A method for removing total nitrogen from wastewater

Abstract

The present application belongs to the technical field of wastewater treatment, and particularly relates to a method for removing total nitrogen in wastewater. Iron salt and carbon material containing hydroxyl and carbonyl are added into water, and then potassium borohydride is added, and the obtained mixture is freeze-dried under argon protection atmosphere to obtain iron-carbon filler; the iron-carbon filler is added into wastewater, the wastewater is adjusted to be weakly acidic, and stirring reaction is carried out for 0.5-1.5 h to obtain reduced effluent; persulfate is added into the reduced effluent, the wastewater is adjusted to be alkaline, and stirring reaction is carried out for 0.5-1.5 h, and then solid-liquid separation is carried out, and the obtained supernatant is treated effluent. The present application can remove total nitrogen in wastewater only by using iron-carbon filler and persulfate at normal temperature and pressure, and has the advantages of fast conversion rate, strong anti-interference ability, no secondary pollution and the like compared with traditional chemical oxidation-reduction technology; the reaction has wide original sources, low price, simple operation, and is environment-friendly, and has obvious economic and environmental benefits.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of wastewater treatment, and particularly relates to a method for removing total nitrogen in wastewater. BACKGROUND

[0002] At present, many wastewaters such as municipal domestic sewage, landfill leachate, livestock and poultry breeding wastewater, food processing wastewater and the like contain a large amount of nitrogen-containing pollutants. These nitrogen-containing pollutants often need to be denitrified by biological nitrification and denitrification. Due to the limitation of full aerobic nitrification and reflux ratio in the traditional AO process, after biological treatment, these wastewaters often contain a certain amount of nitrate nitrogen and ammonia nitrogen, which causes most of the nitrate nitrogen and ammonia nitrogen in the natural water body to come from the discharge of the effluent from the wastewater treatment plant. Excessive nitrate nitrogen and ammonia nitrogen in the water body often leads to water eutrophication, causes black and odorous water, increases the difficulty and cost of water treatment, and even has toxic effects on the population and organisms. In order to further control water eutrophication, China has improved the effluent quality standards of many wastewater treatment plants, and has stipulated the discharge limits of ammonia nitrogen and total nitrogen. Since the concentrations of ammonia nitrogen and total nitrogen in the effluent of many biochemical treatments of wastewater are much higher than the discharge standards, it is necessary to carry out advanced denitrification on the low C / N secondary biochemical effluent.

[0003] At present, the methods for advanced denitrification of the secondary biochemical effluent mainly include biological nitrification and denitrification, membrane separation, adsorption and chemical oxidation-reduction. Although the biological nitrification and denitrification method has low energy consumption and good effect, it has a long reaction period and faces the problem of biological sludge treatment. Although the membrane separation method is fast and efficient, it also faces the problem of further treatment of the concentrated liquid containing high-concentration nitrogen-containing pollutants. The chemical oxidation-reduction method has the advantages of high efficiency, economy and energy saving, and has become a research hotspot. At present, the chemical oxidation-reduction method only removes one kind of nitrogen-containing pollutant in nitrate nitrogen and ammonia nitrogen. For example, the breakpoint chlorination method only oxidizes ammonia nitrogen into nitrogen gas, and faces the problems of poor total nitrogen removal effect and the risk of the generation of chlorine-containing harmful substances. Although the advanced oxidation method has high efficiency in removing ammonia nitrogen, it often over-oxidizes ammonia nitrogen into nitrate. Metals such as iron and aluminum have been used for the removal of nitrate in wastewater, but the reduction efficiency of nitrate needs to be further improved, and the reduction product is mainly ammonia nitrogen. It can be seen that the single chemical oxidation or reduction method often causes the mutual transformation between ammonia nitrogen and nitrate nitrogen when removing ammonia nitrogen and nitrate nitrogen, and it is difficult to achieve the removal of total nitrogen. SUMMARY

[0004] The purpose of the present application is to overcome the problem that the total nitrogen is difficult to be removed due to the high content of nitrate nitrogen and ammonia nitrogen in the effluent of the wastewater biological treatment in the prior art, and to provide a method for removing total nitrogen in wastewater.

[0005] The purpose of the present application is achieved by the following technical scheme: a method for removing total nitrogen in wastewater, comprising the following steps:

[0006] S1. Preparation of iron-carbon filler: Add iron salt and carbon material containing hydroxyl and carbonyl groups to water, then add potassium borohydride, react at 25-35℃ for 20-40 min, and freeze-dry the resulting mixture under an argon protective atmosphere for 9-11 h;

[0007] S2. Wastewater treatment: Add the iron-carbon packing material prepared in step S1 to the wastewater, adjust the pH of the wastewater to weakly acidic, and react under stirring for 0.5 to 1.5 hours to obtain reduced effluent; add persulfate to the reduced effluent, adjust the pH of the wastewater to alkaline, and react under stirring for 0.5 to 1.5 hours to separate solids and liquids, and the resulting supernatant is the treated effluent.

[0008] Furthermore, the carbon material containing hydroxyl and carbonyl groups is at least one of activated coke, activated carbon, or carbon nanotubes.

[0009] Furthermore, in step S1, the mass ratio of the iron salt, potassium borohydride, and carbon material containing hydroxyl and carbonyl groups is 1-4:1-3:1.

[0010] Furthermore, the iron salt is ferric sulfate or ferric chloride.

[0011] Furthermore, in step S2, the mass ratio of the iron-carbon packing material to the nitrate nitrogen in the wastewater is 5 to 15:1.

[0012] Furthermore, in step S2, the mass ratio of persulfate to ammonia nitrogen in the reduced water is 25–55:1.

[0013] Furthermore, the weakly acidic pH value in step S2 is 2-4, and the alkaline pH value is 9-11.

[0014] Furthermore, the stirring rate in step S2 is 100–400 r / min.

[0015] The principle of this invention is as follows:

[0016] Iron salts and activated coke, activated carbon, or carbon nanotubes are placed in a reactor. After adding water and potassium borohydride, the iron salts and potassium borohydride undergo a redox reaction, reducing the iron salts to zero-valent iron, which then deposits on the activated coke surface. When the iron-carbon packing is added to nitrate wastewater, under weakly acidic conditions, nitrate nitrogen is reduced to nitrogen gas and ammonia nitrogen by the zero-valent iron on the iron-carbon packing, with the zero-valent iron becoming iron oxide. Because the zero-valent iron forms a corrosion cell with the activated coke, activated carbon, or carbon nanotubes, it accelerates iron corrosion and improves the efficiency of nitrate nitrogen reduction. The catalytic effect of the carbonyl and carboxyl groups on the surface of the activated coke, activated carbon, or carbon nanotubes further reduces some nitrate nitrogen to nitrogen gas. After the reduction of nitrate nitrogen in the wastewater is complete, the total nitrogen in the water mainly consists of ammonia nitrogen produced from nitrate nitrogen reduction and ammonia nitrogen from the original water. At this point, persulfate is added. The iron oxides on the iron-carbon packing and the activated coke, activated carbon, or carbon nanotubes activate the persulfate into active oxides, rapidly oxidizing the ammonia nitrogen. Under weakly alkaline conditions, ammonia nitrogen mainly exists as NH3, which has strong reducing power and is easily oxidized, thus increasing its oxidation efficiency. Since activated coke, activated carbon, or carbon nanotubes activate persulfate, they primarily oxidize ammonia nitrogen by generating singlet oxygen with moderate oxidizing power and electron transfer, reducing excessive oxidation of ammonia nitrogen. Furthermore, activated coke, activated carbon, or carbon nanotubes, and the groups on their surfaces, can inhibit excessive oxidation of ammonia nitrogen and reduce high-valence nitrogen oxides generated in the solution to nitrogen gas. After solid-liquid separation, the supernatant is the treated effluent.

[0017] This invention has the following advantages: It only requires iron-carbon filler and persulfate at room temperature and pressure to remove total nitrogen from wastewater. The chemical conversion method utilizes a two-step process combining reduction and oxidation to efficiently convert nitrate nitrogen and ammonia nitrogen in wastewater into nitrogen gas, thereby effectively reducing the total nitrogen in the wastewater. Compared to traditional chemical oxidation-reduction technologies, it has advantages such as fast conversion rate, strong anti-interference ability, and no secondary pollution. The activated coke, activated carbon or carbon nanotubes, and iron salts used in this invention are widely available, inexpensive, and environmentally friendly. The method for removing total nitrogen from wastewater is simple to operate, environmentally friendly, and has significant economic and environmental benefits. Detailed Implementation

[0018] The present invention will be further described below with reference to embodiments, but the scope of protection of the present invention is not limited to the following description:

[0019] Example 1: A method for removing total nitrogen from wastewater, comprising the following steps:

[0020] S1. Preparation of iron-carbon filler: Iron salt and activated coke are added to water, then potassium borohydride is added, and the mixture is reacted at 25°C for 20 min. The resulting mixture is freeze-dried under an argon protective atmosphere for 9 h. The iron salt is a sulfate, and the mass ratio of iron salt, potassium borohydride and activated coke is 2:1:1.

[0021] S2. Wastewater treatment: The iron-carbon packing material prepared in step S1 is added to the wastewater, with a mass ratio of iron-carbon packing material to nitrate nitrogen in the wastewater of 5:1. The pH of the wastewater is adjusted to 2, and the reaction is carried out at a stirring rate of 100 r / min for 0.5 h to obtain reduced effluent. Persulfate is then added to the reduced effluent, with a mass ratio of persulfate to ammonia nitrogen in the reduced effluent of 25:1. The pH of the wastewater is adjusted to 9, and the reaction is carried out at a stirring rate of 100 r / min for 0.5 h to separate the solid and liquid. The resulting supernatant is the treated effluent.

[0022] Example 2: A method for removing total nitrogen from wastewater, comprising the following steps:

[0023] S1. Preparation of iron-carbon filler: Add ferric chloride and activated carbon to water, then add potassium borohydride, react at 35°C for 40 min, and freeze-dry the resulting mixture under an argon protective atmosphere for 11 h; the mass ratio of the iron salt, potassium borohydride and activated carbon is 4:3:1.

[0024] S2. Wastewater treatment: The iron-carbon packing material prepared in step S1 is added to the wastewater, with a mass ratio of iron-carbon packing material to nitrate nitrogen in the wastewater of 15:1. The pH of the wastewater is adjusted to 4, and the reaction is carried out for 1.5 hours with a stirring rate of 400 r / min to obtain reduced effluent. Persulfate is then added to the reduced effluent, with a mass ratio of persulfate to ammonia nitrogen in the reduced effluent of 55:1. The pH of the wastewater is adjusted to 11, and the reaction is carried out for 1.5 hours with a stirring rate of 400 r / min. Solid-liquid separation is performed, and the resulting supernatant is the treated effluent.

[0025] Example 3: A method for removing total nitrogen from wastewater, comprising the following steps:

[0026] S1. Preparation of iron-carbon filler: Iron salt and carbon materials containing hydroxyl and carbonyl groups are added to water, then potassium borohydride is added, and the mixture is reacted at 28°C for 25 min. The resulting mixture is freeze-dried under an argon protective atmosphere for 9.5 h. The mass ratio of the iron salt, potassium borohydride and carbon materials containing hydroxyl and carbonyl groups is 1:2:1. The iron salt is a mixture of sulfate and ferric chloride in a weight ratio of 1:1, and the hydroxyl and carbonyl group-containing material is a mixture of activated coke and carbon nanotubes in a weight ratio of 1:1.

[0027] S2. Wastewater treatment: The iron-carbon packing material prepared in step S1 is added to the wastewater, with a mass ratio of iron-carbon packing material to nitrate nitrogen in the wastewater of 7:1. The pH of the wastewater is adjusted to 3, and the reaction is carried out at a stirring rate of 180 r / min for 1 h to obtain reduced effluent. Persulfate is then added to the reduced effluent, with a mass ratio of persulfate to ammonia nitrogen in the reduced effluent of 32:1. The pH of the wastewater is adjusted to 9.5, and the reaction is carried out at a stirring rate of 200 r / min for 1 h to separate the solid and liquid. The resulting supernatant is the treated effluent.

[0028] Example 4: A method for removing total nitrogen from wastewater, comprising the following steps:

[0029] S1. Preparation of iron-carbon filler: Ferric chloride and carbon materials containing hydroxyl and carbonyl groups are added to water, and then potassium borohydride is added. The mixture is reacted at 32°C for 35 min, and the resulting mixture is freeze-dried under an argon protective atmosphere for 10.5 h. The mass ratio of ferric chloride, potassium borohydride and carbon materials containing hydroxyl and carbonyl groups is 3:2:1. The carbon materials containing hydroxyl and carbonyl groups are a mixture of activated coke, activated carbon and carbon nanotubes in a weight ratio of 3:1:2.

[0030] S2. Wastewater treatment: The iron-carbon packing material prepared in step S1 is added to the wastewater, with a mass ratio of iron-carbon packing material to nitrate nitrogen in the wastewater of 12:1. The pH of the wastewater is adjusted to 3.5, and the reaction is carried out for 1.2 hours with a stirring rate of 300 r / min to obtain reduced effluent. Persulfate is then added to the reduced effluent, with a mass ratio of persulfate to ammonia nitrogen in the reduced effluent of 45:1. The pH of the wastewater is adjusted to 10.5, and the reaction is carried out for 1.2 hours with a stirring rate of 350 r / min. Solid-liquid separation is performed, and the resulting supernatant is the treated effluent.

[0031] Example 1:

[0032] The effluent from the biological treatment plant of a kimchi production industrial park had TOC, total nitrogen, nitrate nitrogen, and ammonia nitrogen concentrations of 19.95 mg / L, 22.5 mg N / L, 16.33 mg N / L, and 5.14 mg N / L, respectively, with a pH of 8.60 ± 0.2. 5 L of this wastewater was collected into a 10 L acid- and alkali-resistant container (Container 1). 0.01 kg of iron-carbon packing was added to Container 1 to adjust the pH to 3. The reaction was carried out for 60 min at a stirring rate of 150 r / min. After the reaction was stopped, 0.042 kg of potassium persulfate was added to the wastewater to adjust the pH to 9.5-10. The reaction was carried out again for 60 min at a stirring rate of 150 r / min. After the reaction was stopped, solid-liquid separation was performed, and the supernatant was the final treated effluent.

[0033] The ammonia nitrogen and total nitrogen in the treated effluent were measured to be 0 mg N / L and 2.80 mg N / L, respectively, with a total nitrogen removal rate of 87.56%.

[0034] Example 2:

[0035] The effluent from the secondary biological treatment of domestic sewage in a certain town had TOC, total nitrogen, nitrate nitrogen, and ammonia nitrogen concentrations of 0 mg / L, 47.10 mg N / L, 44.04 mg N / L, and 0.55 mg N / L, respectively, with a pH of 5.63 ± 0.2. 2 L of this wastewater was collected into a 5 L acid- and alkali-resistant container (Container 1). 0.016 kg of iron-carbon packing was added to Container 1 to adjust the pH to 2. The reaction was carried out for 60 min at a stirring rate of 150 r / min. After the reaction was stopped, 0.069 kg of potassium persulfate was added to the wastewater to adjust the pH to 10-11. The reaction was carried out again for 60 min at a stirring rate of 150 r / min. After the reaction was stopped, solid-liquid separation was performed, and the supernatant was the final treated effluent.

[0036] The ammonia nitrogen and total nitrogen in the treated effluent were measured to be 1.61 mg N / L and 7.70 mg N / L, respectively, with a total nitrogen removal rate of 83.65%.

[0037] The preparation method of the iron-carbon filler in Examples 1 and 2 above is as follows: 43.5g of ferric sulfate and 21.0g of activated coke rich in hydroxyl and carbonyl groups are added to water, and then 26.1g of potassium borohydride is added. The mixture is reacted at 32℃ for 35min, and the resulting mixture is freeze-dried for 10.5h under an argon protective atmosphere.

[0038] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, are covered within the scope of protection of the present invention.

Claims

1. A method for removing total nitrogen from wastewater, characterized in that, It includes the following steps: S1. Preparation of iron-carbon filler: Iron salt and carbon material containing hydroxyl and carbonyl groups are added to water, and then potassium borohydride is added. The mixture is reacted at 25-35°C for 20-40 min, and the resulting mixture is freeze-dried under an argon protective atmosphere for 9-11 h; wherein the iron salt is sulfate and / or ferric chloride, and the carbon material containing hydroxyl and carbonyl groups is activated coke; S2. Wastewater treatment: Add the iron-carbon packing material prepared in step S1 to the wastewater, adjust the pH of the wastewater to weakly acidic, and react under stirring for 0.5 to 1.5 hours to reduce some of the nitrate nitrogen to nitrogen gas, thus obtaining reduced effluent; Persulfate is added to the reduced effluent to adjust the pH of the wastewater to alkaline. The reaction is carried out under stirring for 0.5 to 1.5 hours to convert ammonia nitrogen into nitrogen gas. Solid-liquid separation is then performed, and the resulting supernatant is the treated effluent.

2. The method for removing total nitrogen from wastewater according to claim 1, characterized in that, The mass ratio of the iron salt, potassium borohydride and carbon material containing hydroxyl and carbonyl groups in step S1 is 1-4:1-3:

1.

3. The method for removing total nitrogen from wastewater according to claim 1, characterized in that, The mass ratio of the iron-carbon packing material to the nitrate nitrogen in the wastewater in step S2 is 5 to 15:

1.

4. The method for removing total nitrogen from wastewater according to claim 1, characterized in that, The mass ratio of persulfate to ammonia nitrogen in the reduced water in step S2 is 25-55:

1.

5. The method for removing total nitrogen from wastewater according to claim 1, characterized in that, The weakly acidic pH value mentioned in step S2 is 2-4, and the alkaline pH value is 9-11.

6. The method for removing total nitrogen from wastewater according to claim 1, characterized in that, The stirring rate in step S2 is 100–400 r / min.