A sulfur autotrophic denitrification method without sulfide emissions

Abstract

The present invention provides a sulfur autotrophic denitrification method without sulfide emissions, relating to the field of wastewater biological treatment technology. The method comprises the following steps: adding a reducing sulfur source in a sulfur autotrophic denitrification reactor, inoculating activated sludge, acclimation, and entering the early sulfur-type autotrophic denitrification stage; controlling the reaction pH to be 6.5-8.0, and the hydraulic retention time to be 1-12h, the reducing sulfur source is converted into sludge surface or internal biological sulfur; the biological sulfur concentration in the sludge reaches 12-23mg S / g SS, stops adding the reducing sulfur source, and enters the autonomous autotrophic denitrification stage; controlling the reaction pH to be 6.9-8.0, and the hydraulic retention time to be 3-23h, realizes efficient denitrification. The method does not require an external sulfur source and can withstand different nitrogen concentrations; it is necessary to add organic matter, reduce denitrification operating costs, and realize efficient autotrophic denitrification; no sulfide is produced, reducing environmental hazards.

Description

Technical Field

[0001] The invention relates to the technical field of wastewater biological treatment, and in particular to a sulfur autotrophic denitrification method free of sulfide emissions. Background Art

[0002] On the one hand, due to the excessive use of agricultural nitrogen fertilizers, nitrogen accumulates in the form of nitrates in surface soils. Rainfall and irrigation also drive the leaching of nitrates from surface water, causing groundwater pollution. Nitrate contamination of groundwater is a widespread environmental problem. On the other hand, with the rapid development of industrial and agricultural technologies, wastewater discharge has increased, and large amounts of inorganic and organic wastewater rich in sulfides and nitrates are being generated, such as leachate from landfills, paper mills, gas plants, pharmaceutical factories, and other industrial wastewater. These wastewaters not only cause serious environmental pollution but also pose potential risks to human health. Therefore, nitrogen removal in wastewater treatment is a critical process.

[0003] Traditional heterotrophic denitrification technology can effectively treat nitrate-containing wastewater, but it requires the addition of organic carbon, such as methanol, ethanol, and acetic acid, which will greatly increase the treatment cost. At the same time, when excessive organic carbon sources are added, the system cannot degrade organic matter, resulting in the effluent COD not meeting the standard, causing secondary pollution.

[0004] Sulfur autotrophic denitrification is a new denitrification technology that uses low-valent sulfur instead of carbon source as an electron donor to achieve denitrification through autotrophic denitrification. It has become a hot topic in the denitrification field due to its advantages such as no need for external carbon source, low cost and no secondary pollution.

[0005] Sulfur autotrophic denitrification is a process that uses sulfur as an electron donor and nitrate as an electron acceptor, and finally converts them into sulfate and nitrogen gas respectively. Since sulfur is abundant and cheap in nature, and the process is a chemoautotrophic reaction with low sludge yield, sulfur autotrophic denitrification is a relatively economical denitrification method. At present, most sulfur autotrophic denitrification reactions remain in the reaction with elemental sulfur as the sulfur source. Since the elemental sulfur in the elemental sulfur denitrification process is not released excessively, it can form an adaptive anti-fluctuation ability to the water quality fluctuation of the influent, ensuring that the nitrate concentration and COD concentration of the effluent will not exceed the standard. Because the entire reaction process is a solid-liquid reaction, it only unfolds on the surface of the sulfur element. Even if the sulfur element has a large specific surface area, the reaction rate is far lower than the ion reaction in the solution. The rate is low, which poses a major problem in industrial application.

[0006] Patent CN 114409096 A discloses a method for achieving efficient deep denitrification of wastewater by coupling elemental sulfur disproportionation with sulfur autotrophic denitrification, comprising the following steps: inoculating and enriching sulfur disproportionating bacteria and sulfur-oxidizing denitrifying bacteria in a sulfur autotrophic denitrification bioreactor filled with sulfur filler; the pH of the sulfur autotrophic denitrification reactor is 6-9.5. The method of the present invention maintains the symbiotic and cooperative relationship between sulfur disproportionating bacteria and sulfur-oxidizing denitrifying bacteria by controlling the reaction conditions, so that the elemental sulfur in the sulfur autotrophic denitrification reactor is continuously converted into Sn through the sulfur disproportionation reaction. 2 , and Sn 2 Acting as an electron mediator, it participates in and accelerates the sulfur autotrophic denitrification process, significantly increasing the bioavailability of elemental sulfur. This establishes a polysulfide-mediated sulfur autotrophic denitrification (PiSADN) process without the addition of sulfide or carbon sources, achieving efficient, low-cost, and deep nitrogen removal. However, the resulting data indicates that sulfide is still produced, and the use of a fluidized bed for laying elemental sulfur results in a high sulfur consumption.

[0007] Based on this, the present invention provides a sulfur autotrophic denitrification method that eliminates sulfide emissions. This technology is divided into an initial sulfur autotrophic denitrification stage and an autonomous autotrophic denitrification stage. After adding a reducing sulfur source to carry out the initial sulfur-based autotrophic denitrification, the addition of the reducing sulfur source can be stopped to achieve autonomous autotrophic denitrification. The autotrophic denitrification sludge can achieve long-term autonomous autotrophic denitrification by leveraging the biogenic sulfur accumulated within or on the sludge during the initial sulfur-based autotrophic denitrification. Summary of the Invention

[0008] The present invention aims to provide a sulfur autotrophic denitrification method that eliminates sulfide emissions. The method comprises an initial sulfur autotrophic denitrification stage and an autonomous autotrophic denitrification stage. After the initial sulfur-based autotrophic denitrification is initiated by adding a reducing sulfur source, the addition of the reducing sulfur source can be stopped to allow autonomous autotrophic denitrification. The autotrophic denitrification sludge utilizes biogenic sulfur accumulated within or on the sludge during the initial sulfur-based autotrophic denitrification to achieve efficient autonomous autotrophic denitrification.

[0009] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0010] A sulfur autotrophic denitrification method without sulfide emissions comprises the following steps:

[0011] 1) Adding a reducing sulfur source to the sulfur autotrophic denitrification reactor, inoculating activated sludge, and acclimating the reactor to enter the early sulfur autotrophic denitrification stage;

[0012] 2) Controlling the reaction pH to 6.5-8.0 and the hydraulic retention time to 1-12 hours to convert the reduced sulfur source into biological sulfur on the surface or inside the sludge;

[0013] 3) When the biosulfur concentration in the sludge reaches 12-23 mg S / g SS, the addition of the reducing sulfur source is stopped and the process enters the autonomous autotrophic denitrification stage;

[0014] 4) Control the reaction pH to 6.9-8.0 and the hydraulic retention time to 3-23h to achieve efficient denitrification.

[0015] Preferably, the MLVSS of the activated sludge in step 1) is 5-11 g / L, more preferably, 8.2 g / L.

[0016] Preferably, the dominant bacterial species in the activated sludge in step 1) is Sulfurovum, and its relative abundance is higher than 30%; more preferably, its relative abundance is 85%.

[0017] Preferably, the reducing sulfur source in step 1) is selected from at least one of sulfide and thiosulfate, and the concentration is 60-700 mg S / L; further preferably, the reducing sulfur source in step 1) is selected from sulfide, and the concentration is 100-500 mg S / L; further preferably, it is 120-480 mg S / L.

[0018] Preferably, the denitrification substrate in the early sulfur-type autotrophic denitrification stage of step 1) is selected from at least one of nitrate and nitrite, with a concentration of 10-200 mg N / L; further preferably, it is selected from nitrate, with a concentration of 15-150 mg N / L; further preferably, the concentration is 21-132 mg N / L.

[0019] Preferably, in step 1), the ratio of sulfur to nitrogen in the nitrate is 2.5-3.0, and the ratio of sulfur to nitrogen in the nitrite is 1.5-2.9.

[0020] Preferably, the reaction pH in step 2) is 6.8-7.6, and the hydraulic retention time is 2-11 h; further preferably, the reaction pH in step 2) is 7.0-7.5, and the hydraulic retention time is 10 h.

[0021] Preferably, the biosulfur concentration in the sludge in step 3) reaches 15-20 mg S / g SS; more preferably, it is 15 mg S / g SS.

[0022] Preferably, the denitrification substrate in the autonomous autotrophic denitrification stage in step 3) is selected from at least one of nitrate and nitrite, with a concentration of 10-200 mg N / L; more preferably, it is selected from nitrite, with a concentration of 20-140 mg N / L.

[0023] Preferably, in step 3), the autonomous autotrophic denitrification stage promotes mixing of the influent and the sludge by stirring or circulating the reaction solution; further preferably, in step 3), the autonomous autotrophic denitrification stage promotes mixing of the influent and the sludge by circulating the reaction solution.

[0024] Preferably, the stirring rate in step 3) is 40-160 r / min, and the internal circulation ratio of the reaction liquid internal circulation is 1-25; further preferably, the stirring rate in step 3) is 120 r / min, and the internal circulation ratio of the reaction liquid internal circulation is 20.

[0025] Preferably, the reaction pH in step 4) is 7.0-7.6, and the hydraulic retention time is 5-25 h; further preferably, the reaction pH in step 4) is 7.0-7.5, and the hydraulic retention time is 20 h.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. No external sulfur source is required, it can withstand different nitrogen concentrations and achieve autonomous and efficient denitrification.

[0028] 2. No need to add organic matter, reducing denitrification operating costs and achieving efficient autotrophic denitrification.

[0029] 3. No sulfide is produced, reducing environmental harm. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is the performance of sulfur-type autotrophic denitrification in the early stage;

[0031] Figure 2 is the elemental sulfur concentration in the mud phase during the early sulfur-type autotrophic denitrification stage;

[0032] Figure 3 is the denitrification performance at the autonomous autotrophic denitrification stage under low concentration;

[0033] Figure 4 is the relationship between denitrification performance and sulfate production in the autonomous autotrophic denitrification stage at low concentrations;

[0034] Figure 5 is the denitrification performance in the autonomous autotrophic denitrification stage under high concentration;

[0035] Figure 6 This is the relationship between denitrification performance and sulfate production in the autonomous autotrophic denitrification stage under high concentration. DETAILED DESCRIPTION

[0036] In order to make the technical means, creative features, purpose and effect of the present invention easy to understand, the present invention is further illustrated below in conjunction with specific embodiment, but the following embodiment is only a preferred embodiment of the present invention, not all. Based on the embodiment in the embodiment, other embodiments obtained by those skilled in the art without making creative work all fall within the scope of protection of the present invention. It is worth noting that the raw materials used in the present invention are all common commercial products, and their sources are not specifically limited. The technology and scientific terms used in the embodiment have the meanings commonly understood by those of ordinary skill in the art to which the present invention belongs.

[0037] The invention discloses a sulfur autotrophic denitrification method without sulfide emissions, which adopts a CSTR reactor configuration.

[0038] Implementation Method

[0039] In the initial sulfur-based autotrophic denitrification process, sulfide can be used as a reducing sulfur source at a concentration of 120-500 mg S / L; nitrate can be used as a denitrification substrate at a concentration of 21-132 mg N / L. The preferred sulfur-to-nitrogen ratio is controlled between 2.6 and 2.5. No organic carbon source is required, the reaction pH is controlled between 7.0 and 7.5, and the hydraulic retention time is controlled within 10 hours. The initial sulfur-based autotrophic denitrification process requires an MLVSS of 8.2 g / L in autotrophic denitrification sludge, with the dominant bacterial species being Sulfurovum at a relative abundance of 85%. Once the biogenic sulfur concentration in the autotrophic denitrification sludge reaches 15 mg S / g SS, the addition of a reducing sulfur source can be discontinued, and the process enters the autonomous autotrophic denitrification stage. During the autonomous autotrophic denitrification phase, nitrite was used as the denitrification substrate at a concentration of 20-140 mg N / L. No external organic carbon source was required, the reaction pH was controlled between 7.0 and 7.5, the hydraulic retention time was controlled at 20 hours, and internal circulation of the reaction solution was employed to promote mixing of the influent with the bio-sulfur-containing sludge. The internal circulation ratio was 20:1, achieving highly efficient denitrification with a denitrification removal rate of 100%. Sulfide and organic matter were not detected in the influent, effluent, or during the reaction process during the autonomous autotrophic denitrification phase, indicating that the autonomous autotrophic denitrification process relies on bio-sulfur accumulated during the previous sulfur-based autotrophic denitrification process.

[0040] Example 1

[0041] Early sulfur-type autotrophic denitrification performance of autotrophic denitrification technology without the need for an external sulfur source

[0042] When the influent sulfide concentration increased from 120 mg S / L to 480 mg S / L, the effluent sulfide concentration ranged from 1.00 to 17.69 mg S / L, and the sulfide removal efficiency fluctuated between 95.9% and 99.28%, indicating good desulfurization performance. Simultaneously, the effluent nitrate concentration ranged from 1.21 to 3.78 mg N / L, with a nitrate removal efficiency between 94.24% and 97.46%. The initial sulfur-based autotrophic denitrification stage achieved highly efficient denitrification performance. The biogenic sulfur content in the mud phase increased with increasing influent sulfide concentration, from 2.11 mg S / g SS to 46.07 mg S / g SS. This indicates that the initial sulfur-based autotrophic denitrification stage effectively accumulated biogenic sulfur, providing a sulfur source for subsequent autonomous autotrophic denitrification.

[0043] Example 2

[0044] Autonomous autotrophic denitrification performance of autotrophic denitrification technology without the need for an external sulfur source

[0045] When no external sulfur source is added to the influent, only 32.43 mg N / L nitrite is provided, the reaction pH is controlled between 7.0-7.5, the hydraulic retention time is controlled at 20 hours, and the reaction liquid is internally circulated to promote the mixing of the influent and the biological sulfur-containing sludge. The internal circulation ratio is 20, and the nitrite removal rate is maintained at more than 80%. At the same time, the sulfate concentration increases with the increase of the influent nitrite concentration, and no sulfide is produced. It can operate stably for 44 days. This process can achieve long-term autonomous autotrophic denitrification.

[0046] Example 3

[0047] Autonomous autotrophic denitrification performance under different nitrogen concentrations

[0048] When no external sulfur source is added to the influent, the influent nitrite concentration is gradually increased from 47.47 mg N / L to 142.5 mg N / L, the reaction pH is controlled between 7.0-7.5, the hydraulic retention time is controlled at 20 hours, and the reaction liquid is internally circulated to promote the mixing of the influent and the biological sulfur-containing sludge. The internal circulation ratio is 20, and the nitrite removal rate is maintained at more than 99%. At the same time, the sulfate concentration increases with the increase of the influent nitrite concentration, and no sulfide is produced. It can operate stably for 35 days. The process can withstand autonomous autotrophic denitrification with different nitrogen loads.

[0049] The above case study explored the realization of autotrophic denitrification without an external sulfur source, and achieved better denitrification by controlling the influent pH and internal circulation. Therefore, the present invention provides a good guide for the cyclic conversion between elemental sulfur and sulfate to achieve denitrification, and is of great significance to the research on autotrophic denitrification.

[0050] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, rather than to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions of the technical solution of the present invention by ordinary technicians in this field do not deviate from the essence and scope of the technical solution of the present invention.

Claims

1. A sulfur autotrophic denitrification method without sulfide emissions, characterized in that: The following steps are involved: 1) adding a reducing sulfur source to a sulfur autotrophic denitrification reactor, inoculating activated sludge, acclimating, and entering an early sulfur-type autotrophic denitrification stage; the activated sludge has an MLVSS of 5-11 g / L, and the dominant bacterial species in the activated sludge is Sulfurovum with a relative abundance greater than 30%; the reducing sulfur source is selected from sulfide at a concentration of 120-500 mg S / L; the denitrification substrate in the early sulfur-type autotrophic denitrification stage is selected from nitrate at a concentration of 15-150 mg N / L; and the sulfur to nitrogen ratio of the sulfur in the sulfide to the nitrogen in the nitrate is 2.5-3.0; 2) Controlling the reaction pH to 6.5-8.0 and the hydraulic retention time to 1-12 hours to convert the reduced sulfur source into biological sulfur on the surface or inside the sludge; 3) When the biosulfur concentration in the sludge reaches 12-23 mg S / g SS, the addition of the reducing sulfur source is stopped and the process enters the autonomous autotrophic denitrification stage; the denitrification substrate in the autonomous autotrophic denitrification stage is selected from nitrite at a concentration of 20-140 mg N / L; 4) Control the reaction pH to 6.9-8.0 and the hydraulic retention time to 3-23h to achieve efficient denitrification.

2. The sulfur autotrophic denitrification method without sulfide emissions according to claim 1, characterized in that: Step 2) The reaction pH is 6.8-7.6, and the hydraulic retention time is 2-11 hours.

3. The sulfur autotrophic denitrification method without sulfide emissions according to claim 1, characterized in that: Step 3) The biosulfur concentration in the sludge reaches 15-20 mg S / g SS.

4. The sulfur autotrophic denitrification method without sulfide emissions according to claim 1, characterized in that: Step 3) The autonomous autotrophic denitrification stage promotes mixing of the influent and the sludge by stirring or circulating the reaction solution; the stirring rate is 40-160 r / min, and the internal circulation ratio of the reaction solution is 1-25.

5. The sulfur autotrophic denitrification method without sulfide emissions according to claim 1, characterized in that: Step 4) The reaction pH is 7.0-7.6, and the hydraulic retention time is 5-25h.

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