JP2008253860A - Waste water treatment method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a new waste water treatment method by which the power consumption is made lower than that of the conventional method using aerobic biological treatment and a soluble organic component, which is hardly treated by the conventional method using aerobic biological treatment, in waste water can be efficiently decreased. <P>SOLUTION: The waste water treatment method is characterized in that the pressurized waste water is jetted through a nozzle to generate cavitation air bubbles, the generated cavitation air bubbles are brought into contact with the soluble organic component in the presence of an oxidizer, so that the soluble organic component in the waste water is efficiently decreased by the impact force when the minute cavitation air bubbles burst and the action of the oxidizer. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a wastewater treatment method for efficiently decomposing soluble organic components in wastewater by impact force when cavitation is generated and cavitation bubbles collapse.

  In recent years, environmental regulations are becoming stricter, and the demand for wastewater treatment technology is increasing accordingly. Conventionally used wastewater treatment methods include aerobic biological treatment such as activated sludge treatment. Generally, aerobic biological treatment requires a large amount of power for a blower for supplying air and oxygen. That is a problem.

  In activated sludge treatment, wastewater is supplied into a biological treatment tank in which sludge, which is an aerobic microorganism, floats, and aerated with air, so that organic substances contained in the wastewater are oxidized and decomposed by the biological action of the microorganisms. The However, when biologically decomposing organic matter, the grown microorganisms are generated in large quantities as sludge, so a part of the excess sludge separated and concentrated in the sedimentation tank etc. is returned to the biological treatment tank, and the rest as surplus sludge. It is necessary to discharge out of the system. Excess sludge discharged outside the system is concentrated and dehydrated and then disposed of by incineration or landfill, and disposal of this surplus sludge is also costly. In addition to this, there are problems such as the need for a large site because the BOD volumetric load used for operation is low and the facilities are large.

  Japanese Patent Application Laid-Open No. 11-330166 (Patent Document 1) discloses a method of providing a fluidized bed method used when biologically treating wastewater containing a high load of organic matter before the activated sludge treatment. Here, simply by providing activated sludge treatment at the latter stage of the fluidized bed method, the sludge conversion rate is high and the amount of surplus sludge generated increases, so two-stage activated sludge treatment is performed to reduce the amount of surplus sludge generated. It is supposed to be possible. However, in order to perform the two-stage activated sludge treatment in this way, there is a problem that the apparatus becomes large. Moreover, although this method can reduce excess sludge, it is still insufficient.

  JP-B-5-87320 (Patent Document 2) generates or promotes ozone or active oxygen species (OH radicals) directly in water from dissolved air (oxygen) by discharging in wastewater containing COD components. It shows a method of biological treatment after generating ultraviolet rays as an agent to change the wastewater to be easily biodegradable. However, the effect of reducing soluble organic components is unclear. Moreover, practically, it is difficult to realize a stable underwater discharge, so that it has not yet been put into practical use.

  Japanese Patent Laid-Open No. 2001-225060 (Patent Document 3) reports on a water treatment method using cavitation. However, the effect obtained from this technology is that the solute substance can be easily agglomerated and separated almost without using a flocculant by separating the restraint water from the solute using cavitation and preventing the re-restraint. It does not directly reduce dissolved organic matter. Further, since the generation method of cavitation is limited to the ultrasonic vibrator, the degree of the effect is extremely unclear from the viewpoint of reducing soluble organic matter.

  Japanese Unexamined Patent Publication No. 2005-305398 (Patent Document 4) describes an organic waste treatment apparatus that generates cavitation by pressurizing and injecting a waste liquid. However, the effect obtained with this device is to destroy and sterilize cells floating in food waste waste liquid by using the impact force generated by disrupting the cavitation at the center of the eddy current, thereby reducing soluble organic substances. The effect on is unclear.

  Japanese Patent Laid-Open No. 2002-126730 (Patent Document 5) describes a method of treating cleaning wastewater in a semiconductor manufacturing process using cavitation. Here, a method is shown in which cavitation is generated by pressurizing and injecting wastewater, and radical generation promoting means are provided before and after the cavitation generating means to decompose soluble organic components in the wastewater with low energy. . However, since the pressure at the time of injecting the treatment liquid is low, the load of the waste liquid that can be treated by this method is low, and the effect of decomposing soluble organic components is insufficient.

JP-A-11-330166 Japanese Patent Publication No. 5-87320 JP 2001-225060 A JP 2005-305398 A JP 2002-126730 A

  As mentioned above, high blower power consumption and surplus sludge disposal that conventional aerobic biological treatment has, wastewater treatment technology that does not require securing a large site, etc., and versatility for the type of wastewater, A new wastewater treatment technique capable of efficiently reducing soluble organic components has been desired. The present invention provides a new wastewater treatment method that can efficiently reduce soluble organic substances in wastewater, which consumes less power than conventional aerobic biological treatments, etc., and was difficult to treat with biological treatments. It is what.

  Therefore, as a result of intensive studies to solve the above problems, the present inventors have generated cavitation bubbles by injecting pressurized wastewater through a nozzle, and the cavitation in the presence of an oxidizing agent. It has been found that by treating the soluble organic components in the wastewater with bubbles, the soluble organic substances in the wastewater can be efficiently reduced by the impact force when the cavitation bubbles collapse and the action of the oxidizing agent. Furthermore, the present inventors have found that waste ozone treatment equipment and treatment costs can be made unnecessary by using waste ozone discharged in an unreacted state in the pulp bleaching step as an oxidizing agent.

  As shown in Kato's book (edited by Yoji Kato, new edition of Cavitation Basics and Recent Advances, Tsuji Shoten, 1999), cavitation is a high impact pressure that reaches several GPa in the local region of the order of several μm when the cavitation bubbles collapse. The temperature rises to several thousand degrees Celsius when viewed microscopically by adiabatic compression when the bubbles collapse. As a result, when cavitation occurs, the temperature increases. For these reasons, cavitation has been a technical problem to be solved because it causes damage to the fluid machine, such as damage, vibration, and performance degradation. In recent years, research on cavitation has progressed rapidly, and it has become possible to control the cavitation generation region and impact pressure with high accuracy using the mechanical parameters of the cavitation jet as operating factors. As a result, it is beginning to be expected to effectively utilize the powerful energy by controlling the bubble collapse impact force. Therefore, it has become possible to control cavitation with high accuracy by performing operations and adjustments based on hydrodynamic parameters. This shows that it is possible to maintain the stability of the technical effect, and not by cavitation that caused uncontrollable harm that naturally occurs in fluid machinery in the past, but by controlled cavitation. It is a feature of the present invention that the generated bubbles are actively introduced into the waste water and the energy is effectively used.

  According to the present invention, it is possible to efficiently reduce soluble organic substances in waste water, which consumes less power than conventional aerobic biological treatments and is difficult to perform in biological treatments. Furthermore, by using waste ozone, it becomes possible to eliminate the waste ozone processing equipment and processing cost that were required in the past.

  The wastewater containing soluble organic components to be treated according to the present invention is a wastewater in a wide concentration range including papermaking wastewater and chemical wastewater, and is not particularly limited, but is clogged with a nozzle. In view of the above, those having as little foreign matter as possible are preferable. In particular, papermaking wastewater and chemical wastewater are preferable because they contain soluble organic components that are difficult in biological treatment. Of these, papermaking wastewater refers to wastewater generated in the pulp and / or paper manufacturing process. Specifically, white water, irrigation water, industrial water, recycled water generated in the pulp and / or paper manufacturing process. Water for washing, industrial water, water after washing of the washing machine, squeezing of a water pump (eg, DNT washer, extractor, screw press, etc.), floss or rejection of a floatator, scum and accept of a pressure levitation device, shower Examples thereof include water, washing water such as felt, diluted water of raw materials, and water after separation treatment such as flotation separation, foam separation, sedimentation separation, membrane separation, centrifugation, and coagulation separation. Here, the effluent generated in the pulp manufacturing process includes lignin, hemicellulose, and the like, and the effluent generated in the paper manufacturing process includes starch, sizing agent, filler, dye, and the like.

  The solid content concentration in the wastewater to be treated is preferably 0.01 mg / L to 10 g / L, more preferably 0.1 mg / L to 5 g / L. That is, when it is less than 0.01 mg / L or more than 10 g / L, the processing efficiency is poor, which is not preferable.

  In the present invention, cavitation bubbles are generated by injecting pressurized wastewater through the nozzle, that is, the soluble organic component and the cavitation bubbles are effective by injecting the wastewater itself as a liquid jet through the nozzle. Can be contacted. In addition, the fluid in which the liquid jet forms a jet may be a solid such as liquid, gas, powder, or the like as long as it is in a fluid state. Further, if necessary, another fluid can be added as a new fluid to the above fluid. The fluid and the new fluid may be uniformly mixed and ejected, but may be ejected separately.

  The liquid jet is a jet of a fluid or a fluid in which solid particles or gas are dispersed or mixed in the liquid, and in the present invention, a liquid jet containing a slurry of inorganic particles or bubbles is also applicable. The gas referred to here may include bubbles due to cavitation.

  Since cavitation occurs when a liquid is accelerated and the local pressure is lower than the vapor pressure of the liquid, flow rate and pressure are particularly important. From this, the basic dimensionless number representing the cavitation state, the cavitation number σ, is defined as the following Equation 1 (edited by Yoji Kato, new edition of cavitation basics and recent advances, Tsuji Shoten, 1999 ).

（p_∞：一般流の圧力、U_∞：一般流の流速、p_v：流体の蒸気圧、ρ：流体の密度）
ここで、キャビテーション数が大きいということは、その流れ場がキャビテーションを発生し難い状態にあるということを示す。特にキャビテーション噴流のようなノズルあるいはオリフィス管を通してキャビテーションを発生させる場合は、ノズル上流側圧力p₁、ノズル下流側圧力p₂、、試料水の飽和蒸気圧p_vから、キャビテーション数σは下記式（２）のように書きかえることができ、キャビテーション噴流では、p₁、p_2、p_v間の圧力差が大きく、p₁≫p₂≫p_vとなることから、キャビテーション数σはさらに以下のように近似することができる（H. Soyama, J. Soc. Mat. Sci. Japan, 47(4)， 381 1998）。

(P _∞: pressure general flow, U _∞: flow rate of the general flow, p _v: fluid vapor pressure, [rho: the density of the fluid)
Here, a large number of cavitations indicates that the flow field is in a state where cavitation is difficult to occur. In particular, when cavitation is generated through a nozzle or orifice tube such as a cavitation jet, the cavitation number σ is calculated from the following equation (from the nozzle upstream pressure p ₁ , the nozzle downstream pressure p ₂ , and the saturated vapor pressure p _{v of the} sample water: 2) In the cavitation jet, the pressure difference between p ₁ , p _{2 and} p _v is large and p ₁ >> p ₂ >> p _v. Therefore, the cavitation number σ is (H. Soyama, J. Soc. Mat. Sci. Japan, 47 (4), 381 1998).

本発明におけるキャビテーションの条件は、上述したキャビテーション数σが0.001以上0.5以下であることが望ましく、0.003以上0.2以下であることが好ましく、0.01以上0.1以下であることが特に好ましい。キャビテーション数σが0.001未満である場合、キャビテーション気泡が崩壊する時の周囲との圧力差が低いため効果が小さくなり、0.5より大である場合は、流れの圧力差が低くキャビテーションが発生し難くなる。

The cavitation condition in the present invention is preferably such that the cavitation number σ is 0.001 or more and 0.5 or less, preferably 0.003 or more and 0.2 or less, and particularly preferably 0.01 or more and 0.1 or less. If the cavitation number σ is less than 0.001, the effect is small because the pressure difference with the surroundings when the cavitation bubbles collapse is low, and if it is greater than 0.5, the flow pressure difference is low and cavitation is difficult to occur. .

  In the present invention, cavitation due to a liquid jet is generated by ejecting a jet liquid through a nozzle to the waste water in the container. In that case, the pressure of the spray liquid (upstream pressure) is desirably 0.01 MPa or more and 30 MPa or less, preferably 0.7 MPa or more and 15 MPa or less, and particularly preferably 2 MPa or more and 10 MPa or less. When the upstream pressure is less than 0.01 MPa, it is difficult to produce a pressure difference from the downstream pressure, and the effect is small. On the other hand, when the pressure is higher than 30 MPa, a special pump and a pressure vessel are required, and energy consumption increases, which is disadvantageous in terms of cost. On the other hand, the pressure in the container (downstream pressure) is preferably 0.01 MPa or more and 0.5 MPa or less in static pressure, and particularly preferably 0.05 MPa or more and 0.3 MPa or less. Further, the pressure ratio between the pressure in the container and the pressure of the spray liquid is preferably in the range of 0.001 to 0.5.

  Further, the jet velocity of the jet liquid is desirably in the range of 1 m / second to 200 m / second, and preferably in the range of 20 m / second to 100 m / second. When the jet velocity is less than 1 m / sec, the effect is weak because the pressure drop is low and cavitation hardly occurs. On the other hand, when it is higher than 200 m / sec, a high pressure is required and a special device is required, which is disadvantageous in terms of cost.

  A plunger pump is preferable as the type of pump used in the present invention. In addition, a multistage centrifugal pump or the like may be used as the high pressure generation source, but the shaft seal is difficult and the maintainability is poor. Furthermore, since it is high-speed rotation, there is a demerit that it is difficult to balance and stable processing is difficult.

  The nozzle used in the present invention preferably has an opening diameter of φ0.5 to 5.0 mm. When the nozzle opening diameter is smaller than φ0.5 mm, foreign matter or the like is easily clogged in the nozzle opening, and the processing amount at a constant pressure is small and the processing efficiency is low. On the other hand, when it is larger than φ5.0 mm, the generation efficiency of cavitation is low and the effect obtained by the processing is also small. However, the opening of the nozzle does not necessarily have to be a round hole, and can be formed into a slit shape in consideration of the processing target and ease of maintenance.

  In the present invention, the cavitation generation place can be selected from any container such as a tank or inside a pipe, but is not limited thereto. Further, although it is possible to perform processing in one pass, the effect can be further increased by circulating the required number of times. Furthermore, it can be processed in parallel or in permutation using a plurality of generating means.

  Injection for generating cavitation may be performed in a container open to the atmosphere, but is preferably performed in a pressure container in order to control cavitation.

  In the present invention, an oxidizing agent is added before and after the waste water treatment or at the nozzle portion. Examples of the oxidizing agent include ozone, oxygen, hydrogen peroxide, chlorine, and the like, but are not limited thereto. Of these, ozone is preferable because it has a high oxidation potential and a high decomposition effect on soluble organic components. In particular, it is preferable to use waste ozone discharged in an unreacted state in the pulp bleaching step. That is, conventionally, waste ozone that was discharged unreacted in the pulp manufacturing process had to be discharged after being decomposed by the ozone treatment facility. By using this waste ozone in the present invention, waste ozone treatment facility is used. In addition, processing costs can be eliminated. In addition, it is also possible to use unused ozone that has been discharged unreacted after the treatment in the present invention.

  The amount of ozone added is preferably 10 to 10,000 mg / L. That is, when the amount is less than 10 mg / L, the synergistic effect with cavitation becomes small. When the amount is more than 10000 mg / L, a sufficient effect on the addition amount cannot be obtained, and corrosion of the device itself is concerned.

  In the present invention, by increasing the jetting pressure of the liquid, the flow velocity of the jetting liquid is increased, and the pressure is lowered accordingly, and stronger cavitation is generated. Furthermore, by pressurizing the inside of the container for storing the liquid to be jetted, the pressure in the region where the cavitation bubbles collapse is increased, and the pressure difference between the bubbles and the surroundings increases, so that the bubbles collapse violently and the impact force increases. Cavitation is influenced by the amount of gas in the liquid, and when there is too much gas, collision and coalescence of bubbles occur, so that a collapse impact force is absorbed by other bubbles, and the impact force is weakened. Therefore, since it is influenced by dissolved gas and vapor pressure, the treatment temperature is preferably 5 ° C. or more and 70 ° C. or less, and particularly preferably 10 ° C. or more and 60 ° C. or less. In general, the impact force is considered to be maximum at the midpoint between the melting point and the boiling point, so in the case of an aqueous solution, around 50 ° C is suitable, but even at a temperature lower than that, it is not affected by the vapor pressure. Therefore, a high effect can be obtained within the above range.

  In the present invention, the energy necessary for generating cavitation can be reduced by adding a surfactant. As the surfactant to be used, known or novel surfactants, for example, nonionic surfactants such as fatty acid salts, higher alkyl sulfates, alkylbenzene sulfonates, higher alcohols, alkylphenols, alkylene oxide adducts such as fatty acids, etc. , Anionic surfactants, cationic surfactants, amphoteric surfactants and the like. These may be a single component or a mixture of two or more components. The addition amount may be an amount necessary for reducing the surface tension of the jet liquid and / or the liquid to be jetted.

[Action]
The following reasons can be considered as the reason why soluble organic substances in the wastewater are reduced by the present invention. When the fine bubbles generated by cavitation break down, strong energy is generated in the local region. Therefore, when the fine bubbles collapse in the vicinity of the soluble organic component, it is considered that the impact force cuts the bond of the soluble organic substance and lowers the molecular weight. Moreover, it is thought that decomposition | disassembly of a soluble organic component is accelerated | stimulated by the oxidizing action of an oxidizing agent. In particular, when ozone is added as an oxidant, the effect of decomposing soluble organic organisms is improved by the fact that ozone bubbles are miniaturized and the residence time in the liquid is not prolonged when the fine bubbles generated by cavitation collapse. Conceivable. In addition, since the impact force at the time of collapse of cavitation bubbles is strong, it is possible to disperse ozone more efficiently than the method of refining ozone bubbles by mechanical agitation, so that power consumption can be reduced. Conceivable.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the examples.

[Example 1]
Machine system wastewater (COD _Mn : 195 mg / L) collected from a paper mill is jetted through a 1.5 mm diameter nozzle using the cavitation jet type device shown in FIG. 1, and ozone is 140 mg / L from the nozzle part. And added for 30 minutes. At that time, the pressure of the jet liquid (upstream pressure) was 7 MPa (jet flow velocity 70 m / sec), and the pressure of the jetted container (downstream pressure) was 0.1 MPa.
The COD _Mn of the waste water before and after treatment was measured according to JIS K-0102, and the COD _Mn reduction rate was determined. Moreover, the chromaticity shown by the absorption of each wavelength (wavelength: 254 nm, 270 nm, 440 nm) was measured, and the chromaticity reduction rate was obtained. The chromaticity at 254 nm represents a hydrocarbon, the chromaticity at 270 nm represents an aromatic hydrocarbon, and the chromaticity at 440 nm represents turbidity.

[Example 2]
The treatment was performed in the same manner as in Example 1 except that machine-type waste water (COD _Mn : 200 mg / L) collected from a paper mill was used and the upstream pressure was 0.5 MPa and the downstream pressure was 0.01 MPa.

[Comparative Example 1]
The treatment was carried out in the same manner as in Example 1 except that machine-type waste water (COD _Mn : 220 mg / L) collected from a paper mill was used and air was added to 1.0 L / min instead of ozone.

[Comparative Example 2]
Example except that machine drainage (COD _Mn : 210 mg / L) collected from a paper mill was used and ozone was dispersed in water using a Kinoshita ball filter (G4) instead of using a cavitation jet type device The same treatment as in 1 was performed.

[Example 3]
The treatment was performed in the same manner as in Example 1 except that pulp-based wastewater (COD _Mn : 365 mg / L) collected from a paper mill was used. The COD _Mn of the waste water before and after treatment was measured, and the COD _Mn and the decrease rate were obtained.

[Example 4]
The treatment was performed in the same manner as in Example 3 except that pulp-based waste water (COD _Mn : 390 mg / L) collected from a paper mill was used and the upstream pressure was 0.5 MPa and the downstream pressure was 0.01 MPa.

[Comparative Example 3]
Treatment was performed in the same manner as in Example 3 except that pulp-based waste water (COD _Mn : 385 mg / L) collected from a paper mill was used and air was added to 1.0 L / min instead of ozone.

[Comparative Example 4]
Example 4 except that ozone was dispersed in water using a Kinoshita ball filter (G4) instead of using a pulp-based wastewater (COD _Mn : 400 mg / L) cavitation jet-type device collected from a paper mill. Was processed.

Table 1 shows the COD _Mn removal rate in Examples 1 and 2 and Comparative Examples 1 and 2 and the reduction rate of chromaticity indicated by absorption at each wavelength (wavelength: 254 nm, 270 nm, 440 nm).

実施例３、４、比較例３、４におけるCOD_Mn除去率の吸収で示される色度の減少率を表１に示した。

Table 1 shows the chromaticity reduction rate indicated by the absorption of the COD _Mn removal rate in Examples 3 and 4 and Comparative Examples 3 and 4.

表1、２の結果から、製紙工場から採取したマシン系排水(COD_Mn:195〜220ｍｇ／Ｌ)をノズルを介して排水中に噴射しキャビテーション気泡を発生させ、同時にオゾンを含む気体を添加した場合において、高いCOD_Mn除去効果が見られた。また、表２の結果から、製紙工場から採取したパルプ系排水(COD_Mn:365〜400ｍｇ／Ｌ)を用いた場合も同様の結果であった。一方、オゾンを含む気体を添加しなかった場合、さらには、キャビテーション処理装置を用いずにオゾンを含む気体を添加した場合には、COD_Mn除去効果は低かった。
また、表１の結果から、炭化水素(254ｎｍ)、芳香族炭化水素(270ｎｍ)、濁度(440ｎｍ)のいずれにおいても、製紙工場から採取した排水をノズルを介して排水中に噴射しキャビテーション気泡を発生させ、同時にオゾンを含む気体を添加した場合の分解性が最も効果的であった。

From the results in Tables 1 and 2, machine wastewater (COD _Mn : 195 to 220 mg / L) collected from the paper mill was injected into the wastewater through the nozzle to generate cavitation bubbles, and at the same time a gas containing ozone was added. In some cases, a high COD _Mn removal effect was seen. From the results shown in Table 2, the same results were obtained when pulp-based wastewater (COD _Mn : 365 to 400 mg / L) collected from a paper mill was used. On the other hand, when the gas containing ozone was not added, and when the gas containing ozone was added without using a cavitation treatment apparatus, the COD _Mn removal effect was low.
In addition, from the results in Table 1, for any of hydrocarbons (254 nm), aromatic hydrocarbons (270 nm), and turbidity (440 nm), wastewater collected from the paper mill is injected into the wastewater through nozzles and cavitation bubbles. The decomposability when the gas containing ozone was added at the same time was the most effective.

It is the schematic of the cavitation jet type apparatus used in the Example.

Explanation of symbols

1: Sample tank 2: Nozzle 3: Cavitation jet cell 4: Plunger pump 5: Upstream pressure control valve 6: Downstream pressure control valve 7: Upstream pressure gauge 8: Downstream pressure gauge 9: Water supply valve 10: Circulation valve 11: Drain valve 12: Temperature sensor 13: Mixer

Claims (5)

In a wastewater treatment method in which soluble organic components in wastewater are decomposed by impact force when cavitation bubbles collapse, cavitation bubbles are generated in the wastewater and soluble in the wastewater by the cavitation bubbles in the presence of an oxidizing agent. A wastewater treatment method characterized by decomposing organic components. The waste water treatment method according to claim 2, wherein cavitation bubbles are generated by spraying the pressurized waste water through a nozzle. The wastewater treatment method according to claim 1, wherein the oxidizing agent to be added is ozone. The wastewater treatment method according to claim 2, wherein the ozone is waste ozone discharged from a pulp bleaching step. The wastewater treatment method according to any one of claims 1 to 3, wherein the solid content concentration of the wastewater is 0.01 mg / L or more and 5 g / L or less.

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