Wastewater denitrification method

Abstract

To provide a denitrification method for wastewater which is low in energy consumption, high in efficiency and stable.SOLUTION: A method of denitrification of wastewater includes S1 in which Fenton oxidation treatment is performed on wastewater, S2 in which neutralizing precipitation treatment is performed on the wastewater after Fenton oxidation treatment to control the pH value to 4 to 6, S3 in which the wastewater after neutralizing precipitation treatment is directly subjected to iron ammonia oxidation reaction in an anaerobic environment, and S4 in which the wastewater after iron ammonia oxidation treatment is subjected to anoxic treatment, in which no Fe(III) is added in S3.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention belongs to the field of wastewater treatment in environmental engineering, and specifically relates to a method for denitrifying wastewater.

Background Art

[0002] The chemical industry permeates into various fields and is an indispensable and important component in the national economy. The diversity of chemical industry products determines that chemical industry wastewater has the characteristics of large water volume, high toxicity, and complex water quality, and often has high concentrations of COD and ammonia nitrogen.

[0003] In fact, it is common to adopt Fenton treatment for chemical industry wastewater. The Fenton method generates hydroxyl radicals through the reaction of ferrous ions and hydrogen peroxide, destroys the structure of organic substances, and finally oxidizes and decomposes the organic substances to reduce the COD content of water. Its main process flow includes pH adjustment (the pH value is preferably controlled at 3.0 - 4.0), oxidation reaction, neutralization, solid-liquid separation, etc. Also, currently, most wastewater projects are undergoing upgrading and transformation. This is because nitrogen in wastewater cannot be reduced to the discharge standard by biological treatment, and only attention is paid to improving the denitrification part in wastewater treatment. Therefore, there are processes such as MBR and denitrification filters. Denitrification technology includes chemical methods and biological methods. Since chemical methods cause secondary pollution and are costly, it is common to use biological denitrification technology.

[0004] Denitrification by biological treatment of wastewater mainly realizes the conversion of nitrogen forms by several obligate bacteria. The process in which nitrogen-containing organic compounds are first decomposed into ammonium nitrogen NH4 + or NH3 under the action of microorganisms is called the "ammonification reaction", the process in which nitrifying bacteria convert ammonium nitrogen into nitrate is called the "nitrification reaction", the reaction in which denitrifying bacteria convert nitrate into nitrogen gas is called the "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 industrial wastewater mainly consists of two stages: aerobic and anoxic. High-concentration ammonia nitrogen is nitrified into nitrate in the aerobic stage, and then the nitrate flows into the anoxic stage for denitrification and is converted into nitrogen gas, thereby realizing the removal of ammonia nitrogen. However, such a traditional nitrification-denitrification process requires a large amount of aeration, consumes a huge amount of energy, and the denitrification efficiency is not ideal.

[0006] Therefore, it is of great significance to develop a detoxifying denitrification method for wastewater with low energy consumption, high efficiency and stability.

Summary of the Invention

[0007] 1. Problems to be Solved In view of the problems such as energy consumption existing in the existing denitrification process of wastewater, the present invention provides a denitrification method for wastewater.

[0008] 2. Technical Solution In order to solve the above problems, the technical solution adopted in the present invention is as follows.

[0009] The present invention includes S1: performing Fenton oxidation treatment on the wastewater; S2: performing neutralization precipitation treatment on the effluent after Fenton oxidation treatment and controlling the pH value to 4-6; S3: directly subjecting the effluent after neutralization precipitation treatment to an iron-ammonia oxidation reaction in an anaerobic environment; S4: performing anoxic treatment on the effluent after iron-ammonia oxidation treatment, and provides a denitrification method for wastewater in which the addition of an Fe(III) source is not required in S3.

[0010] ​As described herein, in S2, it is very important to "control the pH value to 4 - 6". After Fenton oxidation treatment, the trivalent iron (Fe(III)) contained in the Fenton sludge, which should be treated as dangerous solid waste, is converted into the dissolved state, enters the process of S3 along with the water to be treated, and is applied as the iron source for iron ammonia oxidation treatment, thus avoiding the addition of unnecessary Fe(III). Based on this, more preferably, the pH value is "controlled to 4.5 - 5.5".

[0011] It should be noted that the above - mentioned technical solution realizes a perfect integration of COD removal (Fenton oxidation) of wastewater and denitrification (iron ammonia oxidation) of wastewater, and avoids the consumption of chemicals after treating wastewater by the traditional Fenton oxidation method. Specifically, in the technical code of the wastewater treatment project by the traditional Fenton oxidation method, it is clearly required that the Fenton effluent should be adjusted to 7 - 9 in the neutralization unit (since the pH value during Fenton oxidation is generally controlled below 4, a large amount of alkali will necessarily be consumed in the neutralization unit) to form precipitation after the Fenton oxidation reaction).

[0012] Furthermore, taking the premise that COD can be effectively removed when the content of ammonia - nitrogen in the wastewater to be treated is less than or equal to half of the content of COD as the mass - volume concentration, it can be ensured that the wastewater has the most preferable denitrification effect.

[0013] According to any of the embodiments of the present invention, S1 includes a pH adjustment treatment step before performing Fenton oxidation treatment on the wastewater, and the pH value of the wastewater after the pH adjustment treatment is 3 - 4.

[0014] According to any of the embodiments of the present invention, in S1, before performing Fenton oxidation treatment on the wastewater, the content of suspended solids in the wastewater is controlled to be 200 mg / L or less.

[0015] According to any embodiment according to the object of the present invention, as the mass volume concentration of COD contained in the wastewater, the ratio of the addition amount of the hydrogen peroxide to the content of the COD is (1 to 2):1, and the ratio of the addition amount of the hydrogen peroxide to the addition amount of the ferrous ion is (1 to 10):1.

[0016] According to any embodiment according to the object of the present invention, in the S1, ferrous ions are added to the wastewater, hydrogen peroxide is added at intervals of 5 to 30 minutes to perform Fenton oxidation treatment, and the time of the Fenton oxidation treatment is 2 to 8 hours.

[0017] According to any embodiment according to the object of the present invention, in the S1, while performing the Fenton oxidation treatment, spray treatment may be performed, or a defoaming agent may be added to remove the scum on the surface of the wastewater.

[0018] According to any embodiment according to the object of the present invention, the S2 further includes adding a flocculant, and the input amount of the flocculant is set to 100 to 205 mg / L.

[0019] Preferably, the flocculant consists of polyaluminum chloride and polyacrylamide, the input amount of the polyaluminum chloride is 100 to 200 mg / L, and the input amount of the polyacrylamide is 3 to 5 mg / L.

[0020] According to any embodiment according to the object of the present invention, in the S2, when performing the neutralization precipitation treatment, the hydraulic retention time is 2 to 4 hours.

[0021] According to any embodiment according to the object of the present invention, in the S3, a start-up stage is included.

[0022] According to any embodiment according to the object of the present invention, in the S3, when performing the iron ammonia oxidation treatment, the dissolved oxygen is maintained at 0.2 mg / L or less.

[0023] According to any embodiment according to the object of the present invention, in the step S3, when the iron ammonia oxidation treatment is carried out, the hydraulic retention time is 4 to 8 h.

[0024] According to any embodiment according to the object of the present invention, in the step S3, when the iron ammonia oxidation treatment is carried out, the temperature is 20 to 35 °C.

[0025] According to any embodiment according to the object of the present invention, in the step S4, when the anoxic treatment is carried out, the dissolved oxygen is maintained at 0.2 to 0.4 mg / L.

[0026] According to any embodiment according to the object of the present invention, in the step S4, when the anoxic treatment is carried out, the hydraulic retention time is 4 to 8 h.

[0027] According to any embodiment according to the object of the present invention, it further includes a step S5 of treating the sludge sediment after the anoxic treatment with an acid.

[0028] According to any embodiment according to the object of the present invention, in the step S5, the supernatant obtained by the treatment is reused in the step S1.

[0029] Beneficial effects (1) In fact, for chemical industrial wastewater, generally, by adopting Fenton treatment, the COD content in the water can be reduced. Its main process flow includes pH adjustment, oxidation reaction, neutralization, solid-liquid separation, etc., as shown in Figure 2. And according to the "Technical Code for Wastewater Treatment Projects by Fenton Oxidation Method" in the "National Environmental Protection Standards 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 precipitation, so that the requirements for the subsequent effluent can be met. In this process, a large amount of precipitation agents need to be added, resulting in high running costs. Based on this, the denitrification method for wastewater provided by the present invention realizes the perfect integration of COD removal (Fenton oxidation) of wastewater and denitrification (iron ammonia oxidation) of wastewater, and avoids the consumption of agents after treating wastewater by the traditional Fenton oxidation method.

[0030] In addition, in the denitrification method for wastewater provided by the present invention, the trivalent iron (Fe(III)) contained in the Fenton sludge, which should be treated as dangerous solid waste after Fenton oxidation treatment, is converted into a dissolved state, enters the process of S3 along with the water to be treated, and is applied as the iron source for iron ammonia oxidation treatment, avoiding the addition of extra Fe(III).

[0031] Compared with the traditional nitrification-denitrification process, there is no need to perform aeration.

[0032] Therefore, the denitrification method for wastewater provided by the present invention saves a large amount of energy consumption and greatly reduces the running cost.

[0033] (2) In the denitrification method for wastewater provided by the present invention, the added dissolved iron plays a role in the process of iron being oxidized and organic matter being reduced, has a good decomposition effect on aromatic organic matter, and can contribute to denitrification and detoxification.

[0034] (3) The denitrification method of wastewater provided by the present invention can be directly upgraded in the existing Fenton and biological stage processes in a chemical industrial wastewater treatment plant when applied, with low renovation costs and extremely strong applicability.

[0035] (4) In the denitrification method of wastewater provided by the present invention, after being reduced in the iron ammonia oxidation treatment process, divalent iron (Fe(II)) can be newly eluted by adding a small amount of acid, and then newly applied to the Fenton process, reducing the input of iron salts and realizing clean regeneration.

Embodiments for Carrying Out the Invention

[0036] By referring to the following description combined with examples, the present disclosure can be more easily understood, and all examples constitute 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 shown in the text. Furthermore, the terms used in the text are used only for the purpose of describing specific embodiments by way of example and are not intended to be limiting, unless otherwise specified.

[0037] For clarity, it should be further understood that certain features of the present disclosure may be described in the context of a single embodiment before and after in the text, but may also be provided in combination with each other in one embodiment. That is, each single embodiment can be considered to be combinable with any other embodiment, and this combination is considered to represent another different embodiment, unless clearly incompatible or specifically excluded. On the other hand, for simplicity, the various features of the present disclosure described in the context of one embodiment may also be provided alone or in any sub-combination. Finally, a specific embodiment may be described as part of a series of steps or part of a more general structure, but each step or sub-structure itself may also be considered as an independent embodiment.

[0038] Unless otherwise specified, each individual element in a list and each combination of individual elements in the list should be understood as a different embodiment. For example, a list of embodiments represented as "A, B, or C" should be interpreted as including the embodiments "A", "B", "C", "A or B", "A or C", "B or C", or "A, B, or C".

[0039] In this disclosure, unless otherwise clearly stated in the context, references to the singular forms of the articles "a", "one", and "the" also include the corresponding plural forms, and references to a specific numerical value include at least this specific value. Thus, for example, a reference to "a substance" is a reference to at least one of this substance and its equivalents.

[0040] Terms including ordinal numbers such as "first" and "second" are used to interpret various assemblies or fluids, but these assemblies and fluids are not limited by these terms. Thus, without departing from the teachings of this disclosure, these terms are used only to distinguish this assembly / fluid from another assembly / fluid.

[0041] When describing items by using conjunctive terms such as "... and / or...", it should be understood that the description includes any one of the related listed items and all of one or more combinations thereof.

[0042] Generally, the use of the term "about" indicates an approximation that can vary depending on the desired characteristics obtained by the disclosed subject matter and is to be construed as context - dependent based on the function. Thus, a general technician in the art can interpret a certain degree of difference based on a single case. In some cases, the number of significant digits used when indicating a specific value may be a representative technique for determining the difference tolerated by the term "about". In other cases, the range of differences tolerated by the term "about" may be determined by a gradation of a series of values. Further, all ranges in this disclosure are inclusive and combinable, and references to values within a range include each value within that range.

[0043] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs, and the term "and / or" used herein includes any and all combinations of one or more of the associated listed items.

[0044] Hereinafter, examples where specific conditions are not specified are carried out under normal conditions or conditions proposed by the manufacturer. Reagents or devices used without specifying the manufacturer are all ordinary products obtained by commercial purchase.

[0045] Hereinafter, the present invention will be further described by specific examples, but the present invention is not limited by the examples. Unless otherwise specified, the reagents, methods and equipment adopted in the present invention are ordinary reagents, methods and equipment in the technical field. The substantial features and remarkable effects of the present invention can be expressed by the following examples. The described examples are only a part of the examples of the present invention, not all of them. Therefore, the present invention is not limited by them, and some non - essential improvements and adjustments made by those skilled in the art according to the content of the present invention all belong to the protection scope of the present invention.

Brief Description of the Drawings

[0046]

Figure 1

Figure 2

[0047] Example 1 In this example, a denitrification process of wastewater by the combined use of Fenton and biological iron ammonia oxidation is provided, and its specific steps are as follows.

[0048] S1: Perform pH adjustment treatment on the wastewater The influent water is maintained under acidic conditions with a pH of 3.2. When the pH of the influent water does not meet the requirements, a pH adjustment tank is installed in advance, and 98% concentrated sulfuric acid or 50% dilute sulfuric acid is added to adjust the pH value of the wastewater. Mechanical stirring is adopted, and the mixing time is set to 5 min.

[0049] For the addition of the acid solution, a corrosion-proof metering pump is adopted, and the input amount is automatically adjusted by an on-line pH meter.

[0050] S2: Perform Fenton reaction treatment on the wastewater after pH adjustment in a Fenton oxidation reaction tank In the Fenton oxidation treatment, ferrous sulfate is added (placed in a solution tank in advance with a mass percentage concentration of 20%), and after 15 min, 30 wt% hydrogen peroxide is added. The input ratio is such that the ratio of hydrogen peroxide concentration (mg / L) to COD (mg / L) is 2:1, and the ratio of hydrogen peroxide concentration (mg / L) to ferrous ion (mg / L) concentration is 3:1.

[0051] The hydraulic retention time in the Fenton oxidation reaction tank is 2 h. During this period, if a large amount of scum appears, water spray or defoaming spray may be adopted.

[0052] S3: Perform neutralization precipitation treatment on the effluent water after Fenton reaction treatment in a precipitation neutralization tank It is necessary to add an alkaline solution to the sedimentation and neutralization tank to adjust the pH to 4.5. As the alkaline solution, a 10% sodium hydroxide solution was adopted.

[0053] At the same time, polyaluminum chloride and polyacrylamide were added, and the addition amounts were set to 120 mg / L and 3 mg / L.

[0054] The hydraulic retention time in the sedimentation and neutralization tank was set to 3 h.

[0055] S4: Anaerobic iron ammonia oxidation treatment is carried out on the effluent after neutralization sedimentation treatment in an iron ammonia oxidation reaction tank. In the startup stage (this stage may be carried out in advance), anaerobic sludge from the sewage treatment plant (from the sludge thickening tank) is seeded, the sludge concentration is about 3 g / L MLSS, the temperature is maintained at 30 °C, the pH is maintained at 6.5, the startup time is 2 weeks, and during that time, ammonium chloride and sodium bicarbonate are added to strengthen the adaptability of the iron ammonia oxidation functional bacterial flora.

[0056] After startup, in the iron ammonia oxidation reaction tank, anaerobic iron ammonia oxidation treatment is carried out on the effluent after neutralization sedimentation treatment. During the treatment, the dissolved oxygen is controlled below 0.2 mg / L, the hydraulic retention time is set to 6 h, and the temperature is maintained at 30 °C.

[0057] S5: Anaerobic treatment is carried out on the effluent after iron ammonia oxidation treatment in an anaerobic reaction tank. Glucose with a C / N ratio of 2.5 is added as a carbon source to the effluent after iron ammonia oxidation treatment, and anaerobic treatment is carried out in an anaerobic reaction tank. The denitrifying bacteria in the anaerobic reaction tank can effectively remove iron ammonia oxidation products such as nitrite and nitrate contained in large amounts in the water, and denitrification can be realized.

[0058] During that time, the dissolved oxygen in the anaerobic reaction tank was controlled at 0.2 - 0.4 mg / L, and the hydraulic retention time was set to 4 h.

[0059] S6: Perform precipitation treatment on the oxygen-free treated effluent water in a sedimentation tank. A small amount of acid solution was added to the oxygen-free treated effluent water in the sedimentation tank to elute the divalent iron remaining in the sludge. The effluent water was refluxed to the front stage of the Fenton process through a reflux pipe, reducing the usage amount of ferrous sulfate and realizing clean regeneration.

[0060] As the acid solution, 98% concentrated sulfuric acid was used. The acid solution input amount was 100 mL / t, and the reflux ratio was 50%.

[0061] The basic information before and after the wastewater treatment is as shown in Table 1 below.

[0062]

Table 1

[0063] Example 2 This example is basically the same as Example 1, and the only difference is as follows.

[0064] In S3, when performing neutralization precipitation treatment on the effluent water after Fenton reaction treatment in a precipitation neutralization tank, an alkaline solution was added to adjust the pH to 4.0.

[0065] Example 3 This example is basically the same as Example 1, and the only difference is as follows.

[0066] In S3, when performing neutralization precipitation treatment on the effluent water after Fenton reaction treatment in a precipitation neutralization tank, an alkaline solution was added to adjust the pH to 5.5.

[0067] Example 4 This example is basically the same as Example 1, and the only difference is as follows.

[0068] In S3, when performing neutralization precipitation treatment on the effluent water after Fenton reaction treatment in a precipitation neutralization tank, an alkaline solution was added to adjust the pH to 7.0.

[0069] The basic information before and after the wastewater treatment is as shown in Table 2 below.

[0070]

Table 2

[0071] As can be seen from Table 2, when the pH is 4 - 6, the removal rates of both COD and ammonia nitrogen can reach over 80%. When the pH is 4.5 - 5.5, the effect is the best and the removal rate can reach over 90%. When the pH is greater than 6, for example, when the pH is 7, the removal rate of ammonia nitrogen drops rapidly.

[0072] The above are only preferred embodiments of the present invention. It should be pointed out that for those of ordinary skill in the art, on the premise of not departing from the technical principle of the present invention, some improvements and modifications may be made, and these improvements and modifications should also be regarded as within the protection scope of the present invention.

Claims

1. S1 for performing Fenton oxidation treatment on wastewater; S2 for performing neutralization precipitation treatment on the effluent after Fenton oxidation treatment and controlling the pH value to 4 - 6; S3 for directly subjecting the effluent after neutralization precipitation treatment to an iron - ammonia oxidation reaction in an anaerobic environment; S4 for performing anoxic treatment on the effluent after iron - ammonia oxidation treatment, comprising: In the said S3, the addition of the Fe(III) source is stopped; A method for denitrifying wastewater, characterized by the above.

2. Further comprising S5 for treating the sludge precipitation after anoxic treatment with an acid; The method for denitrifying wastewater according to Claim 1, characterized by the above.

3. In the said S5, the supernatant obtained by the treatment is reused in step S1; The method for denitrifying wastewater according to Claim 2, characterized by the above.

4. In the said S1, as the mass - volume concentration of COD contained in the wastewater, The ratio of the addition amount of hydrogen peroxide to the content of COD is (1 - 2):1, The ratio of the addition amount of hydrogen peroxide to the addition amount of ferrous iron is (1 - 10):1; The method for denitrifying wastewater according to any one of Claims 1 - 3, characterized by the above.

5. The said S2 further comprises adding a flocculant, and the addition amount of the flocculant is set to 100 - 205 mg / L; The method for denitrifying wastewater according to Claim 4, characterized by the above.

6. In the said S2, the hydraulic retention time in the case of performing neutralization precipitation treatment is 2 - 4 h; The method for denitrifying wastewater according to Claim 4, characterized by the above.

7. In the said S3, when performing iron - ammonia oxidation treatment, the dissolved oxygen is maintained at 0.2 mg / L or less; The method for denitrifying wastewater according to Claim 4, characterized by the above.

8. In the said S3, the hydraulic retention time in the case of performing iron - ammonia oxidation treatment is 4 - 8 h; The method for denitrifying wastewater according to Claim 7, characterized by the above.

9. In the said S4, when performing anoxic treatment, the dissolved oxygen is maintained at 0.2 - 0.4 mg / L; The method for denitrifying wastewater according to Claim 7, characterized by the above.

10. In the said S4, the hydraulic retention time in the case of performing anoxic treatment is 4 - 8 h; The method for denitrifying wastewater according to Claim 9, characterized by the above.

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