Method and system for pretreating low-concentration organic wastewater

Abstract

The invention relates to a method and a system for pretreating low-concentration organic wastewater, and the method is characterized in that organic wastewater subjected to homogenization treatment is subjected to flotation treatment, so that suspended matters in the organic wastewater can be efficiently removed; the organic wastewater subjected to flotation treatment is subjected to organic matter removal treatment in the vacuum cooling unit, so that organic matters in the organic wastewater can be efficiently removed. Moreover, compared with the prior art, the method disclosed by the invention has the advantages that the process for treating the organic wastewater is relatively short in flow, simple and convenient to operate and relatively high in adaptability.

Description

Technical Field

[0001] The present disclosure relates to the field of wastewater treatment, and in particular, to a method and system for pretreating low-concentration organic wastewater. Background Art

[0002] With the continuous development of more and more ethylene and downstream high-end new materials industry cluster facilities, the process wastewater generated by high-end new materials facilities contains organic pollutants such as styrene and acrylonitrile.

[0003] Currently, wastewater containing organic pollutants such as styrene, acrylonitrile, toluene, and COD is often treated using traditional biochemical methods to improve water quality before discharge to downstream sewage treatment plants. However, conventional biochemical treatment methods are difficult to treat for pollutants like styrene and acrylonitrile, and strict discharge standards are imposed. In particular, there is no established treatment process for the removal of styrene and acrylonitrile from wastewater. Furthermore, traditional biochemical treatment methods suffer from technical complexity and large footprint. Summary of the Invention

[0004] The purpose of the present disclosure is to provide a method and system for pretreatment of low-concentration organic wastewater to solve the problems existing in the prior art such as difficulty in treating pollutants such as styrene and acrylonitrile, complex technology, and large system footprint.

[0005] In order to achieve the above-mentioned objectives, the first aspect of the present disclosure provides a method for pretreating low-concentration organic wastewater, which comprises: S1, allowing the organic wastewater to enter a homogenization adjustment unit for homogenization treatment to obtain homogenous wastewater and homogenous waste gas; S2, allowing the homogenous wastewater to enter a flotation unit for flotation treatment to obtain flotation wastewater, flotation waste gas and flotation waste residue; S3, allowing the flotation wastewater to enter a vacuum cooling unit for organic matter removal treatment to obtain qualified wastewater and organic-containing waste gas; S4, allowing the homogenous waste gas, the flotation waste gas and the organic-containing waste gas to enter a waste gas treatment unit respectively.

[0006] Optionally, the organic wastewater comes from one or more of an MTO device, a PBST device, an ABS device, a PGA device, an EVA device, a POE device, a POSM device, an ethylene device and a polycarbonate device.

[0007] Optionally, the content of suspended solids in the organic wastewater is 600-1000 mg / L, and the COD is 300-8000 mg / L; the organic matter in the organic wastewater includes one or more of styrene, acrylonitrile, ethylbenzene and toluene; wherein the content of styrene is 50-1500 mg / L, the content of acrylonitrile is 10-350 mg / L, the content of ethylbenzene is 3-150 mg / L, and the content of toluene is 1-100 mg / L.

[0008] Optionally, step S2 further includes: S21, stirring and mixing the homogenized wastewater with a coagulant for coagulation treatment to obtain a coagulated material; S22, stirring and mixing the coagulated material with a flocculant for flocculation treatment to obtain a flocculated material; S23, allowing the flocculated material to enter the flotation unit for flotation treatment to obtain the flotation wastewater, the flotation waste gas and the flotation waste residue.

[0009] Optionally, the coagulant includes one or more of polyaluminium chloride, aluminium sulfate, ferric chloride and alum; the amount of the coagulant added is 0.01 to 20 g / L; the stirring linear velocity of the coagulation treatment is below 0.5 m / s; the flocculant includes one or more of polyacrylamide, polysilicate, iron salt, aluminium salt and polyaluminium chloride; the amount of the flocculant added is 0.001 to 15 g / L; the stirring linear velocity of the flocculation treatment is below 0.2 m / s; the diameter of the bubbles in the flotation unit is 30 to 3000 μm.

[0010] Optionally, step S2 further includes: S24, allowing the flotation waste to enter a sludge storage tank for sedimentation separation treatment to obtain a sedimentation separation gas phase, discharged sludge and sedimentation separation wastewater; returning the sedimentation separation wastewater to the homogenization adjustment unit, and allowing the sedimentation separation gas phase to enter the waste gas treatment unit.

[0011] Optionally, the vacuum cooling unit includes a flash evaporation device, a steam injection device and a condensation device; step S3 also includes: S31, allowing the flotation wastewater and the steam from the steam injection device to enter the flash evaporation device for flash evaporation treatment to obtain a flash gas phase and qualified wastewater; S32, allowing the flash gas phase to enter the condensation device for vacuum cooling treatment to obtain the organic waste gas and the cooling liquid phase; S33, allowing the cooling liquid phase to be partially returned to the condensation device after filtration treatment; preferably, the proportion of the returned cooling liquid in the filtered treatment part is 5% to 65%.

[0012] Optionally, the conditions for the flash treatment include: a temperature of 25 to 100°C, preferably 30 to 70°C; a pressure of 0.01 to 0.20 MPaA, preferably 0.03 to 0.1 MPaA; the temperature of the qualified wastewater is 10 to 50°C, the concentration of styrene is below 10 mg / L, and the concentration of acrylonitrile is below 2 mg / L.

[0013] Optionally, the number of stages of the flash evaporation device is 2 or more.

[0014] According to a second aspect of the present disclosure, a system for pretreating low-concentration organic wastewater using the method described in the first aspect is provided, the system comprising a homogenizing and regulating unit, an air flotation unit and a vacuum cooling unit; the homogenizing and regulating unit comprising an organic wastewater inlet, a homogenizing wastewater outlet and a homogenizing waste gas outlet; the air flotation unit comprising a homogenizing wastewater inlet, a flotation wastewater outlet, a flotation waste gas outlet and a flotation waste residue outlet; the vacuum cooling unit comprising a flotation wastewater inlet, a qualified wastewater outlet and an organic waste gas outlet; the organic wastewater inlet of the homogenizing and regulating unit is used to be connected to an organic wastewater source, the homogenizing wastewater outlet of the homogenizing and regulating unit is connected to the homogenizing wastewater inlet of the air flotation unit; the flotation wastewater outlet of the air flotation unit is connected to the flotation wastewater inlet of the vacuum cooling unit.

[0015] Through the above technical solution, the organic wastewater after homogenization is subjected to flotation treatment, which can effectively remove suspended matter from the organic wastewater. The organic wastewater after flotation treatment is then subjected to de-organization treatment in a vacuum cooling unit, which can effectively remove organic matter from the organic wastewater. Moreover, compared with the existing technology, the method disclosed in this disclosure has the advantages of a shorter process flow, simpler operation, and greater adaptability for treating organic wastewater.

[0016] Other features and advantages of the present disclosure will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The accompanying drawings are used to provide a further understanding of the present disclosure and constitute a part of the specification. Together with the following detailed description, they are used to explain the present disclosure but do not constitute a limitation of the present disclosure. In the accompanying drawings:

[0018] Figure 1 It is a schematic diagram of a system for pretreating low-concentration organic wastewater disclosed in the present invention.

[0019] Figure 2 It is a structural schematic diagram of a flash evaporation device disclosed in the present invention.

[0020] Description of Reference Numerals

[0021] 11 Organic wastewater; 12 Qualified wastewater; 13 Organic waste gas; 14 Mixed waste gas; 15 Discharged sludge; 16 Flushing water; 17 Flotation waste residue; 101 Homogenization adjustment unit; 102 Flotation unit; 103 Vacuum cooling unit; 104 Discharge tank; 105 Sludge storage tank; 106 Wastewater tank; 201 Primary flash evaporator; 202 Secondary flash evaporator; 203 Primary steam ejector; 204 Secondary steam ejector; 205 Valve; A1 Flotation wastewater; A2 Qualified wastewater; A3 Organic waste gas; A4 Steam. DETAILED DESCRIPTION

[0022] The following describes the specific embodiments of the present disclosure in detail with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present disclosure and are not intended to limit the present disclosure.

[0023] In this disclosure, unless otherwise stated, directional terms such as "upper" and "lower" generally refer to the upper and lower parts of a device in normal use. In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of this disclosure, "plurality" means two or more, unless otherwise clearly and specifically defined.

[0024] like Figure 1 As shown, the first aspect of the present disclosure provides a method for pretreating low-concentration organic wastewater, which includes: S1, allowing the organic wastewater 11 to enter the homogenization adjustment unit 101 for homogenization treatment to obtain homogenous wastewater and homogenous waste gas; S2, allowing the homogenous wastewater to enter the flotation unit 102 for flotation treatment to obtain flotation wastewater, flotation waste gas and flotation waste residue 17; S3, allowing the flotation wastewater to enter the vacuum cooling unit 103 for organic matter removal treatment to obtain qualified wastewater 12 and organic waste gas 13; S4, allowing the homogenous waste gas, the flotation waste gas and the organic waste gas 13 to enter the waste gas treatment unit respectively.

[0025] Through the above technical solution, the organic wastewater after homogenization is subjected to flotation treatment, which can effectively remove suspended matter from the organic wastewater. The organic wastewater after flotation treatment is then subjected to de-organization treatment in a vacuum cooling unit, which can effectively remove organic matter from the organic wastewater. Moreover, compared with the existing technology, the method disclosed in this disclosure has the advantages of a shorter process flow, simpler operation, and greater adaptability for treating organic wastewater.

[0026] In one embodiment, the organic wastewater described in the present disclosure is low-concentration organic wastewater, wherein low-concentration organic wastewater refers to organic wastewater with a COD content of less than 8000 mg / L. For example, the organic wastewater described in the present disclosure has a suspended solid content of 600-1000 mg / L, a COD of 300-8000 mg / L, an ammonia nitrogen compound content of 50-350 mg / L, a total nitrogen content of 50-500 mg / L, and a total organic matter content of 250-5000 mg / L.

[0027] The organic matter in the organic wastewater includes one or more of styrene, acrylonitrile, ethylbenzene and toluene; the content of the styrene is 50-1500, preferably 100-1500 mg / L; the content of the acrylonitrile is 10-350 mg / L, preferably 20-300 mg / L; the content of the ethylbenzene is 3-150 mg / L, preferably 10-130 mg / L; the content of the toluene is 1-100 mg / L, preferably 10-100 mg / L.

[0028] Among them, the source of the organic wastewater used in the present disclosure can come from one or more of an MTO (Methanol to olefins) device, a PBST (Poly (1,4-butylene terephthalate)) device, an ABS (Acrylonitrile-butadine-styrene) device, a PGA (Polyglycolic acid) device, an EVA (Ethylene-vinylacetatecopolymer) device, a POE (Polyolefin elastomer) device, a POSM (Propylene oxide-styrene monomer) device, an ethylene device, and a polycarbonate device.

[0029] Among them, in order to further improve the treatment effect of the system, the pH value and temperature of the organic wastewater need to be limited. Specifically, the method also includes, before performing step S1, adjusting the pH value of the organic wastewater to 4-10, preferably 6-9; and adjusting the temperature to 25-80°C, preferably 35-50°C.

[0030] In one embodiment, the homogenization regulating unit 101 used in the present disclosure is a conventional choice in the art. For example, the homogenization regulating unit can be a homogenization regulating tank or a homogenization regulating tank, preferably a homogenization regulating tank. In this embodiment, during the homogenization treatment of the organic wastewater, the volatile organic substances in the wastewater will produce a volatile gas phase to form a homogenized waste gas. In addition, during the homogenization process of the organic wastewater, floating oil, colloids, and some suspended matter can be initially removed, thereby reducing the load of subsequent equipment. The suspended matter that has undergone homogenization treatment is the suspended matter with larger particles in the wastewater.

[0031] In one embodiment, step S2 further includes: S21, mixing the homogeneous wastewater with a coagulant to perform a coagulation treatment to obtain a coagulant material. In this embodiment, since the homogeneous wastewater contains small suspended matter, to remove such suspended matter, a coagulant may be added during the coagulation process to uniformly disperse the agent in the wastewater, followed by slow mixing to form large, settleable flocs. Furthermore, the coagulation process can also remove colloidal particles, certain heavy metals, radioactive substances, and high-molecular-weight organic matter in the homogeneous wastewater, thereby reducing turbidity and color in the wastewater.

[0032] In a preferred embodiment, the stirring speed of the coagulation treatment disclosed herein can be below 0.5 m / s, preferably 0.1 to 0.3 m / s. In this embodiment, the coagulation process is carried out under appropriate stirring conditions, which can make the agent dispersed as evenly as possible in the homogeneous wastewater, thereby improving the effect of the coagulation treatment. Among them, when the stirring speed is relatively high, the size of the settleable flocs formed is relatively small, and the sedimentation effect is relatively poor; when the stirring speed is relatively low, the dispersibility of the agent is relatively poor, and the rate of forming the settleable flocs is relatively low. The stirring device used in the present disclosure is a conventional choice in the field, and this application does not make any special requirements.

[0033] Among them, the coagulant used in the coagulation treatment is a conventional choice in the field, and this application does not make special requirements. For example, the coagulant includes one or more of polyaluminum chloride (abbreviated as PAC), aluminum sulfate, ferric chloride and alum, preferably polyaluminum chloride.

[0034] In order to further improve the effect of coagulation treatment, an appropriate amount of coagulant can be added during the coagulation treatment. For example, the amount of the coagulant added is 0.01 to 20 g / L, preferably 0.02 to 5 g / L. The amount added refers to the amount of coagulant added relative to 1 L of homogeneous wastewater, which is 0.01 to 20 g, preferably 0.02 to 5 g.

[0035] In one embodiment, step S2 further includes: S22, mixing the coagulated material with a flocculant to perform a flocculation treatment to obtain a flocculated material. In this embodiment, the coagulated material obtained after the coagulation treatment contains settleable flocs and dispersed particles that, due to molecular attraction, collide and agglomerate to form flocs. During the sedimentation process, the size and mass of the flocs increase, and the settling rate increases with depth.

[0036] In a preferred embodiment, the stirring speed of the coagulation treatment disclosed herein can be 0.2 m / s or less, preferably 0.05 to 0.15 m / s. The stirring device used in the present disclosure is conventionally selected in the art and is not specifically required by this application. In this embodiment, stirring during the flocculation process can maximize the production of flocs, thereby enhancing the effectiveness of the flocculation treatment. Furthermore, employing the stirring conditions disclosed herein can further enhance the effectiveness of the flocculation treatment.

[0037] Among them, the flocculant used in the flocculation treatment is a conventional choice in the art and is not specifically required in this application. For example, the flocculant includes one or more of polyacrylamide (PAM for short), polysilicate, iron salt, aluminum salt and polyaluminum chloride, preferably polyacrylamide.

[0038] To further enhance the flocculation effect, a suitable amount of flocculant may be added during the flocculation process. For example, the amount of flocculant added is 0.001 to 15 g / L, preferably 0.01 to 10 g / L. The amount added refers to the amount of flocculant added per liter of homogeneous wastewater, which is 0.001 to 15 g, preferably 0.01 to 10 g.

[0039] In one embodiment, step S2 further includes: S23, allowing the flocculated material to enter the flotation flotation machine in the flotation unit 102 for flotation treatment to obtain the flotation wastewater, the flotation waste gas, and the flotation waste residue. In this embodiment, the flocs in the flocculated material continuously rise or fall under the action of bubbles, and the flocs that rise to the surface of the water body are removed to form flotation waste residue; the gas phase generated by the bubbles and volatile organic compounds moves upward to form flotation waste gas; and the remaining wastewater is flotation wastewater. Flotation treatment can reduce some volatile organic matter and suspended matter in the wastewater. Specifically, the suspended solids content of the suspended matter in the flotation wastewater after flotation treatment is 200-600 mg / L, and the COD is 300-8000 mg / L.

[0040] The bubbles are generated by an aerator, which, during high-speed rotation, can cut air into suitable tiny bubbles. To further enhance the flotation process, the diameter of the bubbles can be selected. For example, the diameter of the bubbles in the flotation flotation unit 102 is 30 to 3000 μm, preferably 10 to 1000 μm.

[0041] In one embodiment, step S2 further includes:

[0042] S24, the flotation waste enters the sludge storage tank 105 for sedimentation separation treatment to obtain sedimentation separation gas phase, discharged sludge and sedimentation separation wastewater; the sedimentation separation wastewater is returned to the homogenization adjustment unit 101, and the sedimentation separation gas phase enters the waste gas treatment unit.

[0043] In this embodiment, flotation waste is stored in sludge storage tank 105 and undergoes solid-liquid separation to produce sedimentation wastewater and sedimentation gas phase. The solid-liquid separation method can be conventionally selected in the art and is not specifically required by this application. For example, filtration can be used for separation; in addition, rinse water 16 can be used to rinse the filter residue during filtration. The sedimentation wastewater and rinse water 16 enter wastewater tank 106 for future use; the discharged sludge can be packaged and sent to a solid waste treatment plant for treatment.

[0044] In one embodiment, the vacuum cooling unit 103 includes a flash evaporation device, a steam injection device, and a condensation device.

[0045] In a preferred embodiment, the pressure in the flash evaporation device is maintained at 0.01 to 0.2 MPaA, preferably 0.035 MPaA. In this embodiment, the flash evaporation device can remove organic compounds from the flotation wastewater; when the pressure in the flash evaporation device is too low, the gas phase obtained by flash evaporation will contain more water, increasing the pressure of subsequent treatment; when the pressure in the flash evaporation device is high, the organic compounds in the flotation wastewater cannot be fully removed, reducing the removal rate of organic compounds. In addition, steam can be selectively injected into the flash evaporation device through a steam injection device, which can flexibly adjust the pressure in the flash evaporation device. The flash gas phase obtained by the flash evaporation device is cooled by a condensing device, which can condense the water vapor mixed in the flash gas phase to obtain organic compounds with higher purity and reduce the amount of water loss in the entire system.

[0046] In one embodiment, step S3 further includes: S31, allowing the flotation wastewater and the steam from the steam injection device to enter the flash evaporation device for flash evaporation treatment to obtain a flash gas phase and qualified wastewater.

[0047] The flash evaporation device is a conventional choice in the art and is not specifically required in this application. For example, the flash evaporation device in this application is a flash tower. The flash evaporation device can be multi-stage, that is, the number of stages of the flash evaporation device is 2 or more.

[0048] The steam injection device is a conventional choice in the art and is not specifically required in this application. The steam injection device can be multi-stage, that is, the number of stages of the steam injection device is 2 or more.

[0049] In one embodiment, step S3 further includes: S32, allowing the flash gas phase to enter the condensation device for cooling treatment to obtain the organic waste gas and the cooling liquid phase.

[0050] In one embodiment, the vacuum cooling unit 103 further comprises a liquid ring vacuum pump, a circulation pump, and a filter. The liquid ring vacuum pump is installed on the organic waste gas outlet pipeline of the condensing device, enabling the flash evaporation device and the condensing device to operate under low or even negative pressure conditions, thereby improving the removal rate of organic compounds. The circulation pump is installed on the cooling liquid phase outlet pipeline of the condensing device, and a filter is also installed on this cooling liquid phase outlet pipeline. Preferably, the proportion of the returned cooling liquid in the filtered processing portion is 5% to 65%.

[0051] In one embodiment, step S3 further includes: S33, filtering the cooling liquid phase and returning it to the condensing device.

[0052] In one embodiment, the flash evaporation treatment conditions include: a temperature of 25 to 100° C., preferably 30 to 70° C.; and a pressure of 0.01 to 0.20 MPaA, preferably 0.03 to 0.1 MPaA.

[0053] In one embodiment, the operating conditions of the condensing device include: a temperature of 25 to 60° C., preferably 30 to 42° C.; and a pressure of 0.2 to 0.6 MPaA, preferably 0.25 to 0.45 MPaA.

[0054] In one embodiment, the temperature of the qualified wastewater is 10-50° C., the concentration of styrene is below 10 mg / L, and the concentration of acrylonitrile is below 2 mg / L.

[0055] like Figure 2 As shown, in a specific embodiment, the number of stages of the flash evaporation device in the vacuum cooling unit 103 of the present disclosure is 2, namely, a first-stage flash evaporator 201 and a second-stage flash evaporator 202; the number of stages of the steam injection device is 2, namely, a first-stage steam injector 203 and a second-stage steam injector 204.

[0056] In this embodiment, flotation wastewater A1 enters a primary flash evaporator 201 for a first flash evaporation. The resulting gas phase is mixed with steam A4 via a primary steam ejector 203 and then enters a secondary flash evaporator 202 for a second flash evaporation, producing a top gas phase and a bottom liquid phase. A portion of the bottom liquid phase is returned to the primary flash evaporator 201 as a circulating liquid phase, while another portion of the bottom liquid phase enters an external drainage tank 104 as qualified wastewater A2. The top gas phase and steam A4 are mixed via a secondary steam ejector 204 and then enter a condenser for vacuum cooling. The liquid phase obtained in the condenser is filtered, and a portion is returned to the condenser for countercurrent contact with the top gas phase of the second flash evaporator 202. The organic waste gas obtained in the condenser is pumped out of the system via a liquid ring vacuum pump, while the remaining portion is used as steam A4.

[0057] In one embodiment, the waste gas treatment unit includes at least one of a TO furnace, a catalytic combustion furnace, an organic waste gas incinerator, a regenerative thermal oxidizer (RTO), a regenerative thermal incinerator, and a regenerative thermal combustion device. In this embodiment, the organic waste gas, homogeneous waste gas, flotation waste gas, and sedimentation separation gas phase are respectively introduced into at least one of the TO furnace, catalytic combustion furnace, organic waste gas incinerator, regenerative thermal oxidizer (RTO), regenerative thermal incinerator, and regenerative thermal combustion device for subsequent treatment.

[0058] In a specific embodiment, the homogeneous waste gas, flotation waste gas and sedimentation separation gas phase are mixed and then enter at least one of a TO furnace, a catalytic combustion furnace, a regenerative thermal oxidizer (RTO), a regenerative thermal incinerator, and a regenerative thermal combustion device for subsequent treatment; the organic waste gas enters an organic waste gas incinerator for subsequent treatment.

[0059] In one embodiment, Figure 1 and Figure 2 As shown, the methods for pretreatment of low-concentration organic wastewater include:

[0060] S1. The organic wastewater enters the homogenization regulating unit 101 for homogenization treatment to obtain homogenized wastewater and homogenized waste gas;

[0061] S2, allowing the homogenized wastewater to enter the flotation unit 102 for flotation treatment to obtain flotation wastewater, flotation waste gas and flotation waste residue;

[0062] S21, stirring and mixing the homogeneous wastewater with a coagulant to perform coagulation treatment to obtain a coagulant material; the coagulant includes one or more of polyaluminium chloride, aluminium sulfate, ferric chloride and alum; the amount of the coagulant added is 0.01 to 20 g / L; the stirring linear speed of the coagulation treatment is less than 0.5 m / s;

[0063] S22, stirring and mixing the coagulated material with a flocculant to perform flocculation treatment to obtain a flocculated material; the flocculant comprises one or more of polyacrylamide, polysilicate, iron salt, aluminum salt, and polyaluminum chloride; the amount of the flocculant added is 0.001 to 15 g / L; and the stirring linear speed of the flocculation treatment is less than 0.2 m / s;

[0064] S23, allowing the flocculated material to enter an air flotation machine for flotation treatment to obtain the flotation wastewater, the flotation waste gas and the flotation waste residue; the diameter of the bubbles in the air flotation machine is 30 to 3000 μm.

[0065] S24, the flotation waste enters the sludge storage tank 105 for sedimentation separation treatment to obtain a sedimentation separation gas phase, discharged sludge, and sedimentation separation wastewater; the sedimentation separation wastewater returns to the homogenization adjustment unit 101, and the sedimentation separation gas phase enters the waste gas treatment unit;

[0066] S3, the flotation wastewater enters the vacuum cooling unit 103 for organic matter removal treatment to obtain qualified wastewater and organic waste gas; the conditions of the flash evaporation treatment include: temperature of 25-100° C., preferably 30-70° C.; pressure of 0.01-0.20 MPaA, preferably 0.03-0.1 MPaA;

[0067] S31, passing the flotation wastewater and the steam from the steam injection device into the flash evaporation device for flash evaporation treatment to obtain a flash vapor phase and qualified wastewater; the qualified wastewater has a temperature of 10 to 50° C., a styrene concentration of less than 10 mg / L, and an acrylonitrile concentration of less than 2 mg / L;

[0068] S32, allowing the flash gas phase to enter the condensation device for vacuum cooling treatment to obtain the organic waste gas and the cooling liquid phase; the operating conditions of the condensation device include: temperature of 25 to 60° C., preferably 30 to 42° C.; pressure of 0.2 to 0.6 MPaA, preferably 0.25 to 0.45 MPaA;

[0069] S33, returning the cooling liquid phase to the condensing device after filtering; preferably, the proportion of the returned cooling liquid to the filtered portion is 5% to 65%;

[0070] S4. The organic waste gas, homogeneous waste gas, flotation waste gas and sedimentation separation gas phase are respectively sent into at least one of a TO furnace, a catalytic combustion furnace, an organic waste gas incinerator, a regenerative oxidizer, a regenerative incinerator and a regenerative combustion device for subsequent treatment.

[0071] like Figure 1 As shown, in the second aspect of the present disclosure, a system for pretreating low-concentration organic wastewater using the method described in the first aspect is provided, the system comprising a homogenizing and regulating unit 101, an air flotation unit 102, and a vacuum cooling unit 103; the homogenizing and regulating unit 101 comprises an organic wastewater inlet, a homogenizing wastewater outlet, and a homogenizing waste gas outlet; the air flotation unit 102 comprises a homogenizing wastewater inlet, a flotation wastewater outlet, a flotation waste gas outlet, and a flotation waste residue outlet; the vacuum cooling unit 103 comprises a flotation wastewater inlet, a qualified wastewater outlet, and an organic waste gas outlet; the organic wastewater inlet of the homogenizing and regulating unit 101 is used to communicate with an organic wastewater source, the homogenizing wastewater outlet of the homogenizing and regulating unit 101 is communicated with the homogenizing wastewater inlet of the air flotation unit 102; the flotation wastewater outlet of the air flotation unit 102 is communicated with the flotation wastewater inlet of the vacuum cooling unit 103.

[0072] like Figure 2As shown, flotation wastewater A1 enters the primary flash evaporator 201 for a first flash evaporation. The resulting gas phase is mixed with steam A4 through the primary steam ejector 203 and then enters the secondary flash evaporator 202 for a second flash evaporation, producing a top gas phase and a bottom liquid phase. A portion of the bottom liquid phase is returned to the primary flash evaporator 201 as a circulating liquid phase, while another portion of the bottom liquid phase enters the external drainage tank 104 as qualified wastewater A2. The top gas phase and steam A4 are mixed through the secondary steam ejector 204 and then enter the condenser for vacuum cooling. The liquid phase obtained in the condenser is filtered and then returned to the condenser so that it can come into countercurrent contact with the top gas phase of the second flash evaporator 202. The organic waste gas obtained in the condenser is then pumped out of the system via a liquid ring vacuum pump.

[0073] The following examples will further illustrate the present invention, but are not intended to limit the present invention. The organic wastewater used in the examples and comparative examples is wastewater generated by an ABS device, wherein the properties of the organic wastewater are shown in Table 1.

[0074] Table 1 Properties of organic wastewater

[0075]

[0076] Example 1

[0077] In one embodiment, Figure 1 and Figure 2 As shown, the methods for pretreatment of low-concentration organic wastewater include:

[0078] S1. The organic wastewater enters the homogenization regulating unit 101 for homogenization treatment to obtain homogenized wastewater and homogenized waste gas;

[0079] S2, allowing the homogenized wastewater to enter the flotation unit 102 for flotation treatment to obtain flotation wastewater, flotation waste gas and flotation waste residue;

[0080] S21, stirring and mixing the homogenized wastewater with PAC to perform coagulation treatment to obtain a coagulated material; the amount of PAC added is 300 mg / L; and the stirring linear speed of the coagulation treatment is 0.3 m / s;

[0081] S22, stirring and mixing the coagulated material with PAM to perform flocculation treatment to obtain a flocculated material; the amount of PAM added is 200 mg / L; and the stirring linear speed of the flocculation treatment is 0.15 m / s;

[0082] S23, allowing the flocculated material to enter an air flotation machine for flotation treatment to obtain the flotation wastewater, the flotation waste gas and the flotation waste residue; the diameter of the bubbles in the air flotation machine is 20 to 500 μm.

[0083] S24, the flotation waste enters the sludge storage tank 105 for sedimentation separation treatment to obtain a sedimentation separation gas phase, discharged sludge, and sedimentation separation wastewater; the sedimentation separation wastewater returns to the homogenization adjustment unit 101, and the sedimentation separation gas phase enters the waste gas treatment unit;

[0084] S3, the flotation wastewater enters the vacuum cooling unit 103 for organic matter removal treatment to obtain qualified wastewater and organic waste gas; the conditions of the flash evaporation treatment include: temperature of 55° C. and pressure of 0.03 MPaA;

[0085] S31, the flotation wastewater A1 enters the primary flash evaporator 201 for a first flash evaporation, and the resulting gas phase is mixed with steam A4 through the primary steam ejector 203 and then enters the secondary flash evaporator 202 for a second flash evaporation to obtain a tower top gas phase and a tower bottom liquid phase; a portion of the tower bottom liquid phase is returned to the primary flash evaporator 201 as a circulating liquid phase, and another portion of the tower bottom liquid phase is entered into the external drainage tank 104 as qualified wastewater A2; the properties of the treated wastewater are shown in Table 2;

[0086] S32, mixing the top gas phase with steam A4 through the secondary steam ejector 204 and then entering the condensing device for cooling; wherein the operating conditions of the condensing device include: temperature 42° C., pressure 0.45 MPaA;

[0087] S33. Return the cooling liquid phase to the condensing device after filtering, and the returned cooling liquid accounts for 15% of the filtered portion; the returned cooling liquid can not only wash and cool the gas phase in the secondary flash evaporator, but also maintain the gas-liquid load in the secondary flash evaporator by adjusting the return amount, thereby maintaining stable operation of the flash evaporator.

[0088] S4. The organic waste gas, homogeneous waste gas, flotation waste gas and sedimentation separation gas phase are respectively sent into at least one of a TO furnace, a catalytic combustion furnace, an organic waste gas incinerator, a regenerative oxidizer, a regenerative incinerator and a regenerative combustion device for subsequent treatment.

[0089] Comparative Example 1

[0090] This comparative example uses organic wastewater with the same composition as Example 1. The organic wastewater is first sent to a pretreatment unit for homogenization adjustment. The pretreated organic wastewater is precipitated to remove some suspended matter, and then sent to an ozone oxidation treatment unit to decompose the organic matter therein. The organic wastewater and organic waste gas after ozone oxidation are sent to downstream sewage treatment facilities and waste gas treatment facilities, respectively.

[0091] Table 2 Properties of treated wastewater

[0092]

[0093]

[0094] As can be seen from Table 2, flotation treatment of homogenized organic wastewater can effectively remove suspended solids from the organic wastewater; and de-organization of the flotation-treated organic wastewater in a vacuum cooling unit can effectively remove organic matter from the organic wastewater; the removal efficiency of suspended solids is not less than 80%, and the removal efficiency of styrene, acrylonitrile, and ethylbenzene is not less than 95%. Furthermore, compared with the existing technology, the method disclosed herein has the advantages of a shorter process flow, simpler operation, and greater adaptability for treating organic wastewater.

[0095] The preferred embodiments of the present disclosure are described in detail above in conjunction with the accompanying drawings. However, the present disclosure is not limited to the specific details of the above embodiments. Within the technical concept of the present disclosure, various simple modifications can be made to the technical solutions of the present disclosure, and these simple modifications all fall within the scope of protection of the present disclosure.

[0096] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the present disclosure will not further describe various possible combinations.

[0097] In addition, the various embodiments of the present disclosure may be arbitrarily combined, and as long as they do not violate the concept of the present disclosure, they should also be regarded as the contents disclosed by the present disclosure.

Claims

1. A method for pretreatment of low-concentration organic wastewater, characterized in that: The method includes: S1, allowing the organic wastewater to enter the homogenization adjustment unit (101) for homogenization treatment to obtain homogenized wastewater and homogenized waste gas; S2, allowing the homogenized wastewater to enter the air flotation unit (102) for flotation treatment to obtain flotation wastewater, flotation waste gas and flotation waste residue; S3, allowing the flotation wastewater to enter a vacuum cooling unit (103) for organic matter removal treatment to obtain qualified wastewater and organic waste gas; S4. Allow the homogeneous waste gas, the flotation waste gas and the organic waste gas to enter a waste gas treatment unit respectively.

2. The method according to claim 1, characterized in that The organic wastewater comes from one or more of an MTO device, a PBST device, an ABS device, a PGA device, an EVA device, a POE device, a POSM device, an ethylene device and a polycarbonate device.

3. The method according to claim 1, characterized in that The content of suspended solids in the organic wastewater is 600-1000 mg / L, and the COD is 300-8000 mg / L; The organic matter in the organic wastewater includes one or more of styrene, acrylonitrile, ethylbenzene and toluene; The content of styrene is 50-1500 mg / L, the content of acrylonitrile is 10-350 mg / L, the content of ethylbenzene is 3-150 mg / L, and the content of toluene is 1-100 mg / L.

4. The method according to claim 1, wherein Step S2 further includes: S21, stirring and mixing the homogenized wastewater with a coagulant to perform coagulation treatment to obtain a coagulant material; S22, stirring and mixing the coagulated material with a flocculant to perform flocculation treatment to obtain a flocculated material; S23, allowing the flocculated material to enter the air flotation unit (102) for flotation treatment to obtain the flotation wastewater, the flotation waste gas and the flotation waste residue.

5. The method according to claim 4, characterized in that The coagulant includes one or more of polyaluminium chloride, aluminium sulfate, ferric chloride and alum; the amount of the coagulant added is 0.01 to 20 g / L; the stirring linear speed of the coagulation treatment is below 0.5 m / s; The flocculant includes one or more of polyacrylamide, polysilicate, iron salt, aluminum salt and polyaluminum chloride; the amount of the flocculant added is 0.001 to 15 g / L; the stirring linear speed of the flocculation treatment is below 0.2 m / s; The diameter of the bubbles in the air flotation unit (102) is 30 to 3000 μm.

6. The method according to claim 1, characterized in that Step S2 further includes: S24, allowing the flotation waste to enter the sludge storage tank (105) for sedimentation separation treatment to obtain a sedimentation separation gas phase, discharged sludge, and sedimentation separation wastewater; allowing the sedimentation separation wastewater to return to the homogenization adjustment unit (101), and allowing the sedimentation separation gas phase to enter the waste gas treatment unit.

7. The method according to claim 1, characterized in that The vacuum cooling unit (103) includes a flash evaporation device, a steam injection device and a condensation device; Step S3 further includes: S31, allowing the flotation wastewater and the steam from the steam injection device to enter the flash evaporation device for flash evaporation treatment to obtain a flash gas phase and qualified wastewater; S32, allowing the flash gas phase to enter the condensation device for cooling treatment to obtain the organic waste gas and the cooling liquid phase; S33, returning the filtered cooling liquid phase to the condensing device; preferably, the returned cooling liquid accounts for 5% to 65% of the filtered cooling liquid phase.

8. The method according to claim 7, characterized in that The flash evaporation treatment conditions include: a temperature of 25 to 100° C., preferably 30 to 70° C.; a pressure of 0.01 to 0.20 MPaA, preferably 0.03 to 0.1 MPaA; The temperature of the qualified wastewater is 10-50° C., the concentration of styrene is below 10 mg / L, and the concentration of acrylonitrile is below 2 mg / L.

9. The method according to claim 7, characterized in that The number of stages of the flash evaporation device is 2 or more.

10. A system for pretreating low-concentration organic wastewater using the method according to any one of claims 1 to 9, characterized in that: The system comprises a homogenization adjustment unit (101), an air flotation unit (102) and a vacuum cooling unit (103); The homogenization regulating unit (101) comprises an organic wastewater inlet, a homogenized wastewater outlet, and a homogenized waste gas outlet; The air flotation unit (102) comprises a homogenized wastewater inlet, a flotation wastewater outlet, a flotation waste gas outlet and a flotation waste residue outlet; The vacuum cooling unit (103) includes a flotation wastewater inlet, a qualified wastewater outlet, and an organic waste gas outlet; The organic wastewater inlet of the homogenizing and regulating unit (101) is used to communicate with an organic wastewater source, the homogenizing and regulating unit (101) homogenizing and regulating unit (101) homogenizing and regulating unit (102) homogenizing and regulating unit (102) homogenizing and regulating unit (102) flotation wastewater outlet is connected to the flotation wastewater inlet of the vacuum cooling unit (103).

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