A low-drug method for efficiently removing ammonia nitrogen and toxic organic matters in wastewater

Abstract

The present application belongs to the technical field of sewage treatment, and particularly relates to a low-agent method for efficiently removing ammonia nitrogen and toxic organic matters in wastewater. The present application adopts a double-chamber bioelectrochemical reactor, the biological anode generates electrons by the biological oxidation process of the wastewater containing organic matters, and the electrons are transmitted to the biological cathode through an external circuit; the biological cathode is inoculated with a compound functional microbial system which is enriched and domesticated, ammonia nitrogen in the wastewater is used as a synergistic electron donor to form a double-electron driving mechanism together with the input electrons of the external circuit, so as to promote the in-situ reduction and regeneration of Fe(III) in Fenton iron sludge to Fe(II); Fe(II) is used as a Fenton-like catalyst for the oxidative degradation of toxic organic wastewater; the generated iron-containing precipitate returns to the biological cathode, so that the synergistic conversion and recycling of Fenton iron sludge and ammonia nitrogen are realized. A 20 L double-chamber bioelectrochemical amplification system is constructed, and the applied voltage and cathode pH are optimized, so that the stable operation of the biological cathode and the continuous regeneration of Fe(II) are realized.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, specifically relating to a low-reagent method for efficiently removing ammonia nitrogen and toxic organic matter from wastewater. Background Technology

[0002] Ammonia nitrogen pollution combined with persistent toxic organic pollutants is a common challenge in the treatment of industrial wastewater, pharmaceutical wastewater, and municipal sewage. Conventional wastewater treatment processes often rely on traditional nitrification-denitrification, requiring alternating aerobic and anaerobic environments, resulting in high aeration energy consumption and large external carbon source dosages. This approach is also less effective for wastewater with low C / N ratios. While anaerobic ammonia oxidation can achieve autotrophic ammonia nitrogen removal under anaerobic conditions, the long generation cycles of functional microorganisms, their extreme sensitivity to pH, temperature, and toxic organic stress, and their weak resistance to shock loads limit their large-scale application. Furthermore, the persistent and bioaccumulative toxic organic pollutants in this type of wastewater inhibit microbial activity, leading to low efficiency in traditional biological treatment processes.

[0003] Fenton oxidation technology, with its strong oxidizing power of hydroxyl radicals, can efficiently degrade recalcitrant toxic organic compounds and is widely used in the deep treatment of industrial wastewater. However, the traditional Fenton process has inherent shortcomings: first, it consumes a large amount of Fe(II) catalyst, resulting in high operating reagent costs; second, it produces a large amount of iron-containing hydroxide precipitate, namely Fenton iron sludge, after the reaction, which leads to high solid waste disposal costs and is prone to secondary pollution; third, iron resources cannot be effectively recovered and recycled, resulting in poor long-term economic efficiency; at the same time, the traditional Fenton process has a narrow suitable pH window, requiring a lot of acid and alkali adjustment, further increasing operation and maintenance costs.

[0004] To address the issue of a continuous iron source supply cycle, existing research has attempted to regenerate Fe(III) to Fe(II) in Fenton iron sludge using a hybrid iron reduction and iron-ammonia oxidation system. However, this approach suffers from problems such as poor microbial synergy, disordered electron transfer, low regeneration efficiency, and insufficient operational stability. Conventional pure biological iron reduction systems are greatly affected by substrate concentration and environmental disturbances, making it difficult to achieve continuous and stable Fe(II) production.

[0005] Bioelectrochemical technology relies on electroactive microorganisms to spontaneously generate electricity by degrading organic matter at the bioanode, achieving directional electron transfer and providing a stable electron driving force for the cathodic reduction reaction. It has advantages such as low energy consumption, green and low carbon emissions, and the ability to couple the simultaneous treatment of carbon and nitrogen pollutants. Although existing biocathode systems can achieve Fe(II) regeneration, they still have the following shortcomings: they do not fully utilize ammonia nitrogen in wastewater as a synergistic electron donor; the ammonia nitrogen and iron reduction process lacks an efficient coupling mechanism; and the regulation law of Fe(II) regeneration by different ammonia nitrogen loads is unclear. Moreover, during the process of scaling up from laboratory pilot-scale to pilot-scale and engineering scale-up, problems such as electron transfer efficiency decay, loss of functional microbial communities, and mismatch of process parameters are common, and there is a lack of systematic parameter optimization and scale-up support technologies. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention provides a low-reagent method for efficiently removing ammonia nitrogen and toxic organic matter from wastewater. This method also enables the resource utilization of Fenton iron sludge and the removal of NH4. + Simultaneous N-N conversion, in-situ Fe(II) regeneration, and efficient removal of toxic organic matter demonstrate promising prospects for industrial application. This invention utilizes NH4 in wastewater... + -N, acting as a partial electron donor, synergistically interacts with the biological cathode, significantly enhancing the regeneration efficiency of Fe(II) in Fenton iron sludge. This process not only achieves effective reuse of Fenton iron sludge but also promotes the resource utilization of nitrogen-containing wastewater, solving the problems of iron sludge and NH4+. + The invention addresses the challenges of recycling NH4+ resources. Through systematic research, it successfully scaled up the reaction system and precisely identified the optimal parameter combination for system operation, ensuring the stability and efficiency of Fe(II) generation and providing solid data support for the industrial application of the technology. Furthermore, this invention utilizes regenerated Fe(II) to drive a Fenton-like reaction, efficiently and cost-effectively removing toxic organic compounds such as metronidazole from wastewater. The resulting Fenton iron sludge is recycled into the biocathode system, forming a closed iron cycle and maximizing resource utilization. In summary, the bioelectrochemical system constructed in this invention not only successfully removes difficult-to-treat Fenton iron sludge and NH4+ from wastewater, but also... + -N is transformed into valuable resources, and further research is conducted on different NH4 groups. + The synergistic conversion mechanism at -N concentrations, along with the system's scale-up effect, significantly enhances the technology's economic viability and practicality. Compared to previous technologies, this invention demonstrates significant advantages in resource recovery, treatment efficiency, and cost control, providing new ideas and solutions for the treatment of toxic organic wastewater.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The first aspect of this invention provides a low-reagent method for efficiently removing ammonia nitrogen and toxic organic matter from wastewater, employing a dual-chamber bioelectrochemical reactor. The dual-chamber bioelectrochemical reactor includes a bioanode chamber and a biocathode chamber, separated by a cation exchange membrane. Anaerobic granular sludge (containing electroactive microorganisms) occupying one-third of the reactor's effective volume is added to the anode chamber, while anaerobic granular sludge enriched with iron-reducing bacteria (i.e., a composite functional microbial system formed through domestication and enrichment) occupying one-third of the reactor's effective volume is added to the cathode chamber. Wastewater containing organic matter is passed into the anode chamber, while wastewater containing NH4+ is passed into the cathode chamber. + -N wastewater and Fenton iron sludge are introduced into the cathode chamber; a resistor is connected between the anode and cathode, and multiple continuous reaction cycles are set to regulate the pH of the cathode chamber; the bioanode utilizes electrons generated from the degradation of organic matter in the wastewater containing organic matter, which are then transferred to the biocathode via an external circuit; the biocathode uses NH4+ as the active ingredient. + -N acts as a cooperative electron donor, co-driving the reduction and regeneration of Fe(III) in Fenton iron sludge to Fe(II); the regenerated Fe(II) is recycled into subsequent Fenton-like oxidation processes to remove toxic organic pollutants from toxic organic wastewater, thus realizing the recycling of Fenton iron sludge and NH4+. + -N and iron resources are used in a closed-loop recycling process.

[0008] Furthermore, the electrodes of the dual-chamber bioelectrochemical reactor are made of commercially available carbon fiber brushes.

[0009] Furthermore, the biocathode device of the dual-chamber bioelectrochemical reactor employs a rotor-suspended "pendulum" stirring mechanism to avoid damaging the granular sludge structure during the stirring process.

[0010] Furthermore, the composite functional microbial system in the biocathode is obtained through pre-enrichment culture. This composite functional microbial system includes ammonia-oxidizing microorganisms, iron-reducing microorganisms, and electroactive microorganisms, enabling the cathode system to simultaneously possess NH4+. + -N oxidation, electron transfer, and Fe(III) reduction capabilities, thereby achieving NH4 + The coupling of -N conversion with the iron recycling process.

[0011] Furthermore, in the reaction system of the biocathode, NH4 + -N concentration range is 40~1100 mg / L, preferably 180~200 mg / L; by adjusting NH4 + -N concentration makes NH4 + The -N oxidation process and the Fe(III) reduction process achieve electron supply and demand matching, thereby improving the Fe(II) regeneration efficiency.

[0012] Furthermore, after adding Fenton iron sludge to the cathode chamber, the initial Fe(III) concentration in the system is 300-500 mg / L.

[0013] Furthermore, the multiple consecutive reaction cycles refer to 3-5 reaction cycles, with each cycle lasting 3-6 days.

[0014] Furthermore, the resistance value of the resistor connected between the anode and the cathode is 5-15 Ω.

[0015] Furthermore, the pH of the cathode chamber is adjusted to 5.0-6.5.

[0016] Furthermore, an external voltage of 0-0.8 V is applied between the anode and the cathode.

[0017] Furthermore, the regenerated Fe(II) is reused in subsequent Fenton-like oxidation processes to remove toxic organic pollutants from wastewater. This means using dissolved Fe(II), precipitated Fe(II), or a mixture of dissolved Fe(II) and precipitated Fe(II) regenerated in the cathode chamber as a Fenton-like catalyst, adding hydrogen peroxide to construct a Fenton-like reaction system, and oxidizing and degrading metronidazole-containing toxic organic wastewater, achieving complete degradation of metronidazole within 5 minutes.

[0018] The second aspect of this invention provides a scale-up application of a low-reagent method for efficiently removing ammonia nitrogen and toxic organic matter from wastewater. A 20 L-stage dual-chamber bioelectrochemical reactor is used, with the anode and cathode chambers separated by a cation exchange membrane. Both the anode and cathode chambers are filled with anaerobic granular sludge. Wastewater containing organic matter is introduced into the anode chamber, while wastewater containing ammonia nitrogen and Fenton iron sludge are introduced into the cathode chamber. Each anode and cathode is equipped with 5-15 commercial carbon fiber brushes as electrodes. The device is equipped with an adjustable DC power supply, a fixed resistor, an online pH controller, and a paperless recorder. The applied voltage is adjusted to 0-0.8 V, and the cathode reaction pH is set to 5.0-6.5, enabling the large-scale treatment of Fe(II) regeneration from the biological cathode and the treatment of toxic organic wastewater.

[0019] Compared with the prior art, the beneficial effects of the present invention are: (1) In view of the shortcomings of traditional Fenton iron sludge chemical regeneration Fe(II) technology, such as large reagent consumption, serious secondary pollution, high operating energy consumption and extremely narrow pH applicable window, this invention constructs a biological cathode iron recycling system, which relies on a low-energy-consumption, green and low-carbon microbial electrochemical mechanism to directly utilize the inherent NH4 in the wastewater. +-N, acting as a natural electron donor, works in conjunction with the biocathode's electric field to achieve efficient regeneration of Fe(III) to Fe(II) in Fenton iron sludge. Compared to a purely biological regeneration system without a biocathode, the biocathode provides a sustainable and stable driving force for directional electron transfer, increasing the Fe(II) regeneration rate and enrichment concentration. Simultaneously, it effectively broadens the pH range applicable to iron recycling, enabling efficient Fe(II) regeneration under weakly acidic to near-neutral conditions, and significantly enhancing the system's resistance to pH fluctuations and operational stability.

[0020] (2) This invention further reveals the regulatory mechanism of different ammonia nitrogen concentrations on the iron recycling system of the biological cathode. A comparative study using gradient ammonia nitrogen concentrations confirmed that at 180-200 mg / L NH4... + Under -N conditions, the electron transfer efficiency of the biocathode in the system is optimally matched with the iron reduction reaction rate, which can maximize the activation of the resource regeneration potential of Fenton iron sludge and achieve stable and efficient enrichment of Fe(II). Compared with systems with excessively low or high ammonia nitrogen loads, the regeneration effect is better, the microbial community structure is more stable, and the iron cycle closed loop is more sustainable. This provides the optimal operating condition basis for the simultaneous denitrification of high ammonia nitrogen toxic organic wastewater and the resource utilization of iron sludge.

[0021] (3) This invention successfully constructed a 20 L-scale biocathode reaction system, completing the upgrade and optimization from pilot-scale to large-scale process. By systematically controlling the key process parameters of the reactor operation and matching the reaction characteristics of iron sludge regeneration, the synergistic working conditions of electrochemical reduction, microbial metabolism, and iron valence state cycling were precisely optimized. This effectively solved the technical problems commonly encountered in the process scale-up, such as electron transfer disorder, loss of functional microbial communities, and decay of Fe(II) regeneration efficiency. It significantly improved the Fe(II) regeneration rate and regeneration stability of Fenton iron sludge under the scale-up system, ensuring the long-term continuous, efficient, and stable operation of the scale-up system. This provides reliable scale-up technical support and process parameter basis for the subsequent industrial-scale promotion and application of this technology.

[0022] (4) In practical wastewater treatment applications, this invention achieves closed-loop resource utilization of Fe(II) resources regenerated from Fenton iron sludge. The Fe(II) regenerated from the biological cathode system is directly applied to a Fenton-like reaction system to remove typical toxic organic pollutants such as metronidazole that are difficult to degrade in water. Both the regenerated dissolved Fe(II) and precipitated Fe(II) possess excellent catalytic activity, which can rapidly activate the Fenton-like reaction to achieve the degradation of metronidazole pollutants. The degradation rate can reach approximately 100% in the first five minutes. This invention solves the problems of iron resource waste, low pollutant degradation efficiency, and long treatment cycle in the traditional Fenton process. The practicality and engineering application value of the process are greatly improved, and it meets the needs of rapid and efficient treatment of antibiotic-type toxic organic wastewater. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the bioelectrochemical reaction system of the present invention.

[0024] Figure 2 The concentration of Fe(II) regenerated in the biocathode of the pilot device is shown to vary under different ammonia nitrogen concentrations.

[0025] Figure 3 The variation of ammonia nitrogen concentration in the biological cathode of a small-scale test device under different ammonia nitrogen concentrations.

[0026] Figure 4 The concentration changes of dissolved Fe(II) during biocathode regeneration in a 20 L reactor under different applied voltages.

[0027] Figure 5 The ratio of Fe(II) to total Fe in the bottom precipitate of a 20 L reactor under different applied voltages during biocathode regeneration.

[0028] Figure 6 The concentration of dissolved Fe(II) during biocathode regeneration in a 20 L reactor under different pH conditions is shown.

[0029] Figure 7 The effect of regenerated Fe(II) on the degradation of metronidazole in Fenton-like treatment. Detailed Implementation

[0030] The specific embodiments of the present invention will be further described below. It should be noted that these descriptions are for the purpose of aiding understanding the present invention, but do not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0031] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods, and the experimental materials used in the following embodiments are all available through conventional commercial channels.

[0032] In this invention, the preparation steps of Fenton iron sludge are as follows: Take 200 mL of deionized water, adjust the pH to 2-3 with HCl, add 50-55 g of ferrous chloride tetrahydrate and stir until the ferrous chloride is completely dissolved, add 40 mL of 30% hydrogen peroxide solution, start the Fenton oxidation reaction until the solution turns reddish-brown, after the reaction is completed, adjust the pH of the reaction system to 6-8 with 2 M sodium hydroxide solution, let it stand for one hour to allow all the generated Fenton iron sludge to precipitate, pour off the supernatant, which is Fenton iron sludge.

[0033] Example 1: Investigating the effect of different ammonia nitrogen concentrations on Fe(II) regeneration at a biological cathode A small-scale apparatus for constructing a two-chamber bioelectrochemical reactor, such as... Figure 1As shown on the left, anaerobic granular sludge is added to fill one-third of the device in the anode chamber, and anolyte (anolyte composition: anhydrous disodium hydrogen phosphate 3-8 g / L, potassium dihydrogen phosphate 1-5 g / L, ammonium salt 0.4-0.6 g / L, sodium acetate 0.8-1.5 g / L, trace elements 1-2 ml / L, vitamins 1-2 ml / L) is added to a distance of 1-3 cm from the top of the reactor. Excess potassium ferricyanide is added to the cathode chamber. Potassium ferricyanide is only used for electron acceptor acclimation during the start-up phase and does not participate in the subsequent iron cycle process. The cathode and anode chambers are separated by a cation exchange membrane. Commercial carbon fiber brushes are used as anode and cathode electrodes. A 1000 Ω resistor is used to connect the cathode and anode. A paperless recorder is used to record the voltage changes throughout the cycle. Start-up is successful when the output voltage is stable above 0.6 V.

[0034] Replace the potassium ferricyanide in the cathode chamber with catholyte containing Fenton iron sludge (catholyte composition: sodium bicarbonate 2.7 g / L, ammonium salt 0.2-4 g / L, anhydrous disodium hydrogen phosphate 0.01 g / L, trace elements 1 ml / L, vitamins 2 ml / L, and Fenton iron sludge with Fe(III) concentration of 450-550 mg / L) up to a distance of 1-3 cm from the top of the reactor, and add anaerobic granular sludge enriched with iron-reducing bacteria to fill one-third of the device; the pH of the catholyte is adjusted to 5.0-6.5 using a pH controller; a 10 Ω resistor is used to connect the cathode and anode. Each reaction cycle lasts 3 days. After each cycle, the anolyte and catholyte are replaced, and a new cycle begins with connecting the cathode and anode. After taking out the catholyte sample each day, add 1 M hydrochloric acid solution at a 1:1 ratio and store the sample in a refrigerator at 4 ℃. The detection of ferrous iron was performed using the o-phenanthroline spectrophotometric method, with absorbance measured at a wavelength of 510 nm; the detection of ammonia nitrogen was performed using the Nessler's reagent spectrophotometric method, with absorbance measured at a wavelength of 510 nm. This was based on the NH4+ in the catholyte. + Investigating different NH4+ concentrations with varying -N concentrations + The effect of -N concentration on Fe(II) regeneration at the biocathode.

[0035] Different NH4 + -N concentration synergistic with Fe(II) concentration in biocathode regeneration, such as Figure 2As shown, the Fe(II) concentration in all three systems showed a continuous upward trend over time during the two cycles, indicating that a stable Fe(II) regeneration process existed in the system throughout the experimental period. This regeneration activity was maintained stably throughout the two consecutive cycles without significant activity decay. The Fe(II) regeneration efficiency of the 180-200 mg N / L group was consistently significantly higher than the other two groups, reaching a maximum of approximately 140-160 mg / L, demonstrating optimal Fe(II) regeneration capacity. This indicates that under this concentration, insufficient concentration would not limit microbial proliferation, nor would excessive concentration produce toxicity, maximizing the conversion of Fe(III) to Fe(II) in the iron sludge. The Fe(II) concentration in the 40-60 mg N / L group showed a steady linear increase, reaching 75-90 mg / L at the end of the two cycles. The regeneration efficiency was stable but at a moderate overall level, with low NH4 content. + -N concentrations cannot fully meet the proliferation requirements of functional microorganisms, therefore the Fe(II) generation rate is slow, and the concentration increases steadily in a linear fashion; while high NH4+ concentrations of 900-1100 mg N / L... + The Fe(II) regeneration efficiency of the -N load group was consistently the lowest, significantly lower than the other two groups, indicating that excessive NH4+... + -N loading inhibits the regeneration process of Fe(II). For its NH4+... + The change in -N concentration is as follows Figure 3 As shown, 900-1100 mg N / L high NH4 + The -N loading group showed the largest decrease in ammonia nitrogen concentration, approximately 300 mg N / L, indicating that the system is suitable for high-concentration nitrogen-containing wastewater. The NH4+ concentration in the 180-200 mg N / L group... + -N showed a slight decrease, while the 40-60 mg N / L group showed a slight increase. This is presumably due to the large concentration difference with the anode or the effects of biological growth and metabolism, leading to an increase in NH4+. + -N concentration showed a slight increase. Overall, although high NH4+ concentrations... + -N group utilizes NH4 + The -N content is relatively high, but its regeneration content for Fe(II) is low. Therefore, a concentration of 180-200 mgN / L can achieve better biocathode to regenerate Fe(II) in Fenton iron mud.

[0036] Example 2: Investigating the effect of different voltages on the amplification of Fe(II) regeneration by a biological cathode Constructing a 20 L scale-up device for a two-chamber bioelectrochemical reactor, such as... Figure 1As shown on the right, anaerobic granular sludge was added to fill one-third of the device in the anode chamber, and anolyte (3-8 g / L anhydrous disodium hydrogen phosphate, 1-5 g / L potassium dihydrogen phosphate, 0.4-0.6 g / L ammonium salt, 0.8-1.5 g / L sodium acetate, 1-2 ml / L trace elements, and 1-2 ml / L vitamins) was added to a distance of 1-3 cm from the top of the reactor. Anaerobic granular sludge enriched with iron-reducing bacteria was added to fill one-third of the device in the cathode chamber, and catholyte (composed of 2.7 g / L sodium bicarbonate, 100-150 mg N / L ammonium salt, 0.01 g / L anhydrous disodium hydrogen phosphate, 1 ml / L trace elements, 2 ml / L vitamins, and Fenton iron sludge with a Fe(III) concentration of 450-550 mg / L) was added to a distance of 1-3 cm from the top of the reactor. A 10-ohm resistor was connected in series in the middle of the circuit. Each experimental cycle lasted 5 days, and the cathode pH was 5.0-6.5. After each cycle, the anolyte and catholyte are replaced, the cathode and anode are reconnected, and a new experimental cycle begins.

[0037] The changes in dissolved Fe(II) content in the reactor after applying different voltages are as follows: Figure 4 As shown in the figure. The results indicate that the applied voltage significantly enhances the regeneration efficiency of dissolved Fe(II) in Fenton iron sludge, and there is an optimal voltage control range. Under 0.3 V conditions, the Fe(II) concentration continuously increases over time and stabilizes at 110-140 mg / L on days 4-5, with optimal regeneration efficiency and system stability. Under 0.6 V conditions, the Fe(II) regeneration efficiency is moderate and fluctuates significantly; excessively high voltage may trigger side reactions that weaken the regeneration effect, and the biofilm is not adapted to high voltage conditions. The Fe(II) concentration in the control group without applied voltage can only slowly rise to about 36 mg / L, far lower than that of the electrified system. This result indicates that the ability of iron cycling to regenerate Fe(II) is severely limited without the driving force of the biocathode electric field. Figure 5 This device can not only generate dissolved ferrous iron (Fe2+), but also regenerate Fe2+ from the bottom precipitate, achieving 100% regeneration efficiency at an applied voltage of 0.3 V. In summary, this reactor successfully scales up the regeneration of Fe(II) from Fenton iron sludge using a biocathode. In this scaled-up system, 0.3 V is the optimal applied voltage for the biocathode system. Its advantages include low energy consumption, efficient and stable regeneration of dissolved Fe(II), and efficient regeneration of Fe(II) from the bottom precipitate, aligning with the economical and efficient green resource recycling concept.

[0038] Example 3: Investigating the effect of different pH values ​​on scale-up biological cathode regeneration of Fe(II) Using the 20 L scale-up experimental setup from Example 2, a 10 Ω resistor was connected in series in the middle of the circuit, and a voltage of 0.3 V was applied. Each experimental cycle lasted 5 days. The cathode pH was controlled at 5.6-5.8, 5.8-6.0, and 6.0-6.2, respectively, and the ammonium salt concentration was 100-150 mg N / L. After each cycle, the anolyte and catholyte were replaced. The composition of the anolyte and catholyte was the same as in Example 2. The cathode and anode were then reconnected to start a new experimental cycle.

[0039] pH is a key parameter in the biocathode regeneration of Fe(II) process, directly determining the form of iron and indirectly affecting process cost and operational stability. Figure 6 The results show that the scaled-up device can achieve different degrees of Fe(II) regeneration under weakly acidic to near-neutral conditions. The optimal operating condition for Fe(II) regeneration is achieved at pH 5.8-6.0, with the dissolved Fe(II) concentration reaching approximately 200 mg / L on day 5. This condition ensures high Fe(II) solubility while avoiding the inhibition of iron-oxidizing bacteria and dissimilar iron-reducing bacteria at excessively low pH (<5.6). At pH 5.6-5.8, a rapid increase in Fe(II) concentration occurs in the initial stage (day 1). Although the theoretical solubility of Fe(II) is higher at this pH, long-term operation results in inhibited microbial activity due to strong acid, significantly reducing Fe(II) regeneration efficiency. At pH 6.0-6.2, while a certain amount of Fe(II) can be generated, long-term operation at higher pH levels easily leads to the accumulation of ferric hydroxide precipitation, affecting the stable operation of the system.

[0040] Based on the research results of Example 2 above, the optimal operating parameters for the 20 L pilot-scale biocathode system were determined to be: applied voltage of 0.3 V and cathode pH control of 5.6-5.8. Under these conditions, the system can achieve efficient and stable regeneration of Fe(II) derived from Fenton iron sludge, while maintaining a mild pH, low energy consumption, and requiring no large-scale addition of acid or alkali reagents. The system also exhibits optimal synergistic balance between microbial activity and iron dissolution, demonstrating both excellent treatment efficiency and economic benefits, making it more suitable for large-scale application in actual wastewater treatment.

[0041] Example 4: Exploring the application effect of regenerated Fe(II) in Fenton-like treatment processes The Fenton process is widely used in the treatment of toxic organic wastewater and the removal of recalcitrant pollutants. This process uses Fe(II) as a catalyst, which reacts with hydrogen peroxide in a chain reaction to generate highly oxidizing hydroxyl radicals (…). This method can efficiently oxidize and decompose toxic organic pollutants in wastewater. To investigate the actual catalytic efficiency of biocathode-regenerated Fe(II) as a Fenton-like catalyst, this invention selected metronidazole, a typical recalcitrant antibiotic, as the target pollutant for a control experiment. For each group, 50 mL of simulated metronidazole wastewater with a mass concentration of 20 mg / L was prepared, and 5 mg of three different iron source materials were added: untreated Fenton iron sludge, biocathode-regenerated dissolved Fe(II), and a mixture of biocathode-regenerated precipitated and dissolved Fe(II). Then, 1 mL of hydrogen peroxide was added dropwise to each sample, and timing was started after the addition was complete. At 5 min, 10 min, 20 min, 30 min, and 60 min, 4 mL of water samples were taken, and 0.4 mL of 100 mM sodium carbonate solution was immediately added to terminate the Fenton-like oxidation reaction by complexing with iron ions. After standing and separating, the supernatant was collected, filtered through a 0.45 μm filter membrane, and stored at 4 ℃. The residual concentration of metronidazole was subsequently determined using high-performance liquid chromatography (HPLC).

[0042] Experimental results are as follows Figure 7 As shown, all three systems exhibited significant degradation effects on metronidazole within the first 5 minutes of the reaction. The group using dissolved Fe(II) regenerated from the biocathode and the group using a mixture of precipitated and dissolved Fe(II) achieved near-complete degradation of metronidazole within 5 minutes. The results indicate that Fe(II) obtained through biocathode regeneration, whether in dissolved or precipitated form, can be directly used as a highly efficient catalyst for Fenton-like reactions, demonstrating excellent and rapid degradation capabilities for toxic organic compounds like metronidazole in water. Furthermore, the entire reaction process requires no additional acid or alkali reagents to adjust the pH, significantly reducing chemical reagent consumption and operating costs, demonstrating good economic efficiency and practicality for engineering applications.

[0043] The embodiments of the present invention have been described in detail above, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. A low-reagent method for efficiently removing ammonia nitrogen and toxic organic matter from wastewater, characterized in that, A dual-chamber bioelectrochemical reactor is employed, comprising a bioanode chamber and a biocathode chamber separated by an ion-exchange membrane. Wastewater containing organic matter is introduced into the bioanode chamber, while wastewater containing ammonia nitrogen and Fenton iron sludge containing Fe(III) are introduced into the biocathode chamber. The bioanode chamber is inoculated with electroactive microorganisms capable of degrading organic matter and releasing electrons, utilizing the oxidation of organic matter in the wastewater to generate electrons, which are then transferred to the biocathode via an external circuit. The biocathode chamber is inoculated with a composite functional microbial system formed by the domestication and enrichment of anaerobic granular sludge, utilizing the NH4+ in the ammonia nitrogen wastewater. + -N acts as a cooperative electron donor through NH4 + The -N conversion process provides electron supply capability and, together with the electrons input from the external circuit, forms a dual-electron driving mechanism to promote the in-situ reduction of Fe(III) to Fe(II) in Fenton iron sludge. The Fe(II) obtained by regeneration from the biocathode is used as a Fenton-like catalyst to achieve the oxidative degradation of toxic organic pollutants, and the iron-containing precipitate generated by the reaction is returned to the biocathode to realize the recycling of iron resources.

2. The low-reagent method for efficiently removing ammonia nitrogen and toxic organic matter from wastewater according to claim 1, characterized in that, The biocathode constructs an ammonia nitrogen oxidation-iron reduction coupling system, using NH4 in the wastewater. + The bio-electrons generated by -N oxidation and the electrons transferred by the external circuit form a dual electron supply mechanism, which jointly drives the in-situ reduction of Fe(III) to Fe(II) in Fenton iron mud, thereby realizing the recycling of iron resources.

3. The low-reagent method for efficiently removing ammonia nitrogen and toxic organic matter from wastewater according to claim 1, characterized in that, The composite functional microbial system in the biocathode was obtained through pre-enrichment culture. This system includes ammonia-oxidizing microorganisms, iron-reducing microorganisms, and electroactive microorganisms, enabling the cathode system to simultaneously possess NH4+. + -N oxidation, electron transfer, and Fe(III) reduction capabilities, thereby achieving NH4 + The coupling of -N conversion with the iron recycling process.

4. The low-reagent method for efficiently removing ammonia nitrogen and toxic organic matter from wastewater according to claim 1, characterized in that, The biocathode device of the dual-chamber bioelectrochemical reactor employs a rotor-suspended "pendulum" type stirring to avoid damage to the granular sludge structure during the stirring process.

5. The low-reagent method for efficiently removing ammonia nitrogen and toxic organic matter from wastewater according to claim 1, characterized in that, The Fenton iron sludge is directly added to the biocathode chamber as a circulating iron source, achieving Fe(III) / Fe(II) cycling through a bioelectrochemical process without the need for additional continuous Fe addition. 2+ Salt catalyst; the Fenton iron sludge includes iron hydroxide precipitate, iron oxide precipitate and iron sludge produced during the Fenton reaction, and the initial Fe(III) concentration in the system is 300~500 mg / L.

6. The low-reagent method for efficiently removing ammonia nitrogen and toxic organic matter from wastewater according to claim 1, characterized in that, NH4 in the biocathode reaction system + -N concentration ranges from 40 to 1100 mg / L, and is controlled by adjusting NH4+. + -N concentration makes NH4 + The -N oxidation process and the Fe(III) reduction process achieve electron supply and demand matching, thereby improving the Fe(II) regeneration efficiency.

7. The low-reagent method for efficiently removing ammonia nitrogen and toxic organic matter from wastewater according to claim 1, characterized in that, Fe(II) regeneration is achieved in the range of pH 5.0 to 6.5 in the cathode chamber without the need for acidification to adjust to the strong acid required by traditional Fenton.

8. The low-reagent method for efficiently removing ammonia nitrogen and toxic organic matter from wastewater according to claim 1, characterized in that, An external voltage of 0~0.8V is applied between the anode and the cathode.

9. The low-reagent method for efficiently removing ammonia nitrogen and toxic organic matter from wastewater according to any one of claims 1 to 8, characterized in that, The in-situ reduced Fe(II) is reused in subsequent Fenton-like oxidation processes to remove toxic organic pollutants from wastewater. This means that dissolved Fe(II), precipitated Fe(II), or a mixture of dissolved Fe(II) and precipitated Fe(II) regenerated in the cathode chamber are used as Fenton-like catalysts. Hydrogen peroxide is added to construct a Fenton-like reaction system to oxidize and degrade metronidazole-containing toxic organic wastewater, achieving complete degradation of metronidazole within 5 minutes.

10. A scaled-up application system according to any one of claims 1 to 8, characterized in that, A 20L dual-chamber bioelectrochemical reactor is used, with the anode and cathode chambers separated by a cation exchange membrane; both the anode and cathode chambers are filled with anaerobic granular sludge. Wastewater containing organic matter is introduced into the anode chamber, while wastewater containing ammonia nitrogen and Fenton iron sludge are introduced into the cathode chamber. 5-15 commercial carbon fiber brushes are arranged as electrodes on both the anode and cathode. The device is equipped with an adjustable DC power supply, a fixed resistor, an online pH controller, and a paperless recorder. The applied voltage is adjusted to 0-0.8 V, and the pH of the cathode reaction is adjusted to 5.0-6.

5. Through modular electrode arrangement and operation parameter control, the system maintains stable electron transfer and microbial activity, realizing continuous regeneration of Fe(II) from Fenton iron sludge and large-scale treatment of toxic organic wastewater.

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