JP5782628B2 - Wastewater treatment method - Google Patents

Description

  The present invention relates to a wastewater treatment method for depositing dissolved organic matter in wastewater as a solid (organic matter solid precipitate) by adding an inorganic additive in wastewater treatment utilizing the collapse of microbubbles.

  The main purpose of wastewater treatment for organic wastewater is to remove carbon (organic matter) present in the wastewater. The removing means can be roughly divided into two. One is a physicochemical method for removing carbon dioxide and other gases from waste water. In general, organic substances are thoroughly oxidized and removed as carbon dioxide.

  However, the physicochemical method has a problem in that a large amount of an oxidant is required to oxidize an organic substance, resulting in a processing cost and an environmental load in wastewater.

  The other is a biochemical method for removing carbon as a solid, and generally corresponds to a method using an aerobic microorganism. In the wastewater, the microorganisms are aerated and the microorganisms are propagated, so that organic matter dissolved in the wastewater is ingested into the microorganisms. The taken-in organic matter becomes the body of the microorganism, and the environmental load of the waste water can be reduced by separating and removing it from the waste water.

  However, the biochemical method does not show an effect on non-biodegradable organic substances, and there is a problem that microorganisms are killed depending on the organic substances.

  Therefore, in recent years, for example, a technique using microbubbles (referred to as bubbles having a diameter of μm order) disclosed in Japanese Patent No. 4378543 (Patent Document 1) by the present applicants has attracted attention. .

  In Patent Document 1, a large amount of free radicals (mainly hydroxyl radicals) generated by erasing microbubbles having a diameter of about 10 to 50 μm containing a gas such as ozone in water are generated. A method of oxidizing organic matter and finally removing it as carbon dioxide is disclosed. Since this method is highly versatile, it can handle difficult-to-decompose chemical substances. In addition, when the intermediate product is excellent in biodegradability, it uses aerobic microorganisms as shown above. It has many advantages that can be used in combination.

In the process of advancing technological development related to such microbubble crushing treatment, we discovered that a very strange phenomenon occurred during crushing. It is a phenomenon in which organic components are deposited as solids. The mechanism is considered to be related to the effect of the gas-liquid interface. That is, ions and dissolved organic substances tend to collect at the gas-liquid interface. Ions are involved in the gas-liquid interface being charged. The water in the vicinity of the gas-liquid interface forms a hydrogen bond network different from the bulk. In the bulk water, other water molecules exist around the water molecules, and a network can be formed in all directions. On the other hand, for water molecules present at the gas-liquid interface, there is no water molecule as a partner to be connected to the gas side. For this reason, the network structure itself is different from the bulk at the gas-liquid interface. Due to this structural difference, it is considered that OH ⁻ and H ⁺ generated by ionization of water molecules are present at a high density at the gas-liquid interface. In particular, under normal pH conditions, OH ⁻ is predominantly present at the interface, so the gas-liquid interface is negatively charged. Since various electrolyte ions exist in the aqueous solution, positive ions are attracted to the vicinity of the interface due to electrostatic attraction. In addition to the localization of such ions, organic substances dissolved in water tend to accumulate at the gas-liquid interface. Dissolved organic substances are not uniformly dissolved in an aqueous solution, and organic substances having a higher molecular weight have a hydrophobic property and tend to collect at the gas-liquid interface. In this way, electrolyte ions and dissolved organic substances are collected at the gas-liquid interface, and the concentration of these electrolyte ions and organic substances increases rapidly in inverse proportion to the area under the condition that microbubbles shrink in water. Further, when the bubbles disappear, energy species such as hydroxyl radicals are formed. When these form a reaction field, dissolved organic substances and electrolyte ions are used as raw materials to generate solid precipitates.

  However, when wastewater treatment is performed using the method described in Patent Document 1, even if materials such as dissolved organic matter and electrolyte ions are prepared, solids (organic solid precipitates) are very likely to precipitate when the microbubbles are collapsed. It was also unclear, and it was also unclear what conditions would be reproduced when the wastewater treatment process was satisfied.

Japanese Patent No. 4378543

  The present invention has been made in view of the above-described circumstances, and by using a microbubble crushing technique and an inorganic flocculant, an organic substance dissolved in waste water is precipitated as a solid, that is, an organic solid precipitate. An object of the present invention is to provide a wastewater treatment method that effectively reduces the amount of organic matter in wastewater by separating and removing this.

The object of the present invention is to generate a microbubble having a diameter of 10 to 50 μm in which a gas is contained in the wastewater containing organic matter, and to give a physical stimulus to the micro in the wastewater. a step of crushing the bubble, using a step of adding a free machine flocculant to said waste water, the inorganic coagulant to the inorganic organic based solid precipitates precipitated by aggregating agent and a step of separating and removing A wastewater treatment method, wherein the wastewater has a COD of 1000 mg / L or more, and the organic solid particles are removed in advance by pretreatment before the step of generating the microbubbles. is relative to the waste water, so that 0.1% to 3%, is and added before or during the said crushing step, crushing been the microbubble surface in said crushing step In addition, dissolved organic matter in the waste water and electrolyte ions supplied in the waste water and by the inorganic flocculant are concentrated to a high concentration, and a chemical reaction is caused by the action of free radicals generated by the crushing. by, organic matter contained in the wastewater is precipitated as the organic-based solid deposits, as well as by separating off the organic-based solid precipitates, treated the wastewater COD is before wastewater treatment COD 1 effectively achieved by said Rukoto such to / 8.

The present invention, by pre SL gas is ozone, or the physical stimulation, while circulating waste water containing the microbubbles in the circulation flow rate of 10 to 100 L / min, punched plate drainage containing the microbubbles Or the physical stimulus is by irradiating an ultrasonic wave having an oscillation frequency of 20 to 1000 kHz, or the physical stimulus uses a discharge having a voltage of 2000 to 3000V. by that is, walk by said inorganic coagulant is either an aluminum salt or iron salt, or by the free radicals is a hydroxyl radical, are more effectively achieved.

  According to the wastewater treatment method of the present invention, a chemical reaction is caused with a dissolved organic substance in a reaction field at the time of crushing microbubbles, and as a result, the dissolved organic substance can be precipitated as a solid. Since it coagulates and settles under the original action, it is possible to significantly reduce the environmental load of the wastewater by separating and removing it from the treated water. It can also be applied to all kinds of organic matter.

It is the schematic of the waste water treatment apparatus used with the waste water treatment method which concerns on this invention. It is a flowchart which shows the flow of the waste water treatment method which concerns on this invention.

  Hereinafter, embodiments of the wastewater treatment method according to the present invention will be described. In addition, this invention is not limited to the following embodiment.

  First, the outline | summary of the waste water treatment apparatus used with the waste water treatment method which concerns on this invention is demonstrated.

  FIG. 1 is a schematic view of the waste water treatment apparatus. As shown in FIG. 1, the waste water treatment apparatus 1 is provided with a microbubble generator 3 inside a treatment tank 2, and a circulation pump 4 and a punching plate (porous plate) 5 are provided on the side of the treatment tank 2. A circulation pipe 6 is installed.

  Here, the type of the microbubble generator 3 is not limited, but a shaft type is preferable. Incidentally, the number of installed microbubble generators 3 is not particularly limited.

  In FIG. 1, the circulation pipe 6 provided with the circulation pump 4 and the punching plate 5 is installed on the side surface of the treatment tank 2, but these may be omitted (the reason will be described later).

  The flocculant adding device 7 may be built in the waste water treatment device 1, installed externally to the device 1 with a pipe or the like, or may be omitted.

  Next, the waste water treatment method according to the present invention will be described based on the waste water treatment apparatus of FIG. 1 and the flowchart of FIG.

  First, raw water (drainage) to be treated is introduced into the treatment tank 2 (start). The raw water used in the wastewater treatment method according to the present invention is not particularly limited, but is suitable for those having a COD (chemical oxygen demand) of 1000 mg / L or more. The raw water is preferably pretreated in advance to remove organic solid fine particles (floating matter). The organic solid fine particles (floating matter) as used herein refers to fine particles floating in the wastewater before the wastewater treatment method according to the present invention, and the organic matter deposited by the method of the present invention. It is different from the system solid precipitate.

  Next, after introducing the raw water into the treatment tank 2, microbubbles are generated by the microbubble generator 3 (step S1). The diameter (particle size) of the microbubbles generated at this stage is on the order of several to several hundred μm. At this point, the diameter distribution (range) of the microbubbles is large, but the diameter finally becomes 10 to 50 μm by passing the microbubble generator 3 itself or a punching plate 5 (described later). The gas interposed inside the microbubbles, that is, the gas sucked into the microbubble generator 3 is preferably ozone, but may be gases such as oxygen, nitrogen, rare gases, air, and the like.

  Next, using the circulation pump 4, raw water containing microbubbles (hereinafter referred to as microbubble-containing raw water) is circulated in the circulation pipe 7 (see the arrows shown in FIG. 1 for the circulation path), The microbubble-containing raw water is passed through the punching plate 5 before returning to the treatment tank 2 (step S2). In addition, as for the circulation amount at the time of circulating the microbubble containing raw | natural water in the circulation pipe 6, 10-100 L / min is desirable. The extrusion pressure of the circulation pump 6 is preferably 0.1 to 0.3 MPa. Incidentally, if the circulation amount and the extrusion pressure are below these ranges, the crushing is not sufficient, and if the circulation amount and the extrusion pressure are above the ranges, the efficiency does not increase so much.

  Incidentally, although it has been described above that the circulation pipe 6 provided with the circulation pump 4 and the punching plate 5 does not need to be installed in the waste water treatment apparatus, the reason for passing the punching plate 5 in the first place is that the diameter is 10 to 10. It is intended to be used as a physical stimulus for crushing (disappearing) 50 μm microbubbles, and this physical stimulus can also be performed by ultrasonic irradiation or electric discharge. In addition, when using ultrasonic irradiation as a physical stimulus, the thing with an oscillation frequency of 20-1000k (1M) Hz can be used, and when using discharge, the thing of 2000-3000V can be used.

  Further, before the microbubble-containing raw water is circulated in the circulation pipe 7 or before it is circulated, the flocculant is added using the flocculant addition device 7 (step S3). The amount of the flocculant is desirably added so as to be 0.1 to 3% with respect to the raw water (drainage). If it is 0.1% or less, aggregation does not proceed sufficiently, and if it is 3% or more, surplus flocculant remains in the waste water. As the flocculant, inorganic flocculants such as aluminum salts and iron salts can be used. In addition, when the coagulant | flocculant addition apparatus 8 is used, it is desirable to add 0.1 to 3% of the continuous supply amount of waste_water | drain continuously.

After the microbubble-containing raw water is treated by adding a flocculant, the raw water is allowed to stand, and organic solid precipitates precipitated by the flocculant are appropriately separated and removed (step S4) . The method for separating and removing the precipitate is not particularly limited. Moreover, you may process the liquid part which remained after isolate | separating this deposit by another methods, such as the waste water treatment method of this invention, or an activated sludge method again.

  Examples of the wastewater treatment method according to the present invention will be described below. For the wastewater treatment apparatus used in this example, see FIG. 1 and the above embodiment.

[Example]
Wastewater having a COD (chemical oxygen demand) of about 40,000 mg / L was introduced into the treatment tank at a flow rate of about 0.1 m ³ / hour. For processing raw water has implemented pretreated to remove beforehand organic-based solid fine particles (suspended solids), the amount of the organic-based solid material fine particles treated raw water was less than 1% organic matter . The treatment tank is about 0.5 m ³ , and two shaft type microbubble generators (50 W type) are installed inside the treatment tank. The amount of microbubbles generated was about 2,000 / mL as bubbles of 50 μm or less as measured with a particle counter. Further, ozone was used as the suction gas of the generator, and the suction amount was 4 L / min.

  Next, wastewater containing microbubbles in the treatment tank (hereinafter referred to as microbubble-containing wastewater) is circulated through the circulation pipe using a circulation pump, and the wastewater is passed through a punching plate before returning to the treatment tank. It was. The circulation rate of the pump was about 50 L / min, and the pressure on the extrusion side was about 0.2 MPa. Next, polyaluminum chloride (PAC) was added into the tank at a rate of about 15 mL / min using an inorganic flocculant addition apparatus.

  When the treatment was carried out under the above conditions and the wastewater treated at a stage where the system was stabilized was examined, generation of a large amount of precipitates (organic solid precipitates) was observed. The precipitate contained a complex such as a metal chelate, and when analyzed by TOF-SIMS, Al, Na, K, Ca, and C—H systems were strongly detected. Al is thought to be mainly derived from PAC, but other elements are also considered to be contained in the waste water. This indicates that not only the inorganic components of the inorganic flocculant itself but also the ions originally contained in the wastewater itself are involved in the precipitation of the organic solid precipitate.

  The COD of the treated water was about 5,000 mg / L. As a comparative example, when the same treatment was performed without adding the inorganic flocculant, almost no precipitate was observed, and the COD was about 30,000 mg / L.

  In addition, an Example is an example to the last.

DESCRIPTION OF SYMBOLS 1 Waste water treatment equipment 2 Processing tank 3 Micro bubble generator 4 Circulation pump 5 Punching plate 6 Circulation pipe 7 Flocculant addition device

Claims (7)

For the wastewater containing organic matter, in the wastewater, a step of generating microbubbles having a diameter of 10 to 50 μm in which gas is contained, a step of giving a physical stimulus and crushing the microbubbles in the wastewater, wherein the step of adding a free machine flocculant to the wastewater, a wastewater treatment method using an inorganic flocculant and a step of separating and removing organic-based solid precipitates precipitated by the inorganic coagulant,
The waste water has a COD of 1000 mg / L or more, and before the step of generating the microbubbles, organic solid particles have been removed by pretreatment in advance,
The inorganic flocculant is added to the drainage so as to be 0.1 to 3% and before or during the crushing step ,
On the surface of the microbubbles crushed in the crushing step, the dissolved organic matter in the waste water and the electrolyte ions supplied by the inorganic flocculant in the waste water are concentrated to a high concentration and are generated by the crushing. under the action of free radicals by causing chemical reaction, the organic matter contained in the wastewater is precipitated as the organic-based solid deposits, as well as by separating off the organic-based solid precipitates, it treated the waste water treatment method COD of waste water, characterized in Rukoto such to 1/8 of COD before wastewater treatment. The wastewater treatment method according to claim 1, wherein the gas is ozone. The wastewater treatment method according to claim 1 or 2, wherein the physical stimulation is to pass wastewater containing the microbubbles through a punching plate while circulating the wastewater containing the microbubbles at a circulation rate of 10 to 100 L / min. . The waste water treatment method according to claim 1 or 2, wherein the physical stimulation is irradiation with an ultrasonic wave having an oscillation frequency of 20 to 1000 kHz. The waste water treatment method according to claim 1 or 2, wherein the physical stimulation is to use a discharge having a voltage of 2000 to 3000V. The wastewater treatment method according to any one of claims 1 to 5 , wherein the inorganic flocculant is either an aluminum salt or an iron salt. The waste water treatment method according to any one of claims 1 to 6 , wherein the free radical is a hydroxyl radical.

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