Sewage treatment method

Abstract

The invention belongs to the technical field of sewage treatment, and particularly relates to a sewage treatment method. The method comprises the following steps: 1) injecting sewage into a sedimentation tank for standing, carrying out primary floc filtration on the sewage, adding a coagulant into the sewage, uniformly mixing, standing and filtering, and introducing the sewage into a chemical oxidation tank; (2) putting a photocatalytic material into the sewage, exposing the sewage to light, standing, and introducing the sewage into an aeration biological filter tank; and (3) adding a microbial agent into the sewage to carry out aeration treatment, carrying out electric flocculation and separation treatment on the sewage, and discharging treated water. According to the sewage treatment method provided by the invention, the content of pollutants such as inorganic salt and mineral substances in sewage is remarkably reduced, the degradation rate of the pollutants such as polycyclic aromatic hydrocarbon, long-chain alkane and cyclic compounds is increased, dissolved oxygen refluxed by the biological aerated filter is reduced, the sewage treatment effect is enhanced, and treated water can be directly discharged after the sewage treatment.

Description

Technical Field

[0001] The invention belongs to the technical field of sewage treatment, and in particular relates to a sewage treatment method. Background Art

[0002] With the accelerated development of urbanization and industrialization, the amount of sewage discharge is increasing. In order to reduce the pollution of pollutants to natural water bodies, protect aquatic ecosystems, and recycle and reuse water resources, a variety of sewage treatment methods have been developed in this field. Existing sewage treatment methods include: 1. Such as screening, flotation, and filtration, which can remove suspended solids and sediments in sewage; 2. Such as coagulation, neutralization, oxidation-reduction, and electrochemistry, which can change the properties of soluble pollutants and make them easy to remove; 3. Such as activated sludge method and biofilm reaction, which use the metabolic activities of microorganisms to decompose organic pollutants in sewage; 4. Such as ozone, ultraviolet light / hydrogen peroxide and photocatalytic oxidation, which can mineralize difficult-to-degrade organic matter by producing strong free radicals; 5. Such as microfiltration, ultrafiltration, nanofiltration, and reverse osmosis, which separate solutes in sewage through the selective permeability characteristics of semipermeable membranes.

[0003] For example, patent CN106927640B provides a sewage treatment method, including the following steps: the biochemical liquid enters the biochemical pool group through the biochemical liquid inlet and flows through the anaerobic biochemical pool, the anoxic biochemical pool and four aerobic biochemical pools in an overflow manner under the action of the height difference of the biochemical pool, and finally the light mud is discharged through the light component outlet; the heavy mud flows from the first aerobic biochemical pool to the anaerobic biochemical pool under the action of the conveying equipment, and finally the heavy mud is discharged through the heavy component outlet. This method can well separate suspended matter and water and play a role in purifying water bodies, but this method is not suitable for oilfield sewage treatment.

[0004] Oilfield wastewater contains C12-C40 hydrocarbons, petroleum and its derivatives, inorganic salts, minerals and other substances. In particular, polycyclic aromatic hydrocarbons, which are insoluble substances with high boiling and melting points, complex structures and strong stability, pose a serious potential threat to the ecological environment and human health. In addition, oilfield wastewater also contains other types of difficult-to-degrade pollutants, such as long-chain alkanes, cyclic compounds, etc. These compounds are also difficult to be biodegraded due to the stability of their chemical structures.

[0005] In summary, it is necessary to develop a new wastewater treatment method for highly stable, poorly soluble and difficult to degrade pollutants. Summary of the invention

[0006] In order to solve the problems that the insoluble organic matter in the current oilfield wastewater is difficult to degrade and the existing treatment processes generally have limited degradation rates of organic pollutants, the present invention provides a wastewater treatment method.

[0007] The objects of the present invention are: 1. Provide a method for treating sewage to remove pollutants; 2. Enhance the sewage treatment effect; 3. Improve the degradation rate of pollutants.

[0008] To achieve the above objectives, the present invention adopts the following technical solutions.

[0009] A sewage treatment method, The method comprises: 1) Pour the sewage into the sedimentation tank for static standing, conduct preliminary floc filtration on the sewage, add coagulant into the sewage to mix evenly, and after static standing and filtration treatment, pass the sewage into the chemical oxidation tank; 2) Add photocatalytic materials to the sewage, expose the sewage to light and let it stand, then pass the sewage into an aerated biological filtration tank; 3) Add bacterial agents to the sewage for aeration treatment, perform electrocoagulation and separation treatment on the sewage, and discharge the treated water.

[0010] As a preference, Step 1) The standing time is 5 to 15 hours; Step 1) The preliminary floc filtration is to pass the sewage through a coarse filter and a fine filter in sequence, and repeat the operation until the suspended particles in the sewage are less than or equal to 5000 mg / L; In step 1), the dosage of the coagulant is 0.1-0.2 g / L sewage.

[0011] As a preference, Step 1) The coagulant is prepared by the following method: Take 20-25 mL of water per gram of lignin, disperse the lignin in the water and mix evenly, heat it in a water bath to 70-80 °C, add a mixture of acrylamide and dimethyl carbonate, and drop 0.1-0.15 wt% of ammonium persulfate initiator. After the reaction is completed, wash the product with anhydrous ethanol, dry it, and grind it into powder; The dosage of the mixed liquid is 0.05-0.07 mL / mL of lignin aqueous dispersion, wherein the dosage of dimethyl carbonate is 3.17-3.80 mL / g of acrylamide.

[0012] As a preference, Step 2) the photocatalytic material is used in an amount of 0.1 to 0.2 g / L of sewage; The standing time in step 2) is 12 to 36 hours.

[0013] As a preference, Step 2) The photocatalytic material is prepared by the following method: Take 30-40 mL of hot water per gram of sodium bismuthate, disperse the sodium bismuthate in the hot water and mix evenly under light-proof conditions, add 0.29-0.37 g of titanium dioxide per gram of sodium bismuthate, add the solution to a reactor, keep the temperature at 180-200 °C for 4-5 hours, wait for the reaction to be completed, cool the reactor to room temperature, wash the product and dry it.

[0014] As a preference, Step 3) The dosage of the bacterial agent is 5-10 mL / L sewage.

[0015] As a preference, Step 3) The preparation method of the bacterial agent is: A 1.0-1.5 mg / mL Pseudomonas aeruginosa solution was cultured at 20-28°C with low-speed shaking for 8-12 h, centrifuged for 20-30 min, and the supernatant was added with an equal volume of 0.3-0.8 mg / mL Phanerochaete chrysosporium solution and cultured for 3-5 d.

[0016] As a preference, Step 3) The aeration treatment is to continuously introduce air into the sewage and keep the sewage stirred.

[0017] As a preference, Step 3) The electrocoagulation process is as follows: Aluminum and / or iron and / or graphite are selected as anodes, NaCl is selected as conductive salt, the pH value of the sewage is adjusted to 6-7, the sewage flow rate is 1.5-2.5 L / min, and an external voltage of 10-12 V is maintained.

[0018] In the technical solution of the present invention, sludge particles, mineral particles, fiber suspension and other substances are first separated by floc filtration. However, hydrophilic polymers, extracellular polymers and other substances are closely combined with the water body and cannot be completely removed by simple filter pressing. In order to peel off and aggregate these hydrophilic substances, the present invention uses a coagulant. Based on the fact that lignin is widely available and has not been fully and effectively utilized at present, the present invention modifies lignin and prepares a new type of coagulant.

[0019] First, the rigid aromatic ring structure of lignin provides good support for the coagulant skeleton, which is conducive to the formation of a hard porous grid skeleton. This structure associates with the hydrophobic structure of extracellular polymers, improving their dehydration and thus the compressibility of the flocs. The bound water in the sludge flocs flows out, the overall pH value of the sewage decreases, and the content of organic matter in the sewage that can be oxidized by chemical oxidants increases, which is conducive to the subsequent oxidation treatment to further remove organic pollutants.

[0020] Secondly, with the graft copolymerization reaction of a large amount of acrylamide, the cationic groups on the coagulant and the negatively charged sludge particles and colloids undergo a more complete electrical neutralization. As the compressibility of the sludge flocs increases, the bound water in the sludge flocs flows out, the overall pH value of the sewage decreases, the long-chain bridging causes the flocs to aggregate, and the extracellular polymer content of the sludge flocs decreases rapidly. At the same time, pollutants containing aromatic isocyanates or aromatic primary amines produced by azo dyes and reducing substances have similarities with the aromatic ring structure of the coagulant, the pollutants are hydrophobically associated with the coagulant, and the extracellular polymer content is significantly reduced. The pollutant particles aggregate, the sludge flocs are more compact, high in density, and large in size, and the flocs can be removed by simple operations such as salvage, membrane treatment, and filtration.

[0021] However, the coagulation effect did not increase when the dosage of acrylamide was continued to increase. Instead, the extracellular polymer content of the sludge flocs increased slightly. This is because the grafting rate of the coagulant is limited, the positive charge on the surface of the sludge flocs increased significantly, and a re-stabilization effect occurred. At this time, the dewaterability of the sludge deteriorated, and the overall pH value of the sewage changed little. More importantly, the conversion rate of organic matter that can be removed by oxidation was low. Sampling and characterization of the sewage after oxidation treatment found that the degradation rates of polycyclic aromatic hydrocarbons such as naphthalene and phenanthrene, phenol, and plant surfactant fulvic acid were low. There are also oil agents and polymers of various molecular weights in the sewage. These substances are dispersed in the water and are difficult to coagulate and settle.

[0022] For compounds that are difficult to degrade, the present invention will photocatalytically oxidize sewage. Titanium dioxide is commonly used as a photocatalytic material in this field. Although titanium dioxide is resistant to photocorrosion, non-toxic, and low in cost, it only has a high absorption rate for ultraviolet light and insufficient photocatalytic efficiency, which limits its application. In order to improve the separation ability of titanium dioxide for photogenerated electron-hole pairs and construct a wide spectrum response material, the present invention prepares a new composite catalytic material. The hydroxyl groups on titanium dioxide supplement vacancies, and hydrogen atoms migrate to the vicinity of the lattice oxygen of the bismuth mixed valence compound. When TiO2 is embedded in the bismuth mixed valence compound, the interlayer spacing increases and the pore volume becomes larger. Not only does it increase the specific surface area of ​​the material, it also enhances the flowability of organic pollutants, which is conducive to promoting photocatalytic reactions. Microscopically, the material presents a structure in which nanorods and nanosheets intersect to form a conical protrusion. In coordination with this layered structure, the active sites on the surface of the bismuth mixed valence compound and the electrostatic attraction between the unit cells of titanium dioxide and the bismuth mixed valence compound promote the uniform adsorption of titanium dioxide, which is conducive to the rapid transfer of electrons between interfaces.

[0023] The system is rich in Bi 3+ 、Bi 5+Mixed valence compounds introduce a large number of oxygen vacancies, allowing the photocatalytic material to effectively reduce the recombination rate of photogenerated electron-hole pairs in ultraviolet, visible and near-infrared light environments, while generating strong oxidizing free radicals to adsorb organic pollutants and degrade them efficiently in situ. After the chemical oxidation tank, the content of pollutants such as polycyclic aromatic hydrocarbons in the sewage was significantly reduced.

[0024] After characterization, it was found that sewage still contains a small amount of petroleum hydrocarbons that are difficult to degrade. Bacteria, fungi, and algae are commonly used in the field for degradation. Pseudomonas aeruginosa uses the energy generated by metabolism to transport medium- and long-chain alkanes into cells. In the case of high dissolved oxygen content, pollutants are completely decomposed. However, if the dissolved oxygen content in the water body is insufficient after discharge, Pseudomonas aeruginosa will adaptively mutate to form an anaerobic or facultative anaerobic bacterium, which will produce gases such as ammonia and methane after anaerobic metabolism in coordination with other anaerobic bacteria. At the same time, the cyclic organic matter rich in sewage is also difficult to degrade, and its electrophilic substitution and oxidation activity are poor. The present invention degrades these organic compounds through biological metabolism. In order to ensure the degradation rate of medium- and long-chain alkanes and improve the degradation ability of complex heterocyclic compounds, the present invention compounded a bacterial agent. Another type of chrysosporium tricholoma uses pyrimidine as a carbon and nitrogen source to assist in stimulating the activity of Pseudomonas aeruginosa, avoid anaerobic variation of Pseudomonas aeruginosa, and selectively promote medium- and long-chain alkanes, heterocyclic compounds and other difficult-to-degrade petroleum hydrocarbons. Phanerochaete chrysosporium degrades sulfonamide pyrimidines, such as sulfadimethylpyrimidine, which removes sulfur dioxide to generate pyrimidine ring and aniline ring free radicals. In the product obtained by the inter-ring coupling between the two, the CN bond is attacked by the free radical and broken. A series of ring opening and bond breaking form simple and harmless organic substances such as hydroxylated derivatives, formylated derivatives, deamination products, and open-ring compounds, which are beneficial to reduce the environmental burden.

[0025] After characterization, it was found that the hyphae were entangled and complemented each other. The combination of the two bacterial agents created an environmental condition that was conducive to the long-term survival of the bacterial agents and the stable degradation of petroleum hydrocarbons. Cultivating bacteria in sequence could produce a higher degradation rate. More importantly, the compounding should be based on the physiology of Pseudomonas aeruginosa itself. If Acinetobacter oleophilus was added, the two would compete for the degradation of medium- and long-chain alkanes, which would cause the degradation effect of the bacterial agent to deteriorate, and more oil would be detected in the treated water.

[0026] Finally, the electrocoagulation process of the present invention generates OH in the water. -ions, precipitated insoluble inorganic salts such as iron salts and manganese salts, and the metal salt hydrolysis products formed by hydrolysis aggregated magnetic suspended particles, which can be removed by magnetic separation equipment. In this process, if the pH value of the sewage is too low, the electrodes will be severely corroded, the reduction effect of the metal salts in the sewage will be reduced, and the content of the metal salt hydrolysis products will decrease significantly, resulting in a poor flocculation effect. If the sewage is alkaline, the reduction rate of metal ions with low reduction potential will become slower. At the same time, in order to reduce the concentration difference during sewage electrolysis, the present invention continuously introduces sewage and maintains its flow state, ensuring that a certain concentration of metal ions undergoes a reduction reaction on the electrode. Similarly, in order to ensure that there are enough electrons involved in the reduction reaction, the present invention controls the applied voltage to 10 to 12 V.

[0027] The beneficial effects of the present invention are as follows: (1) The present invention provides a sewage treatment method, which significantly reduces the content of pollutants such as inorganic salts and minerals in sewage; (2) The present invention reduces the dissolved oxygen in the aerated biological filter backflow and enhances the sewage treatment effect; (3) The present invention improves the degradation rate of pollutants such as polycyclic aromatic hydrocarbons, long-chain alkanes, and cyclic compounds. After the sewage treatment method of the present invention, the treated water can be directly discharged. DETAILED DESCRIPTION

[0028] The present invention is further described in detail below in conjunction with specific embodiments. Those of ordinary skill in the art will be able to implement the present invention based on these descriptions. In addition, the embodiments of the present invention involved in the following description are generally only embodiments of a part of the present invention, rather than all embodiments. Therefore, based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work should fall within the scope of protection of the present invention.

[0029] Unless otherwise specified, the raw materials used in the examples of the present invention are all commercially available or available to those skilled in the art; unless otherwise specified, the methods used in the examples of the present invention are all methods known to those skilled in the art.

[0030] Unless otherwise specified, the sewage used in the embodiments of the present invention comes from a sewage treatment plant.

[0031] Embodiment 1: A method for treating sewage, comprising: 1) Take 20 mL of water per gram of lignin, disperse the lignin in the water and mix evenly, heat it in a water bath to 80 °C, add 3.80 mL of dimethyl carbonate per gram of acrylamide and mix evenly, add 0.05 mL of acrylamide and dimethyl carbonate mixture per milliliter of lignin water dispersion, add 0.1 wt% ammonium persulfate initiator dropwise, after the reaction is completed, wash the product with anhydrous ethanol, dry the product, and grind it into powder to obtain a coagulant; 2) Pour the sewage into the sedimentation tank and let it stand for 5 hours. Pass the sewage through the coarse filter and the fine filter in turn. Repeat the operation until the suspended particles in the sewage are 5000 mg / L. Add 0.1 g of coagulant per liter of sewage to mix evenly. After standing and filtering, pass the sewage into the chemical oxidation tank. 3) In addition, 40 mL of hot water is taken for each gram of sodium bismuthate, and the sodium bismuthate is dispersed in the hot water and mixed evenly under light-proof conditions. 0.29 g of titanium dioxide is added for each gram of sodium bismuthate, and the solution is added to the reactor, and the temperature is kept constant at 200 °C for 4 h. After the reaction is completed and the reactor is cooled to room temperature, the product is washed and dried to obtain a photocatalytic material; 4) Add 0.1 g of photocatalytic material per liter of sewage, expose the sewage to 420 nm visible light for 12 hours, and pass the sewage into an aerated biological filtration tank; 5) Incubate the 1.0 mg / mL Pseudomonas aeruginosa solution at 25°C with low-speed shaking for 10 h, centrifuge for 20 min, take the supernatant and continue to add an equal volume of 0.3 mg / mL Phanerochaete chrysosporium solution, and cultivate for 3 days to obtain the bacterial agent; 6) Add 5 mL of bacterial agent per liter of sewage, continuously introduce air into the sewage, and keep stirring the sewage. Use aluminum as the anode and cathode of electrocoagulation, and NaCl as the conductive salt. Adjust the pH value of the sewage to 6, the sewage flow rate to 1.5 L / min, maintain an applied voltage of 10 V for electrocoagulation, and then use magnetic separation equipment to separate the flocculants and discharge the treated water.

[0032] The sewage and treated water in this example were characterized and tested, and the specific methods are as follows.

[0033] 1. Characterization of total organic carbon content of extracellular polymers: Take 10 mL of sewage and centrifuge for 10 min, extract the supernatant and filter it through a 0.5 μm filter membrane to obtain soluble extracellular polymers. Continue to add 0.1 wt% NaCl solution to the sewage to make it up to 10 mL, ultrasonically treat it for 15 min, centrifuge it for 10 min, extract the supernatant and filter it through a 0.5 μm filter membrane to obtain loosely bound extracellular polymers. Continue to add 0.1 wt% NaCl solution to the sewage to make it up to 10 mL, ultrasonically treat it for 5 min, keep it at 60 ℃ for 1 h, then centrifuge it for 10 min, extract the supernatant and filter it through a 0.5 μm filter membrane to obtain tightly bound extracellular polymers.

[0034] The HACH TOC total organic carbon analyzer was used to analyze each extracellular polymer, and the total organic carbon content of each extracellular polymer was determined by subtraction. Based on the total organic carbon content of each extracellular polymer in the untreated sewage, the change in total organic carbon of soluble extracellular polymer was recorded as A1, the change in total organic carbon of loosely bound extracellular polymer was recorded as A2, and the change in total organic carbon of tightly bound extracellular polymer was recorded as A3.

[0035] 2. Photocatalytic degradation effect of naphthalene and phenol: Measure the absorbance at the characteristic wavelengths of naphthalene and phenol before and after sewage treatment, and calculate the degradation rate D of naphthalene and phenol. The formula is: .

[0036] 3. Suspended matter and petroleum hydrocarbon removal performance: Determine the content of suspended matter and petroleum hydrocarbons in treated water.

[0037] 4.Metal ion removal rate experiment: The metal ion content in the sewage before and after treatment was measured by a Prade ion detector, and the metal ion removal rate was calculated.

[0038] The results are as follows.

[0039]

[0040] According to GB 1319391 HJ / T712001 standard, the detection limit of total organic carbon in treated water is 0.10 mg / L, and the lower limit of detection is 0.50 mg / L. According to the results, the total organic carbon detected in the treated water in this case is 0.18 mg / L. After characterization, the metal ion content is lower than 0.05 mg / L, among which no mercury compounds are detected. According to GB18918-2002 standard, it meets the first-level standard for daily surface water discharge. In summary, the treated sewage in this case can be discharged.

[0041] According to the results in the table, it can be seen that the content of soluble extracellular polymers and loosely bound extracellular polymers decreased significantly, while the content of tightly bound extracellular polymers changed little. This result shows that the coagulant removes extracellular polymers through electrical neutralization, especially for soluble extracellular polymers. This is because soluble extracellular polymers are ionic and have rich -OH, C=OO - When the cationic binding sites are in a loose state, the binding sites are fully exposed and can be rapidly aggregated through bridging; while the tightly bound extracellular polymers have abundant hydrophobic groups and their aggregation effect is significantly weaker. Under the irradiation of light, the photogenerated electrons are transferred from the bismuth mixed valence compound to titanium dioxide, promoting the separation of photogenerated electron-hole pairs. The photogenerated electrons react with oxygen to form ·O2 - Free radicals promote strong oxidation and degradation of organic pollutants. After catalytic oxidation by photocatalytic materials, the content of difficult-to-degrade compounds such as polycyclic aromatic hydrocarbons and petroleum hydrocarbons in sewage is significantly reduced; after aeration treatment, the dissolved oxygen concentration of treated water is appropriate, which is conducive to maintaining good water quality.

[0042] Embodiment 2: A method for treating sewage, comprising: 1) Take 20 mL of water per gram of lignin, disperse the lignin in the water and mix evenly, heat it in a water bath to 80 °C, add 3.48 mL of dimethyl carbonate per gram of acrylamide and mix evenly, add 0.05 mL of acrylamide and dimethyl carbonate mixture per milliliter of lignin water dispersion, add 0.1 wt% ammonium persulfate initiator dropwise, after the reaction is completed, wash the product with anhydrous ethanol, dry the product, and grind it into powder to obtain a coagulant; 2) Pour the sewage into the sedimentation tank and let it stand for 5 hours. Pass the sewage through the coarse filter and the fine filter in turn. Repeat the operation until the suspended particles in the sewage are 5000 mg / L. Add 0.1 g of coagulant per liter of sewage to mix evenly. After standing and filtering, pass the sewage into the chemical oxidation tank. 3) In addition, 40 mL of hot water is taken for each gram of sodium bismuthate, and the sodium bismuthate is dispersed in the hot water and mixed evenly under light-proof conditions. 0.29 g of titanium dioxide is added for each gram of sodium bismuthate, and the solution is added to the reactor, and the temperature is kept constant at 200 °C for 4 h. After the reaction is completed and the reactor is cooled to room temperature, the product is washed and dried to obtain a photocatalytic material; 4) Add 0.1 g of photocatalytic material per liter of sewage, expose the sewage to 420 nm visible light for 12 hours, and pass the sewage into an aerated biological filtration tank; 5) Incubate the 1.0 mg / mL Pseudomonas aeruginosa solution at 25°C with low-speed shaking for 10 h, centrifuge for 20 min, take the supernatant and continue to add an equal volume of 0.3 mg / mL Phanerochaete chrysosporium solution, and cultivate for 3 days to obtain the bacterial agent; 6) Add 5 mL of bacterial agent per liter of sewage, continuously introduce air into the sewage, and keep stirring the sewage. Use aluminum as the anode and cathode of electrocoagulation, and NaCl as the conductive salt. Adjust the pH value of the sewage to 6, the sewage flow rate to 1.5 L / min, maintain an applied voltage of 10 V for electrocoagulation, and then use magnetic separation equipment to separate the flocculants and discharge the treated water.

[0043] The sewage and treated water of this example were characterized and tested in the same manner as in Example 1, and the results are as follows.

[0044]

[0045] At a high electrical neutralization efficiency, the sludge has good dewatering property, which makes the sludge particles destabilized and aggregated. Due to the increased compressibility of the sludge flocs, the bound water in the sludge flocs flows out, the overall pH value of the sewage decreases, and the content of organic matter that can be oxidized by chemical oxidants in the sewage increases. Long-chain bridging causes the flocs to aggregate, and the extracellular polymer content of the sludge flocs decreases rapidly. At the same time, pollutants containing aromatic isocyanates or aromatic primary amines produced by azo dyes and reducing substances have similarities with the aromatic ring structure of the coagulant. The pollutants and coagulants are hydrophobically associated, and the extracellular polymer content is significantly reduced. Negatively charged sludge particles are adsorbed near the cationic groups, and ion exchange reactions occur. Due to the support of lignin, the residual mineral particles and fiber suspensions can smoothly enter the flocs, and the content of polluted particles is further reduced. The interlayer spacing of the pollutants increases, the surface area increases, and they carry positive charges, which weakens the electrostatic repulsion to metal ions, and the metal ions are complexed on their surface. According to the results in the table, the addition of acrylamide increases the grafting rate of the effective components and can significantly improve the flocculation effect.

[0046] In addition, the photocatalytic degradation experiment of Example 1 was repeated using 785 nm near-infrared light to excite the photocatalytic material, and the results were as follows.

[0047]

[0048] According to the results in the table, the photocatalytic material maintains good catalytic activity under the excitation of near-infrared light, proving that the photocatalytic material is wide-spectrum responsive and has a high utilization rate of sunlight. The theoretical band gap of the photocatalytic material is 1.6-1.7 eV. This material is superior to commercially available photocatalytic materials and has the ability to capture near-infrared photons.

[0049] Embodiment 3: A method for treating sewage, comprising: 1) Take 20 mL of water per gram of lignin, disperse the lignin in the water and mix evenly, heat it in a water bath to 80 °C, add 3.17 mL of dimethyl carbonate per gram of acrylamide and mix evenly, add 0.05 mL of acrylamide and dimethyl carbonate mixture per milliliter of lignin water dispersion, add 0.1 wt% ammonium persulfate initiator dropwise, after the reaction is completed, wash the product with anhydrous ethanol, dry the product, and grind it into powder to obtain a coagulant; 2) Pour the sewage into the sedimentation tank and let it stand for 5 hours. Pass the sewage through the coarse filter and the fine filter in turn. Repeat the operation until the suspended particles in the sewage are 5000 mg / L. Add 0.1 g of coagulant per liter of sewage to mix evenly. After standing and filtering, pass the sewage into the chemical oxidation tank. 3) In addition, 40 mL of hot water is taken for each gram of sodium bismuthate, and the sodium bismuthate is dispersed in the hot water and mixed evenly under light-proof conditions. 0.29 g of titanium dioxide is added for each gram of sodium bismuthate, and the solution is added to the reactor, and the temperature is kept constant at 200 °C for 4 h. After the reaction is completed and the reactor is cooled to room temperature, the product is washed and dried to obtain a photocatalytic material; 4) Add 0.1 g of photocatalytic material per liter of sewage, expose the sewage to 420 nm visible light for 12 hours, and pass the sewage into an aerated biological filtration tank; 5) Incubate the 1.0 mg / mL Pseudomonas aeruginosa solution at 25°C with low-speed shaking for 10 h, centrifuge for 20 min, take the supernatant and continue to add an equal volume of 0.3 mg / mL Phanerochaete chrysosporium solution, and cultivate for 3 days to obtain the bacterial agent; 6) Add 5 mL of bacterial agent per liter of sewage, continuously introduce air into the sewage, and keep stirring the sewage. Use aluminum as the anode and cathode of electrocoagulation, and NaCl as the conductive salt. Adjust the pH value of the sewage to 6, the sewage flow rate to 1.5 L / min, maintain an applied voltage of 10 V for electrocoagulation, and then use magnetic separation equipment to separate the flocculants and discharge the treated water.

[0050] The sewage and treated water of this example were characterized and tested in the same manner as in Example 1, and the results are as follows.

[0051]

[0052] Continuing to increase the dosage of acrylamide, the coagulation effect did not increase. Due to the limited grafting rate of the coagulant, the positive charge on the surface of the sludge flocs increased significantly, and a re-stabilization effect occurred. In the process of the coagulant inhibiting extracellular polymers, some soluble extracellular polymers and loosely bound extracellular polymers were converted into tightly bound extracellular polymers, resulting in a slight increase in the content of tightly bound extracellular polymers. At the same time, the flocs disintegrated and dispersed. Since the dehydration of the sludge deteriorated and the compressibility decreased at this time, it was difficult to remove fine particles by filtration, resulting in an abnormal increase in the content of suspended matter. In addition, the overall pH value of the sewage changed little, and the conversion rate of organic matter that could be removed by oxidation was low. The sampling and characterization of the sewage after oxidation treatment found that the degradation rates of naphthalene and phenol decreased slightly.

[0053] In combination with Examples 1 to 3, with the graft copolymerization reaction of a large amount of acrylamide, the extracellular polymer content of the sludge flocs decreased rapidly and then tended to be stable, and the coagulant had a strong targeted removal effect on soluble extracellular polymers and loosely bound extracellular polymers.

[0054] Comparative Example 1: A sewage treatment method, the method comprising: 1) Take 20 mL of water per gram of lignin, disperse the lignin in the water and mix evenly, heat it in a water bath to 80 °C, add 3.48 mL of dimethyl carbonate per gram of acrylamide and mix evenly, add 0.05 mL of acrylamide and dimethyl carbonate mixture per milliliter of lignin water dispersion, add 0.1 wt% ammonium persulfate initiator dropwise, after the reaction is completed, wash the product with anhydrous ethanol, dry the product, and grind it into powder to obtain a coagulant; 2) Pour the sewage into the sedimentation tank and let it stand for 5 hours. Pass the sewage through the coarse filter and the fine filter in turn. Repeat the operation until the suspended particles in the sewage are 5000 mg / L. Add 0.1 g of coagulant per liter of sewage to mix evenly. After standing and filtering, pass the sewage into the chemical oxidation tank. 3) Add 0.1 g TiO2 per liter of sewage, expose the sewage to 420 nm visible light for 12 hours, and pass the sewage into an aerated biological filter tank; 4) Incubate the 1.0 mg / mL Pseudomonas aeruginosa solution at 25°C with low-speed shaking for 10 h, centrifuge for 20 min, take the supernatant and continue to add an equal volume of 0.3 mg / mL Phanerochaete chrysosporium solution, incubate for 3 days, and obtain the bacterial agent; 5) Add 5 mL of bacterial agent per liter of sewage, continuously introduce air into the sewage, and keep stirring the sewage. Use aluminum as the anode and cathode of electroflocculation, and NaCl as the conductive salt. Adjust the pH value of the sewage to 6, the sewage flow rate to 1.5 L / min, maintain an applied voltage of 10 V for electrocoagulation, and then use magnetic separation equipment to separate the flocculants and discharge the treated water.

[0055] The sewage and treated water of this example were characterized and tested in the same manner as in Example 1, and the results are as follows.

[0056]

[0057] According to the results in the table, the photocatalytic efficiency of the photocatalytic material in this example is low under visible light. Compared with Example 2, the photocatalytic material in this example has a smaller specific surface area, and the pore volume is not enough to pass organic pollutants; there are fewer active sites, and the photocatalytic material is agglomerated when put into water, which hinders electron transfer. Since the photocatalytic material has few oxygen vacancies, the recombination rate of photogenerated electron-hole pairs is high, and the content of pollutants such as polycyclic aromatic hydrocarbons is high, the treated water cannot be discharged. Moreover, the catalytic activity is poor in the environment of ultraviolet light and near-infrared light. The sewage treatment method in this example has poor utilization of natural sustainable resources and has application limitations.

[0058] Comparative Example 2: A sewage treatment method, the method comprising: 1) Take 20 mL of water per gram of lignin, disperse the lignin in the water and mix evenly, heat it in a water bath to 80 °C, add 3.48 mL of dimethyl carbonate per gram of acrylamide and mix evenly, add 0.05 mL of acrylamide and dimethyl carbonate mixture per milliliter of lignin water dispersion, add 0.1 wt% ammonium persulfate initiator dropwise, after the reaction is completed, wash the product with anhydrous ethanol, dry the product, and grind it into powder to obtain a coagulant; 2) Pour the sewage into the sedimentation tank and let it stand for 5 hours. Pass the sewage through the coarse filter and the fine filter in turn. Repeat the operation until the suspended particles in the sewage are 5000 mg / L. Add 0.1 g of coagulant per liter of sewage to mix evenly. After standing and filtering, pass the sewage into the chemical oxidation tank. 3) In addition, 40 mL of hot water was taken for each gram of bismuth sulfide, and the bismuth sulfide was dispersed in the hot water and mixed evenly under light-proof conditions, and 0.29 g of titanium dioxide was added for each gram of bismuth sulfide. The solution was added to the reactor and kept at 200 °C for 4 h. After the reaction was completed and the reactor was cooled to room temperature, the product was washed and dried to obtain a photocatalytic material; 4) Add 0.1 g of photocatalytic material per liter of sewage, expose the sewage to 420 nm visible light for 12 hours, and pass the sewage into an aerated biological filtration tank; 5) Incubate the 1.0 mg / mL Pseudomonas aeruginosa solution at 25°C with low-speed shaking for 10 h, centrifuge for 20 min, take the supernatant and continue to add an equal volume of 0.3 mg / mL Phanerochaete chrysosporium solution, and cultivate for 3 days to obtain the bacterial agent; 6) Add 5 mL of bacterial agent per liter of sewage, continuously introduce air into the sewage, and keep stirring the sewage. Use aluminum as the anode and cathode of electrocoagulation, and NaCl as the conductive salt. Adjust the pH value of the sewage to 6, the sewage flow rate to 1.5 L / min, maintain an applied voltage of 10 V for electrocoagulation, and then use magnetic separation equipment to separate the flocculants and discharge the treated water.

[0059] The sewage and treated water of this example were characterized and tested in the same manner as in Example 1, and the results are as follows.

[0060]

[0061] In this example, bismuth sulfide is used instead of sodium bismuthate. This photocatalytic material has abundant oxygen vacancies, but the production cost of bismuth sulfide is high and the raw material consumption is high. The SO2 flue gas generated in its production process will pollute the environment. Sodium sulfide has a large band gap and mainly absorbs ultraviolet light, which limits its application. The most important thing is that the photocorrosion and photogenerated electron-hole pair recombination caused by the oxidation of sulfide ions will significantly reduce the photocatalytic efficiency, so the degradation rate of naphthalene and phenol in this example is reduced. In addition, bismuth sulfide is a semiconductor sulfide, and its stability is not as good as that of sodium bismuthate inorganic salt. Under high temperature environment, it is easy to oxidative decomposition. The insufficient stability and short cycle life of the photocatalytic material in this example will significantly increase the cost of sewage treatment.

[0062] Comparative Example 3: A sewage treatment method, the method comprising: 1) Take 20 mL of water per gram of lignin, disperse the lignin in the water and mix evenly, heat it in a water bath to 80 °C, add 3.48 mL of dimethyl carbonate per gram of acrylamide and mix evenly, add 0.05 mL of acrylamide and dimethyl carbonate mixture per milliliter of lignin water dispersion, add 0.1 wt% ammonium persulfate initiator dropwise, after the reaction is completed, wash the product with anhydrous ethanol, dry the product, and grind it into powder to obtain a coagulant; 2) Pour the sewage into the sedimentation tank and let it stand for 5 hours. Pass the sewage through the coarse filter and the fine filter in turn. Repeat the operation until the suspended particles in the sewage are 5000 mg / L. Add 0.1 g of coagulant per liter of sewage to mix evenly. After standing and filtering, pass the sewage into the chemical oxidation tank. 3) In addition, 40 mL of hot water is taken for each gram of sodium bismuthate, and the sodium bismuthate is dispersed in the hot water and mixed evenly under light-proof conditions. 0.29 g of titanium dioxide is added for each gram of sodium bismuthate, and the solution is added to the reactor, and the temperature is kept constant at 200 °C for 4 h. After the reaction is completed and the reactor is cooled to room temperature, the product is washed and dried to obtain a photocatalytic material; 4) Add 0.1 g of photocatalytic material per liter of sewage, expose the sewage to 420 nm visible light for 12 hours, and pass the sewage into an aerated biological filtration tank; 5) Incubate the 1.0 mg / mL Pseudomonas aeruginosa solution at 25°C with low-speed shaking for 10 h, centrifuge for 20 min, and take the supernatant for 3 days to obtain the bacterial agent; 6) Add 5 mL of bacterial agent per liter of sewage, continuously introduce air into the sewage, and keep stirring the sewage. Use aluminum as the anode and cathode of electrocoagulation, and NaCl as the conductive salt. Adjust the pH value of the sewage to 6, the sewage flow rate to 1.5 L / min, maintain an applied voltage of 10 V for electrocoagulation, and then use magnetic separation equipment to separate the flocculants and discharge the treated water.

[0063] The sewage and treated water of this example were characterized and tested in the same manner as in Example 1, and the results are as follows.

[0064]

[0065] Water-soluble or low-molecular-weight short-chain alkanes can be directly absorbed by Pseudomonas aeruginosa, which uses the energy generated by metabolism to transport medium- and long-chain alkanes. In the biological aeration tank, under the condition of high dissolved oxygen content, organic pollutants are thoroughly decomposed into carbon dioxide and water. However, after characterization, the dissolved oxygen content in the water body after discharge is low, which causes Pseudomonas aeruginosa to undergo adaptive mutations and form a facultative anaerobic bacteria, which cooperates with other anaerobic bacteria to produce ammonia, methane and other gases after anaerobic metabolism, and the rate of decomposition of organic pollutants is reduced, making it difficult to meet the national industrial water discharge standards. According to the results of characterization, Example 2 detected substances such as 6-hydroxypyrimidine, 5-formylpyrimidine, and carbon dioxide, while this example detected high levels of complex heterocyclic organics such as pyrimidine and pyridine, and the water quality was significantly deteriorated.

[0066] Comparative Example 4: A sewage treatment method, the method comprising: 1) Take 20 mL of water per gram of lignin, disperse the lignin in the water and mix evenly, heat it in a water bath to 80 °C, add 3.48 mL of dimethyl carbonate per gram of acrylamide and mix evenly, add 0.05 mL of acrylamide and dimethyl carbonate mixture per milliliter of lignin water dispersion, add 0.1 wt% ammonium persulfate initiator dropwise, after the reaction is completed, wash the product with anhydrous ethanol, dry the product, and grind it into powder to obtain a coagulant; 2) Pour the sewage into the sedimentation tank and let it stand for 5 hours. Pass the sewage through the coarse filter and the fine filter in turn. Repeat the operation until the suspended particles in the sewage are 5000 mg / L. Add 0.1 g of coagulant per liter of sewage to mix evenly. After standing and filtering, pass the sewage into the chemical oxidation tank. 3) In addition, 40 mL of hot water is taken for each gram of sodium bismuthate, and the sodium bismuthate is dispersed in the hot water and mixed evenly under light-proof conditions. 0.29 g of titanium dioxide is added for each gram of sodium bismuthate, and the solution is added to the reactor, and the temperature is kept constant at 200 °C for 4 h. After the reaction is completed and the reactor is cooled to room temperature, the product is washed and dried to obtain a photocatalytic material; 4) Add 0.1 g of photocatalytic material per liter of sewage, expose the sewage to 420 nm visible light for 12 hours, and pass the sewage into an aerated biological filtration tank; 5) Incubate the 0.3 mg / mL Phanerochaete chrysosporium solution at 25°C with low-speed shaking for 10 hours, centrifuge for 20 minutes, take the supernatant and continue to add an equal volume of 1.0 mg / mL Pseudomonas aeruginosa solution, and cultivate for 3 days to obtain the bacterial agent; 6) Add 5 mL of bacterial agent per liter of sewage, continuously introduce air into the sewage, and keep stirring the sewage. Use aluminum as the anode and cathode of electrocoagulation, and NaCl as the conductive salt. Adjust the pH value of the sewage to 6, the sewage flow rate to 1.5 L / min, maintain an applied voltage of 10 V for electrocoagulation, and then use magnetic separation equipment to separate the flocculants and discharge the treated water.

[0067] The sewage and treated water of this example were characterized and tested in the same manner as in Example 1, and the results are as follows.

[0068]

[0069] In this case, the speed of establishing the population of Pseudomonas aeruginosa was slow, and the effect of inhibiting the transformation of Pseudomonas aeruginosa into anaerobic or facultative anaerobic bacteria became worse, which not only led to the deterioration of the activity of Pseudomonas aeruginosa, but also affected the degradation effect of the bacterial agent on petroleum hydrocarbons such as medium- and long-chain alkanes and heterocyclic compounds due to the low population concentration. Complex heterocyclic compounds are difficult to break bonds, and the detected petroleum hydrocarbon content is high, which significantly affects the water quality.

[0070] Comparative Example 5: A sewage treatment method, the method comprising: 1) Take 20 mL of water per gram of lignin, disperse the lignin in the water and mix evenly, heat it in a water bath to 80 °C, add 3.48 mL of dimethyl carbonate per gram of acrylamide and mix evenly, add 0.05 mL of acrylamide and dimethyl carbonate mixture per milliliter of lignin water dispersion, add 0.1 wt% ammonium persulfate initiator dropwise, after the reaction is completed, wash the product with anhydrous ethanol, dry the product, and grind it into powder to obtain a coagulant; 2) Pour the sewage into the sedimentation tank and let it stand for 5 hours. Pass the sewage through the coarse filter and the fine filter in turn. Repeat the operation until the suspended particles in the sewage are 5000 mg / L. Add 0.1 g of coagulant per liter of sewage to mix evenly. After standing and filtering, pass the sewage into the chemical oxidation tank. 3) In addition, 40 mL of hot water is taken for each gram of sodium bismuthate, and the sodium bismuthate is dispersed in the hot water and mixed evenly under light-proof conditions. 0.29 g of titanium dioxide is added for each gram of sodium bismuthate, and the solution is added to the reactor, and the temperature is kept constant at 200 °C for 4 h. After the reaction is completed and the reactor is cooled to room temperature, the product is washed and dried to obtain a photocatalytic material; 4) Add 0.1 g of photocatalytic material per liter of sewage, expose the sewage to 420 nm visible light for 12 hours, and pass the sewage into an aerated biological filtration tank; 5) Incubate the 1.0 mg / mL Pseudomonas aeruginosa solution at 25°C with low-speed shaking for 10 h, centrifuge for 20 min, take the supernatant and add an equal volume of 0.3 mg / mL Acinetobacter oleophilus solution, incubate for 3 days, and obtain the bacterial agent; 6) Add 5 mL of bacterial agent per liter of sewage, continuously introduce air into the sewage, and keep stirring the sewage. Use aluminum as the anode and cathode of electrocoagulation, and NaCl as the conductive salt. Adjust the pH value of the sewage to 6, the sewage flow rate to 1.5 L / min, maintain an applied voltage of 10 V for electrocoagulation, and then use magnetic separation equipment to separate the flocculants and discharge the treated water.

[0071] The sewage and treated water of this example were characterized and tested in the same manner as in Example 1, and the results are as follows.

[0072]

[0073] Acinetobacter oleophilus competes with Pseudomonas aeruginosa for carbon sources such as C12-C30 alkanes, benzene, toluene, xylene, and catechol, and is unable to absorb and metabolize C6-C10 short-chain alkanes, and its transport effect on medium- and long-chain alkanes becomes poor. At the same time, carboxylic acid groups and amino groups affect the formation of biofilms by Acinetobacter oleophilus, which reduces the binding effect of cells on petroleum hydrocarbons after biological aeration. A high amount of oil and fat can still be detected in the treated water.

Claims

1. A sewage treatment method, characterized in that: The method comprises: 1) Pour the sewage into the sedimentation tank for static standing, conduct preliminary floc filtration on the sewage, add coagulant into the sewage to mix evenly, and after static standing and filtration treatment, pass the sewage into the chemical oxidation tank; 2) Add photocatalytic materials to the sewage, expose the sewage to light and let it stand, then pass the sewage into an aerated biological filtration tank; 3) Add bacterial agents to the sewage for aeration treatment, perform electrocoagulation and separation treatment on the sewage, and discharge the treated water.

2. A sewage treatment method according to claim 1, characterized in that: Step 1) The standing time is 5 to 15 hours; Step 1) The preliminary floc filtration is to pass the sewage through a coarse filter and a fine filter in sequence, and repeat the operation until the suspended particles in the sewage are less than or equal to 5000 mg / L; In step 1), the dosage of the coagulant is 0.1-0.2 g / L sewage.

3. A sewage treatment method according to claim 1 or 2, characterized in that: Step 1) The coagulant is prepared by the following method: Take 20-25 mL of water per gram of lignin, disperse the lignin in the water and mix evenly, heat it in a water bath to 70-80°C, add a mixture of acrylamide and dimethyl carbonate, and drop 0.1-0.15 wt% of ammonium persulfate initiator. After the reaction is completed, wash the product with anhydrous ethanol, dry it, and grind it into powder; The dosage of the mixed liquid is 0.05-0.07 mL / mL of lignin aqueous dispersion, wherein the dosage of dimethyl carbonate is 3.17-3.80 mL / g of acrylamide.

4. A sewage treatment method according to claim 1, characterized in that: Step 2) the photocatalytic material is used in an amount of 0.1 to 0.2 g / L of sewage; The standing time in step 2) is 12 to 36 hours.

5. A sewage treatment method according to claim 1 or 4, characterized in that: Step 2) The photocatalytic material is prepared by the following method: Take 30-40 mL of hot water per gram of sodium bismuthate, disperse the sodium bismuthate in the hot water and mix evenly under light-proof conditions, add 0.29-0.37 g of titanium dioxide per gram of sodium bismuthate, add the solution to a reactor, keep the temperature at 180-200 °C for 4-5 hours, wait for the reaction to be completed, cool the reactor to room temperature, wash the product and dry it.

6. A sewage treatment method according to claim 1, characterized in that: Step 3) The dosage of the bacterial agent is 5-10 mL / L sewage.

7. A sewage treatment method according to claim 1 or 6, characterized in that: Step 3) The preparation method of the bacterial agent is: A 1.0-1.5 mg / mL Pseudomonas aeruginosa solution was cultured at 20-28°C with low-speed shaking for 8-12 hours, centrifuged for 20-30 minutes, and the supernatant was added with an equal volume of 0.3-0.8 mg / mL Phanerochaete chrysosporium solution and cultured for 3-5 days.

8. A sewage treatment method according to claim 1, characterized in that: Step 3) The aeration treatment is to continuously introduce air into the sewage and keep the sewage stirred.

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