Method for advanced nitrogen removal of sewage based on pyrite mixed culture denitrification system

Abstract

The application discloses a method for deep denitrification of sewage based on a pyrite mixed culture denitrification system, which comprises the following steps: (1) mixing sewage to be treated, sulfur autotrophic denitrification sludge and pyrite sufficiently, filling them in a reactor, and carrying out internal reflux culture for a predetermined time, so that the surface of the pyrite is gradually biofilm-covered, thereby preliminarily denitrifying the sewage; and (2) mixing the sewage to be treated and a predetermined amount of liquid containing NaCl, then continuously flowing the mixture into the reactor in an upward continuous flow mode, and operating the reactor, thereby further denitrifying the sewage. In the sewage denitrification treatment, the liquid containing NaCl is added to successfully improve the deep denitrification efficiency of the pyrite mixed culture denitrification system, and can provide more scientific guidance for popularization and use of the pyrite-mediated denitrification system in sewage treatment plants in coastal cities.

Description

Technical Field

[0001] This invention relates to the field of advanced urban wastewater treatment, and in particular to a method for advanced nitrogen removal from wastewater based on a pyrite co-culture denitrification system. Background Technology

[0002] In recent years, with the rapid growth of urban populations, urban water environments have faced increasing pressure from nitrogen content. Against the backdrop of carbon neutrality and sustainable urban ecological development, countries are imposing increasingly stringent nitrogen emission standards on municipal wastewater treatment plants. Deep denitrification of biological effluent from wastewater treatment plants has become the most direct and effective way to address this severe challenge. Pyrite-mediated denitrification technology has attracted widespread attention due to its advantages such as low cost, safety, and phosphorus removal capabilities, and shows promise for deep denitrification in municipal wastewater treatment plants. However, the crystalline structure of pyrite makes it difficult to continuously provide electron donors for stable and efficient nitrate nitrogen removal, limiting the widespread application of pyrite-mediated denitrification technology.

[0003] It should be noted that the information disclosed in the background section above is only for understanding the background of this application, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0004] The main objective of this invention is to provide a method for deep denitrification of wastewater based on a pyrite co-culture denitrification system, which can improve the denitrification efficiency of wastewater.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for deep nitrogen removal from wastewater based on a pyrite co-culture denitrification system includes the following steps:

[0007] (1) The wastewater to be treated, sulfur autotrophic denitrification sludge and pyrite are thoroughly mixed and filled into the reactor, and internal reflux culture is carried out for a predetermined time so that a film gradually forms on the surface of the pyrite to perform preliminary denitrification of the wastewater.

[0008] (2) The wastewater to be treated and a predetermined amount of NaCl-containing liquid are mixed and fed into the reactor in an upward continuous flow manner, and the reactor is operated to further denitrify the wastewater.

[0009] Furthermore, in step (2), after the wastewater to be treated is mixed with a predetermined amount of NaCl-containing liquid, the salinity is in the range of 0.5 to 10 g / L, preferably in the range of 5 to 10 g / L.

[0010] Furthermore, in step (1), the initial mixed liquor suspended solids concentration of the sulfur autotrophic denitrifying sludge in the reactor is in the range of 3750 to 4500 mg / L.

[0011] Furthermore, in step (1), the particle size of the pyrite is 2-3 mm.

[0012] Furthermore, the reactor is an upflow fixed-bed reactor for pyrite.

[0013] Furthermore, in step (2), the hydraulic retention time of the wastewater is 8 ± 0.5 h.

[0014] Further, in step (1), the sulfur autotrophic denitrification sludge is obtained by the following steps: 2.160-2.165 g / L KNO3, 0.260-0.265 g / L KH2PO4, 0.910-0.915 g / L NaHCO3 and 4.515-4.520 g / L Na2S2O3·5H2O are added to the sludge originating from the oxidation ditch, and the sludge is acclimatized and cultured at room temperature. When the nitrate nitrogen removal rate is stable at more than 70%, the sulfur autotrophic denitrification sludge is considered to have been successfully cultured.

[0015] Furthermore, the internal reflux culture time in step (1) is 3-5 days.

[0016] Furthermore, the NaCl-containing liquid is seawater; the wastewater to be treated is the biochemical effluent from a municipal wastewater treatment plant.

[0017] The present invention has the following beneficial effects:

[0018] (1) This invention utilizes NaCl-containing liquid to successfully enhance the deep denitrification efficiency of the pyrite co-culture denitrification system. This invention does not control the dissolved oxygen concentration of the influent, that is, under normal dissolved oxygen conditions, the denitrifying bacteria can be enhanced, thereby strengthening the pyrite-mediated denitrification and thus enabling the reactor to achieve a better denitrification effect.

[0019] (2) In the preferred technical solution, after adding NaCl-containing liquid, when the influent salinity is 5 and 10 g / L, the average nitrate nitrogen removal rate is significantly improved compared with that without adding NaCl-containing liquid, increasing by 35.8% and 60.3% respectively. The average nitrate nitrogen removal rate increases from 44.3% without adding NaCl-containing liquid to 58.1% and 67.9% respectively, and the average nitrate nitrogen removal rate increases by 31.2% and 53.3% respectively.

[0020] (3) In the preferred technical solution, the liquid containing NaCl is seawater. Seawater is relatively easy to obtain in coastal cities. The salinity of seawater can be made to reach the corresponding concentration range through different degrees of dilution. Compared with other methods to improve the deep denitrification of pyrite co-culture denitrification systems, the cost is lower and the time to achieve the promotion effect is shorter.

[0021] This invention can provide more scientific guidance and reference for the promotion and application of pyrite-mediated denitrification systems in coastal urban wastewater treatment plants. Attached Figure Description

[0022] Figure 1 The figures represent the nitrate nitrogen removal rates under different salinity conditions in the embodiments of the present invention.

[0023] Figure 2 The figures represent the nitrate nitrogen removal rates under different salinity conditions in the embodiments of the present invention.

[0024] Figure 3 The percentage increase in nitrate nitrogen removal rate under different salinity conditions in the embodiments of the present invention. Detailed Implementation

[0025] The embodiments of the present invention will be described in detail below. It should be emphasized that the following description is merely exemplary and not intended to limit the scope and application of the present invention. Unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other.

[0026] In this article, "room temperature" refers to a temperature range of 25℃ to 35℃.

[0027] This invention provides a method for deep denitrification of wastewater based on a pyrite co-culture denitrification system, comprising the following steps:

[0028] (1) The wastewater to be treated, sulfur autotrophic denitrification sludge and pyrite are thoroughly mixed and filled into the reactor, and internal reflux culture is carried out for a predetermined time so that a film gradually forms on the surface of the pyrite to perform preliminary denitrification of the wastewater.

[0029] (2) The wastewater to be treated and a predetermined amount of NaCl-containing liquid are mixed and fed into the reactor in an upward continuous flow manner, and the reactor is operated to further denitrify the wastewater.

[0030] The principle of deep nitrogen removal in wastewater according to this invention is as follows: A certain amount of NaCl-containing liquid is added to a stable reactor. The addition of NaCl-containing liquid promotes the interaction between microorganisms in the pyrite-mediated denitrification system, helps the microbial community form a more compact cluster structure, reduces the formation of modular networks, ensures the stability of the microbial community structure in the pyrite-mediated denitrification system, and improves the nitrogen removal efficiency. On the other hand, the addition of NaCl-containing liquid accelerates the precipitation rate of sulfur ions and ferrous ions from pyrite to a certain extent, constructs a more extensive electron transfer channel between pyrite and denitrifying functional bacteria, thereby improving the electron transfer efficiency of pyrite and ultimately accelerating the removal rate of nitrate nitrogen.

[0031] In some embodiments, in step (2), after the wastewater to be treated is mixed with a predetermined amount of NaCl-containing liquid, the salinity (mass concentration of NaCl) is in the range of 0.5 to 10 g / L, more preferably, the salinity is in the range of 5 to 10 g / L. The NaCl-containing liquid added in this invention has a suitable concentration range. When the salinity of the introduced NaCl-containing liquid is too high, it will have a certain toxic effect on microorganisms, and the action of chloride ions and oxygen may increase the risk of pyrite forming oxides. This also hinders the contact between microorganisms, pyrite and nitrate nitrogen in the wastewater to a certain extent, ultimately affecting the growth of microorganisms and the removal effect of nitrate nitrogen.

[0032] In some embodiments, in step (1), the initial mixed liquor suspended solids (MLSS) concentration of the sulfur autotrophic denitrifying sludge in the reactor is in the range of 3750–4500 mg / L. Mixed liquor suspended solids (MLSS) represents the suspended solids content, measured in mg / L, and specifically refers to the concentration of pure sludge.

[0033] In some embodiments, in step (1), the particle size of pyrite is 2-3 mm.

[0034] In some embodiments, the reactor is an upflow fixed-bed reactor for pyrite.

[0035] In some embodiments, in step (2), the hydraulic retention time is determined according to the degradation of pollutants, and preferably the hydraulic retention time of wastewater is 8 ± 0.5 h.

[0036] In some embodiments, in step (1), the sulfur autotrophic denitrifying sludge is obtained by the following steps: 2.160-2.165 g / L KNO3, 0.260-0.265 g / L KH2PO4, 0.910-0.915 g / L NaHCO3 and 4.515-4.520 g / L Na2S2O3·5H2O are added to the sludge originating from the oxidation ditch, and the sludge is acclimatized and cultured at room temperature. When the nitrate nitrogen removal rate stabilizes at more than 70%, the sulfur autotrophic denitrifying sludge is considered to have been successfully cultured.

[0037] In some implementations, the internal reflux culture time in step (1) is 3-5 days.

[0038] In some embodiments, the NaCl-containing liquid is seawater; the wastewater to be treated is biochemical effluent from a municipal wastewater treatment plant.

[0039] The following describes specific embodiments of the present invention.

[0040] Example

[0041] The reactor used in this embodiment is a pyrite upflow fixed-bed reactor with an effective volume of 1L. The sulfur autotrophic denitrification sludge used in this embodiment can be obtained from a long-term stable oxidation ditch and cultivated and acclimatized in a laboratory SBR mode. The cultivation and acclimatization conditions are as follows: the oxidation ditch sludge is placed in a reactor with a stirring function, and the following substances are added: KNO3 (2.160~2.165g / L), KH2PO4 (0.260~0.265g / L), NaHCO3 (0.910~0.915g / L) and Na2S2O3·5H2O (4.515~4.520g / L). The influent sulfur-nitrogen ratio is controlled at 3.89:1. Acclimatization and cultivation are carried out at room temperature. When the nitrate nitrogen removal rate of the reactor stabilizes at above 70%, the sulfur autotrophic denitrification sludge is considered to have been successfully cultivated. The method for deep nitrogen removal from wastewater (biological effluent from municipal wastewater treatment plants) based on a pyrite co-culture denitrification system includes the following steps:

[0042] (1) Take the wastewater to be treated, sulfur autotrophic denitrification sludge and pyrite with a particle size of 2-3 mm and mix them thoroughly so that the initial sludge concentration (MLSS) in the reactor is about 4000 mg / L. After 3 days of reflux culture in the peristaltic pump, microorganisms will attach to the surface of the pyrite to perform preliminary denitrification of the wastewater.

[0043] (2) Starting from day 4, the wastewater to be treated and a predetermined amount of seawater were mixed and introduced into the reactor in an upward continuous flow manner. The reactor was operated in a continuous flow manner at room temperature, and the flow rate was adjusted to make the hydraulic retention time 8 hours to further denitrify the wastewater. The water quality after the wastewater to be treated and the predetermined amount of seawater were mixed and introduced into the reactor in an upward continuous flow manner was as follows: nitrate nitrogen concentration of 18-22 mg N / L, phosphate concentration of 1.8-2.2 mg P / L, and COD concentration of 38-42 mg / L (corresponding to C / N=2). On day 10 of reactor operation, the COD concentration was adjusted to 58-62 mg / L (corresponding to C / N=3), and the reactor was operated for a total of 21 days.

[0044] This embodiment is divided into 5 groups of seawater ratios. The salinity of the wastewater to be treated and the seawater after mixing in step (2) is 0, 500, 1000, 5000, and 10000 mg / L, respectively, so as to compare the denitrification effect of wastewater with five different influent salinities (with seawater added in different proportions).

[0045] The reactor efficiency is calculated as follows:

[0046] Starting after the addition of seawater, water samples were taken daily from both the inlet and outlet, and NO3 was determined using ultraviolet spectrophotometry. - The nitrate nitrogen removal rate and removal percentage are calculated using the following formula:

[0047] Nitrate nitrogen removal rate (%) = (Influent nitrate nitrogen concentration - Effluent nitrate nitrogen concentration) / Influent nitrate nitrogen concentration * 100.

[0048] Nitrate nitrogen removal rate (mg N / (L·h)) -1 = (Influent nitrate nitrogen concentration - Effluent nitrate nitrogen concentration) / Hydraulic retention time.

[0049] The nitrate nitrogen concentration is expressed in mg / L, and the running time is expressed in h.

[0050] Calculate the increase in nitrate nitrogen removal rate for the experimental group and the control group (without seawater) respectively:

[0051] Increase in nitrate nitrogen removal rate (%) = (Nitrate nitrogen removal rate of experimental group - Nitrate nitrogen removal rate of blank group) / Nitrate nitrogen removal rate of blank group * 100.

[0052] like Figure 1 , 2As shown in Figure 3, compared to the control group (no seawater addition), the average nitrate nitrogen removal rates of reactors with salinities of 500, 1000, 5000, and 10000 mg / L increased by 11.7%, 9.5%, 35.8%, and 60.3%, respectively, and the average nitrate nitrogen removal rates increased by 7.0%, 3.9%, 31.2%, and 53.3%, respectively. This indicates that the addition of seawater successfully improved the nitrogen removal efficiency of the pyrite co-culture denitrification system. Furthermore, compared to the control group (salinity of 500, 1000, 5000, and 10000 mg / L), the average nitrate nitrogen removal rates of the reactors increased by 11.7%, 9.5%, 35.8%, and 60.3%, respectively. At a salinity of 00 mg / L, salinities of 5000 and 10000 mg / L show even better improvement (with influent salinities of 5 and 10 g / L, the average nitrate nitrogen removal rate is significantly improved compared to when no seawater is added, increasing by 35.8% and 60.3% respectively, and the average nitrate nitrogen removal rate increases from 44.3% without seawater addition to 58.1% and 67.9% respectively, with the average nitrate nitrogen removal rate increasing by 31.2% and 53.3% respectively) and lower operating costs.

[0053] The above description provides a further detailed explanation of the present invention in conjunction with specific / preferred embodiments, and it should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various substitutions or modifications can be made to these described embodiments without departing from the concept of the present invention, and all such substitutions or modifications should be considered within the scope of protection of the present invention. In the description of this specification, the reference to terms such as "an embodiment," "some embodiments," "preferred embodiment," "example," "specific example," or "some examples," etc., indicates that the specific features, structures, materials, or characteristics described in connection with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any suitable manner in one or more embodiments or examples. Without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification and the features of different embodiments or examples. Although the embodiments of the present invention and their advantages have been described in detail, it should be understood that various changes, substitutions, and modifications can be made herein without departing from the scope of protection of the patent application.

Claims

1. A method for deep nitrogen removal from wastewater based on a pyrite-based co-culture denitrification system, characterized in that, Includes the following steps: (1) The wastewater to be treated, the sulfur autotrophic denitrification sludge and pyrite are thoroughly mixed and filled into the reactor, and the reactor is refluxed and cultured for a predetermined time so that a film gradually forms on the surface of the pyrite to perform preliminary denitrification of the wastewater. (2) The wastewater to be treated and a predetermined amount of NaCl-containing liquid are mixed and fed into the reactor in an upward continuous flow manner, and the reactor is operated to further denitrify the wastewater; After the wastewater to be treated is mixed with a predetermined amount of NaCl-containing liquid, the salinity is in the range of 5-10 g / L. The addition of NaCl-containing liquid promotes the interaction between microorganisms in the pyrite-mediated denitrification system, which helps the microbial community form a more compact cluster structure, reduces the formation of modular networks, ensures the stability of the microbial community structure in the pyrite-mediated denitrification system, and improves the nitrogen removal efficiency. On the other hand, the addition of NaCl-containing liquid accelerates the precipitation rate of sulfur ions and ferrous ions from pyrite to a certain extent, constructs a more extensive electron transfer channel between pyrite and denitrifying functional bacteria, thereby improving the electron transfer efficiency of pyrite and ultimately accelerating the removal rate of nitrate nitrogen.

2. The method as described in claim 1, characterized in that: In step (1), the initial mixed liquor suspended solids concentration of the sulfur autotrophic denitrification sludge in the reactor is in the range of 3750~4500 mg / L.

3. The method as described in claim 1, characterized in that: In step (1), the particle size of pyrite is 2~3 mm.

4. The method as described in claim 1, characterized in that: The reactor is an upflow fixed-bed reactor for pyrite.

5. The method as described in claim 1, characterized in that: In step (2), the hydraulic retention time of the wastewater is 8 ± 0.5 h.

6. The method as described in claim 1, characterized in that: In step (1), the sulfur autotrophic denitrification sludge is obtained by the following steps: 2.160~2.165 g / L KNO3, 0.260~0.265 g / L KH2PO4, 0.910~0.915 g / L NaHCO3 and 4.515~4.520 g / L Na2S2O3·5H2O are added to the sludge originating from the oxidation ditch, and the sludge is acclimatized and cultured at room temperature. When the nitrate nitrogen removal rate is stable at more than 70%, the sulfur autotrophic denitrification sludge is considered to have been successfully cultured.

7. The method as described in claim 1, characterized in that: The internal reflux culture time in step (1) is 3-5 days.

8. The method as described in claim 1, characterized in that: The NaCl-containing liquid is seawater; the wastewater to be treated is the biochemical effluent from a municipal wastewater treatment plant.

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