JPH07241597A - Treatment of waste water - Google Patents

Abstract

PURPOSE:To efficiently obtain treated water of high quality by highly removing CODMn and a dye in org. waste water by mixing waste water subjected to flocculation treatment with pressurized water obtained by dissolving air iq water under pressure to float and separate a solid component and subsequently subjecting the treated water to ozone treatment before subjecting the same to biological filtering. CONSTITUTION:Raw water is introduced into a flocculation reaction tank and a flocculant is added to raw water from a pipe 12 to subject the raw water to flocculation treatment. The treated water having flocs formed therein by flocculation treatment is supplied to a pressure flotation tank 2 while the pressurized water from a pipe 14 is mixed with the treated water. The treated water to which the pressurized water is added is subjected to pressure flotation treatment in the pressure flotation tank 2 and separated water from which SS is removed is supplied to an ozone contact tank 3. The removal of a chromaticity component and the ozone oxidation of org. matter are performed by ozone injected from a pipe 16 within the ozone contact tank 3 and high mol.wt. CODMn is decomposed to low mol.wt. CODMn. Ozone treated water is introduced into a reaction tank 4 to be sufficiently subjected to ozone oxidizing reaction and subsequently introduced into a biological filter tower 5 to be subjected to biological filtering treatment in the presence of the air from a pipe 20.

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,
In particular, the present invention relates to a method for efficiently treating COD _Mn and chromaticity at a high removal rate as a high-level treatment of activated sludge treatment water of organic wastewater such as food manufacturing wastewater.

[0002]

2. Description of the Related Art Conventionally, as a method for treating organic waste water, after biological treatment by aeration with air containing high-concentration oxygen, separation by coagulation sedimentation or flotation is carried out, and then ozone is converted into ozone by using ozone gas. A treatment method has been proposed (JP-A-59-177192).

Further, a method of performing a fluidized bed type aerobic treatment and then a fixed bed type aerobic treatment after ozone treatment of secondary treated water after precipitation separation (primary treatment) and biological treatment (secondary treatment) Has also been proposed (Japanese Patent Laid-Open No. 4-363199).

On the other hand, organic wastewater such as food manufacturing wastewater is subjected to activated sludge treatment as a secondary treatment after primary treatment such as sedimentation. Further, activated sludge is often treated as integrated wastewater after anaerobic treatment of a concentrated system. The secondary treated water is further subjected to advanced treatment such as filtration treatment, flocculation sedimentation or flocculation pressure flotation treatment.

[0005]

The above-mentioned conventional treatment method is effective in removing turbidity and a part of COD _Mn and chromaticity in the wastewater, but highly soluble COD _Mn and chromaticity can be obtained. It cannot be removed and more advanced processing is required.

[0006] As a method for removing soluble COD _Mn and TOC, an activated carbon adsorption method is generally used. However, since the activated carbon adsorption method requires periodic regeneration of activated carbon, activated carbon is extracted and regenerated. However, there is a drawback in that extremely complicated work is required in the device, the operation management and repair work therefor, and the treatment of generated exhaust gas.

On the other hand, in the coagulation sedimentation treatment method as an advanced treatment, although clear water is obtained, in the continuous treatment system, a part of the sludge precipitated is floated up and flows out together with the treated water, which tends to deteriorate the quality of the treated water. Seen. As a result of the inventors' investigation of this cause, in the coagulation sedimentation treatment method, the sludge zone of the sedimentation portion is in an anaerobic state, and nitrogen gas is generated by a biological reaction with nitrate ions dissolved in the treated water, It was found that sludge floats up with the bubbles of nitrogen gas and deteriorates the quality of treated water.

The present invention solves the above-mentioned problems of the prior art, and it is possible to efficiently remove COD _Mn and chromaticity in organic wastewater such as food manufacturing wastewater to efficiently obtain high-quality treated water. It is intended to provide a processing method.

[0009]

According to the method for treating wastewater of the present invention, after the wastewater is coagulated, air is mixed with pressurized water which is dissolved in water under pressure to float and separate solids, and then after ozone treatment. , Characterized by biological filtration.

The present invention will be described in detail below with reference to the drawings.

FIG. 1 is a system diagram showing an embodiment of a method for treating wastewater according to the present invention.

In the figure, 1 is a flocculation reaction tank, 2 is a pressure floating tank,
3 is an ozone contact tank, 4 is a reaction tank, and 5 is a biological filtration tower. Each symbol of 11 to 22 indicates piping, and P indicates a pump.

In the method for treating wastewater of the present invention, the wastewater to be raw water is preferably obtained by subjecting organic wastewater such as food manufacturing wastewater to primary treatment such as sedimentation and then to activated sludge treatment as secondary treatment. Alternatively, an activated sludge-treated water obtained by treating the activated sludge as the integrated wastewater can be mentioned.

In the present invention, the raw water such as the activated sludge treated water is first introduced into the flocculation reaction tank 1 through the pipe 11, and the flocculating agent is added through the pipe 12 to perform the flocculation treatment. Here, as the aggregating agent, an inorganic aggregating agent such as an aluminum salt such as polyaluminum chloride or an iron salt is used, and it is preferable to additionally use an anionic, nonionic or cationic polymer aggregating agent. The amount of the flocculant added varies depending on the quality of the raw water, but in the normal case, 50
~ 1000 mg / l, polymer flocculant 0.3-2 mg / l
1 is preferably added.

The flocculated water in which flocs are produced by reacting with the flocculant in the flocculation reaction tank 1 is then fed from the pipe 13 to the pressure flotation tank 2, and in the process, the pressurized water is fed from the pipe 14. Mixed.

The pressurized water is prepared by dissolving air in water under pressure, and is preferably dissolved under pressure of ^{2 to} 10 kg · f / cm ² . This pressurized water is usually added in an amount of about 10 to 50% by volume with respect to the coagulated water.

The coagulated water to which the pressurized water has been added is subjected to the pressure floating in the pressure floating tank 2, and the separated water from which SS has been removed is fed to the ozone contact tank 3 through the pipe 15. The pressurized floating treatment water is fed to the ozone contact tank 3 by gravity flow or by a pump.

In the ozone contact tank 3, the chromaticity component is removed and the ozone oxidation of the organic matter is performed by ozone (ozonized air) injected from the pipe 16, and the high molecular weight COD _Mn is biodegraded by the biological filtration in the next step. Low molecular weight COD _{Mn possible}
Is decomposed into. The ozone gas discharged from the ozone contact tank 3 is discharged from the pipe 17.

The amount of ozone injected into the ozone contact tank 3 is preferably such that the chromaticity components are almost completely oxidized and colorless, but COD _Mn is decomposed into CO _2. It doesn't require as much injection amount.

Generally, the greater the ozone injection amount, the higher the chromaticity and COD _Mn removal amount, but on the other hand, the ozone utilization rate,
That is, the amount of ozone consumed per amount of COD _Mn removed increases.
Therefore, it is desirable to set the most economical ozone injection amount from both aspects of the COD _Mn removal amount and chromaticity removal amount and the ozone utilization rate. In the normal case, the ozone injection amount is 5 to 30 mg-O.
_It is preferably about ₃ / l-water.

After the ozone-treated water is introduced into the reaction tank 4 through the pipe 18 and the ozone oxidation reaction is sufficiently performed, the pump P is used.
It is introduced into the biological filtration tower 5 through a pipe 19 equipped with
In the presence of air (oxygen) from 0, biological filtration is performed, and the treated water is discharged from the system through the pipe 22. Further, the exhaust gas is discharged from the pipe 21.

By this biological filtration treatment, easily biodegradable COD _Mn produced by the ozone treatment is removed.

In this biological filtration, since the organic matter load is higher at the portion where the water to be treated is introduced, it is preferable that the oxygen (air) supply amount is larger at this portion. Upflow treatment by is preferable. In this case, as the filter medium, a filter medium having a small flow rate of the filter medium due to an upward flow and having a good turbidity trapping property (having a specific gravity smaller than that of water) is preferable, and specifically, a plastic such as polystyrene, polypropylene or urethane resin. A carrier obtained by foam-molding a material and having a particle diameter of 3 to 10 mm or a long-hair fiber having a length of 10 mm and a diameter of about 100 μm is preferable.

[0024]

In the present invention, the wastewater is subjected to coagulation treatment, pressure floating separation treatment, and then ozone treatment,
Ozone oxidation treatment is efficiently performed with good ozone utilization efficiency to highly oxidize chromaticity components to make them colorless, and at the same time, C
OD _Mn is highly removed, and COD _Mn in the high molecular weight region is decomposed into readily biodegradable COD _Mn .

Easy biodegradable COD in ozone treated water
_Mn is efficiently removed by the biofiltration process.

Thus, according to the method of the present invention, CO
It is possible to efficiently obtain high-quality treated water from which D _Mn and chromaticity are highly removed.

On the other hand, when the activated sludge treated water is directly ozone-treated as in the method described in Japanese Patent Application Laid-Open No. 4-363199, the COD _Mn removal efficiency is poor, and therefore the purpose is rough treatment. Although it can be applied in some cases, in the case of aiming at advanced treatment, the ozone injection amount increases, which is not economically preferable.

This is due to the fact that the present inventors have confirmed that CO in activated sludge treated water, coagulated flotation treated water and ozone treated water.
It is also supported by the examination by the molecular weight fractionation of D _Mn . That is, in ozone treatment, COD _{Mn in the} high molecular weight region is preferentially removed, but high molecular weight COD _Mn has a poor ozone utilization rate due to its high molecular weight. That is, high molecular weight COD
Decomposition of _Mn requires a lot of ozone.

From this, in order to increase the ozone utilization rate and efficiently remove COD _Mn during ozone treatment, the high molecular weight COD _Mn having a poor ozone utilization rate is removed by agglomeration in advance before the ozone treatment. It turns out that it is desirable.

By applying the flocculation pressurization floating process to the flocculation, it is possible to prevent the suspended matter from flowing out and perform the efficient treatment.

Incidentally, if the coagulation sedimentation is carried out instead of the coagulation pressurization floating process, the SS concentration of the outflow water becomes high, so that there is a problem that a further filter is required.

Further, in the present invention, COD _Mn and turbidity can be highly removed by further biologically filtering the ozone-treated water.

Incidentally, in the method described in JP-A-59-177192, in which biological filtration is not carried out after ozone treatment, C
The OD _Mn and turbidity cannot be highly removed.

If a honeycomb type or floating organism treatment is carried out instead of this biological filtration, it is not possible to obtain a microbial cell trapping effect such as biological filtration and a large specific surface area of biological adherents. Induce.

[0035]

EXAMPLES The present invention will be described in more detail with reference to specific examples, comparative examples and experimental examples.

Example 1 According to the method of the present invention shown in FIG. 1, the treated sludge treated water of food production wastewater was treated.

First, in the coagulation reaction tank 1, PAC (polyaluminum chloride) 300 mg / l and nonionic polymer coagulant ("Clifloc-PN133" manufactured by Kurita Water Industries Co., Ltd.) 0.5 mg / After adding 1 and the coagulation treatment, pressurized water was added at a ratio of 30% by volume with respect to the coagulation treated water, and the pressure flotation treatment was performed in the pressure flotation tank 2. afterwards,
After injecting ozonized air into an ozone contact tank (inner diameter 37 cmφ × water depth 300 cm) 3 so as to absorb about 10 mg-O ₃ / l-water, a biological filtration tower (floating filter material (expanded polystyrene resin) 250 liters) ) 5 for residence time 3
Water was passed at a flow rate of 0 minutes.

CO in the effluent of each process after passing water for 30 days
D _Mn , chromaticity, and ozone utilization rate were examined, and the results are shown in Table 1. It should be noted that the ozone utilization rate is the COD _Mn removal amount ΔCOD _Mn (COD _Mn- before ozone treatment) with respect to the ozone consumption amount ΔO ₃ .
It was calculated as the ratio of COD _Mn after ozone treatment.

In addition, regarding the biological filtration treated water, COD _Mn
The molecular weight fraction was measured and the results are shown in Table 2.

Comparative Example 1 Activated sludge treated water was directly ozone treated to increase the amount of ozone blown in the ozone treatment so that the ozone consumption was about 20 mg.
As -O ₃ / l-water, ozone treatment and biological filtration were performed in the same manner as in Example 1, and PAC 300 mg /
1 was added to carry out coagulation-precipitation treatment, and then filtered through filter paper. Three
The COD _Mn , chromaticity, and ozone utilization rate of the effluent water of each step after 0-day water passage were examined, and the results are shown in Table 1.

Further, regarding this coagulated and filtered treated water, CO
The molecular weight fraction of D _Mn was measured and the results are shown in Table 2.

[0042]

[Table 1]

[0043]

[Table 2]

From Tables 1 and 2, the following is clear. That is, according to the present invention, in Example 1 in which the flocculation treatment and the pressure flotation treatment were performed prior to the ozone treatment, the flocculation treatment and the pressure flotation treatment were not performed, the activated sludge treated water was directly ozone treated, and the flocculation was performed after the ozone treatment. COD _Mn can be highly removed at a higher ozone utilization rate, that is, at a lower ozone consumption amount, as compared with Comparative Example 1 in which the filtration treatment is performed.

In particular, according to the invention, the high molecular weight COD _Mn
Has a high removal rate, which leads to a decrease in COD _Mn of the treated water. That is, prior to ozone treatment, agglomeration,
By performing the pressure floating process, the high molecular weight COD _Mn having a poor ozone utilization rate is removed in advance, so that the ozone utilization rate in the post-process is improved and COD _Mn can be highly removed with a small ozone injection amount. Made possible.

Experimental Example 1 PAC3 was added to the activated sludge treated water used as the raw water in Example 1.
The aggregation and precipitation treatment was performed under the chemical injection conditions of 00 mg / l and nonionic polymer flocculant (Clifloc PN-133) 0.5 mg / l. The relationship between the standing time in this treatment and the turbidity of the supernatant water was investigated, and the results are shown in Table 3.

[0047]

[Table 3]

From Table 3, it is clear that the flocculation / precipitation treatment cannot efficiently remove the suspended matter.

Next, the supernatant water and sludge obtained in the above treatment are separated, and water to which a certain amount of the sludge obtained is added to the supernatant water is added to the ozone contact tank at a flow rate of 1.8 liters / hr. Ozone treatment was carried out by bringing the gas into contact with the ozonized air injected under the conditions shown in Table 4. The ozone consumption amount is calculated from the ozone injection amount, the exhaust ozone concentration and the residual ozone amount in the water, and the ozone utilization rate ΔCOD _Mn / ΔO ₃ is calculated from the ozone consumption amount and the COD _Mn removal amount. The results are shown in Table 4. .

[0050]

[Table 4]

From Table 4, it is clear that the greater the amount of ozone injected in the ozone treatment, the greater the amount of COD _Mn removed, but in terms of the ozone utilization rate, the smaller the amount of ozone injected, the better.

[0052]

As described in detail above, according to the wastewater treatment method of the present invention, COD can be highly treated with a small amount of ozone injection as a high-level treatment of activated sludge treatment water of organic wastewater such as food manufacturing wastewater. _Mn and chromaticity can be removed. Compared with the case of adopting activated carbon adsorption treatment, it is easier to operate and economically advantageous. Furthermore, compared with the case of adopting coagulation sedimentation treatment, the quality of treated water is improved and the installation area of the device is reduced. Can be achieved. With such an effect, it is possible to obtain the high-quality treated water easily, efficiently, and inexpensively.

[Brief description of drawings]

FIG. 1 is a system diagram showing an example method of a wastewater treatment method of the present invention.

[Explanation of symbols]

 1 Agglutination reaction tank 2 Pressurized flotation tank 3 Ozone contact tank 4 Reaction tank 5 Biological filtration tower

Continuation of front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical display location C02F 9/00 504 A 1/24 ZAB A 1/78 3/06 ZAB (72) Inventor Hitoshi Amamiya Shinjuku, Tokyo 3-4-7 Nishi-Shinjuku, Tokyo Kurita Industry Co., Ltd.

Claims (1)

[Claims] 1. A method for treating wastewater, which comprises coagulating wastewater, mixing air with pressurized water dissolved in water under pressure to separate solids by flotation, followed by ozone treatment and biological filtration. .