A system and method for treating organic wastewater containing high concentrations of sulfate salts

Abstract

The application provides a system and method for treating high-concentration organic wastewater containing sulfate, belonging to the technical field of industrial wastewater treatment, and is used for solving the problems that in the related art, sulfate-reducing bacteria and methanogens compete for substrates, resulting in low methanogenesis efficiency, and sulfide accumulation inhibits microbial activity. The system separates and couples a methanogenesis electrochemical oxidation unit and a sulfate bioreduction and sulfur fixation unit through an ion exchange membrane and an external circuit, constructs a cross-serial multi-stage treatment structure, integrates intelligent collaborative control and sludge resourceization units, realizes the simultaneous performance of efficient methanogenesis of organic matter, deep sulfate reduction and in-situ sulfur fixation, has high removal rates of COD and sulfate in the treated effluent, has low H2S content in the produced biogas, and can recover sulfur and iron resources.

Description

Technical Field

[0001] This application relates to the technical field of industrial wastewater treatment, and more particularly to a system and method for treating organic wastewater containing high concentrations of sulfate. Background Technology

[0002] In the rapid development of modern industry, the generation of sulfate-containing organic wastewater is increasing daily. This type of wastewater widely originates from industries such as food, pharmaceuticals, chemicals, and dyeing. Its direct discharge without treatment causes serious harm to the environment and ecosystems in many ways. From a water perspective, the discharge of sulfate-containing organic wastewater into natural water bodies leads to acidification and a decrease in pH. From a soil perspective, when sulfate-containing organic wastewater enters farmland, it damages soil structure and causes soil compaction. Furthermore, sulfate-containing organic wastewater also poses potential threats to human health: on the one hand, harmful substances in sulfate-containing organic wastewater may enter the human body through bioaccumulation in the food chain, damaging the nervous, respiratory, and digestive systems and leading to various diseases; on the other hand, toxic gases such as hydrogen sulfide released into the air pollute the atmosphere, and inhalation can irritate the respiratory tract, causing symptoms such as coughing and difficulty breathing; long-term exposure may also lead to chronic diseases.

[0003] Currently, the main methods for treating this type of wastewater include physicochemical and biological methods. Physicochemical methods, such as precipitation and ion exchange, primarily transfer sulfates through chemical transformation. Biological methods mainly rely on sulfate-reducing bacteria to reduce sulfates to sulfides under anaerobic conditions, which are then removed.

[0004] However, physicochemical methods suffer from incomplete treatment, high costs, and a tendency to cause secondary pollution. Biological methods face challenges such as competition for substrates between sulfate-reducing bacteria and methanogens, leading to decreased methanogenesis efficiency, and the inhibitory effect of reduction products (sulfides) on microbial activity, even causing system collapse. Currently, there is a lack of a solution that can efficiently and synergistically achieve both organic matter production and deep, stable sulfate removal. Summary of the Invention

[0005] This application provides a system and method for treating organic wastewater with high concentrations of sulfate, which can simultaneously achieve efficient methanogenesis and deep reduction and stabilization of organic matter in wastewater by coupling electrochemical and biological processes.

[0006] In a first aspect, this application provides a system for treating organic wastewater with high concentrations of sulfate. It includes a methanogenic electrochemical oxidation unit with an anode configured to treat wastewater under anaerobic and applied voltage conditions, causing the organic matter to undergo anaerobic digestion and methanogenesis, followed by electrochemical oxidation at the anode, generating electrons and protons; and a sulfate bioelectrochemical reduction and sulfur fixation unit with a cathode and a sulfur fixation reaction zone. The sulfate bioelectrochemical reduction and sulfur fixation unit is separated from the methanogenic electrochemical oxidation unit by an ion exchange membrane and connected to the anode and cathode by an external circuit. The sulfate bioelectrochemical reduction and sulfur fixation unit is configured to receive protons migrating through the ion exchange membrane and electrons transferred through the external circuit, causing the sulfate to undergo a reduction reaction at the cathode to generate sulfides, and fixing the sulfides within the sulfur fixation reaction zone.

[0007] By adopting the above technical solution, the methanogenesis / electricity generation process and the sulfate reduction / sulfur fixation process are decoupled in space and electron transport path through ion exchange membranes and external circuits. This effectively avoids substrate competition between different functional microorganisms and fixes sulfides in situ, eliminating their inhibition on methanogens. Thus, the efficient energy conversion of organic matter and the deep and stable removal of sulfate are synergistically achieved.

[0008] Furthermore, the system includes at least two stages of processing units connected in series; each stage of the processing unit includes a methanogenic electrochemical oxidation unit as a cation chamber and a sulfate bioelectrochemical reduction and sulfur fixation unit as an anion chamber; the cation chamber and the anion chamber are separated by the ion exchange membrane, and the stages are connected in series in an alternating manner of cation chamber and anion chamber.

[0009] By adopting the above technical solutions, the multi-level cross-connected structure forms a tiered degradation and deep purification path for pollutants, improving the overall treatment efficiency, resistance to load shocks, and stability of the effluent.

[0010] Furthermore, the sulfur fixation reaction zone is equipped with packing material containing zero-valent iron.

[0011] By adopting the above technical solution, the chemical activity of zero-valent iron can be utilized to react rapidly with sulfides produced by biological reduction to generate stable FeS precipitate, thereby achieving rapid fixation of sulfur and efficient separation from the aqueous phase.

[0012] Furthermore, the sulfur fixation reaction zone is an expanded fluidized bed structure; the packing material is zero-valent iron particles, which are filled in the expanded fluidized bed.

[0013] By adopting the above technical solutions, the expanded fluidized bed state ensures full contact between the packing material and the sulfide-containing water flow, greatly improving the sulfur fixation reaction rate and efficiency, while effectively preventing packing material caking and ensuring the long-term stable operation of the unit.

[0014] Furthermore, it also includes a collaborative control unit; the collaborative control unit includes a sensing module, a control module, and an execution module; the sensing module is used to acquire the anolyte current signal of the methanogenic electrochemical oxidation unit; the execution module includes a voltage regulation component and a carbon source addition component; the control module is configured to dynamically adjust the voltage of the external circuit and / or the rate of carbon source addition to the sulfate bioelectrochemical reduction and sulfur fixation unit according to the change of the anolyte current signal through the execution module.

[0015] By adopting the above technical solution and using the anodic current, a core signal that directly reflects bioelectrochemical activity, as the basis for regulation, real-time and precise control of the balance between electron generation and consumption within the system is achieved, ensuring the synergy and efficiency of the two core processes of methanogenesis and sulfate reduction.

[0016] Furthermore, an inter-stage sulfur removal unit is provided on the connecting pipeline between adjacent two-stage treatment units; the inter-stage sulfur removal unit includes a dosing device for adding oxidant into the pipeline.

[0017] By adopting the above technical solution and through interstage oxidation treatment, dissolved sulfides or intermediate sulfur that may remain in the effluent of the previous stage can be completely eliminated, thus eliminating their potential biotoxicity to the next stage methanogenic unit and ensuring the safe and stable operation of the multi-stage series system.

[0018] Furthermore, it also includes a sludge resource utilization unit; the sludge resource utilization unit includes a magnetic separation device and an acid washing and regeneration device; the magnetic separation device is used to separate FeS-containing components from the sludge discharged from the system; the acid washing and regeneration device is used to treat the FeS-containing components with acid to regenerate iron materials and recover sulfur-containing gases.

[0019] By adopting the above technical solution, the resource recovery and recycling of iron and sulfur in the sulfur fixation product FeS has been realized. The iron material can be reused in the sulfur fixation unit, reducing operating costs, forming a material closed loop, and improving the system's economy and environmental protection.

[0020] Furthermore, the sensing module also includes an online water quality analyzer for real-time monitoring of the COD and sulfate concentrations of the influent; the control module is also configured to adjust the voltage of the external circuit and / or the acceleration rate of the carbon source in advance through the execution module according to the change in the ratio of COD to sulfate concentration of the influent.

[0021] By adopting the above technical solution, feedforward adjustment is performed based on the real-time changes in the influent water quality, enabling the system to adjust its operating status in advance before water quality shocks occur, which significantly enhances the system's shock resistance and operational stability.

[0022] Furthermore, the collaborative control unit also includes a digital twin model; the control module is further configured to: when a sudden change in the influent water quality is detected, drive the digital twin model to pre-simulate the system response under different control strategies, and select the control strategy to be executed by the execution module based on the pre-simulation results.

[0023] By adopting the above technical solutions, the simulation and preview of the system's future behavior are realized through digital twin technology, which upgrades the control decision from "stress response" to "predictive optimization". It can intelligently select the optimal control strategy under complex working conditions, and realize the intelligentization and optimization of the entire system operation process.

[0024] Secondly, this application provides a method for treating organic wastewater with high concentrations of sulfate. The system described in any one of the first aspects comprises the following steps: passing the high-concentration sulfate-containing organic wastewater into the methanogenic electrochemical oxidation unit, where a reaction is carried out under anaerobic conditions and an applied voltage, causing the organic matter to degrade and produce biogas, electrons, and protons; passing the effluent from the methanogenic electrochemical oxidation unit into the sulfate bioelectrochemical reduction and sulfur fixation unit, where a reaction is carried out under reducing conditions, utilizing the electrons and protons to reduce the sulfate to sulfides, and fixing the sulfides in the sulfur fixation reaction zone; collecting the generated biogas and discharging the treated effluent.

[0025] By adopting the above technical solution and through the above sequential processing steps, and with the assistance of artificially regulated electrochemical driving force, the biological metabolic pathway is guided and enhanced, and the energy recovery of organic matter and the harmless and stable treatment of sulfate pollutants are completed simultaneously in a coherent process chain.

[0026] In summary, this application has at least the following beneficial effects:

[0027] This application provides a highly efficient and synergistic wastewater treatment system and method, which successfully solves the problem of competition and inhibition between organic matter methane production and sulfate reduction processes, and achieves simultaneous and efficient operation of both processes;

[0028] Through key technologies such as multi-stage series connection, intelligent control and resource recycling, the stability, shock resistance and overall economic efficiency of the system in treating high-concentration organic wastewater have been significantly improved, forming a green closed-loop process.

[0029] It should be understood that the description in the Summary Section is not intended to limit the key or essential features of the embodiments of this application, nor is it intended to restrict the scope of this application. Other features of this application will become readily apparent from the following description. Attached Figure Description

[0030] The above and other features, advantages, and aspects of the embodiments of this application will become more apparent from the accompanying drawings and the following detailed description. In the drawings, the same or similar reference numerals denote the same or similar elements, wherein:

[0031] Figure 1 A schematic diagram of a system for treating organic wastewater with high concentrations of sulfate, according to an embodiment of this application, is shown.

[0032] Figure 2 A schematic diagram illustrating the principle of the cross-connection of the anterior and posterior chambers in an embodiment of this application is shown.

[0033] Figure 3 A flowchart of a method for treating organic wastewater with high concentrations of sulfate, according to an embodiment of this application, is shown. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0035] Furthermore, the term "and / or" in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, the character " / " in this article generally indicates that the preceding and following related objects have an "or" relationship.

[0036] This application provides a system and method for treating organic wastewater with high concentrations of sulfate. Through the ingenious coupling and spatial decoupling of electrochemical and biological processes, it simultaneously achieves efficient energy recovery of organic matter in wastewater and deep reduction and stabilization of sulfate, effectively solving the core problems of microbial competitive inhibition and sulfide toxicity in traditional processes.

[0037] In a first aspect, embodiments of this application disclose a system for treating organic wastewater containing high concentrations of sulfate.

[0038] Reference Figure 1This system is essentially a highly integrated electrochemical-biological coupling treatment platform. Its core innovation lies in the decoupling of the methanogenesis / electromagnetization process of organic matter from the reduction / fixation process of sulfate in terms of space and function through ingenious physical separation and circuit connection. At the same time, it achieves efficient coupling between the two through the directional transfer of protons and electrons and intelligent control. This collaboratively solves the fundamental problems of microbial competition and sulfide inhibition in traditional processes, and simultaneously achieves efficient energy recovery of organic matter in wastewater and deep stabilization removal of sulfate.

[0039] The system's basic architecture consists of two core functional units. The first is the methanogenic electrochemical oxidation unit. This unit contains an anode, whose function is to treat high-concentration organic wastewater flowing in under strictly anaerobic conditions and with the application of a certain range of external voltage. The anode material needs to have a high specific surface area and good biocompatibility to facilitate the attachment and enrichment of electrogenic microbial communities. Optional materials include, but are not limited to, carbon fiber cloth, carbon fiber brushes, carbon felt, graphite felt, and modified graphite felt. This unit typically operates under constant temperature and mesophilic conditions, with the temperature maintained between 35-40℃; for example, 37℃ is a common and efficient setpoint. The pH value within the unit is precisely controlled within a weakly acidic to neutral range of 6.5-7.5 by automatically adding acid, alkali, or buffers, while the oxidation-reduction potential is maintained in a deep reducing environment of -350 to -450 mV, creating optimal metabolic conditions for methanogenic bacteria. The applied external DC voltage can be adjusted between 0.5-1.2V; for example, 0.8V or 1.0V are commonly used values ​​in practice. Within this unit, the complex organic matter in the wastewater undergoes two parallel and synergistic transformation pathways: on the one hand, it is gradually converted into methane and carbon dioxide through a traditional anaerobic digestion metabolic network of hydrolytic fermenting bacteria and methanogenic bacteria; on the other hand, electrogenic microorganisms attached to the anode surface can directly oxidize the organic matter or its metabolic intermediates, releasing electrons and protons in the process, while producing a small amount of carbon dioxide. Electrons are collected by the anode material and exported through an external circuit, while protons remain in the aqueous phase within the unit.

[0040] The second core functional unit is the sulfate bioelectrochemical reduction and sulfur fixation unit. This unit contains a cathode and a dedicated sulfur fixation reaction zone. The cathode material can be selected based on the treatment objectives and economic considerations, such as carbon felt for constructing biocathodes, or foamed nickel or stainless steel felt with good conductivity and stability. This unit is physically separated from the aforementioned methanogenic electrochemical oxidation unit by an ion-exchange membrane. This membrane can be a proton exchange membrane allowing selective proton permeation, a cation exchange membrane allowing cation permeation, or a bipolar membrane with special functions. Its core role is to allow proton migration while blocking the mixing of other substances, maintaining the optimal biochemical environment for each unit. Electrically, the anode of the former unit and the cathode of this unit are connected via external wires, forming a closed loop. A variable resistor or a potentiostat can be connected in series in the loop to precisely control the current. This configuration allows electrons generated by the methanogenic electrochemical oxidation unit to be directionally and forcibly transferred to the cathode of this unit through the external circuit, while protons can migrate through the ion-exchange membrane. Within this unit, migrating protons and transferred electrons jointly drive sulfate-reducing bacteria attached to the cathode surface to carry out a bioelectrochemical reduction reaction, efficiently reducing sulfate ions in the wastewater to sulfides such as sulfur ions or hydrogen sulfide ions. The unit's operating temperature is also controlled within a mesophilic range, and the pH value is maintained in a slightly alkaline range of 7.5-8.0. This is beneficial to the activity of sulfate-reducing bacteria and creates conditions for subsequent chemical sulfur fixation reactions. Its redox potential is controlled between -100mV and -200mV, forming a suitable reducing environment. Subsequently, the generated sulfides are naturally transported to the sulfur fixation reaction zone by the upward flow of water or diffusion. The biogas produced by the system (mainly containing methane and carbon dioxide) is collected by gas collection devices at the top of each reaction unit and output through a central pipeline. This biogas output pipeline can be equipped with a purification and monitoring subsystem for dehydrating and metering the biogas, and monitoring its key components such as hydrogen sulfide concentration. The purification subsystem includes at least a safety desulfurization tank as a final emergency backup. This tank is filled with desulfurizing agent and can be automatically activated when an abnormal hydrogen sulfide concentration is detected to ensure the quality of the output biogas.

[0041] The sulfur fixation reaction zone is the key site for the stable transformation of sulfur from a dissolved state to a solid state. A basic and effective implementation method is to fill this zone with packing material containing zero-valent iron (ZVFe). ZVFe has high chemical reactivity and can react rapidly with sulfides to form chemically stable ferrous sulfide precipitates with extremely low solubility. A more efficient preferred implementation method is to design the sulfur fixation reaction zone as an expanded fluidized bed structure integrated into the upper part of the unit. The packing material uses ZVFe particles or iron filings with a particle size controlled between 1-3 mm; for example, a particle size of about 2 mm can achieve a good balance between reactivity and fluidization characteristics. The packing filling rate is controlled at 30-40% of the reaction zone volume; for example, a filling rate of 35% can simultaneously ensure sufficient sulfur fixation capacity and good fluidization. A specific upward flow velocity generated by the water distribution system at the bottom of the reactor, or the installation of a dedicated internal circulation pump, can ensure that the ZVFe particles are in a uniform suspended fluidized state within the reaction zone. This state greatly increases the contact area and collision frequency between the iron filler and the sulfide, thereby maximizing the sulfur fixation reaction rate and effectively preventing the caking and water flow short-circuiting caused by the accumulation of iron particles.

[0042] To optimize system operation, maintain dynamic balance, and cope with influent fluctuations, the system can be further equipped with an intelligent collaborative control unit. This collaborative control unit consists of a sensing module, a control module, and an execution module, forming a complete "perception-decision-execution" closed loop. The sensing module is the system's "sensors," responsible for collecting a series of key real-time parameters, including but not limited to the pH values ​​of each cation and anion chamber, the redox potential of the anion chamber, the voltage and current of each cation and anode pair, and most importantly—the current signal of the anode in the methanogenic electrochemical oxidation unit. The anode current directly reflects the metabolic activity and electron production rate of the electrogenic microbial community, and is the most direct indicator of the system's "electron supply" status. The execution module is the system's "hands and feet," including at least a voltage regulation component for adjusting the external circuit voltage, and a carbon source addition component for precisely adding additional carbon sources to the sulfate bioelectrochemical reduction and sulfur fixation unit. The control module, as the system's "brain," is composed of, for example, a programmable logic controller or an industrial computer, with built-in specific control algorithms. Based on the real-time data transmitted from the sensing module, especially the changing trend of the anode current signal, it dynamically issues instructions to the execution module. For example, when a significant decrease in anode current is detected but the influent sulfate load monitoring value does not decrease synchronously, the control module can determine that the electron demand of the cathode is relatively insufficient or the activity of sulfate-reducing bacteria needs to be stimulated. At this time, it will automatically increase the carbon source addition acceleration rate proportionally to stimulate the activity of the cathode biofilm. At the same time, by comparing the anode current with the preset optimal operating range threshold, the external voltage is finely adjusted within the safe range of 0.5V-1.2V, thereby intelligently maintaining a fine balance between electron generation and consumption in the system.

[0043] Furthermore, the system integrates multi-source sensor signals to implement targeted sulfur control throughout the entire process. Specifically, the control module receives real-time data on the dissolved sulfide concentration at the anion chamber outlet, the differential pressure signal in the sulfur-fixing fluidized bed zone, and the hydrogen sulfide concentration in the produced biogas. When the sulfide concentration at the anion chamber outlet increases, the control module first instructs to increase the speed of the circulating pump at the bottom of the anion chamber to enhance the agitation intensity of the fluidized bed packing and promote the contact reaction efficiency between zero-valent iron and sulfur ions. If the sulfide concentration remains high, the system automatically triggers the iron packing replenishment procedure. When the fluidized bed differential pressure continues to decrease and is accompanied by an upward trend in sulfide concentration, the system will issue a warning that the sulfur-fixing capacity is nearing saturation and initiate the replenishment process of the backup packing in advance. As an emergency safeguard at the end of the process, when the hydrogen sulfide concentration in biogas exceeds 8 ppm, the control module determines that the upstream sulfur fixation effect is insufficient. Simultaneously, it automatically activates the safety desulfurization tank and sends a command to the control loop of the corresponding anion chamber to moderately adjust the pH to the 7.5-7.8 range and increase the redox potential setpoint (e.g., to -120 mV). In this specific emergency scenario, the system prioritizes ensuring biogas quality, thus slightly inhibiting the metabolic rate of sulfate-reducing bacteria at the source to reduce sulfide formation. This real-time sensor-based adjustment, combined with the abnormal state identification and recovery strategies described later, constitutes a multi-layered safeguard system for maintaining stable sulfur fixation efficiency.

[0044] refer to Figure 2 One enhanced and intensified treatment mode of this system is constructed as a series treatment system comprising at least two stages. Typically, two or three stages in series can meet a wide range of treatment requirements from several thousand to tens of thousands of mg / L of chemical oxygen demand (COD) and achieve highly stable effluent. Each treatment unit can physically be an independent tank or a series of compartments constructed with shared walls within a large container. Essentially, it consists of a methanogenic electrochemical oxidation unit (a cation chamber) and a sulfate bioelectrochemical reduction and sulfur fixation unit (an anion chamber). The treatment units are connected in series sequentially in an alternating cation-anion chamber configuration, forming a cross-series flow of "cation-anion-cation-anion-…". In this multi-stage structure, the first stage primarily removes the core pollutant load, converting most organic matter and sulfates; subsequent stages play a role in deep purification and safeguarding, further degrading recalcitrant organic matter, reducing any remaining sulfates or intermediate sulfur, and ultimately ensuring the quality of the effluent. In each stage, the hydraulic residence time (HRT) of the yang chamber and the yin chamber can be controlled independently, for example, by combining them between 12h and 24h to form a variety of flexible operating modes such as 24h plus 24h, 18h plus 18h.

[0045] In the aforementioned multi-stage series system, to completely eliminate the potential inhibitory risk of residual sulfides from the previous stage on methanogenic bacteria in the next stage, an interstage sulfide removal unit can be installed on the connecting pipeline between adjacent treatment units. This interstage unit is a safety assurance link, primarily responsible for adding oxidant to the effluent from the previous stage anion chamber. It contains a sophisticated dosing device, such as a metering pump linked to an online sulfide detector. When the effluent sulfide concentration exceeds a set threshold, or based on feedback from the anode activity status of the next stage, an appropriate amount of oxidant, such as trace amounts of hydrogen peroxide or ozone, is automatically added to completely oxidize the residual sulfides into toxic elemental sulfur or sulfates, thereby creating a safe influent environment for the next treatment unit.

[0046] Furthermore, to implement the concept of resource recycling and reduce operating costs, the system can also be connected to a sludge resource recovery unit to specifically treat the mixed sludge generated during system operation. This resource recovery unit mainly includes a magnetic separation device and an acid washing and regeneration device. The magnetic separation device, such as a magnetic separator or magnetic drum, cleverly utilizes the paramagnetic properties of ferrous sulfide to efficiently separate ferrous sulfide-rich components from the mixed sludge discharged from the system, which contains both biological sludge and chemical precipitates. The acid washing and regeneration device is a closed reaction vessel that uses 1-2% dilute hydrochloric acid to treat these iron-sulfur-rich components, resulting in a chemical reaction that generates hydrogen sulfide gas and a ferrous ion solution. The generated hydrogen sulfide gas can be collected and further utilized, for example, to produce sulfur or sulfuric acid; the regenerated iron filings, after rinsing and alkaline passivation, can be backfilled into the expanded fluidized bed in the sulfur fixation reaction zone for recycling, while the ferrous ions in the acid washing solution can be recovered as raw materials for preparing inorganic coagulants, thus forming a complete "iron-sulfur" material closed loop.

[0047] The functionality of the collaborative control unit can be further enhanced and expanded. For example, its sensing module can be integrated with an online water quality analyzer installed at the system's main inlet to monitor the chemical oxygen demand (COD) and sulfate (SO4) in the influent in real time. 2- The control module can then instantly calculate the mass concentration ratio (COD / SO4) of the two components. 2- (Ratio). When a dynamic change in this ratio is detected, such as a decrease from 8:1 to 6:1, it indicates a relative increase in sulfate load. The control module can immediately activate the feedforward adjustment logic: increase the external voltage from the reference 0.8V to 0.95V in advance, and send a command to the carbon source dosing system in the first-stage anion chamber to pre-increase the dosing rate by 10%, thereby actively enhancing the system's ability to cope with influent load shocks and transforming passive response into active defense.

[0048] To achieve dynamic optimization between global operating costs and processing efficiency, the control module also deploys a multi-objective dynamic optimization strategy. This strategy revolves around a comprehensive performance index that integrates multiple dimensions, including pollutant removal rate, net energy gain (the difference between biogas production capacity and system power consumption), material consumption costs, and the value of sulfur and iron resource recovery. Built-in optimization algorithms (such as an engineering-simplified version of a non-dominated sorting genetic algorithm) periodically solve for the combination of operating parameters that maximizes this comprehensive index while satisfying the hard constraints of effluent quality. Based on this, the system can implement various advanced operating modes. For example, after connecting to real-time electricity price signals, the system can automatically and moderately increase the external voltage during periods of low electricity prices to enhance electrochemical drive and reserve processing capacity; during periods of high electricity prices, it prioritizes biological metabolism to reduce energy consumption, achieving economical "peak shaving and valley filling" operation. Simultaneously, by analyzing the real-time ratio of influent chemical oxygen demand (COD) to sulfate concentration, the algorithm can dynamically optimize the virtual allocation of carbon sources between the methanogenesis / electrogeneration and sulfate reduction pathways. Furthermore, by fine-tuning the applied voltage in the corresponding anodic chambers, it guides the metabolic flow of the microbial community, achieving global optimization of carbon source utilization. In addition, the system indirectly assesses the activity status of functional microbial communities in each reaction chamber through comprehensive analysis of the waveforms of anode currents at each stage, the ratio of methane to hydrogen in biogas, and the rate of sulfide formation in the anion chamber. Based on this, it implements cross-stage regulation, such as recirculating sludge rich in highly active methanogenic bacteria from the later stage to the earlier stage, or fine-tuning the redox potential gradient between stages to optimize the spatial distribution and metabolic dominance of functional microorganisms.

[0049] Furthermore, the collaborative control unit can incorporate a digital twin model—a high-fidelity virtual model that operates synchronously with the physical reactor, integrating hydraulic flow dynamics, substrate mass transfer, microbial growth, and electrochemical reaction kinetics. When the sensing module detects a drastic change in influent water quality, the control module immediately activates this digital twin model to rapidly simulate and preview various possible combinations of control strategies for the next few hours in the virtual space at a rate measured in minutes. The control module then comprehensively analyzes the results of each preview strategy, weighing multiple objectives such as effluent stability, energy consumption, and biogas quality, automatically selecting the optimal strategy combination, and immediately handing it over to the execution module for implementation in the physical system. This achieves a leap from "stress response" to "predictive intelligent decision-making." The model can also provide early warnings of slow system performance degradation by comparing long-term deviations between predicted and actual values, and automatically optimize underlying control parameters, enabling the system to possess self-learning and adaptive capabilities.

[0050] Furthermore, the system's physical form can be designed as a modular, containerized unit, allowing for flexible adjustments to the number of treatment stages based on treatment scale and water quality characteristics, thus exhibiting excellent engineering adaptability. The structure of the sulfur fixation reaction zone is not limited to an expanded fluidized bed; fixed beds, moving beds, and other forms can be selected according to specific circumstances. The sulfur fixation medium can also be expanded to include other reducing metals or modified mineral materials. The algorithm of the collaborative control unit can also be compatible with advanced intelligent algorithms such as fuzzy control and reinforcement learning to cope with more complex operating environments.

[0051] To ensure long-term stable operation and resilience in the face of abnormal conditions, the collaborative control unit is pre-configured with abnormal state identification and intelligent recovery strategies. The system continuously monitors multiple performance parameters and can define and identify several typical abnormal states. For example, when the current of a certain anode continuously and slowly decreases while the corresponding biogas yield remains stable and volatile fatty acids do not accumulate, the system identifies this as "anodic biofilm passivation" and automatically initiates a recovery program: applying a short, small-amplitude periodic pulse voltage to the anode, while temporarily lowering the pH of its anode chamber by 0.3-0.5 units to promote biofilm renewal. During this period, the system will partially transfer the treatment load of this stage to an adjacent stage. If the pressure difference in a specific anion chamber's solidification fluidized bed abnormally increases but the sulfide removal efficiency decreases, it is identified as "localized fluidized bed caking or channeling." The system will automatically switch to a high-intensity fluidization and backwashing mode, significantly increasing the circulation pump frequency and triggering a pulse aeration device for auxiliary disturbance. When an abnormal increase in transmembrane voltage and a decrease in overall system current are detected, accompanied by an abnormal gradient in the concentration of key ions in the cation and cation chambers, it is determined to be "ion exchange membrane fouling." The system will automatically schedule an online chemical cleaning program for the membrane module and adjust the operating parameters of the preceding and following stages during cleaning to ensure uninterrupted processing. These predefined strategies enable the system to autonomously recover from various potential faults, ensuring continuous and stable operation.

[0052] The practical application and effectiveness of this system can be fully demonstrated and verified through the following specific operating procedures and examples. The system startup and operation begin with the introduction of the target wastewater and system initialization. The wastewater, with a chemical oxygen demand (COD) of not less than 5000 mg / L and a COD / SO4²⁻ ratio between 8:1 and 4:1, is first uniformly introduced into the first-stage methanogenic electrochemical oxidation unit, i.e., the first cation chamber, via a booster pump and distributor. The temperature within this unit is maintained in the medium temperature range, such as 35-40℃, by an external thermostat, while an initial voltage, such as 0.8V, is applied via an external DC power supply. The microbial community within the system, including hydrolytic fermentation bacteria, methanogenic bacteria, and electrogenic microorganisms, forms a stable biofilm on the anode surface after a period of acclimatization and enrichment.

[0053] During operation, wastewater undergoes a set hydraulic retention time, e.g., 24 hours, in the first cation chamber. During this time, complex organic matter is degraded by microorganisms, producing biogas primarily composed of methane and carbon dioxide, which is collected via a three-phase separator and gas collection device at the top. Simultaneously, the electrochemical oxidation reaction at the anode continuously generates electrons and protons. Electrons are led out via external circuit wires, while protons migrate through the ion exchange membrane between the cation and adjacent anion chambers to the first-stage sulfate bioelectrochemical reduction and sulfur fixation unit, i.e., the first anion chamber. The first anion chamber is also maintained at a mesophilic temperature, with its pH controlled between 7.5 and 8.0 by automatic alkali dosing, and receives electrons from the external circuit. Under these conditions, sulfate-reducing bacteria attached to the cathode utilize the migrating protons and transferred electrons to reduce sulfates in the wastewater to sulfides. The sulfide-containing water flows upward into the expanded fluidized bed region integrated above the anion chamber, where it comes into full contact with the fluidized zero-valent iron particles, rapidly generating ferrous sulfide precipitate. The treated mud-water mixture undergoes solid-liquid separation in a three-phase separator at the top of the anion chamber, with clear water flowing out and mixed sludge settling into the bottom sludge hopper.

[0054] When a multi-stage series configuration is adopted, the effluent from the first anion chamber is not directly discharged, but enters the interstage connecting pipeline. Here, the interstage sulfur removal unit automatically adds trace amounts of oxidants such as hydrogen peroxide based on the online monitoring of sulfide concentration to further remove residual sulfides and protect the next stage treatment unit. The pretreated water then enters the second stage treatment unit, repeating a similar "cation chamber methane production and electricity generation - anion chamber sulfate reduction and sulfur fixation" process, but with a lower pollutant load, mainly for deep purification. The operating parameters of each stage unit, including the pH, redox potential, external voltage, and interstage chemical dosage of each chamber, are dynamically optimized and precisely controlled by the collaborative control unit based on real-time sensor data and built-in algorithms. Finally, the effluent from the last anion chamber is the total effluent of the system, while the biogas produced at each stage is collected and output through the main pipe, with the hydrogen sulfide concentration stably controlled at an extremely low level.

[0055] To verify the treatment efficiency, stability, and intelligence of this system, a series of case studies were conducted. In one case study, wastewater with a COD of 20000 mg / L and an SO4²⁻ concentration of 2500 mg / L at a mass ratio of 8:1 was treated. The system adopted a three-stage series configuration, with cation exchange membranes as the diaphragms and an external voltage of 0.8V. The pH of the cation chamber was controlled at 6.5-7.5, with a redox potential of -400mV, and the anode was modified graphite felt. The pH of the anion chamber was controlled at 7.5-8.0, with a redox potential of -150mV, and the cathode was nickel foam. The expanded fluidized bed zero-valent iron packing was filled at 40%. The total residence time for the first and second stages was 48 hours each (24 hours for the anode + 24 hours for the cathode), and the third stage was 24 hours (12 hours for the anode + 12 hours for the cathode). After the system stabilized, the COD of the effluent dropped to 1280 mg / L, with a removal rate of 93.6%; the sulfate dropped to 60 mg / L, with a removal rate of 97.6%; and the H2S concentration in the biogas produced was 7 mg / Nm³ (the symbol "Nm³" represents standard cubic meters).

[0056] In another example, wastewater with a COD of 10000 mg / L and SO4²⁻ of 1670 mg / L at a mass ratio of 6:1 was treated. The system employed a two-stage series configuration with a bipolar membrane diaphragm and an external voltage of 1.2V. The cation chamber pH was controlled at 6.5-7.5, with a redox potential of -450mV, and the anode was made of carbon fiber cloth. The anion chamber pH was controlled at 7.5-8.0, with a redox potential of -200mV, and the cathode was made of an iron-nickel metal-organic framework. The expanded fluidized bed zero-valent iron packing was 35% filled. The total residence time for each stage was 36 hours (18 hours for the anode + 18 hours for the cathode). The final effluent COD was reduced to 720 mg / L (removal rate 92.8%), sulfate was reduced to 58 mg / L (removal rate 96.5%), and the H₂S concentration in the biogas was 5 mg / Nm³.

[0057] In another example, wastewater with a COD of 5000 mg / L and SO4²⁻ of 1250 mg / L (mass ratio 4:1) was treated. The system employed a two-stage series connection with a proton exchange membrane diaphragm and an external voltage of 0.5V. The cation chamber pH was controlled at 6.5-7.5, with a redox potential of -300mV, and the anode was made of carbon felt. The anion chamber pH was controlled at 7.5-8.0, with a redox potential of -100mV, and the cathode was made of stainless steel felt. The expanded fluidized bed used iron filings as packing material, with a filling rate of 30%. The total residence time for each stage was 24 hours (12 hours for anode + 12 hours for cathode). The effluent COD was reduced to 340 mg / L (removal rate 93.2%), sulfate was reduced to 49 mg / L (removal rate 96.1%), and the H₂S concentration in the biogas was 4 mg / Nm³.

[0058] Furthermore, a dynamic example fully demonstrates the superiority of the system's coordinated control in responding to sudden shocks. A secondary system, which had been operating stably and treating the same water quality as the first example, experienced a sudden fluctuation in the influent SO4²⁻ concentration to 3000 mg / L on the eighth day of operation, causing the COD / SO4²⁻ ratio to drop from 8:1 to approximately 6.7:1. The system responded immediately: the sensor module detected the change in influent concentration, and the coordinated control unit immediately initiated feedforward regulation, increasing the external voltage from 0.8V to 0.95V within 0-2 hours and increasing the carbon source addition acceleration rate in the first-stage anion chamber by 12%. In the following 2-12 hours, the system performed multi-variable linkage regulation. When the sulfide concentration at the outlet of the first-stage anion chamber increased, the system automatically increased the frequency of the fluidized bed circulation pump in that chamber to enhance mixing. When the H2S concentration in the biogas of the first-stage branch was detected to rise to 9 ppm, the system, in addition to activating the safety desulfurization tank, simultaneously fine-tuned the pH of the first-stage anion chamber to 7.7 and the oxidation-reduction potential to -130 mV. When a decrease in the second-stage anode current density was detected, the system determined that interstage disruption might be insufficient. It automatically increased the H2O2 dosage between the first and second stages by 30% and applied 0.1V to the second-stage anode to maintain microbial activity. Between 12 and 48 hours, the system gradually returned to equilibrium. During this period, 5% of the volume of zero-valent iron packing was automatically replenished based on changes in the fluidized bed pressure differential. By 48 hours, the system had fully stabilized, with effluent COD at 1320 mg / L, SO4²⁻65 mg / L, and H2S in the biogas from the main pipe stabilized at 6 ppm.

[0059] The above operational examples demonstrate that, under different influent load and fluctuation conditions, this system can achieve efficient and simultaneous removal of organic matter and sulfate through its unique structural design and intelligent collaborative control, producing high-quality biogas. It also exhibits strong shock resistance and self-recovery capabilities, verifying its feasibility and reliability as an advanced industrial wastewater treatment solution.

[0060] Secondly, this application provides a method for treating organic wastewater with high concentrations of sulfate. The core of this method lies in guiding and utilizing the system described in the first aspect through a precisely designed set of process steps and operating conditions to efficiently and synergistically complete the degradation of organic matter and the reduction and fixation of sulfate in the wastewater within a unified process flow, thereby simultaneously achieving energy recovery and deep removal of pollutants.

[0061] Reference Figure 3This method begins by introducing high-concentration sulfate-containing organic wastewater into the system. This wastewater typically has a chemical oxygen demand (COD) of at least 5000 mg / L, and its COD to sulfate mass concentration ratio is adapted to the range of 8:1 to 4:1. The wastewater is first transported to the methanogenic electrochemical oxidation unit, i.e., the cation chamber. Within this unit, process conditions are precisely controlled to create an environment optimal for the metabolism of methanogenic and electrogenic microorganisms. The temperature is maintained in a mesophilic range, specifically adjustable between 35-40°C; for example, 35°C and 40°C can be considered effective operating boundaries, while 37°C is often chosen as the preferred stable operating temperature. The unit's pH is controlled between 6.5 and 7.5 via an automatic dosing system; for example, 6.5 and 7.5 define the permissible fluctuation range of its pH, while around 7.0 is a common setpoint conducive to microbial community balance. The redox potential was maintained within the deep reduction range of -350 to -450 mV. -350 mV and -450 mV defined the upper and lower limits of the potential, while around -400 mV effectively maintained the activity advantage of methanogenic bacteria. Furthermore, a DC voltage of 0.5 V to 1.2 V was applied to the unit via an external power supply. 0.5 V and 1.2 V defined the strong and weak boundaries of the electrochemical driving force, while 0.8 V is a widely validated and commonly used value. The hydraulic retention time of wastewater in this unit was controlled between 12 h and 24 h. For example, 12 h and 24 h represent shorter and longer treatment cycles, respectively, while 18 h may be an optimal value balancing treatment efficiency and reactor volume. Under these conditions, complex organic matter in the wastewater is converted into biogas through microbial action. Simultaneously, an electrochemical oxidation reaction occurs on the anode surface, continuously generating electrons and protons.

[0062] Following this, the effluent from the methanogenic electrochemical oxidation unit, carrying protons migrating out and electrons directionally transferred via an external circuit, is introduced into the sulfate bioelectrochemical reduction and sulfur fixation unit, i.e., the anion chamber. The operating conditions of this unit are designed to optimize the activity of sulfate-reducing bacteria and ensure the efficient execution of subsequent sulfur fixation reactions. The temperature is also controlled within a mesophilic range (35-40°C). The pH value is adjusted to a weakly alkaline environment of 7.5 to 8.0; 7.5 and 8.0 constitute its control boundary. Maintaining it within this range is beneficial for the metabolism of sulfate-reducing bacteria and creates the necessary conditions for subsequent chemical sulfur fixation; 7.8 can be considered a typical control target. The redox potential is controlled between -100 and -200 mV; for example, -100 mV and -200 mV define the intensity range of this reducing environment. In this environment, electrons received at the cathode and migrating protons drive sulfate-reducing bacteria to reduce sulfate ions in the water to sulfides. Subsequently, the generated sulfides immediately enter the integrated sulfur fixation reaction zone within the unit. One efficient implementation of this sulfur fixation reaction zone is an expanded fluidized bed filled with zero-valent iron (ZFI) packing material. The packing material particle size is, for example, between 1 mm and 3 mm (1 mm and 3 mm are particle size boundaries, 2 mm is commonly preferred), and the filling rate is between 30% and 40% (30% and 40% are filling rate boundaries, 35% is commonly preferred). Sulfides and ZFI undergo a rapid chemical reaction here, generating stable ferrous sulfide precipitate, thereby completely separating and fixing sulfur from the aqueous phase. The hydraulic retention time of this unit can also be set as needed within the range of 12 h to 24 h.

[0063] After primary treatment, the system will determine the water flow path based on preset effluent quality standards or real-time monitoring results. For example... Figure 3 As shown, if monitoring indicates that the effluent quality has not yet met the requirements, such as chemical oxygen demand (COD) or sulfate residue exceeding the set threshold, the treatment process will not end directly. At this point, the effluent from the previous anion chamber will first pass through an interstage removal unit. The function of this unit is to add an appropriate amount of oxidant, such as trace amounts of hydrogen peroxide or ozone, to the effluent to thoroughly oxidize and remove any remaining dissolved sulfides or other harmful sulfur forms, eliminating their potential inhibitory risk to subsequent biological units. After interstage removal, the water flow is guided into the next stage of methanogenic electrochemical oxidation unit, repeating the aforementioned "methanogenesis / electrolysis—sulfate reduction / sulfur fixation" treatment cycle. This multi-stage series, cross-treatment mode can be repeated until the final effluent quality stably meets discharge or reuse standards. Figure 3 The "main processing loop" and the judgment step "meets standards?" in the text are abstract summaries of this logical process. If the effluent quality meets the requirements after one or more stages of treatment, the treatment process ends, and the purified effluent can be discharged or enter the subsequent process.

[0064] Throughout the entire process, there are two parallel and continuous resource recovery processes. The first is the biogas produced in the various stages of the methane-producing electrochemical oxidation unit and the sulfate bioelectrochemical reduction and sulfur fixation unit. Its main component is methane, which is continuously collected, purified, and used as an energy source. The second is... Figure 3 The diagram illustrates the sludge resource recovery process. Mixed sludge, containing ferrous sulfide precipitate and biochemical sludge, generated from each stage of the sulfur fixation unit, is collected and transported to the sludge resource recovery unit. In this unit, a magnetic separator is first used to efficiently separate the paramagnetic ferrous sulfide concentrate from the mixed sludge. The separated ferrous sulfide concentrate then enters an acid washing and regeneration unit, where it reacts under closed conditions using 1% to 2% dilute hydrochloric acid (e.g., 1% and 2% as the concentration boundary). This dissolves the ferrous sulfide and releases hydrogen sulfide gas, which can be recycled for the preparation of sulfur resource recovery products. The remaining iron filings after the reaction are cleaned and passivated, and can then be returned to the sulfur fixation reaction zone of the system as recycled iron, achieving the recycling of iron materials. Ferrous ions in the acid washing solution can also be further recovered.

[0065] In summary, this method, through a series of potentially cyclical multi-stage treatment steps combined with precisely controlled electrochemical and biochemical conditions, not only achieves deep purification of high-concentration sulfate-containing organic wastewater, but also simultaneously recovers biomass energy and recycles sulfur and iron resources, forming a complete process route that is efficient, synergistic, and resource-efficient.

[0066] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working process of the described method can be referred to the corresponding process in the foregoing system embodiments, and will not be repeated here.

[0067] The above description is merely a preferred embodiment of this application and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of disclosure in this application is not limited to technical solutions formed by specific combinations of the above-described technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the foregoing disclosed concept. For example, technical solutions formed by substituting the above features with (but not limited to) technical features with similar functions disclosed in this application.

Claims

1. A system for treating organic wastewater with high sulfate concentration, characterized in that, include: The methanogenic electrochemical oxidation unit is equipped with an anode and is configured to treat wastewater under anaerobic and applied voltage conditions, so that organic matter undergoes anaerobic digestion to produce methanogens and electrochemical oxidation at the anode to generate electrons and protons. The sulfate bioelectrochemical reduction and sulfur fixation unit contains a cathode and a sulfur fixation reaction zone. The sulfate bioelectrochemical reduction and sulfur fixation unit and the methanogenic electrochemical oxidation unit are separated by an ion exchange membrane and connected to the anode and the cathode by an external circuit. The sulfate bioelectrochemical reduction and sulfur fixation unit is configured to receive protons migrating through the ion exchange membrane and electrons transferred through the external circuit, causing the sulfate to undergo a reduction reaction at the cathode to generate sulfides, and fixing the sulfides in the sulfur fixation reaction zone.

2. The system according to claim 1, characterized in that, The system includes at least two levels of processing units connected in series. Each stage of the processing unit includes a methanogenic electrochemical oxidation unit as a cation chamber and a sulfate bioelectrochemical reduction and sulfur fixation unit as an anion chamber; The anode chamber and the cathode chamber are separated by the ion exchange membrane, and the various stages are connected in series in an alternating manner between the anode chamber and the cathode chamber.

3. The system according to claim 1 or 2, characterized in that, The sulfur fixation reaction zone is equipped with packing material containing zero-valent iron.

4. The system according to claim 3, characterized in that, The sulfur fixation reaction zone is an expanded fluidized bed structure; The packing material is zero-valent iron particles, which are filled in the expanded fluidized bed.

5. The system according to claim 1 or 2, characterized in that, It also includes a collaborative control unit; The collaborative control unit includes a sensing module, a control module, and an execution module; The sensing module is used to acquire the anolyte current signal of the methanogenic electrochemical oxidation unit; The execution module includes a voltage regulation component and a carbon source dosing component; The control module is configured to dynamically adjust the voltage of the external circuit and / or the rate at which carbon source is added to the sulfate bioelectrochemical reduction and sulfur fixation unit based on changes in the anode current signal, through the execution module.

6. The system according to claim 2, characterized in that, A primary sulfur removal unit is installed on the connecting pipeline between adjacent two-stage treatment units; The interstage sulfur removal unit includes a dosing device for adding oxidant into the pipeline.

7. The system according to claim 1 or 2, characterized in that, It also includes a sludge resource utilization unit; The sludge resource utilization unit includes a magnetic separation device and an acid washing and regeneration device; The magnetic separation device is used to separate FeS-containing components from the sludge discharged from the system. The pickling and regeneration device is used to treat the FeS-containing components with acid to regenerate iron materials and recover sulfur-containing gases.

8. The system according to claim 5, characterized in that, The sensing module also includes an online water quality analyzer for real-time monitoring of COD and sulfate concentrations in the influent; The control module is also configured to adjust the voltage of the external circuit and / or the acceleration rate of the carbon source in advance through the execution module based on the change in the ratio of COD to sulfate concentration in the influent.

9. The system according to claim 5, characterized in that, The collaborative control unit also includes a digital twin model; The control module is further configured to: when a sudden change in the influent water quality is detected, drive the digital twin model to pre-simulate the system response under different control strategies, and select the control strategy to be executed by the execution module based on the pre-simulation results.

10. A method for treating organic wastewater with high concentrations of sulfate, characterized in that, The system according to any one of claims 1 to 9 comprises the following steps: High-concentration organic wastewater containing sulfate is passed into the methanogenic electrochemical oxidation unit, where it reacts under anaerobic and applied voltage conditions, causing the organic matter to degrade and produce biogas, electrons, and protons. The effluent from the methanogenic electrochemical oxidation unit is fed into the sulfate bioelectrochemical reduction and sulfur fixation unit, where the reaction takes place under reducing conditions. The sulfate is reduced to sulfide using electrons and protons, and the sulfide is fixed in the sulfur fixation reaction zone. Collect the biogas produced and discharge the treated effluent.

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