Three-dimensional coupling biochemical oxidation treatment process for RO concentrated water

Abstract

The application relates to the technical field of RO concentrated water treatment, and discloses a three-dimensional coupling biochemical oxidation treatment process for RO concentrated water. The process first adjusts the pH of RO concentrated water and adds nutrient salts, and then loads composite functional fillers with biological membranes in the main electrode plate of a reactor; by applying a low current density polarization electric field and cooperating with aeration, an anaerobic-anoxic-aerobic microenvironment is accurately controlled; electrochemical degradation and biological membrane biochemical reaction are organically combined, so that deep mineralization of COD in RO concentrated water and effective removal of ammonia nitrogen and total nitrogen are realized.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, specifically to a three-dimensional coupled biochemical oxidation treatment process for RO concentrate. Background Technology

[0002] With increasing efforts in industrial water conservation and emission reduction, reverse osmosis (RO) technology has been widely adopted. However, the RO concentrate produced by RO has become a challenge in the water treatment field due to its extremely high salt content, high concentration of recalcitrant organic matter, and complex composition. Currently, the treatment of such wastewater mainly relies on biological and electrochemical methods, both of which have significant drawbacks. Traditional biological processes suffer from inhibited microbial activity in high-salt environments, making them prone to inactivation; while conventional electrochemical oxidation, although capable of degrading recalcitrant pollutants, relies on high current densities, resulting in extremely high energy consumption. Summary of the Invention

[0003] To address the shortcomings of existing technologies, such as insufficient microbial activity in high-salt environments and reliance on high current densities in conventional electrochemical treatments, the present invention aims to provide a three-dimensional coupled biochemical oxidation treatment process for RO concentrate. By organically combining electrochemical degradation with biofilm biochemical reactions, deep mineralization of COD and effective removal of ammonia nitrogen and total nitrogen from RO concentrate are achieved.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] A three-dimensional coupled biochemical oxidation treatment process for RO concentrate includes the following steps:

[0006] S1. Adjust the pH of the RO concentrate and add nutrients to obtain pretreated wastewater;

[0007] S2. Pretreated wastewater is introduced into a reactor filled with composite functional packing material, a low current density polarized electric field is applied, and the current density and oxygen concentration are adjusted to construct an anaerobic-aerobic biochemical reaction system in the reactor to degrade pollutants through electrochemical and biofilm biochemical reactions.

[0008] S3. The reactor effluent is subjected to sedimentation and filtration to obtain qualified effluent, and some of the sludge deposited at the bottom is returned to the water pretreatment end, while maintaining the concentration of suspended solids in the mixed liquor in the reactor.

[0009] Further, in S1, the pH of the RO concentrate is adjusted to 6.5-7.5; the nutrients include a nitrogen source and a phosphorus source; the nitrogen source includes one or more of ammonium chloride, sodium nitrate and urea; the phosphorus source includes any one or more of potassium dihydrogen phosphate and disodium hydrogen phosphate; the C:N:P mass ratio of the pretreated wastewater is controlled to be 100:(3-5):(0.5-1).

[0010] The pH here ensures optimal biological activity of microorganisms; controlling the C:N:P mass ratio of the pretreated wastewater to 100:(3-5):(0.5-1) can effectively meet the metabolic needs of microorganisms, in which carbon source provides energy, nitrogen source is used to synthesize proteins, and phosphorus participates in nucleic acid and energy metabolism; if the ratio is unbalanced, it will lead to limited microbial growth or abnormal metabolism.

[0011] Furthermore, in S2, the anode material of the main electrode plate is titanium plated with ruthenium-iridium, and the cathode material includes any one of stainless steel or titanium alloy; the electrode spacing is 8-20cm; the dissolved oxygen concentration in the anode area is ≤0.2mg / L, and the dissolved oxygen concentration in the cathode area is 2.0-4.0mg / L; the anode area and the cathode area are separated by a diaphragm, and the diaphragm type includes any one of SPEEK-2560a, SPEEK-5060a, Nafion 117 and Nafion 211.

[0012] The anode is made of titanium plated with ruthenium-iridium, and the cathode is made of stainless steel or titanium alloy. Both have high oxygen evolution overpotential and electrochemical stability, and can operate stably for a long time without corrosion under low current density. The electrode spacing is set to 8-20cm, which can not only avoid the blockage of the electrode by suspended matter in RO concentrate, but also ensure that the electric field penetrates the packing bed uniformly under low current and maintains a stable potential gradient.

[0013] The anaerobic environment in the anode zone is created to allow electroactive microorganisms to oxidize organic matter under anaerobic conditions, releasing electrons and protons. Excessive oxygen intrusion directly consumes organic matter, severely inhibiting electricity generation and microbial degradation. The cathode zone utilizes aerobic bacteria for organic matter degradation and water denitrification. Oxygen acts as the electron acceptor, necessitating a certain oxygen content in the water.

[0014] The function of the diaphragm is to prevent oxygen from penetrating the water and affecting the treatment effect between the anode and cathode regions while allowing electron and material transfer.

[0015] Furthermore, the operating temperature inside the reactor in S2 is 20-35℃, and the hydraulic retention time is 12-24h.

[0016] The operating temperature and residence time here ensure that the biological activity of microorganisms is at its optimal level, and that wastewater and activated sludge have sufficient contact and reaction time, so that organic matter and nitrogen-containing pollutants can be fully degraded and transformed by microorganisms.

[0017] Furthermore, the microbial species in the anode zone of S2 include any one or more of Geobacterium, Clostridium, and Tauella; the microbial species in the anode zone include any one or more of Methanogenic bacteria, Nitrosomonas, and Methanobacterium; the initial addition of microbial species is controlled at 1-2% of the treated water volume; in the later stage, microbial species are added every 5-10 days, and the addition of microbial species is controlled at 0.1-0.5% of the treated water volume.

[0018] The anode zone is an anaerobic environment where the main function of microorganisms is to oxidize organic matter, releasing electrons and protons, and simultaneously reducing nitrate and nitrite nitrogen to N2, thus removing total nitrogen. Geobacterium, Clostridium, and Tauella are all well-studied electroactive bacteria that exhibit high activity in various microbial electrolysis cells, while also demonstrating strong salt tolerance and adapting to the salinity of RO concentrate.

[0019] The cathode zone is an aerobic reducing environment where aerobic halophilic bacteria degrade the remaining COD and convert ammonia nitrogen in the water into nitrate or nitrite nitrogen through nitrification, providing electron acceptors for denitrification.

[0020] By adding new bacterial strains, the replacement of old strains with new ones can be ensured, and the composition of bacterial species can be adjusted according to changes in the water body.

[0021] Furthermore, the composite functional packing in S2 is a porous carbon-based composite material doped with non-metallic elements; the non-metallic elements include any one or more of nitrogen, boron, phosphorus and sulfur; the filling amount of the composite functional packing accounts for 40-70% of the effective volume of the reactor.

[0022] The non-metallic element-doped porous carbon-based composite material here completely eliminates the drawbacks of traditional metal catalysts, such as easy oxidation and passivation, easy dissolution and secondary pollution. The 40-70% filling amount not only ensures sufficient microbial attachment area and catalytic active sites, but also maintains good mass transfer channels in the reactor, preventing blockage and short-circuiting.

[0023] Furthermore, the non-metallic element is introduced through a doping precursor; the doping precursor includes one or more of urea, melamine, boric acid, phosphoric acid, ammonium dihydrogen phosphate, and thiourea.

[0024] Furthermore, the mass ratio of the carbon matrix to the non-metallic elements in the porous carbon-based composite material is (20-100):1; the carbon matrix includes one or more of granular activated carbon, carbon nanotubes, and graphite felt.

[0025] The (20-100):1 mass ratio here ensures sufficient doping active sites while avoiding excessive heteroatoms from damaging the conductivity and mechanical strength of the carbon skeleton, thus maintaining the long-term stability of the material. The selection of multi-dimensional conductive matrices such as particulate activated carbon, carbon nanotubes, or graphite felt helps to construct a through-type three-dimensional electron transport channel inside the filler, thereby enhancing electron transfer efficiency.

[0026] Furthermore, the low current density polarized electric field described in S3 is a DC electric field with a current density of 0.5-1.5 mA / cm² and a voltage of 4-6 V.

[0027] The current density here ensures the generation of sufficient ·OH free radicals to break down recalcitrant organic matter while effectively avoiding high energy consumption and electrode passivation. At the same time, this parameter range can precisely activate microbial activity to enhance their salt tolerance, achieving the optimal balance between the energy efficiency of electrochemical and biological treatment.

[0028] Furthermore, in S3, the sludge return ratio is controlled at 50-200%, maintaining the suspended solids concentration in the mixed liquor within the reactor at 2000-6000 mg / L.

[0029] This ratio ensures a sufficient concentration of microorganisms within the reactor, guaranteeing stable wastewater treatment results.

[0030] Furthermore, the sedimentation time in S3 is 3-4 hours; the filtration conditions include either an 800-mesh screen or a 10mm grid.

[0031] Beneficial technical effects:

[0032] This application presents a novel three-dimensional coupled biochemical oxidation treatment process for wastewater, achieving deep synergy between electrocatalytic oxidation and biodegradation. This process establishes a synergistic mechanism of "electrocatalysis enhancing biochemical treatment, and biochemical treatment supplementing electrocatalysis." On one hand, under a low-current electric field without high energy consumption, the catalytic packing particles are polarized and charged, forming numerous micro-electrolysis units and constructing a three-dimensional electrochemical reaction system. The generated strong oxidizing groups, such as ·OH, significantly enhance the system's ability to open rings and break chains of recalcitrant organic matter in RO concentrate. On the other hand, under a low-current-density polarized electric field, the micro-electrolysis reaction on the electrode surface significantly activates microbial enzyme activity, significantly enhancing the decomposition and metabolism of organic matter by microorganisms. Simultaneously, by utilizing the synergy of electric field regulation and aeration, simultaneous nitrification-denitrification denitrification is achieved in a single reactor, eliminating the need for complex multi-stage tank series connection. This solution solves the problem of high salt and high toxicity in RO concentrate leading to the paralysis of the biochemical system, achieving deep removal of COD, ammonia nitrogen, and total nitrogen at operating costs close to conventional biochemical methods. Attached Figure Description

[0033] Figure 1This is a schematic diagram of a three-dimensional coupled biochemical oxidation treatment process for RO concentrate; Detailed Implementation

[0034] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the embodiments of the present invention and the specific features in the embodiments are detailed descriptions of the technical solution of the present invention, rather than limitations thereof.

[0035] In the following examples, the RO concentrate was sourced from the same reference water: COD 500±50 mg / L, ammonia nitrogen 40±5 mg / L, total nitrogen 60±5 mg / L, TDS 25000±1000 mg / L, pH 8.0-8.5.

[0036] Example 1

[0037] like Figure 1 As shown, this embodiment provides a three-dimensional coupled biochemical oxidation treatment process for RO concentrate, including the following steps:

[0038] S1. Adjust the pH of the above RO concentrate to 6.5; add ammonium chloride and potassium dihydrogen phosphate to the concentrate, and control the C:N:P mass ratio of the pretreated wastewater to 100:3:0.5.

[0039] S2. A nitrogen-doped porous carbon-based composite material (using urea as a precursor, loaded onto graphite felt via high-temperature pyrolysis) with an attached biofilm is filled between the main electrode plates in the reactor, accounting for 40% of the reactor's effective volume. The mass ratio of carbon matrix to non-metallic elements in the porous carbon-based composite material is 20:1. The anode is made of titanium plated with ruthenium-iridium, and the cathode is made of stainless steel, with an electrode spacing of 8 cm.

[0040] Pretreated wastewater was introduced, and a low-current-density polarized electric field was applied at a current density of 0.5 mA / cm² and a voltage of 4 V. The reactor operating temperature was 20℃, and the hydraulic retention time was 12 h. The dissolved oxygen concentration in the reactor was controlled by aeration: 0.2 mg / L in the anode zone and 2.0 mg / L in the cathode zone. The anode and cathode zones were separated by a SPEEK-2560a membrane.

[0041] The microorganisms in the anode zone include Geobacterium and Clostridium; the microorganisms in the cathode zone include Methanogenic bacteria and Methanobacterium. Initially, the amount of microbial inoculum added is controlled at 1% of the treated water volume; subsequently, microbial inoculum is added every 5 days, with the amount added controlled at 0.1% of the treated water volume.

[0042] S3. After effluent is discharged, it settles for 3 hours, then filters through an 800-mesh sieve, controlling the sludge return ratio at 50% and maintaining the suspended solids concentration of the mixed liquor in the reactor at 2000 mg / L.

[0043] Example 2

[0044] like Figure 1 As shown, this embodiment provides a three-dimensional coupled biochemical oxidation treatment process for RO concentrate, including the following steps:

[0045] S1. Adjust the pH of the above RO concentrate to 7.0; add sodium nitrate and potassium dihydrogen phosphate to the concentrate, and control the C:N:P mass ratio of the pretreated wastewater to 100:4:0.75.

[0046] S2. A boron-phosphorus co-doped porous carbon-based composite material (using boric acid and ammonium dihydrogen phosphate as precursors, loaded onto carbon nanotubes via high-temperature pyrolysis) is filled between the main electrode plates in the reactor, accounting for 50% of the reactor's effective volume. The mass ratio of carbon matrix to non-metallic elements in the porous carbon-based composite material is 100:1. The anode electrode is made of titanium plated with ruthenium-iridium, and the cathode is made of titanium alloy, with a plate spacing of 20 cm.

[0047] Pretreated wastewater was introduced, and a low-current-density polarized electric field was applied at a current density of 1.5 mA / cm² and a voltage of 6 V. The reactor operating temperature was 27℃, and the hydraulic retention time was 18 h. The dissolved oxygen concentration in the reactor was controlled by aeration: 0.15 mg / L in the anode zone and 3.0 mg / L in the cathode zone. The anode and cathode zones were separated by a SPEEK-5060a membrane.

[0048] The microorganisms in the anode zone include Geobacterium and Tauella; the microorganisms in the cathode zone include Methanotherium and Nitrosomonas. Initially, the amount of microbial inoculum added is controlled at 1.2% of the treated water volume; subsequently, microbial inoculum is added every 8 days, with the added inoculum controlled at 0.3% of the treated water volume.

[0049] S3. After effluent sedimentation for 3.5 hours, the effluent is then filtered through an 800-mesh sieve. Solid-liquid separation is performed on the effluent, and the sludge return ratio is controlled at 125% to maintain the suspended solids concentration in the mixed liquor of the reactor at 4000 mg / L.

[0050] Example 3

[0051] like Figure 1 As shown, this embodiment provides a three-dimensional coupled biochemical oxidation treatment process for RO concentrate, including the following steps:

[0052] S1. Adjust the pH of the above RO concentrate to 7.5; add urea and disodium hydrogen phosphate to the concentrate, and control the C:N:P mass ratio of the pretreated wastewater to 100:5:1.

[0053] S2. A sulfur-doped porous carbon-based composite material (using thiourea as a precursor, loaded onto granular activated carbon via high-temperature pyrolysis) with a biofilm attached is filled between the main electrode plates in the reactor, accounting for 70% of the reactor's effective volume. The mass ratio of carbon matrix to non-metallic elements in the porous carbon-based composite material is 60:1. The anode electrode is made of titanium plated with ruthenium-iridium, and the cathode is made of stainless steel, with a plate spacing of 12 cm.

[0054] Pretreated wastewater was introduced, and a low-current-density polarized electric field was applied at a current density of 1.0 mA / cm² and a voltage of 5 V. The reactor operating temperature was 30℃, and the hydraulic retention time was 18 h. The dissolved oxygen concentration in the reactor was controlled by aeration: 0.1 mg / L in the anode zone and 4.0 mg / L in the cathode zone. The anode and cathode zones were separated by a Nafion 211 membrane.

[0055] The microorganisms in the anode zone include Clostridium and Taunerella; the microorganisms in the cathode zone include Methanogenic bacteria and Methanobacteria. Initially, the amount of microbial inoculum added is controlled at 2% of the treated water volume; subsequently, microbial inoculum is added every 10 days, with the amount added controlled at 0.5% of the treated water volume.

[0056] S3. After effluent sedimentation for 4 hours, the effluent is then filtered through an 800-mesh screen. Solid-liquid separation is performed on the effluent, and the sludge return ratio is controlled at 200% to maintain the suspended solids concentration in the mixed liquor in the reactor at 6000 mg / L.

[0057] Comparative Example 1

[0058] The difference between this comparative example and Example 3 is that no DC electric field was added; all other process conditions are the same.

[0059] Comparative Example 2

[0060] The difference between this comparative example and Example 3 is that no microbial flora or composite functional filler was added; all other process conditions were the same.

[0061] Comparative Example 3

[0062] The difference between this comparative example and Example 3 is that no microbial flora was added, while the other process conditions were the same.

[0063] The wastewater treatment effects of the wastewater prepared in Examples 1-3 and Comparative Examples 1-3 were tested, and the results are shown in Table 1:

[0064] Table 1. Wastewater test results of the examples and comparative examples.

[0065]

[0066] As shown in Table 1, the treatment conditions in Examples 1-4 significantly improved the treatment effect on RO concentrate compared to those in Comparative Examples 1-3, demonstrating that this application organically combines electrochemical degradation with biofilm biochemical reactions, significantly enhancing wastewater treatment performance. This is because:

[0067] 1. In Examples 1-4, under a low current density polarized electric field, the composite functional filler particles are polarized and charged, forming numerous micro-electrolysis units, constructing a three-dimensional electrochemical reaction system. The generated strong oxidizing groups such as ·OH significantly enhance the system's ability to open rings and break chains of recalcitrant organic matter in RO concentrate, creating a non-toxic or low-toxic environment for subsequent microbial metabolic activities, and effectively removing ammonia nitrogen and total nitrogen from the wastewater.

[0068] 2. Low current density polarized electric fields can promote wastewater dissociation, producing trace amounts of hydrogen peroxide and nascent oxygen, which can provide sufficient dissolved oxygen for biofilms. At the same time, the electric field and the micro-electrolysis reaction on the electrode surface can activate the activity of microbial enzymes, significantly improving the decomposition and metabolism of organic matter by microorganisms. In addition, by utilizing the synergy of electric field regulation and aeration, simultaneous nitrification-denitrification denitrification is achieved in a single reactor, realizing the synergistic effect of biological denitrification and electrochemical denitrification.

[0069] Compared to Example 3, Comparative Example 1 did not apply a low-current-density polarized electric field. As a result, the large, recalcitrant organic molecules in the RO concentrate could not be polarized or broken down, nor could they generate in-situ strong oxidants (such as ·OH) to assist in chain disruption. Faced with high-concentration, recalcitrant RO concentrate, ordinary microorganisms exhibited extremely low metabolic activity due to the lack of electric field activation, and some even died in large numbers, leading to the system almost losing its biodegradation capacity and resulting in extremely poor RO concentrate treatment performance.

[0070] Compared with Example 3, Comparative Example 2 lacks microbial communities and its composite functional fillers. Under a low current density polarized electric field, it can only react inefficiently on the electrode surface and cannot generate sufficient amounts of strong oxidants such as ·OH. At the same time, the absence of a biofilm to block the biological denitrification pathway leads to the failure of deep denitrification.

[0071] Compared to Example 3, Comparative Example 3 lacked microbial community attachment, resulting in the packing material only being able to exert limited physical adsorption and electrochemical catalysis effects, failing to form a complete biodegradation system. Due to the lack of microbial metabolic activity on the biofilm, the biological denitrification pathway was completely blocked. Relying solely on the low current density polarized electric field and the electrolytic reaction of the packing material was insufficient to complete the complex biochemical reaction process, ultimately leading to an extremely low total nitrogen removal rate.

[0072] In summary, this invention overcomes the bottleneck of traditional high-salinity wastewater treatment by organically combining a low-current polarized electric field, composite functional packing material, and a biofilm biochemical system. This system utilizes a low-current micro-electric field to activate microbial activity and induce the packing material to generate ·OH free radicals, achieving a highly efficient connection between "electrochemical catalysis and deep biofilm degradation." Simultaneously, a synchronous nitrification-denitrification microenvironment is constructed within a single reactor, achieving deep mineralization of recalcitrant organic matter and complete removal of total nitrogen with low energy consumption. Compared to single treatment processes, this invention exhibits significant synergistic effects and promising prospects for industrial application.

[0073] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A three-dimensional coupled biochemical oxidation treatment process for RO concentrate, characterized in that, Includes the following steps: S1. Adjust the pH of the RO concentrate and add nutrients to obtain pretreated wastewater; S2. Pretreated wastewater is introduced into a reactor filled with composite functional packing material, a low current density polarized electric field is applied, and the current density and oxygen concentration are adjusted to construct an anaerobic-aerobic biochemical reaction system in the reactor to degrade pollutants through electrochemical and biofilm biochemical reactions. S3. The reactor effluent is subjected to sedimentation and filtration to obtain qualified effluent, and some of the sludge deposited at the bottom is returned to the water pretreatment end, while maintaining the concentration of suspended solids in the mixed liquor in the reactor.

2. The three-dimensional coupled biochemical oxidation treatment process for RO concentrate according to claim 1, characterized in that, In S1, the pH of the RO concentrate is adjusted to 6.5-7.5; the nutrients include nitrogen and phosphorus sources; the nitrogen source includes any one or more of ammonium chloride, sodium nitrate and urea; the phosphorus source includes any one or more of potassium dihydrogen phosphate and disodium hydrogen phosphate; the C:N:P mass ratio of the pretreated wastewater is controlled to be 100:(3-5):(0.5-1).

3. The three-dimensional coupled biochemical oxidation treatment process for RO concentrate according to claim 1, characterized in that, In S2, the anode material of the main electrode plate used for electrochemical degradation includes titanium plated with ruthenium-iridium, and the cathode material includes any one of stainless steel or titanium alloy; the distance between the anode and cathode plates is 8-20 cm; the dissolved oxygen concentration in the anode area is ≤0.2 mg / L, and the dissolved oxygen concentration in the cathode area is 2.0-4.0 mg / L; the anode area and the cathode area are separated by a diaphragm, and the diaphragm type includes any one of SPEEK-2560a, SPEEK-5060a, Nafion 117 and Nafion 211.

4. The three-dimensional coupled biochemical oxidation treatment process for RO concentrate according to claim 1, characterized in that, The operating temperature inside the reactor in S2 is 20-35℃, and the hydraulic retention time is 12-24h.

5. The three-dimensional coupled biochemical oxidation treatment process for RO concentrate according to claim 3, characterized in that, In S2, the microbial species in the anode zone include any one or more of Geobacterium, Clostridium, and Tauella; the microbial species in the cathode zone include any one or more of Methanogenic bacteria, Nitrosomonas, and Methanobacterium; the initial addition of microbial species is controlled at 1-2% of the treated water volume; in the later stage, microbial species are added every 5-10 days, and the addition of microbial species is controlled at 0.1-0.5% of the treated water volume.

6. The three-dimensional coupled biochemical oxidation treatment process for RO concentrate according to claim 1, characterized in that, The composite functional packing in S2 is a porous carbon-based composite material doped with non-metallic elements; the non-metallic elements include any one or more of nitrogen, boron, phosphorus and sulfur; the filling amount of the composite functional packing accounts for 40-70% of the effective volume of the reactor.

7. The three-dimensional coupled biochemical oxidation treatment process for RO concentrate according to claim 6, characterized in that, The mass ratio of carbon matrix to non-metallic elements in the porous carbon-based composite material is (20-100):1; the carbon matrix includes any one or more of granular activated carbon, carbon nanotubes, and graphite felt.

8. The three-dimensional coupled biochemical oxidation treatment process for RO concentrate according to claim 1, characterized in that, The low current density polarized electric field described in S2 is a DC electric field with a current density of 0.5-1.5 mA / cm² and a voltage of 4-6 V.

9. The three-dimensional coupled biochemical oxidation treatment process for RO concentrate according to claim 1, characterized in that, In S3, the sludge return ratio is controlled at 50-200%, and the suspended solids concentration in the mixed liquor in the reactor is maintained at 2000-6000 mg / L.

10. The three-dimensional coupled biochemical oxidation treatment process for RO concentrate according to claim 1, characterized in that, The settling time in S3 is 3-4 hours; filtration conditions include using either an 800-mesh sieve or a 10mm grid.

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