CN111392933A

CN111392933A - Method for reducing COD in wastewater and wastewater treatment method

Info

Publication number: CN111392933A
Application number: CN202010159274.0A
Authority: CN
Inventors: 李诺; 刘苏宁; 曹敏; 孙宁磊; 刘国
Original assignee: China ENFI Engineering Corp
Current assignee: China ENFI Engineering Corp
Priority date: 2020-03-09
Filing date: 2020-03-09
Publication date: 2020-07-10

Abstract

The invention provides a method for reducing COD in wastewater and a wastewater treatment method. The method for reducing COD in wastewater comprises the following steps: carrying out low-temperature treatment on the wastewater at a temperature of-5-10 ℃ to separate out a crystalline hydrate from the wastewater, and separating the crystalline hydrate to obtain a first treatment solution; and carrying out physical adsorption treatment on the first treatment liquid to remove organic matters in the first treatment liquid. Before the wastewater is treated by physical adsorption, the wastewater is treated at a low temperature of-5-10 ℃ to separate out salt in the wastewater in the form of crystalline hydrate, so that the water in the wastewater is reduced, the treatment capacity of the wastewater is reduced, the wastewater can be treated by physical adsorption with less adsorbent, the process cost is reduced, and the process is simple and is easy to use in a large scale.

Description

Method for reducing COD in wastewater and wastewater treatment method

Technical Field

The invention relates to the technical field of wastewater treatment, in particular to a method for reducing COD in wastewater and a wastewater treatment method.

Background

China has no independent or definite standard for the discharge of high-salinity wastewater, and generally executes industrial wastewater discharge standards, while various industries execute the discharge standards according to industrial pollutants. Generally speaking, two most important indicators of high-salinity organic wastewater are organic matter content and salinity. The salinity interaction mechanism has an unappreciable influence on the osmotic regulation of organisms, the intake of mineral nutrients and the activity of dehydrogenase. The organic nutrient contained in the wastewater is directly discharged to accelerate river eutrophication and bring great pressure to the water environment, and in addition, the salt-containing wastewater has higher density to influence the aggregation of activated sludge, so the reasonable process has important significance for the treatment of high-concentration high-salinity organic chemical wastewater.

The current common methods for treating dye wastewater mainly comprise: adsorption, biological, photocatalytic, and the like. Among them, the adsorption method has attracted extensive attention because of its high efficiency, simplicity and rapidity, and the adsorption method usually uses activated carbon as an adsorbent for reducing COD in high-salinity wastewater, however, activated carbon has disadvantages of high price and poor regeneration capability, and is not suitable for large-scale use.

Disclosure of Invention

The invention mainly aims to provide a method for reducing COD in wastewater and a wastewater treatment method, so as to solve the problem that the process cost for reducing the COD in the wastewater by an adsorption method in the prior art is higher and is not suitable for large-scale use.

In order to achieve the above objects, according to one aspect of the present invention, there is provided a method for reducing COD in wastewater, comprising the steps of: carrying out low-temperature treatment on the wastewater at a temperature of-5-10 ℃ to separate out a crystalline hydrate from the wastewater, and separating the crystalline hydrate to obtain a first treatment solution; and carrying out physical adsorption treatment on the first treatment liquid to remove organic matters in the first treatment liquid.

Further, the pH value of the wastewater is 5-10.

Further, Na is precipitated by low-temperature treatment₂SO₄·10H₂A first crystalline product of O.

Further, the temperature of the low-temperature treatment is 0-10 ℃.

Further, after the step of low-temperature treatment, a denitration wastewater containing a first crystal product is obtained, and the denitration wastewater is filtered to obtain a first treatment liquid.

Further, a filter screen with the mesh number of 150-400 is adopted to filter the denitration wastewater.

Further, the adsorbent for physical adsorption treatment comprises diatomite and/or activated carbon, preferably diatomite and activated carbon, and more preferably, the mass ratio of the diatomite to the activated carbon is 0.5: (1-5).

According to another aspect of the present invention, there is provided a method for treating wastewater, comprising the steps of: s1, treating the wastewater by using the method for reducing COD in wastewater according to any one of claims 1 to 7 to obtain a second treatment solution; s2, the second processing liquid is subjected to an evaporation crystallization process to precipitate a salt in the second processing liquid, thereby obtaining purified water.

Further, the evaporative crystallization treatment comprises: carrying out evaporation concentration treatment on the second treatment liquid to obtain a concentrated liquid, wherein the temperature of the evaporation concentration treatment is preferably 100-105 ℃; and crystallizing the concentrated solution to obtain a second crystallized product, wherein the temperature of the crystallization treatment is preferably 90-100 ℃.

Further, after the step of evaporative crystallization treatment, a treatment liquid containing a second crystallized product is obtained, and the treatment method further comprises the steps of: and centrifuging the treatment liquid to separate the second crystallized product to obtain purified water.

By applying the technical scheme of the invention, the method for reducing COD in the wastewater is provided, and before the wastewater is treated by adopting physical adsorption, the wastewater is treated at a low temperature of-5-10 ℃ to separate out salt in the wastewater in the form of crystalline hydrate, so that the water content in the wastewater is reduced, the treatment capacity of the wastewater is reduced, and the wastewater can be treated by utilizing less adsorbent through physical adsorption, so that the process cost is reduced, and the process is simple and is easy to use in a large scale.

Detailed Description

It should be noted that the embodiments and features of the embodiments may be combined with each other without conflict.

In order to make the technical solutions of the present invention better understood by those skilled in the art, the technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

It is noted that the terms first, second and the like in the description and in the claims of the present invention are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used may be interchanged under appropriate circumstances in order to facilitate the description of the embodiments of the invention herein. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.

As described in the background art, the adsorption method is a main method for treating dye wastewater, and usually adopts activated carbon as an adsorbent to reduce COD in high-salinity wastewater, however, activated carbon has disadvantages of high price and poor regeneration capability, and is not suitable for large-scale use.

In order to solve the technical problems, the application provides a method for reducing COD in wastewater, which comprises the following steps: carrying out low-temperature treatment on the wastewater at a temperature of-5-10 ℃ to separate out a crystalline hydrate from the wastewater, and separating the crystalline hydrate to obtain a first treatment solution; and carrying out physical adsorption treatment on the first treatment liquid to remove organic matters in the first treatment liquid.

Before the method is used for treating the wastewater by adopting physical adsorption, the wastewater is subjected to low-temperature treatment at-5-10 ℃ to separate out salt in the wastewater in the form of crystalline hydrate, so that the water content in the wastewater is reduced, the treatment capacity of the wastewater is reduced, and the wastewater can be treated by utilizing less adsorbents through physical adsorption, so that the process cost is reduced, the process is simple and easy for large-scale use.

An exemplary embodiment of the method for reducing COD in wastewater according to the present invention will be described in more detail below. These exemplary embodiments may, however, be embodied in many different forms and should not be construed as limited to only the embodiments set forth herein. It should be understood that these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of these exemplary embodiments to those skilled in the art.

Firstly, the wastewater is subjected to low-temperature treatment at-5 to 10 ℃ to precipitate crystalline hydrate from the wastewater, and the crystalline hydrate is separated to obtain a first treatment liquid. The wastewater to be treated mainly contains Na₂SO₄NaCl, organics, and fluorides.

In the step, the wastewater is subjected to low-temperature treatment at-5 to 10 ℃ to obtain a first crystallization product, and in order to improve the treatment efficiency of the high-COD wastewater, the wastewater with the pH value of 5.0 to 10 is preferably treated by adopting the process conditions, or the pH value of the wastewater is adjusted to 5.0 to 10 before the low-temperature treatment.

The crystalline salt precipitated as a crystalline hydrate contained in the first crystalline product may be Na₂SO₄·10H₂And O. Due to Na₂SO₄Has a lower solubility than other salts in the wastewater in the above temperature range, is easily precipitated, and Na₂SO₄Can be expressed as Na₂SO₄·10H₂Precipitating in the form of O, thereby obtaining Na in the wastewater₂SO₄Can be treated at a low temperature within the above temperature range when the content of (A) is highTakes away a large amount of water in the wastewater. For example, the salt content in the waste water contains NaCl and Na₂SO₄Na when the solute mass fraction of NaCl is 10-25% in the temperature range of-5-10 DEG C₂SO₄The solute mass fraction of (A) is 0 to 10%, and thus, Na₂SO₄More Na is precipitated than NaCl and Na is added₂SO₄·10H₂The form of O carries away a large amount of water.

In order to make more Na₂SO₄With Na₂SO₄·10H₂The precipitation of O is preferably carried out at a temperature of 0 to 10 ℃ in the low-temperature treatment.

When the first crystalline product contains Na₂SO₄·10H₂In the case of O (mirabilite), the denitration wastewater containing the first crystal product is obtained after the low-temperature treatment step, and the denitration wastewater can be filtered to obtain the first treatment liquid, and in order to separate the first crystal product from the denitration wastewater more preferably, the denitration wastewater is filtered by using a filter screen having a mesh number of 150 to 400.

Obtaining a first treatment liquid after the above steps, and then performing the following steps: and carrying out physical adsorption treatment on the first treatment liquid to remove organic matters in the first treatment liquid.

The physical adsorption-treated adsorbent may include diatomaceous earth and/or activated carbon, but is not limited to the above-mentioned species, and may be appropriately selected by those skilled in the art according to the prior art. Specifically, the first treatment liquid obtained after the low-temperature treatment is introduced into an adsorption unit using an adsorbent as a filler, and the first treatment liquid is physically adsorbed by the adsorbent filler.

In order to enhance the adsorption effect, in a preferred embodiment, the first treatment liquid is physically adsorbed by an adsorbent comprising a combination of diatomaceous earth and activated carbon, and more preferably, the mass ratio of diatomaceous earth to activated carbon is 0.5: (1-5). The adsorbent consisting of the two adsorbing materials can adsorb organic matters which are difficult to treat and can decolorize wastewater.

According to another aspect of the present invention, there is also provided a method for treating wastewater, comprising the steps of: s1, treating the wastewater by using the method for reducing COD in wastewater according to any one of claims 1 to 7 to obtain a second treatment solution; s2, the second processing liquid is subjected to an evaporation crystallization process to precipitate a salt in the second processing liquid, thereby obtaining purified water.

Before the wastewater is treated by physical adsorption, the wastewater is treated at a low temperature of-5-10 ℃ to separate out salt in the wastewater in the form of crystalline hydrate, so that the treatment capacity of the wastewater is reduced by reducing the water in the wastewater, and the wastewater can be treated by less adsorbent through physical adsorption, so that the process cost is reduced, and the process is simple and is easy to use in a large scale.

In the step S2, the evaporative crystallization process may include two steps, namely, an evaporative concentration process and a crystallization process, in which the second process liquid is first subjected to the evaporative concentration process to obtain a concentrated liquid, and then the concentrated liquid is subjected to the crystallization process to obtain a second crystallized product.

In the evaporation concentration treatment step, a vapor compressor can be adopted to compress vapor, so that the utilization rate of the vapor is improved, and the evaporation concentration treatment can be selected from any one of single-effect evaporation, multi-effect evaporation and MVR evaporation. In order to improve the treatment efficiency, the temperature of the evaporation concentration treatment is preferably 100 to 105 ℃.

The crystallization treatment is mainly to precipitate salts remaining in the concentrated solution, and the obtained second crystallized product is mainly composed of crystallized salts, and in the crystallization treatment step, the temperature of the crystallization treatment is preferably 90 to 100 ℃ in order to improve the crystallization efficiency.

After the step of crystallization treatment, a treatment solution containing a second crystallized product is obtained, and the step S2 may further include the steps of: and centrifuging the treatment liquid to separate the second crystallized product to obtain purified water. The centrifugal treatment can be performed by a centrifugal machine, preferably, the mesh number of the centrifugal machine is 150 meshes, and the water content of the separated crystal salt can reach 3-5%.

The step S2 may further include a step of preheating the second treatment solution before the step of performing the evaporative crystallization treatment on the second treatment solution, and the preheating temperature is preferably 80 to 110 ℃ in order to improve the preheating efficiency and reduce the influence on the pretreatment solution. And, preferably, the waste water is preheated by using steam generated after the evaporation concentration treatment, so as to save energy consumption.

In a preferred embodiment, the steps S1 and S2 are repeated, and in step S1, the partial treatment liquid and/or the partial purified water is mixed with the wastewater and then treated at a low temperature of-5 to 10 ℃. By recycling a part of the above-mentioned treatment liquid (i.e., the crystallization mother liquid), the salt content in the treatment liquid, which is not crystallized in the primary crystallization treatment, can be further reduced by forming crystallized salt through the recrystallization treatment in step S2; similarly, by recycling a part of the purified water (i.e., the centrifuged mother liquor), the crystallized salts remaining in the purified water after the primary centrifugation can be removed by the secondary centrifugation in step S2, thereby further reducing the salt content in the purified water obtained after the final circulation.

The present invention is described in further detail below with reference to specific examples, which are not to be construed as limiting the scope of the invention as claimed.

Example 1

This example provides a process for reducing COD in wastewater containing Na as the principal component₂SO₄NaCl, organic matter and fluoride, the salt content is 30%, the COD is 10000 mg/L, the pH value is 4, the processing method comprises the following steps:

firstly, performing low-temperature freezing treatment on wastewater at the temperature of-5 ℃, filtering by adopting a filter screen with the mesh number of 120 to obtain first treatment liquid, and then performing physical adsorption on the first treatment liquid by adopting a kieselguhr/activated carbon adsorbent combination to obtain second treatment liquid, wherein the dosage mass ratio of the kieselguhr to the activated carbon is 1: 1.

example 2

The wastewater treated by the method provided by the embodiment is the same as the wastewater treated by the embodiment 1, and is different from the wastewater treated by the embodiment 1 in that:

the wastewater is subjected to low-temperature freezing treatment at 0 ℃.

Example 3

the wastewater is subjected to low-temperature freezing treatment at 10 ℃.

Example 4

the pH of the wastewater was adjusted to 5.0 prior to cryogenic treatment of the wastewater.

Example 5

the pH of the wastewater is adjusted to 10 prior to cryogenic treatment of the wastewater.

Example 6

the mass ratio of the dosage of the diatomite to the dosage of the active carbon is 0.5: 1.

example 7

the mass ratio of the dosage of the diatomite to the dosage of the active carbon is 0.5: 5.

example 8

filtering with a filter screen with 150 meshes.

Example 9

filtering with a filter screen with 400 meshes.

Example 10

This example provides a process for reducing COD in wastewater containing Na as the principal component₂SO₄NaCl, organic matter and fluoride, the salt content is 30%, the COD is 10000 mg/L, the pH value is 7, the treatment method comprises the following steps:

firstly, performing low-temperature freezing treatment on wastewater at 5 ℃, filtering by using a filter screen with the mesh number of 300 to obtain first treatment liquid, and then performing physical adsorption on the first treatment liquid by using a kieselguhr/activated carbon adsorbent combination to obtain second treatment liquid, wherein the dosage mass ratio of kieselguhr to activated carbon is 1: 4.

example 11

The embodiment provides a wastewater treatment method, which comprises the following steps:

the method of example 10 was used to obtain the second treatment solution, which was then preheated to 100 ℃, and then evaporated and concentrated in an evaporator at 95 ℃ to 50%, and the concentrated solution was then crystallized in a crystallizer at 85 ℃ to further concentrate the concentrated solution to separate out crystalline salts, thus obtaining the treatment solution. And (4) allowing the treatment solution with the crystallized salt to enter a centrifugal machine, wherein the mesh number of a filter screen of the centrifugal machine is 150 meshes, and performing centrifugal separation to obtain the crystallized salt and purified water.

Example 12

The treatment method provided in this example treats the same wastewater as in example 1, and differs from example 11 in that:

the temperature for the evaporation concentration treatment was 100 ℃ and the temperature for the crystallization treatment was 90 ℃.

Example 13

the temperature for the evaporation concentration treatment was 105 ℃ and the temperature for the crystallization treatment was 100 ℃.

Comparative example 1

The method provided by the comparative example for treating the same wastewater as in example 1 comprises the following steps:

firstly, performing low-temperature freezing treatment on wastewater at the temperature of-10 ℃, filtering by adopting a filter screen with the mesh number of 120 to obtain first treatment liquid, and then performing physical adsorption on the first treatment liquid by adopting a kieselguhr/activated carbon adsorbent combination to obtain second treatment liquid, wherein the dosage mass ratio of the kieselguhr to the activated carbon is 1: 1.

comparative example 2

directly adopting diatomite/activated carbon adsorbent combination to physically adsorb the first treatment liquid to obtain a second treatment liquid, wherein the dosage mass ratio of diatomite to activated carbon is 1: 1.

comparative example 3

the first treatment liquid was physically adsorbed directly with an individual adsorbent of activated carbon in the same amount as the total amount of the adsorbent combination in comparative examples 1 to 2 to obtain a second treatment liquid.

Comparative example 4

The comparative example provides a method of treating wastewater comprising the steps of:

and (3) obtaining a second treatment solution by adopting the method in the comparative example 3, preheating the second treatment solution at the preheating temperature of 100 ℃, then, entering an evaporation tank for evaporation concentration treatment after preheating, concentrating the second treatment solution at the temperature of 95 ℃ until the concentration is 50%, entering a crystallization tank for the concentrated solution, controlling the temperature in the crystallization tank to be 85 ℃, and further concentrating the concentrated solution to separate out crystal salt to obtain the treatment solution. And (4) allowing the treatment solution with the crystallized salt to enter a centrifugal machine, wherein the mesh number of a filter screen of the centrifugal machine is 150 meshes, and performing centrifugal separation to obtain the crystallized salt and purified water.

The purified water obtained in examples 1 to 13 and comparative examples 1 to 4 was sampled, the salt content and COD of each sample were measured, and the chromaticity of each wastewater sample was obtained by a chromium-cobalt colorimetric method, and the test results are shown in the following table.

From the test results, compared with comparative examples 1 to 3, the method for reducing COD in wastewater in examples 1 to 10 of the invention can make the treatment fluid have lower salt content and COD; in addition, as can be seen from recording the use amounts of the adsorbents in the examples and the comparative examples, compared with the comparative examples 2 to 3, the use amounts of the adsorbents in the examples 1 to 10 are greatly reduced, so that the process cost is reduced. Furthermore, compared with comparative example 4, the purified water obtained by the treatment method of examples 11 to 13 can have lower salt content and COD, wherein the difference between examples 11 to 13 and example 10 is only that the concentrated crystallization treatment is further performed, and it can be seen from the above table that the salt content of the treated wastewater in examples 11 to 13 is reduced and the COD is increased, because the salt crystallization brings out a part of the crystal water, the amount of the wastewater is reduced, the COD in the wastewater is increased, and the COD content after the treatment is increased.

From the above description, it can be seen that the above-described embodiments of the present invention achieve the following technical effects:

before the wastewater is treated by physical adsorption, the wastewater is treated at a low temperature of-5-10 ℃ to separate out salt in the wastewater in the form of crystalline hydrate, so that the water in the wastewater is reduced, the treatment capacity of the wastewater is reduced, the wastewater can be treated by physical adsorption with less adsorbent, the process cost is reduced, and the process is simple and is easy to use in a large scale.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for reducing COD in wastewater is characterized by comprising the following steps:

carrying out low-temperature treatment on the wastewater at a temperature of-5-10 ℃ to separate out a crystalline hydrate from the wastewater, and separating the crystalline hydrate to obtain a first treatment liquid;

and carrying out physical adsorption treatment on the first treatment liquid to remove organic matters in the first treatment liquid.

2. The method according to claim 1, wherein the pH value of the wastewater is 5-10.

3. The method according to claim 1 or 2, wherein Na is precipitated by the low-temperature treatment₂SO₄·10H₂A first crystalline product of O.

4. The method according to claim 3, wherein the low-temperature treatment is performed at a temperature of 0 to 10 ℃.

5. The method according to claim 3, wherein a denitration wastewater containing the first crystal product is obtained after the low-temperature treatment step, and the denitration wastewater is filtered to obtain the first treatment liquid.

6. The method according to claim 5, wherein the denitration wastewater is filtered by a filter screen with the mesh number of 150-400.

7. The process according to claim 1 or 2, wherein the physical adsorption-treated adsorbent comprises diatomaceous earth and/or activated carbon, preferably the diatomaceous earth and the activated carbon, more preferably the mass ratio of the diatomaceous earth to the activated carbon is 0.5: (1-5).

8. A method of treating wastewater, comprising the steps of:

s1, treating the wastewater by using the method for reducing COD in wastewater according to any one of claims 1 to 7 to obtain a second treatment solution;

and S2, carrying out evaporation crystallization treatment on the second treatment liquid to precipitate salt in the second treatment liquid to obtain purified water.

9. The process according to claim 8, characterized in that said evaporative crystallization process comprises:

carrying out evaporation concentration treatment on the second treatment liquid to obtain a concentrated liquid, wherein the temperature of the evaporation concentration treatment is preferably 100-105 ℃;

and crystallizing the concentrated solution to obtain a second crystallized product, wherein the temperature of the crystallization treatment is preferably 90-100 ℃.

10. The process of claim 8, wherein a process liquor containing the second crystalline product is obtained after the step of evaporative crystallization, the process further comprising the steps of:

and centrifuging the treatment liquid to separate the second crystallized product to obtain the purified water.