Landfill leachate denitrification system and method based on sulfur circulation and flora cooperation

Abstract

The invention discloses a landfill leachate denitrification system and method based on sulfur circulation and flora cooperation. The system is composed of a sulfur conversion reactor, a sulfur autotrophic denitrification reactor and a circulation regulation and control system, sulfur disproportionation bacteria and sulfate reducing bacteria are inoculated in the sulfur conversion reactor, S < 2-> is generated through a sulfur disproportionation reaction to provide electron donors for autotrophic denitrification, and sulfate by-products are reduced through a sulfate reduction reaction. Effluent of the sulfur conversion reactor and the nitrified leachate flow through a sulfur autotrophic denitrification reactor together for nitrogen removal by denitrification. The system is provided with external circulation to enable effluent of the sulfur autotrophy reactor to flow back to the sulfur conversion reactor, disproportionation reaction is strengthened through internal circulation, and sulfate is further removed. The process realizes deep denitrification without an external carbon source, synchronously controls sulfate accumulation, and is suitable for high nitrate nitrogen wastewater treatment.

Description

Technical Field

[0001] The present invention relates to the technical field of biological wastewater treatment, and particularly to a process and system for realizing the recycling of sulfur through coupling sulfur-disproportionating bacteria and sulfate-reducing bacteria, and simultaneously removing nitrate and sulfate in landfill leachate. Background Art

[0002] Landfill leachate is a complex wastewater containing high concentrations of organic matter, ammonia nitrogen, heavy metals and salts generated during the landfill or incineration of garbage, and its treatment is extremely difficult. Among them, nitrogen pollution (mainly ammonia nitrogen and nitrate nitrogen) is one of the core challenges in leachate treatment. Traditional processes usually adopt the "nitrification-denitrification" biological nitrogen removal process, that is, ammonia nitrogen is converted into nitrate (NO3 - ) through nitrification, and then nitrate is reduced to nitrogen gas (N2) through denitrification. However, the carbon-nitrogen ratio (C / N) of landfill leachate is extremely low (usually <3), and a large amount of exogenous organic matter such as methanol and sodium acetate needs to be added during the denitrification stage due to insufficient carbon source, resulting in high treatment costs (the cost per ton of water increases by 20% - 40%), an increase in sludge production, and a risk of secondary pollution.

[0003] To reduce the dependence on carbon sources, sulfur autotrophic denitrification technology has been widely studied. This technology uses elemental sulfur (S 0 ) or sulfide (S 2- ) as an electron donor, and nitrate is reduced to nitrogen gas by sulfur-oxidizing bacteria (such as Thiobacillus). The reaction formula is as follows: 5S 0 +6NO3 - +2H2O→3N2↑+5SO4 2- +4H + . Although the sulfur autotrophic process does not require external carbon sources, its inherent defects severely restrict engineering applications: (1) Accumulation of sulfate by-products. For every 1 g of NO3 - -N removed, about 4.5 g of SO4 2- is produced, resulting in an increase in the salinity of the effluent (>500 mg / L), affecting subsequent reuse or exceeding the discharge standard limit (such as the "Pollution Control Standard for Domestic Waste Landfills" requires SO4 2- <250 mg / L); (2) Low utilization rate of electron donors. Elemental sulfur has strong hydrophobicity and low mass transfer efficiency, and the reaction rate is only 1 / 3 - 1 / 5 of that of heterotrophic denitrification; (3) Continuous consumption of sulfur sources. Sulfur or sulfide needs to be added regularly, and the long-term operation cost is still relatively high (the sulfur addition cost is about 0.8 - 1.2 yuan / ton of water).

[0004] To address the problem of sulfate by-product accumulation, existing technologies have attempted to reduce SO4 2- to S 2-, Patent CN 113716689 B discloses a hybrid nutrition denitrification method based on sulfur reduction and sulfur autotrophic denitrification, which uses the reduced sulfur produced by sulfate reduction as an electron donor to promote sulfur autotrophic denitrification. However, there are the following limitations in using SRB alone: First, the reaction conditions conflict. SRB requires a strictly anaerobic environment [dissolved oxygen (DO) < 0.1 mg / L], while sulfur autotrophic denitrification requires a microaerobic condition (DO = 0.2 - 0.5 mg / L), and it is difficult for the two to coexist. Second, the toxicity of sulfide. The accumulation of S 2- (>50 mg / L) will inhibit the activity of denitrifying bacteria, and an additional sulfide oxidation unit needs to be added, which complicates the process chain. In addition, the existing processes generally lack the design of sulfur cycle, resulting in waste of sulfur resources and secondary pollution.

[0005] Aiming at the problem of low utilization rate of elemental sulfur as an electron donor, sulfur-disproportionating bacteria (such as Desulfuromonas) can disproportionate S 0 into S 2- and SO4 2- (Reaction formula: 4S 0 + 4H2O → S 2- + 3SO4 2- + 8H+), which can theoretically provide an electron donor (S 2- ) for autotrophic denitrification. Patent CN 114409096 A discloses a method for coupling elemental sulfur disproportionation and sulfur autotrophic denitrification to achieve efficient deep denitrification of sewage, which effectively improves the effect of sulfur autotrophic denitrification by using in-situ disproportionation reaction. However, sulfur disproportionation further exacerbates the risk of excessive sulfate in the effluent.

[0006] By coupling the sulfur disproportionation and sulfate reduction processes, sulfur disproportionation is used to convert S 0 into S 2- and SO4 2- , and the simultaneously generated SO4 2- can be converted into S 2- through sulfate reduction, forming a closed sulfur cycle. However, the realization of this path faces two major technical bottlenecks: one is the problem of microbial community synergy. The metabolic activities of sulfur-disproportionating bacteria and sulfate-reducing bacteria are affected by multiple factors such as pH, DO, and sulfur form, and it is difficult for the existing processes to maintain the efficient synergy of the two types of microbial communities; the other is the low coupling efficiency of sulfur transformation - denitrification. The sulfur disproportionation reaction rate is slow [0.1 - 0.3 g S 0 / (L·d)], which is difficult to match the denitrification demand, and there is a lack of an effective control mechanism for the reflux of by-product SO4 2- .

[0007] In summary, developing a landfill leachate denitrification process based on self-sufficient sulfur cycle, complementary functions of microbial communities, and synchronous removal of nitrate and sulfate is of great significance for breaking through the existing technical bottlenecks and promoting the green treatment of high-salt wastewater. Summary of the Invention

[0008] The core objective of the present invention is to overcome the defects in the existing sulfur autotrophic denitrification technology, such as low utilization rate of electron donors, serious accumulation of sulfate by-products, and insufficient synergy efficiency of bacterial communities. A denitrification system and method for landfill leachate based on a closed-loop sulfur cycle are provided. By constructing a functional synergy system of sulfur-disproportionating bacteria and sulfate-reducing bacteria, and coupling the process chains of a sulfur conversion reactor and a sulfur autotrophic denitrification reactor, efficient removal of nitrate and synchronous control of sulfate are achieved, ultimately reaching the goal of deep denitrification without the need for external carbon / sulfur sources, low sludge production, and low operating costs.

[0009] The denitrification system of the present invention consists of three major parts: a sulfur conversion reactor, a sulfur autotrophic denitrification reactor, and a circulation regulation system. Its core features are as follows:

[0010] 1. Sulfur conversion reactor

[0011] As the core unit of the sulfur cycle, it undertakes the dual functions of elemental sulfur disproportionation and sulfate reduction. The reactor form adopts a closed stirred tank reactor (CSTR), and the effective volume ratio is 1:1.5 (matched with the subsequent sulfur autotrophic reactor). The packing area is filled with sulfur particles with a particle size of 2 - 5 mm (purity > 99%), and the filling rate is 30% - 50%, forming a stable sulfur slow-release matrix. A double-layer paddle agitator (rotation speed 30 - 60 rpm) is configured. The upper paddle is close to the bottom of the mixed liquid area to promote sludge suspension; the lower paddle is located in the sulfur packing area to prevent sulfur particle caking. An internal circulation pump is set to return the top effluent to the bottom of the reactor, with a flow ratio of 100% - 300%, to maintain a sludge concentration of 8 - 15 g / L and ensure the activity of the bacterial community.

[0012] The sulfur-disproportionating bacteria are preferably Desulfomonile spp., which catalyze the sulfur disproportionation reaction under anoxic conditions (DO = 0.2 - 0.5 mg / L): 4S 0 + 4H2O → S 2- + 3SO4 2- + 8H + . The sulfate-reducing bacteria are preferably Desulfovibrio spp., which use H2 or organic matter as electron donors to reduce SO4 2- to S 2- : SO4 2- + 4H2 → S 2- + 4H2O. The inoculation volume ratio of sulfur-disproportionating bacteria to sulfate-reducing bacteria is 1:1 - 1:3, forming a closed-loop sulfur transformation through metabolic complementarity.

[0013] 2. Sulfur autotrophic denitrification reactor

[0014] Utilize the S generated by the sulfur conversion reactor 2-As an electron donor, the efficient conversion of NO3 - to N2 is completed. The reactor form is an upflow fixed-bed reactor (UFBR) with a height-to-diameter ratio of 2.5:1 and a hydraulic retention time (HRT) of 8 - 12 h. It is filled with a composite filler of pyrite (FeS2) and sulfur (S 0 ) (mass ratio 1:3 - 1:5), and the conductivity of FeS2 is used to enhance the electron transfer rate. An external circulating water jacket is provided to maintain the reaction temperature at 25 - 35 °C to avoid the decrease in enzyme activity caused by low temperature.

[0015] Under the action of sulfur autotrophic denitrifying bacteria (such as Thiobacillus denitrificans), S 2- acts as an electron donor to drive the denitrification reaction: 5S 2- + 16NO3 - + 16H + → 8N2↑ + 5SO4 2- + 8H2O.

[0016] 3. Circulation regulation system

[0017] Thirty to seventy percent of the effluent from the sulfur autotrophic reactor is refluxed to the inlet end of the sulfur conversion reactor, and sulfate-reducing bacteria are used to perform secondary reduction on SO4 2- to form an internal sulfur cycle. An on-line sulfate monitor and a PLC controller are integrated on the external circulation pipeline. When the detected SO4 2- concentration in the effluent > 60 mg / L, the external circulation ratio is automatically increased to 70% - 90% to ensure that the sulfate removal rate > 65%.

[0018] Five to ten percent of the excess sludge from the sulfur conversion reactor is regularly refluxed to the sulfur autotrophic reactor to supplement the active microbial population and prevent the attenuation of denitrification efficiency caused by biofilm aging.

[0019] The denitrification method of the present invention is implemented according to the following steps:

[0020] Step 1: Start-up of the sulfur conversion reactor and activation of sulfur

[0021] Sulfur disproportionating bacteria and sulfate-reducing bacteria are inoculated in the sulfur conversion reactor (1), and S is generated through the sulfur disproportionation reaction 2- to provide an electron donor for autotrophic denitrification, and at the same time, the sulfate by-product is reduced by the sulfate reduction reaction. A mixed bacterial solution of sulfur disproportionating bacteria and sulfate-reducing bacteria (inoculation amount 10% - 15%) is added to the sulfur conversion reactor, and simulated leachate (NO3 - -N = 100 mg / L, SO4 2- = 50 mg / L) is used for domestication for 15 - 20 days, and the sulfur addition amount is gradually increased to 5 - 15 g S 0 / L. Maintain the DO at 0.2 - 0.5 mg / L through micro-aerobic aeration (air flow rate 0.05 - 0.1 L / min) to meet the micro-aerobic requirements of sulfur-disproportionating bacteria while inhibiting the overgrowth of strict anaerobes. Add NaHCO3 buffer to stabilize the pH at 7.0 - 7.8 and avoid a sudden drop in pH caused by the acid production (H+) during the sulfur disproportionation reaction (when the pH < 6.5, the microbial activity decreases by more than 50%). Under the synergistic action of sulfur-disproportionating bacteria and sulfate-reducing bacteria, S 0 is converted to S 2- (yield 0.8 - 1.2 g S 2- / g S 0 ), and at the same time, part of the SO4 2- is reduced to S 2- .

[0022] Step Two: Sulfur autotrophic denitrification

[0023] The effluent from the sulfur conversion reactor (1) and the nitrified leachate flow through the sulfur autotrophic denitrification reactor (2) together for denitrification. The nitrified leachate (NO3 - -N 100 - 300 mg / L, pH 7.5 - 8.0) and the effluent from the sulfur conversion reactor rich in S 2- enter the sulfur autotrophic denitrification reactor together. Under the action of sulfur autotrophic bacteria, denitrification is completed, generating N2 and SO4 2- (for every 1 g of NO3 - -N removed, 2.8 - 3.2 g of SO4 2- is produced).

[0024] Step Three: External circulation sulfate reflux control

[0025] The system is set with an external circulation to return the effluent from the sulfur autotrophic denitrification reactor (2) to the sulfur conversion reactor (1) to remove SO4 2- . 30% - 70% of the effluent from the sulfur autotrophic reactor is refluxed to the sulfur conversion reactor through an external circulation pump. The sulfate-reducing bacteria in it are used to perform secondary reduction on SO4 2- , forming a closed-loop cycle of "S 0 →S 2- →SO4 2- →S 2- ", reducing the total sulfate yield of the system to 1.2 - 1.5 g of SO4 2- / g of NO3 - -N, which is 60% - 70% less than the traditional process.

[0026] Step Four: Internal circulation strengthening and sludge regulation

[0027] The sulfur conversion reactor (1) enhances the disproportionation reaction through internal circulation and further removes sulfates. The sludge concentration is maintained at 8 - 15 g / L by the circulation pump in the sulfur conversion reactor, improving the contact efficiency between the microbial community and the substrate, and increasing the sulfur disproportionation rate by 20% - 30%. 5% - 10% of the sludge in the sulfur conversion reactor is refluxed to the sulfur autotrophic reactor every week to supplement the sulfur autotrophic microbial community, ensuring the system stability under fluctuating denitrification loads, i.e., the TN removal rate fluctuation < 5%.

[0028] The key innovation points of the present invention are as follows:

[0029] Firstly, the sulfur closed-loop circulation mechanism. Through the sulfur disproportionation reaction, S 0 is converted into S 2- (electron donor). Meanwhile, the by-product SO4 2- is re-converted into S 2- through the sulfate reduction reaction, forming an internal sulfur cycle and increasing the sulfur utilization rate from 30% - 40% in the traditional process to 75% - 85%. The synergistic effect of the external circulation and the internal circulation achieves the dynamic balance of "generation - reduction" of SO4 2- , and the concentration of SO4 2- in the effluent is stably < 50 mg / L.

[0030] Secondly, the functional zoning and cooperation of the microbial community. The spatial zoning (sulfur filler area and mixed liquor area) and metabolic complementarity of sulfur-disproportionating bacteria and sulfate-reducing bacteria in the sulfur conversion reactor solve the problem of competitive inhibition of the microbial community in the traditional process. Through the DO gradient control (micro-aerobic - anoxic), the two types of microbial communities coexist efficiently in the same reactor, and the microbial community density is increased by 2 - 3 times (> 10 8 CFU / mL).

[0031] Thirdly, the intelligent control system. Based on the dynamic external circulation control of online sulfate monitoring, the system can still operate stably under high-load (NO3 - -N > 200 mg / L) shocks (recovery time < 24 h). The real-time matching of the internal circulation flow rate and the sludge concentration avoids sulfur particle blockage and sludge loss, and extends the packing replacement cycle to 6 - 8 months.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0033] Firstly, the denitrification efficiency is significantly improved. Under the condition that the influent NO3 - -N concentration is 150 - 300 mg / L, the system TN removal rate > 92%, the effluent TN < 15 mg / L, and the denitrification load reaches 0.8 - 1.2 kgN / (m 3 ·d), which is 40% - 60% higher than that of the single sulfur autotrophic process.

[0034] Secondly, the accumulation of sulfate is effectively controlled. Through the sulfur cycle, the net sulfate production rate is reduced to 1.2 - 1.5 g / g N, and the SO4 2- concentration in the effluent is < 50 mg / L, meeting the first-class A standard of the "Discharge Standard of Pollutants for Municipal Wastewater Treatment Plants" (GB 18918 - 2002).

[0035] Meanwhile, the operating cost is significantly reduced. Without adding external carbon sources or sulfides, the water treatment cost per ton is reduced by 50% - 60% compared with heterotrophic denitrification and by 30% - 40% compared with traditional sulfur autotrophic processes.

[0036] In addition, the process stability is enhanced. The double - cycle system has a remarkable ability to buffer water quality fluctuations. When the influent NO3 - -N fluctuates by ±30%, the TN removal rate remains > 90%, and the sludge production is reduced by 50% - 70%. Description of the Drawings

[0037] Figure 1 Process Flow Chart

[0038] This figure shows the treatment process after the nitrified leachate enters the system. First, it is mixed with the effluent from the sulfur conversion reactor and then enters the sulfur autotrophic denitrification reactor together for denitrification and nitrogen removal. After that, part of the effluent is refluxed to the sulfur conversion reactor through the external circulation for sulfate removal, and the remaining effluent is further treated through the advanced treatment unit and finally meets the treatment requirements.

[0039] Figure 2 System Structure Schematic Diagram

[0040] Illustration: Sulfur conversion reactor (1), sulfur autotrophic denitrification reactor (2), external circulation pipeline (3), internal circulation unit (4), sulfur packing area (5), stirring device (6), on - line sulfate monitor (7), advanced treatment unit (8), influent tank (9). The arrows mark the water flow direction and the circulation path.

[0041] Figure 3 Internal Structure Diagram of Sulfur Conversion Reactor

[0042] The internal structure of the sulfur conversion reactor includes: influent port, mixed liquid area, perforated water distribution pipe, sulfur packing area, stirring paddle, DO probe, pH sensor, internal circulation inlet, internal circulation pump, sludge sedimentation area, and effluent port.

[0043] Figure 4 Control Logic Diagram

[0044] This figure reflects the control logic of the circulation control system. It includes the process of adjusting the external circulation reflux ratio of the external circulation system according to the sulfate concentration and the process of adjusting the internal circulation reflux ratio of the internal circulation system in the sulfur conversion reactor according to the dissolved oxygen condition. Detailed Implementation Modes

[0045] Example 1: Treatment of landfill leachate at conventional concentration

[0046] In this example, a sulfur cycle-coupled microbial consortium synergistic system was used to treat the nitrified leachate (NO3 - -N = 150 mg / L, SO4 2- = 80 mg / L, pH = 7.6) from a certain landfill. The sulfur conversion reactor was a 10 m 3 closed stirred tank filled with sulfur particles with a particle size of 3 mm (dosage 10 g / L), inoculated with a mixed bacterial solution of Desulfomonile spp. and Desulfovibrio spp. (volume ratio 1:2), and the sludge concentration was maintained at 12 g / L by a double-layer paddle stirrer (rotation speed 40 rpm). The internal circulation pump returned the bottom mixed liquid to the top inlet end at a flow ratio of 200%, controlling DO = 0.3 mg / L, pH = 7.2, and HRT was 6 hours. The sulfur autotrophic denitrification reactor was a 15 m 3 upflow fixed-bed reactor filled with a composite filler of FeS2 and sulfur (mass ratio 1:4), HRT = 10 hours, temperature 30 °C, and 50% of the effluent was returned to the sulfur conversion reactor through an external circulation pipeline. After 30 days of operation, the TN removal rate reached 95.4% (effluent TN = 14.7 mg / L), the net production rate of SO4 2- was 1.3 g / g N (effluent SO4 2- = 42 mg / L), the treatment cost per ton of water was only 0.8 yuan, and the sludge production rate was 0.12 kg / m 3 , and the system had good stability.

[0047] Example 2: Verification of adaptability to high-concentration leachate shock load

[0048] For the high-concentration leachate (NO3 - -N = 280 mg / L, SO4 2- = 150 mg / L, pH = 7.8) from a certain waste incineration plant, the system parameters were adjusted to cope with the load shock. The sulfur dosage in the sulfur conversion reactor was increased to 15 g / L, the internal circulation flow ratio was increased to 300%, and the sludge reflux system (from the sulfur conversion reactor to the sulfur autotrophic reactor, reflux ratio 8%) was started. The HRT of the sulfur autotrophic denitrification reactor was extended to 12 hours, the temperature was increased to 35 °C, the external circulation ratio was increased to 70%, and at the same time, an on-line sulfate monitor was added to the external circulation pipeline (the detection threshold was set to trigger flow regulation when SO4 2- > 60 mg / L). During the operation, when the influent NO3 -When the -N concentration suddenly increases to 300 mg / L, the system restores stability within 24 hours by dynamically adjusting the external circulation ratio (70%-90%) and supplementing sulfur. Finally, the effluent TN = 19.3 mg / L (removal rate 93.1%), SO4 2- = 58 mg / L (net production rate 1.5 g / g N), the cost per ton of water is 1.0 yuan, and the sludge production rate is 0.15 kg / m 3 , verifying the strong adaptability of the system to high-load shocks.

[0049] Example 3: Long-term operation stability and maintenance optimization

[0050] To verify the long-term stability of the system, a certain landfill leachate (NO3 - -N fluctuates between 120 - 220 mg / L) was continuously treated for 6 months. The sulfur conversion reactor adopts dynamic internal circulation control (flow ratio 100%-300%), and precise regulation is achieved through an online DO sensor (maintaining 0.2 - 0.5 mg / L) and a pH probe (automatically adding NaHCO3 buffer to 7.0 - 7.8). The sludge concentration is stable at 12 g / L. The external circulation pipeline of the sulfur autotrophic denitrification reactor integrates a PLC control system. When the SO4 2- concentration > 60 mg / L, the external circulation ratio is automatically increased to 70%, and sulfur packing is supplemented every 2 months (loss rate < 5%). Long-term operation data shows that the average TN removal rate is 94.2% (effluent TN < 15 mg / L), the SO4 2- concentration is always < 50 mg / L, the cost per ton of water is 0.9 yuan, and the sludge production rate is 0.10 kg / m 3 (65% lower than the traditional process), and the packing replacement cycle > 6 months, proving that the system has low maintenance costs and long-term operation reliability.

[0051] Comparative example: Traditional sulfur autotrophic denitrification process

[0052] The same raw water as in Example 1 (NO3 - -N = 150 mg / L) was treated using a single sulfur autotrophic denitrification reactor. The reactor was filled with sulfur packing (dosage 10 g / L, no composite pyrite), HRT = 12 hours, and no internal or external circulation system and bacterial community co-inoculation were set up. The operation results show that the TN removal rate is only 72.5% (effluent TN = 41.3 mg / L), and the SO4 2- net production rate is as high as 4.2 g / g N (effluent SO4 2- = 320 mg / L), the cost per ton of water is 1.5 yuan (sulfur needs to be supplemented every 15 days), and the sludge production rate is 0.35 kg / m 3 . The comparison data shows that the traditional process has defects such as low denitrification efficiency, serious sulfate accumulation, and high operation costs due to the lack of a sulfur closed-loop cycle and bacterial community cooperation mechanism.

[0053] The effects of the examples and comparative examples are compared as shown in Table 1.

[0054] Table 1 Comparative analysis of the effects of each example

[0055]

[0056] Through the collaborative design of the sulfur conversion-autotrophic denitrification dual-cycle system and the microbial community, the present invention significantly improves the nitrogen removal efficiency of landfill leachate and inhibits sulfate accumulation. Examples 1-3 show that during conventional load, high-load shock and long-term operation of the system, the TN removal rate is >93%, and the net production rate of SO4 2- is reduced by 65%-70% compared with the traditional process (comparative example), the cost per ton of water is saved by 30%-50%, and the sludge production is reduced by more than 65%. The comparative example further verifies the limitations of the traditional process, highlighting the comprehensive advantages achieved by the present invention through the closed-loop circulation of sulfur, functional zoning of the microbial community and intelligent regulation, providing an efficient, economical and sustainable solution for the treatment of high-nitrate nitrogen wastewater.

Claims

1. A landfill leachate denitrification system based on sulfur cycle and bacterial community collaboration, characterized in that: It includes a sulfur conversion reactor (1) and a sulfur autotrophic denitrification reactor (2). Sulfur disproportionating bacteria and sulfate-reducing bacteria are inoculated in the sulfur conversion reactor (1); the water outlet of the sulfur conversion reactor (1) is connected to the water inlet end of the sulfur autotrophic denitrification reactor (2); the water outlet of the sulfur autotrophic denitrification reactor (2) is connected to the water inlet end of the sulfur conversion reactor (1) through an external circulation pipeline (3); an internal circulation unit (4) is provided inside the sulfur conversion reactor (1).

2. The system according to claim 1, wherein: The external circulation flow ratio is 30% - 70%, and the internal circulation flow ratio is 100% - 300%.

3. The system according to claim 1, wherein A sulfur packing area (5) and a stirring device (6) are provided inside the sulfur conversion reactor (1). The sulfur packing is sulfur particles with a particle size of 2 - 5 mm, and the filling rate is 30% - 50%.

4. The system according to claim 1, wherein The sulfur autotrophic denitrification reactor (2) is filled with pyrite fillers, and the mass ratio of pyrite (FeS2) to sulfur (S 0 ) is 1:3 to 1:

5. An on-line sulfate monitor (7) is installed on the external circulation pipeline (3), and the external circulation flow rate is dynamically adjusted according to the SO4 2- concentration in the effluent.

5. The system according to claim 1, wherein The inoculation volume ratio of the sulfur disproportionating bacteria to the sulfate-reducing bacteria is 1:1 - 1:

3.

6. A method for denitrification of landfill leachate based on sulfur cycle and bacterial community collaboration, characterized in that: It includes the following steps: a) Inoculate sulfur-disproportionating bacteria and sulfate-reducing bacteria in the sulfur conversion reactor (1), and generate S through the sulfur disproportionation reaction 2- to provide an electron donor for autotrophic denitrification, and at the same time utilize the sulfate reduction reaction to reduce sulfate by-products; b) The water outlet of the sulfur conversion reactor (1) and the nitrified leachate flow through the sulfur autotrophic denitrification reactor (2) together for denitrification and nitrogen removal; c) The system is set to have an external loop to return the effluent of the sulfur autotrophic denitrification reactor (2) to the sulfur conversion reactor (1), and use the sulfate reduction reaction to remove SO4 2- ; d) The sulfur conversion reactor (1) strengthens the disproportionation reaction through internal circulation and further removes sulfate.

7. The method according to claim 6, characterized in that, The dissolved oxygen concentration of the sulfur conversion reactor (1) is controlled at 0.2 - 0.5 mg / L, the pH value is 7.0 - 7.8, the sulfur filler dosage is 5 - 15 g S 0 / L, and the hydraulic retention time is 4 - 8 h.

8. The method according to claim 6, characterized in that The hydraulic retention time of the sulfur autotrophic denitrification reactor (2) is 8 - 12 h, and the reaction temperature is 25 - 35 °C.

9. The method according to claim 6, wherein The sludge of the sulfur conversion reactor (1) needs to be regularly refluxed to the sulfur autotrophic denitrification reactor (2), and the reflux ratio is 5% - 10% to supplement the activity of the bacterial community.

10. The method according to claim 6, wherein When the influent NO3 - -N concentration > 200 mg / L, the external circulation flow ratio is increased to 70% - 90%.

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