A method for removing high concentration nitrates from wastewater

Abstract

The invention discloses a method for removing high-concentration nitrates in wastewater, wherein the iron powder after pickling is put into the wastewater containing nitrates together with nitrite and copper ion for stirring reaction, and sulfuric acid is continuously added to control the pH value of the reaction solution to 3-5, and the reaction is stirred under room temperature and anaerobic conditions. After the reaction is completed, solid-liquid separation is performed, and the supernatant after separation is discharged as qualified wastewater, and the solid is reused for further processing of nitrate wastewater. The reductive iron powder used in the present invention has low purity requirements, and the pharmaceutical cost required for the process is relatively low; the iron powder can be recycled 1-3 times; (2) the efficiency in the treatment of high-concentration nitrate wastewater is relatively high, higher than 50% of the existing method, reaching 98%; (3) the ratio of the harmless gas nitrogen produced is relatively high.

Description

(I) Technical field

[0001] The invention relates to a method for removing high-concentration nitrate in wastewater. (II) Background technology

[0002] High concentrations of nitrates in water bodies have direct or indirect hazards to the human body and the environment. Domestic and foreign researchers have been conducting research on nitrate wastewater. At present, the removal methods of nitrate wastewater are mainly physical, chemical, and biological methods. In addition, some new processes have emerged in recent years for the treatment of nitrate wastewater, but most of them are combined processes.

[0003] The biological method mainly utilizes the action of denitrifying bacteria to convert nitrate nitrogen into nitrogen gas for denitrification. The biological method is mainly carried out in the form of a bioreactor. This method has a rapid response and low cost, but there are also some follow-up problems. The metabolic process of nitrifying bacteria will cause an increase in the amount of sludge, which is particularly important for the treatment and disposal of sludge.

[0004] The chemical method is to reduce nitrates into other products through reducing substances for removal. The chemical method is divided into metal reduction method, catalytic reduction method, and electrochemical method. Iron powder has strong reducing properties, a wide source, a low price, and is easy to obtain. Therefore, it has received widespread attention in the metal reduction method. At the same time, research on the use of zinc powder to treat nitrate wastewater is also underway; and in recent years, research on the reduction of nitrate wastewater with zero-valent iron is still continuing.

[0005] Compared with aluminum powder and nano zero-valent iron to reduce nitrate, the iron powder reduction method to remove nitrate from water is the most common and most studied technology among metal reduction methods. This is because iron powder is widely available, inexpensive, and environmentally friendly. The iron powder reduction method to remove nitrate from water has been widely used to remove nitrate from groundwater. Although the reaction pathway is different when using iron powder to reduce pollutants in the solution, many experimental studies have shown that the reduction reaction starts with the corrosion of the iron powder surface. During the entire reaction process, iron powder, Fe 2+and hydrogen will participate in the reduction reaction process. Yao Songtao pointed out in the experimental study of reducing nitrate in groundwater with zero-valent iron that lower pH and higher iron powder dosage promote the reduction of nitrate by iron powder. At the same time, the longer the reaction time, the more thorough the reduction of nitrate nitrogen. Huang et al. pointed out in the experiment of studying the effect of pH on the reduction of nitrate by iron powder in nitrate wastewater that nitrate in the pH range of 2-4.5 will be quickly reduced to ammonium in the water. Zawaideh et al. found in the nitrate reduction experiment that under the condition of pH <2, iron powder can quickly reduce nitrate, and the removal rate of nitrate nitrogen can reach 95% to 100%. However, under the condition of pH>11, iron powder has a removal effect on wastewater with very low nitrate concentration.

[0006] Iron powder is the most popular metal reducing agent due to its strong reducing properties and low price. However, many experimental studies have shown that ammonia nitrogen is the main product of iron powder reducing nitrates, rather than the most ideal nitrogen. Therefore, the subsequent products need to be further treated, otherwise the effluent quality will be affected.

[0007] At present, the research and application of zero-valent iron reduction of nitrate wastewater mainly focuses on the treatment of low-concentration nitrate groundwater. When the low-concentration nitrate wastewater reaches 50 mg / L, the iron powder surface will be passivated and there will be no removal efficiency. There is a lack of research on high-concentration nitrate wastewater, and the treatment of high-salt nitrate wastewater has not been solved. (III) Summary of the invention

[0008] The purpose of the present invention is to provide a novel, environmentally friendly and efficient method for removing high-concentration nitrate in wastewater. When zero-valent iron is used to treat high-concentration nitrate wastewater, nitrate is reduced in the coexistence of nitrite and nitrate, and the reaction pH is controlled to be 3-5 by continuous flow addition of sulfuric acid, thereby overcoming the defect of the existing method that the pH is controlled at the beginning of the reaction, resulting in the nitrate concentration reaching a certain concentration and the reaction stops. At the same time, by adding nitrite, the reaction speed can be increased, and the reaction is more inclined to react in the direction of harmless nitrogen, thereby overcoming the defect of the existing reaction of generating ammonia.

[0009] The technical solution adopted by the present invention is:

[0010] The present invention provides a method for removing high-concentration nitrates in wastewater, the method comprising the following steps:

[0011] The iron powder after pickling, nitrite and copper ions are put into the nitrate-containing wastewater for stirring reaction, and sulfuric acid is continuously added to control the pH of the reaction solution to 3-5. The reaction is stirred at room temperature (preferably 25°C) and anaerobic conditions. After the reaction is completed, the solid and liquid are separated, and the supernatant after separation is discharged as qualified wastewater (industrial wastewater discharge standard or groundwater quality standard IV), and the solid is reused for further treatment of nitrate wastewater.

[0012] Preferably, the iron powder is ordinary reducing iron powder, and the particle size distribution is as follows: 17.14% are above 75 microns, 56.47% are between 38.5 and 75 microns, and 26.39% are below 38.5 microns.

[0013] Preferably, the method for preparing the pickled iron powder is: pickling the iron powder with a 0.05 mol / L H2SO4 aqueous solution to remove the surface oxide film, thereby obtaining the pickled iron powder. The pickling is performed at 25°C and 300 rpm with constant temperature shaking for 1 minute.

[0014] Preferably, the amount of iron powder added after pickling is 0.01-0.1 g / mL, preferably 0.1 g / mL, based on the volume of wastewater.

[0015] Preferably, the concentration of the copper ions added to the wastewater is 0.5 to 1.5 mmol / L, preferably 1.5 mmol / L.

[0016] Preferably, the concentration of nitrate in the wastewater is 1-10000 mmol / L, preferably 1000 mmol / L.

[0017] Preferably, the concentration ratio of nitrogen in the nitrate to that in the nitrite is 1:0.05-1, preferably 1:0.1.

[0018] Preferably, the reaction time is 0.5 to 8 h, more preferably 4 h.

[0019] Compared with the prior art, the beneficial effects of the present invention are mainly reflected in: (1) the reduced iron powder used in the present invention does not have high purity requirements, and the cost of reagents required in the process is relatively low; the iron powder can be recycled 1-3 times; (2) the efficiency in the treatment of high-concentration nitrate wastewater is relatively high, higher than 50% of the existing method, reaching 98%; (3) the proportion of harmless gas nitrogen generated is relatively high. (IV) Description of the drawings

[0020] Figure 1 This is Example 1, which shows the removal of nitrite-containing nitrate wastewater by continuous acid reduction with zero-valent iron and the change curve of the reduction product over time.

[0021] Figure 2 This is the comparative example 1, which shows the removal of nitrate wastewater without nitrite by continuous acid reduction with zero-valent iron and the change curve of the reduction product over time.

[0022] Figure 3 This is comparative example 2, which shows the removal of nitrate wastewater containing nitrite by reducing it with zero-valent iron by controlling the initial pH, and the change curve of the reduction product over time.

[0023] Figure 4The curves of nitrate nitrogen concentration change over time between Example 1 and Comparative Example 1 and Comparative Example 2 are shown. (V) Specific implementation methods

[0024] The technical solution of the present invention is further described below in conjunction with the accompanying drawings.

[0025] The iron powder is common reducing iron powder, and the particle size distribution is as follows: 17.14% are above 75 microns, 56.47% are between 38.5 and 75 microns, and 26.39% are below 38.5 microns.

[0026] Embodiment 1:

[0027] The iron powder was washed with a 0.05 mol / L H2SO4 aqueous solution at 25°C and 300 rpm for 1 min to remove the surface oxide film. It can be seen that the surface of the iron powder exhibits an obvious metallic luster, and the iron powder after acid washing is obtained.

[0028] A closed three-necked flask (the three flasks are used for 1. placing a pH meter for real-time monitoring; 2. adding acid using a controllable flow meter to change the flow rate according to the real-time pH; 3. sampling at each time period; and all are sealed.) was used for the reaction under anaerobic conditions. The solution volume in the experiment was 200 ml (the solvent was water), the initial concentration of NO3--N was 1000 mg / L with sodium nitrate, and the concentration of NO2--N was 100 mg / L with sodium nitrite. The mass of iron powder after pickling was 10.00 g, and copper sulfate was added to prepare Cu 2+ The concentration was 1.5mmol / L, and the pH of the solution was controlled at 3.5 by continuously adding a 10% sulfuric acid aqueous solution. Samples were taken regularly during the period, and the concentration of nitrate nitrogen was detected by ultraviolet spectrophotometry, the concentration of nitrite nitrogen was determined by N-(1-naphthyl)-ethylenediamine photometry, and the concentration of ammonia nitrogen was determined by salicylic acid-hypochlorite photometry; the total nitrogen concentration was determined by ultraviolet spectrophotometry to estimate the concentration of escaped nitrogen. The results are as follows: Figure 1 As shown in Table 1, the nitrate concentration change curve is shown in Figure 1 .

[0029] Table 1 Changes in concentration of each component in the reaction solution (unit: mg / L)

[0030]

[0031] Table 1: The whole reaction was basically completed after four hours, and the removal rate of nitrate reached 98%; since the whole reaction process was carried out under acidic conditions, the generated escaped nitrogen was basically nitrogen gas. The conversion rates of ammonia nitrogen and nitrogen gas generated were 54.8% and 45.2% respectively.

[0032] from Figure 1It can be seen that nitrate has a higher reaction rate in the first 30 minutes, and tends to be stable afterwards, showing an excellent removal effect on high-concentration nitrate throughout the whole process.

[0033] Example 2

[0034] The iron powder was washed with a 0.05 mol / L H2SO4 aqueous solution at 25°C and 300 rpm for 1 min to remove the surface oxide film. It can be seen that the surface of the iron powder exhibits an obvious metallic luster, and the iron powder after acid washing is obtained.

[0035] A closed three-necked flask (the three flasks are used for 1. placing a pH meter for real-time monitoring; 2. adding acid using a controllable flow meter to change the flow rate according to the real-time pH; 3. sampling at each time period; and all are sealed.) was used for the reaction under anaerobic conditions. The solution volume in the experiment was 200 ml (the solvent was water), the initial concentration of NO3--N was 1000 mg / L with sodium nitrate, and the concentration of NO2--N was 100 mg / L with sodium nitrite. The mass of iron powder after pickling was 10.00 g, and copper sulfate was added to prepare Cu 2+ The concentration was 1.5mmol / L, and the pH of the solution was controlled at 5 by continuous flow addition of a 10% volume concentration sulfuric acid aqueous solution. During the period, samples were taken regularly, and the concentration of nitrate nitrogen was detected by ultraviolet spectrophotometry, the concentration of nitrite nitrogen was determined by N-(1-naphthyl)-ethylenediamine photometry, and the concentration of ammonia nitrogen was determined by salicylic acid-hypochlorite photometry; the concentration of total nitrogen was determined by ultraviolet spectrophotometry to estimate the concentration of escaped nitrogen, and the results are shown in Table 2.

[0036] Table 2 Changes in concentration of each component in the reaction solution (unit: mg / L)

[0037]

[0038] Table 2: After the whole reaction was carried out for six hours, the reaction was basically completed, and the nitrate removal rate reached 92.2%; compared with Example 1, the reaction time was increased by two hours, and a relatively high removal effect was basically maintained, indicating that the reaction efficiency decreased after the pH rose to 5, but overall it still had an excellent removal effect.

[0039] Example 3

[0040] The iron powder was washed with a 0.05 mol / L H2SO4 aqueous solution at 25°C and 300 rpm for 1 min to remove the surface oxide film. It can be seen that the surface of the iron powder exhibits an obvious metallic luster, and the iron powder after acid washing is obtained.

[0041] A closed three-necked flask (the three flasks are used for 1. placing a pH meter for real-time monitoring; 2. adding acid using a controllable flow meter to change the flow rate according to the real-time pH; 3. sampling at each time period; and all are sealed) is used for the reaction under anaerobic conditions. The solution volume in the experiment is 200 ml (the solvent is water), the initial concentration of NO3--N prepared with sodium nitrate is 1000 mg / L, the concentration of NO2--N prepared with sodium nitrite is 500 mg / L, the mass of iron powder after pickling is 10.00 g, and copper sulfate is added to prepare Cu 2+ The concentration was 1.5mmol / L, and the pH of the solution was controlled at 3.5 by continuous flow addition of a 10% volume concentration sulfuric acid aqueous solution. Samples were taken regularly during the period, and the concentration of nitrate nitrogen was detected by ultraviolet spectrophotometry, the concentration of nitrite nitrogen was determined by N-(1-naphthyl)-ethylenediamine photometry, and the concentration of ammonia nitrogen was determined by salicylic acid-hypochlorite photometry; the total nitrogen concentration was determined by ultraviolet spectrophotometry to estimate the concentration of escaped nitrogen, and the results are shown in Table 3.

[0042] Table 3 Changes in concentration of each component in the reaction solution (unit: mg / L)

[0043]

[0044] Table 3: When the whole reaction was carried out for four hours, the reaction was basically completed, and the removal rate of nitrate nitrogen reached 92.4%; because the whole reaction process was carried out under acidic conditions, the escaped nitrogen generated was basically nitrogen gas. The conversion rates of ammonia nitrogen and nitrogen gas generated were 36.2% and 63.8%. Compared with the 5.6% reduction in the removal efficiency of nitrate nitrogen in Example 1 within four hours, the proportion of the target product nitrogen gas generated increased, indicating that it has an excellent removal effect in treating nitrate wastewater containing high concentrations of nitrite nitrogen.

[0045] Comparative Example 1:

[0046] The reaction was carried out in a closed three-necked flask in Example 1 under anaerobic conditions. The volume of the solution in the experiment was 200 ml (the solvent was water). The initial concentration of NO3--N prepared with sodium nitrate was 1000 mg / L. The mass of the acid-washed iron powder prepared by the method of Example 1 was 10.00 g. Copper sulfate was added to prepare Cu 2+ The concentration was 1.5mmol / L, and a 10% sulfuric acid aqueous solution was continuously added to control the solution pH at 3.5. During this period, samples were taken regularly, and the concentrations of nitrate nitrogen, nitrite nitrogen, ammonia nitrogen and escaped nitrogen were detected using the method of Example 1. The results are as follows: Figure 2 As shown in Table 4, the nitrate concentration change curve is shown in Figure 2 .

[0047] Table 4 Changes in concentration of each component in the reaction solution (mg / L)

[0048]

[0049] Table 4: When the whole reaction was carried out for four hours, the removal rate of nitrate reached 87.5%, and the removal efficiency within four hours was reduced by 10.5% compared with Example 1. The conversion rates of ammonia nitrogen and nitrogen produced were 72% and 28%, and the proportion of target product nitrogen produced also decreased.

[0050] Depend on Figure 2 It can be seen that the reaction rate of the whole process is also reduced compared with Example 1.

[0051] Comparative Example 2:

[0052] The reaction was carried out under anaerobic conditions in a closed three-necked flask of Example 1. The volume of the solution in the experiment was 200 ml (the solvent was water). The initial concentration of NO3--N prepared with sodium nitrate was 1000 mg / L, and the concentration of NO2--N prepared with sodium nitrite was 100 mg / L. The mass of the acid-washed iron powder prepared by the method of Example 1 was 10.00 g. Copper sulfate was added to prepare Cu 2+ The concentration was 1.5 mmol / L, and a 10% volume concentration of sulfuric acid aqueous solution was used to control the initial pH of the solution to 2. Samples were taken regularly during the period, and the concentrations of nitrate nitrogen, nitrite nitrogen, ammonia nitrogen and escaped nitrogen were detected using the method of Example 1. The results are as follows: Figure 3 And as shown in Table 5.

[0053] Table 5 Changes in concentration of each component in the reaction solution (mg / L)

[0054]

[0055] Table 5: When the entire reaction is carried out for one to four hours, the removal of nitrate is basically stable, and the removal rate is only 27.4%. Compared with Example 1, the effective time of the reaction is greatly reduced, and the conversion rates of the generated ammonia nitrogen and nitrogen are 52.3% and 47.7%.

[0056] According to the comparison between Example 1, Example 2, Example 3 and Comparative Example 1 and Comparative Example 2, it can be found that the continuous addition of acid to control the pH in the process of reducing high-concentration nitrate with zero-valent iron can effectively promote the progress of the entire reaction and the thoroughness of the entire reaction ( Figure 4 ), adding nitrite can increase the reaction rate to a certain extent, and improve the conversion rate of nitrogen.

Claims

1. A method for removing high-concentration nitrates in wastewater, characterized in that: The method comprises the following steps: The iron powder after pickling is added together with nitrite and copper ions into nitrate-containing wastewater for stirring reaction, and sulfuric acid is continuously added to control the pH value of the reaction solution to 3-5. The reaction is stirred at room temperature and anaerobic conditions. After the reaction is completed, the solid and liquid are separated, and the supernatant after separation is discharged as qualified wastewater, and the solid is reused to continue to treat nitrate wastewater; the amount of the iron powder after pickling added is 0.01-0.1g / mL based on the volume of wastewater; the concentration of the copper ions added to the wastewater is 0.5-1.5mmol / L; the concentration of nitrate in the wastewater is 1-10000 mmol / L; the concentration ratio of nitrogen in nitrate to nitrite is 1:0.05-1; and the reaction time is 0.5-8h.

2. The method according to claim 1, characterized in that The iron powder is ordinary reducing iron powder, and the particle size distribution is as follows: 17.14% are above 75 microns, 56.47% are between 38.5 and 75 microns, and 26.39% are below 38.5 microns.

3. The method according to claim 1, characterized in that The acid-washed iron powder is prepared as follows: the iron powder is washed with a 0.05 mol / L H2SO4 aqueous solution at 25°C and 300 rpm for 1 min to remove the surface oxide film, thereby obtaining the acid-washed iron powder.

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