CN111704482B

CN111704482B - Processing system and method for preparing ammonium nitrate

Info

Publication number: CN111704482B
Application number: CN202010525673.4A
Authority: CN
Inventors: 刘艳臣; 左志强; 郑敏
Original assignee: Tsinghua University
Current assignee: Tsinghua University
Priority date: 2020-06-10
Filing date: 2020-06-10
Publication date: 2021-10-01
Anticipated expiration: 2040-06-10
Also published as: CN111704482A

Abstract

The invention provides a processing system and a method for preparing ammonium nitrate, wherein the processing system comprises: the biological reactor is used for preparing ammonium nitrite from ammonia nitrogen through biological nitrosation reaction; a chemical reactor for producing ammonium nitrate from ammonium nitrite by a chemical oxidation reaction; the water outlet of the bioreactor is connected to the water inlet of the chemical reactor. The invention provides a two-section reaction system and a method for preparing ammonium nitrate for the first time, and realizes the recycling of high-concentration ammonia nitrogen-containing wastewater. The treatment system and the method have the advantages of stable effect, automatic control, high reaction rate, no nitrogen loss, no environmental risk and the like, and have very wide application prospect in the aspect of recycling operation management of high-concentration ammonia nitrogen-containing wastewater such as urine and the like.

Description

Processing system and method for preparing ammonium nitrate

Technical Field

The invention relates to the technical field of ammonia nitrogen recycling, and particularly relates to a treatment system and method for preparing ammonium nitrate.

Background

Driven by the current energy-intensive nitrogen fertilizer production, more sustainable fertilizers are being developed to meet the rapidly growing food demand. On the other hand, wastewater is increasingly being viewed as a renewable resource to restore nutrients, particularly nitrogen nutrients, to high concentrations of ammonia nitrogen. Such as urine, which contributes about 80% of the total nitrogen of the wastewater, but accounts for about 1% of the total wastewater. Therefore, the application of the wastewater containing high-concentration ammonia nitrogen as fertilizer in agriculture is a potential and sustainable option. Urine is directly used as fertilizer in many agricultural productions in the world, but the ammonia is volatilized, so that the loss of nitrogen and environmental risks are caused. To address this problem, nitrogen stabilization prior to fertilizer application is a critical step.

Biological nitrification (ammonia nitrogen → nitrous nitrogen → nitric nitrogen) is a common method for stabilizing nitrogen at present. Biological nitrification can produce ammonium nitrate fertilizer, which is the most important nitrogen fertilizer in the world. However, the biological nitrification process requires the simultaneous action of Ammonia Oxidizing Bacteria (AOB) and Nitrite Oxidizing Bacteria (NOB), which is very challenging in environments with high concentrations of ammonia, as the intermediate Free Nitrous Acid (FNA) significantly inhibits the activity of NOB, resulting in the bioreactor staying continuously in the nitrosation stage (ammonia → nitrite).

Disclosure of Invention

The embodiment of the invention provides a treatment system for preparing high-concentration ammonium nitrate, which enables ammonia nitrogen to be smoothly converted into ammonium nitrate through a two-section reaction system, and realizes recycling of the ammonia nitrogen.

The embodiment of the invention provides a processing system for preparing ammonium nitrate, which comprises: the biological reactor is used for preparing ammonium nitrite from ammonia nitrogen through biological nitrosation reaction; and a chemical reactor for producing ammonium nitrate from ammonium nitrite by a chemical oxidation reaction; the water outlet of the bioreactor is connected to the water inlet of the chemical reactor.

Further, the inlet water of the bioreactor is wastewater with ammonia nitrogen concentration of more than 400 mgN/L.

Further, the feed water to the bioreactor is source separated urine that is stored for 3-7 days.

Further, the bioreactor is a sequencing batch reactor and comprises a reaction chamber and a first aeration device, wherein the reaction chamber comprises activated sludge inoculated with nitrosobacteria; the first aeration device provides oxygen to the reaction chamber.

Further, a stirring device is also included in the reaction chamber.

Further, the chemical reactor is closed.

Further, the chemical reactor comprises a closed reaction chamber, a second aeration device, a dissolved oxygen control device and an acid adding device; the second aeration device is used for aerating pure oxygen and supplying oxygen for the chemical oxidation reaction; the dissolved oxygen control device is used for controlling the dissolved oxygen range in the chemical reactor through the switch of the second aeration device; the acid adding device is used for regulating and controlling the initial pH of the solution in the chemical reactor.

In another aspect, embodiments of the present invention provide a method for preparing ammonium nitrate, including: performing biological nitrosation reaction on the wastewater with ammonia nitrogen concentration of more than 400mg N/L in a reaction vessel to prepare ammonium nitrite solution; and carrying out chemical oxidation reaction on the ammonium nitrite solution in another reaction vessel to prepare the ammonium nitrate solution.

The method of the embodiment of the invention divides the nitration process into biological nitrosation of ammonia nitrogen and chemical oxidation of ammonium nitrite, thereby smoothly preparing the ammonium nitrate and realizing the recycling of the ammonia nitrogen. Wherein the ammonium nitrite is chemically oxidized with oxygen at low pH value, and can be realized by acid-resistant ammonia oxidizing bacteria or by adding acid.

Further, the chemical oxidation reaction is carried out in a closed environment, and pure oxygen is intermittently supplied during the reaction. A disadvantage of chemical oxidation processes is that a large amount of nitrogen oxides volatilize, causing nitrogen loss and environmental risks. The invention provides pure oxygen intermittently in a closed environment, can completely convert ammonia nitrogen in chemical oxidation reaction into ammonium nitrate, and prevents nitrogen loss and environmental risk.

Further, before the chemical oxidation reaction, the pH of the ammonium nitrite solution is adjusted to be below 5.

The invention has the beneficial effects that:

the invention provides a two-section reaction system and a method for preparing ammonium nitrate for the first time, and realizes the recycling of high-concentration ammonia nitrogen-containing wastewater. The treatment system and the method have the advantages of stable effect, automatic control, high reaction rate, no nitrogen loss, no environmental risk and the like, and have very wide application prospect in the aspect of recycling operation management of high-concentration ammonia nitrogen-containing wastewater such as urine and the like.

Drawings

Fig. 1 is a schematic diagram of a process system for producing ammonium nitrate according to an embodiment of the present invention;

FIG. 2 is a graph of nitrogen evolution in a biological nitrosation reaction monitored in accordance with an embodiment of the present invention;

FIG. 3 is a graph showing the ammonia nitrogen, nitrite nitrogen, nitrate nitrogen and pH changes of a chemical oxidation reaction monitored by an embodiment of the present invention.

Detailed Description

The following examples are intended to illustrate the invention but are not intended to limit the scope of the invention. The examples do not show the specific techniques or conditions, according to the technical or conditions described in the literature in the field, or according to the product specifications. The reagents or instruments used are conventional products available from regular distributors, not indicated by the manufacturer.

Wherein the ammonia nitrogen is provided by the wastewater containing high-concentration ammonia nitrogen, namely the inlet water of the bioreactor is the wastewater containing high-concentration ammonia nitrogen. The wastewater containing high-concentration ammonia nitrogen of the invention refers to wastewater with ammonia nitrogen concentration more than 400mg N/L.

In a preferred embodiment of the invention, the feed water to the bioreactor is source separated urine that has been stored for 3-7 days.

With the development of the urine source separation technology, urine can be independently collected for resource treatment. The nitrogen element in the urine contributes about 80% of the total nitrogen of the wastewater, and the urine can completely generate an ammonium nitrate solution through the treatment system, and the ammonium nitrate is the most common nitrogen fertilizer in all over the world at present and has important significance. The invention provides a new idea and a new method for preparing ammonium nitrate from urine. The urea is hydrolyzed into ammonia nitrogen by the urine which is stored for 3-7 days before entering the treatment system, then the ammonia nitrogen is subjected to biological nitrosation reaction by the bioreactor to prepare ammonium nitrite solution, the ammonium nitrite solution obtained in the bioreactor is subjected to chemical oxidation reaction by the chemical reactor to prepare ammonium nitrate solution, and the defect that the existing biological nitrification is difficult to prepare ammonium nitrate is overcome.

In a preferred embodiment of the present invention, the bioreactor is a Sequencing Batch Reactor (SBR) comprising a reaction chamber and a first aeration means; the reaction chamber comprises activated sludge inoculated with nitrosobacteria; the first aeration device provides oxygen to the reaction chamber.

Further, a stirring device is also included in the reaction chamber. The stirring device is used for fully contacting the activated sludge in the reaction chamber with the wastewater containing ammonia nitrogen, so that the utilization rate of the activated sludge is improved.

In a preferred embodiment of the invention, the bioreactor can use membrane effluent to obtain a particulate-free effluent to avoid potential environmental risks of antibiotics and resistance genes carried by the particulate.

In a preferred embodiment of the present invention, the chemical reactor comprises a closed reaction chamber, a second aeration device, a dissolved oxygen control device and an acid adding device; the second aeration device is used for aerating pure oxygen and supplying oxygen for the chemical oxidation reaction; the dissolved oxygen control device is used for controlling the dissolved oxygen range in the chemical reactor through the switch of the second aeration device; the acid adding device is used for regulating and controlling the initial pH of the solution in the chemical reactor.

In the above preferred embodiment, the reaction chamber of the chemical reactor is designed to be closed, so that nitrogen loss caused by discharge of nitrogen oxides can be effectively prevented, and the ammonium nitrite solution obtained from the bioreactor can be completely converted into the ammonium nitrate solution.

In order to maintain constant air pressure in the closed reaction chamber, intermittent pure oxygen aeration is adopted. In the preferred embodiment, the intermittent aeration can be achieved without affecting the reaction effect by providing the dissolved oxygen control device.

Preferably, the dissolved oxygen control device comprises a dissolved oxygen control instrument and a dissolved oxygen electrode, the dissolved oxygen electrode is inserted into the reaction liquid in the closed reaction chamber, the concentration of the dissolved oxygen is monitored and fed back to the dissolved oxygen control instrument, and the dissolved oxygen control instrument controls the switch of the second aeration device according to the set dissolved oxygen level. Specifically, when the monitored dissolved oxygen concentration is lower than the set dissolved oxygen low value, the switch of the second aeration device is turned on for aeration, and when the monitored dissolved oxygen concentration is higher than the set dissolved oxygen high value, the switch of the second aeration device is turned off to realize pure oxygen intermittent aeration.

In another aspect, an embodiment of the present invention provides a method for preparing ammonium nitrate, including: performing biological nitrosation reaction on the wastewater with ammonia nitrogen concentration of more than 400mg N/L in a reaction vessel to prepare ammonium nitrite solution; and carrying out chemical oxidation reaction on the ammonium nitrite solution in another reaction vessel to prepare the ammonium nitrate solution.

Wherein, when the biological nitrosation reaction is carried out, only a part of ammonia nitrogen is converted into ammonium nitrite due to the characteristic of insufficient alkalinity. Specifically, when the ammonia nitrogen is provided as urine, about half of the ammonia nitrogen is converted into ammonium nitrite, and the pH is reduced to about 5.6. If ammonia nitrogen is provided for other waste water containing ammonia nitrogen instead of urine, the proportion is slightly deviated.

Further, the chemical oxidation reaction is carried out in a closed environment, and pure oxygen is intermittently supplied during the reaction. Preferably, the dissolved oxygen concentration in the reaction system is maintained at 3 to 15 mg/L. Thus, nitrogen loss can be prevented and the reaction effect can be ensured.

In order to rapidly convert ammonium nitrite to ammonium nitrate, the pH of the ammonium nitrite solution is adjusted to below 5 prior to the chemical oxidation reaction.

Example 1

As shown in fig. 1, the present example provides a process system for producing ammonium nitrate that includes a biological reactor and a chemical reactor.

The bioreactor is a Sequencing Batch Reactor (SBR) with the volume of 1.5L and comprises a water inlet 1, a water outlet 2, a peristaltic pump 3, a reaction chamber 4, a stirring paddle 5, a first aeration head 6 and a first aeration device 7, wherein the peristaltic pump 3 is arranged at the water inlet 1 and the water outlet 2. The reaction chamber 4 comprises activated sludge inoculated with nitrosobacteria, the first aeration device 7 provides oxygen for biological nitrosation reaction in the reaction chamber 4 through the first aeration head 6 arranged at the bottom of the reaction chamber 4, and the stirring paddle 5 makes the activated sludge fully mixed and contacted with wastewater containing ammonia nitrogen.

The chemical reactor comprises a water inlet 8, a water outlet 9, a peristaltic pump 10, a closed reaction chamber 11, a stirring paddle 12, a second aeration head 13, a second aeration device 14, a dissolved oxygen controller 15, a dissolved oxygen electrode 16, an acid inlet 17 and an acid inlet peristaltic pump 18, wherein the peristaltic pump 10 is arranged at the water inlet 8 and the water outlet 9. In this embodiment, the liquid volume of the closed reaction chamber 11 is 3.2L, and the headspace volume is 0.8L. The second aeration device 14 is used for pure oxygen aeration, oxygen is provided for chemical oxidation reaction in the closed reaction chamber 11 through the second aeration head 13, acid is supplied to the closed reaction chamber 11 through the acid inlet 17 for regulating and controlling initial pH of solution in the closed reaction chamber 11, the dissolved oxygen electrode 16 is inserted into reaction liquid in the closed reaction chamber 11, the dissolved oxygen concentration is monitored and fed back to the dissolved oxygen controller 15, the dissolved oxygen controller 15 controls the switch of the second aeration device 14 according to the set dissolved oxygen high-low value, specifically, when the monitored dissolved oxygen concentration is lower than the set dissolved oxygen low value, the switch of the second aeration device 14 is opened for aeration, and when the monitored dissolved oxygen concentration is higher than the set dissolved oxygen high value, the switch of the second aeration device 14 is closed, so that pure oxygen intermittent aeration is realized.

The water outlet 2 of the bioreactor is connected to the water inlet 8 of the chemical reactor, so that the ammonium nitrite solution prepared in the bioreactor is conveyed to the chemical reactor for chemical oxidation reaction to prepare ammonium nitrate solution.

Example 2

This example provides a process for producing ammonium nitrate using the treatment system of example 1, wherein the feed is urine that has stayed in the holding tank for 3 days, as follows:

firstly pumping urine into a reaction chamber of an SRB (anaerobic-baffled anaerobic baffled bioreactor), aerating (the concentration of dissolved oxygen does not need to be controlled) to enable ammonia nitrogen in the urine to generate biological nitrosation reaction, keeping the time for 1 day, then pumping effluent water of the SBR (the ratio of the ammonia nitrogen to the nitrosation nitrogen is 1:1) into a closed reaction chamber of a chemical reactor, and adding 1:9 hydrochloric acid to enable the initial pH of the solution to be 3 (the concentration of free nitrous acid in the solution is about 240HNO₂-N/L), controlling pure oxygen intermittent aeration by using a dissolved oxygen electrode and a dissolved oxygen controller to keep the concentration of dissolved oxygen in the closed reaction chamber at 3-15mg/L (at the moment, the internal pressure of the closed reaction chamber is basically constant), and oxidizing ammonium nitrite into ammonium nitrate after 3-4 hours of residence time, wherein the effluent is an ammonium nitrate solution with the ratio of ammonia nitrogen to nitrate nitrogen being 1: 1.

Wherein, the hydraulic retention time of the SBR reactor is usually 24 hours, and every 8 hours is a period, 1/3 volumes of sewage are discharged, and then a new 1/3 volumes of sewage are introduced again. The first 0.5h is reactor water intake, the next 6 h is reactor aeration reaction, and the last 1.5 h is standing and water discharge.

During the 140-day operation period, the nitrogen component of the effluent is monitored 3-6 times per week, and the results of the biological nitrosation reaction are shown in fig. 2, including the ammonia nitrogen concentration of the inlet water, the ammonia nitrogen concentration of the effluent, the nitrite nitrogen concentration of the effluent and the nitrate nitrogen concentration of the effluent. The result shows that the concentration ratio of ammonia nitrogen and nitrite nitrogen in the effluent of the bioreactor is close to 1, no nitrate product is produced, and the realization of the nitrosation of the bioreactor is established.

After the effluent of SBR enters a chemical reactor, water samples are taken every 15-20 minutes, the concentration of ammonia nitrogen, nitrite nitrogen and nitrate nitrogen is immediately measured, meanwhile, a pH/DO meter (WTW, pH340i) is used for automatically recording pH and DO, and sampling monitoring is continued until all indexes are kept unchanged. The results are shown in FIG. 3, which shows that the continuous supply of pure oxygen oxidizes the majority of the ammonium nitrite to ammonium nitrate during the first 1.3 hours, indicating that at pH3, pure oxygen reacts rapidly with ammonium nitrite. Subsequently, intermittent aeration of pure oxygen is achieved by a pure oxygen controller, which is critical for complete conversion of residual ammonium nitrite to ammonium nitrate. The final accumulation ratio of ammonium nitrite (ammonium nitrite/(ammonium nitrate + ammonium nitrite)) is close to 0%, indicating complete oxidation of ammonium nitrite. On the other hand, the total ammonia nitrogen is not changed by the chemical oxidation reaction. Therefore, the ratio of ammonia nitrogen to nitrate nitrogen in the final effluent solution is 1:1, and the feasibility of the system is proved.

In the chemical oxidation process, the initial pH was adjusted to 3 using 1:9 hydrochloric acid. However, these acids are not consumed in the reaction. In contrast, the pH decreased further during the reaction from 3 to 1.8, indicating that chemical oxidation of nitrite is an acid release process.

In conclusion, the treatment system and the method provided by the embodiment of the invention can be used for effectively preparing the ammonium nitrate solution, finally realize the characteristic of no nitrogen loss, avoid the emission of nitrogen oxides and effectively utilize urine in an environment-friendly manner. The invention provides a rapid, stable and automatic control processing system and method. Through the experimental investigation and model optimization of the method, the feasibility and the optimal state of the method are determined, and a new thought is provided for the resource utilization of the ammonia nitrogen-containing wastewater such as urine and the like.

Although the invention has been described in detail hereinabove with respect to a general description and specific embodiments thereof, it will be apparent to those skilled in the art that modifications or improvements may be made thereto based on the invention. Accordingly, such modifications and improvements are intended to be within the scope of the invention as claimed.

Claims

1. A process system for producing ammonium nitrate, comprising

The biological reactor is used for preparing ammonium nitrite from ammonia nitrogen through biological nitrosation reaction; and

the chemical reactor is used for preparing ammonium nitrate from ammonium nitrite through a chemical oxidation reaction;

the water outlet of the bioreactor is connected to the water inlet of the chemical reactor;

the inlet water of the bioreactor is wastewater with ammonia nitrogen concentration more than 400mg N/L.

2. The treatment system of claim 1, wherein the feed water to the bioreactor is source separated urine that has been stored for 3-7 days.

3. A treatment system as claimed in claim 1, wherein the bioreactor is a sequencing batch reactor comprising a reaction chamber and a first aeration device; the reaction chamber comprises activated sludge inoculated with nitrosobacteria; the first aeration device provides oxygen to the reaction chamber.

4. The processing system of claim 3, further comprising a stirring device in the reaction chamber.

5. A treatment system according to any one of claims 1 to 4, wherein the chemical reactor comprises a closed reaction chamber, a second aeration device, a dissolved oxygen control device and an acid adding device; the second aeration device is used for aerating pure oxygen and supplying oxygen for the chemical oxidation reaction; the dissolved oxygen control device is used for controlling the dissolved oxygen range in the chemical reactor through the switch of the second aeration device; the acid adding device is used for regulating and controlling the initial pH of the solution in the chemical reactor.

6. A method of producing ammonium nitrate comprising:

performing biological nitrosation reaction on the wastewater with ammonia nitrogen concentration of more than 400mg N/L in a reaction vessel to prepare ammonium nitrite solution;

and carrying out chemical oxidation reaction on the ammonium nitrite solution in another reaction vessel to prepare the ammonium nitrate solution.

7. The method of claim 6, wherein the chemical oxidation reaction is conducted in a closed environment, and pure oxygen is provided intermittently during the reaction.

8. The method according to claim 6 or 7, wherein the pH of the ammonium nitrite solution is adjusted to below 5 before the chemical oxidation reaction is performed.