Sulfur-manganese composite autotrophic denitrification nitrogen removal device and nitrogen removal method at low temperature

Abstract

The invention belongs to the technical field of nitrogen removal, and particularly relates to a low-temperature sulfur-manganese composite autotrophic denitrification nitrogen removal device and a nitrogen removal method. The low-temperature sulfur-manganese composite autotrophic denitrification nitrogen removal device comprises a main body reactor, a water inlet tank and a constant-temperature water bath kettle, the main body reactor is provided with an inner cavity, and a gravel layer, a sulfur-rhodochrosite layer and a quartz sand layer are sequentially arranged in the inner cavity from bottom to top; four sampling ports are formed in the side wall of the main body reactor from top to bottom, and each sampling port is communicated with the inner cavity; a water outlet of the water inlet tank is connected with a water inlet pump; the water inlet pump is communicated with the inner cavity; one end of the constant-temperature water bath kettle is communicated with the top of the main body 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 body reactor.

Description

Technical Field

[0001] The invention belongs to the technical field of denitrification, and in particular relates to a sulfur-manganese composite autotrophic denitrification device and a denitrification method at low temperature. Background Art

[0002] At present, most urban sewage discharges implement the Class A discharge standard in the "Pollutant Discharge Standard for Urban Sewage Plants (GB18918-2002)", which requires that the total nitrogen (TN) concentration does not exceed 15 mg / L. The "Surface Water Environmental Quality Standard (GB3838-2002)" Class V water requires TN (lakes, reservoirs) to be no more than 1.5 mg / L. High nitrogen content can easily lead to eutrophication of water bodies, so the sewage tail water needs to be deeply denitrified. However, the current C / N ratio of the tail water of domestic urban sewage treatment plants is generally less than 2, which is a typical low C / N ratio sewage. With a low C / N ratio, microorganisms enter the endogenous respiration state due to insufficient carbon source, resulting in a decrease in the concentration of activated sludge, which restricts the denitrification effect. Therefore, deep denitrification under low C / N is one of the hot and difficult issues in the current water treatment field. In order to achieve the denitrification of NO3 - -N, NO2 - The autotrophic denitrification technology that effectively removes nitrogen-containing pollutants such as -N and does not require the addition of external organic carbon sources has gradually attracted attention. 2- ,HCO3 - As inorganic carbon sources for cell synthesis, reduced sulfur and its compounds elemental sulfur (S 0 ), sulfite (SO3 2- ), ferrous iron (Fe 2+ ), and manganese ions (Mn 2+ ) and other reducing substances as inorganic electron donors for autotrophic denitrification.

[0003] Among them, sulfur autotrophic denitrification (SAD) process is also the focus of current research on autotrophic denitrification due to its economical operation and high denitrification efficiency. Sulfur autotrophic denitrification refers to the process of sulfur oxidizing bacteria through the oxidation of reduced sulfur (S) under anoxic or anaerobic conditions. 0 、S 2- 、SO3 2- , S2O3 2- and FeS2, etc.) to obtain energy and convert NO3 - -N is reduced to nitrogen gas. However, sulfur autotrophic denitrification produces H + It is easy to cause the pH value in water to decrease, SO4 2- The yield was higher than the limit of 250mg / L in water.

[0004] In order to further improve the denitrification efficiency of autotrophic denitrification technology, many scholars have been conducting continuous research on autotrophic denitrification technology constructed with composite substrates. Sahinkaya et al. combined elemental sulfur with limestone to construct a sulfur-limestone autotrophic denitrification (SLAD) device, that is, a sulfur-limestone denitrification system was formed by configuring a sulfur layer and a limestone layer in the reactor. In the system, elemental sulfur acts as an electron donor for NO3 - -N reduction, limestone continues to dissolve and acts as a pH buffer and inorganic carbon source. The reaction formula is as follows: CaCO3 + H + →Ca 2+ +HCO3 - There are also SLAD systems built in reactors, such as Figure 2 The reactor is widely used for off-site and on-site wastewater treatment because it combines ease of use, high efficiency and convenience. However, the limestone in the reactor cannot provide additional electrons for denitrification, and the area occupied by it forms a passivation zone, which hinders the further removal of nitrogen and induces SO4 2- On the other hand, although limestone is the most commonly used low-cost alkalinity source, Ca 2+ The release of FeCO3 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 reduce NO3 under the action of sulfur autotrophic denitrifying bacteria such as T. denitrificans. - -N is N2. Therefore, the researchers introduced siderite into the sulfur-driven autotrophic denitrification reactor to construct a sulfur-siderite autotrophic denitrification (SSAD) system. In the reactor, elemental sulfur and siderite can both serve as electron donors for denitrification, while siderite acts as a pH buffer and provides an inorganic carbon source. Compared with the SLAD system, the SSAD system is Figure 3 As shown in the figure, the SLAD system has the characteristic of efficient denitrification without being restricted by carbon source, while at the same time 2+ Providing additional electrons for denitrification to reduce SO4 2- Therefore, it is more excellent than SLAD system in treating wastewater with low C / N ratio. 2+ Can serve as an electron donor for denitrification, but Fe 2+ It may be oxidized by organisms to form precipitates such as hexapyroxene (g-FeOOH), Fe3O4 and Fe(OH)3. They are wrapped on the surface of fillers and bacteria, hindering the electron transfer between solid and liquid, and ultimately leading to limited denitrification. Studies have also shown that Mn 2+Substances such as manganese can provide electrons for denitrification and drive manganese autotrophic denitrification. However, single manganese autotrophic denitrification technology is also easily limited by slow bacterial growth and low denitrification efficiency. Temperature changes have a profound impact on the metabolic activity of microorganisms, which in turn leads to a decrease in the denitrification rate, making it impossible for the nitrate nitrogen in the effluent to meet the discharge standards. Groundwater temperature is often below 10°C, and even reaches 3°C to 4°C. Sewage treatment currently mainly uses biological methods. The key to this method lies in the growth and metabolic activity of functional microorganisms, which will directly affect the treatment efficiency of the sewage treatment system. Temperature, as an important ecological factor for microbial growth and metabolic activity, significantly affects microbial activity. Therefore, the application of biological denitrification technology at low temperatures is seriously challenged.

[0005] Denitrifying Thiobacillus is sensitive to temperature changes. Studies have shown that the optimal temperature range for Denitrifying Thiobacillus is 20℃~35℃. Too high a temperature will basically inactivate the microorganisms. Li Yingying explored the effect of temperature on the operation of the sulfur autotrophic denitrification system. The results showed that when the system temperature fluctuates between 6.4℃~19.2℃, the lower the temperature, the worse the denitrification effect. When the HRT is 6h and the temperature is around 10℃, the total nitrogen removal rate is only 53.7%. Zheng Shaozhi built four packed bed reactors using volcanic rock, volcanic rock / iron-carbon filler, volcanic rock / sulfur, and volcanic rock / iron-carbon filler / sulfur as fillers. When the system temperature dropped from 30℃ to 15℃, NO3 - -N average removal rate dropped from 91.5% to 41.5%, and even NO2 - -N accumulation phenomenon.

[0006] To improve the denitrification performance of autotrophic denitrification systems under low-temperature conditions, a composite autotrophic denitrification process can be used. Sulfur autotrophic denitrification systems contain a certain amount of manganese autotrophic denitrifying bacteria. Studies have shown that microorganisms inhabiting metal nodule sediment environments face challenges from extreme environmental conditions such as heavy metals, oligotrophy, and low temperatures. Gammaproteobacteria, as the dominant group in deep-sea manganese nodules, play an important role in the manganese cycle within these nodules. Therefore, manganese redox bacteria may have a certain tolerance to low temperatures. To date, cumulative identified manganese ore reserves exceed 1.8 billion tons, representing abundant reserves. Natural rhodochrosite, a solid-phase matrix primarily composed of MnCO3, is inexpensive. However, rhodochrosite utilization is low, leading to resource waste. Summary of the Invention

[0007] In order to solve the above technical problems, the present invention provides a low-temperature sulfur-manganese composite autotrophic denitrification denitrification device and denitrification method, which can still have a good denitrification effect at a low temperature of 5°C to 10°C.

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

[0009] A low-temperature sulfur-manganese composite autotrophic denitrification device comprises a main reactor, a water inlet tank and a constant-temperature water bath;

[0010] The main reactor has an inner cavity, in which a gravel layer, a sulfur-rhodochrosite layer, and a quartz sand layer are sequentially arranged 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 connection between the gravel layer and the sulfur-rhodochrosite layer, and the third sampling port and the fourth sampling port are both connected to the sulfur-rhodochrosite layer;

[0011] The water outlet of the water inlet tank is connected to a water inlet pump, and the water inlet pump is connected to the bottom of the inner cavity;

[0012] One end of the constant temperature water bath is connected to the top of the main reactor through a pipeline, and the other end of the constant temperature water bath is connected to a water bath inlet pump, and the water bath inlet pump is connected to the main reactor (1).

[0013] 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.

[0014] In another preferred embodiment, the porosity of the sulfur-rhodochrosite layer is 40% to 50%.

[0015] In another preferred embodiment, the sulfur-rhodochrosite layer is obtained by mixing sulfur and rhodochrosite in an equal volume ratio.

[0016] In another preferred embodiment, the particle sizes of the sulfur and the rhodochrosite are both 2 mm to 5 mm.

[0017] In another preferred embodiment, a backwash port is provided at the bottom of the main reactor, and a water outlet is provided at the top of the main reactor.

[0018] In another preferred embodiment, a porous partition is provided below the gravel layer, and the lower layer of the porous partition is a water distribution area.

[0019] 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.

[0020] The second aspect of the present invention provides a method for sulfur-manganese composite autotrophic denitrification and denitrification using the low-temperature sulfur-manganese composite autotrophic denitrification and denitrification device. The specific process is as follows:

[0021] The sludge from the sewage treatment plant is sieved through 100 mesh and poured into the main reactor. The water inlet pump is started to pump the synthetic wastewater in the water inlet tank into the water distribution area, and then enters the gravel layer through the porous filter plate and into the sulfur-rhodochrosite layer. After the synthetic wastewater fills the entire main reactor, the pumping of synthetic wastewater is stopped. The synthetic wastewater and sludge undergo autotrophic denitrification reaction in the sulfur-rhodochrosite layer for acclimation. During the acclimation process, the water bath inlet pump is started to pump water from the constant temperature water bath into the main reactor to maintain the temperature of the inner cavity.

[0022] After the acclimation is completed, the water bath inlet pump is turned off, impurities are filtered through the quartz sand layer, the filtered wastewater is discharged through the outlet, and the nitrogen generated in the autotrophic denitrification reaction process is discharged through the exhaust port on the top of the reactor.

[0023] In another preferred embodiment, each liter of the synthetic wastewater contains 0.144 g / LKNO3, 0.004 g / LKH2PO4, 0.1 g / L MgCl2·6H2O, 0.01 g / L CaCl2·2H2O and 1 mL / LWolfe 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a structural schematic diagram of the low-temperature sulfur-manganese composite autotrophic denitrification and denitrification device of the present invention; the length of L1 is 2cm to 5cm, the length of L2 is 5cm to 20cm, the length of L3 is 20cm to 35cm, the length of L4 is 35cm to 50cm, and the length of L5 is 50cm to 65cm.

[0025] Figure 2 This is the reaction principle diagram of the SLAD system.

[0026] Figure 3 This is the reaction principle diagram of the SSAD system.

[0027] Figure 4 is the change of water quality index in sulfur-manganese composite system at different stages; a ) is the change of TN index, (b) NO3 - -N index changes, (c) NO2 - -N indicator changes.

[0028] Figure 5The changes of water quality indicators along 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.

[0029] Figure 6 SO4 for SD and SMCD systems 2- Actual production / TN removal.

[0030] Figure 7 Mn in MCD and SMCD systems 2+ Dissolution amount.

[0031] Figure 8 This is the contribution rate analysis of SAD and MAD reactions.

[0032] Figure 9 The sludge particle size distribution of different systems.

[0033] Figure 10 Denitrifying enzyme activities in different systems; (a) is nitrate reductase, and (b) is nitrite reductase.

[0034] Figure 11 Live / dead cell staining images under confocal microscopy: (a) is SD, (b) is MCD, and (c) is SMCD system.

[0035] Description of the drawings: 1-main reactor, 11-inner cavity, 12-water outlet, 13-backwash port, 14-first sampling port, 15-second sampling port, 16-third sampling port, 17-fourth sampling port, 18-porous partition, 2-water inlet tank, 3-water inlet pump, 4-water bath inlet pump, 5-constant temperature water bath. DETAILED DESCRIPTION

[0036] The present invention is described in detail below with reference to specific examples, but should not be construed as limiting the present invention. Unless otherwise specified, the technical means used in the following examples are conventional means well known to those skilled in the art, and the materials, reagents, etc. used in the following examples, unless otherwise specified, can be obtained from commercial sources.

[0037] The present 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 Formula 2. The H generated by the SAD reaction +Reacting with rhodochrosite, rhodochrosite dissolves, produces Mn(II) to provide additional electrons for denitrification, drives manganese autotrophic denitrification (MAD) reaction, the reaction process is shown in formula 3, and reduces SO4 2- The MAD reaction will also produce H + , promoting the dissolution of rhodochrosite and accelerating the rate at which rhodochrosite donates electrons. The manganese oxides produced simultaneously can enhance the removal of organic matter and increase its bioavailability, while the manganese oxides are reduced and utilized again. Furthermore, small amounts of Ca, Mg, Fe, and Zn in the ore can provide a certain amount of trace elements for bacterial growth. Therefore, under low-temperature conditions of 5°C to 10°C, coupling sulfur with rhodochrosite and utilizing a sulfur-manganese composite electron donor may enhance the denitrification capacity of the denitrification system, aiming to provide technical support for maintaining stable denitrification performance in autotrophic denitrification systems at low temperatures.

[0038] MnCO3+H + →Mn 2+ +HCO3 - (Formula 2);

[0039] 5Mn 2+ +2NO3 - +4H2O→5MnO2+N2+8H + (Formula 3).

[0040] The embodiment of the present invention provides a sulfur-manganese composite autotrophic denitrification denitrification device and a denitrification method at low temperature.

[0041] The low temperature sulfur-manganese composite autotrophic denitrification and denitrification device in the embodiment of the present invention is as follows: Figure 1 As shown, it includes a main reactor 1, a water inlet tank 2 and a constant temperature water bath 5.

[0042] The main reactor 1 is a hollow organic glass column with a height of 70 cm, an inner diameter of 10 cm, and an effective volume of 5.5 L. 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 from bottom to top. The gravel layer is 3 cm thick, the sulfur-rhodochrosite layer is 45 cm thick, and the quartz sand layer is 15 cm 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 sulfur and rhodochrosite is 5 mm. Rhodochrosite is obtained by crushing natural rhodochrosite ore in a crusher and sieving it through a screen. Rhodochrosite is obtained by crushing natural rhodochrosite ore in a crusher and sieving it through a screen.

[0043] 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 and an exhaust port. Four sampling ports are provided on the side wall of the main reactor from top to bottom, and each of the sampling ports is connected to the inner cavity; the four sampling ports are respectively the first sampling port 14, the second sampling port 15, the third sampling port 16 and the fourth sampling port 17, and the distances between the four sampling ports and the bottom of the main reactor 1 are 20 cm, 35 cm, 50 cm and 65 cm 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 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. A porous partition 18 is provided at a height of 2 cm between the fourth sampling port 17 and the backwash port 13 . The upper layer of the porous partition 18 is a gravel layer with a thickness of 3 cm. The lower layer of the porous partition 18 is a water distribution area.

[0044] The water outlet of the water inlet box 2 is connected to the water inlet pump 3 , and the water inlet pump 3 is communicated with the inner cavity 11 .

[0045] One end of the constant temperature water bath 5 is connected to the top of the main reactor 1 through a pipeline, 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.

[0046] This device is used to carry out autotrophic denitrification and denitrification of sludge in urban wastewater. The specific process is as follows:

[0047] First, the sludge used in the experimental device was selected from the return sludge of the secondary sedimentation tank of the municipal sewage treatment plant. After being sieved through 100 mesh, it was inoculated into the sulfur-rhodochrosite layer of the device. The inoculated sludge volume was 2200 mL, and the volatile suspended solids concentration in the sludge was 3000 mg / L.

[0048] Start the water inlet pump 3, the wastewater enters the inner cavity 11, passes through the porous partition 18 and the gravel layer into the sulfur-rhodochrosite layer, and stops pumping the synthetic wastewater after the synthetic wastewater fills the entire main reactor 1. The synthetic wastewater and sludge undergo autotrophic denitrification reaction in the sulfur-rhodochrosite layer.

[0049] The acclimation is divided into three stages; the first stage is the filling stage, after the activated sludge is mixed with the first synthetic wastewater and kept in the inner cavity 11 for 48 hours, the activated sludge is emptied and collected in a bucket and settled for 6 hours, the supernatant is mixed with the synthetic wastewater again to obtain a mud-water mixture, and the new mud-water mixture is pumped back into the inner cavity 11 with a peristaltic pump, and the above 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, a pH of 7.5-8.5, and contains 0.144 g / L KNO3, 0.004 g / L KH2PO4, 0.1 g / L MgCl2·6H2O, and 0.01 g / L It consists of CaCl2·2H2O and 1mL / LWolfe trace element solution; each liter of Wolfe trace element solution contains 0.3g / LMgSO4·7H2O, 0.5g / LMnSO4·4H2O, 0.1g / L FeSO4·7H2O, 0.1g / L CoCl2·6H2O, 0.1g / L ZnSO4·7H2O, 0.01g / LCuSO4·5H2O and 0.01g / LNa2MoO4·2H2O.

[0050] The second stage is the continuous water flow stage: the second synthetic wastewater is pumped in. At this time, the second synthetic wastewater has a residence time of 24 hours and is continuously circulated 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 0.217g / LKNO3, 0.004g / LKH2PO4, 0.1g / LMgCl2·6H2O, 0.01g / LCaCl2·2H2O and 1mL / LWolfe trace element solution.

[0051] The third stage is the stable operation stage: gradually increase the flow rate of the second synthetic wastewater until the hydraulic retention time is 6 hours; the synthetic wastewater circulates in the reactor for 30 days, and NO3 - -N removal is stable until a visible biofilm is formed on the surface of the biological carrier, and the biofilm formation is completed.

[0052] 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 through the first sampling port 14, the second sampling port 15, the third sampling port 16 and the fourth sampling port 17 to judge the progress of the reaction. After the reaction is completed, the water bath inlet pump 4 is turned off, impurities are filtered through the quartz sand layer, and the filtered wastewater is discharged through the outlet 13. The nitrogen generated during the autotrophic denitrification reaction is discharged through the exhaust port on the top of the reactor 1.

[0053] The specific process of using the above-mentioned low-temperature sulfur-manganese composite autotrophic denitrification denitrification device is as follows:

[0054] In order to further illustrate the effect of the sulfur-manganese composite autotrophic denitrification and denitrification device at low temperature of the present invention, the following experiments were conducted.

[0055] 1. Denitrification efficiency and recovery period of autotrophic denitrification system at low temperature

[0056] Three different temperature stages were set: 10.1°C to 15.3°C, 4.5°C to 9.7°C, and 20.9°C to 23.1°C to investigate the effects of different temperatures on the efficiency of the sulfur-manganese composite autotrophic denitrification integrated denitrification device. Detailed operating parameters are shown in Table 1.

[0057] Table 1 System operating parameters at each stage

[0058]

[0059] Note: HRT refers to the residence time of synthetic wastewater in the reactor, and TP refers to the total phosphorus content.

[0060] The changes of water quality indicators at different temperature stages were measured respectively, and the results are as follows: Figure 4 shown.

[0061] Figure 4 The operating conditions of the sulfur denitrification (SD) system, the rhodochrosite denitrification (MCD) system, and the sulfur-rhodochrosite (SMCD) system at different temperatures are described. The operating period of the acclimation phase I and acclimation phase II is 1 day to 79 days. The temperature is not artificially controlled and is the measured inlet water temperature in winter. The inlet water temperature range of the acclimation phase I is 10.1℃~15.3℃, and the average inlet NO3 - -N concentration was 16.06 mg / L, and HRT was 3h. The average effluent concentrations of total nitrogen (TN) in the SMCD system were 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 at 36.28%. However, the NO3 - The average removal rate of -N is lower than that of the SD system. The reason is that in the SD system, sulfur itself directly participates in the denitrification process as an electron donor, which has a faster rate. In the SMCD system, sulfur participates in the denitrification reaction and produces H + Mn(II) is dissolved only after reacting with rhodochrosite. The temperature reduction not only weakens the SAD process, but also leads to the + At the same time, the kinetic energy of the ions is reduced, and the probability of effective collisions between ions is reduced, which leads to the H generated by the SAD reaction in the SMCD system. + The reaction between the quartz and rhodochrosite is inhibited, the dissolution of Mn(II) is reduced, and NO3 - -N reduction rate decreased. In the acclimation stage II, the inlet water temperature was maintained at 4.5℃~9.7℃, and the inlet NO3 --N is 21.31 mg / L. Since the decrease in temperature will have an adverse effect on the removal of nitrogen, the HRT is extended to 6h in this stage to alleviate the inhibitory effect of the temperature decrease on denitrification. At this time, the TN concentration of the SD system effluent increased to 17.43 mg / L, and the average removal rate of TN was significantly worse than before, only 18.01%. The average removal rate of TN by the SMCD system was 70.56%, which was still significantly higher than that of the SD system, maintaining a high denitrification efficiency. The results show that the denitrification of the SD and SMCD systems is inhibited to varying degrees at low temperatures. On the one hand, due to the influent NO 3- As the -N concentration increases, the pollutant load increases. On the other hand, the significant decrease in temperature leads to a decrease in denitrification efficiency during this stage. However, the SMCD system can still maintain high denitrification efficiency at low temperatures.

[0062] In order to restore the denitrification performance of the system, in the acclimation stage III, the inlet water temperature is maintained at 20.9℃~23.1℃ by controlling the constant temperature water bath 5. At this time, the average inlet NO3 - -N was 20.97 mg / L and HRT was 3h. The results showed that after 3 days of operation, the SMCD system recovered to the denitrification performance at room temperature, and TN and NO 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 level. This indicates that the SMCD system has good tolerance to temperature fluctuations and stable denitrification performance. No denitrification occurred in the MCD system throughout the entire process.

[0063] A decrease in temperature can easily lead to incomplete denitrification. Figure 4 (c) shows that in the acclimation stage I, the SD system showed obvious NO2 - -N accumulation is 10.06 mg / L, and the average effluent NO2 - -N concentration is significantly higher than NO3 - -N concentration. Phase II, SD system average outlet NO2 - -N concentration increased sharply to 16.59 mg / L. At the same time, it was observed that NO 2- -N accumulation reached a maximum of 17.95 mg / L on the 63rd day. The low temperature environment seriously affected the NO2 in the SD system. - -N reduction. However, the SMCD system did not show NO2 in both stages. - -N accumulation.

[0064] In summary, low temperatures have a greater inhibitory effect on sulfur-only 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 fluctuations. The SMCD system, on the other hand, is highly tolerant to low temperatures and can recover its denitrification capacity relatively quickly even during significant changes in ambient temperature.

[0065] In order to further compare the denitrification process of different systems at low temperature, after the end of acclimation phase II, the effluent of the system was collected along the way for denitrification efficiency analysis. Figure 5 The results show that the TN removal rate of the SMCD system is significantly higher than that of the MCD and SD systems, reaching 74.34% at 20 cm. The TN removal rates of the MCD and SD systems are only 1.21% and 37.93% respectively. - The removal rate of -N is slower than that of SMCD system at 20cm. With the increase of height, NO3 - The -N removal rate is gradually faster than that of the SMCD system. The reason is that the H generated by the SAD reaction under low temperature conditions + The reaction between Mn(II) and rhodochrosite is inhibited, and the dissolution of Mn(II) is limited. The MAD reaction driven by Mn(II) as an electron donor is inhibited, resulting in NO3 - -N→NO2 - -N conversion rate is lower than that of SD system. - -N reduction rate is faster, but NO2 - -N reduction was significantly inhibited, ranging from 9.85 to 11.91 mg / L, such as Figure 5 (c) NO2 - -N accumulation is the main reason for the high TN concentration in the effluent of the SD system. In addition, there is a certain concentration of NH4 + -N as Figure 5 (d) As shown. Studies have shown that a decrease in temperature will cause the death of microorganisms in the reactor, releasing some organic nitrogen and organic carbon. However, the SD system has poor tolerance to low temperatures. Under the influence of low temperatures, the organic nitrogen released into the solution after the biofilm in the system falls off may be converted into NH4 + -N, resulting in an increase in effluent concentration.

[0066] The average S / N of SD and SMCD systems is as follows: Figure 6As shown. In the acclimation stages I to III, the average S / N of the SD system were 16.63, 25.56 and 10.50, respectively. The results showed that the S / N of the SD system in stage II was significantly higher than that in other stages. This is consistent with the above inference, that is, the lower the temperature, the greater the adverse effect on the system microorganisms. The average S / N of the SMCD system were 9.63, 9.41 and 8.08, respectively. Although the average S / N of the SMCD system is also higher than the theoretical value, the S / N of the SMCD system is significantly lower than that of the SD system. Studies have shown that in the sulfur-pyrite denitrification system, as the temperature gradually decreases, the proportion of pyrite denitrification gradually increases. This is because the particle size of pyrite becomes smaller and the specific surface area increases during the denitrification process, which accelerates the contact between the biofilm and the water body and makes it easier to be utilized. Therefore, in the present invention, although low temperature affects the denitrification effect of the SMCD system, the coupling of sulfur-rhodochrosite also controls the SO4 in the system to a certain extent. 2- The production of.

[0067] Figure 7 The results show that no significant Mn(II) dissolution was detected in the MCD system. In contrast, the average Mn(II) dissolution in the SMCD system was 2.20 mg / L to 3.78 mg / L in stages I to II. However, in stage III, the Mn(II) dissolution showed a decreasing trend of 3.28 mg / L. - -N removal results showed that the average NO3 - -N removal is significantly greater than that in stage I-II. Theoretically, the amount of Mn(II) dissolution should be greater. Studies have shown that the decrease in temperature will significantly weaken the autotrophic denitrification reaction of pyrite. The decrease in the reaction activity of pyrite makes Fe in the system 2+ The dissolution is reduced, and the activity of iron oxidizing bacteria is significantly affected by low temperature, resulting in Fe 2+ →Fe 3+ The conversion of Mn(II) is limited. Therefore, during acclimation stages I and II, the oxidation of Mn(II) is inhibited to a certain extent by the low temperature. However, as the temperature rises during acclimation stage III, the activity of microorganisms involved in Mn(II) oxidation recovers, and Mn(II) dissolution decreases.

[0068] The calculation results of the contribution rates of sulfur and manganese in the autotrophic denitrification process in the SMCD system at different temperatures are as follows: Figure 8As shown, the contribution of the MAD reaction initially increases and then decreases as the reaction progresses. Its contribution rate is 42.08% in stage I, increases to 63.18% in stage II, and finally decreases to 23.07% in stage III. In contrast, the contribution rate of the SAD reaction decreases from 57.82% in stage I to 36.82% in stage II, and then increases to 76.93% in stage III. These results indicate that the SAD reaction is significantly inhibited at low temperatures, while the contribution rate of the MAD reaction increases significantly. The contribution rate increases with lower temperatures. This indicates that the MAD reaction is crucial for maintaining the efficient denitrification of the SMCD system at low temperatures. Specifically, at low temperatures, the MAD reaction supplements the nitrogen removal capacity gap, effectively offsetting the shortcomings of the SAD reaction alone and enabling the SMCD system to exhibit good low-temperature tolerance. The SAD reaction is the primary denitrification process at ambient temperatures. The coexistence of the SAD and MAD reactions enables the SMCD system to maintain high denitrification efficiency despite large temperature fluctuations.

[0069] 2. Characteristics of denitrification microenvironment

[0070] The particle size of activated sludge in different systems was analyzed using a laser particle size analyzer after the operation was completed. Figure 9 The results show that there are significant differences in the sludge particle size distribution of different systems. The average sludge particle sizes in the SD, MCD and SMCD systems are 17.84μm, 133.8μm and 97.47μm, respectively, as shown in Table 2. Hydraulic shear force is an important factor affecting the properties of granular sludge. When the hydraulic load is large, it promotes sludge compaction, while when the hydraulic load is small, it is difficult to form granules. The formation of sludge granulation by hydraulic shear force is the result of a positive / inhibitory effect. Positive effect: high hydraulic load enhances the mass transfer between microorganisms and pollutants, promotes microbial proliferation and EPS secretion. Inhibitory effect: high hydraulic load increases the risk of sludge being flushed out and broken. The sludge particle size of the SD and SMCD systems is significantly larger than that of the MCD system, indicating that the positive effect of sludge granulation has a greater impact on the SD and SMCD systems.

[0071] In addition, the sludge specific surface area of ​​the SMCD system is 218.8m 2 / kg, significantly greater than the SD system 99.05m 2 / kg. Research shows that larger granular sludge particle size is not necessarily better. Smaller granular sludge particles have a larger relative surface area, resulting in a larger relative area of ​​contact with water, and exhibiting better biological activity. Conversely, as sludge particle size increases, denitrification-generated gases overflow, filling the sludge with pores. This facilitates the entry of other substrates into the granular sludge, disrupting the established microenvironment. Therefore, SMCD systems with larger sludge surface area may result in better mass transfer efficiency.

[0072] Table 2 Activated sludge properties parameters

[0073] system Average particle size (μm) Peak particle size (μm) <![CDATA[Specific surface area (m 2 / kg)]]> SD 133.8 238.1 99.05 MCD 17.84 23.31 412.9 SMCD 97.47 204.3 218.8

[0074] Comparison of denitrification enzyme activity

[0075] The results of the denitrification enzyme activity test showed that the activities of nitrate reductase and nitrite reductase in the SMCD system were 0.51 and 3.85 U / g, respectively, which were significantly higher than those in the SD and SMCD systems. Figure 10 As shown in Figure 2, high microbial enzyme activity within the system promotes denitrification and results in more complete denitrification. This is consistent with the SMCD system's highest denitrification efficiency and lack of intermediate product accumulation. On the one hand, the SMCD system provides an additional inorganic carbon source, enriching the system with nutrients. On the other hand, the system's stable pH environment is conducive to microbial growth and accumulation, resulting in higher denitrifying enzyme activity. In contrast, other systems, affected by nutrients and acidic pH, have low denitrifying enzyme activity, resulting in poor denitrification.

[0076] Comparison of spatial distribution of live and dead cells in biofilms

[0077] The spatial distribution of live / dead cells in each system was characterized by confocal microscopy to assess the viability of microorganisms in the system, e.g. Figure 11 As shown in the figure, different colors of fluorescence reflect microbial activity. Live bacteria stained with SYTO-9 emit green light, while dead bacteria stained with PI emit red light. Fluorescence staining results indicate that bacteria in all three systems have normal life functions. However, green fluorescence clearly predominates over red fluorescence in the SMCD system, indicating a high proportion of live cells within the system. In contrast, red fluorescence predominates in the SD and MCD systems, indicating a high proportion of dead cells and damaged biofilm cells within both systems.

[0078] From the above experimental data, it can be seen that under low temperature autotrophic conditions, when the inlet water temperature is reduced to 4.5-9.7℃, NO3 - When the -N concentration was 21.31 mg / L and the HRT was 6h, the average TN removal rate of the SMCD system reached 70.56%, which was significantly higher than that of the control system. At this time, the contribution rate of the MAD reaction reached 63.18%, which was significantly higher than that of 10.1-15.3℃ (42.08%) and 20.9-23.1℃ (23.07%). The MAD effect effectively compensated for the deficiency of the single SAD effect at low temperatures, making the SMCD system have good low temperature tolerance. The SMCD system has a short recovery period. After running at room temperature for 3 days, TN and NO3 - The average -N removal rate recovered to over 90%, with the SAD reaction becoming the primary denitrification process. The coexistence of SAD and MAD reactions enabled the SMCD system to maintain high denitrification efficiency even in the face of large temperature fluctuations.

[0079] Although preferred embodiments of the present invention have been described, further changes and modifications may be made to these embodiments by those skilled in the art once the basic inventive concepts are understood. It is apparent that various modifications and variations may be made by those skilled in the art without departing from the spirit and scope of the present invention. Thus, the present invention is intended to encompass such modifications and variations as fall within the scope of equivalents of the present invention.

Claims

1. A sulfur-manganese composite autotrophic denitrification and denitrification device, characterized in that: It includes a main reactor (1), a water 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 sequentially arranged from bottom to top; a first sampling port (14), a second sampling port (15), a third sampling port (16) and a fourth sampling port (17) are provided on the side wall of the main reactor (1) from top to bottom; the first sampling port (14) is connected to the upper part 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 water outlet of the water inlet box (2) is connected to a water inlet pump (3), and the water inlet pump (3) is in communication with 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 pipeline, and the other end of the constant temperature water bath (5) is connected to a water bath inlet pump (4), and the water bath inlet pump (4) is connected to the main reactor (1).

2. The sulfur-manganese composite autotrophic denitrification and denitrification device according to claim 1, characterized in that: The height ratio of the gravel layer, the sulfur-rhodochrosite layer and the quartz sand layer is 3-4:45:

15.

3. The sulfur-manganese composite autotrophic denitrification and denitrification device according to claim 1, characterized in that: The porosity of the sulfur-rhodochrosite layer is 40% to 50%.

4. The sulfur-manganese composite autotrophic denitrification and denitrification device according to claim 1, characterized in that: The sulfur-rhodochrosite layer is obtained by mixing sulfur and rhodochrosite in an equal volume ratio.

5. The sulfur-manganese composite autotrophic denitrification and denitrification device according to claim 1, characterized in that: The particle sizes of the sulfur and the rhodochrosite are both 2 mm to 5 mm.

6. The sulfur-manganese composite autotrophic denitrification and denitrification device according to claim 1, characterized in that: A backwash port (13) is provided at the bottom of the main reactor (1), and a water outlet (12) is provided at the top of the main reactor (1).

7. The sulfur-manganese composite autotrophic denitrification and denitrification device according to claim 6, characterized in that: A porous partition (18) is provided below the gravel layer, and the lower layer of the porous partition (18) is a water distribution area.

8. The sulfur-manganese composite autotrophic denitrification and denitrification device according to claim 7, characterized in that: The backwash port (13) is connected to the water distribution area; and the water inlet pump (3) is connected to the water distribution area.

9. A method for sulfur-manganese composite autotrophic denitrification and denitrification using the sulfur-manganese composite autotrophic denitrification and denitrification device according to any one of claims 1 to 8, characterized in that: The specific process is as follows: The sludge in the sewage treatment plant is filtered and poured into the main reactor (1), and the water inlet pump (3) is started to pump the synthetic wastewater in the water inlet tank (2) into the water distribution area, and enter the gravel layer through the porous filter plate and into the sulfur-rhodochrosite layer. After the synthetic wastewater fills the entire main reactor (1), the pumping of the synthetic wastewater is stopped, and the synthetic wastewater and the sludge are acclimated by autotrophic denitrification reaction in the sulfur-rhodochrosite layer. 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); After the acclimation is completed, the water bath inlet pump (4) is turned off, impurities are filtered through the quartz sand layer, and the filtered wastewater is discharged through the outlet (13). The nitrogen generated during the autotrophic denitrification reaction is discharged through the exhaust port at the top of the reactor (1).

10. The method according to claim 9, characterized in that 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 / LFeSO4·7H2O, 0.1 g / L CoCl2·6H2O, 0.1 g / L ZnSO4·7H2O, 0.01 g / L CuSO4·5H2O and 0.01 g / LNa2MoO4·2H2O.

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