Iron-based biochar mediated sulfur autotrophic denitrification granular sludge cultivation, denitrification method and device

Abstract

This invention discloses a method and apparatus for cultivating and denitrifying granular sludge in sulfur autotrophic denitrification mediated by iron-based biochar. The apparatus uses an upflow anaerobic sludge blanket (UASB) reactor as its core, with anaerobic sludge inoculated into the reaction zone. Hydraulic shear is controlled to promote sludge aggregation into stable granules, maintaining anaerobic conditions throughout the process to ensure the activity of functional microorganisms. Iron-based biochar is added to the apparatus, allowing it to adhere to the anaerobic granular sludge, thus achieving sulfur autotrophic denitrification (SVI). 30 This method significantly reduces and improves settling properties, solves the problem of sludge loss, and the iron element can participate in electron transfer, enhancing the reaction rate and improving denitrification performance. The system's total nitrogen removal rate is superior to conventional processes. This method has high treatment efficiency, low material and energy consumption, and is easy to operate. It can also promote the settling of sulfur autotrophic granular sludge, improve the system's operational stability, and provide a new pathway for denitrification treatment of carbon-poor nitrogen-containing wastewater, with good prospects for industrial application and environmental benefits.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, specifically relating to a method and apparatus for cultivating and denitrifying granular sludge mediated by iron-based biochar and sulfur autotrophic denitrification, which is suitable for deep denitrification treatment of typical carbon-poor (low carbon-to-nitrogen ratio) wastewater. Background Technology

[0002] With the acceleration of urbanization, expansion of industrial scale, and intensive development of aquaculture in my country, the demand for wastewater treatment has continued to surge. Aquaculture wastewater is a typical example of low carbon-to-nitrogen ratio (C / N≤2), carbon-poor nitrogen-containing wastewater (this also includes secondary effluent from municipal wastewater treatment plants, industrial circulating water, and slightly polluted river water). Its denitrification treatment has become a core challenge in water environment management. Aquaculture wastewater is characterized by "high ammonia nitrogen, high suspended solids, and low organic carbon," with nitrogen mainly in the form of ammonia nitrogen (NH4). + Nitrate nitrogen exists in the form of NO3- (NO3-). After front-end anaerobic digestion and aerobic nitrification treatment, the effluent nitrate nitrogen (NO3-) exists in the form of NO3- (NO3-). - The accumulation of nitrogen (TN) leads to low C / N ratio nitrogen-containing wastewater, which, if directly discharged, can easily cause eutrophication of receiving water bodies. The Class A standard of the "Discharge Standard of Pollutants for Municipal Wastewater Treatment Plants" (GB 18918-2002) clearly requires that the total nitrogen (TN) in the effluent be ≤ 5 mg / L. The "Discharge Standard of Pollutants for Livestock and Poultry Farming" (GB 18596-2001) also imposes strict limits on nitrogen emissions from livestock and poultry wastewater. However, traditional denitrification technologies often suffer from low denitrification efficiency due to insufficient carbon sources, and require the addition of external carbon sources such as methanol and sodium acetate. This significantly increases operating costs and may also lead to excessive COD in the effluent due to excessive carbon sources, posing a risk of secondary pollution. This situation clearly contradicts the actual need for "low-cost treatment" in the livestock and poultry industry.

[0003] To overcome this challenge, sulfur autotrophic denitrification technology has gradually attracted attention. This technology uses inorganic sulfur, such as thiosulfate, as an electron donor, and can convert nitrate nitrogen (NO3) into nitrogen without the need for an external carbon source. - -N), nitrite nitrogen (NO2) - -N) is reduced to nitrogen gas (N2), while inorganic sulfur is converted to sulfate (SO4). 2- This technology combines advantages such as low carbon source dependence, low operating costs, and low sludge production, making it particularly suitable for denitrification of carbon-poor nitrogen-containing wastewater such as aquaculture wastewater. It is considered an ideal pathway for denitrification of low C / N ratio wastewater. However, this technology still faces several bottlenecks in practical applications such as aquaculture wastewater treatment: Firstly, sulfur-autotrophic denitrification microorganisms (such as sulfur-oxidizing bacteria SOB) are mostly flocculent sludge with poor settling performance (SVI). 30First, the sludge concentration is often higher than 100 mL / g, which is easily lost with the effluent, resulting in insufficient biomass in the reactor and large fluctuations in denitrification efficiency. Second, the reaction is sensitive to environmental parameters. Small changes in temperature, pH, and hydraulic retention time (HRT) can inhibit microbial activity. Especially in short HRT (≤ 4 h) scenarios, the problem of sludge erosion is aggravated, and the stability of the system is difficult to guarantee. Third, sulfur conversion and denitrification efficiency are difficult to improve in a coordinated manner. Some sulfur sources may be converted into elemental sulfur and attached to the surface of microorganisms, hindering cell metabolism and electron transfer, and further weakening the reaction efficiency.

[0004] To overcome the aforementioned limitations, sludge granulation technology has attracted attention for improving system performance. Granular sludge has a compact structure, settles quickly, has high biomass enrichment, and strong shock resistance, effectively solving the problem of flocculent sludge loss. However, sulfur autotrophic denitrifying microorganisms have weak aggregation ability, with a natural granulation cycle exceeding 200 days, and the particles are easily loosened and broken, making it difficult to form a stable system. Existing research has attempted to promote granulation by adding carriers such as activated carbon and ceramsite, but these carriers only have physical adsorption functions and cannot actively regulate microbial metabolism, resulting in limited induction effects on sulfur autotrophic denitrifying granular sludge and difficulty in simultaneously improving the synergistic efficiency of sulfur conversion and nitrogen removal.

[0005] CN119118356A describes a method for denitrifying low-ammonia nitrogen wastewater using iron-loaded granular activated carbon coupled with an anaerobic fluidized bed membrane bioreactor. It leverages the electron transfer properties of the iron-loaded carbon material and the fluidization characteristics of the reactor to enhance denitrification. However, this technology focuses on the anaerobic ammonia oxidation process for low-ammonia nitrogen wastewater and is adapted to an anaerobic fluidized bed membrane bioreactor system. Its research object, core reaction mechanism, and reactor type differ fundamentally from sulfur autotrophic denitrification systems. It does not address the granular cultivation of sulfur autotrophic denitrification sludge, nor does it consider the impact of iron-based materials on the settling performance (SVI) of sulfur autotrophic denitrification sludge. 30 The strengthening of sulfur-nitrogen synergistic conversion and regulation cannot solve the core problems of easy sludge loss, long granulation cycle and insufficient efficiency synergy in sulfur autotrophic denitrification systems.

[0006] Biochar, due to its low cost and high specific surface area, is increasingly used in environmental remediation. Its porous structure provides attachment sites for microorganisms. After modification with metals such as iron, cobalt, and nickel, it can also promote microbial metabolism and enhance pollutant degradation through electron transport-mediated processes. Iron is an essential trace element for microorganisms, participating not only in the synthesis of sulfur autotrophic denitrification-related enzymes (such as nitrite reductase and sulfide oxidase) to maintain cellular physiological functions, but also through Fe... 2+ / Fe 3+Valence state cycling accelerates electron transfer, enhancing the coupling efficiency of sulfur oxidation and denitrification. Current technologies have not combined the granular cultivation, electron transfer enhancement, and efficient nitrogen removal of iron-based biochar with sulfur autotrophic denitrification. The specific process coupling pathway and efficiency synergistic regulation mechanism for this system have not yet been disclosed. Summary of the Invention

[0007] This invention relates to the field of wastewater treatment technology, and in particular to the core treatment challenges of low carbon-to-nitrogen ratio (C / N≤2) carbon-poor wastewater such as aquaculture wastewater, which are characterized by "low organic carbon content, large nitrogen load fluctuations, poor sludge settling, and low denitrification efficiency". Combining the functional regulation characteristics of iron-based biochar with the granular advantages of upflow anaerobic sludge blanket (UASB) reactors, this invention provides a method and apparatus for iron-based biochar-mediated sulfur autotrophic denitrification granular sludge cultivation and denitrification. This method uses an upflow anaerobic sludge blanket (UASB) reactor as its core, with a blank control group without added iron-based biochar (the remaining operating conditions are consistent with this invention, including gradient carbon reduction, hydraulic shear regulation, and hydraulic retention time optimization). The experimental group uses synthesized iron-based biochar to provide a carrier for microbial attachment and electron transport, combined with gradient carbon reduction (C / N ratio gradually decreasing from 2 to 0) and hydraulic shear regulation (adjusting the return flow rate via an internal circulation pump), promoting the directional enrichment of sulfur-autotrophic denitrifying bacteria and the granular sedimentation of sludge. After system startup, a carbon-free influent is maintained, and stable operation is achieved by shortening the hydraulic retention time (HRT optimized from 8 h to 4 h). When treating low-nitrogen wastewater (TN concentration 20-50 mg / L), both groups of granular sludge can form and mature in 25-30 days, with the experimental group showing SVI (sulfuric acid viscosity). 30 Significantly lower than the control group (experimental group SVI) 30 ≤80 mL / g, control group SVI 30 With a TN removal rate of ≥150 mL / g, the sludge settling performance was significantly improved. Under stable operation, the experimental group showed better denitrification efficiency and sulfur conversion efficiency than the control group. The experimental group achieved a TN removal rate of 90.7% and a sulfur conversion rate of 92.4%, with an effluent TN concentration ≤5 mg / L. In contrast, the control group achieved a TN removal rate of only 65.3% and a sulfur conversion rate of only 71.8%, with an effluent TN concentration ≥12 mg / L. The experimental group's denitrification efficiency and sulfur conversion efficiency were increased by 25.4 and 20.6 percentage points, respectively, compared to the control group. This effectively overcomes the problems of sludge loss, long granulation cycle, and insufficient synergistic effect of traditional sulfur autotrophic denitrification technology. It has application value that is low-cost, high-efficiency, and easy to promote industrially.

[0008] The present invention is as follows: This invention provides a method and apparatus for cultivating and denitrifying granular sludge mediated by iron-based biochar for sulfur autotrophic denitrification. The apparatus includes an anaerobic bioreactor (i.e., an upflow anaerobic sludge blanket reactor), an internal circulation pump, a water bath heating system, and a one-way gas valve. The anaerobic bioreactor has a main body made of plexiglass, an effective volume of 3 L, and the outer wall of the reaction zone is wrapped with 2... A cm thick insulation layer is provided. A bioreactor inlet is located on the lower part of the side wall, and an outlet is located on the upper part. A three-phase separator is installed inside. The water bath heating system consists of a warm water circulation pump and a water bath heating device, connected to the insulation layer via pipelines. A one-way gas valve is installed at the exhaust port at the top of the anaerobic bioreactor. An inlet tank is located in front of the anaerobic bioreactor, connected to an inlet pump via an inlet pipe. The output of the inlet pump is connected to the bioreactor inlet and the internal circulation port via a three-way valve. The internal circulation port is connected to the input of the internal circulation pump via a pipeline, and the output of the internal circulation pump is connected to the bioreactor inlet pipeline. The three-phase separator is located in the upper middle part of the anaerobic bioreactor and is used to separate water, sludge, and gas phases. The outlet is connected to the outlet tank via a pipeline for collecting treated wastewater.

[0009] The upflow anaerobic sludge blanket reactor (UASB reactor) is equipped with a three-phase separator, exhaust port, inlet, return outlet, outlet and insulation layer. The internal circulation pump is connected to the reflux outlet and inlet of the anaerobic bioreactor via pipelines. A one-way gas valve is installed at the exhaust port of the anaerobic bioreactor; it only allows gas to be discharged outwards, preventing backflow of air from disrupting the anaerobic environment; An inlet tank is installed in front of the upflow anaerobic sludge blanket (UASB) reactor. The inlet tank is connected to the input end of the inlet pump, and the output end of the inlet pump is connected to the inlet of the anaerobic bioreactor via a three-way valve. The water bath heating device is connected to the insulation layer of the anaerobic bioreactor via a warm water circulation pump. At the same time, the outlet of the upflow anaerobic sludge blanket (UASB) reactor is connected to the effluent tank. The exhaust port of the anaerobic bioreactor is connected to a one-way gas valve to prevent backflow of air from disrupting the anaerobic environment.

[0010] Preferably, the anaerobic bioreactor is inoculated with sludge from the anaerobic biological treatment process of the wastewater treatment plant, with an inoculation sludge concentration of 2.8~3.2 g TS / L and an iron-based biochar dosage of 1.5~1.7 g / L.

[0011] Preferably, the iron-based biochar is prepared by mixing rice husk biochar powder and ferric chloride at a mass ratio of 1 to 10:1. A mass ratio of 5:1 yields the optimal specific surface area and iron loading. Preferably, the inlet pump, internal circulation pump, and warm water circulation pump are all peristaltic pumps to ensure stable and controllable water flow.

[0012] Preferably, the anaerobic bioreactor operates at a temperature of 30 ± 2 ℃, the influent pH is adjusted to 7.13 ± 0.10, and the pH of the system is maintained stable by using NaHCO3.

[0013] Preferably, the wastewater to be treated is low carbon-to-nitrogen ratio synthesis wastewater (C / N≤2), low nitrogen wastewater, with a TN concentration of 20~50 mg / L, containing KNO3 (nitrogen source), Na2S2O3•5H2O (sulfur source) and trace elements.

[0014] Preferably, before starting the device, the sulfur-autotrophic denitrifying bacteria are acclimatized by gradually reducing the influent carbon source concentration (C / N ratio from 2→1→0). The purpose of acclimatization is to adapt the functional microorganisms to a carbon-free environment and ensure the efficiency of sulfur-nitrogen co-conversion. After acclimatization, an extracellular polymeric substance (EPS) layer of 200~500 nm is formed on the surface of the sludge, and iron-based biochar is loaded on the surface of the granular sludge. After acclimatization, the particle size of the granular sludge reaches 1050~1100 μm.

[0015] A method for cultivating and denitrifying granular sludge mediated by iron-based biochar in sulfur autotrophic denitrification specifically includes the following steps: (1) Synthesis of iron-based biochar: The synthesis of iron-based biochar requires raw material pretreatment, mixing and grinding, heat treatment, and subsequent processing to ensure high microbial adhesion and electron transfer efficiency. Specifically: Raw material pretreatment: Wash and dry the dried agricultural biochar (such as rice husks and corn stalks), crush it through an 80-mesh sieve, pass 99.99% nitrogen gas (400~600 mL / min) through a tube furnace, heat it to 700℃ at 4~6℃ / min for 1.5~2.5 h, cool it and grind it through an 80-mesh sieve to obtain 60~70 μm biochar fine powder; then, according to a preset mass ratio of 1~10:1, dissolve the biochar fine powder and ferric chloride in pure water and stir at 500 rpm for 1 h, dry it and grind it.

[0016] Heat treatment and post-treatment: The mixture was spread evenly on a corundum boat (thickness ≤ 5 mm) and placed in a tube furnace. Nitrogen gas was introduced (200~400 mL / min), and the temperature was increased to 400 ℃ at 2~4 ℃ / min. The mixture was kept at a constant temperature for 1.5~2.5 h to decompose ferric chloride and bind biochar functional groups. After cooling, the mixture was rinsed with deionized water and vacuum dried at 55~65 ℃ for 12 h. The product was then pulverized and passed through an 80-mesh sieve. The product was then subjected to performance characterization and monitoring, and was screened.

[0017] (2) Start-up of the iron-based biochar-mediated sulfur autotrophic denitrification granular sludge cultivation device: Anaerobic activated sludge from municipal wastewater treatment plants was co-inoculated with iron-based biochar into a UASB reactor. Hydraulic shearing was employed by controlling the influent flow rate to promote sludge aggregation, gradually reducing the influent carbon source concentration until it was completely stopped, thus constructing a fully autotrophic sulfur-based denitrification system. S2O3 levels were monitored regularly. 2- SO4 2- Conversion rate and NO3 - NO2 - TN removal rate, while tracking sludge particle size and SVI 30 until SO4 2- When the conversion rate and TN removal rate are stable and the sludge is granulated, the reactor startup is complete.

[0018] Specifically, the concentration of inoculated sludge was controlled at 2.8~3.2 g TS / L, and the dosage of iron-based biochar was 1.5~1.7 g / L. Hydraulic conditions were regulated by the coordinated operation of the internal circulation pump and the influent pump to create suitable hydraulic shear at an HRT of 8 h to promote sludge aggregation. At the same time, a gas check valve was used to maintain the anaerobic environment of the reactor throughout the process.

[0019] Synthetic wastewater containing nitrogen, sulfur, phosphorus, trace elements, and regulating agents is introduced. During the start-up phase, a gradient carbon reduction strategy is adopted: when the C / N ratio is 2, the system operates for 35-45 days; when it is reduced to 1, the system operates for 25-35 days; and finally, the system stops carbon production (C / N=0) and operates for 45-55 days, gradually building a completely sulfur-autotrophic denitrification system.

[0020] The entire process of sludge granulation and reaction efficiency is tracked, and effluent indicators, including denitrification efficiency, sulfur conversion rate and microbial activity, are monitored regularly until a stable state is reached to complete the start-up.

[0021] (3) Stable operation and performance optimization of iron-based biochar-mediated sulfur autotrophic denitrification granular sludge unit: After the UASB reactor is started up, synthetic wastewater is introduced to maintain a carbon-free influent. The concentrations of nitrogen, sulfur, and phosphorus sources in the influent are consistent with the initial carbon-free influent during the start-up phase. Magnesium and calcium salts are continuously added, and the influent pH is stabilized using NaHCO3. A trace element reserve solution is still added to the influent. The impact of different operating parameters on the system's denitrification performance is investigated by shortening the hydraulic retention time. Effluent parameters, including S2O3, are monitored regularly during this period. 2- SO4 2- Conversion rate and NO3 - NO2 - TN removal rate, while simultaneously tracking microbial activity, granular sludge particle size distribution, and SVI. 30 Changes, until SO4 2- The conversion rate and TN removal rate remain continuous and stable, thus achieving stable operation of the device.

[0022] During operation, hydraulic conditions are regulated in tandem by the influent pump and the internal circulation pump to maintain stable hydraulic shearing and ensure the structural integrity of the granular sludge. Sulfur conversion and denitrification related indicators are monitored regularly, and the particle size distribution and SVI of the granular sludge are tracked simultaneously. 30 Microbial activity was detected. When the HRT was shortened to 4 h (target value), the granular sludge further solidified, and the particle size grew to 1050~1100 μm, with SVI... 30 When the concentration drops to 40.0~42.5 mL / g and reaches a stable state, the system's denitrification efficiency and sulfur conversion rate are significantly improved. After 15 days of continuous monitoring, the fluctuation of the indicators is ≤±3%. The iron-based biochar has a clear advantage in electron transfer efficiency, which means that the device can be operated stably and can treat wastewater with low carbon-to-nitrogen ratio and low nitrogen. The TN concentration of the effluent meets the Class A standard.

[0023] Step (1) The synthesized iron-based biochar was characterized by specific surface area and porosity, XPS, Fourier transform infrared spectroscopy, and XRD: specific surface area and porosity analysis was used to assess the number of microbial attachment sites and electron transfer efficiency; XPS analysis was used to analyze the valence state distribution of iron; Fourier transform infrared spectroscopy and XRD were used to characterize functional groups and crystal structure. The results showed that the material had the best overall performance when the mass ratio of rice husk biochar powder to ferric chloride was 5:1.

[0024] The reactor described in step (2) is an upflow anaerobic bioreactor. It is made of plexiglass and consists of an inlet and outlet water system, a reaction zone, and a three-phase separation system, with water entering from the bottom. It comprises an inlet tank, an inlet peristaltic pump, a reflux peristaltic pump, an inlet pipe, an outlet pipe, an inlet valve, an outlet valve, and the reactor body.

[0025] The process operating conditions for steps (2) and (3) are as follows: the upflow anaerobic bioreactor is in an anaerobic state with an effective volume of 3.0 L, and operates in continuous flow. The hydraulic shear is provided by both the influent and reflux peristaltic pumps. The temperature of the reaction zone is maintained at 30 ± 2℃ by water bath heating. The pH of the influent is 7.13 ± 0.10. After treatment, the wastewater is discharged through the outlet, and the gas is discharged through the three-phase separation system.

[0026] In steps (2) and (3), the synthesized wastewater contains nitrogen, sulfur, phosphorus, carbon, MgCl2•6H2O, CaCl2, and NaHCO2. The nitrogen source is KNO3, the sulfur source is Na2S2O3•5H2O, the phosphorus source is KH2PO4, and the carbon source is sodium acetate. MgCl2•6H2O provides magnesium ions to the sulfur autotrophic denitrification system to maintain enzyme activity and cell structure, CaCl2 provides calcium ions to participate in cell physiological functions and sludge flocculation, and NaHCO3 is used to buffer the pH of the system, all of which together ensure the stable growth and metabolism of sulfur-oxidizing bacteria (SOB) and the denitrification reaction. The synthetic wastewater contained nitrogen source concentrations of 48.3 ± 1.6 mg-N / L, sulfur source concentrations of 160.8 ± 13.5 mg-S / L, and phosphorus source concentrations of 56.2 ± 2.5 mg-P / L, with the C / N ratio gradually decreasing from 2 to 0; MgCl2•6H2O concentrations of 36.3 ± 1.5 mg-Mg / L and CaCl2 concentrations of 70 ± 1.3 mg-Ca / L; and the influent pH was adjusted to 7.13 ± 0.10 using NaHCO3.

[0027] In steps (2) and (3), 1 mL of trace element reserve solution needs to be added to 1 L of synthetic wastewater. The reserve solution contains ZnSO4•5H2O 1.5 g / L, NiCl2•6H2O 0.25 g / L, H3BO3 0.5 g / L, CuSO4•5H2O 0.25 g / L, MnCl2•4H2O 1.0 g / L, CoCl2•2H2O 0.25 g / L, and HCl 5.0 ml / L.

[0028] In step (2), the anaerobic bioreactor operates in an HRT=8 h mode. The parameters corresponding to different C / N conditions are as follows: when C / N=2, the flow rates of the influent pump and the return pump are 8~10 L / d and 135~150 L / d, respectively, and the upward flow velocity is 0.95~1.05 m / h; when C / N=1, the flow rates of the influent pump and the return pump are 8~10 L / d and 165~175 L / d, respectively, and the upward flow velocity is 1.25~1.35 m / h; when C / N=0, the flow rates of the influent pump and the return pump are 8~10 L / d and 190~205 L / d, respectively, and the upward flow velocity is 1.45~1.55 m / h.

[0029] In step (3), the anaerobic bioreactor adopts the HRT=4 h operation mode, with the influent pump and return pump flow rates of 17~19 L / d and 385~405 L / d, respectively, and the upward flow velocity maintained at 1.65~1.75 m / h to ensure stable hydraulic conditions in the reactor.

[0030] In steps (2) and (3), the anaerobic sludge morphology gradually evolves from a flocculent structure in the early stages of cultivation to a dense, sulfur-autotrophic granular morphology mediated by the addition of iron-based biochar. A thick extracellular polymeric substance (EPS) layer forms on its surface, and the iron-based biochar is loaded onto the surface of the granular sludge, effectively improving the settling properties of the sulfur-autotrophic granular sludge. With acclimatization and process operation, the sludge particle size continues to increase, eventually reaching a median diameter of approximately 1000 μm. At this point, the granular sludge has a regular spherical appearance and good settling performance (SVI). 30 (Keep the value below 50 mL / g).

[0031] In both steps (2) and (3), the sulfur autotrophic granular sludge exhibited excellent treatment efficiency. The low-carbon synthetic wastewater treated in step (2) achieved an average total nitrogen removal rate of over 93% and an average sulfide conversion rate of over 95%. The low-carbon synthetic wastewater treated in step (3) achieved an average total nitrogen removal rate of over 90% and an average sulfide conversion rate of over 85%. After treatment, the effluent quality indicators met the Class A standard of the "Discharge Standard of Pollutants for Municipal Wastewater Treatment Plants" (GB 18918-2002).

[0032] Compared with the prior art, the present invention has the following advantages: 1. Compared to traditional low C / N ratio wastewater denitrification technologies, this invention specifically addresses the core technical bottlenecks of low denitrification efficiency, poor sludge stability, and weak shock resistance in carbon-poor (C / N≤2) wastewater such as aquaculture wastewater. At the technical principle level, this invention is the first to apply iron-based biochar to a sulfur autotrophic denitrification granularization and denitrification system, breaking through the limitations of traditional carriers that only possess physical adsorption functions. This iron-based biochar is prepared by targeted modification using rice husk as a precursor, achieving an optimal 4.2850 m³ / h. 2 The high specific surface area of ​​ / g provides stable attachment sites for microorganisms, and the loaded iron can be transferred through Fe 2+ / Fe 3+ Valence cycling participates in the electron transfer process, significantly enhancing the metabolic activity of sulfur-oxidizing bacteria (SOB), and achieving an integrated effect of "carrier-induced granulation - enhanced electron transfer - synergistic denitrification and sulfur conversion - improved shock resistance". This effectively makes up for the technical defects of traditional carriers such as activated carbon and ceramsite, which are difficult to regulate microbial metabolism and cannot be adapted to the complex matrix of carbon-poor wastewater.

[0033] 2. Regarding treatment efficiency, this invention significantly shortens the granulation cycle of sulfur autotrophic denitrification sludge through a gradient carbon reduction strategy (C / N gradually decreasing from 2 to 0) and the synergistic regulation of hydraulic shear. In traditional processes, the natural granulation cycle of sulfur autotrophic denitrification sludge typically exceeds 200 days and is prone to loosening and loss. In contrast, this invention induces the formation of tightly structured granular sludge in only 25-30 days, with a final particle size of 1050-1100 μm and SVI (sulfuric acid viscosity). 30 The total nitrogen (TN) concentration in the effluent is consistently below 50 mL / g, successfully solving the key problems of poor settling performance and easy loss of traditional flocculent sludge in carbon-poor wastewater environments. Simultaneously, the system achieves a nitrogen removal efficiency of 90.7%, a sulfur conversion rate of 92.4%, and an effluent TN concentration ≤5 mg / L, while also reducing the suspended solids content in the effluent, meeting the Class A standard requirements of the "Discharge Standard of Pollutants for Municipal Wastewater Treatment Plants" (GB 18918-2002). Even under conditions where the hydraulic retention time (HRT) is shortened to 4 h, or where there are fluctuations in the temperature and nitrogen load of the aquaculture wastewater, the core treatment indicators of total nitrogen removal and sulfur conversion rate still fluctuate within ±3%, demonstrating significantly better shock resistance than traditional processes and adapting to the dynamic characteristics of carbon-poor wastewater discharge.

[0034] At the process design and application level, this invention constructs a low-cost, easily scalable standardized process system that highly meets the treatment requirements of "low cost and high efficiency". The device uses an upflow anaerobic sludge blanket (UASB) reactor as its core unit, equipped with an internal circulation pump and a gas check valve. It achieves precise control of the anaerobic environment and flexible adjustment of hydraulic conditions without complex equipment modifications, adapting to the site requirements for treating carbon-poor wastewater. The influent system does not require additional external carbon sources. By precisely proportioning nitrogen (KNO3, suitable for the nitrate nitrogen accumulation characteristics after nitrification in aquaculture wastewater), sulfur (Na2S2O3•5H2O), and trace elements, combined with the protective effects of MgCl2•6H2O and CaCl2 on microbial physiological functions, it significantly reduces operating costs and avoids the risk of excessive COD in the effluent caused by excessive carbon sources, resolving the contradiction between traditional processes and the low-cost treatment needs of aquaculture. This technology is specifically designed to address the treatment needs of low-carbon-nitrogen-ratio, carbon-poor wastewater, such as aquaculture wastewater, secondary effluent from municipal sewage treatment plants, and industrial circulating water. Its advantages of high efficiency, stability, low energy consumption, ease of operation, and strong resistance to impact make it highly compatible with the actual needs of industrialization. It provides an innovative technical path for denitrification of carbon-poor wastewater that balances environmental benefits and economic efficiency, and has broad prospects for engineering applications and academic promotion value. Attached Figure Description

[0035] Figure 1This is a schematic diagram of the anaerobic biological process device used in the embodiments of the present invention. Wherein: 1-one-way exhaust valve, 2-three-phase separation device, 3-outlet, 4-reflux port, 5-reflux pump, 6-outlet tank, 7-insulation layer, 8-water bath heating device, 9-warm water circulation pump, 10-inlet tank, 11-inlet pump, 12-anaerobic bioreactor, 13-inlet, 14-tee connector.

[0036] Figure 2 This is the Fourier transform infrared (FTIR) spectrum of biochar-based materials.

[0037] Figure 3 The images show X-ray photoelectron spectroscopy (XPS) spectra of biochar-based materials, where (a) is the full spectrum of the biochar-based material and (b) is the Fe2p spectrum of the biochar-based material.

[0038] Figure 4 X-ray diffraction (XRD) patterns of biochar-based and composite materials.

[0039] Figure 5 Scanning electron microscope image of biochar-based materials.

[0040] Figure 6 This is a graph showing the variation of SVI in sulfur-autotrophic granular sludge.

[0041] Figure 7 This is a particle size distribution diagram of sulfur-autotrophic granular sludge.

[0042] Figure 8 Microscopic image of sulfur-autotrophic granular sludge particles.

[0043] Figure 9 This image shows the effect of TN removal from sulfur-autotrophic granular sludge.

[0044] Figure 10 This image shows the effect of sulfur removal from autotrophic granular sludge.

[0045] Notes: BC represents unmodified biochar; FeBC (10:1) is an iron-based biochar material prepared by a biochar-ferric chloride mass ratio of 10:1; FeBC (5:1) is an iron-based biochar material prepared by a biochar-ferric chloride mass ratio of 5:1; FeBC (5:2) is an iron-based biochar material prepared by a biochar-ferric chloride mass ratio of 5:2. S1: Sulfur autotrophic reactor; S2: Iron-carbon-sulfur autotrophic reactor. Detailed Implementation

[0046] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the implementation of the present invention is not limited thereto.

[0047] Example 1: Synthesis of Iron-Based Biochar (1) Synthesis of iron-based biochar Dried rice husks were selected as raw material, washed, and dried in a 60 ℃ oven for 24 h. After pulverization, the husks were passed through an 80-mesh sieve for later use. The pretreated rice husks were placed in a tube furnace, and 99.99% nitrogen gas (flow rate 500 mL / min) was introduced. The temperature was increased to 700 ℃ at 5 ℃ / min and carbonized at a constant temperature for 2 h. After cooling, the carbonized product was removed, ground in a ceramic mortar, and passed through an 80-mesh sieve to obtain rice husk biochar fine powder with a particle size of 60~70 μm. The rice husk biochar fine powder and ferric chloride were weighed at mass ratios of 10:1, 5:1, and 5:2, respectively, dissolved in deionized water, and stirred at 500 rpm for 1 h until uniformly mixed. The mixture was dried in a 60 ℃ oven to constant weight, removed, ground again, and spread evenly in a corundum boat (thickness ≤5 mm). The corundum boat was placed in a tube furnace, and nitrogen gas was introduced (flow rate 300 mL / min). The temperature was increased to 400 ℃ at 3 ℃ / min and heat-treated at this temperature for 2 h. After cooling, the product was removed and repeatedly washed with deionized water until the pH of the filtrate was 7.0 ± 0.1. It was then placed in a vacuum oven at 60 ℃ and dried for 12 h. The product was then pulverized and passed through an 80-mesh sieve to obtain three iron-based biochar products with different ratios, labeled as FeBC (10:1), FeBC (5:1), and FeBC (5:2), respectively.

[0048] (2) Performance characterization of iron-based biochar: Performance tests were conducted on three types of iron-based biochar and unmodified rice husk biochar (BC): Three types of iron-based biochar (labeled FeBC (10:1), FeBC (5:1), and FeBC (5:2) respectively) prepared by mixing rice husk biochar powder and ferric chloride at mass ratios of 10:1, 5:1, and 5:2, as well as unmodified rice husk biochar (BC), were systematically characterized using X-ray diffraction (XRD). Figure 4 Analysis showed that all three types of iron-based biochar exhibited characteristic diffraction peaks corresponding to the FeCl2 phase (PDF#01-1106) at 2θ=35.7°, with the peak signals of FeBC (5:1) and FeBC (5:2) being more significant; X-ray photoelectron spectroscopy (XPS) also showed these peaks. Figure 3 This indicates that Fe is present in all three types of iron-based biochar in the form of Fe. 2+ with Fe 3+ The uniform distribution of mixed valence states is beneficial to the electron transport cycle of sulfur autotrophic denitrification, and the Fe 2p characteristic peak in FeBC (5:1) and FeBC (5:2) is relatively strong, which is consistent with the XRD results; Fourier transform infrared spectroscopy (FTIR) also shows this effect. Figure 2 The results showed that iron-based biochar at 1205 cm⁻¹... -1 (COC vibration), 1650 cm-1 The characteristic peak at the (CN vibration) is stronger than that of unmodified biochar, confirming that iron combines with functional groups on the surface of biochar to form a stable composite structure; the Brunauer-Emmett-Teller (BET) method (Table 1) shows that the specific surface area of ​​FeBC (5:1) is lower than that of FeBC (10:1) but higher than that of FeBC (5:2), and its microporous specific surface area is greater than that of mesoporous specific surface area, possessing both moderate pore size and outstanding small molecule adsorption capacity; the scanning electron microscope (SEM) of biochar-based materials, Figure 5 Characterization showed that the pore structure of FeBC (5:1) was moderately filled, forming a more regular surface morphology. As shown in Table 1, based on the above multi-dimensional characterization results, including specific surface area, elemental valence distribution, functional group binding state, and crystal structure, the optimal preparation mass ratio of rice husk biochar powder to ferric chloride was determined to be 5:1. The FeBC (5:1) prepared in this ratio will be used in subsequent experiments on the cultivation and denitrification of granular sludge mediated by iron-based biochar for sulfur autotrophic denitrification.

[0049] Table 1. BET results and porosity characterization of biochar-based materials

[0050] Example 2: Start-up of an iron-based biochar-mediated sulfur autotrophic denitrification granular sludge cultivation device (1) Acclimation of iron-based biochar-mediated sulfur autotrophic denitrification granular sludge Sludge from the anaerobic biological treatment process of a municipal wastewater treatment plant is inoculated into an upflow anaerobic sludge blanket reactor (see schematic diagram of the anaerobic biological process device). Figure 1 As shown, the sludge inoculum concentration was 3 g TS / L, and the inoculum amount accounted for 30% of the effective reactor volume. It synergistically constructed the initial reaction system with pretreated and optimized iron-based biochar. 1.67 g / L of pre-optimized FeBC (5:1) iron-based biochar (rice husk biochar powder to ferric chloride mass ratio 5:1, specific surface area 4.2850 m²) was precisely added. 2 / g). Components of the synthetic wastewater: nitrogen source is KNO3, concentration is 48.3±1.6 mg-N / L; sulfur source is Na2S2O3•5H2O, concentration is 160.8±13.5 mg-S / L; phosphorus source is KH2PO4, concentration is 56.2±2.5 mg-P / L; MgCl2•6H2O and CaCl2 are added simultaneously, with concentrations of 36.3±1.5 mg-Mg / L and 70±1.3 mg-Ca / L, respectively. The pH was adjusted to 7.13 ± 0.10 using NaHCO3. 1 mL of a trace element reserve solution was added to every 1 L of wastewater. The reserve solution contained ZnSO4•5H2O 1.5 g / L, NiCl2•6H2O 0.25 g / L, H3BO3 0.5 g / L, CuSO4•5H2O 0.25 g / L, MnCl2•4H2O 1.0 g / L, CoCl2•2H2O 0.25 g / L, and HCl 5.0 mL / L, providing essential trace elements for microbial growth. During the acclimation period, a stepped low-carbon synthesis wastewater model was used as the influent, creating favorable conditions for the granulation of sulfur-autotrophic denitrification granular sludge. During this period, the S2O3 levels in the influent and effluent were monitored regularly. 2- SO4 2- NO3 - NO2 - TN, while simultaneously tracking sludge particle size and SVI 30 Parameters such as pH value were used to evaluate the formation status of granulated sulfur-autotrophic denitrification sludge within the reactor. To maintain stable influent quality, the influent was changed daily to ensure consistency and controllability of the reaction environment. The operating conditions for this stage were: a hydraulic retention time of 8 hours, continuous influent, with influent and effluent controlled by a peristaltic pump via the influent pipeline per cycle, an influent flow rate of 18 L / d, and a 2 cm thick polyurethane insulation layer covering the outer wall of the reaction zone, combined with a bottom water bath heating circulation system, maintaining a temperature of 30 ± 2℃. Shear force provided by the reflux and influent promoted sludge granulation.

[0051] During the initial operation, a small amount of sodium acetate was added as a carbon source to promote the granulation of sulfur-autotrophic denitrification sludge. The carbon source concentration was 106.6 ± 3.2 mg-COD / L. The influent pH was adjusted to 7.13 ± 0.10 using NaHCO3, and the reaction temperature was maintained at room temperature (30 ± 2℃). When the sulfur-autotrophic denitrification sludge began to granulate, the sludge SVI (sulfur-to-vitrification sludge viscosity) was achieved. 30 Below 50 mL / g, S2O3 2- and NO3 - Once the TN removal rate stabilizes, the sulfur autotrophic denitrification sludge acclimatization stage ends.

[0052] (2) Start-up of the iron-based biochar-mediated sulfur autotrophic denitrification granular sludge denitrification performance optimization device The start-up phase of the iron-based biochar-mediated sulfur autotrophic denitrification granular sludge denitrification optimization device adopts a gradient carbon reduction strategy. Based on granulated sludge, a fully sulfur autotrophic denitrification system is gradually constructed, specifically in three stages: Stage 1: The C / N ratio is controlled at 2, the sodium acetate concentration is 106.6 ± 3.2 mg-COD / L, the influent pump flow rate is set at 9 L / d, the return pump flow rate is 144 L / d, and the upflow velocity in the reaction zone is 1.00 m / h, operating for 40 days. Stage 2: The C / N ratio is reduced to 1, the sodium acetate concentration is adjusted to 53.3 ± 1.6 mg-COD / L, the influent pump flow rate remains unchanged at 9 L / d, the return pump flow rate is increased to 171 L / d, and the upflow velocity is increased to 1.3 m / h, operating for 30 days, gradually reducing the sludge's dependence on carbon sources and strengthening the sulfur autotrophic metabolic pathway. Stage 3: Sodium acetate addition is stopped, making the C / N ratio 0, while the influent pump flow rate remains at 9 L / d. The flow rate of the return pump was further increased to 198 L / d, and the upward flow velocity reached 1.5 m / h. After 50 days of operation, the formation of a fully autotrophic denitrification system was promoted.

[0053] The upflow anaerobic sludge bed reactor is made of plexiglass, with an inner diameter of 90 cm, an outer diameter of 140 mm, a total height of 520 mm, and an effective volume of 3.2 L. The outer wall of the reaction zone is wrapped with a 2 cm thick insulation layer. The interior is equipped with a three-phase separator, an exhaust port, a water inlet, a return water outlet, and a water outlet. The device also includes an internal circulation pump (peristaltic pump, with the input end connected to the reactor return water outlet and the output end connected to the reactor water inlet), a gas check valve (installed at the exhaust port to prevent air backflow), a water inlet tank, and a water inlet pump. The reactor return water outlet and the water inlet tank outlet merge and are then connected to the reactor water inlet through the water inlet pump to achieve uniform mixing of the inlet water and return water and provide hydraulic shearing action.

[0054] Water quality and sludge characteristics were monitored using daily sampling: Reactor effluent was filtered through a 0.45 μm PTFE filter and stored at 4 °C. Within 24 hours, total nitrogen (TN) (potassium persulfate oxidation method) and nitrogen oxides (NO3) were measured using a UV spectrophotometer (UV-2600). - (Ultraviolet spectrophotometry), NO2 - (N-(1-naphthyl)-ethylenediamine spectrophotometry), S2O3 2- With SO4 2- The content changes were measured by (ion chromatography), and the sludge particle size changes were tracked by a laser particle size analyzer. The SVI was determined by the 30-minute settling method. 30 Figures 6, 7, 9, and 10 show the sulfur-autotrophic denitrification granular sludge (SVI) under low-carbon simulated municipal wastewater treatment. 30The graphs show the removal effect, particle size distribution, TN removal effect, and sulfide conversion rate. As can be seen from the graphs, after 28 days of operation, the sludge has formed particles with a diameter of 227 μm, and the SVI... 30 The concentration was 45.0 mL / g; by the end of the start-up phase (120 days of cumulative operation), the particle size of the granular sludge had grown to 986 μm, the nitrogen removal efficiency reached 95.7%, the sulfur conversion rate reached 98.3%, and all indicators remained stable for 10 consecutive days, marking the completion of the start-up of the device and the establishment of a mature, fully autotrophic denitrification system.

[0055] Example 3: Iron-based biochar-mediated sulfur autotrophic denitrification granular sludge stabilization and denitrification To further investigate the stable operation performance and synergistic efficiency of denitrification and sulfur conversion of the iron-based biochar-mediated sulfur autotrophic denitrification granular sludge system under short hydraulic retention time (HRT) conditions, a 54-day stable operation experiment was conducted using the iron-based biochar-mediated sulfur autotrophic denitrification granular anaerobic sludge blanket (UASB) reactor that was successfully started up in Example 2.

[0056] After the UASB reactor in Example 2 is started up, it enters the stable operation stage, and the core control objective is to shorten the hydraulic residence time to increase the system's processing load. During this phase, the carbon-free influent mode is maintained. The concentrations of nitrogen, sulfur, and phosphorus sources in the influent are consistent with the initial carbon-free influent during the start-up phase: nitrogen (KNO3) concentration is 48.3±1.6 mg-N / L, sulfur (Na2S2O3•5H2O) concentration is 160.8 ± 13.5 mg-S / L, and phosphorus (KH2PO4) concentration is 56.2±2.5 mg-P / L. Simultaneously, magnesium salts, calcium salts, and buffers are continued, with MgCl2•6H2O concentration at 36.3±1.5 mg-Mg / L and CaCl2 concentration at 70±1.3 mg-Ca / L. The pH of the influent is adjusted to 7.13±0.10 using NaHCO3 to maintain system stability. 1 mL of trace element reserve solution is added per 1 L of influent, consisting of 1.5 g / L ZnSO4•5H2O and 0.25 g / L NiCl2•6H2O. The following components were added: g / L of H3BO3, 0.5 g / L of CuSO4•5H2O, 1.0 g / L of MnCl2•4H2O, 0.25 g / L of CoCl2•2H2O, and 5.0 ml / L of HCl to ensure the physiological and metabolic needs of functional microorganisms such as sulfur-oxidizing bacteria (SOB).

[0057] The optimized operating conditions during the stable operation phase are as follows: the effective reactor volume is maintained at 3L, and the reaction zone temperature is controlled at 30±2℃ using a 2 cm thick insulation layer on the outer wall in conjunction with a water bath heating system; the hydraulic retention time (HRT) is gradually shortened from 8 hours during the start-up phase to 4 hours, corresponding to an adjustment of the influent pump flow rate to 18 L / d and an increase in the return pump flow rate to 396 L / d, ensuring a stable upward flow velocity of 1.7 m / h within the reactor. The synergistic effect of the influent and return water provides stable hydraulic shear force, guaranteeing a dense and intact granular sludge structure. To ensure the stability of the influent water quality, the influent is replaced daily, and water quality monitoring is conducted daily by sampling and testing both influent and effluent, while sludge characteristic indicators are tracked periodically.

[0058] During operation, the particle size change of granular sludge was continuously monitored using a laser particle size analyzer, and the SVI was determined by sedimentation method. 30 The total nitrogen (TN) and nitrogen oxides (NO3) in the effluent were detected using a UV spectrophotometer (model UV-2600). - -N (ultraviolet spectrophotometry), NO2 - The content of -N (N-(1-naphthyl)-ethylenediamine spectrophotometric method) was analyzed by ion chromatography for S2O3. 2- With SO4 2- Concentration, to assess sulfur conversion and denitrification efficiency.

[0059] Monitoring results showed that as the hydraulic shear time (HRT) was gradually shortened from 8 h to 4 h, the granular sludge further solidified under stable hydraulic shear force, and the particle size showed a continuous increasing trend: at the initial stage of operation (HRT=8 h), the median diameter of the granular sludge was 986 μm, which increased to 1023 μm after 10 days of operation, reached 1058 μm after 20 days of operation, and after the HRT stabilized at 4 h and continued to operate for 40 days, the median diameter of the granular sludge stabilized at 1050~100 μm, with a regular spherical shape and a dense structure (e.g., ...). Figure 8 (As shown). SVI 30 The value gradually decreased from 48.9 mL / g at the end of the initial stage and stabilized at 39.4~2.1 mL / g (e.g., Figure 6 As shown in the figure, it has excellent settling performance and effectively solves the problem of easy loss of traditional sulfur autotrophic denitrification flocculent sludge.

[0060] In terms of denitrification and sulfur conversion efficiency (such as...) Figure 9 , Figure 10As shown in the figure, the system exhibits highly efficient synergistic characteristics: when the HRT is shortened to 4 hours and operates stably, the TN removal rate remains high, with a total nitrogen removal rate of 90.7%, and the fluctuation of monitoring indicators is ≤±3% for 15 consecutive days. The effluent TN concentration is stable at 1.2-2.8 mg / L, far below the 5 mg / L limit specified in the Class A standard of the "Discharge Standard of Pollutants for Municipal Wastewater Treatment Plants" (GB 18918-2002); the sulfur conversion rate is simultaneously increased to 98.7%, and S2O3... 2- Almost completely converted to SO4 2- No elemental sulfur was observed accumulating and adhering to the surface of microorganisms, confirming that iron-based biochar is produced through Fe²⁺. + / Fe³ + Valence state cycling accelerates electron transfer, effectively enhancing the coupling efficiency of sulfur oxidation and denitrification.

[0061] Example 4: Comparison of nitrogen removal performance of iron-based biochar-mediated enhanced sulfur autotrophic denitrification granular sludge with the control group without additives. To clarify the mediating and enhancing effect and core efficiency-enhancing mechanism of iron-based biochar on sulfur autotrophic denitrification systems, this embodiment uses an upflow anaerobic sludge blanket (UASB) reactor with specifications identical to those in Examples 2 and 3 to construct a parallel experimental system: In Examples 2 and 3, anaerobic sludge from a municipal wastewater treatment plant was inoculated (inoculation concentration 3 g TS / L, inoculation amount accounting for 30% of the effective reactor volume), and 1.67 g / L of FeBC (5:1) iron-based biochar (rice husk biochar to ferric chloride mass ratio 5:1, specific surface area 4.2850 m²) optimized and prepared in Example 1 was precisely added. 2 / g); the control group was inoculated with anaerobic sludge of the same source, concentration, and inoculation amount, without the addition of any biochar or iron-based modifiers. The influent water quality, operating parameters, and monitoring conditions were completely identical for both groups. The nitrogen removal efficiency, sulfur conversion efficiency, and sludge characteristic parameters were systematically tracked, and the enhancing effect of iron-based biochar was quantitatively compared. Details of changes in relevant indicators can be found in [link to relevant documentation]. Figure 6 (Graph showing the change in SVI of sulfur autotrophic granular sludge) Figure 9 (Image showing the effect of TN removal from sulfur-autotrophic granular sludge) Figure 10 (Image showing the effect of sulfur autotrophic granular sludge sulfide removal) Figure 7 (Particle size distribution diagram of sulfur autotrophic granular sludge) and Figure 8 (Microscopic image of sulfur autotrophic granular sludge particles).

[0062] As shown in Table 2, the experimental group exhibited significantly better overall performance than the control group throughout the entire operation phase. The mediated enhancement effect of iron-based biochar persisted throughout the entire operation cycle, effectively improving the nitrogen removal efficiency, sulfur conversion efficiency, and sludge settling characteristics of the sulfur autotrophic denitrification system. As the C / N ratio gradually decreased from 2 to 0, at hydraulic retention times (HRT) of 8 h and 4 h, the SVI of both groups decreased significantly. 30 The differences in denitrification efficiency and sulfur conversion efficiency are particularly prominent. Specifically, at HRT=8h, the denitrification efficiency (see...) Figure 9 The experimental group achieved a total nitrogen (TN) removal rate of 95.7%, with the effluent TN concentration consistently meeting the standard. The control group achieved a TN removal rate of 91.9%, with the effluent TN concentration exceeding the Class A standard. Regarding sulfur conversion performance (see...), Figure 10 In the experimental group, the sulfide conversion rate reached 98.3%, with no accumulation of elemental sulfur. In the control group, the sulfide conversion rate was 97.7%, with a small amount of elemental sulfur adhering to the surface of microorganisms (see...). Figure 8 Regarding sludge settling performance (see...) Figure 6 ), experimental group SVI 30 It remained stable at 41.7~48.9 mL / g, exhibiting excellent sedimentation performance, compared to the control group's SVI. 30 Fluctuations ranged from 45.3 to 68.3 mL / g, indicating poor sedimentation stability. Under high-load conditions (HRT=4h, C / N=0 without carbon source), the denitrification efficiency was significantly superior (see...). Figure 9 In the experimental group, the TN removal rate remained at 90.7%, and the effluent TN concentration consistently met the Class A standard of the "Discharge Standard of Pollutants for Municipal Wastewater Treatment Plants" (GB 18918-2002). In contrast, the TN removal rate in the control group dropped significantly to 68.2%, and the effluent TN concentration exceeded the standard. Regarding sulfur conversion performance (see...), Figure 10 In the experimental group, the sulfide conversion rate remained at 92.4%, and the mass transfer efficiency of the reaction system was good. In the control group, the sulfide conversion rate dropped to 78.9%, and the mass transfer efficiency was significantly affected.

[0063] Table 2. Operating parameters and performance of the sulfur autotrophic denitrification reactor at different operating stages

[0064] In summary, this embodiment, through parallel control experiments, demonstrates that the iron-based biochar-mediated sulfur autotrophic denitrification granular sludge cultivation and denitrification optimization device can achieve stable granular sludge existence and efficient denitrification and sulfur conversion synergistic effects under carbon source-free influent conditions. All core treatment indicators meet emission standards, and the device possesses technical advantages such as low operating energy consumption, no need for external organic carbon sources, and simple operation. This technology effectively solves the technical pain points of traditional sulfur autotrophic denitrification processes, such as easy sludge loss and weak resistance to shock loads, through the triple effects of iron-based biochar carrier enrichment, accelerated electron transfer, and enhanced particle sedimentation. It is suitable for treating carbon-poor wastewater scenarios such as municipal sewage and aquaculture wastewater, aligning with current environmental policies for low-carbon emission reduction. It has broad industrial application prospects in the deep treatment of low-carbon-to-nitrogen ratio wastewater and the upgrading and renovation of existing sewage treatment plants, providing reliable technical support for the synergistic effect of pollution reduction and carbon reduction in the sewage treatment industry.

Claims

1. A method for treating nitrogen-containing wastewater using iron-based biochar-mediated sulfur autotrophic denitrification granular sludge, characterized in that, The specific steps are as follows: (1) Synthesis of iron-based biochar: Biochar was placed in a tube furnace and carbonized under a nitrogen atmosphere to obtain carbonized products. The carbonized products were then transferred, ground, and sieved. The resulting fine powder was hydrothermally mixed with ferric chloride in a preset ratio. After drying, the mixture was ground in a grinding device and then heat-treated under a nitrogen atmosphere to obtain iron-based biochar. (2) Start-up of the iron-based biochar-mediated sulfur autotrophic denitrification granular sludge cultivation device: Anaerobic activated sludge and the iron-based biochar obtained in step (1) were co-inoculated into an upflow anaerobic sludge bed reactor. By controlling the influent flow rate to create hydraulic shear, sludge aggregation was promoted. The influent carbon source concentration was gradually reduced until the addition was completely stopped to construct a fully sulfur-autotrophic denitrification system. S2O3 was monitored regularly. 2- SO4 2- Conversion rate and NO3 - NO2 - TN removal rate, while tracking sludge particle size and SVI 30 until SO4 2- When the conversion rate and TN removal rate are stable and the sludge is granulated, the reactor startup is complete. (3) Stable operation and performance optimization of iron-based biochar-mediated sulfur autotrophic denitrification granular sludge unit: After the upflow anaerobic sludge blanket reactor was started up, synthetic wastewater was introduced, maintaining a carbon-free influent. The effects of different operating parameters on the system's denitrification performance were investigated by shortening the hydraulic retention time. During this period, effluent parameters, including S2O3, were monitored regularly. 2- SO4 2- Conversion rate and NO3 - NO2 - TN removal rate, while simultaneously tracking microbial activity, granular sludge particle size distribution, and SVI. 30 Changes, until SO4 2- The conversion rate and TN removal rate remain continuous and stable, thus achieving stable operation of the device.

2. The method of claim 1, wherein, In step (1), the biochar is first carbonized at 700℃ for 1.5~2.5 h under a nitrogen atmosphere to obtain the carbonized product, then ground and sieved to obtain 60~70 μm fine biochar powder, and finally the fine biochar powder and ferric chloride are dissolved in pure water at a mass ratio of 1~10:1 and stirred to obtain iron-based biochar.

3. The method of claim 1, wherein, In step (2), the concentration of inoculated sludge is controlled at 2.8~3.2 g TS / L and the amount of iron-based biochar added is 1.5~1.7 g / L. The hydraulic conditions are controlled by the internal circulation pump and the influent pump in coordination to form a suitable hydraulic shearing effect at an HRT of 8h to promote sludge aggregation. At the same time, the anaerobic environment of the reactor is maintained throughout the process by the gas check valve.

4. The method of claim 1, wherein, In steps (2) and (3), the upflow anaerobic bioreactor is in an anaerobic state and operates in continuous flow. The hydraulic shear is provided by the influent and the return peristaltic pump. The temperature of the reaction zone is maintained at 30 ± 2℃ by water bath heating. The pH of the influent is 7.13 ± 0.

10. After treatment, the wastewater is discharged through the outlet and the gas is discharged through the three-phase separation system.

5. The method of claim 1, wherein, In steps (2) and (3), the synthetic wastewater contains a nitrogen source, a sulfur source, a phosphorus source, a carbon source, MgCl2•6H2O, CaCl2, and NaHCO2. The nitrogen source is KNO3, the sulfur source is Na2S2O3•5H2O, the phosphorus source is KH2PO4, and the carbon source is sodium acetate. The synthetic wastewater contained nitrogen source concentrations of 48.3 ± 1.6 mg-N / L, sulfur source concentrations of 160.8 ± 13.5 mg-S / L, phosphorus source concentrations of 56.2 ± 2.5 mg-P / L, MgCl2•6H2O concentrations of 36.3 ± 1.5 mg-Mg / L, and CaCl2 concentrations of 70 ± 1.3 mg-Ca / L. The influent pH was adjusted to 7.13 ± 0.10 using NaHCO3.

6. The method of claim 1, wherein, In steps (2) and (3), 1 mL of trace element reserve solution needs to be added to 1 L of synthetic wastewater. The reserve solution contains ZnSO4•5H2O 1.5 g / L, NiCl2•6H2O 0.25 g / L, H3BO3 0.5 g / L, CuSO4•5H2O 0.25 g / L, MnCl2•4H2O 1.0 g / L, CoCl2•2H2O 0.25 g / L, and HCl 5.0 ml / L.

7. The method of claim 1, wherein, In step (2), the anaerobic bioreactor operates in an HRT=8 h mode. The parameters corresponding to different C / N conditions are as follows: when C / N=2, the flow rates of the influent pump and the return pump are 8~10 L / d and 135~150 L / d, respectively, and the upward flow velocity is 0.95~1.05 m / h; when C / N=1, the flow rates of the influent pump and the return pump are 8~10 L / d and 165~175 L / d, respectively, and the upward flow velocity is 1.25~1.35 m / h; when C / N=0, the flow rates of the influent pump and the return pump are 8~10 L / d and 190~205 L / d, respectively, and the upward flow velocity is 1.45~1.55 m / h.

8. The method of claim 1, wherein, In step (3), the anaerobic bioreactor adopts the HRT=4 h operation mode, with the flow rates of the influent pump and the return pump being 17~19 L / d and 385~405 L / d, respectively, and the upward flow velocity maintained at 1.65~1.75 m / h.

9. The method of claim 1, wherein, When treating low-carbon-to-nitrogen (C / N) wastewater with a C / N ratio ≤ 2 using the above method, granular sludge can be formed within 25-30 days after startup, achieving SVI (Sludge Viscosity Index). 30 Stable concentration below 50 mL / g; system denitrification efficiency of over 90.0%, sulfur conversion rate of over 92.0%, and effluent TN concentration ≤ 5 mg / L.

10. An apparatus for treating nitrogen-containing wastewater using iron-based biochar-mediated sulfur autotrophic denitrification granular sludge, characterized in that, Includes the upflow anaerobic sludge bed reactor, internal circulation pump, and gas check valve as described in claim 1; The upflow anaerobic sludge bed reactor is equipped with a three-phase separator, an exhaust port, an inlet, a return outlet, an outlet, and an insulation layer. The internal circulation pump is a peristaltic pump, with its input end connected to the reflux outlet of the anaerobic bioreactor and its output end connected to the inlet of the anaerobic bioreactor. The gas check valve is installed at the exhaust port of the anaerobic bioreactor. The reflux outlet of the anaerobic bioreactor is also connected to the outlet of the inlet tank. After the two are combined, they are connected to the inlet of the anaerobic bioreactor through the inlet pump to achieve uniform mixing of inlet and reflux water.

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