A system and method for treating and recycling high-sulfate waste liquor containing microorganisms

Abstract

The present application belongs to the technical field of wastewater treatment and resource utilization, and particularly relates to a system and method for treating and recycling high-sulfate waste liquid containing microorganisms. The system comprises a pretreatment unit, a nanofiltration desalination and concentration unit, a bipolar membrane electrodialysis unit and a reflux unit connected in sequence. The present application takes high-sulfate waste liquid containing hydrogen sulfide and other foul-smelling gases generated after biological treatment as the treatment object, and performs deep treatment and resource utilization. After neutralization, ultrafiltration and softening, the waste liquid is concentrated on the enrichment side of the nanofiltration to enrich sulfate and make at least part of monovalent salt permeate, and then the bipolar membrane electrodialysis is used to obtain acid and alkali, part of which is recycled to the front end for neutralization. The present application realizes the synergy of pre-removal of microorganisms and hardness ions, selective desalination and concentration of sulfates, acid-alkali resource utilization and internal circulation, which is conducive to improving the continuous operation stability and resource utilization degree of the system.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment and resource utilization technology, specifically relating to a system and method for the treatment and resource utilization of microbial high-sulfate wastewater. Background Technology

[0002] In the biological purification of waste gas, sulfur-containing odorous pollutants can be gradually converted into sulfates through microbial metabolism and accumulate in the circulating nutrient solution. Taking the biological treatment of hydrogen sulfide, a typical odorous gas, as an example, after sulfur-oxidizing bacteria oxidize H2S, SO4 in the circulating nutrient solution will increase. 2- Continuous accumulation and pH decline inhibit microbial activity, necessitating timely replacement of the nutrient solution. The specific method for replacement is to periodically discharge a portion of the high-sulfate circulating waste liquid containing microorganisms and replenish it with fresh culture medium. The discharged waste liquid contains not only recyclable sulfates but also active microbial cells and calcium. 2+ Mg 2+ Ions of equal hardness, if not handled properly, can cause secondary pollution and waste of resources.

[0003] For the aforementioned waste liquid, if only direct discharge or conventional treatment methods are used, the sulfur resources corresponding to sulfates cannot be fully utilized. While electrochemical methods for resource recovery of the waste liquid are employed, they are affected by microbial cells, suspended solids, and hardness ions. Currently, bipolar membrane electrodialysis can convert salts into corresponding acidic and alkaline solutions through bipolar membrane water dissociation, effectively recovering sulfur resources. However, microorganisms and suspended solids easily form membrane fouling, leading to calcium... 2+ Mg 2+ Such conditions may cause scaling, thereby increasing the operating resistance of the membrane stack and affecting continuous operation.

[0004] On the other hand, this wastewater often contains monovalent salts such as NaCl. If the saline solution, after removing microorganisms and hardness, is directly fed into bipolar membrane electrodialysis, the sulfate concentration in the feed water may still be insufficient to achieve suitable resource recovery efficiency. Monovalent anions will migrate into the acid chamber via electromigration and affect the composition of the resulting acid solution. Therefore, before bipolar membrane electrodialysis, it is necessary not only to reduce the risk of contamination and scaling, but also to selectively separate and enrich sulfate and monovalent salts.

[0005] Existing technologies such as ultrafiltration, softening, nanofiltration, and electrodialysis are all applicable to water treatment. However, for wastewater containing high sulfate levels and microorganisms, if each unit is used independently or simply connected in series, it is still difficult to simultaneously address issues such as upstream pollutant load, downstream influent composition, effective sulfate enrichment, and internal reagent circulation. In particular, the key to achieving stable treatment and resource recovery of this type of wastewater lies in how to match the pretreated water quality from ultrafiltration and softening with that from nanofiltration, how to match the nanofiltration concentrate with that from bipolar membrane electrodialysis, and how to use the alkali solution produced by the bipolar membrane for upstream neutralization.

[0006] Therefore, it is necessary to provide a treatment and resource recovery system for high sulfate wastewater containing microorganisms. Before resource recovery, the system should reduce the adverse effects of microorganisms and hardness ions in sequence, use nanofiltration to selectively retain and enrich sulfate ions, and obtain acid and alkali solutions through bipolar membrane electrodialysis. At the same time, an appropriate internal reflux relationship should be constructed to improve the water quality adaptability, resource utilization rate and continuous operation stability of the entire system. Summary of the Invention

[0007] To address the problems of interference from microbial cells and hardness ions in microbial high-sulfate wastewater with subsequent membrane treatment and resource recovery processes, unfavorable sulfate concentration and salt composition for direct resource recovery, and lack of material circulation within the system, this invention provides a system and method for the treatment and resource recovery of microbial high-sulfate wastewater.

[0008] The main objective of this invention is: I. Constructing a pretreatment process compatible with microbial-containing, high-sulfate wastewater before nanofiltration desalination. This involves neutralizing and adjusting the acidity to reduce its adverse effects on membrane and resin operation, using ultrafiltration to retain microbial cells, and then using a sodium-type cation exchange resin to reduce calcium levels. 2+ and Mg 2+ The presence of equal hardness ions makes the water entering nanofiltration and bipolar membrane electrodialysis more stable.

[0009] II. Nanofiltration for SO4 prior to bipolar membrane electrodialysis 2- Selective separation from monovalent salts. On the one hand, SO42- 2- On the one hand, the sulfate concentration is increased by enriching the sulfate on the concentration side, thus increasing the sulfate concentration entering the bipolar membrane electrodialysis. On the other hand, the entry of monovalent salts into the subsequent acid chamber will adversely affect the purity of the product. Therefore, nanofiltration in this invention simultaneously performs the functions of "concentration" and "salt separation", and forms a connection with the subsequent bipolar membrane electrodialysis in terms of feed water composition.

[0010] III. Utilizing the alkaline solution produced by bipolar membrane electrodialysis for internal reuse. The bipolar membrane dissociates water under a DC electric field to produce H₂. + and OH - These microorganisms combine with anions and cations in the salt system to form acidic and alkaline solutions, respectively. The alkaline solution is returned to the front end to neutralize and adjust the pH of the circulating liquid, significantly reducing the amount of external alkaline solution required to adjust the pH of the pretreatment system. For microorganisms with reuse value, the microorganisms in the ultrafiltration concentrate can also be reused in the corresponding front-end waste gas biological purification process.

[0011] To achieve the above objectives, the present invention adopts the following technical solution.

[0012] A system for the treatment and resource recovery of microbial high-sulfate wastewater includes: A pretreatment unit, a nanofiltration salt concentration unit, and a bipolar membrane electrodialysis unit are connected in sequence, and a reflux unit is connected to at least one of the pretreatment unit, the nanofiltration salt concentration unit, and the bipolar membrane electrodialysis unit. The microbial high-sulfate waste liquid is derived from the circulating nutrient solution of the hydrogen sulfide bio-trickling filter tower; The pretreatment unit includes a neutralization and adjustment component, an ultrafiltration and separation component, and a softening component, which are used to neutralize and adjust, retain microorganisms and remove calcium and magnesium ions in sequence to obtain pretreated wastewater containing microorganisms and high sulfates, thereby obtaining pretreated permeable water. The softening component includes a sodium-type cation exchange resin, the regenerated sodium-type cation exchange resin containing Ca... 2+ Mg 2+ The recycled waste liquid is transported to the front-end hydrogen sulfide bio-trickling filter tower and utilized as a micronutrient element required for microbial growth. The nanofiltration salt concentration unit is used to selectively separate monovalent salts and sulfates in the pretreated product water, so that sulfate ions are enriched on the concentration side to obtain sulfate concentrate. The bipolar membrane electrodialysis unit is used to receive the sulfate concentrate and utilize the H2O generated by bipolar membrane hydrolysis under the action of a DC electric field. + and OH - The sulfate concentrate is converted into acid and alkali solutions. The reflux unit includes at least an alkali reuse pipeline; The alkali reuse pipeline is used to transport a portion of the alkali solution generated by the bipolar membrane electrodialysis unit to the neutralization and adjustment component for pH adjustment of the microbial high-sulfate waste liquid.

[0013] Preferably, the circulating nutrient solution in the hydrogen sulfide biotrickling filter has a pH of 1-2, a conductivity of 20-30 mS / cm, a TDS of 15-20 g / L, and a Ca content of [missing information]. 2+ Concentration of 50–100 mg / L, Mg 2+ The concentration is 20–50 mg / L.

[0014] Preferably, the neutralization and adjustment component is used to adjust the pH of the waste liquid to 5-7; The ultrafiltration separation component uses an ultrafiltration membrane made of polysulfone or polyethersulfone, with a molecular weight cutoff of 15,000–30,000 Da and an operating flux of 150–300 L·m⁻¹. -2 ·h -1 ·bar -1 ; The softening assembly includes a resin column filled with sodium-type cation exchange resin, and controls the hardness of the softened water to below 0.5 mg / L.

[0015] Preferably, the nanofiltration salt concentration unit uses a polyamide nanofiltration membrane with a molecular weight cutoff of 100–300 Da, which is effective for SO42-. 2- The retention rate is greater than 99% for Cl - The retention rate is less than 20%; The nanofiltration salt concentration unit operates at a pressure of 8–12 bar, has a throughput of 50–70 LMH, and a concentration factor of 4–6 times.

[0016] Preferably, the bipolar membrane electrodialysis unit adopts a three-compartment configuration, in which bipolar membranes, anion exchange membranes and cation exchange membranes are arranged alternately to form an acid compartment, an alkali compartment and a salt compartment; The salt chamber is used to receive the sulfate concentrate; The acid chamber is used to obtain a sulfuric acid solution; The alkali chamber is used to obtain a sodium hydroxide solution; The current density of the bipolar membrane electrodialysis unit is 30–60 mA / cm². 2 .

[0017] Preferably, the reflux unit further includes: Ultrafiltration concentrate recirculation and / or recovery pipelines are used to transport ultrafiltration concentrate rich in microbial cells to the front-end biological treatment unit or microbial recovery unit that generates the waste liquid; And / or a nanofiltration concentrate return line for conveying a portion of the nanofiltration concentrate to the inlet side of the nanofiltration salt concentration unit.

[0018] Preferably, the system also includes a monitoring and control unit; The monitoring and control unit includes a pH meter and / or conductivity meter and / or TDS meter and / or sulfate online analyzer and / or membrane differential pressure sensor and / or flow meter and / or PLC control system; The PLC control system is used to adjust the neutralization dosage and / or ultrafiltration backwash and / or nanofiltration operating pressure and / or concentrate reflux ratio and / or alkali reuse flow rate according to the monitoring results.

[0019] A method for treating and recycling microbial-containing high-sulfate wastewater, the method comprising: 1) Neutralize and adjust the wastewater containing microorganisms and high sulfate, and then remove the microbial cells by ultrafiltration and soften and remove calcium and magnesium ions by cation exchange resin to obtain pretreated product water; 2) The pretreated permeate is subjected to nanofiltration for salt concentration, so that sulfate ions are enriched on the concentration side and at least some monovalent salts are permeated to obtain sulfate concentrate; 3) The sulfate concentrate is fed into a bipolar membrane electrodialysis device to convert the sulfate into acid and alkali solutions; 4) Reuse a portion of the alkaline solution obtained in step 3) for neutralization and adjustment in step 1); 5) Regenerate the cation exchange resin obtained in step 1) to obtain a Ca-containing solution. 2+ Mg 2+ The recycled waste liquid is transported to the front-end hydrogen sulfide bio-trickling filter tower and utilized as a micronutrient element required for microbial growth.

[0020] Preferably, the neutralization and adjustment in step 1) involves adjusting the pH of the waste liquid to 5-7, so that the hardness of the softened water is controlled below 0.5 mg / L and the microbial content is controlled below 1 mg / L. Step 2) The nanofiltration salt concentration operation pressure is 8-12 bar, the concentration factor is 4-6 times, and a sodium sulfate concentrate with a mass concentration of 4%-6% is obtained; Step 3) The bipolar membrane electrodialysis device is controlled with a current density of 30–60 mA / cm². 2 .

[0021] Preferably, when the microbial high-sulfate waste liquid originates from the front-end biological treatment process and the retained microorganisms have reuse value, the ultrafiltration concentrate is transported to the front-end biological treatment process for microbial reuse.

[0022] It should be noted first that the "microbial-containing high-sulfate waste liquid" referred to in this invention mainly refers to waste liquid that simultaneously contains microbial cells and sulfate, and has the need for selective enrichment and further resource conversion of sulfate. The microorganisms can originate from the upstream biological treatment process that generates the waste liquid; in one specific embodiment, the waste liquid originates from the circulating nutrient solution of a hydrogen sulfide bio-trickling filter, wherein the microorganisms are mainly sulfur-oxidizing bacteria. This specific source is used to illustrate one implementable scenario of the invention and does not limit the invention to only the waste nutrient solution after biological deodorization.

[0023] Furthermore, considering the changes in material morphology and ionic composition between each treatment unit, this invention does not simply connect neutralization, ultrafiltration, softening, nanofiltration, and bipolar membrane electrodialysis in series. Instead, it reconstructs the treatment system step by step based on the limiting factors of microbial high-sulfate waste liquid at different treatment stages, so that the material state obtained from the previous stage of treatment and the influent conditions required for the next stage of treatment form a continuous matching relationship.

[0024] For highly acidic wastewater containing microorganisms and high levels of sulfate, neutralization is primarily used to reduce the acidity, bringing it into a pH range suitable for subsequent membrane separation and ion exchange treatment. When the acidity of the wastewater mainly originates from sulfuric acid and its acidic sulfate ions, neutralization with NaOH will gradually convert the sulfuric acid system into a sulfate system existing in the form of sodium salts. Taking H₂SO₄ as an example, its idealized neutralization relationship can be expressed as: H2SO4+2NaOH→Na2SO4+2H2O.

[0025] Therefore, the neutralization process in this invention not only has the conventional pH adjustment function, but also pre-adjusts the ionic form of sulfate to be recycled in the corresponding waste liquid system, creating conditions for the formation of sulfate-containing influent suitable for nanofiltration desalination and bipolar membrane electrodialysis treatment.

[0026] Building upon this foundation, ultrafiltration separation and resin softening further regulate the feed water from two aspects: dispersed phase loading and ionic composition, respectively. The ultrafiltration membrane, through size retention, retains microbial cells and their associated suspended or colloidal components on the concentrate side, significantly reducing the microbial load in the liquid phase entering the subsequent nanofiltration process. This reduces the likelihood of biomass deposition on the membrane surface, forming a filter cake layer, or clogging mass transfer channels. For microorganisms with reuse value, this retention also creates different material flows between the microorganisms and the resource-recovery salt system, allowing the microorganisms to return to the upstream biological treatment process, while the sulfate-containing liquid phase continues into the subsequent resource recovery process.

[0027] Resin softening further reduces Ca 2+ Mg 2+ Equal hardness ion content. Especially under conditions of continuous sulfate concentration and potential changes in local ion concentration and pH during subsequent electrodialysis, reducing the hardness ion content can decrease the likelihood of corresponding sparingly soluble salts or deposits forming on the membrane surface and in the flow channels. When using sodium-type cation exchange resin, the resin uses Na... + Exchange Ca in waste liquid 2+ and Mg 2+ While reducing hardness, it also further increases the cation composition in the liquid phase towards Na. + System adjustment. Therefore, the pretreatment process of this invention does not simply aim to remove pollutants, but simultaneously adjusts acidity, microorganisms and suspended load, hardness, and the composition of major cations.

[0028] Following the above pretreatment, nanofiltration salt concentration further selectively regulates the mass transfer differences between sulfate and monovalent salts. Without limiting this invention to a single membrane separation mechanism, the separation of ions with different valence states by nanofiltration membranes is typically influenced by factors such as membrane pore size, membrane surface charge, ion hydration state, and electroneutrality constraints. This invention utilizes a selected nanofiltration membrane for SO4... 2- The selectivity difference between SO4 and monovalent salts makes SO4 2- The main salts are retained and gradually enriched on the concentration side, while at least some of the monovalent salts enter the permeate side.

[0029] Therefore, the nanofiltration unit in this invention simultaneously performs two related functions: On the one hand, it increases the effective concentration of sulfate before it enters the bipolar membrane electrodialysis system; On the other hand, the salt composition in the subsequent electrodialysis feed is adjusted.

[0030] The former helps reduce the impact of high membrane stack resistance and insufficient resource utilization efficiency under low salt concentration conditions, while the latter can reduce, for example, Cl... - This introduces the possibility that monovalent anions may migrate into the acid chamber via electromigration and form non-target acid components. Therefore, the concentrate obtained from nanofiltration is not merely "raw water with a higher concentration," but rather an intermediate stream, after compositional selection, more suitable for sulfate-base resource recovery.

[0031] During the bipolar membrane electrodialysis stage, the bipolar membrane interface promotes water dissociation and the formation of H+ under the action of a DC electric field. + and OH - Furthermore, in conjunction with anion and cation exchange membranes, the directional migration of ions in the salt system is facilitated, transforming the sulfate system formed and enriched through the aforementioned steps into the corresponding acid and alkali solutions. For the Na₂SO₄ system, its idealized overall material relationship can be summarized as follows: Na2SO4+2H2O→H2SO4+2NaOH.

[0032] The process is powered by external electrical energy and enables the recombination of anions and cations in the sulfate. This invention thus transforms the sulfate in wastewater from a salt component requiring treatment into an acidic solution that can be further reused or utilized, while simultaneously obtaining NaOH alkaline solution.

[0033] It is worth noting that combining the above-mentioned bipolar membrane electrodialysis process with the front-end NaOH neutralization process can form a more complete material cycle: the front-end NaOH participates in the neutralization of acidic waste liquid and promotes the conversion of the sulfur system to be treated into salt forms such as sodium sulfate; the sulfate formed is pretreated and concentrated by nanofiltration and then enters the bipolar membrane electrodialysis to obtain H2SO4 and NaOH again; among which, NaOH is returned to the front-end for neutralization.

[0034] Therefore, NaOH is no longer just a consumable reagent that is continuously added externally, but can play the role of a process medium that can be recycled within the system, while the sulfur element in the waste liquid is gradually transferred from the original waste liquid to the resource-recovered acid liquid.

[0035] Therefore, it can be seen that there is a front-to-back matching relationship of influent conditions and a back-to-front material feedback relationship among the various treatment units of this invention: neutralization, ultrafiltration, and softening establish a suitable material state for nanofiltration; nanofiltration establishes suitable salt composition and concentration conditions for bipolar membrane electrodialysis through salt separation and concentration; and bipolar membrane electrodialysis supplies the resulting alkaline solution back to the front-end neutralization process. When further combined with the reuse of microorganisms in ultrafiltration concentrate, the reflux of nanofiltration concentrate, the reuse of calcium and magnesium trace elements in resin regeneration waste liquid, and the monitoring and control of operating parameters, multiple internal material circulation and feedback regulation paths can be formed. Therefore, the present invention forms a comprehensive treatment system with multi-stage water quality adaptation, target salt composition regulation, and internal reuse of resource products as its core, rather than a simple parallel arrangement of several independent water treatment units.

[0036] The beneficial effects of this invention are as follows: 1) This invention addresses the simultaneous presence of microbial cells, suspended solids, and hardness ions in high-sulfate wastewater containing microorganisms. Before nanofiltration salt concentration and bipolar membrane electrodialysis, neutralization, ultrafiltration, and resin softening processes are sequentially set up. By reducing acidity, microbial load, and calcium and magnesium ion content through different treatment units, the pre-treated water is seamlessly integrated with the subsequent membrane salt concentration and electrodialysis resource recovery processes. This helps reduce membrane fouling and scaling risks and improves the stability of continuous operation.

[0037] 2) The nanofiltration salt concentration in this invention is not merely used to increase salt concentration, but rather utilizes the selectivity of the nanofiltration membrane for sulfate and monovalent ions to reduce SO42-. 2- The solution enriches on the concentration side while simultaneously allowing at least some monovalent salts to enter the permeate side. This increases the sulfate concentration entering the bipolar membrane electrodialysis unit and reduces the likelihood of monovalent anions migrating into the acid chamber and affecting the composition of the resulting acid solution, thus achieving a match between the feed water composition and the subsequent acid-base resource recovery process.

[0038] 3) This invention utilizes bipolar membrane electrodialysis to convert sulfates after salt separation and concentration into acid and alkali solutions. The resulting alkali solution is then transported to the front end to neutralize and adjust the pH of the circulating liquid, significantly reducing the amount of external alkali solution required for pH adjustment in the pretreatment system. Simultaneously, the Ca-containing solution obtained from the regeneration of the softening resin... 2+ and Mg 2+ The recycled waste liquid is transported to the front-end bio-trickling filter tower and used as a source of trace element nutrients for the growth of microorganisms in the tower. This forms an internal material cycle with two parallel lines: "waste liquid reuse - neutralization and adjustment" and "recycled waste liquid reuse - bio-trickling filter" (dilute sulfuric acid is sold externally). This helps to reduce the consumption of added alkali and microbial nutrients and improve the resource utilization of waste liquid.

[0039] 4) For wastewater originating from biological treatment processes where the retained microorganisms still have reuse value, the ultrafiltration concentrate can be further returned to the corresponding front-end biological treatment process to achieve microbial reuse; at the same time, combined with online monitoring and PLC control, the neutralization dosing, membrane backwashing, nanofiltration pressure and reflux status can be adjusted according to parameters such as pH, membrane pressure difference, flow rate, conductivity and sulfate concentration, so that a continuous and adjustable synergistic operation relationship can be formed between the treatment units. Attached Figure Description

[0040] Figure 1 This is a block diagram of the overall structure of the microbial high-sulfate wastewater treatment and resource recovery system of the present invention; Figure 2 This is a schematic diagram of the equipment and pipeline connections of the microbial high-sulfate wastewater treatment and resource utilization system in Embodiment 1 of the present invention; Figure 3 This is a process flow diagram of the method for treating and recycling microbial high-sulfate wastewater according to the present invention.

[0041] In the diagram: 100, Pretreatment unit; 200, Nanofiltration salt concentration unit; 300, Bipolar membrane electrodialysis unit; 400, Reflux unit; 500, Monitoring and control unit; 600, Reuse unit; 700, Resource recovery unit. Detailed Implementation

[0042] The present invention will be further described clearly and in detail below with reference to specific embodiments and the accompanying drawings. Those skilled in the art will be able to implement the present invention based on these descriptions. Furthermore, the embodiments of the present invention described below are generally only some, not all, of the embodiments of the present invention. Therefore, all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0043] In the description of this invention, it should be understood that the terms "thickness," "upper," "lower," "horizontal," "top," "bottom," "inner," "outer," "circumferential," etc., indicating orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified, and "several" means one or more.

[0044] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0045] Unless otherwise specified, all raw materials used in the embodiments of the present invention are commercially available or obtainable by those skilled in the art; unless otherwise specified, all methods used in the embodiments of the present invention are methods mastered by those skilled in the art.

[0046] Example 1

[0047] like Figure 1 As shown, the system described in this embodiment includes a pretreatment unit 100, a nanofiltration salt concentration unit 200, and a bipolar membrane electrodialysis unit 300 connected in sequence, as well as a reflux unit 400, a monitoring and control unit 500, and a reuse unit 600 connected to the corresponding treatment units.

[0048] like Figure 2 As shown, in one specific device and pipeline connection method of this embodiment, the pretreatment section includes a neutralization system, an ultrafiltration separation system, and a resin softening system; the nanofiltration salt concentration section includes a nanofiltration concentration tank, a pressure pump, and a salt concentration system; the bipolar membrane electrodialysis section is connected to the aforementioned nanofiltration salt concentration section and is equipped with corresponding acid and alkali recovery paths. The system is also equipped with a feed pump, a reflux valve, an electrically controlled valve, and a conductivity monitoring system, etc., to complete material conveying, reflux, and operation regulation.

[0049] Figure 2 The specific equipment connection shown is used to illustrate one implementation method of this embodiment and does not limit the present invention to using the exact same number of pumps, valves, tanks and spatial arrangement.

[0050] like Figure 3 As shown, the processing flow of this embodiment includes waste liquid inlet, neutralization and adjustment, ultrafiltration separation, resin softening, nanofiltration salt concentration, bipolar membrane electrodialysis, NaOH recycling and resource recovery output, and sets up corresponding bypass reflux.

[0051] The microbial high-sulfate wastewater treated in this embodiment originated from the circulating nutrient solution of a hydrogen sulfide bio-trickling filter tower at a certain enterprise. The wastewater was pale yellow, showed no obvious precipitation after prolonged standing, and had a certain odor. Testing revealed that the original solution had a pH of approximately 1.25, a conductivity of approximately 30.4 mS / cm, a TDS of approximately 16.03 g / L, a salinity of approximately 1.91%, and a Ca content of approximately [missing information]. 2+ The concentration is approximately 80 mg / L, Mg 2+ The concentration is approximately 35 mg / L, and it contains sulfur-oxidizing bacteria cells detached from the bio-trickling filtration system.

[0052] This waste liquid is characterized by its strong acidity, the presence of microbial cells, a certain amount of hardness ions, and sulfates, which possess further resource recovery value. If it directly enters a nanofiltration or bipolar membrane electrodialysis process, the microbial cells and related suspended components may increase the risk of membrane fouling, and the calcium content may also be high. 2+ Mg 2+ Pretreatment may increase the risk of scaling during subsequent concentration and ion migration, therefore it is necessary to perform pretreatment first.

[0053] Pretreatment includes neutralization and conditioning, ultrafiltration separation, and resin softening.

[0054] First, the waste liquid was fed into a neutralization system, and a 10 wt% NaOH solution was added to adjust the pH of the original solution from approximately 1.25 to 6.0 ± 0.5. After neutralization, the conductivity of the waste liquid was approximately 26 mS / cm.

[0055] For the acidic waste liquid treated in this embodiment, the neutralization process, on the one hand, brings the waste liquid into a pH range suitable for subsequent membrane separation and ion exchange treatment; on the other hand, since the acidity of the waste liquid is mainly related to the sulfuric acid system, the addition of NaOH helps to further convert the sulfur components to be recycled into sulfates in the form of sodium salts, thus preparing for subsequent SO42- treatment. 2- This creates conditions for salt concentration and bipolar membrane electrodialysis treatment of the Na2SO4 system.

[0056] The neutralized waste liquid is fed into an external pressure ultrafiltration membrane module via a feed pump. The ultrafiltration membrane used is a polyethersulfone hollow fiber membrane with a molecular weight cutoff of 20,000 Da and a membrane area of ​​0.05 m². 2 It operates under external pressure with an operating pressure of 0.1 MPa and an operating throughput of 200 L·m³. -2 ·h -1 ·bar -1 .

[0057] Under the above conditions, the ultrafiltration membrane has a retention rate of ≥99.5% for microbial cells in the waste liquid, and the resulting ultrafiltration effluent is clear and transparent with no obvious suspended matter.

[0058] In this embodiment, the microorganisms originate from the upstream hydrogen sulfide bio-trickling filtration process. Therefore, the ultrafiltration concentrate enriched with microbial cells can be returned to the corresponding upstream biological treatment process via a reflux pipeline to recover the microorganisms with utilization value. In other embodiments, when the retained microorganisms are not suitable for direct return to the original treatment process, they can also enter a separate microbial recovery or subsequent treatment unit.

[0059] The ultrafiltration permeate then enters a resin column filled with 001×7 type sodium cation exchange resin for softening treatment. The sodium cation exchange resin passes through Na... + With Ca in the liquid phase 2+ Mg 2+ Ion exchange is performed to control the hardness of the treated water below 0.5 mg / L.

[0060] After the resin reaches the set regeneration conditions, it is regenerated in situ using a 5–10 wt% NaCl solution. The resulting product contains Ca. 2+ Mg 2+ The recycled wastewater is transported to the upstream hydrogen sulfide biotrickling filter, where Ca... 2+ Mg 2+ As micronutrients required for the growth of microorganisms in the bio-trickling filter, they are utilized to achieve the resource-based recycling of regenerated waste liquid.

[0061] Thus, neutralization, ultrafiltration, and resin softening sequentially adjust acidity, reduce microorganisms and suspended load, and remove hardness ions, making the liquid phase state more stable before entering the subsequent nanofiltration salt concentration process.

[0062] The softened pretreated water enters the nanofiltration concentration tank and is then pumped to the salt concentration system via a pressure pump.

[0063] This embodiment uses a spiral-wound nanofiltration membrane made of polyamide, with a molecular weight cutoff of approximately 150 Da and an effective membrane area of ​​approximately 15 cm². 2 The operating pressure is 10 bar and the operating flux is 50 LMH.

[0064] Under the above conditions, using nanofiltration membranes to filter SO4 2- The selectivity difference between SO4 and monovalent salts makes SO4 2- It is mainly retained on the concentration side, while allowing at least some monovalent salts to enter the permeate side. After concentrating the pretreated permeate by about 5 times, a concentrate with a Na2SO4 mass concentration of about 5.6 wt% is obtained.

[0065] During operation, a portion of the nanofiltration concentrate is returned to the nanofiltration feed water side to further increase and maintain the sulfate concentration in the concentrate.

[0066] This step, on the one hand, makes SO4 2-The solution is enriched before entering bipolar membrane electrodialysis, and at the same time, the proportion of monovalent salts entering the subsequent electrodialysis process is reduced, so that the resulting concentrate is more suitable for subsequent acid-base resource recovery processes in terms of salt concentration and ionic composition.

[0067] This embodiment employs a laboratory-scale bipolar membrane electrodialysis device with a three-compartment configuration. The membrane stack consists of alternating bipolar membranes, anion exchange membranes, and cation exchange membranes, with an effective membrane area of ​​0.017 m². 2 It forms acid chambers, alkali chambers and salt chambers, with each chamber equipped with a circulating liquid storage container and corresponding conveying device.

[0068] The salt chamber is filled with the Na2SO4 concentrate obtained by nanofiltration, which has a mass concentration of about 5.6 wt%. The acid chamber and the alkali chamber are initially filled with about 500 mL of deionized water, and the electrode chamber is filled with a NaOH solution with a mass fraction of about 2 wt% as the electrode electrolyte.

[0069] It operates in constant current mode with a current density of 58 mA / cm². 2 The operating voltage is 25–30 V, the circulation flow rate of each compartment is approximately 30 L / h, and the conductivity and pH changes of each compartment are monitored in real time.

[0070] Under the influence of a DC electric field, the bipolar film promotes water dissociation to generate H+. + and OH - SO4 in the Na2SO4 system 2- With H + H₂SO₄ and Na₂SO₄ are formed on the acidic side. + With OH - NaOH is formed on one side of the alkali chamber, thereby realizing the acid-base resource conversion of sulfate.

[0071] After running for approximately 27 minutes, the remaining salt in the salt chamber had a mass fraction of approximately 0.7 wt%, and SO42- wt%. 2- The conversion rate reached over 90%. Approximately 190 mL of H₂SO₄ solution with a concentration of approximately 0.45 mol / L was obtained, along with approximately 405 mL of NaOH solution with a concentration of approximately 0.17 mol / L.

[0072] Based on the above, this embodiment sets up multiple return paths for different purposes.

[0073] The microbial cells enriched in the ultrafiltration concentrate are returned to the front-end biological treatment process for microbial reuse. The resin regeneration waste liquid is transported to the front-end hydrogen sulfide biotrickling filter tower to provide calcium and magnesium trace elements for the microorganisms there; A portion of the nanofiltration concentrate is returned to the nanofiltration feed side to improve and maintain the concentration level; The NaOH obtained from bipolar membrane electrodialysis is returned to the neutralization and adjustment process, serving as part of the alkali agent required for upstream pH adjustment.

[0074] The reuse of NaOH allows one of the resource-based products obtained from bipolar membrane electrodialysis to re-enter the front-end treatment process, thus forming an alkaline solution cycle within the system. Under continuous operation, the ratio of added NaOH to reused NaOH can be adjusted based on the acidity of the front-end waste liquid and the concentration and yield of NaOH obtained from the bipolar membrane.

[0075] The monitoring and control section includes online monitoring instruments and a PLC control system.

[0076] Online monitoring instruments include pH meters and conductivity meters installed in the neutralization and adjustment process; membrane differential pressure sensors and flow meters installed at the inlet and outlet of ultrafiltration; and conductivity meters and SO4 meters installed at the inlet and outlet of nanofiltration. 2- The system includes an online analyzer, a conductivity meter and a pH meter installed in the corresponding compartment of the bipolar membrane electrodialysis unit, and a liquid level detection device installed on the alkali side.

[0077] The PLC control system adjusts the corresponding equipment based on each detection signal.

[0078] Among them, the amount of NaOH added is adjusted according to the pH signal of the neutralization and adjustment process to keep the pH of the neutralized waste liquid at 5-7; The degree of membrane fouling is determined based on the changes in ultrafiltration membrane pressure difference and flux. Backwashing is performed when the membrane pressure difference exceeds a set value. In this embodiment, the trigger membrane pressure difference is set to be approximately 0.05 MPa. Based on the conductivity of nanofiltration concentrate and SO4 2- Adjust operating pressure and concentrate reflux ratio to control concentration; Adjust the NaOH reuse status according to the liquid level and concentration on the alkali side.

[0079] Thus, each processing unit not only forms a series connection and reflux of materials, but also forms a feedback regulation relationship based on operating parameters.

[0080] Combination Figure 3 The specific processing procedure in this embodiment can be summarized as follows: Step S1: Introduce the waste liquid containing microorganisms and high sulfate content into the treatment system; Step S2: The waste liquid is neutralized and adjusted with NaOH to achieve a pH of 5-7. In this embodiment, the pH is controlled at 6.0±0.5. Step S3: Ultrafiltration is performed on the neutralized waste liquid to separate and retain the microbial cells. Step S4: The ultrafiltration permeate is softened by passing it through a sodium-type cation exchange resin to reduce the hardness of the permeate to below 0.5 mg / L. Step S5 involves nanofiltration to concentrate the softened permeate water, reducing SO4 levels. 2- Na2SO4 concentrate was obtained by enrichment on the concentration side. Step S6: The obtained Na2SO4 concentrate is fed into a bipolar membrane electrodialysis device to convert it into H2SO4 and NaOH. Step S7: Return the obtained NaOH to the front-end neutralization and adjustment process; Step S8: The obtained H2SO4 and the usable NaOH that was not used for internal recycling are recycled or exported as resource products.

[0081] Under the conditions of this embodiment, the sulfur resource recovery rate is approximately 64.8%. The obtained H2SO4 can be used for pH adjustment, cleaning, or other suitable applications depending on specific production conditions; the obtained NaOH is used for internal neutralization within this system.

[0082] This embodiment demonstrates that by sequentially establishing pretreatment water quality conditions and controlling SO4... 2- By selectively separating and enriching salts, followed by bipolar membrane acid-base conversion, and feeding the resulting NaOH back to the front end, a continuous technical route can be formed that couples the treatment and resource utilization of microbial high-sulfate wastewater.

[0083] Example 2

[0084] To further investigate the state changes of the system in Example 1 during continuous operation, the system described in Example 1 was run continuously for 72 hours, and tests were performed at 0.5 h, 24 h, 48 h and 72 h respectively.

[0085] The testing items include ultrafiltration membrane differential pressure, ultrafiltration membrane flux, nanofiltration membrane differential pressure, nanofiltration flux, and SO4. 2- Concentration. Experimental results are shown in Table 1.

[0086] Table 1: Results of 72-hour continuous operation test

[0087] As shown in Table 1, during 72 hours of continuous operation, the ultrafiltration membrane flux decreased from 205 LMH to 180 LMH, but still maintained approximately 87.8% of the initial detection value at 72 hours; the nanofiltration flux decreased from 62.1 LMH to 57.2 LMH, but still maintained approximately 92.1% of the initial detection value at 72 hours.

[0088] During the same period, the pressure differentials of the ultrafiltration and nanofiltration membranes showed a gradual increasing trend, but there was no sudden and significant flux decline in a short period of time; SO4 2- The concentration was gradually increased from 58.2 g / L to 61.8 g / L.

[0089] The above results indicate that, under the experimental conditions and within the 72-hour observation period, the feed water after neutralization, ultrafiltration, and softening can support the continuous operation of the subsequent nanofiltration process, maintaining a high membrane flux ratio, while SO4 levels are relatively low. 2- It can still maintain the trend of concentration.

[0090] It should be noted that this test is used to reflect the changes in the system of Example 1 within a 72-hour operating cycle, and does not mean that the continuous operating cycle of the present invention is limited to 72 hours.

[0091] Example 3

[0092] This embodiment adopts the same overall processing route as Example 1, namely, neutralization and adjustment, ultrafiltration separation, resin softening, nanofiltration salt concentration and bipolar membrane electrodialysis are performed in sequence, and corresponding reflux and resource recovery treatment are carried out.

[0093] Unlike Example 1, this example uses a different batch of waste liquid generated by a biological hydrogen sulfide treatment system. This batch of stock solution has a pH of approximately 1.8, a conductivity of approximately 25 mS / cm, a TDS of approximately 18.5 g / L, and a Ca content of... 2+ The concentration is approximately 60 mg / L, Mg 2+ The concentration is approximately 25 mg / L.

[0094] During the pretreatment process, the ultrafiltration membrane is made of polysulfone with a molecular weight cutoff of 30,000 Da and an operating flux of 220 L·m⁻¹. -2 ·h -1 ·bar -1 The softening resin used is D001 type macroporous sodium cation exchange resin.

[0095] During the nanofiltration salt concentration stage, the operating pressure was 12 bar, the operating flux was 66.7 LMH, the concentration factor was approximately 6 times, and the mass concentration of the resulting Na2SO4 concentrate was approximately 6%.

[0096] During the bipolar membrane electrodialysis stage, the current density was controlled at 60 mA / cm². 2 The running time is approximately 35 minutes, SO4 2- The conversion rate is approximately 88%.

[0097] The remaining processing steps and reflux methods are the same as in Example 1.

[0098] Under the conditions of this embodiment, the sulfur resource recovery rate is approximately 58%.

[0099] The results of Examples 1 and 3 show that, even with differences in the pH, hardness composition of the original solution, and the operating parameters of the ultrafiltration membrane, cation exchange resin, and nanofiltration used, the pretreatment-salt concentration-bipolar membrane electrodialysis treatment route described in this invention can still effectively treat SO4.2- The enrichment and subsequent resource conversion demonstrate that this technology system does not correspond to only a single set of equipment parameters in Example 1.

[0100] Comparative Example 1 This comparative example is used to examine the impact of omitting microbial retention and hardness removal on membrane operation when neutralization and subsequent nanofiltration salt concentration are performed.

[0101] This comparative example uses the same batch of waste liquid as in Example 1. First, NaOH neutralization and adjustment are performed according to the method in Example 1. However, after neutralization, ultrafiltration separation and resin softening are not performed. Instead, the waste liquid is directly sent to the nanofiltration salt concentration system. The remaining nanofiltration operating conditions are the same as in Example 1.

[0102] Because the influent still contains a large number of microorganisms and calcium. 2+ Mg 2+ With equal-hardness ions, the nanofiltration membrane showed significant fouling and increased operating resistance after approximately 2 hours of operation. The nanofiltration operating pressure increased from approximately 10 bar initially to over 15 bar, and the flux decreased by more than 50%.

[0103] Compared with the operating state of Example 1, this comparative example showed a significant decrease in flux in a shorter period of time, indicating that for the microbial high sulfate waste liquid treated in this application, neutralization and adjustment alone are insufficient to form an influent state suitable for stable nanofiltration operation.

[0104] Ultrafiltration is used to reduce the load on the membrane surface from microbial cells and related suspended and colloidal substances, while resin softening is used to reduce calcium content. 2+ Mg 2+ Plasma carries the risk of deposition or scaling under concentrated conditions. Both plasma and nanofiltration work together in this invention to establish the feed water conditions prior to nanofiltration.

[0105] Therefore, this comparative example illustrates that the ultrafiltration separation and resin softening in this invention are not simply to add conventional wastewater treatment steps, but to transform the original complex state of microbial high-sulfate wastewater into an influent state that is more suitable for subsequent selective salt separation and resource recovery.

[0106] Comparative Example 2 This comparative example is used to investigate the situation where microbial cells and hardness ions have been removed, but SO42- is not used. 2- The impact of selective salt concentration followed by direct bipolar membrane electrodialysis on the resource recovery process.

[0107] The waste liquid was first neutralized, adjusted, separated by ultrafiltration, and softened by resin according to the method in Example 1. After obtaining the pretreated permeate, without nanofiltration for salt concentration, the pretreated permeate was directly sent to a bipolar membrane electrodialysis device, and the remaining bipolar membrane electrodialysis conditions were kept as consistent as possible with those in Example 1.

[0108] The Na2SO4 concentration in the pretreated product water without nanofiltration salt concentration is approximately 1.6 wt%, and it also contains a certain amount of monovalent salts such as NaCl.

[0109] Because the sulfate concentration entering the bipolar membrane electrodialysis is lower, the salt chamber ion concentration and conductivity conditions are different from those of the feed after nanofiltration concentration in Example 1, resulting in a relative increase in membrane stack operating resistance and energy consumption.

[0110] On the other hand, due to the lack of nanofiltration for SO4 2- Selective separation from monovalent salts, Cl - Monovalent anions can still pass through the corresponding ion exchange membrane into the acid chamber under the action of an electric field, thus causing non-target acid components to appear in the resulting acid solution.

[0111] The purity of H2SO4 obtained in this comparative example is approximately 72%, SO4 2- The conversion rate is approximately 78%, and the sulfur resource recovery rate is approximately 35%.

[0112] Compared with Example 1, this comparative example shows that the technical role of the nanofiltration step in this invention includes at least two aspects: firstly, it increases the concentration of SO4 entering the bipolar membrane electrodialysis process. 2- Effective concentration; secondly, through the reaction of monovalent salts with SO4 2- The selectivity differences between them adjust the salt composition of subsequent feeds.

[0113] Therefore, even if the problems of microorganisms and hardness ions have been solved through ultrafiltration and softening, it is still not equivalent to having formed a feed suitable for efficient bipolar membrane resource utilization; nanofiltration salt concentration constitutes a further composition adjustment link between pretreatment and bipolar membrane electrodialysis.

[0114] Based on the above Examples 1 and 3 and Comparative Examples 1 and 2, the main indicators are compared as shown in Table 2 below.

[0115] Table 2: Comparison of Key Indicators As can be seen from the comparison of the embodiments and comparative examples in Table 2, the various processing steps of the present invention are not independent of each other.

[0116] First, the difference between Example 1 and Comparative Example 1 illustrates that before microbial-containing high-sulfate wastewater enters nanofiltration, it is necessary to reduce the microbial and hardness ion load. If ultrafiltration and softening are omitted, even if the same nanofiltration conditions are subsequently used, significant membrane fouling and flux reduction will occur more quickly.

[0117] Secondly, the differences between Example 1 and Comparative Example 2 illustrate that achieving microbial removal and softening does not necessarily mean that a suitable bipolar membrane feed water can be directly obtained. Further utilization of nanofiltration to increase SO4 levels... 2- Reducing the concentration and at least some of the monovalent salt content is beneficial to improving the concentration and ionic composition of subsequent bipolar membrane feeds, and correspondingly improving resource utilization efficiency and target acid composition.

[0118] Furthermore, the NaOH obtained from bipolar membrane electrodialysis can be returned to the front-end neutralization process. Therefore, the back-end resource recovery process is not simply the end of the system, but can form a reverse material connection with the front-end pretreatment.

[0119] The 72-hour operation results from Example 2 further demonstrate that, under the pretreatment and salt separation conditions employed in this invention, both ultrafiltration and nanofiltration fluxes maintained a high proportion throughout the observation period, and SO4 levels were low. 2- The continued enrichment trend indicates that the water quality matching relationship between the above-mentioned treatment units can be maintained during continuous operation.

[0120] Therefore, the technical relationships formed by this invention can be summarized as follows: Water quality reconstruction of raw complex wastewater, removal of microorganisms and hardness ions, SO4 2- Selective salt separation and concentration, bipolar membrane acid and alkali resource utilization, and internal reuse of NaOH.

[0121] For waste liquids originating from upstream biological treatment processes where the microorganisms still have utilization value, a microbial reuse pathway can be further formed, as well as a reuse pathway for calcium and magnesium trace elements in the regenerated waste liquid to the bio-trickling filter.

[0122] The above technical approach enables both front-to-back matching of influent conditions and back-to-front feedback of resource-based products among the processing units, thus distinguishing it from a simple series connection where the units are independent of each other.

[0123] The above embodiments and comparative examples are used to illustrate the technical solution of the present invention and the interaction between the various processing stages, and are not intended to limit the scope of protection of the present invention. Those skilled in the art can make corresponding adjustments to the membrane area, circulation flow rate, reflux ratio, equipment specifications, and specific operating parameters according to the composition of the waste liquid to be treated, the treatment scale, the target product concentration, and the specific performance of the selected membrane module; as long as they still adopt the technical concept described in the present invention, they should fall within the scope covered by the technical solution of the present invention.

[0124] Comparative Example 3 This comparative example is used to examine the impact of replacing the nanofiltration salt concentration treatment of the present invention with reverse osmosis treatment on the subsequent bipolar membrane electrodialysis feed composition and resource utilization effect under basically the same pretreatment conditions and bipolar membrane electrodialysis conditions.

[0125] In this comparative example, another batch of wastewater containing microorganisms and high sulfate was taken from the same source and type as the wastewater treated in Example 1. Neutralization, ultrafiltration, and softening with sodium cation exchange resin were carried out in sequence according to the conditions of Example 1 to obtain pretreated permeable water.

[0126] The same batch of pretreated permeate was divided into two streams. One stream was subjected to nanofiltration salt separation and concentration under the nanofiltration operating conditions of Example 1, with the volume concentration factor controlled at approximately 5 times to obtain nanofiltration concentrate. The other stream was concentrated using a conventional reverse osmosis membrane, and its feed water flow rate, permeate recovery rate, and volume concentration factor were controlled to be basically consistent with the nanofiltration group, so that the volume concentration factor of the reverse osmosis concentrate was also approximately 5 times.

[0127] SO4 was detected in nanofiltration concentrate and reverse osmosis concentrate, respectively. 2- Concentration, Cl - Concentration, Na + Concentration, conductivity, and calculation of Cl - SO4 2- Molar ratio. The results are shown in Table 3.

[0128] Table 3: Comparison of feed composition between nanofiltration concentration and reverse osmosis concentration At essentially the same volumetric concentration factor, the two groups of SO4 2- The concentrations were similar, but the Cl in the nanofiltration concentrate was higher. - SO4 2- The molar ratio is significantly lower than that of the reverse osmosis concentrate, with a reduction of approximately 78.3%.

[0129] Subsequently, nanofiltration concentrate and reverse osmosis concentrate were collected and subjected to resource recovery treatment in the same bipolar membrane electrodialysis device. Both groups adopted the same membrane stack structure as in Example 1, and the current density, initial liquid volume of each compartment, circulation flow rate, and end-point criteria were basically the same.

[0130] After bipolar membrane electrodialysis, the H2SO4 content and Cl content in the obtained acid solution were measured respectively. - Content and SO4 in the remaining brine 2- Content, and calculate the purity of H2SO4 and SO4. 2- Conversion rate and sulfur resource recovery rate. The results are shown in Table 4.

[0131] Table 4: Comparison of Bipolar Membrane Resource Utilization Effects Between Nanofiltration Concentration Group and Reverse Osmosis Concentration Group

[0132] Experimental results show that, under the condition of controlling the same volume concentration factor, both nanofiltration concentration and reverse osmosis concentration can increase the salt concentration in the feed, but the two have significantly different ways of adjusting the ion composition.

[0133] Reverse osmosis membrane for SO4 2- and Cl - Plasma has a high retention capacity, therefore it mainly manifests as the overall concentration of mixed salts, and the Cl in the concentrated solution... - SO4 2- The molar ratio is maintained at a high level; nanofiltration utilizes SO4. 2- The selectivity difference between SO4 and monovalent ions makes SO4 2- Primarily retained and enriched on the concentrated side, while at least some Cl... - When monovalent ions enter the permeate side, the Cl in the nanofiltration concentrate... - SO4 2- The molar ratio is much lower than that of reverse osmosis membrane modules.

[0134] Following further bipolar membrane electrodialysis, Cl- was simultaneously enriched in the reverse osmosis concentrate. - It can migrate into the acid chamber via electromigration, resulting in a greater presence of non-target acid components in the obtained acid solution, and a significant decrease in the purity of the obtained H2SO4. The nanofiltration concentrate has already undergone SO4 targeting before entering the bipolar membrane electrodialysis. 2- Selective composition adjustment, the Cl in the resulting acid solution - The content was significantly lower, and the purity of H2SO4 reached approximately 95.6%, which is about 15.8 percentage points higher than that of the reverse osmosis concentration group.

[0135] Meanwhile, the nanofiltration concentration group SO4 2- The conversion rate is as high as approximately 92%, and the sulfur resource recovery rate is as high as 66.2%; the corresponding indicators of the reverse osmosis concentration group are only approximately 86% and 61.9%, respectively.

[0136] Therefore, the nanofiltration salt concentration in this invention does not simply replace the reverse osmosis device with a membrane concentration device, but rather, while increasing the sulfate concentration, it directionally adjusts the ionic composition entering the bipolar membrane electrodialysis unit. Reverse osmosis primarily achieves overall concentration of mixed salts, while the nanofiltration treatment of this invention selectively reduces the concentration of monovalent salts relative to SO4 in the concentrate. 2- The ratio of these factors transforms the subsequent bipolar membrane electrodialysis process from a mixed hydrochloric acid-base conversion to a resource utilization process using sulfate as the primary target salt system.

[0137] Therefore, a specific matching relationship is formed in terms of feed composition between nanofiltration salt concentration and subsequent bipolar membrane electrodialysis, and the technical effects produced by the two cannot be obtained by conventional equivalent replacement with reverse osmosis treatment.

[0138] Comparative Example 4 This comparative example is used to investigate the impact of different material flow directions after nanofiltration treatment on the resource utilization effect of bipolar membrane electrodialysis.

[0139] To further verify the influence of different material flow directions after nanofiltration on the resource utilization effect of bipolar membrane electrodialysis, nanofiltration concentrate and nanofiltration permeate generated in the same nanofiltration process were collected during the nanofiltration process of the supplementary verification experiment described in Comparative Example 3.

[0140] The nanofiltration concentrate is directly used as the feed for the first group of bipolar membrane electrodialysis. The nanofiltration permeate is further concentrated using a concentration method that does not change the proportion of its main ions, so that its conductivity is adjusted to about 65-85 mS / cm, which is similar to that of the nanofiltration concentrate, and is used as the feed for the second group of bipolar membrane electrodialysis.

[0141] SO4 in the two groups of feeds were detected separately. 2- Concentration, Cl - Concentration, Na + Concentration, conductivity, and calculation of Cl - SO4 2- Molar ratio. The results are shown in Table 5.

[0142] Table 5: Comparison of feed composition between nanofiltration concentration side and nanofiltration permeation side

[0143] The results showed that even when the conductivity of the two feeds was within a similar range, the ionic composition of the two liquids still differed significantly. SO4 in the nanofiltration concentration side... 2- The concentration was 59.2 g / L, while the SO4 after further concentration on the nanofiltration permeate side... 2- The concentration remained at only 0.8 g / L, approximately 1.35% of that on the nanofiltration concentration side; meanwhile, the Cl in the nanofiltration permeate concentrate increased. - The concentration reached 26.7 g / L. Therefore, the Cl- concentration of the concentrate on the nanofiltration concentration side and the nanofiltration permeate side was... - SO4 2- The molar ratios were 0.073 and 90.44, respectively, with a difference of approximately 1.24 × 10⁻⁶. 3 The difference was approximately three orders of magnitude. Subsequently, the two sets of feeds were fed into the same bipolar membrane electrodialysis device, and the current density, circulation flow rate, initial volume of each compartment, and running time were controlled to be basically the same.

[0144] After bipolar membrane electrodialysis, the H2SO4 content and Cl content in the obtained acid solution were measured respectively. - Content and SO4 in the remaining brine 2- Content, and calculate the purity of H2SO4 and SO4. 2- Conversion rate and sulfur resource recovery rate. The results are shown in Table 6.

[0145] Table 6: Resource Utilization Effect of Bipolar Membranes with Different Nanofiltration Material Flow Directions

[0146] Experimental results show that even if the nanofiltration permeate is further concentrated to achieve a conductivity similar to that of the nanofiltration concentrate, there are still significant differences in their ionic composition and subsequent bipolar membrane resource utilization results.

[0147] When the nanofiltration concentration side is used as the bipolar membrane feed, SO4 2- After selective retention, Cl becomes the main target anion. - SO4 2- The molar ratio is extremely low, resulting in high purity H2SO4 and SO4. 2- The conversion rate and sulfur resource recovery rate were both far superior to the control.

[0148] When using the nanofiltration permeate concentrate as the bipolar membrane feed, although its conductivity is in a similar range to that of the nanofiltration concentration side, the SO4 content... 2- The concentration was only 0.8 g / L, while Cl - The concentration can reach 26.7 g / L. After bipolar membrane electrodialysis, the Cl in the resulting acid solution... - The concentration further reached 16.72 g / L, with a significant increase in non-target acid components; the purity of H2SO4 was only 3.6%, and SO4... 2- The conversion rate was 79.6%, and the sulfur resource recovery rate was 0.6%.

[0149] The above results indicate that the effectiveness of subsequent bipolar membrane electrodialysis in resource recovery is not solely determined by the overall conductivity of the feed, nor solely by whether nanofiltration is performed, but is closely related to the selected material stream after nanofiltration and the composition of the target ions therein.

[0150] This invention selects SO4 2- The enriched nanofiltration concentration side is used as feed for bipolar membrane electrodialysis, transforming the nanofiltration process from a general divalent ion removal process into a selective salt separation and target salt enrichment process targeting sulfate resource utilization. This enables subsequent bipolar membrane electrodialysis to obtain H2SO4 and NaOH with sulfate as the main target salt system.

[0151] Therefore, the nanofiltration permeate side is further concentrated and fed into bipolar membrane electrodialysis, which, in accordance with the present invention, concentrates SO4.2- Enriched nanofiltration concentration for bipolar membrane resource recovery involves different material selection and technical routes, and the resource recovery results produced by the two are also significantly different.

[0152] Comparative Example 5 This comparative example is used to investigate the Ca-containing substances produced during the resin softening process. 2+ Mg 2+ The impact of recycled wastewater on the activity of sulfur-oxidizing microorganisms after it is returned to the front-end biological treatment process.

[0153] A sulfur-oxidizing bacteria system with the same source as the hydrogen sulfide bio-trickling filtration system in Example 1 was selected, and three groups of experiments were set up under the same initial bacterial count, the same sulfur-containing substrate concentration, and the same culture conditions.

[0154] The first group does not receive additional Ca. 2+ and Mg 2+ As a control group lacking calcium and magnesium nutrients; The second group used fresh Ca 2+ Mg 2+ Nutrients were supplemented and adjusted to the set concentration according to the standard culture system; The third group was added to the sodium-type cation exchange resin of the present invention, which was regenerated to contain Ca. 2+ Mg 2+ Regenerated waste liquid, and based on the Ca in the regenerated liquid 2+ and Mg 2+ The actual content of Ca is adjusted to control the dosage, so that the Ca provided by the third group... 2+ Mg 2+ The quantity is basically the same as that of the second group.

[0155] To reduce Na in the regenerated solution + and Cl - The impact of background differences on microbial activity, based on the Na content in the regeneration solution. + and Cl - Concentration: Supplement the first and second groups with the corresponding amount of NaCl to adjust the salinity and Na+ concentration of each system. + Cl - The backgrounds are basically the same.

[0156] All groups were cultured under the same temperature, pH, and oxygen supply conditions, and SO4 levels were measured at 0 h, 24 h, and 48 h, respectively. 2- Production amount and sulfur oxidation activity. The results are shown in Table 7.

[0157] Table 7: Comparison of the activity of resin regeneration waste liquid reused in sulfur oxidizing bacteria system

[0158] Experimental results show that without supplementing Ca 2+Mg 2+ At 48 h, the sulfate ion production and sulfur oxidation activity of the sulfur-oxidizing bacteria system decreased significantly. Without Ca supplementation... 2+ Mg 2+ The sulfate ion production of the group was approximately 6.9 g / L, and the relative sulfur oxidation activity was only about 67.6%.

[0159] Using fresh Ca 2+ Mg 2+ After nutrient salts were applied, SO4 levels decreased at 48 hours. 2- The yield was increased to 10.2 g / L, and was 100% based on its sulfur oxidation activity.

[0160] The resin regeneration yield containing Ca 2+ Mg 2+ When the regenerated waste liquid is used for microbial culture, SO4 48 h 2- The amount produced reached 9.3 g / L, and its sulfur oxidation activity reached that of fresh Ca. 2+ Mg 2+ The nutrient salt group had a 91.2% mortality rate, with the difference from the fresh nutrient salt group controlled within 10%, and the group that did not supplement with calcium was less affected. 2+ Mg 2+ The group increased by 23.6 percentage points.

[0161] The above results indicate that the resin regeneration yield contains Ca. 2+ Mg 2+ Waste liquid can basically replace fresh Ca 2+ Mg 2+ Nutrients maintained the metabolic activity of sulfur-oxidizing bacteria and did not have a significant inhibitory effect due to the salt background in the regeneration solution.

[0162] This explains why the Ca removed from the waste liquid during the resin softening process... 2+ and Mg 2+ In subsequent nanofiltration and bipolar membrane electrodialysis processes, these are hardness ions that need to be reduced; however, when the resin is regenerated and returned to the front-end biological treatment system, they can be converted into trace nutrients that can be utilized by sulfur-oxidizing microorganisms.

[0163] Therefore, the relationship between softening with sodium-type cation exchange resin and reuse of regenerated wastewater in this invention is not a simple removal and discharge relationship, but rather a functional conversion of the same component between membrane treatment and biological treatment processes. By using Ca-containing... 2+ Mg 2+ Returning regenerated wastewater to the upstream biological treatment process can reduce the risk of subsequent membrane fouling, reduce the need for replenishing fresh calcium and magnesium nutrients, and further form an internal material cycle between the biological treatment unit and the membrane resource recovery unit.

Claims

1. A system for the treatment and resource recovery of microbial high-sulfate wastewater, characterized in that, include: A pretreatment unit, a nanofiltration salt concentration unit, and a bipolar membrane electrodialysis unit are connected in sequence, and a reflux unit is connected to at least one of the pretreatment unit, the nanofiltration salt concentration unit, and the bipolar membrane electrodialysis unit. The microbial high-sulfate waste liquid is derived from the circulating nutrient solution of the hydrogen sulfide bio-trickling filter tower; The pretreatment unit includes a neutralization and adjustment component, an ultrafiltration and separation component, and a softening component, which are used to neutralize and adjust, retain microorganisms and remove calcium and magnesium ions in sequence to obtain pretreated wastewater containing microorganisms and high sulfates, thereby obtaining pretreated permeable water. The softening component includes a sodium-type cation exchange resin, the regenerated sodium-type cation exchange resin containing Ca... 2+ Mg 2+ The recycled waste liquid is transported to the front-end hydrogen sulfide bio-trickling filter tower and utilized as a micronutrient element required for microbial growth. The nanofiltration salt concentration unit is used to selectively separate monovalent salts and sulfates in the pretreated product water, so that sulfate ions are enriched on the concentration side to obtain sulfate concentrate. The bipolar membrane electrodialysis unit is used to receive the sulfate concentrate and utilize the H2O generated by bipolar membrane hydrolysis under the action of a DC electric field. + and OH - The sulfate concentrate is converted into acid and alkali solutions. The reflux unit includes at least an alkali reuse pipeline; The alkali reuse pipeline is used to transport a portion of the alkali solution generated by the bipolar membrane electrodialysis unit to the neutralization and adjustment component for pH adjustment of the microbial high-sulfate waste liquid.

2. The system for treating and recycling microbial-containing high-sulfate wastewater according to claim 1, characterized in that, The circulating nutrient solution in the hydrogen sulfide biotrickling filter contains sulfur-oxidizing bacteria, Ca 2+ Concentration of 50–100 mg / L, Mg 2+ The concentration is 20–50 mg / L.

3. The system for treating and recycling microbial-containing high-sulfate wastewater according to claim 1, characterized in that, The neutralization and adjustment component is used to adjust the pH of the waste liquid to 5-7; The ultrafiltration separation component uses an ultrafiltration membrane made of polysulfone or polyethersulfone, with a molecular weight cutoff of 15,000 to 30,000 Da. The softening assembly includes a resin column filled with sodium-type cation exchange resin.

4. The system for treating and recycling microbial high-sulfate wastewater according to claim 1, characterized in that, The nanofiltration salt concentration unit uses a polyamide nanofiltration membrane with a molecular weight cutoff of 100–300 Da. The nanofiltration salt concentration unit operates at a pressure of 8–12 bar, has a throughput of 50–70 LMH, and a concentration factor of 4–6 times.

5. The system for treating and recycling microbial high-sulfate wastewater according to claim 1, characterized in that, The bipolar membrane electrodialysis unit adopts a three-compartment configuration, which consists of bipolar membranes, anion exchange membranes, and cation exchange membranes arranged alternately to form an acid compartment, an alkali compartment, and a salt compartment. The salt chamber is used to receive the sulfate concentrate; The acid chamber is used to obtain a sulfuric acid solution; The alkali chamber is used to obtain a sodium hydroxide solution; The current density of the bipolar membrane electrodialysis unit is 30–60 mA / cm². 2 .

6. The system for treating and recycling microbial high-sulfate wastewater according to claim 1, characterized in that, The recirculation unit further includes: Ultrafiltration concentrate recirculation and / or recovery pipelines are used to transport ultrafiltration concentrate rich in microbial cells to the front-end biological treatment unit or microbial recovery unit that generates the waste liquid; And / or a nanofiltration concentrate return line for conveying a portion of the nanofiltration concentrate to the inlet side of the nanofiltration salt concentration unit.

7. The system for treating and recycling microbial high-sulfate wastewater according to claim 1, characterized in that, The system also includes a monitoring and control unit; The monitoring and control unit includes a pH meter and / or conductivity meter and / or TDS meter and / or sulfate online analyzer and / or membrane differential pressure sensor and / or flow meter and / or PLC control system; The PLC control system is used to adjust the neutralization dosage and / or ultrafiltration backwash and / or nanofiltration operating pressure and / or concentrate reflux ratio and / or alkali reuse flow rate according to the monitoring results.

8. A method for treating and recycling microbial-containing high-sulfate wastewater, characterized in that, The method includes: 1) Neutralize and adjust the wastewater containing microorganisms and high sulfate, and then remove the microbial cells by ultrafiltration and soften and remove calcium and magnesium ions by sodium cation exchange resin to obtain pretreated product water; 2) The pretreated permeate is subjected to nanofiltration for salt concentration, so that sulfate ions are enriched on the concentration side and at least some monovalent salts are permeated to obtain sulfate concentrate. 3) The sulfate concentrate is fed into a bipolar membrane electrodialysis device to convert the sulfate into acid and alkali solutions; 4) Reuse a portion of the alkaline solution obtained in step 3) for neutralization and adjustment in step 1); 5) Regenerate the sodium-type cation exchange resin obtained in step 1) to obtain a Ca-containing solution. 2+ Mg 2+ The recycled waste liquid is transported to the front-end hydrogen sulfide bio-trickling filter tower and utilized as a micronutrient element required for microbial growth.

9. A method for treating and utilizing microbial-containing high-sulfate wastewater according to claim 8, characterized in that, Step 1) Neutralization adjustment involves adjusting the pH of the waste liquid to 5-7, so that the hardness of the softened water is controlled below 0.5 mg / L and the microbial content is controlled below 1 mg / L; Step 2) The nanofiltration salt concentration operation pressure is 8-12 bar, the concentration factor is 4-6 times, and a sodium sulfate concentrate with a mass concentration of 4%-6% is obtained; Step 3) The bipolar membrane electrodialysis device is controlled with a current density of 30–60 mA / cm². 2 .

10. A method for treating and utilizing microbial-containing high-sulfate wastewater according to claim 8 or 9, characterized in that, When the microbial high-sulfate waste liquid originates from the front-end biological treatment process and the retained microorganisms have reuse value, the ultrafiltration concentrate is transported to the front-end biological treatment process for microbial reuse.

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