CN113511731A

CN113511731A - Method for improving nitrite accumulation in short-range denitrification process

Info

Publication number: CN113511731A
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: 2021-10-19
Anticipated expiration: 2041-07-30
Also published as: CN113511731B

Abstract

The invention provides a method for improving nitrite accumulation in a short-cut denitrification process, belonging to the technical field of wastewater treatment. The method comprises the following steps: s1, inoculating denitrification activated sludge into the anaerobic reactor, and adding 0.05-15mmol of oxidant per gram of denitrification activated sludge; s2, feeding water into the anaerobic reactor to form a reaction mixed solution, and starting the anaerobic reactor to carry out denitrification reaction. According to the invention, the specific oxidant is added, so that the reduction of the nitrate is selectively promoted, the further reduction of the nitrite can be inhibited, 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-term, 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-cut denitrification process.

Background

With the rapid development of economy and the continuous improvement of living standard, the discharge amount of urban sewage is increased day by day, and nitrogen compounds are excessively discharged into water bodies, so that algae and other microorganisms are excessively propagated, and the eutrophication of the water bodies is caused, and becomes a common phenomenon of the water bodies in China and has a further development trend. Eutrophication of the water body seriously damages the water ecology and harms human health. Therefore, the removal of nitrogen pollution in water has become a hot 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 is characterized in that ammonia nitrogen in sewage is converted into nitrite by aerobic nitrification and then converted into nitrate, and then the nitrate passes through a series of intermediate products (NO) by using the anoxic denitrification effect₂ ^-、NO、N₂O) is reduced into nitrogen and other nitrogen-containing gases, and finally the nitrogen-containing gases escape from the sewage to achieve the aim of denitrification. The nitrification and denitrification are mature denitrification processes at present, but have the problems of long flow, large occupied area, large amount of aeration, additional addition of organic carbon sources and the like, so that the energy consumption, investment and operating cost are high. 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 the anaerobic or anoxic condition, the anaerobic ammonia oxidation bacteria convert the ammonia nitrogen and the nitrite into nitrogen by taking the ammonia nitrogen as an electron donor and the nitrite as an electron acceptor. Compared with the nitrification-denitrification technology, the anaerobic ammonia oxidation process does not need oxygen, the aeration energy consumption is saved, and the reduction of nitrite does not need an additional carbon source, so the method has obvious advantages in the aspects of energy consumption and material consumption. However, the short-cut nitrification process cannot completely inhibit the growth of nitrite oxidizing bacteria, so that a large amount of nitrite is further oxidized into nitrate, and nitrate is generated in the anaerobic ammonia oxidation process, thereby limiting the efficient removal of total nitrogen. Therefore, how to ensure the accumulation of nitrite is the key for improving the high-efficiency denitrification of the anaerobic ammonia oxidation technology.Based on the above, the short-cut denitrification-anaerobic ammonia oxidation technology is produced. 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 problems existing in the short-cut nitrification-anaerobic ammonia oxidation technology at present are solved, the short-cut denitrification and the anaerobic ammonia oxidation reaction both occur under the anoxic or anaerobic condition, the reaction condition is convenient to control, and the operation is simpler and more convenient.

Factors affecting the shortcut denitrification include the kind of carbon source, C/N ratio, pH, and the kind of microorganism, etc. Among them, the regulation of the microbial species is the most effective method for achieving the short-cut denitrification. The Thauera genus was found to be the dominant genus in the short-cut denitrification process. In the prior art, research on the control of the short-cut denitrification process mainly focuses on improvement of enrichment culture methods of Thauera and the like. However, the enrichment efficiency of Thauera is generally low and unstable, and it is difficult to realize short-cut denitrification quickly, easily and efficiently, which limits the applicability of short-cut denitrification-anammox denitrification. The accumulation of nitrite in denitrification is realized by accurately controlling external conditions such as sludge concentration, carbon source, C/N ratio, pH and the like 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 popularization of the anaerobic ammonia oxidation application is greatly restricted.

Disclosure of Invention

In view of the above problems in the prior art, the present invention provides a method for increasing nitrite accumulation during a short-cut denitrification process.

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

a method for improving nitrite accumulation in a short-cut denitrification process comprises the following steps:

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

s2, feeding water into the anaerobic reactor to form a reaction mixed solution, and starting the anaerobic reactor to carry out denitrification reaction.

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

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

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

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

In step S2, the carbon-nitrogen ratio of the reaction mixture is 0.3 to 4.0, and the carbon-nitrogen ratio of the reaction mixture is 0.5 to 3.

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

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

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

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

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

1. according to the invention, the specific oxidant is added, so that the reduction of the nitrate is selectively promoted, the further reduction of the nitrite can be inhibited, 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 high-efficiency and stable accumulation of the nitrite can be realized.

2. The invention can control the short-cut denitrification to produce NO only by adding a proper amount of oxidant₂ ^-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 in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.

FIG. 1 shows the effect of Persulfate (PDS), an oxidant, on nitrite biological reduction in example 1 of the present invention, wherein (a) is a kinetic curve of persulfate chemically oxidizing nitrite, (b) is a kinetic curve of persulfate inhibiting nitrite biological reduction, and (c) is SO₄ ^2-The change curves of the concentration and the decomposition rate of the persulfate along with the reaction time;

FIG. 2 shows the effect of Persulfate (PDS), an oxidant, on the biological reduction of nitrate, in example 1 of the present invention, wherein (a) shows NO in the control group₂ ^--N、NO₃ ^--N concentration and NO₂ ^-The accumulation of N as a function of the reaction time, FIG. (b) is the NO of the experimental group₂ ^--N、NO₃ ^--N concentration and NO₂ ^-The curve of accumulation of N as a function of the reaction time, FIG. (c) SO for the experimental group₄ ^2-The concentration and the decomposition rate of persulfate vary with the reaction time;

FIG. 3 shows the effect of different concentrations of persulfate on denitrification reaction in example 2 of the present invention, wherein (a) shows NO in the presence of different concentrations of persulfate₂ ^--N、NO₃ ^--N concentration and NO₂ ^-Accumulation of-N, FIG (b) is SO at different concentrations of persulfate₄ ^2-Concentration and PDS decomposition rate.

Detailed Description

It should be noted that the embodiments and features of the embodiments may be combined with each other without conflict. In addition, the terms "comprising," "including," and "having" are intended to be non-limiting, i.e., other steps and other ingredients can be added that do not affect the results. Materials, equipment and reagents are commercially available unless otherwise specified.

For a better understanding of the invention, and not as a limitation on the scope thereof, all numbers expressing quantities, proportions and other numerical values used in the present invention are to be understood as being modified in all instances by the term "about". Accordingly, unless expressly indicated otherwise, the numerical parameters set forth in the specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained. At the very least, 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 to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below.

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 the nitrite accumulation in the short-cut denitrification process, which comprises the following steps:

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

In the conventional denitrification process, denitrifying bacteria take an organic carbon source as an electron donor, reduce nitrate into nitrogen through multi-step reaction,specifically, the method comprises the following steps: in the first step, nitrate reductase converts Nitrate (NO)₃ ^-) Reduction to Nitrite (NO)₂ ^-) (ii) a In the second step, Nitrite (NO) is converted by nitrite reductase (NiRs)₂ ^-) Reducing to Nitric Oxide (NO), nitrous oxide (N)₂O), etc.; third step, NO, N₂O is reduced to nitrogen; thus, NO can be controlled by denitrification₃ ^-→NO₂ ^-And (3) reducing the reduction speed of the nitrite to realize the accumulation of the nitrite.

In the invention, the addition of the oxidant can selectively promote the reduction of the nitrate so that the reduction rate of the nitrate is greater than that of the nitrite, and on the other hand, the addition of the oxidant can inhibit the further reduction of the nitrite so as to reduce the consumption of the nitrite, namely, the consumption of the nitrite is reduced by increasing the generation amount of the nitrite, so that the Nitrite (NO) is accelerated₂ ^-) To obtain a large amount of Nitrite (NO)₂ ^-) Realization of NO₂ ^-Short, efficient, stable accumulation. Furthermore, the short-cut denitrification can be controlled to NO only by adding a proper amount of oxidant₂ ^-Is a target product and has the advantages of simple operation, easy control and the like.

It is to be noted that although the oxidizing agent such as persulfate is added in the present invention, although the oxidizing agent such as persulfate has a higher oxidation-reduction potential than oxygen, it cannot be utilized as an electron acceptor by the denitrifying microorganism and does not have the characteristic of shutting down the denitrification process.

Utilizing the large amount of Nitrite (NO) produced by the short-cut denitrification process of the invention₂ ^-) As an electron acceptor for anaerobic ammonia oxidation, nitrate Nitrogen (NO) in wastewater can be realized₃ ^-) And ammonium salts (NH)₄ ⁺) The method has the advantages of high efficiency and stability in removal, greatly improving the denitrification rate and efficiency, realizing low-carbon denitrification of the wastewater and having wide application prospect.

The key point of maintaining the anaerobic ammonia oxidation high-efficiency denitrification process is to maintain the accumulation of nitrite in short-cut denitrification, and preferably, the ratio of the oxidant to the denitrification activated sludge is 1-10.5 mmol: 1g of the total weight of the composition. Being lower than the proportional relation, the improving effect of the oxidant on the accumulation rate of the nitrite is not obvious, and being higher than the mass ratio, the reducing time of the nitrate can be prolonged, so that the accumulation rate of the nitrite is reduced, and the content of the oxidant is further increased, so that the oxidation-reduction potential can be obviously improved, the activity of microorganisms in the denitrification activated sludge is influenced, and the integral denitrification effect is weakened. More preferably, the ratio of the oxidant to the denitrification-activated sludge is 4.5-10.5 mmol: 1g, more preferably 7.5 mmol: 1g of the total weight of the composition.

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 order of the oxidant and the water inlet is defined in steps S1 and S2, one skilled in the art should understand that the oxidant and the water inlet may be added after the water inlet, or the oxidant and the water inlet may be performed simultaneously, but not limited to the mode of adding the oxidant before the water inlet.

In step S1, the inoculated denitrification activated sludge is preferably a stable mature granular sludge, and is usually obtained by acclimatization, for example, a common activated sludge is taken, then sufficient carbon source and nitrate are added, gradient acclimatization is performed in an anoxic or anaerobic environment, denitrification bacteria are screened out and become dominant bacteria, and when the removal ratio of nitrate and Chemical Oxygen Demand (COD) is observed to be stable, the successful culture of the denitrification activated sludge can be determined. The domestication method is a conventional technical means in the field, and is not described herein again. 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 to carry out denitrification reaction under the conditions of temperature of 30 +/-5 ℃, pH of 7.5 +/-0.5 and Hydraulic Retention Time (HRT) of 1-96 h.

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

In the present invention, when the concentration of the denitrification activated sludge is low, since nitrite continues to be reduced with the extension of the reaction time, thereby causing the consumption of nitrite, the hydraulic retention time is preferably 8-48h, more preferably 16-24h, to ensure that the nitrite is maintained stably after accumulation.

Proper carbon-nitrogen ratio is favorable for denitrifying activity of denitrifying bacteria and increasing accumulation of nitrite, and only NO is carried out in the denitrifying process₃ ^-→NO₂ ^-In this step, the required carbon source can be reduced appropriately; if the C/N ratio is too high, nitrite Nitrogen (NO) is not easily generated₂ ^--N) because denitrifying bacteria would use excess carbon source to convert NO₂ ^--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 0.5 to 3, and still more preferably 1 to 2.5. The C/N ratio is the COD and the nitrogen content in the nitrate (i.e. nitrate nitrogen, NO)₃ ^--N) mass ratio.

Chemical Oxygen Demand (COD) can be regulated by the organic contaminants inherently contained in influent water sources such as municipal sewage, industrial wastewater, or by an external carbon source such as glucose, sodium acetate or methanol. When organic wastewater such as municipal sewage, industrial wastewater and the like can meet the demand of COD, a carbon source does not need to be added at the moment, and only when the content of organic pollutants in the organic wastewater to be treated is low and sufficient electron donors cannot be provided, the carbon source needs to be added at the moment to adjust the C/N ratio so as to meet the consumption of a denitrification process on the carbon source.

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. with NO₃ ^-The nitrogen content is 50-300mg/L calculated by-N.

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

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

The type of the anaerobic reactor is not particularly limited in the present invention, and it is sufficient that the anaerobic environment can be effectively formed and the agitation reaction environment can be formed, and in some embodiments, it is preferable that the anaerobic reactor includes, but not limited to, a Sequencing Batch Reactor (SBR) reactor, an Upflow Anaerobic Sludge Blanket (UASB) reactor, an anaerobic biological fluidized bed reactor.

The invention will be further illustrated with reference to the following specific examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. The following examples are examples of experimental procedures not specified under specific conditions, generally according to the conditions recommended by the manufacturer.

In the following embodiments of the present invention, the denitrification activated sludge is selected from sludge in a secondary sedimentation tank of a municipal sewage plant, and specifically comprises: inoculating sludge of a secondary sedimentation tank of a municipal sewage treatment plant of Dongguan into an acclimation tank of a laboratory for acclimation and culture of denitrification sludge, wherein the C/N ratio of an acclimation culture solution is 4.0, and NO is₃ ^-The N concentration was increased stepwise from 100mg/L to 600mg/L, 50% of the supernatant being replaced every 24 h. After running for 30d, sludge activity of 4.17mg NO is obtained₃ ^-N/g MLSS · h. MLSS is mixed solution suspensionThe solids concentration.

Example 1

This example mainly studies the effect of the oxidizing agent potassium Persulfate (PDS) on the accumulation efficiency of nitrite nitrogen in the denitrification reaction system.

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

1) Persulfate chemical oxidation nitrite kinetics: to 100mL of a phosphate buffer solution (pH7.5) were added potassium persulfate at a final concentration of 1.2mM and 100mg/L of NO₂ ^--N, charging N₂Removing oxygen in the anaerobic bottle for 2min, placing in an air bath shaker, reacting at 30 deg.C and 180rpm, collecting samples with different reaction time, and measuring NO in the samples₂ ^--N、NO₃ ^--N and SO₄ ^2-Concentration of concentration, the results are shown in FIG. 1 (a).

2) Persulfate inhibition kinetics for nitrite bioreduction: an anaerobic reactor was simulated by using an anaerobic reaction flask, and potassium persulfate having a final concentration of 1.2mM and 100mg/L of NO were added to 100mL of the sludge-water mixed solution (corresponding to the mixed solution reacted in step S2, having a sludge concentration of 1000mg/L)₂ ^-N, adding glucose as carbon source to adjust C/N ratio to 2, i.e. final concentration of glucose (COD) of 200mg/L, charging N₂Removing oxygen in the anaerobic bottle for 2min, placing in an air bath shaking table, reacting at 30 deg.C and 180rpm, collecting water samples with different reaction times without adding PDS as control group, and determining NO in the water samples₂ ^--N、NO₃ ^--N and SO₄ ^2-The results are shown in (b) to (c) of FIG. 1, and (b) of FIG. 1 shows NO₂ ^-N concentration as a function of reaction time, SO of the experimental group is shown in FIG. 1 (c)₄ ^2-Concentration and PDS decomposition rate were varied with reaction time.

The method for measuring the components comprises the following steps:

1)NO₃-N and SO₄ ^2-: the determination is carried out by ion chromatography, wherein the chromatographic column of the ion chromatography is AS11-HC (ThermoFisher scientific), and the eluent is 30mM sodium hydroxide;

2)NO₂ ^--N: measuring by adopting an N- (1-naphthyl) -ethylenediamine spectrophotometry;

3) the sludge concentration MLSS is determined by a gravimetric method.

Respectively calculating NO by using the following formula₂ ^--N nitrogen accumulation rate and persulfate decomposition rate:

1) nitrite nitrogen accumulation rate: NAE (%) ═ NO₂ ^--N_t/(NO₃ ^--N_In-NO₃ ^--N_t)×100％；

In the above formula, NO₃ ^--N_InAnd NO₃ ^--N_tRespectively mean NO₃ ^--concentration of N at initial and reaction time t, NO₂ ^--N_InAnd NO₂ ^--N_tRespectively mean NO₂ ^--concentration of Ninitial and reaction time t.

2) Decomposition rate of persulfate:

in the above formula, c_In(S₂O₈ ^2-) Is the concentration (mM) of the initial PDS, c_t(SO₄ ^2-) The concentration of sulfate in the reaction t (mg/L) was used.

As can be seen from (a) in FIG. 1, in the absence of denitrification activated sludge, the concentration of nitrite nitrogen is only slightly reduced along with the reaction time, and within 48 hours of the reaction, the concentration of nitrite nitrogen is between 95 and 100mg/L, and the variation range is lower than 5 mg/L; meanwhile, the nitrate nitrogen generation concentration is lower than 1mg/L, and no sulfate is generated, thereby indicating that the persulfate does not generate chemical oxidation effect on the nitrous acid. As can be seen from (b) in FIG. 1, as the reaction proceeds, the difference between the residual nitrite nitrogen concentrations in the blank group (0mM PDS) and the experimental group (1.2mM PDS) increases, and when the reaction proceeds for 48h, the activity of reducing nitrite by sludge in the 1.2mM PDS reaction system is reduced by 58% compared with the blank group, which indicates that persulfate has a significant inhibitory effect on nitrite biological reduction. As can be seen from FIG. 1 (c), in the presence of the denitrification activated sludge, the sulfate concentration gradually increases with the increase of the reaction time, and reaches 33.2mg/L until 48h, and the decomposition rate of the persulfate is 14%, which indicates that in the denitrification system of the present invention, the persulfate itself generates only a small amount of decomposition, and thus the microbial reduction effect of stably inhibiting nitrite can be achieved.

2. Effect of oxidizing agent Potassium Persulfate (PSD) on biological reduction of nitrates

1) Persulfate promotes kinetics for biological reduction of nitrate: an anaerobic reactor was simulated by using an anaerobic reaction flask, and potassium persulfate having a final concentration of 1.2mM and NO having a final concentration of 250mg/L were added to 100mL of the sludge-water mixed solution (the reaction mixed solution in step S2, the sludge concentration was 1500mg/L)₃ ^-N, adding glucose as carbon source to adjust C/N ratio to 2, i.e. final concentration of glucose is 500mg/L COD, filling N₂Removing oxygen in the anaerobic bottle for 2min, placing in an air bath shaking table, reacting at 30 deg.C and 180rpm, collecting water samples with different reaction times without adding PDS as control group, and determining NO in the water samples₂ ^--N、NO₃ ^--N and SO₄ ^2-The results are shown in FIG. 2, and NO is shown in FIG. 2 (a) for the control group₂ ^--N、NO₃ ^--N concentration and NO₂ ^-The variation of the N accumulation rate (Nitrite accumulation efficiency) with reaction time, and NO in the experimental group is shown in (b) of FIG. 2₂ ^--N、NO₃ ^--N concentration and NO₂ ^-The variation of the accumulation rate of N (Nitrite accumulation efficiency) with the reaction time, SO of the experimental group is shown in (c) of FIG. 2₄ ^2-The concentration and the PDS decomposition efficiency (PDS decomposition efficiency) varied with the reaction time.

As can be seen from (a) and (b) in fig. 2, the nitrate nitrogen concentration continued to decrease 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 decreased to 40.3mg/L in the denitrification reaction system to which PDS was added, and the nitrate reduction activity increased by 47%, thereby confirming that PDS has a significant accelerating effect on the reduction of nitrate. For nitrite, the nitrite nitrogen concentration continuously increased along with the extension of the reaction time, the nitrite nitrogen accumulation rate of the control group ranged from 13% to 25%, the nitrite nitrogen concentration was 22.0mg/L at 96h, while the nitrite nitrogen concentration in the denitrification reaction system added with PDS was 157.9mg/L at 96h, and the nitrite nitrogen accumulation rate was maintained at 74% to 85%, further indicating that PDS has an inhibitory effect on nitrite reduction. As shown in FIG. 2 (c), the persulfate concentration continued to increase with the progress of the reaction and reached 158.7mg/L at 96 hours of the reaction, and sulfate was generated as a result of decomposition of the persulfate, and the persulfate concentration was 1.22mM at 96 hours of the reaction by mass balance, and the decomposition rate was 39%.

The above results show that the persulfate is added, the persulfate does not oxidize nitrite and does not have the characteristic of shutting down the denitrification process, but on one hand, the biological reduction of nitrate is accelerated by the oxidant, so that the nitrogen content of nitrate is rapidly reduced, on the other hand, the biological reduction of nitrite is inhibited, the consumption of nitrite is reduced, the two aspects act together to cause that the nitrate reduction rate and the nitrite reduction rate have a larger difference, and further the instantaneous and efficient accumulation of nitrite is realized, which also indicates that the 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 16-24 h.

This example further investigated the effect of Potassium Monopersulfate (PMS) on the denitrification reaction system, which resulted in an increase in nitrite production while reducing nitrite consumption similar to potassium persulfate, and is not repeated here.

Example 2

This example mainly investigated the effect of different concentrations of persulfate on the denitrification reaction.

s1, inoculating denitrification activated sludge into the anaerobic reactor to enable the sludge concentration to be 1000mg/L, and then adding an oxidant, namely 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 to study the influence of persulfate with different concentrations on denitrification reaction;

s2, feeding water into the anaerobic reactor to form a reaction mixed solution, and controlling the initial NO of the reaction mixed solution₃ ^-the-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 of the temperature of 30 +/-5 ℃, the rotating speed of 180rpm, the pH value of 7.5 +/-0.5 and the Hydraulic Retention Time (HRT) of 48 h. At HRT of 48h, samples were taken for nitrate Nitrogen (NO)₃ ^--N), nitrite Nitrogen (NO)₂ ^--N) and calculating the nitrite nitrogen accumulation rate NAE. The control group was prepared without adding the oxidizing agent but by the same treatment. The results of the experiment are shown in FIG. 3, and FIG. 3(a) shows NO at various concentrations of persulfate₂ ^--N、NO₃ ^--N concentration and NO₂ ^-Accumulation rate of N (Nitrite accumulation efficiency), SO in FIG. 3 (b) showing different concentrations of persulfate₄ ^2-Concentration and PDS decomposition efficiency (PDS decomposition efficiency).

As can be seen from FIG. 3(a), the nitrate nitrogen concentration continuously decreased with the increase in the persulfate concentration (0mM-7.5mM), reached the lowest value (2.5mg/L) at 7.5mM, and then began to rise as the nitrate nitrogen concentration continued to increase to 10.5 mM. Nitrite nitrogen concentration shows a trend opposite to nitrate nitrogen concentration, which continues to increase with increasing persulfate concentration (0mM-7.5mM), reaching a maximum value (90.4mg/L) at 7.5mM, after which nitrite nitrogen concentration decreases to 11.4mg/L when increasing further to 10.5 mM. The total nitrogen removal decreased with increasing persulfate concentration (0mM-7.5mM), reaching a minimum of 7.1mg/L at 7.5mM, which also indicates that persulfate inhibited further reduction of nitrite to some extent, 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 increases continuously with increasing persulfate concentration (0mM-7.5mM), reaching 93% at 7.5mM, and then decreases with increasing persulfate concentration, decreasing to 90% at 10.5 mM. Therefore, the persulfate salt concentration is preferably 1 to 10.5mM, more preferably 4.5 to 10.5mM, and further preferably 7.5 mM.

As shown in fig. 3 (b), the amount of sulfate produced continuously increases with the increase in the concentration of persulfate, but the decomposition rate of persulfate continuously decreases. When the concentration of the persulfate is lower than 0.1mM, the decomposition rate of the persulfate is higher than 75%, which also results in that the removal of nitrate nitrogen by a low-concentration oxidant and the accumulation rate of nitrite are not obviously improved; at persulfate concentrations above 0.1mM, the decomposition rate of persulfate was less than 30%. Therefore, a suitable increase in the persulfate concentration facilitates the removal of nitrate nitrogen and the accumulation of nitrite in the denitrification reaction system.

Example 3

This example mainly investigates the effect of different C/N ratios on the denitrification reaction.

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

TABLE 1 Effect of different C/N ratios on the Denitrification reaction

As can be seen from Table 1, the nitrate nitrogen concentration continuously decreases as the C/N ratio increases, the nitrite nitrogen continuously increases as the C/N ratio increases, but the nitrite nitrogen accumulation rate continuously decreases as the C/N ratio increases, because the C/N ratio affects the total nitrogen removal, and when the carbon source increases, the nitrite nitrogen produced is reduced to a nitrogen-containing gas by an excess carbon source (N is increased)₂O_x) When the C/N ratio is equal to 3, the total nitrogen removal amount reaches a maximum value of 31.2mg/L, which results in an increase in nitrite nitrogen that is less than the decrease in nitrate nitrogen concentration, resulting in a decrease in nitrite nitrogen accumulation rate. This also indicates that in the denitrification reaction system containing persulfate,the C/N ratio has a positive correlation with nitrate and total nitrogen removal, with some 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 is increased, the generation amount of sulfate and the decomposition rate of persulfate are increased in a small range, and the decomposition rate of persulfate is increased by 7%, but the decomposition amount does not affect the promotion of the accumulation of nitrite nitrogen due to the excessive addition of persulfate.

Example 4

This example mainly investigates the effect of different nitrate nitrogen and carbon source concentrations on the denitrification reaction at a fixed C/N ratio.

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

TABLE 2 influence of different nitrate nitrogen and carbon source concentrations on the denitrification reaction at fixed C/N ratios

As can be seen from Table 2, the nitrite nitrogen concentration increased with the increase in the nitrate nitrogen concentration, indicating that the increase in the nitrate nitrogen concentration favors the accumulation of nitrite nitrogen, but at the same time the residual nitrate nitrogen in the reaction system increased, and that at a nitrate nitrogen concentration of 100mg/L, the nitrite nitrogen accumulation rate was 73%, and N was increased₂The 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 higher the concentration of nitrate nitrogen is, the nitrate nitrogen load of sludge is correspondingly increased, the accumulated nitrite in the same time is also higher, and the strengthening effect of persulfate is added, so that the accumulation rate of nitrite with high nitrate nitrogen is increased; second, persulfate and nitrateThe lower the nitrogen ratio, the higher the nitrate nitrogen, the persulfate dominates the process, and the nitrite accumulation rate may also increase. Thus, 100mg/L of initial nitrate nitrogen may be near the intersection (weakness) of the driving force of nitrate nitrogen sludge load and persulfate/nitrate nitrogen ratio, resulting in the highest total nitrogen removal and the lowest nitrite nitrogen accumulation rate. It can be seen that the present invention is particularly suitable for the treatment of high nitrogen-containing wastewater. When the concentration of the nitrate nitrogen is in the range of 50-300mg/L, the generation amount of the sulfate is increased, and the decomposition rate of the persulfate is increased, but the increase range of the decomposition rate of the persulfate is smaller in the range of 100-300 mg/L.

Example 5

This example mainly investigated the effect of different sludge concentrations on the denitrification reaction.

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

TABLE 3 Effect of different sludge concentrations on the denitrification reaction

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

Although the present disclosure has been described above, the scope of the present disclosure is not limited thereto. Various changes and modifications may be effected therein by one of ordinary skill in the pertinent art without departing from the spirit and scope of the present disclosure, and these changes and modifications are intended to be within the scope of the present disclosure.

Claims

1. A method for improving nitrite accumulation in a short-cut denitrification process is characterized by comprising the following steps:

2. The method according to claim 1, wherein in step S1, 1-10.5mmol of oxidizing agent per gram of the denitrification-activated sludge is added.

3. The method of claim 1 or 2, wherein the oxidizing agent comprises one or more of a persulfate, hydrogen peroxide, percarbonate, hypochlorite.

4. The method of claim 3, wherein the oxidizing agent comprises a persulfate salt comprising one or more of a peroxymonosulfate salt and a peroxydisulfate salt;

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 persulfate and sodium persulfate.

5. The method according to claim 1, wherein in step S2, the anaerobic reactor is started to carry out denitrification reaction under the conditions that the temperature of the reaction mixed liquid is 30 +/-5 ℃, the pH value is 7.5 +/-0.5 and the hydraulic retention time is 1-96 h.

6. The method of claim 5, wherein in step S2, the hydraulic retention time is 8-48 h.

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

8. The method of claim 7, wherein the carbon to nitrogen ratio is adjusted by adding a carbon source comprising one or more of glucose, sodium acetate and methanol and a nitrate.

9. The method according to claim 7, wherein in step S2, the initial nitrate nitrogen content in the reaction mixture is 50-300 mg/L.

10. The method as claimed in claim 1, wherein in step S2, the sludge concentration of the denitrification activated sludge in the reaction mixed liquid is 500-3000 mg/L.