CN113511731B

CN113511731B - Method for improving nitrite accumulation in short-range denitrification process

Info

Publication number: CN113511731B
Application number: CN202110877914.6A
Authority: CN
Inventors: 潘建新; 魏任; 苏美蓉; 刘亮亮
Original assignee: Dongguan University of Technology
Current assignee: Dongguan University of Technology
Priority date: 2021-07-30
Filing date: 2021-07-30
Publication date: 2023-08-04
Anticipated expiration: 2041-07-30
Also published as: CN113511731A

Abstract

The invention provides a method for improving nitrite accumulation in a short-range denitrification process, and belongs to the technical field of wastewater treatment. The method comprises the following steps: s1, inoculating denitrification activated sludge into an anaerobic reactor, and adding 0.05-15mmol of oxidant into each gram of denitrification activated sludge; s2, water is fed into the anaerobic reactor to form a reaction mixed solution, and the anaerobic reactor is started to perform denitrification reaction. According to the invention, the specific oxidant is added to selectively promote the reduction of the nitrate, and meanwhile, the further reduction of the nitrite can be restrained, so that the accumulation of the nitrite is accelerated by increasing the generation amount of the nitrite and reducing the consumption amount of the nitrite, and the short-time, efficient and stable accumulation of the nitrite is realized.

Description

Method for improving nitrite accumulation in short-range denitrification process

Technical Field

The invention relates to the technical field of wastewater treatment, in particular to a method for improving nitrite accumulation in a short-range denitrification process.

Background

With the rapid development of economy and the continuous improvement of living standard, the urban sewage discharge is increasingly increased, and nitrogen compounds are excessively discharged into the water body, so that algae and other microorganisms are excessively propagated, and the water body is caused to be eutrophicated, which becomes a common phenomenon of the water body in China and has a trend of further development. Eutrophication of water severely damages water ecology and endangers human health. Therefore, the removal of nitrogen pollution in water has become a hotspot problem in the field of water pollution control nowadays.

At present, biological denitrification is the most economical, efficient and stable nitrogen pollution treatment method and mainly comprises a nitrification-denitrification technology, a short-cut nitrification-anaerobic ammonia oxidation technology and a short-cut denitrification-anaerobic ammonia oxidation technology. The nitrification-denitrification technology, namely, the ammonia nitrogen in the sewage is converted into nitrite by utilizing aerobic nitrification, and then is converted into nitrateThe acid salt, then the nitrate is passed through a series of intermediates (NO ₂ ^- 、NO、N ₂ O) is reduced to nitrogen and other nitrogen-containing gases, which eventually escape the wastewater to achieve denitrification. The nitrification and denitrification process is a mature denitrification process at present, but has the problems of long flow, large occupied area, large amount of aeration, additional addition of organic carbon source and the like, so that the energy consumption, the investment and the operation cost are higher. The short-cut nitrification-anaerobic ammonia oxidation technology is a technology that nitrifying bacteria are utilized to oxidize ammonia nitrogen into nitrite, and then under anaerobic or anoxic conditions, the anaerobic ammonia oxidation bacteria take the ammonia nitrogen as an electron donor, and nitrite as an electron acceptor to convert the ammonia nitrogen and the nitrite into nitrogen. Compared with the nitrification-denitrification technology, the anaerobic ammonia oxidation process does not need oxygen to participate, so that aeration energy consumption is saved, and the reduction of nitrite does not need additional carbon source, so that the anaerobic ammonia oxidation process has remarkable advantages in the aspects of energy consumption and material consumption. However, the growth of nitrite oxidizing bacteria cannot be completely inhibited in the short-cut nitrification process, so that a large amount of nitrite is further oxidized into nitrate, and nitrate is generated in the anaerobic ammonia oxidation process, so that the efficient removal of total nitrogen is limited. Therefore, how to ensure the accumulation of nitrite is a key to improving the efficient denitrification of the anaerobic ammonia oxidation technology. Based on this, short-cut denitrification-anaerobic ammoxidation techniques have been developed. The high-efficiency accumulation of nitrite is obtained by controlling the short-cut denitrification process, an electron acceptor is provided for the anaerobic ammonia oxidation reaction, the current problems of the short-cut nitrification-anaerobic ammonia oxidation technology are solved, the short-cut denitrification reaction and the anaerobic ammonia oxidation reaction both occur under anoxic or anaerobic conditions, the reaction conditions are convenient to control, and the operation is simpler and more convenient.

Factors influencing short-range denitrification include carbon source species, C/N ratio, pH, microbial species, and the like. Among them, the regulation of microorganism species is the most effective method for achieving short-cut denitrification. The research shows that the Thauera genus is the dominant genus in the short-range denitrification process. In the prior art, researches on controlling the short-cut denitrification process mainly focus on improvement of enrichment culture methods of Thauera bacteria and the like. However, the enrichment efficiency of Thauera bacteria is generally low and unstable, and short-cut denitrification is difficult to realize quickly, simply and efficiently, thus limiting the applicability of short-cut denitrification-anaerobic ammonia oxidation denitrification. Nitrite accumulation in denitrification is realized by accurately controlling external conditions such as the sludge concentration, the carbon source, the C/N ratio and the pH of the reactor, however, the reaction process is indicated by controlling the change of a plurality of external conditions, the problems of difficult management, low efficiency and the like exist, the accumulation efficiency is often unstable, and the promotion of anaerobic ammonia oxidation application is greatly restricted.

Disclosure of Invention

Aiming at the problems in the prior art, the invention provides a method for improving nitrite accumulation in a short-range denitrification process.

In order to achieve the above purpose, the present invention is specifically realized by the following technical scheme:

a method for increasing nitrite accumulation in a short-cut denitrification process, comprising the steps of:

s1, inoculating denitrification activated sludge into an anaerobic reactor, and adding 0.05-15mmol of oxidant into each gram of denitrification activated sludge;

s2, water is fed into the anaerobic reactor to form a reaction mixed solution, and the anaerobic reactor is started to perform denitrification reaction.

Further, in step S1, 1 to 10.5mmol of the oxidizing agent is added per gram of the denitrification active sludge, and further, 4.5 to 10.5mmol of the oxidizing agent is added per gram of the denitrification active sludge.

Further, the oxidizing agent comprises one or more of persulfate, hydrogen peroxide, percarbonate and hypochlorite.

Further, the oxidizing agent includes a persulfate including one or more of a peroxymonosulfate and a peroxydisulfate.

Further, the peroxymonosulfate comprises one or more of ammonium peroxymonosulfate, potassium peroxymonosulfate and sodium peroxymonosulfate; the peroxodisulfate comprises one or more of ammonium persulfate, potassium persulfate and sodium persulfate.

Further, in the step S2, the anaerobic reactor is started to carry out denitrification reaction under the conditions that the temperature of the reaction mixture is 30+/-5 ℃, the pH is 7.5+/-0.5 and the hydraulic retention time is 1-96 hours. Still further, the hydraulic retention time is 8-48 hours.

Further, in step S2, the carbon-nitrogen ratio of the reaction mixture is 0.3 to 4.0, and still further, the carbon-nitrogen ratio of the reaction mixture is 0.5 to 3.

Further, the carbon to nitrogen ratio is adjusted by adding a carbon source and nitrate.

Further, the carbon source includes one or more of glucose, sodium acetate, and methanol.

Further, in the step S2, the initial nitrate nitrogen content in the reaction mixture is 50-300mg/L.

Further, in the step S2, the sludge concentration of the denitrification activated sludge in the reaction mixed solution is 500-3000mg/L.

Compared with the prior art, the invention has the following advantages:

1. according to the invention, the specific oxidant is added to selectively promote the reduction of the nitrate, and meanwhile, the further reduction of the nitrite can be restrained, and the accumulation of the nitrite is accelerated by increasing the generation amount of the nitrite and reducing the consumption amount of the nitrite, so that the efficient and stable accumulation of the nitrite can be realized.

2. The invention can control the short-range denitrification to NO by only adding a proper amount of oxidant ₂ ^- The method is a target product and has the advantages of simple operation, easy control and the like.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for the description of the embodiments will be briefly described below, and it is apparent that the drawings in the following description are only some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.

FIG. 1 is a chart of the oxidant Persulfate (PDS) versus nitrite of example 1 of the inventionThe effect of biological reduction, wherein, figure (a) is the kinetics curve of persulfate chemical oxidation nitrite, figure (b) is the kinetics curve of persulfate versus nitrite biological reduction inhibition, and figure (c) is SO ₄ ^2- Concentration and persulfate decomposition rate over time;

FIG. 2 is a graph showing the effect of the oxidant Persulfate (PDS) of example 1 on the biological reduction of nitrate, wherein FIG. (a) is the NO in the control group ₂ ^- -N、NO ₃ ^- -N concentration and NO ₂ ^- -N accumulation rate versus reaction time, graph (b) is NO of the experimental group ₂ ^- -N、NO ₃ ^- -N concentration and NO ₂ ^- -N accumulation rate versus reaction time, graph (c) is SO for the experimental group ₄ ^2- Concentration and persulfate decomposition rate as a function of reaction time;

FIG. 3 shows the effect of persulfate at different concentrations on denitrification in example 2 of the present invention, wherein FIG. (a) shows NO at different concentrations of persulfate ₂ ^- -N、NO ₃ ^- -N concentration and NO ₂ ^- -N accumulation rate, graph (b) SO at different concentrations of persulfate ₄ ^2- Concentration and PDS decomposition rate.

Detailed Description

It should be noted that, without conflict, the embodiments of the present invention and features of the embodiments may be combined with each other. In addition, the terms "comprising," "including," "having," and "containing" are not limiting, as other steps and other ingredients may be added that do not affect the result. Materials, equipment, reagents are commercially available unless otherwise specified.

For a better understanding of the present invention, and not to limit its scope, all numbers expressing quantities, proportions, and other values used in the present invention, are to be understood as being modified in all instances by the term "about". Accordingly, unless indicated otherwise, the numerical parameters set forth in the specification and claims are approximations that may vary depending upon the desired properties sought to be obtained. Each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

In order that the above-recited objects, features and advantages of the present invention will become more readily apparent, a more particular description of the invention briefly described above will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings.

In order to solve the problems of low nitrite accumulation efficiency and unstable accumulation amount in the short-cut denitrification process, the embodiment of the invention provides a method for improving nitrite accumulation in the short-cut denitrification process, which comprises the following steps:

s1, inoculating denitrification activated sludge into an anaerobic reactor, and adding 0.05-15mmol of oxidant per gram of the denitrification activated sludge, wherein the ratio of the oxidant to the denitrification activated sludge is 0.05-15mmol:1g, in other words, when the sludge concentration of the denitrification activated sludge is 1000mg/L, the molar concentration of the corresponding oxidizing agent is 0.05-15mM;

In the conventional denitrification process, denitrifying bacteria take an organic carbon source as an electron donor, and nitrate is reduced into nitrogen through multi-step reaction, specifically: in a first step, nitrate (NO ₃ ^- ) Reduction to Nitrite (NO) ₂ ^- ) The method comprises the steps of carrying out a first treatment on the surface of the In the second step, nitrite reductase (NiRs) converts nitrite (NO ₂ ^- ) Reduced to Nitric Oxide (NO), nitrous oxide (N) ₂ O), and the like; third step, NO, N ₂ O is reduced to nitrogen; thus, NO can be controlled by denitrification ₃ ^- →NO ₂ ^- Stage or reduce the speed of nitrite reduction, and realize accumulation of nitrite.

In the invention, the addition of the oxidant can selectively promote the reduction of nitrate to ensure that the reduction rate of nitrate is larger than that of nitrite, and on the other hand, the addition of the oxidant can inhibit the further reduction of nitrite so as to reduce the consumption thereof, namely, the reduction rate of nitrite is improvedThe consumption is reduced, and the Nitrite (NO) is accelerated ₂ ^- ) Is accumulated to obtain a large amount of nitrite (NO ₂ ^- ) Realize NO ₂ ^- Is effective and stable. Moreover, short-range denitrification can be controlled to NO only by adding a proper amount of oxidant ₂ ^- The method is a target product and has the advantages of simple operation, easy control and the like.

It should be noted that although the oxidant such as persulfate added in the present invention has a higher oxidation-reduction potential than oxygen, the oxidant such as persulfate cannot be utilized as an electron acceptor by denitrifying microorganisms, and does not have the property of shutting down the denitrification process.

A large amount of Nitrite (NO) produced by the short-cut denitrification process of the present invention ₂ ^- ) As an electron acceptor for anaerobic ammoxidation, nitrate nitrogen (NO ₃ ^- ) And ammonia salt (NH) ₄ ⁺ ) The method has the advantages of high-efficiency and stable removal, greatly improved denitrification rate and efficiency, realization of low-carbon denitrification of wastewater, and wide application prospect.

The key to maintaining an anaerobic ammoxidation efficient denitrification process is to maintain nitrite accumulation in short-cut denitrification, preferably, the ratio of the oxidant to the denitrification activated sludge is 1-10.5mmol:1g. Under the proportional relation, the oxidant has no obvious effect of improving the nitrite accumulation rate, and when the oxidant is higher than the mass ratio, the reduction time of the nitrate can be prolonged, the nitrite accumulation rate can be further reduced, the oxidation-reduction potential can be obviously improved due to the further increase of the content of the oxidant, the activity of microorganisms in the denitrification activated sludge can be further influenced, and the integral denitrification effect can be weakened. More preferably, the ratio of the oxidizing agent to the denitrifying activated sludge is 4.5-10.5mmol:1g, more preferably 7.5mmol:1g.

The oxidant comprises one or more of persulfate, hydrogen peroxide, percarbonate and hypochlorite. The persulfate comprises one or more of peroxymonosulfate and peroxydisulfate, the peroxydisulfate comprises one or more of ammonium persulfate, potassium persulfate and sodium persulfate, and the peroxymonosulfate comprises one or more of ammonium peroxymonosulfate, potassium peroxymonosulfate and sodium peroxymonosulfate.

It should be noted that, although the sequence of the oxidizing agent and the water inlet is limited in the step S1 and the step S2, those skilled in the art should appreciate that the oxidizing agent may be added first, or the oxidizing agent and the water inlet may be performed simultaneously, and the method is not limited to the mode of adding the oxidizing agent first and then adding the water.

In the step S1, the inoculated denitrification activated sludge is preferably stable mature granular sludge, which is usually obtained through domestication, such as taking common activated sludge, then adding sufficient carbon source and nitrate, carrying out gradient domestication in an anoxic or anaerobic environment, screening out denitrification bacteria and enabling the denitrification bacteria to become dominant bacteria, and when the removal ratio of nitrate to Chemical Oxygen Demand (COD) is observed to be stable, determining that the denitrification activated sludge culture is successful. The domestication method is a conventional technical means in the art, and is not described herein. Of course, the invention can also directly use the denitrification activated sludge which stably runs in the sewage plant.

Optionally, in step S2, the anaerobic reactor is started up for denitrification reaction under the conditions that the temperature is 30+/-5 ℃, the pH is 7.5+/-0.5 and the Hydraulic Retention Time (HRT) is 1-96 hours.

It should be noted that the hydraulic retention time varies according to the concentration of the denitrified activated sludge and the concentration of nitrate nitrogen in the influent water, for example, if the concentration of the denitrified activated sludge is high and/or the nitrate nitrogen content in the influent water is low, the hydraulic retention time may be appropriately shortened, for example, 30min, 45min or 1h, whereas if the concentration of the denitrified activated sludge is low and/or the nitrate nitrogen content in the influent water is high, the hydraulic retention time may be appropriately prolonged, which is common knowledge in the art and will not be repeated herein. The hydraulic retention time refers to the average retention time of wastewater to be treated in the anaerobic reactor, namely the average reaction time of a water inlet source and microorganisms in the anaerobic reactor.

In the present invention, when the concentration of the denitrification activated sludge is low, since nitrite is continuously reduced with the extension of the reaction time, so that the consumption of nitrite is caused, the hydraulic retention time is preferably 8-48h, more preferably 16-24h, so as to ensure that nitrite is stably stored after accumulation.

The proper carbon-nitrogen ratio is favorable for the denitrification activity of denitrifying bacteria and improves the accumulation of nitrite, and only NO is carried out in the denitrification process ₃ ^- →NO ₂ ^- In this step, the required carbon source can be appropriately reduced; if the C/N ratio is too high, nitrite Nitrogen (NO) ₂ ^- -N) accumulation, since denitrifying bacteria will utilize excess carbon source to convert NO ₂ ^- -N is further reduced to a nitrogen-containing gas. Alternatively, in step S2, the carbon nitrogen ratio (C/N ratio) of the reaction mixture is 0.3 to 4.0, more preferably the C/N ratio is 0.5 to 3, still more preferably 1 to 2.5. The C/N ratio is the content of nitrogen in COD and nitrate (namely nitrate nitrogen, NO) ₃ ^- -N) mass ratio.

Chemical Oxygen Demand (COD) can be regulated by organic contaminants contained in the influent water source such as municipal wastewater, industrial wastewater itself, or by an additional carbon source such as glucose, sodium acetate, or methanol. When municipal wastewater, industrial wastewater and other organic wastewater can meet the COD requirement, a carbon source is not needed to be added at the moment, and only when the organic wastewater to be treated has low organic pollutant content and cannot provide enough electron donors, the carbon source is needed to be added at the moment to adjust the C/N ratio so as to meet the consumption of the carbon source in the denitrification process.

Preferably, the carbon source is glucose. A large number of experiments show that glucose is the optimal carbon source, and the accumulation efficiency of nitrite is improved most obviously.

Optionally, in step S2, the initial nitrate nitrogen content in the reaction mixture is 50-300mg/L, i.e. NO ₃ ^- And the nitrogen content is 50-300mg/L based on N.

Optionally, in step S2, the concentration of the denitrified activated sludge in the reaction mixture is 500-3000mg/L, more preferably 500-2500mg/L, still more preferably 1000-2000mg/L.

It should be noted that, in order to accelerate the reaction, the reaction mixture may be stirred at a proper time during the denitrification reaction to accelerate the mass transfer and reaction rate.

The invention is not particularly limited in the nature of the anaerobic reactor, and can be effective in forming an anaerobic environment as well as in forming a stirred reaction environment, and in some embodiments, preferably the anaerobic reactor includes, but is not limited to, a Sequencing Batch Reactor (SBR), an Upflow Anaerobic Sludge Blanket (UASB) reactor, and an anaerobic biological fluidized bed reactor.

The invention will be further illustrated with reference to specific examples. It is to be understood that these examples are illustrative of the present invention and are not intended to limit the scope of the present invention. The experimental methods, which do not address specific conditions in the following examples, are generally in accordance with the conditions recommended by the manufacturer.

The denitrification activated sludge in the following embodiments of the invention is selected from municipal sewage plant secondary sedimentation tank sludge, and specifically comprises the following steps: inoculating sludge from a secondary sedimentation tank of a municipal sewage treatment plant of Dongguan into a domestication tank of a laboratory for domestication and cultivation of denitrifying sludge, wherein the C/N ratio of a domestication culture solution is 4.0, and NO ₃ ^- The N concentration was gradually increased from 100mg/L to 600mg/L, with 50% of the supernatant replaced every 24h. After 30d of operation, sludge activity 4.17mg of NO was obtained ₃ ^- N/g MLSS.h. MLSS is the mixed liquor suspended solids concentration.

Example 1

The influence of the oxidant potassium Persulfate (PDS) on the nitrite nitrogen accumulation efficiency in the denitrification reaction system is mainly studied in the embodiment.

1. Effect of the oxidant Potassium Persulfate (PDS) on nitrite biological reduction

1) Kinetics of persulfate chemical oxidation nitrite: to 100mL of phosphate buffer solution (pH 7.5) were added potassium persulfate at a final concentration of 1.2mM and 100mg/L of NO ₂ ^- -N, N-filled ₂ Removing oxygen in anaerobic bottle for 2min, placing in air bath table, reacting at 30deg.C and 180rpm, collecting samples with different reaction times, and measuring NO in the samples ₂ ^- -N、NO ₃ ^- -N and SO ₄ ^2- Concentration of concentrationThe results are shown in FIG. 1 (a).

2) Kinetics of inhibition of nitrite biological reduction by persulfate: an anaerobic reactor was simulated by using an anaerobic reactor bottle, and 100mL of a slurry mixture (corresponding to the reaction mixture in step S2, the sludge concentration was 1000 mg/L) was added with 1.2mM potassium persulfate and 100mg/L NO ₂ ^- Adding glucose as carbon source to regulate C/N ratio to 2, i.e. glucose (COD) final concentration to 200mg/L, and charging N ₂ Removing oxygen in anaerobic bottle for 2min, placing in air bath table, reacting at 30deg.C and 180rpm, collecting water samples with different reaction times without adding PDS as control group, and measuring NO in water sample ₂ ^- -N、NO ₃ ^- -N and SO ₄ ^2- The results are shown in FIGS. 1 (b) - (c), and FIG. 1 (b) shows NO ₂ ^- Variation of N concentration with reaction time, SO for the experimental group is shown in FIG. 1 (c) ₄ ^2- Concentration and PDS decomposition rate as a function of reaction time.

The method for measuring each component comprises the following steps:

1)NO ₃ -N and SO ₄ ^2- : measuring by ion chromatography, wherein the chromatographic column of the ion chromatography is AS11-HC (ThermoFisher Scientific), and the eluting solution is 30mM sodium hydroxide;

2)NO ₂ ^- -N: measuring by adopting an N- (1-naphthyl) -ethylenediamine spectrophotometry;

3) The sludge concentration MLSS was measured gravimetrically.

NO was calculated by the following formula ₂ ^- -N nitrogen accumulation rate and persulfate decomposition rate:

1) Nitrite nitrogen accumulation rate: NAE (%) =NO ₂ ^- -N _t /(NO ₃ ^- -N _In -NO ₃ ^- -N _t )×100％；

In the above, NO ₃ ^- -N _In And NO ₃ ^- -N _t Respectively refer to NO ₃ ^- -N initial and concentration at reaction time t, NO ₂ ^- -N _In And NO ₂ ^- -N _t Respectively refer to NO ₂ ^- -concentration at initial and reaction time of N t.

2) Persulfate decomposition rate:

in the above, c _In (S ₂ O ₈ ^2- ) C is the initial PDS concentration (mM) _t (SO ₄ ^2- ) Is the sulfate concentration (mg/L) at reaction t.

As can be seen from FIG. 1 (a), in the absence of denitrification activated sludge, the concentration of nitrite nitrogen is only slightly reduced along with the progress of the reaction, and the concentration of nitrite nitrogen is between 95 and 100mg/L and the variation range is lower than 5mg/L within 48 hours of the reaction; meanwhile, the concentration of the generated nitrate nitrogen is lower than 1mg/L, and no sulfate is generated, so that the persulfate does not generate chemical oxidation effect on nitrous acid. As can be seen from fig. 1 (b), the difference between the nitrite nitrogen residual concentration in the blank (0 mM PDS) and the experimental (1.2 mM PDS) groups increased as the reaction proceeded, and the activity of the persulfate in reducing nitrite in the 1.2mM PDS reaction system was reduced by 58% as compared with the blank group at 48 hours, indicating that the persulfate has a significant inhibitory effect on nitrite biological reduction. As is clear from FIG. 1 (c), in the presence of the denitrified activated sludge, the sulfate concentration gradually increased to 48 hours with the increase of the reaction time, the sulfate concentration reached 33.2mg/L, and the decomposition rate of the persulfate was 14%, indicating that the persulfate itself was decomposed only slightly in the denitrifying system of the present invention, and thus the microbial reduction effect of stably suppressing nitrite was achieved.

2. Effect of the oxidant Potassium Persulfate (PSD) on the biological reduction of nitrate

1) Persulfate promotes kinetics for biological reduction of nitrate: an anaerobic reactor was simulated by using an anaerobic reactor bottle, and 100mL of a slurry mixture (the reaction mixture in step S2, the sludge concentration was 1500 mg/L) was added with potassium persulfate at a final concentration of 1.2mM and NO at a final concentration of 250mg/L ₃ ^- -N, with additional glucose as carbon sourceThe ratio of C/N of the section is 2, namely the final concentration of glucose is 500mg/L COD, and N is filled ₂ Removing oxygen in anaerobic bottle for 2min, placing in air bath table, reacting at 30deg.C and 180rpm, collecting water samples with different reaction times without adding PDS as control group, and measuring NO in water sample ₂ ^- -N、NO ₃ ^- -N and SO ₄ ^2- The results are shown in FIG. 2, and (a) in FIG. 2 shows the concentration of NO in the control group ₂ ^- -N、NO ₃ ^- -N concentration and NO ₂ ^- Variation of the N accumulation rate (Nitrite accumulation efficiency) with reaction time, NO in the experimental group is shown in FIG. 2 (b) ₂ ^- -N、NO ₃ ^- -N concentration and NO ₂ ^- Variation of the accumulation rate of N (Nitrite accumulation efficiency) with reaction time, SO for the experimental group is shown in FIG. 2 (c) ₄ ^2- Concentration and PDS decomposition rate (PDS decomposition efficiency) as a function of reaction time.

As can be seen from fig. 2 (a) and (b), the nitrate nitrogen concentration was continuously decreased with the increase of the reaction time, and after 96 hours, the residual nitrate nitrogen concentration of the control group was 107.8mg/L, whereas the nitrate nitrogen concentration in the denitrification reaction system to which PDS was added was decreased to 40.3mg/L, and the nitrate reduction activity was increased by 47%, thereby confirming that PDS has a significant promoting effect on the reduction of nitrate. For nitrite, the nitrite nitrogen concentration continuously rises along with the extension of the reaction time, the nitrite nitrogen accumulation rate of the control group ranges from 13% to 25%, the nitrite nitrogen concentration is 22.0mg/L at 96h, the nitrite nitrogen concentration in a denitrification reaction system added with PDS is 157.9mg/L at 96h, and the nitrite nitrogen accumulation rate is maintained at 74% to 85%, which further indicates that the PDS has an inhibition effect on nitrite reduction. As is clear from FIG. 2 (c), the concentration of the persulfate continuously increased as the reaction proceeded, and reached 158.7mg/L at the time of 96 hours, and the sulfate was produced as a result of decomposition of the persulfate, and the concentration of the persulfate at the time of 96 hours was 1.22mM by mass balance, and the decomposition rate was 39%.

The result shows that the persulfate does not oxidize nitrite and does not have the characteristic of closing the denitrification process, but rather the oxidant accelerates the biological reduction of the nitrate on one hand, so that the nitrogen content of the nitrate is rapidly reduced, on the other hand, the biological reduction of the nitrite is inhibited, the consumption of the nitrite is reduced, the two aspects work together to cause a large difference between the reduction rates of the nitrate and the nitrite, and further the instantaneous and efficient accumulation of the nitrite is realized, which also indicates that a shorter hydraulic retention time can be adopted in the denitrification reaction, and the hydraulic retention time of an anaerobic reactor is preferably 8-48h, more preferably 16-24h.

This example further investigated the effect of Potassium Monopersulfate (PMS) on the denitrification reaction system, with results similar to potassium persulfate, which also increased nitrite production while reducing nitrite consumption, and was not repeated here.

Example 2

The influence of persulfate with different concentrations on denitrification reaction is mainly studied in the embodiment.

s1, inoculating denitrification activated sludge into an anaerobic reactor to enable the sludge concentration to be 1000mg/L, and then adding oxidant potassium persulfate, wherein the potassium persulfate concentration is 0, 0.05, 0.1, 0.7, 1.2, 1.5, 2, 2.5, 4.5, 7.5 and 10.5mM in sequence so as to study the influence of persulfate with different concentrations on denitrification reaction;

s2, water is fed into the anaerobic reactor to form a reaction mixed solution, and initial NO of the reaction mixed solution is controlled ₃ ^- -N is 100mg/L, glucose is added as a carbon source to adjust the C/N ratio to 2, and then the anaerobic reactor is started to carry out denitrification reaction under the conditions that the temperature is 30+/-5 ℃, the rotating speed is 180rpm, the pH is 7.5+/-0.5 and the Hydraulic Retention Time (HRT) is 48 hours. At HRT 48h, samples were taken to determine nitrate nitrogen (NO ₃ ^- -N), nitrite nitrogen (NO ₂ ^- -N), and calculates the nitrite nitrogen accumulation rate NAE. The same treatment was used as a control group without the addition of an oxidizing agent. The experimental results are shown in FIG. 3, and FIG. 3 (a) shows N under the condition of different concentrations of persulfateO ₂ ^- -N、NO ₃ ^- -N concentration and NO ₂ ^- N accumulation Rate (Nitrite accumulation efficiency), FIG. 3 (b) shows SO at different concentrations of persulfate ₄ ^2- Concentration and PDS decomposition rate (PDS decomposition efficiency).

As is clear from FIG. 3 (a), the nitrate nitrogen concentration was continuously decreased with an increase in persulfate concentration (0 mM-7.5 mM), reaching the minimum value (2.5 mg/L) at 7.5mM, and then the nitrate nitrogen concentration was started to increase with continued increase to 10.5 mM. Nitrite nitrogen concentration showed an opposite trend to nitrate nitrogen concentration, which continued to rise with increasing persulfate concentration (0 mM-7.5 mM), reaching a maximum at 7.5mM (90.4 mg/L), followed by a continued increase to 10.5mM Shi Ya nitrate nitrogen concentration down to 11.4mg/L. The total nitrogen removal decreased with increasing persulfate concentration (0 mM-7.5 mM), reaching a minimum of 7.1mg/L at 7.5mM, which also indicated that persulfate inhibited some further reduction of nitrite, after which the total nitrogen concentration increased to 9.0mg/L with continued increase to 10.5 mM; wherein the total nitrogen is the sum of nitrite nitrogen and nitrate nitrogen. The nitrite nitrogen accumulation rate continuously increased with an increase in persulfate concentration (0 mM-7.5 mM), reaching 93% at 7.5mM, and then decreased with an increase in persulfate concentration, and decreased to 90% at a persulfate concentration of 10.5 mM. Therefore, the persulfate concentration is preferably 1 to 10.5mM, more preferably 4.5 to 10.5mM, still more preferably 7.5mM.

As is clear from fig. 3 (b), the amount of sulfate produced continuously increases with an increase in the concentration of persulfuric acid, but the decomposition rate of persulfuric acid continuously decreases. At persulfate concentrations below 0.1mM, the rate of decomposition of persulfate is above 75%, which also results in insignificant removal of nitrate nitrogen and accumulation of nitrite by low concentration oxidants; at persulfate concentrations above 0.1mM, the rate of decomposition of persulfate was less than 30%. Therefore, a proper increase in persulfate concentration contributes to the removal of nitrate nitrogen and the accumulation of nitrite in the denitrification reaction system.

Example 3

The influence of different C/N ratios on denitrification reaction is mainly studied in the embodiment.

Example 3 is substantially the same as example 2, except that: in step S1, the concentration of potassium persulfate is 1.2mM; in step S2, the C/N ratio was adjusted to 0.7, 1, 2, 3 and 4, respectively, with the addition of glucose as a carbon source, i.e., glucose concentrations of 70, 100, 200, 300, 400mg/L, respectively. The experimental results are shown in Table 1.

TABLE 1 influence of different C/N ratios on denitrification

As is clear from Table 1, the concentration of nitrate nitrogen continuously decreases with increasing C/N ratio, the nitrite nitrogen continuously increases with increasing C/N ratio, but the accumulation rate of nitrite nitrogen continuously decreases with increasing C/N ratio, because the C/N ratio affects the removal of total nitrogen, and when the carbon source increases, the generated nitrite nitrogen is reduced to nitrogen-containing gas (N) ₂ O _x ) At a C/N ratio equal to 3, the total nitrogen removal amount reached a maximum value of 31.2mg/L, thereby resulting in an increase in nitrite nitrogen that was smaller than the decrease in nitrate nitrogen concentration, resulting in a decrease in nitrite nitrogen accumulation rate. This also shows that in persulfate-containing denitrification systems, the C/N ratio has a positive correlation with nitrate and total nitrogen removal, while having a negative effect on nitrite nitrogen accumulation rate. Therefore, the C/N ratio is preferably 0.5 to 3, more preferably 1 to 2.5. In addition, as the C/N ratio increases, the amount of sulfate produced and the persulfate decomposition rate increase slightly by 7%, but since persulfate is excessively added, the decomposition amount does not affect the acceleration of nitrite nitrogen accumulation.

Example 4

The influence of different nitrate nitrogen concentrations and carbon source concentrations on denitrification reactions under fixed C/N ratio is mainly studied in the embodiment.

Example 4 is substantially the same as example 2, except that: in step S1, the concentration of potassium persulfate is 1.2mM; in the step S2, the fixed C/N ratio is 2.0, the nitrate nitrogen concentration and the glucose concentration are changed, the nitrate nitrogen concentration is 30 mg/L, 50mg/L, 100mg/L, 200mg/L and 300mg/L, and the glucose-COD concentration is 60 mg/L, 100mg/L, 200mg/L, 400mg/L and 600mg/L respectively. The experimental results are shown in Table 2.

TABLE 2 influence of different nitrate nitrogen concentration and carbon Source concentration on denitrification at fixed C/N ratio

As is clear from Table 2, the nitrite nitrogen concentration increased with the increase in the nitrate nitrogen concentration, which indicates that the increase in the nitrate nitrogen concentration contributes to the accumulation of nitrite nitrogen, but at the same time, the residual nitrate nitrogen in the reaction system increased with the increase in the nitrite nitrogen concentration, and the nitrite nitrogen accumulation rate was 73% at a nitrate nitrogen concentration of 100mg/L, N ₂ The generation amount of Ox reaches the maximum value of 21.5mg/L, because the generation of nitrogen-containing gas and the accumulation of nitrite are influenced by two key factors in the system, firstly, the proportion of nitrate nitrogen to sludge is higher, the nitrate nitrogen concentration is higher, the nitrate nitrogen load of sludge is correspondingly improved, the nitrite accumulated in the same time is higher, and the accumulation rate of nitrite of high nitrate nitrogen is increased due to the strengthening effect of persulfate; second, the lower the ratio of persulfate to nitrate nitrogen, the greater this ratio, the persulfate plays a dominant role in this process and the nitrite accumulation rate may also increase. Thus, an initial nitrate nitrogen of 100mg/L may be near the junction (weak) of the driving force constituted by the nitrate nitrogen sludge load and the persulfate/nitrate nitrogen ratio, resulting in the highest total nitrogen removal and the lowest nitrite nitrogen accumulation rate. It can be seen that the invention is particularly suitable for the treatment of wastewater containing high nitrogen content. When the concentration of nitrate nitrogen is 50-300mg/L, the sulfate production is increased, the persulfate decomposition rate is increased, but in the range of 100-300mg/L, the persulfate decomposition rate is increased slightly.

Example 5

The influence of different sludge concentrations on denitrification reaction is mainly studied in the embodiment.

Example 5 is substantially the same as example 2, except that: in step S1, the concentration of potassium persulfate is 1.2mM; in the step S2, the sludge concentrations were respectively 500, 1000, 1500, 2000, 2500 and 3000mg/L, and then glucose was added as a carbon source to adjust the C/N ratio to 2.0. The experimental results are shown in Table 3.

TABLE 3 influence of different sludge concentrations on denitrification

As can be seen from table 3, the nitrate nitrogen continuously decreases with the increase of the sludge concentration, the nitrite nitrogen concentration increases with the increase of the sludge concentration when the sludge concentration is 500-2000mg/L, the nitrite nitrogen concentration decreases with the increase of the sludge concentration when the sludge concentration is 2000-3000mg/L, that is, the sludge concentration is 2000mg/L, the nitrite nitrogen concentration reaches the maximum value, and the nitrite nitrogen accumulation rate decreases with the increase of the sludge concentration; thus, increasing the sludge concentration may facilitate removal of nitrate nitrogen, and appropriate sludge concentrations facilitate accumulation of nitrite nitrogen, preferably at a sludge concentration of 500-2500mg/L, more preferably 1000-2000mg/L.

Although the present disclosure is disclosed above, the scope of the present disclosure is not limited thereto. Various changes and modifications may be made by one skilled in the art without departing from the spirit and scope of the disclosure, and these changes and modifications will fall within the scope of the disclosure.

Claims

1. A method for increasing nitrite accumulation in a short-cut denitrification process, comprising the steps of:

s1, inoculating denitrification activated sludge into an anaerobic reactor, and adding 1-10.5mmol of oxidant into each gram of denitrification activated sludge; the oxidizing agent comprises persulfate, and the persulfate comprises one or more of peroxymonosulfate and peroxydisulfate;

the peroxymonosulfate comprises one or more of ammonium peroxymonosulfate, potassium peroxymonosulfate and sodium peroxymonosulfate, and the peroxydisulfate comprises one or more of ammonium persulfate, potassium peroxydisulfate and sodium peroxydisulfate;

2. The method according to claim 1, wherein in step S2, the anaerobic reactor is started up to perform denitrification under the conditions that the temperature of the reaction mixture is 30±5 ℃, the pH is 7.5±0.5, and the hydraulic retention time is 1 to 96 hours.

3. The method according to claim 2, wherein in step S2, the hydraulic retention time is 8-48h.

4. The method according to claim 1, wherein in step S2, the carbon-nitrogen ratio of the reaction mixture is 0.3 to 4.0.

5. The method of claim 4, wherein the carbon to nitrogen ratio is adjusted by adding a carbon source and a nitrate, the carbon source comprising one or more of glucose, sodium acetate, and methanol.

6. The method according to claim 4, wherein in step S2, the initial nitrate nitrogen content in the reaction mixture is 50-300mg/L.

7. The method according to claim 1, wherein in step S2, the sludge concentration of the denitrification activated sludge in the reaction mixture is 500-3000mg/L.