A device and method for sulfur-manganese composite autotrophic denitrification at low temperature

Abstract

The application belongs to the technical field of denitrification, and particularly relates to a sulfur-manganese composite autotrophic denitrification device and a denitrification method at low temperature. The sulfur-manganese composite autotrophic denitrification device at low temperature comprises a main reactor, a water inlet tank and a constant-temperature water bath kettle. The main reactor has an inner cavity, and the inner cavity is sequentially provided with a gravel layer, a sulfur-rhodochrosite layer and a quartz sand layer from bottom to top. Four sampling ports are arranged on the side wall of the main reactor from top to bottom, and each sampling port is in communication with the inner cavity. The water outlet of the water inlet tank is connected with a water inlet pump, the water inlet pump is in communication with the inner cavity, one end of the constant-temperature water bath kettle is communicated with the top of the main reactor through a pipeline, the other end of the constant-temperature water bath kettle is connected with a water bath water inlet pump, and the water bath water inlet pump is communicated with the main reactor.

Description

Technical Field

[0001] This invention belongs to the field of denitrification technology, specifically relating to a low-temperature sulfur-manganese composite autotrophic denitrification device and denitrification method. Background Technology

[0002] Currently, most urban sewage discharges comply with the Class A discharge standard of the "Urban Wastewater Treatment Plant Pollutant Discharge Standard (GB18918-2002)," requiring a total nitrogen (TN) concentration not to exceed 15 mg / L. However, the "Surface Water Environmental Quality Standard (GB3838-2002)" requires a TN concentration (for lakes and reservoirs) of no more than 1.5 mg / L for Class V water. High nitrogen content easily leads to eutrophication, thus necessitating deep denitrification of sewage effluent. However, the C / N ratio of effluent from urban sewage treatment plants in China is generally less than 2, representing typical low C / N ratio sewage. A low C / N ratio leads to insufficient carbon sources for microorganisms, causing them to enter endogenous respiration, resulting in a decrease in activated sludge concentration and limiting the denitrification effect. Therefore, deep denitrification under low C / N ratio conditions is one of the hot and challenging research topics in the water treatment field. To achieve NO3... − -N, NO2 − The effective removal of nitrogen-containing pollutants such as -N, and the autotrophic denitrification technology that does not require the addition of external organic carbon sources, is gradually gaining attention. Autotrophic denitrification technology utilizes CO3... 2- HCO3 - Sulfur and its compounds, such as elemental sulfur (S), serve as inorganic carbon sources for cell synthesis. 0 ), sulfites (SO3) 2− ), Fe 2+ ), and manganese ions (Mn 2+ Reducing substances such as electron donors are used for autotrophic denitrification.

[0003] Sulfur autotrophic denitrification (SAD) is a key research area in autotrophic denitrification due to its economical operation and high denitrification efficiency. Sulfur autotrophic denitrification refers to the process by which sulfur-oxidizing bacteria oxidize reduced sulfur (S₂O₃) under anoxic or anaerobic conditions. 0 S 2- SO3 2- S2O3 2- (and FeS2, etc.) to obtain energy, and NO3 − The process of reducing -N to nitrogen gas. However, sulfur autotrophic denitrification produces H2. + It can easily cause a decrease in the pH value of water, SO4 2- The yield exceeds the limit of 250 mg / L in water.

[0004] To further improve the nitrogen removal efficiency of autotrophic denitrification technology, many scholars have been conducting continuous research on autotrophic denitrification technology constructed with composite substrates. Sahinkaya et al. constructed a sulfur-limestone autotrophic denitrification (SLAD) device by combining elemental sulfur with limestone. This involves configuring sulfur and limestone layers in a reactor to form a sulfur-limestone denitrification system, in which elemental sulfur acts as an electron donor for NO3. − The reduction of -N occurs as limestone continuously dissolves, acting as a pH buffer and inorganic carbon source. The reaction is as follows: CaCO3 + H+ + → Ca 2+ +HCO3 - There are also SLAD systems constructed in reactors, such as... Figure 2 The aforementioned system combines ease of use, high efficiency, and convenience, and is widely used in both off-site and on-site wastewater treatment. However, the limestone in the reactor cannot provide additional electrons for denitrification; the area it occupies forms a passivation zone that hinders further nitrogen removal and simultaneously triggers SO42-. 2- The problem of overproduction. On the other hand, although limestone is the most commonly used low-cost source of alkaline substances, Ca... 2+ The release of phosphorus increases the hardness of the treated water and induces phosphorus precipitation, which may limit bacterial growth. Studies have found that under neutral pH conditions, siderite (FeCO3) can... T. denitrificans NO3 is reduced by sulfur-autotrophic denitrifying bacteria. − -N is N2. Therefore, researchers introduced siderite into a sulfur-driven autotrophic denitrification reactor to construct a sulfur-siderite autotrophic denitrification (SSAD) system. In the reactor, both elemental sulfur and siderite can serve as electron donors for denitrification, while siderite acts as a pH buffer and provides an inorganic carbon source. Compared to the SLAD system, the SSAD system... Figure 3 As shown, this system retains the high-efficiency nitrogen removal characteristics of the SLAD system, which is not limited by carbon sources, while also utilizing Fe... 2+ Providing additional electrons for denitrification reduces SO4. 2- The higher yield makes it superior to SLAD systems when treating wastewater with low C / N ratios. Although dissolved Fe in siderite... 2+ It can serve as an electron donor for denitrification, but Fe 2+ It may be bio-oxidized into precipitates such as hexazonite (g-FeOOH), Fe3O4, and Fe(OH)3. These precipitates coat the packing material and bacterial surfaces, hindering electron transfer between solids and liquids, ultimately limiting denitrification. Studies have also shown that Mn... 2+Substances such as manganese autotrophic denitrification can provide electrons to drive denitrification, but single manganese autotrophic denitrification technology is easily limited by slow bacterial growth and low nitrogen removal efficiency. Temperature changes profoundly affect the metabolic activity of microorganisms, leading to a decrease in the nitrogen removal rate and preventing the effluent from meeting nitrate nitrogen discharge standards. Groundwater temperatures are often below 10℃, even reaching 3℃~4℃. Wastewater treatment currently mainly employs biological methods, the key to which lies in the growth and metabolic activity of functional microorganisms, which directly affects the treatment efficiency of the wastewater treatment system. Temperature, as a crucial ecological factor for microbial growth and metabolic activity, significantly influences microbial activity. Therefore, the application of biological denitrification technology at low temperatures faces serious challenges.

[0005] Thiobacillus denitrifyingis is sensitive to temperature changes. Studies have shown that its optimal temperature range is 20℃~35℃, and excessively high temperatures can lead to near-inactivation of the microorganisms. Li Yingying investigated the effect of temperature on the operation of a sulfur autotrophic denitrification system. The results showed that when the system temperature fluctuated within the range of approximately 6.4℃~19.2℃, the lower the temperature, the worse the denitrification effect. When the HRT was 6h and the temperature was around 10℃, the total nitrogen removal rate was only 53.7%. Zheng Shaozhi constructed four packed bed reactors using volcanic rock, volcanic rock / iron-carbon packing, volcanic rock / sulfur, and volcanic rock / iron-carbon packing / sulfur as packing materials, respectively. When the system temperature decreased from 30℃ to 15℃, NO3... − The average removal rate of NO2 decreased from 91.5% to 41.5%, and even NO2 was detected. − -N accumulation phenomenon.

[0006] To improve the nitrogen removal performance of autotrophic denitrification systems under low-temperature conditions, one can start with the composite autotrophic denitrification process. Sulfur-autotrophic denitrification systems contain a certain amount of manganese-autotrophic denitrifying bacteria. Studies have shown that microorganisms inhabiting metal nodule deposits face challenges from extreme environmental conditions such as heavy metals, oligotrophic environments, and low temperatures. Gammaproteobacteria As a dominant group among deep-sea manganese nodules, manganese redox bacteria play a crucial role in the manganese cycle within deep-sea manganese nodules. Therefore, manganese redox bacteria may exhibit some tolerance to low temperatures. To date, proven manganese ore reserves exceed 1.8 billion tons, indicating abundant reserves. Natural rhodochrosite, with its MnCO3-based solid matrix, is inexpensive. However, rhodochrosite has low utilization rates, easily leading to resource waste. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention provides a low-temperature sulfur-manganese composite autotrophic denitrification denitrification device and method, which can still achieve good denitrification effects at low temperatures of 5℃~10℃.

[0008] To achieve the above objectives, the technical solution of the present invention is as follows.

[0009] A low-temperature sulfur-manganese composite autotrophic denitrification denitrification device includes a main reactor, an inlet tank, and a constant temperature water bath. The main reactor has an inner cavity in which a gravel layer, a sulfur-rhodochrosite layer, and a quartz sand layer are arranged sequentially from bottom to top. A first sampling port, a second sampling port, a third sampling port, and a fourth sampling port are provided on the side wall of the main reactor from top to bottom. The first sampling port is connected to the top of the quartz sand layer; the second sampling port is connected to the junction of the gravel layer and the sulfur-rhodochrosite layer; and the third and fourth sampling ports are both connected to the sulfur-rhodochrosite layer. The outlet of the water inlet tank is connected to a water inlet pump, which is connected to the bottom of the inner cavity; One end of the constant temperature water bath is connected to the top of the main reactor via a pipe, and the other end of the constant temperature water bath is connected to a water bath inlet pump, which is connected to the main reactor.

[0010] In another preferred embodiment, the height ratio of the gravel layer, the sulfur-rhodochrosite layer, and the quartz sand layer is 3~4:45:15.

[0011] In another preferred embodiment, the porosity of the sulfur-rhodochrosite layer is 40% to 50%.

[0012] In another preferred embodiment, the sulfur-rhodochrosite layer is obtained by mixing sulfur and rhodochrosite in an equal volume ratio.

[0013] In another preferred embodiment, the sulfur and the rhodochrosite both have a particle size of 2 mm to 5 mm.

[0014] In another preferred embodiment, the bottom of the main reactor is provided with a backwash port, and the top of the main reactor is provided with a water outlet.

[0015] In another preferred embodiment, a porous baffle is provided below the gravel layer, and the lower layer of the porous baffle is a water distribution area.

[0016] In another preferred embodiment, the backwash port is connected to the water distribution area; the water inlet pump is connected to the water distribution area.

[0017] The second aspect of this invention provides a method for sulfur-manganese composite autotrophic denitrification using the aforementioned low-temperature sulfur-manganese composite autotrophic denitrification device, the specific process of which is as follows: Sludge from the wastewater treatment plant is sieved through a 100-mesh screen and poured into the main reactor. The influent pump is started to pump the synthetic wastewater from the influent tank into the distribution area. The wastewater then passes through a porous filter plate into the gravel layer and into the sulfur-rhodochrosite layer. Once the synthetic wastewater fills the entire main reactor, the pumping of synthetic wastewater is stopped. The synthetic wastewater and sludge undergo an autotrophic denitrification reaction in the sulfur-rhodochrosite layer to acclimate the sludge. During the acclimatization process, the water bath influent pump is started to pump water from the constant temperature water bath into the main reactor to maintain the temperature of the inner cavity. After acclimatization, the water bath inlet pump is turned off, and impurities are filtered through the quartz sand layer. The filtered wastewater is discharged through the outlet, and the nitrogen gas generated in the autotrophic denitrification process is discharged through the exhaust port at the top of the reactor.

[0018] In another preferred embodiment, each liter of the synthetic wastewater contains 0.144 g / L KNO3, 0.004 g / L KH2PO4, 0.1 g / L MgCl2·6H2O, 0.01 g / L CaCl2·2H2O, and 1 mL / L Wolfe trace element solution; each liter of the Wolfe trace element solution contains 0.3 g / L MgSO4·7H2O, 0.5 g / L MnSO4·4H2O, 0.1 g / L FeSO4·7H2O, 0.1 g / L CoCl2·6H2O, 0.1 g / L ZnSO4·7H2O, 0.01 g / L CuSO4·5H2O, and 0.01 g / L Na2MoO4·2H2O. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the low-temperature sulfur-manganese composite autotrophic denitrification device of the present invention; L1 has a length of 2cm~5cm, L2 has a length of 5cm~20cm, L3 has a length of 20cm~35cm, L4 has a length of 35cm~50cm, and L5 has a length of 50cm~65cm.

[0020] Figure 2 This is a schematic diagram of the reaction principle of the SLAD system.

[0021] Figure 3 This is a schematic diagram of the reaction principle of the SSAD system.

[0022] Figure 4 The changes in water quality indicators within the sulfur-manganese composite system at different stages; where (a) represents the change in TN, and (b) represents the change in NO3. − -N index change, (c)NO2 − -N indicator changes.

[0023] Figure 5 Changes in water quality parameters along the path within the SD, MCD, and SMCD systems: (a) TN, (b) NO3. −-N, (c) is NO2 − -N, (d) is NH4 + -N; SD represents sulfur denitrification system, MCD represents rhodochrosite denitrification system, and SMCD represents sulfur-rhodochrosite system.

[0024] Figure 6 SO4 for SD and SMCD systems 2- Actual output / TN removal.

[0025] Figure 7 Mn in MCD and SMCD systems 2+ Dissolution amount.

[0026] Figure 8 Analysis of the contribution rate of SAD and MAD reaction.

[0027] Figure 9 The particle size distribution of sludge in different systems.

[0028] Figure 10 The denitrifying enzyme activities of different systems are shown; (a) represents nitrate reductase and (b) represents nitrite reductase.

[0029] Figure 11 Images of live / dead cells stained under a confocal microscope: (a) is SD, (b) is MCD, and (c) is SMCD system.

[0030] Figure descriptions: 1-Main reactor, 11-Inner cavity, 12-Outlet, 13-Backwash port, 14-First sampling port, 15-Second sampling port, 16-Third sampling port, 17-Fourth sampling port, 18-Porous baffle, 2-Inlet tank, 3-Inlet pump, 4-Water bath inlet pump, 5-Constant temperature water bath. Detailed Implementation

[0031] The present invention will be described in detail below with reference to specific embodiments, but should not be construed as limiting the present invention. Unless otherwise specified, the technical means used in the following embodiments are conventional means well known to those skilled in the art, and the materials, reagents, etc. used in the following embodiments can be obtained commercially unless otherwise specified.

[0032] This invention introduces rhodochrosite into the SAD process in the main reactor to construct a sulfur-rhodochrosite autotrophic denitrification system. Rhodochrosite acts as an alkalinity buffer and provides an inorganic carbon source. The reaction process is shown in Equation 2. The H2 produced by the SAD reaction... + Reacting with rhodochrosite, the rhodochrosite dissolves, producing Mn(II), which provides additional electrons for denitrification, driving the manganese autotrophic denitrification (MAD) reaction. The reaction process is shown in Equation 3, while simultaneously reducing SO4 levels. 2- Production. The MAD reaction will also produce H again.+ This process promotes the self-dissolution of rhodochrosite and accelerates the rate at which rhodochrosite donates electrons. Simultaneously, the generated manganese oxides can enhance the removal of organic matter and improve its bioavailability, while the manganese oxides are then reduced and reused. Furthermore, trace amounts of Ca, Mg, Fe, and Zn in the ore can provide certain amounts of micronutrients for bacterial growth. Therefore, coupling sulfur with rhodochrosite at low temperatures of 5℃~10℃, utilizing a sulfur-manganese composite electron donor, may enhance the nitrogen removal capacity of the denitrification system, aiming to provide technical support for maintaining stable nitrogen removal performance in autotrophic denitrification systems at low temperatures.

[0033] MnCO3+ H + → Mn 2+ + HCO3 - (Formula 2); 5Mn 2+ + 2NO3 − + 4H₂O → 5MnO₂ + N₂ + 8H₂O + (Formula 3).

[0034] This invention provides a low-temperature sulfur-manganese composite autotrophic denitrification denitrification device and method.

[0035] The low-temperature sulfur-manganese composite autotrophic denitrification denitrification device in this embodiment of the invention, such as... Figure 1 As shown, it includes the main reactor 1, the inlet tank 2, and the constant temperature water bath 5.

[0036] The main reactor 1 is a hollow plexiglass column, 70cm high, 10cm inner diameter, and with an effective volume of 5.5L. The main reactor 1 has an inner cavity 11, in which a gravel layer, a sulfur-rhodochrosite layer, and a quartz sand layer are arranged sequentially from bottom to top. The gravel layer is 3cm thick, the sulfur-rhodochrosite layer is 45cm thick, and the quartz sand layer is 15cm thick. The porosity of the sulfur-rhodochrosite layer is 50%. The sulfur-rhodochrosite layer is obtained by mixing sulfur and rhodochrosite in an equal volume ratio. The particle size of both sulfur and rhodochrosite is 5mm. Rhodochrosite is obtained by crushing natural rhodochrosite ore using a crusher and sieving it through a screen.

[0037] The main reactor 1 has a backwash port 13 at its bottom and a water outlet 12 and an exhaust port at its top. Four sampling ports are located on the side wall of the main reactor from top to bottom, each connected to the inner cavity. The four sampling ports are designated as the first sampling port 14, the second sampling port 15, the third sampling port 16, and the fourth sampling port 17. The distances of the four sampling ports from the bottom of the main reactor 1 are 20cm, 35cm, 50cm, and 65cm, respectively. Specifically, the first sampling port 14 is connected to the top of the quartz sand layer; the second sampling port 15 is connected to the junction of the gravel layer and the sulfur-rhodochrosite layer; and the third and fourth sampling ports 16 and 17 are both connected to the sulfur-rhodochrosite layer. Among them, a porous baffle 18 is provided at a height of 2cm between the fourth sampling port 17 and the backwash port 13. The upper layer of the porous baffle 18 is a gravel layer with a thickness of 3cm, and the lower layer of the porous baffle 18 is a water distribution area.

[0038] The outlet of the water inlet tank 2 is connected to the water inlet pump 3, and the water inlet pump 3 is connected to the inner cavity 11.

[0039] One end of the constant temperature water bath 5 is connected to the top of the main reactor 1 through a pipe, and the other end of the constant temperature water bath 5 is connected to a water bath inlet pump 4, which is connected to the main reactor 1.

[0040] The specific process of using this device for autotrophic denitrification of sludge in urban wastewater is as follows: First, sludge for the experimental device was selected from the reflux sludge of the secondary sedimentation tank of the municipal wastewater treatment plant. After being sieved through a 100-mesh screen, it was inoculated into the sulfur-rhodochrosite layer of the device. The amount of sludge inoculated was 2200 mL, and the concentration of volatile suspended solids in the sludge was 3000 mg / L.

[0041] Start the inlet pump 3, and the wastewater enters the inner cavity 11, passes through the porous baffle 18 and the gravel layer, and enters the sulfur-rhodochrosite layer. After the synthetic wastewater fills the entire main reactor 1, stop pumping the synthetic wastewater. The synthetic wastewater and sludge undergo an autotrophic denitrification reaction in the sulfur-rhodochrosite layer.

[0042] The acclimatization process is divided into three stages. The first stage is the immersion irrigation stage, where activated sludge is mixed with the first synthetic wastewater and left in the inner cavity 11 for 48 hours. The activated sludge is then drained and collected in a bucket for settling for 6 hours. The supernatant is then mixed with the synthetic wastewater again to obtain a sludge-water mixture. A peristaltic pump is used to pump the new sludge-water mixture back into the inner cavity 11. This process is repeated four times. The first synthetic wastewater has a nitrate concentration of 20 mg / L, a total phosphorus concentration of 1 mg / L, and a pH of 7.5–8.5. Each liter of synthetic wastewater contains 0.144 g / L KNO3, 0.004 g / L KH2PO4, 0.1 g / L MgCl2·6H2O, 0.01 g / L CaCl2·2H2O, and 1 mL / L Wolfe trace element solution. Each liter of Wolfe trace element solution contains 0.3 g / L MgSO4·7H2O, 0.5 g / L MgSO4·7H2O, and 0.5 g / L MgSO4·7H2O. The solution consists of MnSO4·4H2O, 0.1 g / L FeSO4·7H2O, 0.1 g / L CoCl2·6H2O, 0.1 g / L ZnSO4·7H2O, 0.01 g / L CuSO4·5H2O, and 0.01 g / L Na2MoO4·2H2O.

[0043] The second stage is the continuous water supply stage: the second synthetic wastewater is pumped in, and the retention time of the second synthetic wastewater is 24 hours. The water supply is continuous for 7 days to allow the microorganisms in the activated sludge to gradually adapt to the environment. Each liter of the second synthetic wastewater contains 0.217 g / L KNO3, 0.004 g / L KH2PO4, 0.1 g / L MgCl2·6H2O, 0.01 g / L CaCl2·2H2O and 1 mL / L Wolfe trace element solution.

[0044] The third stage is the stable operation stage: gradually increase the flow rate of the second synthesis wastewater until the hydraulic retention time is 6 hours; the synthesis wastewater is circulated in the reactor for 30 days, NO3 − -N is removed to stabilize the biofilm until a visible biofilm forms on the surface of the biological carrier, at which point biofilm formation is complete.

[0045] During the acclimation process, the water bath inlet pump 4 is started to pump water from the constant temperature water bath 5 into the main reactor 1 to maintain the temperature of the inner cavity 11. Samples are taken at the first sampling port 14, the second sampling port 15, the third sampling port 16 and the fourth sampling port 17 to determine the progress of the reaction. After the reaction is completed, the water bath inlet pump 4 is turned off, and impurities are filtered through the quartz sand layer. The filtered wastewater is discharged through the outlet 12, and the nitrogen gas generated in the autotrophic denitrification process is discharged through the exhaust port at the top of the main reactor 1.

[0046] The specific process of using the above-mentioned low-temperature sulfur-manganese composite autotrophic denitrification denitrification device is as follows: To further illustrate the effectiveness of the low-temperature sulfur-manganese composite autotrophic denitrification device in this invention, the following experiments were conducted.

[0047] 1. Nitrogen removal efficiency and recovery cycle of autotrophic denitrification system at low temperature The effects of different temperatures on the efficiency of the sulfur-manganese composite autotrophic denitrification integrated denitrification unit were investigated by setting three different temperature stages: 10.1℃~15.3℃, 4.5℃~9.7℃, and 20.9℃~23.1℃. Detailed operating parameters are shown in Table 1.

[0048] Table 1 System operating parameters at each stage Note: HRT represents the residence time of the synthetic wastewater in the reactor, and TP represents the total phosphorus content.

[0049] The changes in water quality indicators were measured under different temperature conditions, and the results are as follows: Figure 4 As shown.

[0050] Figure 4 The operation of sulfur denitrification (SD), rhodochrosite denitrification (MCD), and sulfur-rhodochrosite (SMCD) systems at different temperatures is described. The acclimatization phases I and II had operating periods ranging from 1 to 79 days, with temperatures not artificially controlled and based on actual measured influent temperatures during winter. The influent temperature range for acclimatization phase I was 10.1℃ to 15.3℃, with an average influent NO3... − The NO3- concentration was 16.06 mg / L, and the HRT was 3 h. The average effluent total nitrogen (TN) concentration of the SMCD system was 10.19 mg / L and 2.95 mg / L, respectively. The average TN removal rate of the SMCD system was 81.66%, significantly higher than that of the SD system (36.28%). However, the NO3- concentration of the SMCD system was significantly lower. − The average nitrogen removal rate was lower in the SMCD system than in the SD system. The reason is that in the SD system, sulfur itself acts as an electron donor, directly participating in the denitrification process at a faster rate. However, in the SMCD system, sulfur generates hydrogen sulfide (H₂O) during the denitrification reaction. + Mn(II) dissolution only occurs after reaction with rhodochrosite. Lowering the temperature not only weakens the SAD process, but also leads to the release of H... + This reduces the amount of H produced. Simultaneously, it decreases the kinetic energy of the ions, reducing the probability of effective collisions between ions, and consequently leading to a decrease in the amount of H produced by the SAD reaction in the SMCD system. + The reaction with rhodochrosite is inhibited, Mn(II) dissolution is reduced, and NO3- − -N reduction rate decreases. During acclimatization phase II, the influent water temperature is maintained at 4.5℃~9.7℃, and the influent NO3... −-N was 21.31 mg / L. Since lower temperatures negatively impact nitrogen removal, the HRT was extended to 6 hours at this stage to mitigate the inhibitory effect of temperature reduction on denitrification. At this point, the TN concentration in the SD system effluent increased to 17.43 mg / L, and the average TN removal rate significantly worsened to only 18.01%. The SMCD system maintained a high average TN removal rate of 70.56%, significantly higher than the SD system, demonstrating superior nitrogen removal efficiency. The results indicate that denitrification in both the SD and SMCD systems was inhibited to varying degrees at low temperatures, partly due to the reduced NO influent at this stage. 3- Increased -N concentration leads to a greater pollutant load. On the other hand, the significant decrease in temperature results in a reduction in denitrification efficiency at this stage. However, the SMCD system can still maintain high denitrification efficiency at low temperatures.

[0051] To restore the system's denitrification performance, during the acclimatization phase III, the influent water temperature was maintained at 20.9℃~23.1℃ by controlling the constant temperature water bath 5. At this time, the average influent NO3 − -N was 20.97 mg / L, and HRT was 3 h. Results showed that after 3 days of operation, the SMCD system recovered to its denitrification performance at room temperature, with TN and NO levels decreasing. 3− The average removal rates of -N were 94.72% and 97.55%, respectively. The SD system took 13 days to recover to its initial levels. This indicates that the SMCD system has good tolerance to temperature fluctuations and stable denitrification performance, while the MCD system did not experience any denitrification reaction throughout the entire process.

[0052] Lower temperatures can lead to incomplete denitrification. Figure 4 (c) shows that during acclimatization phase I, the SD system exhibited significant NO2 activity. − -N accumulation reached 10.06 mg / L, at which point the average effluent NO2... − -N concentration was significantly higher than NO3. − -N concentration. Stage II, average effluent NO2 in the SD system. − -N concentration increased sharply to 16.59 mg / L. Simultaneously, NO concentration was observed at 6.5℃. 2− -N accumulation reached its maximum of 17.95 mg / L on day 63, indicating that the low-temperature environment severely affected NO2 levels within the SD system. − -N reduction. However, NO2 was not observed in either stage of the SMCD system. − -N accumulation.

[0053] In summary, low temperatures have a greater inhibitory effect on single-sulfur autotrophic denitrification than on the sulfur-rhodochrosite combined autotrophic denitrification process. The SD system has poor low-temperature tolerance and cannot adapt to large temperature changes. In contrast, the SMCD system has strong low-temperature tolerance and can recover its denitrification capacity in a relatively short time even during significant changes in ambient temperature.

[0054] To further compare the denitrification process of different systems at low temperatures, nitrogen removal efficiency was analyzed by collecting effluent samples from the systems along the process after the acclimatization phase II. Figure 5 As shown in the figure. The results show that the TN removal rate of the SMCD system along the process is significantly higher than that of the MCD and SD systems, reaching 74.34% at 20cm. In contrast, the TN removal rates of the MCD and SD systems are only 1.21% and 37.93%, respectively. (SD system NO3) − -N removal rate is slower than SMCD system at 20 cm, and increases with altitude. − The removal rate of -N gradually increases faster than that of the SMCD system. This is likely because, under low-temperature conditions, the H+ produced by the SAD reaction... + The reaction with rhodochrosite was inhibited, limiting Mn(II) dissolution. The inhibition of the MAD reaction, driven by Mn(II) as an electron donor, led to NO3-... − -N→NO2 − -N conversion rate is lower than SD system. Although SD system NO3 − -N has a faster reduction rate, but NO2 − The reduction of -N was significantly inhibited, ranging from 9.85 to 11.91 mg / L. Figure 5 As shown in (c). NO2 − The accumulation of -N is the main reason for the high TN concentration in the effluent of the SD system. In addition, the effluent of the SD system contains a certain concentration of NH4+. + -N like Figure 5 As shown in (d), the study indicates that a decrease in temperature leads to the death of microorganisms within the reactor, releasing some organic nitrogen and organic carbon. The SD system has poor low-temperature tolerance; under the influence of low temperatures, the organic nitrogen released into the solution after the biofilm detaches may be converted into NH4. + -N leads to an increase in the concentration of effluent.

[0055] The average S / N of SD and SMCD systems, for example Figure 6As shown in the figure, the average S / N ratios of the SD system in acclimatization stages I-III were 16.63, 25.56, and 10.50, respectively. The results show that the S / N ratio of the SD system in stage II was significantly higher than in other stages. This is consistent with the above inference that lower temperatures have a greater adverse effect on the system's microorganisms. The average S / N ratios of the SMCD system were 9.63, 9.41, and 8.08, respectively. Although the average S / N ratio of the SMCD system was also higher than the theoretical value, it was significantly lower than that of the SD system. Previous studies have shown that in sulfur-pyrite denitrification systems, the proportion of nitrogen removal by pyrite gradually increases as the temperature decreases. This is because pyrite particles become smaller and their specific surface area increases during denitrification, accelerating contact with the biofilm and water, making it easier to utilize. Therefore, in this invention, although low temperature affects the denitrification effect of the SMCD system, the coupling of sulfur and rhodochrosite also controls SO4 levels within the system to some extent. 2- The generation of.

[0056] Figure 7 The results show the dissolution of Mn(II) throughout the entire operation. The results indicate that no significant Mn(II) dissolution was detected in the MCD system. In contrast, the SMCD system showed average Mn(II) dissolution ranging from 2.20 mg / L to 3.78 mg / L in stages I and II, respectively. However, in stage III, Mn(II) dissolution showed a decreasing trend, reaching 3.28 mg / L. − -N removal results showed that the average NO3 in Stage III was... − The removal of -N was significantly greater than in stages I-II, theoretically the dissolution of Mn(II) should be even greater. Previous studies have shown that decreasing temperature significantly weakens the autotrophic denitrification reaction of pyrite. The reduced reactivity of pyrite leads to a decrease in Fe within the system. 2+ Reduced dissolution, coupled with significantly reduced iron-oxidizing bacteria activity at low temperatures, led to Fe... 2+ →Fe 3+ The conversion of Mn(II) is limited. Therefore, during the domestication stages I-II, the oxidation of Mn(II) is inhibited to some extent due to the influence of low temperature. However, as the temperature rises during the domestication stage III, the activity of microorganisms involved in the oxidation of Mn(II) recovers, and the dissolution of Mn(II) decreases.

[0057] The calculated contribution rates of sulfur and manganese in the autotrophic denitrification process of the SMCD system at different temperatures are as follows: Figure 8As shown, the contribution rate of the MAD reaction first increases and then decreases with the occurrence of the reaction. The contribution rate is 42.08% in stage I, increases to 63.18% in acclimatization stage II, and finally decreases to 23.07% in acclimatization stage III. Conversely, the contribution rate of the SAD reaction decreases from 57.82% in stage I to 36.82% in acclimatization stage II, and then increases to 76.93% in acclimatization stage III. The results indicate that the SAD reaction is significantly inhibited at low temperatures, while the contribution rate of the MAD reaction increases significantly, and the lower the temperature, the higher the contribution rate. This shows that the MAD reaction is an important reason for maintaining the high efficiency of nitrogen removal in the SMCD system at low temperatures. That is, at low temperatures, the MAD reaction fills the gap in nitrogen removal, effectively compensating for the inadequacy of the single SAD reaction, giving the SMCD system good low-temperature tolerance. The SAD reaction is the main nitrogen removal process at room temperature, and the coexistence of SAD and MAD reactions allows the SMCD system to maintain high nitrogen removal efficiency even when facing significant temperature changes.

[0058] 2. Characteristics of the microenvironment for denitrification Laser particle size analyzer was used to analyze the particle size of activated sludge in different systems after operation. Figure 9 The results show significant differences in sludge particle size distribution across different systems. The average sludge particle sizes in the SD, MCD, and SMCD systems are 17.84 μm, 133.8 μm, and 97.47 μm, respectively, as shown in Table 2. Hydraulic shear force is a crucial factor influencing the properties of granular sludge. Higher hydraulic loads promote sludge compaction, while lower hydraulic loads hinder granulation. Hydraulic shear force has a positive / inhibitory effect on sludge granulation. Positive effect: High hydraulic loads enhance mass transfer between microorganisms and pollutants, promoting microbial proliferation and EPS secretion. Inhibitory effect: High hydraulic loads increase the risk of sludge being washed out and fragmented. The significantly larger sludge particle sizes in the SD and SMCD systems compared to the MCD system indicate that the positive effect of sludge granulation is more pronounced in the SD and SMCD systems.

[0059] In addition, the sludge specific surface area of ​​the SMCD system is 218.8 m². 2 / kg, significantly greater than the SD system's 99.05m 2 / kg. Studies show that larger particle size is not always better for granular sludge. Smaller granular sludge particles have a larger relative specific surface area, resulting in a larger contact area with water and exhibiting better biological activity. Conversely, as sludge particle size increases, the gas generated during internal denitrification escapes, creating numerous pores within the sludge. This facilitates the entry of other substrates into the granular sludge, disrupting the established microenvironment. Therefore, SMCD systems with larger sludge specific surface areas may exhibit better mass transfer efficiency.

[0060] Table 2. Properties of activated sludge SD 133.8 238.1 99.05 MCD 17.84 23.31 412.9 SMCD 97.47 204.3 218.8 Comparison of denitrifying enzyme activities The denitrifying enzyme activity test results showed that the nitrate reductase and nitrite reductase activities of the SMCD system were 0.51 and 3.85 U / g, respectively, which were significantly higher than those of the SD and SMCD systems. Figure 10 As shown, the high activity of microbial enzymes within the system is conducive to denitrification, leading to more complete denitrification. This aligns with the fact that the SMCD system boasts the highest nitrogen removal efficiency and exhibits no intermediate product accumulation. On one hand, the SMCD system provides an additional inorganic carbon source, resulting in abundant nutrients. On the other hand, the stable pH environment within the system promotes microbial growth and accumulation, thus leading to higher denitrifying enzyme activity. In contrast, other systems, influenced by both nutrient availability and acidic pH, exhibit low denitrifying enzyme activity, resulting in poor denitrification performance.

[0061] Spatial distribution comparison of live / dead cells in biofilm Confocal microscopy was used to characterize the spatial distribution of live / dead cells within each system to assess the viability of microorganisms within the system, such as... Figure 11 As shown, different colors of fluorescence reflect the activity of microorganisms. Live bacteria stained with SYTO-9 emit green light, while dead bacteria stained with PI emit red light. The fluorescence staining results indicate that the bacteria in all three systems possess normal life functions. However, in the SMCD system, green fluorescence significantly predominates compared to red fluorescence, indicating a high proportion of live cells. In contrast, red fluorescence significantly predominates in the SD and MCD systems, suggesting a high proportion of dead cells and damaged biofilm cells in these two systems.

[0062] The experimental data above show that under low-temperature autotrophic conditions, when the influent temperature drops to 4.5-9.7℃, NO3... − At a -N concentration of 21.31 mg / L and an HRT of 6 h, the average TN removal rate of the SMCD system reached 70.56%, significantly higher than the control system. At this point, the MAD reaction contribution rate reached 63.18%, significantly higher than at 10.1–15.3℃ (42.08%) and 20.9–23.1℃ (23.07%). The MAD effect effectively compensated for the shortcomings of the single SAD effect at low temperatures, giving the SMCD system good low-temperature tolerance. The SMCD system has a short recovery period; after 3 days of operation at room temperature, TN and NO3... − -N removal rate recovers to over 90%, at which point SAD reaction becomes the main denitrification process. The coexistence of SAD and MAD reactions allows the SMCD system to maintain high denitrification efficiency even when facing significant temperature changes.

[0063] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Clearly, those skilled in the art can make various alterations and variations to the invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of equivalents of the invention, the invention is also intended to include these modifications and variations.

Claims

1. A method for low-temperature sulfur-manganese composite autotrophic denitrification, employing a sulfur-manganese composite autotrophic denitrification device, characterized in that... The sulfur-manganese composite autotrophic denitrification denitrification device includes a main reactor (1), an inlet tank (2), and a constant temperature water bath (5). The main reactor (1) has an inner cavity (11), in which a gravel layer, a sulfur-rhodochrosite layer and a quartz sand layer are arranged sequentially from bottom to top; the side wall of the main reactor (1) is provided with a first sampling port (14), a second sampling port (15), a third sampling port (16) and a fourth sampling port (17) from top to bottom; the first sampling port (14) is connected to the top of the quartz sand layer, the second sampling port (15) is connected to the connection between the gravel layer and the sulfur-rhodochrosite layer, and the third sampling port (16) and the fourth sampling port (17) are both connected to the sulfur-rhodochrosite layer; The outlet of the water inlet tank (2) is connected to a water inlet pump (3), and the water inlet pump (3) is connected to the bottom of the inner cavity (11); One end of the constant temperature water bath (5) is connected to the top of the main reactor (1) through a pipe, and the other end of the constant temperature water bath (5) is connected to a water bath inlet pump (4), which is connected to the main reactor (1). The height ratio of the gravel layer, the sulfur-rhodochrosite layer, and the quartz sand layer is 3~4:45:15; the porosity of the sulfur-rhodochrosite layer is 40%~50%; the sulfur-rhodochrosite layer is obtained by mixing sulfur and rhodochrosite in an equal volume ratio. The specific process of the method is as follows: After filtering the sludge from the wastewater treatment plant, pour it into the main reactor (1). Start the inlet pump (3) to pump the synthetic wastewater in the inlet tank (2) into the distribution area. It then enters the gravel layer through the porous baffle and into the sulfur-rhodochrosite layer. After the synthetic wastewater fills the entire main reactor (1), stop pumping the synthetic wastewater. The synthetic wastewater and sludge undergo autotrophic denitrification reaction in the sulfur-rhodochrosite layer. During the acclimatization process, start the water bath inlet pump (4) to pump water from the constant temperature water bath (5) into the main reactor (1) to maintain the temperature of the inner cavity (11). After acclimatization, the water bath inlet pump (4) is turned off, and impurities are filtered through the quartz sand layer. The filtered wastewater is discharged through the outlet (12), and the nitrogen gas generated in the autotrophic denitrification process is discharged through the exhaust port at the top of the reactor (1). The low temperature is 5℃~10℃.

2. The method for low-temperature sulfur-manganese composite autotrophic denitrification nitrogen removal according to claim 1, characterized in that, The sulfur and the rhodochrosite both have a particle size of 2mm to 5mm.

3. The method for low-temperature sulfur-manganese composite autotrophic denitrification nitrogen removal according to claim 1, characterized in that, The bottom of the main reactor (1) is provided with a backwash port (13), and the top of the main reactor (1) is provided with a water outlet (12).

4. The method for low-temperature sulfur-manganese composite autotrophic denitrification nitrogen removal according to claim 3, characterized in that, A porous baffle (18) is provided below the gravel layer, and the lower layer of the porous baffle (18) is a water distribution area.

5. The method for low-temperature sulfur-manganese composite autotrophic denitrification nitrogen removal according to claim 4, characterized in that, The backwash port (13) is connected to the water distribution area; the water inlet pump (3) is connected to the water distribution area.

6. The method for low-temperature sulfur-manganese composite autotrophic denitrification nitrogen removal according to claim 1, characterized in that, The synthetic wastewater contains 0.144 g / L KNO3, 0.004 g / L KH2PO4, 0.1 g / L MgCl2·6H2O, 0.01 g / L CaCl2·2H2O, and 1 mL / L Wolfe trace element solution; the Wolfe trace element solution contains 0.3 g / L MgSO4·7H2O, 0.5 g / L MnSO4·4H2O, 0.1 g / L FeSO4·7H2O, 0.1 g / L CoCl2·6H2O, 0.1 g / L ZnSO4·7H2O, 0.01 g / L CuSO4·5H2O, and 0.01 g / L Na2MoO4·2H2O.

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