A method for denitrifying wastewater

Abstract

The present invention discloses a method for denitrifying wastewater, achieving a perfect integration of COD removal from wastewater (Fenton oxidation) and nitrogen removal from wastewater (ferroammonium oxidation), and avoiding the chemical consumption after treating wastewater by the traditional Fenton oxidation method.

Description

Technical Field

[0001] The present invention belongs to the field of wastewater treatment in environmental engineering, and more specifically, relates to a method for nitrogen removal from wastewater. Background Art

[0002] The chemical industry permeates all aspects and is an important and indispensable part of the national economy. The diversity of chemical products determines that chemical wastewater has the characteristics of large water volume, high toxicity, and complex water quality, and is often accompanied by high concentrations of COD and ammonia nitrogen.

[0003] In fact, chemical wastewater generally undergoes Fenton treatment. The Fenton method generates hydroxyl radicals through the reaction of ferrous ions and hydrogen peroxide, destroys the organic structure, and finally oxidizes and decomposes the organic matter to reduce the COD content in the water body. Its main process flow includes acid adjustment (pH value should be controlled at 3.0 - 4.0), oxidation reaction, neutralization, solid-liquid separation, etc. In addition, nowadays, most wastewater project upgrading and transformation are due to the fact that biological treatment cannot reduce the nitrogen in the wastewater to the discharge standard, and only focuses on improving the denitrification link in wastewater treatment. Therefore, processes such as MBR and denitrification filters have emerged. Denitrification technologies include chemical methods and biological methods. Since chemical methods will produce secondary pollution and are costly, biological denitrification technologies are generally used.

[0004] Wastewater biological treatment for nitrogen removal mainly relies on some specific bacteria to achieve the conversion of nitrogen forms; nitrogen-containing organic compounds are first decomposed and converted into ammonia nitrogen NH 4 + or NH 3 , this process is called "ammonification reaction"; nitrifying bacteria convert ammonia nitrogen into nitrate, this process is called "nitrification reaction"; denitrifying bacteria convert nitrate into nitrogen gas, this reaction is called "denitrification reaction", and nitrogen-containing organic compounds are finally converted into nitrogen gas and removed from the wastewater.

[0005] Based on the above, the existing denitrification treatment process for chemical wastewater mainly consists of aerobic and anoxic sections. High-concentration ammonia nitrogen is first nitrified into nitrate in the aerobic section, and then the nitrate flows into the anoxic section for denitrification and is converted into nitrogen gas to achieve ammonia nitrogen removal. However, this traditional nitrification-denitrification process requires a large amount of aeration, has huge energy consumption, and the denitrification efficiency is not ideal.

[0006] Therefore, it is of great significance to develop a method for wastewater detoxification and nitrogen removal with low energy consumption, high efficiency and stability. Summary of the Invention

[0007] 1. Problems to be Solved

[0008] Aiming at the problems such as energy consumption existing in the existing wastewater denitrification process, the present invention provides a method for nitrogen removal from wastewater.

[0009] 2. Technical Solution

[0010] To solve the above problems, the technical solution adopted by the present invention is as follows:

[0011] The present invention provides a method for denitrifying wastewater, comprising:

[0012] S1. Performing Fenton oxidation treatment on the wastewater;

[0013] S2. Performing neutralization precipitation treatment on the effluent after Fenton oxidation treatment, and controlling the pH value between 4 and 6;

[0014] S3. Directly subjecting the effluent after neutralization precipitation treatment to iron ammonia oxidation treatment in an anaerobic environment;

[0015] S4. Performing anoxic treatment on the effluent after iron ammonia oxidation treatment;

[0016] Wherein, in the step S3, no Fe(Ⅲ) source is added any more.

[0017] As described herein, in S2, it is very important to "control the pH value between 4 and 6", which can convert the trivalent iron (Fe(Ⅲ)) contained in the Fenton iron sludge that should be regarded as hazardous solid waste after Fenton oxidation treatment into a dissolved state and follow the water body to be treated into the process of S3, and be used as the iron source for iron ammonia oxidation treatment, thus avoiding the addition of extra Fe(Ⅲ). Based on this, it is more preferable to "control the pH value between 4.5 and 5.5".

[0018] In addition, it should be noted that the above-mentioned technical solution realizes the perfect integration of COD removal (Fenton oxidation) and denitrification (iron ammonia oxidation) of wastewater, and avoids the consumption of chemicals after treating wastewater by the traditional Fenton oxidation method. Specifically, the requirements clearly stated in the engineering technical specifications for treating wastewater by the traditional Fenton oxidation method (after the Fenton oxidation reaction) need to adjust the Fenton effluent to 7 - 9 in the neutralization unit (because the pH value during Fenton oxidation is generally controlled below 4, which will inevitably lead to a large consumption of alkali in the neutralization unit) to form precipitation.

[0019] It is further explained that, in terms of mass - volume concentration, when the ammonia nitrogen content in the wastewater to be treated does not exceed half of the COD content, it can ensure the optimal denitrification effect of the wastewater while effectively removing COD.

[0020] According to any implementation scheme of the purpose of the present invention, in the step S1, before performing Fenton oxidation treatment on the wastewater, it includes an acid - adjusting treatment step, and the pH value of the wastewater after the acid - adjusting treatment is 3 - 4.

[0021] According to any embodiment of the object of the present invention, in S1., before the wastewater is subjected to Fenton oxidation treatment, the suspended solid content in the wastewater should be controlled to be less than 200 mg / L.

[0022] According to any embodiment of the object of the present invention, based on the mass-volume concentration of COD contained in the wastewater,

[0023] the ratio of the addition amount of hydrogen peroxide to the content of COD is (1-2):1,

[0024] the ratio of the addition amount of hydrogen peroxide to the addition amount of ferrous ions is (1-10):1.

[0025] According to any embodiment of the object of the present invention, in S1., ferrous ions are first added to the wastewater, and after an interval of 5-30 min, hydrogen peroxide is added for Fenton oxidation treatment. The time for the Fenton oxidation treatment is 2-8 h.

[0026] According to any embodiment of the object of the present invention, in S1., during the Fenton oxidation treatment, spraying treatment can be carried out, or an antifoaming agent can be added to remove the foam on the surface of the wastewater.

[0027] According to any embodiment of the object of the present invention, in S2., a flocculant is further added, and the addition amount of the flocculant is set to 100-205 mg / L.

[0028] Preferably, the flocculant is composed of polyaluminum chloride and polyacrylamide. Among them, the addition amount of polyaluminum chloride is 100-200 mg / L, and the addition amount of polyacrylamide is 3-5 mg / L.

[0029] According to any embodiment of the object of the present invention, in S2., the hydraulic retention time for the neutralization precipitation treatment is 2-4 h.

[0030] According to any embodiment of the object of the present invention, in S3., it includes a startup stage,

[0031] According to any embodiment of the object of the present invention, when the iron ammonia oxidation treatment is carried out in S3., the dissolved oxygen is maintained below 0.2 mg / L.

[0032] According to any embodiment of the object of the present invention, in S3., the hydraulic retention time for the iron ammonia oxidation treatment is 4-8 h.

[0033] According to any embodiment of the object of the present invention, when the iron ammonia oxidation treatment is carried out in S3., the temperature is 20-35 °C.

[0034] According to any embodiment of the object of the present invention, in S4., when performing anoxic treatment, the dissolved oxygen is maintained at 0.2 - 0.4 mg / L.

[0035] According to any embodiment of the object of the present invention, in S4., the hydraulic retention time for anoxic treatment is 4 - 8 h.

[0036] According to any embodiment of the object of the present invention, it further includes: S5. Treating the sludge precipitate after anoxic treatment with acid.

[0037] According to any embodiment of the object of the present invention, in S5, the supernatant obtained after treatment is recycled to S1.

[0038] Beneficial effects

[0039] (1) In fact, chemical industrial wastewater generally uses Fenton treatment to reduce the COD content in the water body. Its main process flow is as Figure 2 shown, including acid adjustment, oxidation reaction, neutralization, solid - liquid separation, etc. And according to the "Engineering Technical Specification for Fenton Oxidation Method Wastewater Treatment" in the "National Environmental Protection Standard of the People's Republic of China" (HJ 1095 - 2020), it is necessary to adjust the Fenton effluent to 7 - 9 in the neutralization unit to form a precipitate in order to meet the subsequent effluent requirements. This process requires adding a large amount of precipitation agents, increasing the operating cost. Based on this, the wastewater denitrification method provided by the present invention realizes the perfect integration of wastewater de - COD (Fenton oxidation) and wastewater denitrification (ferroammonium oxidation), avoiding the consumption of agents after treating wastewater by the traditional Fenton oxidation method;

[0040] In addition, for the wastewater denitrification method provided by the present invention, the trivalent iron (Fe(Ⅲ)) contained in the Fenton iron sludge, which should be regarded as hazardous solid waste after Fenton oxidation treatment, is converted into a dissolved state and enters the process of S3 following the water body to be treated, and is used as the iron source for ferroammonium oxidation treatment, avoiding the addition of extra Fe(Ⅲ);

[0041] Compared with the traditional nitrification - denitrification denitrification process, there is no need for aeration anymore;

[0042] In summary, the wastewater denitrification method provided by the present invention saves a large amount of energy consumption and greatly reduces the operating cost.

[0043] (2) For the wastewater denitrification method provided by the present invention, the added dissolved iron can play a role in the process of iron - reducing organic matter oxidation, and has a good degradation effect on aromatic organic matter, which is beneficial to denitrification and detoxification.

[0044] (3) For the wastewater denitrification method provided by the present invention, during application, it can directly rely on the original Fenton and biological section processes of the chemical industrial wastewater treatment plant for in - situ upgrading, with low transformation cost and extremely strong applicability.

[0045] (4) The wastewater denitrification method provided by the present invention can redissolve the reduced divalent iron (Fe(Ⅱ)) during the iron ammonia oxidation treatment process by adding a small amount of acid, and reapply it to the Fenton process, reducing the addition of iron salts and achieving clean regeneration. Detailed implementation manners

[0046] The present disclosure can be more easily understood by referring to the following description in combination with examples, and all examples form a part of the present disclosure. It should be understood that the present disclosure is not limited to the specific products, methods, conditions or parameters described and / or illustrated herein. Further, the terms used herein are for the purpose of describing specific embodiments by way of example only and are not intended to be limiting unless otherwise stated.

[0047] It should also be understood that, for the sake of clarity, certain features of the present disclosure may be described herein in the context of separate embodiments, but may also be provided in combination with each other in a single embodiment. That is, unless clearly incompatible or specifically excluded, each separate embodiment is considered combinable with any other embodiment, and such combination is considered to represent another different embodiment. Conversely, for the sake of brevity, the various features of the present disclosure described in the context of a single embodiment may also be provided separately or in any sub-combination. Finally, although a particular embodiment may be described as part of a series of steps or part of a more general structure, each step or sub-structure itself may also be considered an independent embodiment.

[0048] Unless otherwise stated, it should be understood that each individual element in a list and each combination of the individual elements in the list will be construed as a different embodiment. For example, a list of embodiments expressed as "A, B or C" should be construed as including the embodiments "A", "B", "C", "A or B", "A or C", "B or C", or "A, B or C".

[0049] In the present disclosure, the singular forms of the articles "a", "an" and "the" also include the corresponding plural referents, and the reference to a specific numerical value includes at least that specific value, unless the context clearly indicates otherwise. Thus, for example, the reference to "a substance" is a reference to at least one of such a substance and its equivalents.

[0050] Terms including ordinal numbers such as "first" and "second" may be used to explain various components or fluids, but these components and fluids are not limited by these terms. Thus, without departing from the teachings of the present disclosure, these terms are only used to distinguish the component / fluid from another component / fluid.

[0051] When describing items by using conjunctive terms such as “... and / or...”, the description should be understood to include any one of the associated listed items and all combinations of one or more of them.

[0052] Generally, the use of the term “about” indicates an approximation that can vary according to the desired characteristics obtained from the disclosed subject matter and will be interpreted in a context-dependent manner based on functionality. Thus, one of ordinary skill in the art will be able to interpret a certain degree of difference on a case-by-case basis. In some cases, the number of significant digits used when expressing a particular value can be a representative technique for determining the difference allowed by the term “about”. In other cases, the gradient in a series of values can be used to determine the range of difference allowed by the term “about”. Further, all ranges in this disclosure are inclusive and combinable, and references to values stated in a range include each value within that range.

[0053] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the technical field to which this invention pertains; the terms used herein and / or include any and all combinations of one or more of the associated listed items.

[0054] In the following examples, those without specific conditions noted were carried out under conventional conditions or conditions recommended by the manufacturer. Reagents or instruments without the manufacturer indicated were all conventional products that could be obtained through commercial purchase.

[0055] The present invention will be further illustrated below in conjunction with specific embodiments, but the embodiments do not limit the present invention in any form. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in the technical field. The essential features and remarkable effects of the present invention can be reflected from the following embodiments. The described embodiments are some embodiments of the present invention, rather than all embodiments. Therefore, they do not limit the present invention in any way. Non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention all fall within the protection scope of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 It is a schematic flow diagram for wastewater denitrification provided in Embodiment 1 of the present invention;

[0057] Figure 2 It is a schematic process flow diagram of a general Fenton oxidation wastewater treatment project.

[0058] Embodiment 1

[0059] In this embodiment, a wastewater denitrification process combining Fenton and biological iron ammonia oxidation is provided, and the specific steps are as follows:

[0060] S1: Acidify the wastewater

[0061] Keep the influent at an acidic condition with a pH of 3.2. If the influent pH does not meet the requirement, a pre-set acidification tank is used to add 98% concentrated sulfuric acid or 50% dilute sulfuric acid to adjust the pH value of the wastewater. Mechanical stirring is adopted with a mixing time of 5 min.

[0062] Among them, the addition of the acid solution is carried out by an anti-corrosion metering pump, and the dosing amount is automatically adjusted by an on-line pH meter.

[0063] S2: Conduct Fenton reaction treatment on the acidified wastewater in the Fenton oxidation reaction tank;

[0064] For the above-mentioned Fenton oxidation treatment, ferrous sulfate (pre-prepared in the solution tank with a mass percentage concentration of 20%) is added first, and after waiting for 15 min, 30 wt% hydrogen peroxide is added. The dosing ratio is that the ratio of the hydrogen peroxide concentration (mg / L) to the COD (mg / L) is 2:1, and the hydrogen peroxide concentration (mg / L) and the ferrous ion (mg / L) concentration is 3:1;

[0065] The hydraulic retention time in the Fenton oxidation reaction tank is 2 h. During this period, if a large amount of foam appears, water spraying or defoaming spraying can be adopted.

[0066] S3: Conduct neutralization and precipitation treatment on the effluent after Fenton reaction treatment in the neutralization sedimentation tank

[0067] Alkali solution needs to be added to the neutralization sedimentation tank to adjust the pH to 4.5, and the alkali solution used is 10% sodium hydroxide solution.

[0068] At the same time, polyaluminum chloride and polyacrylamide are added, and the dosing amounts are set to 120 mg / L and 3 mg / L;

[0069] The hydraulic retention time in the neutralization sedimentation tank is set to 3 h.

[0070] S4: Conduct anaerobic iron-ammonium oxidation treatment on the effluent after neutralization and precipitation treatment in the iron-ammonium oxidation reaction tank

[0071] In the startup stage (this stage can be carried out in advance), inoculate the anaerobic sludge from the sewage treatment plant (from the sludge thickening tank), with a sludge concentration of about 3 g / L MLSS, the temperature is maintained at 30 °C, the pH is maintained at 6.5, and the startup time is 2 weeks. During this period, the adaptability of the iron-ammonium oxidation functional bacteria group is strengthened by adding ammonium chloride and sodium bicarbonate.

[0072] After the startup is completed, in the iron-ammonium oxidation reaction tank, conduct anaerobic iron-ammonium oxidation treatment on the effluent after neutralization and precipitation treatment. During the treatment process, control the dissolved oxygen below 0.2 mg / L, the hydraulic retention time is set at 6 h, and the temperature is maintained at 30 °C.

[0073] S5: Perform anoxic treatment on the effluent after the iron ammonia oxidation treatment in the anoxic reaction tank.

[0074] Adding glucose with a C / N ratio of 2.5 as a carbon source to the effluent after the iron ammonia oxidation treatment and performing anoxic treatment in the anoxic reaction tank can effectively remove a large amount of products of iron ammonia oxidation in the water, such as nitrite and nitrate, by using denitrifying bacteria in the anoxic reaction tank, achieving nitrogen removal.

[0075] During this period, control the dissolved oxygen in the anoxic reaction tank to be 0.2 - 0.4 mg / L, and set the hydraulic retention time to 4 h.

[0076] S6: Perform sedimentation treatment on the effluent after the anoxic treatment in the sedimentation tank.

[0077] Add a small amount of acid solution to the effluent after the anoxic treatment in the sedimentation tank to dissolve the residual divalent iron in the sludge. The effluent is refluxed to the front end of the Fenton process through the reflux pipe, reducing the usage amount of ferrous sulfate and achieving clean regeneration.

[0078] Among them, 98% concentrated sulfuric acid is used as the acid solution, the dosage of the acid solution is 100 mL / t, and the reflux ratio is 50%.

[0079] The basic information of the wastewater before and after treatment is shown in Table 1 below:

[0080] Table 1. Water body information before and after treatment

[0081] Item Before treatment (mg / L) After treatment (mg / L) Removal rate COD 600 30 95％ Ammonia nitrogen 240 5 97.9％

[0082] Example 2

[0083] This example is basically the same as Example 1, with the only difference being:

[0084] In S3, when performing neutralization precipitation treatment on the effluent after the Fenton reaction treatment in the neutralization sedimentation tank, add an alkali solution to adjust the pH to 4.0.

[0085] Example 3

[0086] This example is basically the same as Example 1, with the only difference being:

[0087] In S3, when performing neutralization precipitation treatment on the effluent after the Fenton reaction treatment in the neutralization sedimentation tank, add an alkali solution to adjust the pH to 5.5.

[0088] Example 4

[0089] This example is basically the same as Example 1, with the only difference being:

[0090] In S3, when performing neutralization precipitation treatment on the effluent after the Fenton reaction treatment in the neutralization sedimentation tank, add an alkali solution to adjust the pH to 7.0.

[0091] The basic information before and after the wastewater treatment is shown in Table 2 below:

[0092] Table 2. Water body information before and after treatment

[0093]

[0094] It can be seen from Table 2 that when the pH is between 4 and 6, the removal rates of COD and ammonia nitrogen can both reach over 80%. When the pH is between 4.5 and 5.5, the effect is the best, and the removal rate can reach over 90%. When the pH is greater than 6, such as pH = 7, the removal rate of ammonia nitrogen drops rapidly.

[0095] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the technical principle of the present invention, several improvements and modifications can still be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A denitrification method for wastewater containing COD, characterized in that, it includes: S1. Performing Fenton oxidation treatment on the wastewater; S2. Performing neutralization precipitation treatment on the effluent after Fenton oxidation treatment, controlling the pH value between 4.5 and 5.5; S3. Directly subjecting the effluent after neutralization precipitation treatment to iron ammonia oxidation treatment in an anaerobic environment; S4. Performing anoxic treatment on the effluent after iron ammonia oxidation treatment; Wherein, in the said S3, no Fe(III) source is added anymore, and the Fe(III) contained in the Fenton iron sludge is converted into a dissolved state and follows the water body to be treated into the process of S3; when performing iron ammonia oxidation treatment, the dissolved oxygen is maintained below 0.2 mg / L.

2. The denitrification method for wastewater containing COD according to claim 1, characterized in that, it further includes: S5. Treating the sludge precipitation after anoxic treatment with acid.

3. The denitrification method for wastewater containing COD according to claim 2, characterized in that, in the said S5, the supernatant obtained after treatment is recycled to S1.

4. The denitrification method for wastewater containing COD according to any one of claims 1 to 3, characterized in that, in the said S1, calculated by the mass volume concentration of COD contained in the wastewater, the ratio of the addition amount of hydrogen peroxide to the content of the said COD is (1 - 2):1, the ratio of the addition amount of hydrogen peroxide to the addition amount of ferrous ions is (1 - 10):

1.

5. The denitrification method for wastewater containing COD according to claim 4, characterized in that, in the said S2, a flocculant is further added, and the addition amount of the flocculant is set to 100 - 205 mg / L.

6. The denitrification method for wastewater containing COD according to claim 4, characterized in that, in the said S2, the hydraulic retention time for performing neutralization precipitation treatment is 2 - 4 h.

7. The denitrification method for wastewater containing COD according to claim 6, characterized in that, in the said S3, the hydraulic retention time for performing iron ammonia oxidation treatment is 4 - 8 h.

8. The denitrification method for wastewater containing COD according to claim 6, characterized in that, in the said S4, when performing anoxic treatment, the dissolved oxygen is maintained at 0.2 - 0.4 mg / L.

9. The denitrification method for wastewater containing COD according to claim 8, characterized in that, in the said S4, the hydraulic retention time for performing anoxic treatment is 4 - 8 h.

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