Electrochemical oxidation method for improving the biodegradability of organic wastewater through a non-radical route

Abstract

The application belongs to the field of water pollution control, and discloses an electrochemical oxidation method for improving the biodegradability of organic wastewater through a non-radical route, which comprises the following steps: sequentially pumping the organic wastewater into a grit chamber, a pH adjusting tank, a coagulation sedimentation tank, an electric conductivity adjusting tank, an electrochemical oxidation tank, a biochemical tank and a reverse osmosis device; wherein the sludge in the coagulation sedimentation tank enters a sludge thickening tank, and the supernatant in the sludge thickening tank is backflowed to the pH adjusting tank and the electric conductivity adjusting tank. The application is a method for improving the biodegradability of refractory organic wastewater by changing the active species in the electrochemical oxidation process, and the core idea is to convert the radical species OH originally playing a major role in organic pollutants into non-radical species singlet oxygen, and then generate organic matter with low toxicity and high molecular weight in the electrochemical oxidation process. The application greatly reduces the energy consumption of electrochemical oxidation treatment while improving the biodegradability of effluent, and expands the application of the electrochemical oxidation treatment method in refractory organic wastewater.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of water pollution control, and relates to an electrochemical oxidation method for improving the biodegradability of organic wastewater through a non-radical pathway. BACKGROUND

[0002] With the rapid development of China's industry, various chemical agents are applied to various industries, including pesticides, medicines, textiles, papermaking, printing and dyeing, chemical industry, etc. In the production and use of chemical drugs, wastewater containing refractory organic matter is generated. With the increase of synthetic organic matter, new types of organic compounds with complex structure are generated, including pesticides, surfactants, dyes, anilines and nitrobenzenes, polycyclic aromatic hydrocarbons, halogenated hydrocarbons, phenols, aromatic compounds, and lipids and oils in nitrogen-free organic matter. Most of the refractory organic wastewater has the characteristics of high chemical oxygen demand, high toxicity, high color, complex chemical composition, and poor biodegradability. If such wastewater is not properly treated, it will cause irreversible damage to the ecological environment.

[0003] The biological method has low treatment cost and low energy consumption, but the refractory organic wastewater has the characteristics of low biodegradability and high toxicity, so the refractory organic wastewater is not suitable for biological treatment; the traditional physical and chemical method has high economic cost and is easy to cause secondary pollution. In order to realize the safe treatment of refractory organic wastewater, high-efficiency and environmentally friendly treatment technology needs to be adopted to reduce the toxic effect of organic matter on microorganisms and improve the biodegradability of refractory organic wastewater, so as to provide favorable conditions for subsequent biochemical treatment, so as to realize the discharge or recycling of refractory organic wastewater.

[0004] Electrochemical oxidation method is widely used in the treatment of refractory organic wastewater due to its strong oxidation ability, strong controllability, no secondary pollution and mild reaction conditions. Electrochemical oxidation method is based on the electrochemical process of the oxidation of pollutants on the surface of the anode. According to different oxidation pathways, it can be divided into "direct electrochemical oxidation" and "indirect electrochemical oxidation". Direct electrochemical oxidation refers to that the organic pollutant molecules in the solution diffuse to the surface of the anode first, and then the organic pollutant molecules directly transfer electrons on the surface of the anode. Indirect electrochemical oxidation refers to the formation of active species (ROS) with strong oxidation performance on the surface of the anode, which further oxidizes the pollutant molecules. Finally, the pollutant molecules are degraded into small molecular organic matter or mineralized into carbon dioxide and water, realizing the purification of water quality. ROS includes free radical species (such as: ·OH, HO2·, O2 ·-) and non-radical species (such as: O3, singlet oxygen). Patent 202210383452.7 provides an electrochemical treatment device and process for improving the biodegradability of traditional Chinese medicine wastewater. The ·OH generated by the electrochemical oxidation process can increase the B / C of traditional Chinese medicine wastewater from about 0.5 to 0.8. However, ·OH is not selective in reaction, and is easily consumed by non-target pollutants in water, resulting in low current Faraday efficiency and high energy consumption in the actual application process. In addition, the biodegradability of the effluent treated by the technology through free radical species is improved by a small margin, which is not conducive to subsequent biochemical treatment. Compared with free radical species, singlet oxygen has a longer lifetime and stronger resistance to environmental medium interference. Patent 202311078342.0 externally adds excess peroxide (such as H2O2, persulfate) to the electrochemical system to generate non-radical species singlet oxygen, effectively improving the utilization efficiency of ROS. However, the generation of singlet oxygen by external chemicals is easy to produce by-products and cause secondary pollution to the water body, which is limited in actual application. SUMMARY

[0005] The present application is made in view of the above problems in the prior art. The purpose of the present application is to provide an electrochemical oxidation method for improving the biodegradability of organic wastewater through a non-radical route, which can greatly improve the biodegradability of organic wastewater, increase the utilization rate of energy, and reduce the consumption of external chemicals.

[0006] The technical scheme of the present application is as follows:

[0007] An electrochemical oxidation method for improving the biodegradability of organic wastewater through a non-radical route, comprising the following steps:

[0008] Step 1: Pump the organic wastewater into the sand settling tank through the conveying pipeline to remove part of the suspended solids and solid particles with relatively large specific gravity and particle size in the organic wastewater, and obtain the sand settling tank effluent;

[0009] Step 2: Pump the sand settling tank effluent into the pH adjusting tank through the conveying pipeline, adjust the pH to 6-9, and use the supernatant of the sludge concentration tank as pH adjusting water to obtain the pH adjusting tank effluent;

[0010] Step 3: Pump the pH adjusting tank effluent into the coagulation sedimentation tank through the conveying pipeline, remove part of the calcium and magnesium hardness, suspended solids and chemical oxygen demand in the wastewater, and then pump the generated sludge into the sludge concentration tank through the conveying pipeline to obtain the coagulation sedimentation tank effluent;

[0011] Step 4: Pump the coagulation sedimentation effluent into the conductivity adjusting tank through the conveying pipeline, adjust the conductivity to 500-5000 μS / cm, and use the supernatant of the sludge concentration tank as conductivity adjusting water to obtain the conductivity adjusting tank effluent;

[0012] Step 5, the conductivity adjustment tank effluent is pumped into the electrochemical oxidation tank through the conveying pipeline for electrochemical oxidation reaction to obtain the electrochemical oxidation tank effluent;

[0013] Step 6, the electrochemical oxidation tank effluent is pumped into the biochemical tank through the conveying pipeline, and the microorganisms are used to further treat the organic matters in the high biochemical wastewater to generate sludge which is conveyed into the sludge concentration tank, and the biochemical tank effluent is obtained;

[0014] Step 7, the biochemical tank effluent is pumped into the reverse osmosis device through the conveying pipeline, and the reverse osmosis membrane is used to remove the charged ions, inorganic matters, colloidal particles, bacteria and organic matters in the water to obtain the reverse osmosis product water which is discharged for use through the conveying pipeline.

[0015] The organic wastewater in step 1 includes the wastewater of agricultural activities such as farmland irrigation, crop planting and breeding industry, and the wastewater of industries such as metallurgy, papermaking, oil refining, pharmaceutical production, printing and dyeing and electroplating;

[0016] The types of the grit chamber in step 1 include horizontal flow grit chamber, aeration grit chamber, cyclone grit chamber, Dorr grit chamber, gravity grit chamber, pneumatic grit chamber and mechanical grit chamber, etc.

[0017] The pH adjusting agent used in the pH adjusting tank in step 2 includes acid adjusting agent and alkali adjusting agent, the acid adjusting agent includes hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, acetic acid and citric acid, etc., and the alkali adjusting agent includes sodium hydroxide, potassium hydroxide, sodium carbonate, sodium bicarbonate, potassium carbonate and potassium bicarbonate, etc.

[0018] The coagulant used in the coagulation sedimentation tank in step 3 is polyaluminum chloride, aluminum sulfate, ferric sulfate, ferric chloride, polyacrylamide, etc., the dosing range of aluminum sulfate, ferric sulfate and ferric chloride is 10-100 mg / L, the dosing range of polyaluminum chloride is 5-50 mg / L, and the dosing range of polyacrylamide is 1-5 mg / L;

[0019] The conductivity adjusting agent used in the conductivity adjusting tank in step 4 includes sodium chloride, sodium sulfate, potassium chloride and potassium sulfate, etc.

[0020] The electrode used in the electrochemical oxidation tank in step 5 has a shape including flat plate, net and porous, etc.

[0021] The anode used in the electrochemical oxidation tank in step 5 includes BDD, PbO2, SnO2, TiO2, Ti4O7, RuO2, IrO2 and modified materials thereof, and the cathode includes metal materials such as stainless steel, copper, iron, nickel, chromium and titanium, and carbon materials such as graphite, graphene, carbon black and carbon nanotube, etc.

[0022] The electrochemical oxidation tank described in step 5 is provided with multiple pairs of anode and cathode, and the distance between the anode and the cathode ranges from 1.5 to 4 cm;

[0023] The anode potential in the electrochemical oxidation tank described in step 5 is set to 1.23 to 2.73 V;

[0024] The hydraulic retention time in the electrochemical oxidation tank described in step 5 is set to 5 to 30 min;

[0025] The water flow operation mode in the electrochemical oxidation tank described in step 5 includes the zigzag type, Flow-by and Flow-through, etc.

[0026] The biochemical tank type described in step 6 includes anaerobic tank, aerobic tank, facultative tank, contact oxidation tank and biosorption tank, etc.

[0027] The reverse osmosis device described in step 7 adopts a tubular reverse osmosis membrane, the pore size is 0.1 to 10 nm, the diameter is 4 to 8 inches, and the length is 40 to 80 inches.

[0028] The mechanism of the method is that the main reason for the high energy consumption of electrochemical oxidation treatment of refractory organic wastewater and the small improvement range of the biodegradability of the effluent is the poor reaction selectivity of free radical species. By adjusting the anode-cathode distance, the operating anode potential and the hydraulic retention time and other conditions in the electrochemical system, the electrochemical system is changed from the free radical degradation path to the non-free radical degradation path. The advantage of the non-free radical path over the free radical path is that it is less affected by non-target substances in the actual water body. The low mineralization intermediates produced after key bond breaking or ring opening may have lower biological toxicity and higher biodegradability, and can be used as energy sources for microorganisms, thereby reducing the overall treatment energy consumption. Therefore, the method proposed in the present application avoids the high treatment energy consumption of organic wastewater caused by the poor reaction selectivity of free radical species, and changes ROS to singlet oxygen by controlling the electrochemical oxidation reaction conditions, effectively improves the energy utilization rate and the biodegradability of the effluent, so that the organic matter in the wastewater can be effectively utilized by the microorganisms in the subsequent biochemical treatment.

[0029] Compared with the prior art, the electrochemical oxidation method for improving the biodegradability of organic wastewater by a non-free radical pathway proposed in the present application has the following advantages:

[0030] (1) The application provides a method for improving the biodegradability of refractory organic wastewater by changing ROS of an electrochemical oxidation process, the core idea of which is to convert free radical species ·OH originally playing a major role in organic pollutants into non-free radical species singlet oxygen, and then generate organic matter with low toxicity and high molecular weight in the electrochemical oxidation process. The application greatly reduces the energy consumption of electrochemical oxidation treatment while improving the biodegradability of effluent, and expands the application of electrochemical oxidation treatment method in refractory organic wastewater.

[0031] (2) Non-free radical species have higher catalytic efficiency and stronger selectivity in complex water matrix, and are less affected by water quality. The invalid consumption of interfering substances to ROS can be effectively solved, and the utilization efficiency of ROS is improved, which widens the types of wastewater that can be used for electrochemical oxidation treatment and the application scenarios.

[0032] (3) The electrochemical oxidation effluent of the application can provide an energy source for microorganisms in subsequent biochemical treatment, and is friendly and green to biochemical treatment. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 Flow chart of the electrochemical oxidation method for improving the biodegradability of organic wastewater by non-free radical pathway according to the application;

[0034] Figure 2 Variation of chemical oxygen demand and biological oxygen demand with hydraulic retention time. DETAILED DESCRIPTION

[0035] The specific embodiments of the application will be further described in combination with the drawings and technical solutions.

[0036] Example 1:

[0037] A porous SnO2-Sb electrode was placed in an electrochemical oxidation tank as an anode, and a porous stainless steel electrode was used as a cathode, with an electrode spacing of 3 cm and an anode potential of 2.0 V. Wastewater with a conductivity of 500 μS / cm and containing 2.5 mg / L sulfamethoxazole (SMX) was added to the electrochemical oxidation tank. A peristaltic pump was started to circulate at a flow rate of 50 mL / min, and the electrolysis time was 14 min. The variation of chemical oxygen demand and biological oxygen demand of SMX in the electrochemical oxidation process with hydraulic retention time was determined by a chemical oxygen demand detector and a biological oxygen demand detector, and the B / C was calculated. The results are as follows Figure 2As shown, the B / C of SMX wastewater before electrolysis was 0.44, and the B / C of SMX wastewater decreased to 0.18 after 7.0 min of electrochemical oxidation treatment, at which time the SMX wastewater was less biodegradable, which can be due to the high toxicity of the degradation intermediates. When electrolysis was performed for 10.5 min, the B / C of SMX wastewater increased to 0.95, which was 2.2 times that before electrolysis, at which time the SMX wastewater was completely biodegradable. By controlling the hydraulic retention time of the reaction system, the biodegradability of the effluent can be effectively adjusted, thereby facilitating subsequent biochemical treatment.

[0038] Example 2

[0039] Based on Example 1, the anode material in the electrochemical oxidation tank was changed, and the other treatment conditions were the same as in Example 1. The anode materials used are shown in Table 1. After 14 min of electrolysis using a PbO2-Ce electrode, the B / C of SMX wastewater increased to 0.90, which was 2.0 times that before electrolysis. After 14 min of electrolysis using a Ti4O7-La electrode, the B / C of SMX wastewater increased to 1.08, which was 2.5 times that before electrolysis. After 14 min of electrolysis using a TiO2-Ga electrode, the B / C of SMX wastewater increased to 0.96, which was 2.2 times that before electrolysis. After 14 min of electrolysis using an IrO2 electrode, the B / C of SMX wastewater increased to 0.88, which was 2.4 times that before electrolysis. This shows that the electrochemical oxidation method for improving the biodegradability of organic wastewater through a non-radical pathway is suitable for different anode materials.

[0040] Table 1 B / C of SMX wastewater after treatment with different anode materials

[0041]

[0042]

[0043] Example 3

[0044] Based on Example 1, the electrode spacing in the electrochemical oxidation tank was changed, and the other treatment conditions were the same as in Example 1. The electrode spacing settings are shown in Table 2. When the electrode spacing was 0.5 cm, the B / C of SMX wastewater decreased from 0.44 to 0.36 after 14 min of electrolysis, which was because the electrode spacing was too small to achieve the transition from the radical pathway to the non-radical pathway, resulting in a high degree of mineralization of SMX in water and an inability to increase the B / C of the effluent. When the electrode spacing was 1.5 cm and 4 cm, the B / C changed similarly to Example 1. When the electrode spacing was 5 cm, the B / C of SMX wastewater was 0.47 after 14 min of electrolysis, which changed little compared to before electrolysis, which was because the electrode spacing was too large, resulting in a decrease in the transmission speed of electric charges, thereby reducing the efficiency of the reaction. This shows that a certain electrode spacing needs to be controlled to effectively achieve an increase in the B / C of the effluent of electrochemical oxidation.

[0045] Table 2 B / C of SMX wastewater after treatment with different electrode spacing

[0046]

[0047] Example 4:

[0048] Based on Example 1, the anode potential in the electrochemical oxidation tank was changed, and other treatment conditions were the same as those in Example 1. The anode potential settings are shown in Table 3. When the anode potential was 0.5 V, the B / C of the SMX wastewater after electrolysis for 14 min was still 0.44, which was consistent with that before degradation, because the anode potential was too low to effectively generate ROS to oxidize and degrade SMX. When the electrode spacing was 1.5 cm and 4 cm, the change in B / C was similar to that in Example 1. When the anode potential was 4.0 V, the B / C of the SMX wastewater after electrolysis for 14 min decreased from 0.44 to 0.18, because the anode potential was too high to make SMX degrade through the free radical pathway, resulting in a high degree of mineralization of SMX and an inability to improve the B / C of the effluent. This shows that a certain anode potential needs to be controlled to effectively improve the B / C of the electrochemical oxidation effluent.

[0049] Table 3 B / C of SMX wastewater after treatment with different anode potentials

[0050]

[0051] The specific embodiments described above are intended to be illustrative only and are not intended to limit the scope of the present application. For example, the skilled person will appreciate that other embodiments can be readily formed by modification, substitution or adaptation of the disclosed technology, and that such other embodiments are intended to fall within the scope of the present application.

Claims

1. An electrochemical oxidation method for improving the biodegradability of organic wastewater through a non-radical route, characterized by, The method comprises the following steps: Step 1, organic wastewater is pumped into a grit chamber through a conveying pipeline to remove part of suspended solids and solid particles with relatively large specific gravity and particle size in the organic wastewater, and to obtain effluent from the grit chamber; Step 2, the effluent from the grit chamber is pumped into a pH adjusting tank through a conveying pipeline, the pH is adjusted to 6-9, and the supernatant of the sludge concentration tank is used as pH adjusting water to obtain effluent from the pH adjusting tank; Step 3, the effluent from the pH adjusting tank is pumped into a coagulation sedimentation tank through a conveying pipeline, part of calcium and magnesium hardness, suspended solids and chemical oxygen demand in the wastewater are removed, the generated sludge is conveyed into a sludge concentration tank, and effluent from the coagulation sedimentation tank is obtained; Step 4, the effluent from the coagulation sedimentation tank is pumped into an electrical conductivity adjusting tank through a conveying pipeline, the electrical conductivity is adjusted to 500-5000 µS / cm, the supernatant of the sludge concentration tank is used as electrical conductivity adjusting water to obtain effluent from the electrical conductivity adjusting tank; Step 5, the effluent from the electrical conductivity adjusting tank is pumped into an electrochemical oxidation tank for electrochemical oxidation reaction to obtain effluent from the electrochemical oxidation tank; Step 6, the effluent from the electrochemical oxidation tank is pumped into a biochemical tank through a conveying pipeline, microorganisms are used to further treat organic matter in the high-biodegradability wastewater, the generated sludge is conveyed into a sludge concentration tank, and effluent from the biochemical tank is obtained; Step 7, the effluent from the biochemical tank is pumped into a reverse osmosis device, and the reverse osmosis membrane is used to remove charged ions, inorganic matter, colloidal particles, bacteria and organic matter in the water, and the produced reverse osmosis product water is discharged through a conveying pipeline for use; The electrochemical oxidation tank is provided with multiple pairs of anode and cathode, and the distance between the anode and the cathode is 1.5-4 cm; The electrochemical oxidation tank is provided with an anode potential of 1.23-2.73 V; The electrochemical oxidation tank is provided with a hydraulic retention time of 5-30 min.

2. The electrochemical oxidation method for improving the biodegradability of organic wastewater through a non-radical route according to claim 1, wherein in step 1, The organic wastewater includes wastewater from farmland irrigation, crop planting, aquaculture, metallurgy, papermaking, oil refining, pharmaceutical production, printing and dyeing, and electroplating; The type of the grit chamber is a horizontal flow grit chamber, an aerated grit chamber, a cyclone grit chamber, a Dorr grit chamber, a gravity grit chamber, a pneumatic grit chamber or a mechanical grit chamber.

3. The electrochemical oxidation method for improving the biodegradability of organic wastewater through a non-radical route according to claim 1, wherein in step 2, The pH adjusting tank additionally adds a pH adjusting agent, which includes an acidic adjusting agent and an alkaline adjusting agent, the acidic adjusting agent includes hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, acetic acid and citric acid, and the alkaline adjusting agent includes sodium hydroxide, potassium hydroxide, sodium carbonate, sodium bicarbonate, potassium carbonate and potassium bicarbonate.

4. The electrochemical oxidation method for improving the biodegradability of organic wastewater through a non-radical route according to claim 1, wherein in step 3, ​ ​ ​ The coagulant used in the coagulation sedimentation tank includes polyaluminum chloride, aluminum sulfate, ferric sulfate, ferric chloride and polyacrylamide; when aluminum sulfate, ferric sulfate or ferric chloride is selected, the dosing concentration is 10-100 mg / L; when polyaluminum chloride is selected, the dosing concentration is 5-50 mg / L; when polyacrylamide is selected, the dosing concentration is 1-5 mg / L.

5. The electrochemical oxidation method for improving the biodegradability of organic wastewater through a non-radical route according to claim 1, characterized in that, in step 4, The conductivity regulator additionally added in the conductivity adjustment tank includes sodium chloride, sodium sulfate, potassium chloride and potassium sulfate.

6. The electrochemical oxidation method for improving the biodegradability of organic wastewater through a non-radical route according to claim 1, characterized in that, in step 5, The shape of the electrode used is a flat plate; The anode used includes BDD, PbO2, SnO2, TiO2, Ti4O7, RuO2, IrO2 and modified materials thereof; The cathode used includes stainless steel, copper, iron, nickel, chromium, titanium, graphite, graphene, carbon black, carbon nanotubes; The water flow operation mode in the electrochemical oxidation tank includes a baffle type.

7. The electrochemical oxidation method for improving the biodegradability of organic wastewater through a non-radical route according to claim 1, characterized in that, in step 6, The type of the biochemical tank includes an anaerobic tank, an aerobic tank, a facultative tank, a contact oxidation tank and a biosorption tank.

8. The electrochemical oxidation method for improving the biodegradability of organic wastewater through a non-radical route according to claim 1, characterized in that, in step 7, The reverse osmosis device uses a tubular reverse osmosis membrane, the pore size is 0.1-10 nm, the diameter is 4-8 inches, and the length is 40-80 inches.

9. The electrochemical oxidation method for improving the biodegradability of organic wastewater through a non-radical route according to claim 1, characterized in that, in step 5, The shape of the electrode used is a mesh.

10. The electrochemical oxidation method for improving the biodegradability of organic wastewater through a non-radical route according to claim 1, characterized in that, in step 5, The shape of the electrode used is porous.

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