JP2006007145A - Method for treating drainage in general refuse incineration plant - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To further make an apparatus compact and operation management easy in a method for treating inorganic and organic drainage in a general refuse incineration plant. <P>SOLUTION: In the apparatus for treating drainage generated in the refuse incineration plant, the apparatus for treating drainage includes a flocculation tank for mixing the drainage together with a flocculant and a heavy metal chelating agent to carry out flocculation or insolubilization of a suspended solid content and heavy metal ions, and a microfiltration membrane treatment tank for filtrating the drainage from the flocculation tank by a microfiltration membrane to carry out solid-liquid separation. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a general waste incineration plant wastewater treatment method.

  In general, in a waste incineration plant, due to environmental considerations, all wastewater generated in the plant is discharged after being treated by wastewater treatment facilities, or reused as combustion gas cooling water, etc. A recirculation closed system has been introduced that does not discharge any treated water.

  In such waste incineration plant wastewater treatment facilities, wastewater is usually treated with a liquid chelating agent to remove heavy metals in the wastewater, with a flocculant to flocate suspended solids, etc., and further By subjecting it to a treatment with a coagulant aid such as a polymer aid for increasing floc, the floating substance in the waste water is flocked or heavy metal ions are insolubilized. Usually, the treatment with the chelating agent, the flocculant, and the coagulant aid is performed in separate tanks, and a total of three tanks are required as the coagulation tank.

  Moreover, the treated water after passing through the three tanks is further sent to a settling tank (or a settling basin), where the aggregates settle by natural sedimentation. The supernatant wastewater is further subjected to sand filtration and then reused (or discharged in some cases). On the other hand, the sediment is subjected to a dehydrator, the solid content is again returned to the garbage pit and burned, and the dehydrated filtrate is returned to the raw water for wastewater treatment again.

  Thus, in a general waste incineration plant, three tanks as a coagulation tank, a settling tank, and a sand filtration tank are required, and a site area for these devices is required. Moreover, in order to utilize natural sedimentation, an agglomeration aid for promoting flocification of the agglomerates is necessary.

  However, it would be advantageous in terms of cost, management operation, time, and the like if the number of equipment, site area, and chemicals added for aggregation are small.

  As an attempt to deal with such a problem, a wastewater treatment facility of an incineration plant in which the entire facility is miniaturized is disclosed (Patent Document 1). As shown in FIG. 2, the wastewater treatment facility of Patent Document 1 is contacted with activated sludge and a first filtration device 121 that filters inorganic solid wastewater to which a flocculant is added through a filtration membrane to separate contaminated solids. And a second filtration device 122 for separating the sludge solid matter by filtering the wastewater from the first filtration device 121 on which the sludge solid matter is adsorbed and the organic wastewater through a filtration membrane.

  In this prior art wastewater treatment facility, inorganic wastewater is supplied to the first raw water tank 101 and then supplied to the chemical mixing tank 102, and a flocculant is added to agglomerate suspended solids. Next, the waste water is introduced into the first filtration device 121, and the inorganic waste water to which the flocculant is added is filtered through the filter membrane 123 to separate the solid contaminants. The waste water that has passed through the filtration membrane 123 is supplied to the neutralization tank 104, neutralized by the chemicals added there, and then discharged to the second raw water tank 105 (indicated by B in the figure). The sludge concentrated in the first filtration device 121 is sent to the first dehydrator 106 and dehydrated, and then discarded, and the drainage C is returned to the first raw water tank 101.

  Organic wastewater is supplied to the second raw water tank 105. These wastewater is introduced into the contact oxidation tank 107, adsorbed solid contaminants with activated sludge to reduce the concentration in water, and then the second filtration. It is sent to the apparatus 122 where the contaminated solids are separated by the filter membrane 124. The waste water that has passed through the filtration membrane 124 is introduced into the discharge tank 112 and discharged. The sludge concentrated in the second filtration device 122 is sent to the second dehydrator 113 and dehydrated, then discarded, and the drainage C is returned to the first raw water tank 101.

  In the wastewater treatment facility of Patent Document 1, a filtration device equipped with a filtration membrane capable of removing sludge solids is used, so that the size can be greatly reduced as compared with a conventional sedimentation tank having the same ability. In addition, by selecting a filtration membrane that can remove fine sludge solids, the sand filtration tank and sterilizer that were required in the past can be eliminated, simplifying the equipment and making the whole compact. It can be configured.

However, in the wastewater treatment facility of Patent Document 1, the treatment of inorganic wastewater and the treatment of organic wastewater are separately performed in the wastewater treatment flow, and the treatment process is therefore multistage, and In view of the need for such equipment (for example, the neutralization tank 104, the contact oxidation tank 107, the second filtration device 122, etc.), there are still many processing steps and a large number of equipment.
Japanese Patent Laid-Open No. 08-108178

  Therefore, an object of the present invention is to further reduce the size of equipment and facilitate operation management in an inorganic / organic wastewater treatment method for a general waste incineration plant.

  In one aspect, the present invention provides equipment for treating wastewater generated in a waste incineration plant. This waste water treatment facility comprises a single agglomeration tank for flocking or insolubilizing floating solids and heavy metal ions in the waste water by mixing waste water with a flocculant and a heavy metal chelating agent, and the agglomeration A microfiltration membrane treatment tank is provided for filtering the waste water from the tank through a microfiltration membrane for solid-liquid separation.

  Thus, since the wastewater treatment facility of the present invention requires only one tank as a coagulation tank, the number of equipment can be reduced, and organic microparticles can be separated with a microfiltration membrane. There is no need to provide a separate treatment tank for system wastewater treatment (or biological treatment), and therefore, the facility itself has the advantage of being compact and further reducing the time for wastewater treatment.

In a preferred embodiment of the wastewater treatment facility of the present invention, sodium carbonate is further mixed together with the wastewater in the aggregation tank 2. As a result, the Ca component that causes clogging due to scale generation in the microfiltration membrane can be preliminarily granulated as CaCO ₃ and removed.

  In another aspect, the present invention provides a method for treating wastewater generated in a waste incineration plant. This wastewater treatment method comprises a step of flocking or insolubilizing floating solids and heavy metal ions in the wastewater by mixing the wastewater together with the flocculant and the heavy metal chelating agent in a single agglomeration tank, A step of filtering the waste water from the coagulation tank through a microfiltration membrane and separating it into solid and liquid.

  The wastewater treatment method of the present invention can complete the flocculation of floating solids or insolubilization of heavy metals in a single agglomeration tank, and further separate the suspended solids using a microfiltration membrane. In addition, since it is not necessary to provide a separate treatment tank for biological treatment), there is an advantage that waste water treatment is easy and the time required for the treatment is shortened.

In a preferred embodiment of the wastewater treatment method of the present invention, sodium carbonate is further mixed together in the flocking or insolubilizing step. As a result, it is possible to preliminarily remove the Ca component that causes the clogging of the microfiltration membrane as CaCO ₃ .

  By using a microfiltration membrane filtration device as a filtration device, the present invention eliminates the need to distinguish between inorganic and organic wastewater treatment (or does not require separate treatment such as biological treatment) and agglomeration It is based on what this inventor discovered that it is not necessary to use an auxiliary agent, and that the process with a chelating agent and a flocculant can be performed in the same tank.

  As described above, according to the present invention, the drainage facility can be made compact, the power cost can be reduced, and the running cost can be reduced.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings, but this does not limit the scope of the present invention.

  FIG. 1 is a schematic diagram illustrating an overall configuration of a wastewater treatment facility 11 for treating wastewater generated in a waste incineration plant according to an embodiment of the present invention. As shown in FIG. 1, the waste water treatment facility 11 of the present embodiment includes a MF membrane treatment tank 13 including a coagulation tank 12 and a microfiltration membrane (hereinafter abbreviated as MF (Micro Filtration) membrane) filtration device 14 as main components. It is a component. Typically, a dehydrator 15, pumps 16 and 17, and a blower 18 are further provided.

  First, wastewater generated in a waste incineration plant (not shown) is sent to the agglomeration tank 12, where insoluble heavy metals in the wastewater and flocs of suspended solids (hereinafter abbreviated as SS (Suspended Solid)) may be used. Etc. are performed. Here, it does not matter whether the waste water is inorganic waste water, organic waste water, or both.

In the flocculation tank 12, the wastewater is mixed with a flocculant such as ferric chloride or a sulfuric acid band at an ordinary temperature under an appropriate pH condition (usually pH 6-8, preferably pH 7), and heavy metals in the wastewater. And SS are insolubilized or flocked as hydroxides. In the agglomeration tank 12, a liquid chelating agent for insolubilizing the heavy metal in the waste water into a chelate compound is further mixed. Further, sodium carbonate may be mixed into the agglomeration tank 12 in order to granulate the Ca content in the waste water as CaCO ₃ . Thereby, scale generation in the MF membrane can be prevented.

  As described above, in the wastewater treatment facility 11 of the present invention, the wastewater treatment with the sodium carbonate for granulating the flocculant, the liquid chelating agent, and Ca can be simultaneously performed in one coagulation tank. This is very advantageous.

  In addition, as a coagulant | flocculant used with the coagulation tank 12 of the waste water treatment facility 11 of this invention, a ferric chloride, a sulfuric acid band, etc. may be used. As the Ca particle forming agent, potassium carbonate or the like can be used in addition to the above sodium carbonate.

  Next, the wastewater treated in the coagulation tank 12 is sent to the MF membrane treatment tank 13 provided with the MF membrane filtration device 14 by natural flow, where the insoluble or flocked solids are removed. The MF membrane is a filtration membrane suitable for removing solids (eg, suspensions, colloids, aggregates, microparticles, bacteria, etc.) having a size of about 10 μm to 0.1 μm. In the waste water treatment facility 11 of the present invention, as the MF membrane filtration device 14, a filtration device using an immersion type MF membrane is typically used, but is not limited thereto. A filtration apparatus using an MF membrane is commercially available from a vendor well known to those skilled in the art. In general, those using an MF membrane made of a material such as polyvinylidene fluoride (PVDF) or a polyethylene porous film are readily available, and those skilled in the art can select an optimal one according to the application. Since the MF membrane is a hollow membrane and it is necessary to always clean the surface, in the MF membrane treatment tank 13, air is always sent from the lower part of the MF membrane treatment device 14 by the blower 18 and adhered to the membrane surface by bubbles. Remove floating substances.

  The waste water that has permeated through the MF membrane filtration device 14 is usually sent by a pump 17 to a gas cooling tower 19 of a waste incineration plant (not shown), where it is used to cool the gas. On the other hand, the concentrated wastewater containing solids that could not pass through the MF membrane filtration device 14 is sent to the dehydrator 15 by the pump 16 and dehydrated, where it is separated into sludge and dehydrated filtrate A. The dewatered sludge is usually returned to the waste pit 20 of the waste incineration plant and burned again (in some cases, it may be carried out of the field alone). On the other hand, the dehydrated filtrate A is returned to the raw water of the wastewater treatment flow and again subjected to wastewater treatment.

  In the wastewater treatment facility 11 of the present invention, the wastewater can be concentrated in the MF membrane treatment tank 13 typically to an SS concentration of about 20,000 ppm, and a conventional sedimentation tank (or sedimentation basin) or sand can be obtained. Can be replaced with filtration tank.

  Conventionally, when wastewater is treated with a flocculant, stirring is performed at a high rotational speed for the purpose of mixing (typically 200 to 400 rpm), and when wastewater is treated with a flocculant aid, the floc is increased. For this purpose, it was necessary to stir slowly at a lower rotational speed (typically 200 rpm or less) than when treating with a flocculant. Therefore, it is necessary to separately provide a tank for the treatment with the flocculant and a tank for the treatment with the flocculant aid. However, since the MF membrane used in the wastewater treatment facility 11 of the present invention can capture and separate fine particles having a size of about 10 μm to 0.1 μm, after treating wastewater with a flocculant, Thus, there is no need to provide a step (or a tank therefor) for further increasing the floc using the coagulant aid. Further, in the MF membrane treatment tank 13 (by the MF membrane), organic substances and the like can be removed, so that there is an advantage that it is not necessary to separately provide a process or treatment tank for treating organic wastewater (or biological treatment). It is done.

  Furthermore, in the wastewater treatment facility of the present invention, the treatment with the chelating agent and the treatment with the flocculant are performed together in one tank. Normally, according to the instructions of the chelating agent manufacturer, it is recommended to perform the treatment with the chelating agent alone, but it has been found by the inventor's experiment that the chelating agent can be used in the same tank as the flocculant. It has been found that there is no.

  As described above, according to the wastewater treatment facility 11 of the present invention, the number of equipment can be significantly reduced, and the equipment can be remarkably compacted. The wastewater treatment procedure is simplified, the equipment cost is reduced, and the management operation is performed. Significant benefits can be obtained in terms of simplification of the process.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the examples do not limit the scope of the present invention.

  In the waste water treatment facility 11 of the present invention similar to that shown in FIG. 1, waste water treatment was performed as follows.

First, various sewage including inorganic and organic waste water from a waste incineration plant was put into one coagulation tank 12. The agglomeration tank 12 contains 20 to 50 ppm of a liquid chelating agent for removing heavy metals, 100 to 300 ppm of sodium carbonate (NaCO ₃ ) as a scale inhibitor, and 100 ppm of ferric chloride (FeCl ₃ ) as an aggregating agent. And mixed with the waste water.

  The wastewater that had been subjected to the particleization treatment in the aggregation tank 12 as described above was caused to flow into the MF membrane treatment tank 13. In the MF membrane treatment tank 13, an immersion type MF membrane filtration device (manufactured by Mitsubishi Rayon Co., Ltd.) is installed, and solid-liquid separation was performed here.

The results are shown in Table 1 below.

  As described above, it can be seen that the SS in the treated water treated by the wastewater treatment facility 11 of the present invention is completely removed, and the BOD is also reduced to less than 1/10 compared to before the treatment. Moreover, it turns out that the density | concentration of heavy metals, such as Pb and Cd, has also decreased significantly compared with the raw | natural water before a process.

  Therefore, it was shown that the waste water treatment facility 11 of the present invention is effective in waste water treatment.

  The wastewater treatment facility of the present invention is useful as a wastewater treatment facility for a waste incineration plant or the like because the drainage facility can be made compact, the power cost can be reduced, and the running cost can be reduced.

The schematic diagram which shows the whole structure of the waste water treatment facility 11 for processing the waste_water | drain generated in the waste incineration plant based on one Embodiment of this invention. Schematic diagram showing the overall configuration of wastewater treatment equipment in a conventional waste incineration facility

Explanation of symbols

11 Wastewater treatment facility 12 of the present invention Coagulation tank 13 MF membrane treatment tank 14 MF membrane filtration device 15 Dehydrator 16, 17 Pump 18 Blower 19 Gas cooling tower 20 Garbage pit

Claims (4)

A facility for treating wastewater generated in a waste incineration plant,
A coagulation tank for flocking or insolubilizing floating solids and heavy metal ions in the wastewater by mixing the wastewater together with a flocculant and a heavy metal chelating agent;
A wastewater treatment facility comprising a microfiltration membrane treatment tank for solid-liquid separation of the wastewater from the aggregation tank through a microfiltration membrane.   The waste water treatment facility according to claim 1, wherein sodium carbonate is further mixed together with the waste water in the coagulation tank. A method for treating wastewater generated in a waste incineration plant,
In one flocculation tank, the waste water, the flocculant and the heavy metal chelating agent are mixed together to flock or insolubilize the suspended solids and heavy metal ions in the waste water;
The waste water treatment method including the step of filtering the solid waste from the coagulation tank through a microfiltration membrane and solid-liquid separation.   The wastewater treatment method according to claim 3, wherein sodium carbonate is further mixed together in the step of flocking or insolubilizing.

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