addition, if iron chloride or polyiron is used as a coagulant for coagulation and sedimentation generally used in water treatment, soluble iron that did not contribute to coagulation may flow out into the water for treatment. Iron chloride and polyiron used as flocculants contain manganese of several thousand ppm, and soluble manganese also flows out into the treatment water.

When the wastewater containing a large amount of iron, manganese, etc. is subjected to the treatment using ozone and light as described above, insolubilized substances are generated from the iron, manganese, etc., and light is transmitted into the wastewater. And the scaling of the surface of the lamp as a light source to reduce the irradiation capability of the lamp. To remove iron, manganese, etc.
Conventionally, potassium permanganate oxidation precipitation method, contact filtration method, alkali coagulation method and the like have been used.

In the potassium permanganate oxidation precipitation method, potassium permanganate is added to wastewater to oxidize and insolubilize soluble iron and manganese, and is separated from wastewater by a method such as sand filtration. It is a method of removing. The contact filtration method is a method in which a chlorine-based oxidizing agent such as sodium hypochlorite is added to wastewater, and soluble manganese is adsorbed and removed by sand filtration using manganese sand. Manganese sand refers to sand with manganese oxide attached to the particle surface and is standardized by the Japan Water Works Association. This method is a treatment method in which manganese oxide adhering to the surface of sand particles is used as a catalyst to oxidize and insolubilize manganese even with a chlorine-based oxidizing agent having weak oxidizing power and remove it. The alkali coagulation method is a method in which an alkali agent such as sodium hydroxide is added to wastewater to form a floc-like hydroxide of soluble iron or manganese at a pH of 10 or more, and coagulation precipitation and membrane separation are performed. Similarly, there is a method of removing the coagulant using a heavy metal collector in the coagulation process.

[0006]

However, the conventional methods for removing iron and manganese have the following problems, respectively. In the potassium permanganate oxidation method, it is very difficult to adjust the amount of the potassium permanganate solution to be added, and manganese is eluted even if the amount of addition is large or small. In the contact filtration method, an organic chlorine compound is synthesized due to an increase in residual chlorine due to the use of a chlorine-based oxidizing agent, which adversely affects the original purpose of treating organic substances. The method of removing iron and manganese in the coagulation process requires a chemical solution for pH adjustment and a heavy metal collecting agent.

In view of the above problems, a wastewater treatment method according to the present invention, in a wastewater treatment method containing an organic compound using ozone and light, removes iron and manganese contained in the wastewater effectively and at low cost. It is an object to provide a wastewater treatment method including a pretreatment step.

[0008]

In order to solve the above-mentioned problems, a wastewater treatment method of the present invention is directed to a wastewater treatment method for irradiating ozone-added wastewater with light to oxidatively decompose organic compounds in the wastewater. Prior to the oxidative decomposition treatment, (1) injecting ozone into wastewater to oxidize and insolubilize soluble metals in the wastewater, and (2) separating the insolubilized product from the wastewater. It is characterized by having.

On the other hand, the wastewater treatment apparatus according to the present invention
(1) storing wastewater, injecting ozone into the wastewater, oxidizing soluble metals in the wastewater to insolubilize the wastewater, and (2) separating insolubilized substances from the treated wastewater in the ozone treatment tank. It is characterized by comprising a separation device and (3) an organic material treatment device that injects ozone into wastewater from which insolubilized substances have been separated by the separation device and irradiates light to oxidatively decompose organic materials.

[0010] When ozone is injected into wastewater, metal ions of soluble metals such as iron and manganese contained in the liquid are oxidized using ozone as an oxidizing agent and insolubilized as oxides. By separating this insolubilized material, iron, manganese and the like can be effectively removed, and the oxidative decomposition treatment using ozone-light in the subsequent step can also be effectively performed. Since the existing ozone equipment for the post-process can be used, there is no cost increase, and there is no occurrence of an organic chlorine compound generation reaction at the time of insolubilization, which is preferable.

In this separation step, it is preferable to separate the insolubilized matter by sand filtration or membrane separation. Physically separating the insolubilized substance is preferable because it is low in cost and no new reactant is generated during the separation.

The insolubilization step is preferably performed while maintaining the wastewater in a neutral or acidic state. Ozone has self-decomposition property in a liquid, and its self-decomposition rate depends on the pH of the liquid. The higher the pH value, the faster the decomposition. By maintaining the wastewater in a neutral or acidic state, the self-decomposition of the injected ozone can be suppressed, and the wastewater can be effectively used for the reaction with the soluble metal.

[0013] After the separation step, it is preferable to further comprise an adsorption step of passing the treated filtrate through the granular activated carbon and adsorbing the organic compound in the wastewater to the activated carbon. Ozone is
It also has the function of lowering the molecular weight of a high molecular weight organic compound. By adsorbing low molecular organic compounds on activated carbon,
The load of the subsequent oxidative decomposition treatment step using ozone-light can be reduced, and the high-molecular organic compound can be effectively treated in this step.

In the insolubilization step, it is preferable to use ozone discharged from the oxidative decomposition treatment as injected ozone.
The injected ozone concentration required in this insolubilization step is lower than the ozone concentration in the subsequent oxidative decomposition treatment, and the exhausted ozone concentration after the oxidative decomposition treatment is sufficient as the injected ozone concentration in the insolubilization step. Therefore, by using the waste ozone as the injected ozone, the ozone can be effectively used, and the consumption can be reduced.

[0015]

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. In order to facilitate understanding of the description, the same constituent elements are denoted by the same reference numerals as much as possible in each drawing, and redundant description will be omitted.

FIG. 1 is a schematic configuration diagram of a first apparatus for implementing a wastewater treatment method according to the present invention. The apparatus includes an ozone treatment tank 1 for injecting ozone into wastewater to insolubilize soluble metals, a sand filtration tank 3 for filtering insoluble matter, and irradiating light such as ultraviolet rays while injecting ozone into wastewater. And an organic substance processing device 2 for oxidatively decomposing organic substances. The wastewater is supplied from the line L1 to the ozone treatment tank 1, and the treated wastewater from the ozone treatment tank 1 is supplied to the sand filtration tank 3 via the line L2. Filtrate of sand filter tank 3 is line L
By 3, it is supplied to the organic matter processing device 2. The treated waste liquid from the organic matter treatment device 2 is discharged via a line L4. Ozone used in the ozone treatment tank 1 and the organic matter treatment device 2 is supplied from an ozone generator 7 via lines L5 and L6.

The wastewater treatment method of the present invention using this apparatus will be specifically described. First, wastewater is supplied to the ozone treatment tank 1 from a line L1. In the ozone treatment tank 1, the ozone generated by the ozone generator 7 in the wastewater is supplied to a line L5.
This ozone oxidizes iron, manganese, and the like, which are soluble metals in the wastewater, thereby generating iron oxide, manganese oxide, and the like, and insolubilizing them. Ozone is about 10 times more water-soluble than oxygen and has a high oxidizing power, and thus is effective as an oxidizing agent. In addition, since it does not generate organic chlorine compounds unlike chlorine-based oxidizing agents,
Very preferred. Ozone has a self-decomposition property, and its decomposition rate is dependent on the pH value, and the decomposition rate tends to increase as the pH value increases. .5 or less). Furthermore, a pH value of 4 to 7.5 is particularly preferred. For this reason, it is preferable that the ozone treatment tank 1 includes a pH adjusting device that adjusts the pH of the waste liquid in the treatment tank using a chemical or the like. The waste ozone that has not been dissolved in the waste liquid is discharged from the line L7. In addition, the ozone treatment also has an effect of decomposing high molecular organic substances to lower the molecular weight.

The waste liquid in which the soluble metal has been insolubilized is sent to the sand filtration tank 3 via the line L2 to remove the insoluble matter. The wastewater from which most of the soluble metal has been removed is sent to the organic matter treatment device 2, where the organic matter in the wastewater is oxidatively decomposed by light-ozone treatment. Since the soluble metal is removed from the wastewater, no insolubilized substances are generated during the light-ozone treatment, the light transmittance in the wastewater is not hindered, and efficient light-ozone treatment can be performed. it can.
Further, scaling to a lamp serving as a light source does not occur. The treated wastewater is discharged via line L4.

Since the waste ozone of the organic matter treatment device 2 has a relatively high concentration, the waste ozone may be led to the ozone treatment tank 1 via the line L8. This is preferable because ozone can be efficiently consumed. In addition, backwashing is performed at appropriate time intervals so as not to block the sand filtration tank 3.
Backwash wastewater is discharged out of the system in the same way as sludge.

The apparatus of FIG. 2 differs from the apparatus of FIG. 1 in that a membrane separation tank 4 for filtering insolubles is integrated with an ozone treatment tank 1. Since the partition 8 between the ozone treatment tank 1 and the membrane separation tank 4 is stirred and mixed in the ozone treatment tank 1 by injecting ozone through the line L5, an overflow type partition plate as shown in the figure is sufficient. It is. In the membrane separation tank 4, a membrane separation device 6 using an MF membrane (microfiltration membrane) is provided. Further, an aeration device 9 for aerating the membrane surface with air is provided below the membrane separation tank 4 in order to avoid blocking of the membrane of the membrane separation device 6.

The wastewater treatment method according to the present invention using this apparatus is substantially the same as the wastewater treatment method using the apparatus shown in FIG. 1, and the separation of the insolubilized material is performed in the sand filtration tank 3 or in the membrane separation device 6. The only difference is. Here, in order to prevent the concentration of suspended substances such as insolubilized substances in the membrane separation tank 4 from becoming too high, the concentrated liquid should be withdrawn through the line L9 at appropriate time intervals and discharged out of the system in the same manner as sludge. Is preferred.

The apparatus shown in FIG. 3 is such that a granular activated carbon packed tower 5 filled with granular activated carbon is disposed between the sand filtration tank 3 and the organic substance treatment apparatus 2 of the apparatus shown in FIG. As described above, ozone not only has an action of oxidizing soluble metals and the like, but also has an action of lowering the molecular weight of high-molecular organic matter. Organic substances degraded by ozone in the ozone treatment tank 1 are adsorbed and removed by activated carbon in the granular activated carbon packed tower 5 to remove organic substances.
In the subsequent organic substance processing apparatus 2, the added ozone can be efficiently reacted with the remaining high molecular organic substances. This is expected to improve the effect of decomposing the high molecular organic substance in the organic substance processing device 2. Here, the activated carbon to be packed in the packed tower 5 is more preferably a biological activated carbon, since BOD and the like in wastewater can be effectively treated.

Here, an example in which the granular activated carbon packed tower 5 is arranged in the apparatus shown in FIG. 1 has been described, but the present invention can also be applied to the apparatus shown in FIG.

[0024]

EXAMPLES The present inventors conducted comparative experiments to confirm the effect of removing soluble metals by the wastewater treatment method of the present invention.
Hereinafter, the experimental results will be described.

Example 1 At a leachate treatment facility in a landfill, treated water subjected to biological treatment and coagulation treatment is used as raw water, and membrane filtration (MF membrane, pore size 1.0 μm) is performed before and after ozone treatment. The manganese concentration of each filtrate was compared. Here, the pH of the wastewater during the ozone treatment was set to 5, and the ozone consumption was set to 22.7 mg / l. As a result, the manganese concentration of the filtrate before the ozone treatment was 5.80 mg / l, but the manganese concentration of the filtrate after the ozone treatment was reduced to less than 0.1 mg / l. The composition of the suspended solid (SS) captured by the membrane filtration after the ozone treatment was analyzed by X-ray fluorescence analysis. As a result, the composition of SS was manganese 49%, aluminum 25%, iron 6%, silicon 5%, phosphorus 5%, and calcium 3% (all by weight). When ozone was further injected into the ozone-treated liquid, generation of SS was not confirmed.

Thus, it was confirmed that the ozone treatment effectively removed soluble metals such as manganese.

Example 2 The amount of ozone consumed to insolubilize almost all the soluble manganese and the like in water was examined by changing the pH of the waste liquid during ozone treatment. The initial manganese concentration is 5.80 mg / l, which is the same as the raw water of Example 1. The results are summarized in Table 1.

[0028]

[Table 1] As is clear from Table 1, it was confirmed that the higher the pH value, the higher the ozone consumption. This is, as mentioned above,
This is because the higher the pH value, the higher the self-decomposition rate of ozone. When the pH value is 8 or more, the consumption of ozone is greatly increased, and it is confirmed that the ozone treatment is preferably performed in a pH value of 7.5 or less, that is, in a neutral or acidic region. . When the pH value is less than 4, the ozone consumption is reduced, but since the treatment liquid needs to be adjusted to at least a weakly acidic level when the treatment liquid is discharged, the use amount of the pH adjusting agent increases. Is not preferred.
Therefore, it is more preferable that the wastewater at the time of treatment is neutral or weakly acidic. It was also confirmed that the amount of ozone required in the pre-treatment was much smaller than the amount of ozone (several hundred mg / l or more) required in the subsequent light-ozone treatment.

Example 3 The same raw water as in Example 1 was used, and the ozone treatment was not performed (no pre-treatment) and the ozone treatment of the present invention was performed (with pre-treatment). Each of them is subjected to light-ozone treatment, and dioxins (DXN
) Were compared. In the pretreatment, the same ozone consumption of 22.7 mg / l as in Example 1 and the removal of insolubles such as manganese by membrane filtration were performed. The light-ozone treatment was performed under the conditions of injecting about 900 mg / l of ozone and irradiating an ultraviolet lamp with a sterilization line output of 20 W.

As a result of the experiment, the removal rate of DXNs without pre-treatment was 59%, whereas the removal rate of DXNs with pre-treatment reached 98%, which was markedly improved. Was confirmed.

Example 4 Using the ozone treatment / filtration filtrate of Example 1, the filtrate was passed through an activated carbon tower, and the water quality after the treatment was changed due to a change in the empty tower speed (SV [1 / h]) of the activated carbon packed tower. Was examined. For comparison, the quality of the treated water passed through only the activated carbon packed tower without performing the ozone pretreatment was also examined. At this time, the activated carbon packed tower was filled with 2.5 liters of biological activated carbon. Table 2 summarizes the quality (BOD and COD) of the treated water and the raw water before the treatment. Further, the removal rate of DXN when each of these treated waters was treated with ultraviolet rays and ozone in the same manner as in Example 3 is also shown in Table 2.

[0032]

[Table 2] As is evident from Table 2, the ozone pretreatment resulted in CO 2
The effect of reducing D and BOD was confirmed. Further, by passing the biological activated carbon, the BOD can be particularly effectively reduced. This effect is improved as the superficial velocity becomes lower. Furthermore, the higher the effect of reducing BOD and COD, the more DXN in the subsequent light-ozone treatment.
Class removal rate also improved. The good treatment of the BOD with activated carbon is considered to be evidence that the low molecular weight organics were degraded very well. Due to this effect, in the organic matter treatment apparatus, as a result of the ozone efficiently reacting with the target polymer organic matter, DXN
It is considered that the removal rate of the class was improved. This confirmed that it was effective to pass the filtrate after the ozone treatment through activated carbon.

[0033]

As described above in detail, according to the wastewater treatment method of the present invention, soluble metals and the like in wastewater which are a factor inhibiting light-ozone treatment can be effectively removed in the pretreatment. The target organic compound can be efficiently removed by light-ozone treatment.

In addition, since the amount of ozone consumed in the pretreatment is much smaller than the amount of ozone used in the subsequent organic matter treatment, there is no need to separately install an ozone generator.
Raw material costs and maintenance costs associated with the generation of ozone are also kept low and relatively inexpensive. And without the use of chlorine oxidants,
There is no need to worry about the synthesis of organic chlorine compounds. Unlike alkaline coagulation, the amount of chemical for pH adjustment is minimal, so that the cost of chemical is also reduced.

By maintaining the pH at neutral or slightly acidic, the amount of ozone consumed for autolysis can be reduced. Furthermore, by adding ozone and separating and removing the insolubilized substance, the organic compound is removed by passing through activated carbon, and the ozone can be efficiently used in the subsequent organic substance treatment apparatus, so that the decomposition efficiency of the target organic substance is improved.

If the waste ozone in the organic matter treatment device is effectively used in the pretreatment, the amount of ozone generated can be further suppressed, and the labor involved in the treatment of the waste ozone can be reduced.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of an apparatus for performing a wastewater treatment method according to the present invention.

FIG. 2 is an overall configuration diagram of another apparatus for performing the wastewater treatment method according to the present invention.

FIG. 3 is an overall configuration diagram of still another apparatus for performing the wastewater treatment method according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Ozone treatment tank, 2 ... Organic substance treatment apparatus, 3 ... Sand filtration tank, 4 ... Membrane separation tank, 5 ... Granular activated carbon packed tower, 6 ... Membrane separation apparatus, 7 ... Ozone generator, 8 ... Partition wall, 9 ... Aeration Device, L
1 to L9 ... piping.

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) 4D038 AA04 AA08 AB07 AB14 AB66 AB89 BA02 BA04 BB06 BB07 BB09 BB13 BB16 BB17 4D050 AA02 AA04 AA12 AA20 AB07 AB11 AB19 AB55 BB02 BC05 BC09 BD02 BD03 BD04 BD06 CA37 CA0 CA13 A BA06 BB04 BD03 BD13 BD16 BD26 BD27 CA05 CA32 CA54 CA57 DA01 DA13 EB09 EB32 EC26 FC02

Claims (10)

[Claims] 1. A wastewater treatment method in which ozone-added wastewater is irradiated with light to oxidatively decompose organic compounds in the wastewater, wherein ozone is injected into the wastewater prior to the oxidative decomposition treatment, A wastewater treatment method, comprising: an insolubilization step of oxidizing and insolubilizing a soluble metal therein, and a separation step of separating an insolubilized substance from the wastewater. 2. The wastewater treatment method according to claim 1, wherein in the separation step, the insoluble matter is separated by sand filtration or membrane separation. 3. The wastewater treatment method according to claim 1, wherein the insolubilizing step is performed while maintaining the wastewater in a neutral or acidic state. 4. The method further comprises, after the separation step, an adsorption step of guiding the filtrate treated in the separation step to a granular activated carbon packed tower filled with the filtrate and adsorbing the organic compound in the wastewater to the activated carbon. 2. The method according to claim 1, wherein
Wastewater treatment method as described. 5. The wastewater treatment method according to claim 1, wherein in the insolubilization step, waste ozone in the oxidative decomposition treatment is used as injected ozone. 6. A wastewater treatment apparatus for oxidatively decomposing organic compounds in wastewater, wherein the wastewater is stored, ozone is injected into the wastewater, and a soluble metal in the wastewater is oxidized and insolubilized. An ozone treatment tank, a separation device that separates insoluble matter from the treatment wastewater of the ozone treatment tank, and ozone is injected into the wastewater from which the insolubilized material has been separated by the separation device, and the organic matter is oxidatively decomposed by irradiating light. A wastewater treatment device, comprising: an organic matter treatment device. 7. The wastewater treatment device according to claim 6, wherein the separation device is a sand filtration or a membrane separation device. 8. The wastewater treatment apparatus according to claim 6, wherein the ozone treatment tank includes a pH adjusting device for maintaining the wastewater in a neutral or acidic state. 9. The wastewater treatment apparatus according to claim 6, further comprising a granular activated carbon packed tower filled with granular activated carbon between the separation device and the organic matter treatment device. 10. The wastewater treatment apparatus according to claim 6, further comprising a pipe for guiding a part of the ozone discharged from the organic matter treatment apparatus to the ozone treatment tank.