A method for optimizing sulfur autotrophic denitrification for advanced nitrogen removal of municipal wastewater by HRT

Abstract

The application discloses a kind of by HRT optimization for municipal sewage advanced denitrification sulfur autotrophic denitrification method.The sludge after concentration is filled into reactor, and filler is added;Simulated municipal sewage with nitrate nitrogen (NO3 ‑ -N) concentration of 20mg / L is entered into sulfur autotrophic denitrification area, the DO of reactor is controlled below 0.1mg / L, water temperature is controlled at 25±2°;Influent pH is controlled at 7~8, and influent DO is 5±2mg / L;Adjust HRT to 20, 16, 8, 4, 1h, and sulfur autotrophic denitrification bacteria population that adapts to the characteristics of municipal sewage is domesticated in reactor.HRT is 20h, and the period is operated for 30 days, and the rest is each operated for 10 days in each period, and the concentration of nitrate nitrogen (NO3 ‑ -N) and nitrite nitrogen (NO2 ‑ -N) in effluent tank is monitored every day.The municipal sewage can be deeply denitrified under short time HRT=1h, and operation and maintenance cost can be effectively reduced.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, and specifically relates to a sulfur autotrophic denitrification method for deep denitrification of municipal wastewater through HRT optimization. Background Technology

[0002] Nitrogen is a major cause of eutrophication in water bodies. The "Discharge Standard of Pollutants for Municipal Wastewater Treatment Plants" (GB18918-2002) stipulates a Class A discharge standard with a total nitrogen (TN) limit of 15 mg / L. Some regions have issued even stricter local standards; for example, the Kunming local standard "Discharge Limits of Major Pollutants for Municipal Wastewater Treatment Plants" (DB 5301 / T 43-2020) requires effluent TN to be as low as 5 mg / L for Class A. Currently, urban wastewater denitrification mainly relies on biological denitrification processes. However, the biological denitrification capacity of existing urban wastewater treatment systems generally cannot meet the current high discharge standards. Therefore, addressing the shortcomings in denitrification and enhancing denitrification performance are key aspects of upgrading and retrofitting urban wastewater treatment plants.

[0003] Traditional biological nitrogen removal technologies, while achieving nitrogen removal from wastewater, often involve high energy and material consumption, and generate significant amounts of residual sludge and greenhouse gas emissions. Improving the efficiency and effectiveness of traditional biological nitrogen removal processes and promoting the application of novel low-carbon autotrophic biological nitrogen removal technologies will be the core driving force for the future development of the wastewater biological nitrogen removal field. Sulfur autotrophic denitrification nitrogen removal technology utilizes sulfur-oxidizing bacteria to produce sulfur... 0 S 2- S2O3 2－ Reducible inorganic sulfides act as electron donors, converting NO3- into electrons under anaerobic conditions. － Restore to N 2， It has the advantages of low sludge production, saving carbon source and low COD of effluent, and has begun to be gradually applied to the treatment of urban sewage.

[0004] Yin Juan et al. investigated the effects of different sulfur-containing packing reactors on the deep denitrification of simulated municipal wastewater (Environmental Ecology, 2023, 5(06): 111-118). They used pyrite and sulfur as reactor packings, combined with zeolite and limestone, to study the enhanced denitrification effects of the two packings on simulated municipal wastewater effluent under different HRTs. They found that at HRT = 12 h, pyrite and sulfur significantly reduced NO3- concentration. - The removal rates of NO3- were 85.64% and 92.46%, respectively. At HRT = 6 h and HRT = 2 h, sulfur effectively removed NO3-. --N removal rates were 91.47% and 89.40%, respectively. Guo Qichen et al. investigated the sulfur autotrophic denitrification performance of constructed wetlands for municipal wastewater (Water Treatment Technology, 2020, 46(09):104-107), and found that Na2S2O3 as a sulfur autotrophic denitrification source had the highest efficiency, while NO3... - -N removal rate was 90.9%; under optimized sulfur to ash mass ratio of 2:1, the system NO3 removal rate was 90.9%. - The nitrogen removal rate was 91.6%. Based on the above research, it was found that the current sulfur autotrophic denitrification technology for treating municipal wastewater still has problems such as long hydraulic retention time and insufficient nitrate nitrogen removal rate. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the present invention aims to provide a sulfur autotrophic denitrification method for deep denitrification of municipal wastewater through HRT optimization, so as to solve at least one of the technical problems mentioned in the background art. The present invention achieves effective enrichment of sulfur autotrophic denitrifying bacteria in the reactor, enabling efficient denitrification of municipal wastewater in a short time.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A sulfur autotrophic denitrification method for deep nitrogen removal from municipal wastewater, optimized by HRT, includes the following steps:

[0008] Step 1: Add sludge and packing material to the sulfur autotrophic denitrification reactor to construct the sulfur autotrophic denitrification zone;

[0009] Step 2: Wastewater containing nitrate nitrogen is fed into the sulfur autotrophic denitrification zone. The influent flow rate and reaction conditions are controlled to allow sulfur autotrophic denitrifying bacteria to accumulate in the reactor. When the denitrification efficiency reaches more than 95% and the effluent is stable, the sulfur autotrophic denitrification reactor is started up.

[0010] Step 3: Adjust the influent flow rate and gradually shorten the HRT to allow the microorganisms sufficient time to adapt.

[0011] In one embodiment, the sludge is bottom sludge from the secondary sedimentation tank of an urban wastewater treatment plant, with an MLSS of 8000–10000 mg / L. After natural sedimentation, the supernatant is discarded and the sludge is concentrated for use. The wastewater containing nitrate nitrogen has a nitrate nitrogen concentration of 20–30 mg / L.

[0012] In one embodiment, the filler is a composite filler made by mixing and pressing magnesite, sulfur, and boron mud. By weight, the proportions are 10%–15% magnesite powder, 10%–15% boron mud, and 70%–80% sulfur, with a particle size of 4–5 mm and a bulk density of 1–1.5 cm³. 3 / g.

[0013] In one embodiment, the sulfur autotrophic denitrification zone is a sludge and packing area within the sulfur autotrophic denitrification reactor, with a packing height of 85% to 90% of the height of the sulfur autotrophic denitrification reactor.

[0014] In one embodiment, the composition ratio of the wastewater is as follows: KNO3, 144.43–216.65 mg / L; NaHCO3, 137.70–206.55 mg / L; FeSO4·7H2O, 44.68 mg / L; NH4Cl, 1.91–3.82 mg / L; CaCl2·2H2O, 18.38 mg / L; MgSO4·7H2O, 102.50 mg / L; KH2PO4, 2.20–4.39 mg / L.

[0015] In one embodiment, step 2 involves controlling the influent flow rate and reaction conditions to achieve a hydraulic retention time (HRT) of 18–22 h, reactor DO below 0.1 mg / L, and water temperature of 25 ± 2°C; influent pH of 7–8 and influent DO of 5 ± 2 mg / L.

[0016] In one embodiment, step 2 is a continuous operation, and the sulfur autotrophic denitrification reactor is started up when the denitrification efficiency reaches more than 95% and the effluent is stable.

[0017] In one embodiment, after continuous operation for 20 to 30 days, the denitrification efficiency reaches over 95% and the effluent is stable.

[0018] In one embodiment, step 3 involves gradually adjusting the HRT to 16, 8, 4, and 1 hour to cultivate sulfur-autotrophic denitrifying bacteria adapted to the characteristics of municipal wastewater within the reactor. Each HRT cycle lasts for 10 to 15 days.

[0019] In one embodiment, step 3 involves starting the next operating cycle when the denitrification efficiency reaches over 95% and the effluent stabilizes. After the HRT is 1 hour, the system operates for an extended period of 1 hour to achieve highly efficient denitrification.

[0020] For example, first run for 10 days with an HRT of 16h, then run for 10 days with an HRT of 8h, then run for 10 days with an HRT of 4h, and then run for 1 hour with an HRT. Thus, the optimized HRT is 1 hour, which can be used for long-term operation to achieve efficient nitrogen removal.

[0021] Compared with the prior art, the beneficial effects of the present invention are:

[0022] 1. This invention can directly cultivate sulfur autotrophic denitrifying bacteria adapted to the characteristics of municipal wastewater in a reactor. These bacteria can stably exert sulfur autotrophic denitrification under different HRT conditions.

[0023] 2. The method of the present invention, in the influent nitrate nitrogen (NO3)- The concentration of nitrate nitrogen (NO3) was 20 mg / L, and the final HRT was 1 h. - The removal rate of nitrate nitrogen (N) is 96% to 98%, achieving highly efficient removal of nitrate nitrogen.

[0024] 3. The present invention has a low frequency of filler replenishment and backwashing, which can effectively reduce operation and maintenance costs. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of a sulfur autotrophic denitrification reactor.

[0026] Figure 2 It refers to the nitrate nitrogen concentration and nitrate nitrogen removal rate in the effluent from the water tank.

[0027] Figure 3 It refers to the concentration of nitrite nitrogen in the effluent from the outlet tank.

[0028] Figure 4 It refers to the COD concentration of the water leaving the outlet tank.

[0029] Figure 5 It represents the relative abundance of microorganisms at the phylum level in the reactor.

[0030] Figure 6 It represents the relative abundance of microorganisms at the genus level in the reactor. Detailed Implementation

[0031] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings and examples.

[0032] like Figure 1 As shown, this invention constructs a simulated sulfur autotrophic denitrification reactor system, including an inlet tank 1, an inlet pipe 2, a peristaltic pump 3, an inlet 4, a reactor base 5, a sulfur autotrophic denitrification zone 6, sludge 7, packing material 8, an outlet 9, an outlet pipe 10, and an outlet tank 11. The reactor body is mounted on the reactor base 5. The inlet tank 1 is connected to the inlet 4 of the reactor body via the inlet pipe 2 and the peristaltic pump 3. Sludge 7 and packing material 8 are filled into the reactor body to form the sulfur autotrophic denitrification zone 6, with a filling height of 85%–90% of the reactor body height being preferred. The outlet 9 of the reactor body is connected to the outlet tank 11 via the outlet pipe 10.

[0033] This invention optimizes the sulfur autotrophic denitrification method for deep nitrogen removal from municipal wastewater using HRT, and includes the following steps:

[0034] 1) Preparation stage of sulfur autotrophic denitrification reactor.

[0035] Turn off peristaltic pump 3, pour the concentrated sludge 7 into the reactor, add packing material 8, and fill the packing material to a height of 90% of the main body height of the reactor, and control the DO to below 0.1 mg / L.

[0036] In this embodiment of the invention, the inoculated sludge was taken from the secondary sedimentation tank of a municipal wastewater treatment plant, with an MLSS of 10,000 mg / L. After natural sedimentation, the supernatant was discarded and concentrated for use, providing the initial microbial community.

[0037] The filler is a composite filler made by mixing and pressing magnesite, sulfur, and boron mud. The ratio is magnesite powder (10%–15%) + boron mud (10%–15%) + sulfur (70%–80%), with a particle size of 4–5 mm and a bulk density of 1.08 m³. 3 / g. The packing material provides a carrier for microorganisms to attach, forming a biofilm, and provides sulfur as an electron donor for denitrification. Furthermore, the metal oxides in boron mud and magnesite produce OH- upon contact with water. - It can provide alkalinity for sulfur autotrophic denitrification systems; Mg 2+ It reacts with phosphates in water to form insoluble magnesium phosphate, thereby achieving phosphorus removal; magnesium, boron, iron and other elements can also provide trace elements necessary for microbial growth.

[0038] 2) Start-up of the sulfur autotrophic denitrification reactor.

[0039] Start peristaltic pump 3 to allow nitrate nitrogen (NO3) to be released. - Simulated municipal wastewater with a sulfur-N concentration of 20 mg / L enters the sulfur autotrophic denitrification zone 6. The influent flow rate is controlled by adjusting the peristaltic pump 3 to make the hydraulic retention time (HRT) of the simulated municipal wastewater 20 h.

[0040] The simulated municipal wastewater composition was as follows: KNO3, 144.43 mg / L; NaHCO3, 137.70 mg / L; FeSO4·7H2O, 44.68 mg / L; NH4Cl, 3.82 mg / L; CaCl2·2H2O, 18.38 mg / L; MgSO4·7H2O, 102.50 mg / L; and KH2PO4, 4.39 mg / L. The reactor DO was controlled below 0.1 mg / L, and the water temperature was controlled at 25±2°C. The influent pH was controlled at 7–8, and the influent DO was controlled at 5±2 mg / L, allowing sulfur-autotrophic denitrifying bacteria to accumulate in the reactor. Nitrate nitrogen (NO3) in the tank was detected every 2–3 days during reactor operation. - With a nitrogen concentration of -N, the sulfur autotrophic denitrifying bacteria community adapted to the characteristics of municipal wastewater was acclimated in the reactor after one month of continuous operation. When the nitrogen removal efficiency reached more than 95% and the effluent stabilized, the sulfur autotrophic denitrification reactor was successfully started up.

[0041] In this invention, the wastewater is a simulated mixture, and the main indicator is the nitrate nitrogen concentration, which is typically in the range of 20-30 mg / L, corresponding to KNO3 of 144.43-216.65 mg / L. The other indicators are the conventional components of municipal wastewater, and their adjustment does not significantly affect the effectiveness of this invention.

[0042] 3) After the sulfur autotrophic denitrification reactor is started, first adjust the peristaltic pump 3 to control the influent flow rate, set the HRT to 16h, and run it for 10-15 days. During this period, monitor the nitrate nitrogen (NO3) in the effluent from the outlet tank daily. - -N) and nitrite nitrogen (NO2) - The concentration of nitrate nitrogen (NO3) should be adjusted to ensure that the microorganisms are fully adapted to the load. The denitrification efficiency should be stabilized above 95% and the nitrate nitrogen (NO3) concentration should be adjusted accordingly. - After the nitrogen removal rate fluctuates by ≤1% for 3 consecutive days, the reactor sequentially enters operating cycles with HRTs of 8h, 4h, and 1h, each cycle lasting 10–15 days. Based on daily monitoring data, once the nitrogen removal efficiency reaches the target and the effluent stabilizes, the peristaltic pump flow rate is adjusted to enter the next stage. By gradually shortening the HRT in stages, the reactor's hydraulic load tolerance is progressively improved. After optimization, the HRT is 1h, allowing the reactor to effectively and efficiently remove nitrogen under a 1h HRT condition for extended periods.

[0043] This invention enables deep denitrification of municipal wastewater under a short time HRT=1h, which can effectively reduce operation and maintenance costs.

[0044] This invention aims to achieve microbial domestication by providing suitable packing materials and sulfur autotrophic denitrification conditions, gradually shortening the HRT, and establishing a sulfur autotrophic denitrification microbial community that can achieve efficient nitrogen removal under short HRT conditions.

[0045] In a specific embodiment of the present invention, the reactor operating conditions and parameters are as follows:

[0046] The sulfur autotrophic denitrification reactor used is a bottom-in, top-out upflow reactor. The specific structure of the reactor is shown in [reference needed]. Figure 1 The structure of the reactor is described as follows: The reactor is made of cylindrical plexiglass, 80cm high, with an inner diameter of 10cm. The outlet is 8cm from the top, and the inlet is 3cm from the base. The outer diameter of the top and bottom inlets and outlets is 0.8cm, connected to external inlet and outlet pipes. The effective volume of this sulfur autotrophic denitrification reactor is 5.5L, and the effective volume after adding the packing material is 1.5L. The sulfur autotrophic denitrification packing material is densely distributed inside the reactor under gravity, creating a low dissolved oxygen environment, which is beneficial to the growth of autotrophic denitrifying bacteria and is less likely to flow out of the reactor with the effluent. The bottom-inlet, top-outlet design of the sulfur autotrophic denitrification reactor facilitates the discharge of gas from the reactor, which is also beneficial to the growth of sulfur autotrophic denitrifying bacteria.

[0047] The entire reaction process of the reactor is described as follows: Simulated municipal wastewater flows from the inlet tank 1 into the sulfur autotrophic denitrification zone 6 under the suction of the peristaltic pump 3 via the inlet pipe 2. Within the sulfur autotrophic denitrification zone 6, the simulated municipal wastewater undergoes sulfur autotrophic denitrification under the action of microbial communities. The effluent from the denitrification process flows into the effluent tank 11 under atmospheric pressure.

[0048] During the preparation stage of the sulfur autotrophic denitrification reactor, the DO is controlled below 0.1 mg / L, and sludge and packing are loaded into the reactor. During the reactor start-up and operation stage, the DO is controlled below 0.1 mg / L, the water temperature is controlled at 25±2°C, the influent pH is controlled at 7-8, the influent DO is controlled at 5±2 mg / L, the start-up time is 1 month, and the operation stage is 10 days per operation cycle.

[0049] Reactor treatment effect and microbial community analysis.

[0050] The influent to the sulfur autotrophic denitrification reactor has always been artificially prepared simulated urban sewage, with an influent nitrate nitrogen concentration of 20 mg / L. The effluent nitrate nitrogen concentration in effluent tank 11 is shown in the attached figure. Figure 2 As shown, phases I (reactor start-up), II, III, IV, and V of the reaction correspond to hydraulic retention times (HRTs) of 20, 16, 8, 4, and 1 h, respectively. Throughout the five phases, the nitrate nitrogen concentration in effluent tank 11 ranged from 0.4 to 0.8 mg / L, with an average effluent nitrate nitrogen concentration of 0.53 mg / L. The nitrate nitrogen removal rate was above 95.5%, with a maximum removal rate of 98%. Even after optimizing the hydraulic retention time from 20 h to 1 h, the nitrate nitrogen removal rate of the sulfur autotrophic denitrification reactor remained above 96%, achieving rapid and efficient removal of 20 mg / L nitrate nitrogen from urban wastewater. (Reference) Figure 3 During stages I, II, III, IV, and V of the reaction, the nitrite nitrogen concentration in effluent tank 11 was 0–0.007 mg / L, achieving extremely low nitrite nitrogen accumulation and demonstrating relatively complete denitrification. The COD concentration in the effluent from the tank was as follows: Figure 4 As shown, in Stage I, the overall COD level remained below 10 mg / L. With optimization of the hydraulic retention time, the effluent COD fluctuated slightly, but remained generally below 30 mg / L, with an average of 11.27 mg / L. Furthermore, this reactor operated for over three months without significant packing layer degradation or blockage. The frequency of packing replenishment and backwashing was low, effectively reducing operation and maintenance costs while ensuring effective denitrification of municipal wastewater. (Reference) Figure 4 and Figure 6In this embodiment, the abundance of Proteobacteria in the reactor was 40.93% and 36.17% at HRTs of 20 h and 1 h, respectively. The abundances of the genera *Sulfurimonas*, *Thiomonas*, and *Thiobacillus*, which are responsible for sulfur autotrophic denitrification, were 0.01% and 7.49%, 4.43% and 2.64%, and 0.004% and 1.59% at HRTs of 20 h and 1 h, respectively. This indicates that after HRT optimization and microbial acclimatization, the phyla and genera of microorganisms with denitrification capabilities were enriched.

Claims

1. A method for optimizing sulfur autotrophic denitrification for advanced nitrogen removal of municipal wastewater by HRT, characterized in that, It comprises the following steps: Step 1, adding sludge and filler into the sulfur autotrophic denitrification reactor to construct a sulfur autotrophic denitrification zone; Step 2, feeding the wastewater containing nitrate nitrogen into the sulfur autotrophic denitrification zone, controlling the influent flow rate and reaction conditions, so that the hydraulic retention time (HRT) is 18-22 h, the DO in the reactor is below 0.1 mg / L, the water temperature is 25±2°, the influent pH is 7-8, and the influent DO is 5±2 mg / L; so that the sulfur autotrophic denitrification bacteria are enriched in the reactor, and when continuously running for 20-30 days, the denitrification efficiency reaches more than 95% and the effluent is stable, and the sulfur autotrophic denitrification reactor is started up; Step 3, adjusting the influent flow rate, gradually adjusting the HRT to 16, 8, 4, and 1 h, and domesticating a sulfur autotrophic denitrification bacterial community that is suitable for the characteristics of municipal wastewater in the reactor, each HRT cycle running for 10-15 days, so that the microorganisms have sufficient time to adapt; when the denitrification efficiency reaches more than 95% and the effluent is stable, the next running cycle is performed, and after the HRT is 1 h, it is run for 1 h in the long term.

2. The process for sulphur autotrophic denitrification optimized by HRT for advanced nitrogen removal from municipal wastewater according to claim 1, characterized by, The sludge is the sludge at the bottom of the secondary sedimentation tank of a municipal wastewater treatment plant, the MLSS is 8000-10000 mg / L, the supernatant is discarded after natural sedimentation, and the concentrated sludge is used; the wastewater containing nitrate nitrogen has a nitrate nitrogen concentration of 20-30 mg / L.

3. The process for sulphur autotrophic denitrification by HRT optimization for advanced nitrogen removal from municipal wastewater according to claim 1, characterized by, The filler is a composite filler mixed and pressed by magnesite, sulfur and boron mud, and the proportion by weight is 10-15% of magnesite powder, 10-15% of boron mud and 70-80% of sulfur, the particle size is 4-5 mm, and the bulk density is 1-1.5 cm 3 / g.

4. The process for sulphur autotrophic denitrification for advanced nitrogen removal from municipal wastewater by HRT optimization according to claim 1, characterized by, The sulfur autotrophic denitrification zone is the sludge and filler filling area in the sulfur autotrophic denitrification reactor, and the filling height is 85%-90% of the height of the sulfur autotrophic denitrification reactor.

5. The process for sulphide autotrophic denitrification by HRT optimization for advanced nitrogen removal from municipal wastewater according to claim 1, characterized by, The composition and proportion of the wastewater are as follows: KNO3, 144.43-216.65 mg / L; NaHCO3, 137.70-206.55 mg / L; FeSO4·7H2O, 44.68 mg / L; NH4Cl, 1.91-3.82 mg / L; CaCl2·2H2O, 18.38 mg / L; MgSO4·7H2O, 102.50 mg / L; and KH2PO4, 2.20-4.39 mg / L.

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