TWI679172B - Wastewater treatment method of incineration plant - Google Patents

Abstract

The invention provides a waste water treatment method for an incineration plant that efficiently recovers the heat of the combustion exhaust gas in an incineration plant and stably and efficiently performs concentrated treatment of the waste water. The wastewater treatment method of an incineration plant is a wastewater treatment method of wastewater discharged from an incineration plant provided with an incineration device 1, a heat recovery device for burning exhaust gas 2, and a temperature reduction device 3 for further lowering the temperature by the combustion waste heat recovered by the heat recovery device. It performs a membrane separation step 6 of separating the waste water discharged from the incineration plant into permeate water and concentrated water by using a separation membrane, and blowing at least a part of the concentrated water to the cooling device 3, thereby cooling the combustion exhaust gas. At least two kinds of mixed waste water including boiler tank water, boiler waste water, cooling tower waste water, and miscellaneous waste water mixed with incineration plant waste water are supplied to the membrane separation processing step 6.

Description

Wastewater treatment method of incineration plant

The invention relates to a method for treating wastewater discharged from a self-incineration plant.

Wastewater treatment methods from incineration plants equipped with an incineration device for burning organic matter, a heat recovery device for recovering the heat of the combustion exhaust gas discharged from the incinerator, and a temperature reduction device for further cooling the heat recovered combustion exhaust gas A wastewater treatment method in which the wastewater is subjected to a coagulation treatment using a coagulant or the like and then subjected to a filtration treatment is known.

In addition, a wastewater treatment method in which a waste water discharged from an incineration plant is subjected to agglomeration treatment by a coagulant or the like and then biologically treated, and then filtered by sand filtration is also known (Patent Document 1). Patent Document 1 describes that most of purified water that can be purified by this wastewater treatment method can be discharged.

In recent years, it has been required that the purified water generated by the treatment of waste water discharged from the incineration plant is not released as much as possible.

In order not to release the purified water generated by the treatment of the waste water discharged from the incineration plant as much as possible, a part of the purified water is sprayed into a cooling device such as a cooling tower to vaporize it and reduce the capacity of the purified water. In this method, in detail, in a cooling device, purified water is injected into a combustion exhaust gas that has been thermally recovered from the combustion exhaust gas by using a heat recovery device such as a waste heat boiler, thereby purifying the purified water and reducing its capacity. On the other hand, the combustion exhaust gas is cooled by its heat of vaporization.

In this way, when as much purified water is supplied to the cooling device as possible so as not to release purified water purified by wastewater treatment, in a heat recovery device such as a waste heat boiler located upstream of the cooling device, The heat recovered from the combustion exhaust gas must be set low. That is, in order to evaporate a large amount of purified water in the cooling device, the heat recovery amount from the combustion exhaust gas in the heat recovery device must be reduced, and the heat recovery efficiency from the combustion exhaust gas in the incineration plant becomes low.

In order to reduce the amount of water sprayed into the cooling device, Patent Document 2 describes that a microfiltration (MF) membrane is used to treat incineration plant wastewater, and the permeate water is subjected to reverse osmosis (RO) membrane treatment. Then, the concentrated water of the MF membrane and the concentrated water of the RO membrane are supplied to a cooling device.

According to this method, by using MF membrane and RO membrane to concentrate wastewater, the amount of water sprayed into the cooling device can be reduced, and the reduction in heat recovery amount can be suppressed.

However, there are various types of wastewater discharged from self-incineration plants. There are problems such as membrane clogging due to water quality, insufficient reduction, unstable operation, or frequent maintenance, cleaning, and other problems. In addition, the backwash water of the membrane filtration device is water in a state in which a solid suspended substance (Suspend Solid, SS) in the wastewater is concentrated, so that there are disadvantages such as clogging of the nozzle during spraying and maintenance.

Patent Document 1: Japanese Patent Laid-Open No. 10-99898

Patent Document 2: Japanese Patent No. 5636163

An object of the present invention is to provide an incineration that can efficiently recover the heat of the combustion exhaust gas in an incineration plant and can stably and efficiently perform concentrated treatment of wastewater. Wastewater treatment method of the plant.

The waste water treatment method of the incineration plant of the present invention is further provided with an incineration device for burning organic matter, a heat recovery device for recovering heat of the combustion exhaust gas discharged from the incineration device, and a combustion waste gas recovered by the heat recovery device. A method for treating waste water discharged from an incineration plant of a temperature-reduction cooling device, which performs a membrane separation step of separating the waste water discharged from the incineration plant into permeated water and concentrated water using a separation membrane, and supplying at least a part of the concentrated water to the A cooling device is blown into the combustion exhaust gas to evaporate it, thereby cooling the combustion exhaust gas. The waste water treatment method of the incineration plant is characterized in that the boiler holding tank water and the boiler drainage are mixed with the incineration plant wastewater. A mixed wastewater of at least two types of sewage, cooling tower drainage, and miscellaneous wastewater is supplied to the membrane separation processing step.

In one aspect of the present invention, the mixed wastewater is treated as a mixed wastewater by a first pretreatment step including at least one of neutralization, coagulation, precipitation, filtration, and biological treatment.

In one aspect of the present invention, after the mixed wastewater is treated by a pretreatment device using a filter, an MF membrane, or an ultrafiltration (UF) membrane, in the membrane separation step, an RO membrane is used. To perform a membrane separation process.

In one aspect of the present invention, after the mixed wastewater is treated by a pretreatment device using a filter, an MF membrane, or a UF membrane, in the membrane separation step, the membrane separation process is performed by an RO membrane. The concentrated water or backwash wastewater of the pre-processing device is sent to the first pre-treatment step.

In one aspect of the present invention, the floor cleaning waste water and the washing of the incineration plant are not performed. At least one of the vehicle wastewater is subjected to a reverse osmosis treatment and is supplied to the cooling device.

In one aspect of the present invention, at least one of a floor cleaning wastewater and a car washing wastewater is treated in a second pretreatment step including at least one of neutralization, coagulation, precipitation, filtration, and biological treatment. After that, it is supplied to the cooling device.

In the wastewater treatment method of the present invention, as in Patent Document 2, in the membrane separation step, the wastewater discharged from the incineration plant is concentrated using a separation membrane to make concentrated water having a reduced volume, and the concentrated water is concentrated. Since water is supplied to the cooling device, a small amount of concentrated water is supplied to the cooling device, and the temperature of the combustion exhaust gas introduced into the cooling device can be reduced. As a result, in the heat recovery device provided on the upstream side of the cooling device, the heat recovered from the combustion exhaust gas can be increased.

In the wastewater treatment method of the present invention, it is preferable to perform membrane separation treatment on the mixed wastewater using an RO membrane.

In order to stabilize and improve the treatment, water treatment chemicals such as a dispersant or slime control agent are contained in the boiler tank water, boiler waste water, and cooling tower waste water. By selecting stabilizers that do not adversely affect the membrane treatment and contribute to the stabilization of the membrane treatment, the RO membrane treatment can be performed stably with little or no re-addition of water treatment chemicals. Membrane separation process.

The dispersant contained in the boiler sewage and cooling tower sewage has become a hindrance factor for the coalescence treatment. Sludge control agents have an adverse effect on biological treatment and there are examples of reduced biological activity. In one aspect of the present invention, sand is contained in the water. After simple pretreatment of filters, MF membranes or UF membranes, membrane separation is performed, so the size of wastewater treatment equipment can be reduced.

In one form of the wastewater treatment method of the present invention, the heterogeneous wastewater is treated by a pretreatment step having at least one of neutralization, coagulation, precipitation, filtration, and biological treatment, and the SS component and organic in the wastewater are treated. After the components are removed, a concentration operation is performed by a membrane treatment. In this way, by pre-treating the miscellaneous wastewater, it is possible to reduce SS components and organic components contained in the wastewater, it is difficult to cause clogging of the separation membrane, and it is possible to extend the continuous use life of the separation membrane. Thereby, the replacement frequency of the separation membrane becomes low, the concentrated water can be efficiently obtained, and the heat of the combustion exhaust gas in the incineration plant can be recovered more efficiently.

Regarding the concentrated water or the backwash water of the pre-treatment device, it is preferred that the SS component and the organic component are also removed by the first pre-treatment step. However, the processing may be performed in the second pre-processing step.

Regarding the car-washing wastewater and the floor-cleaning wastewater, it is preferred to perform spraying in a cooling device without performing a membrane treatment. The car washing wastewater or the floor washing wastewater may contain substances that block the MF membrane or the RO membrane, such as oil components and surfactants. In addition, the concentration may not be constant, and it may be difficult to perform stable treatment. Therefore, it is preferable to treat the car-washing wastewater and the floor-washing wastewater by a second pre-treatment step having at least one of neutralization, coagulation, precipitation, filtration, and biological treatment to perform solid-liquid separation and organic component removal. Then, spraying was performed in a cooling device.

In the present invention, the mixed wastewater may be a wastewater mixed with other than the boiler tank water.

1‧‧‧ incineration plant

2‧‧‧heat recovery device

3‧‧‧ Cooling device

4‧‧‧ Dust Collector

5‧‧‧ pre-processing steps

6‧‧‧ membrane separation steps

7‧‧‧The first pretreatment

8‧‧‧ 2nd pretreatment

11, 23‧‧‧MF film

12, 24‧‧‧RO membrane

13, 16, 21‧‧‧ agglomeration treatment

14, 17, 22‧‧‧‧ gravity double sand filter treatment

15, 25‧‧‧ biological treatment

Figure 1 is a block diagram of an incineration plant.

Fig. 2 is a flowchart of the embodiment.

FIG. 3 is a flowchart of the embodiment.

FIG. 4 is a flowchart of a comparative example.

Hereinafter, one embodiment of the wastewater treatment method of the present invention will be described with reference to the drawings.

As shown in FIG. 1, the incineration plant to which the waste water treatment method of this embodiment is applied includes an incineration device for burning organic matter 1, a heat recovery device 2 for recovering heat of the combustion exhaust gas discharged from the incineration device 1, and a heat recovery device using the The temperature reduction device 3 that further reduces the temperature of the combustion exhaust gas (hereinafter, also referred to as a heat recovery combustion exhaust gas) heat recovered by the recovery device. It may further include other devices.

As the incineration device 1, an incineration plant such as a coal adding furnace, a fluidized bed furnace, a gasification melting furnace, and an ash melting furnace can be used.

The organic substance to be burned is not particularly limited, and examples thereof include municipal waste, industrial waste, sewage sludge, and waste wood. The combustion exhaust gas discharged from the self-incineration device 1 usually has a temperature of about 800 ° C to 1300 ° C.

The heat recovery device 2 recovers the heat of the combustion exhaust gas discharged from the incineration device 1. Examples of the heat recovery device 2 include a waste heat boiler and the like.

The cooling device 3 enables the combustion exhaust gas heat recovered by the heat recovery device 2 (Heat recovery combustion exhaust gas) The temperature is further reduced. The temperature reduction device 3 is configured to inject or spray water into the heat recovery combustion exhaust gas introduced from the heat recovery device 2 and reduce the temperature of the heat recovery combustion exhaust gas by the heat of vaporization of water. The heat recovery combustion exhaust gas introduced into the temperature reduction device 3 usually has a temperature of about 250 ° C to 400 ° C. The water sprayed or sprayed in the cooling device 3 uses a separation membrane to condense at least two kinds of mixed waste water including boiler holding water, boiler waste water, cooling tower waste water, and miscellaneous waste water mixed with incineration plant waste water. Into concentrated water.

In the present invention, since the amount of water blown into the cooling device 3 is smaller than that in Patent Document 2, the temperature of the exhaust gas introduced into the cooling device 3 can be lower than that in Patent Document 2. Thereby, the heat recovery amount in the heat recovery device 2 can be increased.

The temperature of the exhaust gas cooled by the temperature reduction device 3 usually becomes about 150 ° C to 200 ° C. The gas contains water vapor obtained by vaporizing the concentrated water. The exhaust gas is purified by the dust collector 4 or the like, and then released into the atmosphere.

The so-called waste water discharged from the incineration plant refers to the waste water generated in the land of the incineration plant. As the waste water generated in the site of the incineration plant, for example, the boiler waste water discharged from the heat recovery device 2 such as a waste heat boiler is filled in the tank of the heat recovery device when stopped, and the boiler holding water discharged before restarting, Cooling tower drainage, floor cleaning waste water generated when cleaning floors and the like located in the incineration plant, and car wash waste water generated when cleaning waste collection vehicles include domestic wastewater or miscellaneous wastewater. Examples of the miscellaneous waste water include a residue cooling waste water that cools incineration residues or slag generated in an incinerator 1 such as a self-incinerator, or a waste water other than the above that does not contain a surfactant or an oil component and is generated in an incineration plant. .

As shown in FIG. 2, it is preferable to perform pretreatment on the mixed waste water mixed with boiler tank water, boiler drainage water and cooling tower drainage water (where the boiler tank water can also be excluded), and then use a membrane separation step. 6 to perform a membrane separation process. At least a part of the concentrated water is supplied to the temperature reduction device 3 to evaporate the concentrated water, thereby reducing the temperature of the combustion exhaust gas.

Regarding the miscellaneous waste water, it is preferred that after the first pretreatment 7 is performed, it is mixed with the boiler holding water, the boiler sewage and the cooling tower sewage, and then supplied to the pretreatment 5. By pretreating the miscellaneous waste water as described above, clogging of the membrane in the membrane separation step 6 is suppressed.

As the pretreatment 5, a sand filter, an MF membrane, a UF membrane, or the like can be used.

By pre-treating the mixed wastewater as described above, clogging of the membrane in the membrane separation step 6 is suppressed. As the membrane in the membrane separation step 6, an RO membrane is suitable.

As the first pretreatment 7 for treating the miscellaneous wastewater, at least one of neutralization, coagulation, precipitation, filtration, and biological treatment is preferable.

The car-washing wastewater and the floor-cleaning wastewater are preferably subjected to the second pretreatment 8 for removing the SS component and the organic component, and then mixed with the membrane concentrated water from the membrane separation step 6 and then supplied to the cooling device 3. The second pre-treatment is preferably at least one of neutralization, aggregation, precipitation, filtration, and biological treatment.

When the MF membrane or the UF membrane is used in the pretreatment 5, it is preferable to treat the MF membrane concentrated water or the UF membrane concentrated water by the first pretreatment 7 to remove the SS component and the organic component. However, the processing may be performed by the second pre-processing 8. Because the MF membrane concentrated water or UF membrane concentrated in the cooling device 3 is not sprayed in the pretreatment 5 Water to prevent clogging of the spray nozzles and perform stable cooling.

As mentioned above, for the stabilization and efficiency of the treatment, water treatment such as corrosion protection agent, dispersant or sludge control agent, condensation amine agent, and deoxidizer is included in the boiler tank water, boiler waste water, and cooling tower waste water. Chemicals. Select those who do not adversely affect membrane treatment and contribute to the stabilization of membrane treatment as these chemicals, and only perform pretreatment on the boiler tank water, boiler drainage and cooling tower drainage to perform RO membrane 5 By doing so, it is possible to perform efficient membrane separation treatment without adding water treatment chemicals for RO membrane treatment. When the chemical concentration is insufficient, the required chemical can also be added.

The dispersant contained in the boiler sewage and cooling tower sewage has become a hindrance factor for the coalescence treatment. Therefore, if the boiler sewage and the cooling tower sewage are allowed to flow into the first pretreatment 7, the required amount of coagulant will increase significantly. Sludge control agents have an adverse effect on biological treatment, and there are examples of reduced biological activity. When wastewater treatment is carried out, it is necessary to perform harmless treatment. Therefore, the water is supplied to the pretreatment 5 without being pretreated, whereby the pretreatment equipment can be reduced.

The car-washing wastewater and the floor-cleaning wastewater are sprayed in the cooling device 3 after the second pretreatment 8. Car wash wastewater or floor cleaning wastewater may contain substances that block MF membrane or RO membrane, such as oil components and surfactants. In addition, the concentration is not fixed, and it is difficult to perform a stable membrane separation process. Therefore, the second pretreatment 8 having at least one of neutralization, coagulation, precipitation, filtration, and biological treatment is used to treat the car washing wastewater and the floor washing wastewater, and then perform solid-liquid separation and organic component removal. Spraying is performed in the cooling device 3.

In the first pretreatment 7 and the second pretreatment 8, in order to reduce the SS component and the organic component contained in the water to be treated, a coagulant may be added to the wastewater. Instead of filtering, a filtering treatment such as filtering or a precipitation step is performed. When the load is high, a pressure floating step may be added. In order to appropriately perform the aggregation treatment, a pH adjustment step may be added. By implementing a series of pre-treatment steps, aggregates can be removed from the wastewater, and SS and organic components that can be contained in the car wash wastewater and floor cleaning wastewater can be reduced.

In the first pretreatment 7 and the second pretreatment 8, an MF membrane (impregnated membrane) may be used instead of a sand filtration device and a membrane separation activated sludge method may be used. After the agglomerates captured by the MF membrane (impregnated membrane) are extracted, they are put into a garbage pit, and incinerated by the incinerator 1.

Examples of the coagulant include iron-based coagulants such as ferrous sulfate, ferric sulfate, and ferric chloride; aluminum-based coagulants such as aluminum sulfate and polyaluminium chloride (PAC); and these The mixture and so on. The addition amount of the coagulant can be appropriately adjusted.

Examples of the polymer flocculant added to the treated water as the flocculant include poly (meth) acrylic acid, copolymers of (meth) acrylic acid and (meth) acrylamide, and alkali metal salts thereof. Anionic organic polymer flocculants, non-ionic organic polymer flocculants such as poly (meth) acrylamide, including dimethylaminoethyl (meth) acrylate or its quaternary ammonium salt, Homopolymers of cationic monomers such as dimethylaminopropyl (meth) acrylamidine or its quaternary ammonium salt, and copolymers of these cationic monomers and non-ionic monomers that can be copolymerized Isocationic organic polymers A flocculant, and an amphoteric organic polymer flocculant as the anionic monomer, the cationic monomer, or a copolymer of these monomers and a nonionic monomer that can be copolymerized. The addition amount of the polymer flocculant is not particularly limited as long as it can be adjusted according to the properties of the water to be treated, but it is about 0.01 mg / L to 10 mg / L in terms of solid content relative to the water to be treated. A phenol type aggregating agent described in WO2011 / 018978 can also be used.

When an RO membrane is used in the membrane separation step 6, examples of impurities to be removed by the RO membrane include an ionic component, an organic substance, and the like. Examples of the ionic component include a cationic substance and an anionic substance. Specific examples include calcium ions and magnesium ions which easily form ionic bonds with anions and generate scale which is difficult to dissolve in water. Examples of the organic substance include a water-soluble organic substance dissolved in wastewater.

When the MF membrane is used in the pretreatment 5, since scale, suspended matter, organic matter, and the like adhere to the surface of the MF membrane, the differential pressure of the MF membrane rises. In this case, back pressure cleaning or chemical cleaning of the MF membrane is performed. In the back pressure cleaning of the MF membrane, from the viewpoint that the increase in the differential pressure of the MF membrane can be further suppressed, it is preferred to perform periodic / irregular cleaning with water containing hypochlorite such as sodium hypochlorite.

The MF film usually has pores with a pore diameter of about 50 nm to 10 μm. As the MF membrane, for example, a membrane unit holding a hollow fiber membrane, a spiral membrane, or a tubular membrane in a container can be used. A hollow fiber membrane or a flat sheet membrane may be directly immersed in the water to be treated and used. Instead of the MF membrane, an ultrafiltration membrane (UF membrane) having a pore size of about 2 nm to 200 nm may be used.

As the MF film, polyvinylidene fluoride (Polyvinylidene) can be suitably used. Difluoride (PVDF), as the UF film, polyfluorene can be suitably used, and as the RO film, polyamine can be suitably used as the material, but it is not limited to this.

Examples of the RO membrane include a composite membrane including a dense layer and a fine porous layer of an asymmetric membrane.

As the RO membrane, a unit in which a filter membrane provided in a state such as a hollow fiber membrane, a spiral membrane, or a tubular membrane is held in a container can be used.

As the dispersant used in cooling water treatment, inorganic polyphosphoric acids such as sodium hexametaphosphate or sodium tripolyphosphate, phosphonic acids such as hydroxyethylene diphosphonic acid or phosphinobutanetricarboxylic acid, and the like can be used. Raw materials containing carboxyl groups such as butenedioic acid, acrylic acid, itaconic acid, etc., if necessary, with sulfonic acids such as vinylsulfonic acid, allylsulfonic acid, 2-methacrylamido-2-methylpropanesulfonic acid, etc. Acid-based vinyl monomers, or copolymers made of a combination of nonionic vinyl monomers such as acrylamide, can also be applied to raw materials other than those listed here. A terpolymer may be used as a third component of the dispersant other than the other components. For example, as the third component, N-third butylacrylamide and the like are used. As the dispersant, a polymer containing HAPS, AMPS, and acrylic acid and / or methacrylic acid is particularly preferred. HAPS is 3-allyloxy-2-hydroxy-1-propanesulfonic acid, and AMPS is 2-propenylamine-2-methylpropanesulfonic acid.

The molecular weight of the dispersant is preferably 1,000 or more and 30,000 or less. If the molecular weight is 1,000 or less, a sufficient dispersion effect cannot be obtained, and if it is 30,000 or more, it may be removed by a pretreatment film.

As a slime control agent, it can be applied: hypochlorites such as sodium hypochlorite (NaClO), chlorinating agents such as chlorine gas, chloramine, and isocyanuric chloride, monochloramine sulfonic acid, etc. Bonding chlorinating agent formed by the reaction of chlorine with ammonium sulfate and a compound having an ammonium sulfate group, a brominating agent such as dibromo-haiyin, a hypobromite such as sodium hypobromite, and a dibromo-nitrosine propionate Organic agents such as amine (Dibromonitrilo propionamide, DBNPA), methyl isothiazolinone (MIT). As the chlorine-based oxidant that can be used in the present invention, in addition to the chlorine gas, hypochlorous acid, or a salt thereof, chlorous acid or a salt thereof, chloric acid or a salt thereof, perchloric acid or a salt thereof, and chloroisotrimer can be used. Cyanic acid or a salt thereof. Examples of the salt include alkali metal salts such as sodium and potassium, alkaline earth metal salts such as barium, other metal salts such as nickel, and ammonium salts. These may use more than one kind. Among these, sodium hypochlorite is preferred because of its excellent handleability.

Examples of the nitrogen compound to which the free chlorine is bonded include ammonia or a compound thereof, melamine, urea, acetamide, thiamidine, cyclic lactic acid, sulfamic acid, tosylate, and succinimide , Phthalimide, isocyanuric acid, N-chlorotoluamide, uric acid, saccharin, or some of these salts. The bonding chlorinating agent used in the present invention is obtained by bonding the free chlorine to the nitrogen compounds. The bonding chlorinating agent used in the present invention is preferably one obtained by mixing and reacting the nitrogen compound and free chlorine, and particularly one obtained by mixing and reacting the two in a state of an aqueous solution.

Examples of such a bonding chlorinating agent include chloramine-T (N-chloro-4-methylbenzenesulfonamide) in addition to a chlorinating agent containing chloramine or a chlorine-based oxidizing agent and an sulfamic acid compound. Sodium salt), chloramine-B (sodium salt of N-chloro-benzenesulfonamide), sodium salt of N-chloro-p-nitrobenzenesulfonamide, trichloromelamine, mono- or di-chloromelamine Sodium or potassium salt, trichloro-isocyanurate, sodium or potassium salt of mono- or di-chloroisocyanuric acid, mono- or di -Sodium or potassium salt of chloramine sulfonic acid, monochloro or 1,3-dichloro hai, a 5,5-alkyl derivative such as 5,5-dimethyl hai, and the like.

In boiler water treatment, can cleaning agents, deoxidants, and amines are used alone or in combination. As the can-cleaning agent, phosphoric acid and / or a salt thereof, polymeric phosphoric acid and / or a salt thereof, phosphonic acid and / or a salt thereof, chelating agents such as ethylene diamine tetraacetic acid (EDTA), and poly (methyl formazan) may be used. Group) acrylic acid and / or a salt thereof, a polymer including AMPS and acrylic acid and / or methacrylic acid, and the like. As a deoxidizing agent, 1-amino-4-methylpiperazine, hydrazine, carbazine, erythorbic acid and / or a salt thereof, gluconic acid and / or a salt thereof, and N, N-diethylhydroxyl group can be applied. Amine, sulfurous acid and / or a salt thereof, bisulfite and / or a salt thereof, tannic acid and / or a salt thereof, gallic acid and / or a salt thereof, isopropylhydroxylamine and the like. As amines: monoisopropanolamine, 3-methoxy-propylamine, cyclohexylamine, 2-aminoethanol, 2-amino-2-methyl-1-propanol, morpholine Film-forming amines such as neutralizing amines such as 2-diethylaminoethanol or octadecylamine.

A part of the MF membrane permeated by the pretreatment 5 can be used as car washing water or the like. The RO membrane permeated water of the membrane separation step 6 can be used as boiler raw water, machine cooling water, factory water, etc. of the waste heat boiler. The MF membrane permeate water, the RO membrane permeate water, etc. may be released into the sea, river, or sewer.

In the incineration plant, in order to remove the NOx gas which can be contained in the combustion exhaust gas, a mixed gas mixed with the combustion exhaust gas and ammonia is contacted with a denitration catalyst, and the NOx gas is decomposed by a contact reduction reaction. Since ammonia remains in the combustion exhaust gas, ammonia (ammonium ion) may be contained in the waste water discharged from the incineration plant. Therefore, a biological treatment device may be provided upstream of the pretreatment step to reduce ammonium ions and the like.

The biological treatment step may be, for example, a biological treatment device including a nitrification tank that performs a nitrification step with aerobic microorganisms, and a denitrification tank that performs a denitrification step with facultative anaerobic microorganisms.

Although detailed description is omitted, if incineration of garbage in an incineration plant, harmful gases such as HCl, SO _X , dioxin, fly ash containing heavy metals, and the like are generated, it is necessary to deal with these steps. For example, when performing acid gas treatment in front of the dust collector, add slaked lime or sodium bicarbonate, dolomite hydroxide, or when performing acid gas treatment in a cooling device or scrubber, use an alkali such as NaOH to neutralize Known processing methods such as processing. A well-known method is also applied to dioxin treatment or fly ash treatment.

Examples

[Example 1]

The boiler waste water, cooling tower waste water, miscellaneous waste water, domestic waste water, car washing waste water and floor washing waste water discharged from the incineration plant that burns combustible garbage are processed according to the flow chart in FIG. 3.

The boiler sewage 10m ³ / h and cooling tower sewage 10m ³ / h were directly supplied to the pretreatment (MF membrane 11).

The miscellaneous wastewater 2m ³ / h is processed by the first pretreatment (agglomeration treatment 13 and a gravity double-layer sand filtration treatment 14 by adding PAC 10mg / L and polymer 2mg / L), and then supplied to In the MF film 11. Permeate water (recovery rate: 95%) of the MF membrane 11 was supplied to the RO membrane 12, and permeate water (recovery rate of 75%) of 17 m ³ / h was supplied to the cooling tower as make-up water.

The RO concentrated water was sprayed in the cooling device 3 at 6 m ³ / h. The concentrated water of the MF membrane 11 is supplied to the aggregation treatment 13.

The domestic wastewater 2m ³ / h is supplied to the agglomeration treatment 13 after the biological treatment 15.

Carry out a second pretreatment of carwash wastewater 1m ³ / h and floor cleaning wastewater 1m ³ / h (using PAC 10mg / L and polymer 2mg / L agglomeration treatment 16 and gravity double-layer sand filtration treatment 17), and then Spraying is performed in the cooling device 3.

A dispersant is contained in the boiler effluent, and a dispersant and a slime control agent are contained in the cooling tower effluent. After the mixed wastewater containing the MF membrane 11 is processed, the RO membrane 12 is processed. Even without adding a slime control agent and a dispersant, processing can be performed stably. In addition, by using a system different from these to treat floor washing wastewater and car washing wastewater, the recovery rate of the RO membrane 12 can be improved. As shown in FIG. 1, the amount of water sent to the cooling device 3 is as small as 8 m ³ / h, and the heat recovery amount of the heat recovery device 2 (FIG. 2) is increased. 17m ³ / h of the recovered water of the RO membrane 12 can be used as make-up water of the cooling tower again, and the corresponding amount of make-up water can be reduced.

[Comparative Example 1]

Each wastewater of the incineration plant of Example 1 was processed according to the flowchart of FIG. 4. That is, the agglomeration treatment 21 by adding 200 mg / L of PAC and 2 mg / L of polymer is directly performed on each of the waste waters (the respective flow rates are the same as in Example 1) other than the domestic waste water. About 2 m ³ / h of domestic wastewater, after biological treatment 25 is performed, it is supplied to agglomeration treatment 21. The treated water of the coacervation treatment 21 is subjected to gravity double-layer sand filtration treatment and filtration 22, and then supplied to the MF membrane 23, and permeate water (95% recovery rate) is supplied to the RO membrane 24, and RO permeate water is 15 m ³ h (recovery rate 60%) is used as cooling tower make-up water. In the cooling device 3, 1 m ³ / h of concentrated water of the MF film 23 and 9 m ³ / h of concentrated water of the RO film 24 were sprayed.

In Comparative Example 1, since the amount of concentrated water supplied to the cooling device 3 was as high as 10 m ³ / h, it was necessary to reduce the heat recovery amount in the heat recovery device 2 and increase the temperature of the exhaust gas introduced into the cooling device 3.

Due to the dispersant contained in the boiler sewage and cooling tower sewage, the amount of PAC added needs 200mg / L. In order to stabilize the film processing, a slime control agent and a dispersant are required. As a film treatment slime control agent, 5 mg / L of Kuriverter EC-503 was used. As a film treatment dispersant, 5 mg / L of Kuriverter N-500 was used.

In Comparative Example 1, since the oil component was mixed into the floor washing wastewater and the car washing wastewater, the RO recovery rate was reduced to 60%. In Comparative Example 1, the amount of water for agglomeration treatment was increased, and a huge pre-treatment facility was required.

Although the present invention has been described in detail using a specific aspect, it is clear to those skilled in the art that various changes can be made without departing from the spirit and scope of the present invention.

This application is based on Japanese Patent Application No. 2015-072958 filed on March 31, 2015, and the entire contents thereof are incorporated by reference.

Claims (7)

A waste water treatment method for an incineration plant includes a heat recovery device including an incineration device for burning organic matter, a heat recovery device that recovers heat of combustion exhaust gas discharged from the incineration device, and a combustion that recovers heat by the heat recovery device. A waste water treatment method for waste water discharged from an incineration plant of a cooling device for further reducing exhaust gas, which performs a membrane separation step of separating a waste water discharged from the incineration plant into permeated water and concentrated water by using a separation membrane, and supplying at least a part of the concentrated water To the cooling device and blowing it into the combustion exhaust gas to evaporate it, thereby cooling the combustion exhaust gas, the waste water treatment method of the incineration plant is characterized in that the boiler holding water mixed with the incineration plant waste water At least two kinds of mixed wastewater including boiler wastewater, cooling tower wastewater, and miscellaneous wastewater are supplied to the membrane separation treatment step, wherein the miscellaneous wastewater is for cooling incineration residues or slag generated in the incineration device. Residual cooling wastewater, or boiler tank water, boiler drainage, cooling tower drainage, floor cleaning waste generated in the incineration plant The incineration plant other than the washing wastewater, domestic wastewater, wastewater and wastewater residues cooling. The wastewater treatment method of an incineration plant according to item 1 of the scope of patent application, wherein the miscellaneous wastewater is performed by a first pretreatment step having at least one of neutralization, coagulation, precipitation, filtration, and biological treatment. After the treatment, they are mixed and used as the mixed wastewater. The wastewater treatment method of an incineration plant according to item 1 of the scope of patent application, wherein the mixed wastewater is treated by a pretreatment device using a filter, a microfiltration membrane, or an ultrafiltration membrane, and then the membrane is applied to the membrane. In the separation step, a membrane separation process is performed by a reverse osmosis membrane. The wastewater treatment method of an incineration plant according to item 2 of the scope of patent application, wherein the mixed wastewater is treated by a pretreatment device using a filter, a microfiltration membrane, or an ultrafiltration membrane, and then the membrane is treated in the membrane. In the separation step, a membrane separation process is performed by a reverse osmosis membrane. The wastewater treatment method of an incineration plant according to item 2 of the scope of patent application, wherein the mixed wastewater is treated by a pretreatment device using a filter, a microfiltration membrane, or an ultrafiltration membrane, and then the membrane is treated in the membrane. In the separation step, a membrane separation treatment is performed by a reverse osmosis membrane, and the concentrated water or the backwash wastewater of the pretreatment device is sent to the first pretreatment step. The wastewater treatment method of an incineration plant according to any one of the scope of claims 1 to 5, wherein at least one of the floor washing wastewater and the car washing wastewater of the incineration plant is not subjected to a reverse osmosis treatment and is supplied to the incineration plant. Cooling device. The method for treating waste water of an incineration plant according to any one of claims 1 to 5, wherein the second pretreatment includes at least one of neutralization, condensation, precipitation, filtration, and biological treatment. The step is to process at least one of the floor cleaning wastewater and the car cleaning wastewater of the incineration plant, and then supply it to the cooling device.