A sewage treatment process for removing polymorphous phosphorus pollutants

Abstract

The present application relates to the field of sewage treatment, and particularly relates to a sewage treatment process for removing multi-form phosphorus pollutants. The sewage treatment process comprises the following steps: putting sewage into a primary coagulation and sedimentation reaction tank, adding a water treatment coagulant for primary coagulation treatment, separating and precipitating to obtain first intermediate sewage; discharging the first intermediate sewage into a secondary biochemical tank for biological treatment to obtain second intermediate sewage; discharging the second intermediate sewage into a tertiary coagulation and sedimentation reaction tank, adding a water treatment coagulant and a multi-form phosphorus adsorbent for secondary coagulation treatment; the multi-form phosphorus adsorbent is a biochar modified by a metal salt and an organic nitrogen quaternary ammonium salt; the organic nitrogen quaternary ammonium salt is a short-chain organic nitrogen quaternary ammonium salt with a chain length of C3-C6; adding a flocculating agent for flocculation treatment, and separating and precipitating. The sewage treatment process can improve the effect of deep phosphorus removal, does not need to add new structures, is suitable for deep phosphorus removal in most sewage plants with tertiary coagulation reaction, and has low transformation cost.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of sewage treatment, in particular to a sewage treatment process for removing multi-form phosphorus pollutants. BACKGROUND

[0002] China is facing a serious water environmental pollution problem, among which phosphorus pollution has caused great influence on water ecological system and human life. Although phosphorus is essential for the growth and metabolism of living organisms, when it enters water bodies in excess, it will cause water eutrophication, thereby causing a series of serious ecological problems. In view of the fact that total phosphorus has become the main pollutant of surface water environment in China, many regions and basins have raised the sewage discharge standard based on their own water environmental conditions and pollution prevention and control needs, and have raised the total phosphorus discharge standard to 0.3 mg / L or 0.2 mg / L. The implementation of these more stringent standards is of great significance for reducing phosphorus pollution and improving water environmental quality.

[0003] At present, sewage treatment plants mainly add chemical phosphorus removal reagents, mainly iron salts or aluminum salts and the like coagulants, to the sewage in the reaction tank, so that the phosphorus is precipitated in the form of insoluble phosphate, thereby removing the phosphorus in the sewage. In order to meet the higher phosphorus removal standard, the sewage treatment plant needs to improve its phosphorus treatment capacity. In the pursuit of higher total phosphorus removal efficiency, the sewage treatment plant often chooses to increase the amount of chemical phosphorus removal reagents, especially iron salts or aluminum salts and the like coagulants, because this method is simple to operate and easy to implement. However, the effect of this method is affected by many factors. Anions such as silicate, bicarbonate and sulfate commonly existing in sewage can compete with phosphate for active binding sites of phosphorus removal reagents, thereby reducing the effective adsorption of reagents to phosphate. In addition, chemical phosphorus removal reagents mainly target inorganic phosphorus, and the treatment effect on organic phosphorus is poor. These factors together lead to a problem: in the process of pursuing deep phosphorus removal, a large amount of reagents must be put in, while the effective utilization rate of the reagents is relatively low. This not only increases the operating cost, but also leads to a significant increase in sludge production. The treatment and disposal of a large amount of sludge not only increases the environmental burden, but also increases the operating cost. Therefore, how to provide a sewage phosphorus removal method with high phosphorus removal efficiency and good economy has attracted more and more attention of those skilled in the art. SUMMARY

[0004] To solve or partially solve the problems in the related art, the present application provides a sewage treatment process for removing multi-form phosphorus pollutants.

[0005] The present application provides a sewage treatment process for removing multi-form phosphorus pollutants, which comprises:

[0006] Step a), putting the sewage into a primary coagulation and sedimentation reaction tank, adjusting the pH to 6.5-8.5, adding a water treatment coagulant for primary coagulation treatment, and separating and precipitating to obtain first intermediate sewage;

[0007] Step b), the first intermediate wastewater is discharged into a secondary biochemical tank for biological treatment to obtain second intermediate wastewater;

[0008] Step c), the second intermediate wastewater is discharged into a tertiary coagulation sedimentation tank, a water treatment coagulant and a multi-form phosphorus adsorbent are added for secondary coagulation treatment; the multi-form phosphorus adsorbent is a biochar modified by a metal salt and an organic nitrogen quaternary ammonium salt; the metal ion of the metal salt includes one or more of Ca 2+ , Mg 2+ , Mn 2+ and Fe 3+ , and the organic nitrogen quaternary ammonium salt is a short-chain organic nitrogen quaternary ammonium salt with a chain length of C3-C6;

[0009] Step d), a flocculating agent is added for flocculation treatment to separate and precipitate.

[0010] Further, the water treatment coagulant is an aluminum salt coagulant and / or an iron salt coagulant.

[0011] Further, the addition amount M1 of the water treatment coagulant in step a) is calculated according to formula I in terms of iron and / or aluminum:

[0012] M1 = a x B1 / 100 Formula I;

[0013] In formula I, a is an empirical constant, and the value range is 2-9; B1 is the concentration of total suspended phosphorus in the influent, g / m 3 ;

[0014] The addition amount M2 of the water treatment coagulant in step c) is calculated according to formula II in terms of iron and / or aluminum, and the addition amount M3 of the multi-form phosphorus adsorbent is calculated according to formula III:

[0015] M2 = b x 5 x C1 Formula II;

[0016] In formula II, b is an empirical constant, and the value range is 2-9; C1 is the concentration of dissolved orthophosphate phosphorus in the influent, g / m 3 ;

[0017] M3 = k x C2 Formula III;

[0018] In formula III, k is an empirical constant, and the value range is 100-500; C2 is the concentration of dissolved organic total phosphorus in the influent, g / m 3 .

[0019] Further, the primary coagulation treatment specifically includes rapid stirring for 1-5 min, slow stirring for 2-10 min, and standing for 1-4 h; the speed gradient value of the rapid stirring is >500 s -1, the speed gradient value of slow stirring is less than 100 s -1 ; the time of the secondary coagulation treatment is 1-10 min.

[0020] Further, the multi-form phosphorus adsorbent is prepared by the following method:

[0021] Step c1), the biochar material is placed in a nitric acid solution for stirring activation; the activated biochar material is sequentially washed and dried to obtain activated biochar;

[0022] Step c2), the activated biochar material is ball milled to obtain powder biochar with a diameter less than 0.1 mm;

[0023] Step c3), the powder biochar is added to a metal salt solution for impregnation treatment to obtain an impregnation treatment solution; the metal ions of the metal salt solution include one or more of Ca 2+ , Mg 2+ , Mn 2+ and Fe 3+ , and the solvent is water;

[0024] Step c4), an organic nitrogen quaternary ammonium salt is added to the impregnation treatment solution for hydrothermal reaction, the organic nitrogen quaternary ammonium salt is a short-chain organic nitrogen quaternary ammonium salt with a chain length of C3-C6; the reaction product is washed and dried to obtain a multi-form phosphorus adsorbent.

[0025] Further, in the step c1), the concentration of the nitric acid solution is 1-4 mol / L, and the mixing ratio of the biochar material to the nitric acid solution is 10-50 ml:1 g.

[0026] Further, in the step c3), the metal salt solution is a mixed solution of calcium chloride, magnesium chloride and manganese chloride; the concentration of calcium chloride, magnesium chloride and manganese chloride in the metal salt solution is 1-2 mol / L; and the mixing ratio of the metal salt solution to the biochar is 10-30 ml:1 g.

[0027] Further, in the step c3), the impregnation treatment is carried out under stirring, the stirring speed is 150-350 r / min, and the impregnation time is 20-30 h.

[0028] Further, in the step c4), the organic nitrogen quaternary ammonium salt is 3-chloropropyl trimethyl ammonium chloride, tetramethyl ammonium chloride or tetraethyl ammonium chloride; and the mass ratio of the added amount of the organic nitrogen quaternary ammonium salt to the biochar material is 2-5:1.

[0029] Further, in the step d), the temperature of the hydrothermal reaction is 70-80℃, and the reaction time is 4-8 h.

[0030] The sewage treatment process for removing polymorphic phosphorus pollutants provided by the application has the following beneficial effects:

[0031] 1) The method effectively removes polymorphic phosphorus pollutants in sewage through the combined action of physical, chemical and biological methods, thereby meeting more stringent discharge standards. In particular, in the final high-efficiency precipitation process, a traditional water treatment coagulant is used in combination with a polymorphic phosphorus adsorbent. The polymorphic phosphorus adsorbent has metal cations and quaternary ammonium cations loaded on the surface, so that the positively charged sites thereof are enhanced in adsorption capacity for low-concentration phosphate ions and anionic organic phosphorus in sewage; in addition, the functional groups such as metal complexes and quaternary ammonium salt groups loaded on the surface of the polymorphic phosphorus adsorbent further enhance the adsorption capacity for phosphate ions, while reducing the competitive effect of silicates on the active sites of the water treatment coagulant, reducing the interference effect of phosphorus adsorption, and the use of the polymorphic phosphorus adsorbent in combination with the water treatment coagulant can improve the effect of deep phosphorus removal.

[0032] 2) The polymorphic phosphorus adsorbent used in the method is prepared by modification of biomass charcoal, has a large specific surface area, a multi-level pore structure, and is widely available and easy to obtain, so it is easy to be applied in industry and realizes resource reuse.

[0033] 3) The method does not require the addition of new structures, is suitable for deep phosphorus removal in most sewage treatment plants containing a three-stage coagulation reaction, and has low modification cost.

[0034] It should be understood that the above general description and the following detailed description are only exemplary and explanatory, and cannot limit the application. DETAILED DESCRIPTION

[0035] The technical solutions in the embodiments of the application will be described below in a clear and complete manner. Obviously, the described embodiments are only some of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the application.

[0036] The terms used in the application are only for the purpose of describing specific embodiments, and are not intended to limit the application. The singular forms "a", "an" and "the" used in the application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise. It should also be understood that the term "and / or" used herein means and includes any or all possible combinations of one or more associated listed items.

[0037] It should be understood that, although the terms "first", "second", "third", etc. can be employed in describing various information in the present application, the information should not be limited to these terms. These terms are only used to distinguish one type of information from another. For example, the first information can also be referred to as the second information, and similarly, the second information can also be referred to as the first information, without departing from the scope of the present application. Therefore, the features defined with "first", "second" can explicitly or implicitly include one or more of the features. In the description of the present application, the meaning of "multiple" is two or more, unless otherwise specifically limited.

[0038] Currently, sewage treatment mainly adopts chemical precipitation method and biological phosphorus removal method. Compared with other processes, the adsorption method is simple to operate and raw materials are easy to obtain. In particular, the carbon-rich porous biochar produced by high-temperature pyrolysis of agricultural and forestry waste biomass under limited oxygen conditions has the characteristics of wide source, low cost, diverse functional groups and rich porous structure, and has great potential for removing pollutants in water. At the same time, biochar itself can be used as a soil conditioner, and the adsorbed phosphorus is not only a pollutant but also a nutrient. The biochar after adsorbing phosphorus can be applied to agriculture as a fertilizer, realizing resource recycling. Therefore, the present inventors consider applying biochar to the phosphorus adsorption treatment of sewage.

[0039] However, the present inventors have found through research that although biochar has adsorption properties, its adsorption capacity for phosphate and organic phosphorus is poor, and even negative adsorption occurs. The inventors further analyzed the reasons, which are related to the presence of oxygen-containing functional groups that easily adsorb cations on the surface of biochar, and the electronegativity of the surface. Direct application of biochar to phosphorus adsorption has the following disadvantages: electronegativity of the surface, low adsorption capacity, and competition for adsorption sites between silicate anions and phosphate.

[0040] Therefore, the present inventors consider that the biochar should be treated to regulate the surface charge of the material and load functional groups to improve its adsorption performance for phosphorus, especially organic phosphorus, in sewage. The biochar is used in combination with a traditional water treatment coagulant to improve the effect of deep phosphorus removal.

[0041] Based on the above inventive concept, the present embodiment provides a sewage treatment process for removing multi-form phosphorus pollutants, which comprises the following steps:

[0042] Step a), putting sewage into a primary coagulation and sedimentation reaction tank, adjusting the pH to 6.5-8.5, adding a water treatment coagulant for primary coagulation treatment, and separating and precipitating to obtain first intermediate sewage;

[0043] Step b), discharging the first intermediate into a secondary biochemical tank for biological treatment to obtain second intermediate sewage;

[0044] Step c), the second intermediate sewage is discharged into a third coagulation sedimentation tank, a water treatment coagulant and a multi-form phosphorus adsorbent are added for secondary coagulation treatment; the multi-form phosphorus adsorbent is a biochar modified by a metal salt and an organic nitrogen quaternary ammonium salt; the metal ion of the metal salt includes one or more of Ca 2+ , Mg 2+ , Mn 2+ and Fe 3+ , and the organic nitrogen quaternary ammonium salt is a short-chain organic nitrogen quaternary ammonium salt with a chain length of C3-C6;

[0045] Step d), a flocculating agent is added for flocculation treatment, and the precipitate is separated.

[0046] The step a) is a step of discharging sewage into a first coagulation sedimentation tank and treating suspended phosphorus by using a water treatment coagulant. The water treatment coagulant can help the suspended phosphorus to gather into larger flocs, which is convenient for subsequent precipitation and removal. Before adding the water treatment coagulant, the pH of the sewage in the coagulation sedimentation tank is adjusted to 6.5-8.5 to optimize the effect of the water treatment coagulant. In the primary coagulation treatment, the suspended phosphorus is removed through the precipitation process, and the first intermediate sewage is obtained after the separation of the precipitate.

[0047] The water treatment coagulant is preferably an aluminum salt coagulant and / or an iron salt coagulant. The colloidal particles formed by the aluminum salt and iron salt coagulant in water have adsorption effect, which can adsorb the suspended phosphorus in the wastewater and make it coagulate into larger flocs. These flocs are removed in the subsequent precipitation process, thereby achieving the purpose of phosphorus removal.

[0048] The addition amount M1 of the water treatment coagulant in this step is calculated according to formula I:

[0049] M1=a×B1 / 100 Formula I;

[0050] In formula I, a is an empirical constant, and the value range is 2-9, preferably 5-9; B1 is the total suspended phosphorus concentration of the influent, g / m 3 .

[0051] The primary coagulation treatment in this step is preferably as follows: fast stirring for 1-5 min, slow stirring for 2-10 min, and standing for 1 h-4 h; the speed gradient value of the fast stirring is >500 s -1 , and the speed gradient value of the slow stirring is <100 s -1 . The purpose of the fast stirring (speed gradient value G value >500 s -1 ) is to quickly and uniformly disperse the water treatment coagulant into the sewage, promote the contact and reaction between the coagulant and the suspended particles in the sewage, and form small flocs. The high G value ensures that the coagulant can be quickly and uniformly mixed. The slow stirring (G value <100 s -1) help the growth and maturation of flocs, reduce the shear force between flocs, prevent the destruction of already formed flocs, and facilitate the subsequent sedimentation process. The standing phase allows the flocs to settle under the action of gravity, and the supernatant becomes clear.

[0052] The above step b) is to discharge the first intermediate sewage into a secondary biochemical tank for biological treatment, and microorganisms in the secondary biochemical tank remove part of the organic pollutants in the sewage through metabolic action, and also remove part of the dissolved phosphorus.

[0053] The above step c) is a step for treating dissolved orthophosphate and organic phosphorus in the second intermediate sewage to achieve deep phosphorus removal. Two agents are used in this step, namely a water treatment coagulant and a polymorphic phosphorus adsorbent. The water treatment coagulant is used to remove dissolved orthophosphate in the water, and on the other hand, it uses its flocculation effect to remove the added polymorphic phosphorus adsorbent. The polymorphic phosphorus adsorbent is used to remove organic phosphorus and dissolved phosphate that has not been removed by the water treatment coagulant. The time for secondary coagulation treatment in this step is preferably 1-10 min.

[0054] The polymorphic phosphorus adsorbent used in this step is a biochar modified by a metal salt and an organic nitrogen quaternary ammonium salt; the metal ions of the metal salt include one or more of Ca 2+ , Mg 2+ , Mn 2+ and Fe 3+ , and the organic nitrogen quaternary ammonium salt is a short-chain organic nitrogen quaternary ammonium salt with a chain length of C3-C6. The modification by the metal salt can be specifically by impregnation modification of the metal salt, and the metal ions Ca 2+ , Mg 2+ , Mn 2+ and Fe 3+The metal ions form metal complexes with the functional groups on the surface and inside of the biochar. These metal ions form positively charged sites on the surface of the biochar, thereby changing the surface charge properties of the biochar. This change in charge can enhance the adsorption capacity of the biochar for negatively charged phosphate ions (such as phosphate, hydrogen phosphate and dihydrogen phosphate), i.e. charge regulation is achieved. The reaction of metal ions with the functional groups on the surface of the biochar not only changes the surface charge, but also introduces metal complexes as functional groups, which can form coordinate bonds with phosphate ions, thereby enhancing the adsorption of phosphorus, i.e. functional group loading is achieved. The organic nitrogen quaternary ammonium salt modification can be specifically: hydrothermal modification of organic nitrogen quaternary ammonium salt, the biochar modified by metal salt impregnation is subjected to high temperature and high pressure with quaternary ammonium salt, quaternary ammonium cations are formed on the surface of the biochar, and are deposited on the surface of the biochar, thereby further playing a role in charge regulation. In addition, the quaternary ammonium salt group has an adsorption effect on the silicate ions in the wastewater that interfere with the adsorption of phosphorus, thereby reducing the interference effect of phosphorus adsorption. In summary, the metal cations and quaternary ammonium cations loaded on the surface of the multi-morphology phosphorus adsorbent make the positively charged sites, thereby enhancing the adsorption capacity of the biochar for negatively charged phosphate ions (such as phosphate, hydrogen phosphate and dihydrogen phosphate); the functional groups such as metal complexes and quaternary ammonium salt groups loaded on the surface of the multi-morphology phosphorus adsorbent further enhance the adsorption capacity for phosphate ions, while reducing the competition of silicates for the active sites of the water treatment coagulant, thereby reducing the interference effect of phosphorus adsorption. The use of the multi-morphology phosphorus adsorbent and the water treatment coagulant in combination can improve the removal effect of the water treatment coagulant on dissolved orthophosphate.

[0055] The multi-morphology phosphorus adsorbent is preferably prepared by acid pickling modification, metal salt solution impregnation modification and organic nitrogen quaternary ammonium salt hydrothermal modification. Specifically, it is preferably prepared according to the following method:

[0056] Step c1), stirring and activating the biochar material in a nitric acid solution; and then washing and drying the activated biochar material to obtain an activated biochar;

[0057] Step c2), ball milling the activated biochar material to obtain a powder biochar with a diameter of less than 0.1 mm;

[0058] Step c3), adding the powder biochar into a metal salt solution for impregnation treatment to obtain an impregnation treatment solution; the metal ions of the metal salt solution include one or more of Ca 2+ , Mg 2+ , Mn 2+ and Fe 3+ , and the solvent is water;

[0059] Step c4), adding organic nitrogen quaternary ammonium salt into the impregnation treatment solution to perform hydrothermal reaction, the organic nitrogen quaternary ammonium salt is a short-chain organic nitrogen quaternary ammonium salt with C3-C6; the reaction product is washed and dried to obtain a multi-form phosphorus adsorbent.

[0060] The step c1) is a step of acid activation, and the step has the following effects: on the one hand, removing inorganic minerals and part of organic substances in the biochar material, increasing the porosity and specific surface area, and thus improving the adsorption performance; on the other hand, introducing or changing the functional groups on the surface of the biochar; for example, the acid can react with the hydrocarbons in the biochar to generate hydroxyl and carboxyl groups, and these functional groups can provide active sites for subsequent coordination with metal ions. The nitric acid solution in the step is preferably 1-4 mol / L nitric acid solution, and the mixing ratio of the biochar material to the nitric acid solution is preferably 10-50 ml: 1 g. More preferably, the acid solution is 2-3 mol / L nitric acid solution, and the mixing ratio of the biochar material to the nitric acid solution is 30-40 ml: 1 g. Most preferably, the acid solution is 2 mol / L nitric acid solution, and the mixing ratio of the biochar material to the nitric acid solution is 35 ml: 1 g. Stirring helps to improve the activation efficiency, and in the step, the stirring activation time is preferably 4-8 h, and the stirring speed is preferably 150-350 r / min. After stirring and activation, the activated biochar material is sequentially washed and dried to obtain the activated biochar. Specifically, the activated biochar material can be washed to neutral with deionized water and then dried in a 105℃ oven.

[0061] The step c2) is a step of ball milling, which is used to further refine the biochar material, increase the specific surface area, and improve the adsorption efficiency. Specifically, the activated biochar material is ball milled and sieved with a 200-mesh sieve to obtain a powder biochar with a diameter of less than 0.1 mm.

[0062] The step c3) is a step of impregnating the powder biochar with a metal salt solution. The impregnation is preferably carried out under stirring, and the stirring speed of the impregnation treatment is preferably 150-350 r / min, and the impregnation time is preferably 20-30 h. During the impregnation process, the metal ions are easily adsorbed by the biochar powder; the metal ions can coordinate with or chemically react with the functional groups (such as hydroxyl, carboxyl, etc.) on the surface and inside of the biochar to form metal complexes. These metal ions form positively charged sites on the surface of the biochar, thereby changing the surface charge properties of the biochar. This change in charge can enhance the adsorption capacity of the biochar for negatively charged phosphate ions (such as phosphate, hydrogen phosphate and dihydrogen phosphate), i.e. charge regulation is achieved. The reaction of metal ions with the functional groups on the surface of the biochar not only changes the surface charge, but also introduces metal complexes as functional groups, which can form coordinate bonds with phosphate ions, thereby enhancing the adsorption of phosphorus, i.e. functional group loading is achieved.

[0063] Furthermore, the inventors of the present application have found that the valence state of the metal of the metal salt has an important influence on the performance of the product, and when a divalent and / or trivalent metal salt is used, the product has excellent phosphorus adsorption performance. In this step, the metal ions of the metal salt solution include one or more of Ca 2+ , Mg 2+ , Mn 2+ and Fe 3+ . More preferably, the metal salt solution is a mixed solution of calcium chloride, magnesium chloride and manganese chloride, and in this way the product obtained has the highest phosphorus adsorption rate; the concentration of calcium chloride, magnesium chloride and manganese chloride in the metal salt solution is preferably 1-2 mol / L; and the mixing ratio of the metal salt solution to the biochar is preferably 10-30 ml: 1 g. More preferably, the concentration of calcium chloride, magnesium chloride and manganese chloride in the metal salt solution is 1.5 mol / L, and the mixing ratio of the metal salt solution to the biochar is preferably 20 ml: 1 g.

[0064] Step c4) is a step of adding an organic nitrogen quaternary ammonium salt to the impregnation treatment solution (solid-liquid mixture) obtained in step c3) to carry out a hydrothermal reaction. In this step, the impregnated biochar and the quaternary ammonium salt form quaternary ammonium cations on the surface of the biochar under high temperature and pressure, which are deposited on the surface of the biochar and further play a role in charge regulation; in addition, the quaternary ammonium salt group has an adsorption effect on the silicate ions in the wastewater that interfere with the adsorption of phosphorus, i.e. the phosphorus adsorption interference effect is reduced.

[0065] Specifically, when the impregnated biochar and the organic nitrogen quaternary ammonium salt solution are subjected to a hydrothermal reaction, the following reaction processes can occur:

[0066] 1. Interaction of metal ions with organic nitrogen quaternary ammonium salt:

[0067] The organic nitrogen quaternary ammonium salt may undergo pyrolysis under hydrothermal conditions, producing amino, pyridine and other nitrogen-containing groups. These nitrogen-containing groups may undergo coordination, ion exchange and other reactions with metal ions already present on the surface of activated carbon. New metal-nitrogen complexes or ionic bond structures are formed, further changing the surface chemistry of the activated biochar.

[0068] 2. Formation of metal oxides:

[0069] Under hydrothermal conditions, metal ions may undergo oxidation reactions to form metal oxide nanoparticles. These metal oxide particles may adhere to the surface and pore structure of activated carbon, changing the physical properties of activated carbon.

[0070] 3. Catalytic effect:

[0071] Some transition metal ions (such as Fe, Mn, etc.) may exhibit catalytic activity under hydrothermal conditions. They can promote the pyrolysis and chemical reaction of organic nitrogen quaternary ammonium salt, accelerating the introduction process of nitrogen-containing functional groups. At the same time, metal ions may also participate in redox reactions on the surface of activated carbon, triggering other chemical changes.

[0072] 4. Formation of composite structures:

[0073] Metal ions and nitrogen-containing functional groups may combine through coordination bonds, ionic bonds and other means to form new composite structures. This composite structure may change the electronic properties, pore structure and surface chemistry of activated carbon.

[0074] In summary, when biochar impregnated with metal ions continues to undergo hydrothermal reaction with organic nitrogen quaternary ammonium salt, a series of reaction processes such as metal-nitrogen species formation, metal oxide generation, catalytic effect and composite structure formation may occur. These reaction processes can further optimize the physicochemical properties of biochar and improve its adsorption performance for phosphorus pollutants.

[0075] The above-mentioned organic nitrogen quaternary ammonium salt is a short-chain organic nitrogen quaternary ammonium salt with C3-C6. The modified biochar obtained after hydrothermal reaction with short-chain organic nitrogen quaternary ammonium salt with C3-C6 has relatively good hydrophilicity and is easy to adsorb silicate ions and other interfering ions. The mass ratio of the amount of organic nitrogen quaternary ammonium salt added to the mass of biochar material is preferably 2-5:1, more preferably 3-4:1, and most preferably 3.5:1. The short-chain organic nitrogen quaternary ammonium salt can be 3-chloropropyltrimethylammonium chloride, tetramethylammonium chloride or tetraethylammonium chloride. The most preferred embodiment uses 3-chloropropyltrimethylammonium chloride. The temperature of the hydrothermal reaction is preferably 70-80°C, and the reaction time is preferably 4-8h. More preferably, the temperature of the hydrothermal reaction is 80°C, and the reaction time is 6h.

[0076] After the hydrothermal reaction, the reaction product is washed and dried, and the multi-form phosphorus adsorbent is obtained. Specifically, the reaction product is washed with deionized water after the hydrothermal reaction, and the operation is repeated until the last washing liquid is neutral, and the obtained powder is dried in a 105℃ oven, and the multi-form phosphorus adsorbent is obtained.

[0077] The addition amount M2 of the water treatment coagulant in this step is calculated according to formula II, and the addition amount M3 of the multi-form phosphorus adsorbent is preferably calculated according to formula III:

[0078] M2 = b x 5 x C1 formula II;

[0079] In formula II, b is an empirical constant, and the value range is 2-9, and more preferably 5-9; C1 is the dissolved phosphorus concentration of the influent, g / m 3 ;

[0080] M3 = k x C2 formula III;

[0081] In formula III, k is an empirical constant, and the value range is 100-500; C2 is the dissolved total phosphorus concentration of the influent, g / m 3 .

[0082] The above step d) is a step of adding a flocculating agent for flocculation and precipitation and separation, the flocculating agent helps to form larger flocs, so that the precipitation process is more efficient, and the flocculating agent is preferably PAM. By separating and precipitating, the flocs are removed, and the advanced phosphorus removal of the wastewater is realized.

[0083] From the above, the wastewater treatment process for removing multi-form phosphorus pollutants provided by the application has the following advantages:

[0084] 1) The method effectively removes multi-form phosphorus pollutants in wastewater through the combined action of physical, chemical and biological methods, thereby meeting more stringent discharge standards. In particular, in the last efficient precipitation process, the traditional water treatment coagulant is mixed with the multi-form phosphorus adsorbent. The multi-form phosphorus adsorbent has metal cations and quaternary ammonium cations loaded on the surface, so that the positively charged sites are increased, thereby enhancing the adsorption capacity of low-concentration phosphate and anionic organic phosphorus in wastewater; in addition, the functional groups such as metal complexes and quaternary ammonium salt groups loaded on the surface of the multi-form phosphorus adsorbent further enhance the adsorption capacity of phosphate ions, and reduce the competition of silicates for active sites of the water treatment coagulant, thereby reducing the interference effect of phosphorus adsorption. The use of multi-form phosphorus adsorbent and water treatment coagulant can improve the effect of advanced phosphorus removal.

[0085] 2) The multi-form phosphorus adsorbent used in the method is prepared by modification of biomass charcoal, has a large specific surface area, a multi-stage pore structure, is widely available, and is easy to industrialize, and also realizes resource reuse.

[0086] 3) The method does not need to add new structures, is suitable for most sewage plants containing a three-stage coagulation reaction for deep phosphorus removal, and has low transformation costs.

[0087] The technical solutions of the present application will be further described below in combination with specific examples:

[0088] Example 1

[0089] The treatment facilities of a certain sewage treatment plant include a first-stage coagulation sedimentation reaction tank, a second-stage biochemical tank, and a third-stage coagulation sedimentation reaction tank arranged in sequence.

[0090] Influent wastewater: the pH value of the wastewater is 7.2, the wastewater contains suspended phosphorus, dissolved orthophosphate, and organic phosphorus, and the total phosphorus is 3.80 mg / L, and the silicate concentration of the influent is about 32 mg / L.

[0091] Traditional treatment process: aluminum salt coagulant is added for phosphorus removal in the first-stage coagulation sedimentation reaction tank and the third-stage coagulation sedimentation reaction tank, and the second-stage biochemical tank adopts AAO activated sludge method. In order to ensure that the total phosphorus of the effluent is less than 0.5 mg / L, the dosage of the aluminum salt coagulant is large (the dosage of the aluminum salt coagulant added in the first-stage coagulation sedimentation reaction tank is about 11-15.4 mg / L in terms of aluminum; the dosage of the aluminum salt coagulant added in the third-stage coagulation sedimentation reaction tank is about 10.6-14.7 mg / L in terms of aluminum), and it is difficult to stabilize the total phosphorus to be less than 0.3 mg / L.

[0092] The specific treatment process of this example is as follows:

[0093] First-stage coagulation sedimentation reaction tank: aluminum salt coagulant is added, and the dosage is calculated according to formula I: B1 is 1.1 mg / L, a is 9; the calculated dosage of the aluminum salt coagulant is M1=9.9 mg / L in terms of aluminum; after the addition of the aluminum salt coagulant, rapid stirring is performed for 3 min (G value 600 s -1 ), slow stirring is performed for 5 min (G value 50 s -1 ), and standing is performed for 2 h; after coagulation and sedimentation, the supernatant enters the second-stage biochemical tank.

[0094] Second-stage biochemical tank: AAO activated sludge method is adopted, and the biochemical effluent enters the third-stage coagulation sedimentation reaction tank;

[0095] The three-stage coagulation sedimentation reaction tank: adding aluminum salt coagulant and multi-form phosphorus adsorbent; the dosage of aluminum salt coagulant is calculated according to formula II: C1 is 0.83 mg / L of soluble orthophosphate state phosphorus, b is 5, and the calculated dosage of aluminum salt coagulant is M2=4.15 mg / L in terms of aluminum; the dosage of multi-form phosphorus adsorbent is calculated according to formula III: C2 is 0.23 mg / L of soluble organic total phosphorus (0.13 mg / L of total phosphorus contributed by dimethoate and 0.10 mg / L of total phosphorus contributed by glyphosate), and k is 100, and the calculated dosage of multi-form phosphorus adsorbent is M3=23 mg / L. After adding the aluminum salt coagulant and the multi-form phosphorus adsorbent, the mixture is reacted for 1-10 min, and then PAM coagulant aid is added and sedimentation is performed according to the conventional three-stage coagulation sedimentation reaction process of the sewage plant, so as to realize the separation of phosphorus adsorption agents and phosphorus-containing sludge.

[0096] The preparation method of the multi-form phosphorus adsorbent used in the embodiment is as follows:

[0097] (1) 1 g of wood biochar is placed in a 50 ml, 1 mol / L nitric acid solution and stirred at 150 r / min for 4 h, then washed with deionized water until neutral, and then placed in a 105°C oven for drying;

[0098] (2) The material obtained in step (1) is ball milled and sieved with a 200 mesh sieve to obtain a powder biochar;

[0099] (3) The powder biochar obtained in step (2) is placed in a 30 ml impregnation solution and stirred at 350 r / min for 24 h, the impregnation solution is a mixed solution of calcium chloride, magnesium chloride and manganese chloride, and the concentrations of calcium chloride, magnesium chloride and manganese chloride are all 2 mol / L; then 5 g of 3-chloropropyltrimethylammonium chloride is slowly added to the solution and mixed uniformly, and then poured into a hydrothermal reaction kettle, placed in a 80°C oven and reacted for 6 hours to complete the hydrothermal reaction. After the reaction is completed, the reaction product is filtered and washed with deionized water, and the operation is repeated until the last washing liquid is neutral, and then placed in a 105°C oven for drying. The obtained powder is the multi-form phosphorus adsorbent.

[0100] Example 2

[0101] The same sewage treatment plant as in Example 1 is used in this embodiment, and the treatment facilities and the wastewater entering the plant are the same.

[0102] The difference from Example 1 is that:

[0103] In the first-stage coagulation sedimentation reaction tank, the calculation of the dosage of aluminum salt coagulant M1, a is 5, and the calculated dosage of aluminum salt coagulant in terms of aluminum is M1=5.5 mg / L;

[0104] In the tertiary coagulation sedimentation reaction tank, the calculation of the dosage M2 of the aluminum salt coagulant, C1 is the soluble orthophosphate state phosphorus of 1.05 mg / L, and b is 9, so the calculated dosage of the aluminum salt coagulant is 9.45 mg / L in terms of aluminum; the calculation of the dosage of the multi-form phosphorus adsorbent, C2 is the soluble organic state total phosphorus of 0.23 mg / L (of which 0.13 mg / L is contributed by spinosad and 0.10 mg / L is contributed by glyphosate), and k is 350, so the calculated dosage of the multi-form phosphorus adsorbent is 80.50 mg / L.

[0105] The preparation method of the multi-form phosphorus adsorbent used in the embodiment is as follows:

[0106] (1) 1 g of coal-based biochar was placed in 10 ml of 3.5 mol / L nitric acid solution under the condition of stirring at 150 r / min for 4 h, then washed with deionized water until neutral, and then placed in a 105°C oven for drying;

[0107] (2) The material obtained in step (1) was ball milled and sieved with a 200 mesh sieve to obtain a powder biochar;

[0108] (3) The powder biochar obtained in step (2) was placed in 10 ml of an impregnation solution under the condition of stirring at 350 r / min for 24 h, the impregnation solution was a mixed solution of calcium chloride, magnesium chloride and manganese chloride, and the concentrations of calcium chloride, magnesium chloride and manganese chloride were all 1 mol / L; then 2 g of 3-chloropropyl trimethylammonium chloride was slowly added to the solution and mixed uniformly, and then poured into a hydrothermal reaction kettle, placed in a 80°C oven for reaction for 6 hours to complete the hydrothermal reaction. After the reaction was completed, the reaction product was filtered and washed with deionized water, and the operation was repeated until the last water washing liquid was neutral, and then placed in a 105°C oven for drying. The obtained powder is the multi-form phosphorus adsorbent.

[0109] The remaining steps and process parameters are the same as those of Example 1.

[0110] Comparative Example 1

[0111] The difference between this comparative example and Example 1 is only that the multi-form phosphorus adsorbent added is coal-based biochar without modification treatment, and the dosage M3 is the same as that of Example 1, and the remaining steps and process parameters are also the same as those of Example 1.

[0112] Comparative Example 2

[0113] The difference between this comparative example and Example 1 is only that no multi-form phosphorus adsorbent is added in the tertiary coagulation sedimentation reaction tank, i.e. only the aluminum salt coagulant is added in the tertiary coagulation sedimentation reaction tank, and the dosage M2 is the same as that of Example 1, and the remaining steps and process parameters are also the same as those of Example 1.

[0114] Comparative Example 3

[0115] The difference between the comparative example and example 2 is only that no multi-form phosphorus adsorbent is added in the three-stage coagulation sedimentation reaction tank, i.e. only aluminum salt coagulant is added in the three-stage coagulation sedimentation reaction tank, the addition amount M2 is the same as that of example 2, and the remaining steps and process parameters are also the same as those of example 2.

[0116] The total phosphorus, dissolved orthophosphate and organic phosphorus contents of the effluent from the three-stage coagulation sedimentation reaction tank in the above examples and comparative examples are detected, and the detection results are shown in Table 1.

[0117] Table 1: Treatment results of multi-form phosphorus pollutants in examples 1-2 and comparative examples 1-3 (unit: mg / L)

[0118]

[0119] As shown in Table 1, the sewage treatment process provided by the embodiments of the present application has good removal effect on multi-form phosphorus such as suspended total phosphorus, dissolved orthophosphate, dissolved organic phosphorus, dissolved dimethoate phosphorus and dissolved glyphosate phosphorus in wastewater.

[0120] The above has described various embodiments of the present application, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes are obvious to those skilled in the art without departing from the scope and spirit of the described embodiments. The selection of terms used herein is intended to best explain the principles, practical application or improvement of technology in the market of the embodiments, or to enable other ordinary skilled persons in the art to understand the embodiments disclosed herein.

Claims

1. A wastewater treatment process for removing polymorphous phosphorus contaminants, characterized in that, Comprising: Step a), sewage is put into a primary coagulation and sedimentation reaction tank, the pH is adjusted to 6.5-8.5, a water treatment coagulant is added for primary coagulation treatment, and the first intermediate sewage is obtained after separation and sedimentation; Step b), the first intermediate sewage is discharged into a secondary biochemical tank for biological treatment, and the second intermediate sewage is obtained; Step c), the second intermediate sewage is discharged into a tertiary coagulation and sedimentation reaction tank, a water treatment coagulant and a multi-form phosphorus adsorbent are added for secondary coagulation treatment; The multi-form phosphorus adsorbent is a biochar modified by a metal salt and an organic nitrogen quaternary ammonium salt; The metal ions of the metal salt include: Ca 2+ , Mg 2+ , and Mn 2+ The organic nitrogen quaternary ammonium salt is a short-chain organic nitrogen quaternary ammonium salt with C3-C6 Step d), a flocculating agent is added for flocculation treatment, and the sediment is separated.

2. The sewage treatment process according to claim 1, characterized in that, The water treatment coagulant is an aluminum salt coagulant and / or an iron salt coagulant.

3. The sewage treatment process according to claim 2, characterized in that, The addition amount M1 of the water treatment coagulant in step a) is calculated according to formula I, and the addition amount M2 of the water treatment coagulant in step c) is calculated according to formula II, and the addition amount M3 of the multi-form phosphorus adsorbent is calculated according to formula III: M1 = a x B1 / 100 formula I; In formula I: a is an empirical constant, ranging from 2 to 9; B1 is the total suspended phosphorus concentration of the influent, g / m 3 ; M2 = b x 5 x C1 formula II; M3 = k x C2 formula III; In formula II, b is an empirical constant, and has a value ranging from 2 to 9; C1 is the concentration of water-soluble orthophosphate state phosphorus, g / m 3 ; The multi-form phosphorus adsorbent is prepared by the following method: In formula III: k is an empirical constant, ranging from 100 to 500; C2 is the concentration of total dissolved organic phosphorus in the influent, g / m 3 .

4. The sewage treatment process according to claim 1, characterized in that, The primary coagulation treatment is: fast stirring for 1-5 min, slow stirring for 2-10 min, and standing for 1-4 h; the speed gradient value of the fast stirring is >500 s -1 , the speed gradient value of the slow stirring is <100 s -1 ; the time of the secondary coagulation treatment is 1-10 min.

5. The sewage treatment process according to any one of claims 1 to 4, characterized in that, Step c1), the biochar material is stirred and activated in a nitric acid solution; the activated biochar material is washed and dried in sequence to obtain activated biochar; Step c2), the activated biochar material is ball milled to obtain powder biochar with a diameter of less than 0.1 mm; Step c3), the powder biochar is immersed in a metal salt solution to obtain an immersion treatment solution; Step c4), an organic nitrogen quaternary ammonium salt is added to the immersion treatment solution for hydrothermal reaction, the organic nitrogen quaternary ammonium salt is a short-chain organic nitrogen quaternary ammonium salt with a chain length of C3-C6; the reaction product is washed and dried to obtain a multi-form phosphorus adsorbent. The metal ions of the metal salt solution include: Ca 2+ , Mg 2+ , and Mn 2+ , and the solvent is water; In step c1), the concentration of the nitric acid solution is 1-4 mol / L, and the mixing ratio of the biochar material to the nitric acid solution is 10 ml-50 ml:1 g.

6. The sewage treatment process according to claim 5, characterized in that, In step c3), the metal salt solution is a mixed solution of calcium chloride, magnesium chloride and manganese chloride; the concentration of calcium chloride, magnesium chloride and manganese chloride in the metal salt solution is 1-2 mol / L; the mixing ratio of the metal salt solution to the biochar is 10 ml-30 ml:1 g.

7. The sewage treatment process according to claim 5, characterized in that, In step c3), the immersion treatment is carried out under stirring, the stirring speed is 150-350 r / min, and the immersion time is 20-30 h.

8. The sewage treatment process according to claim 5, characterized in that, In step c4), the organic nitrogen quaternary ammonium salt is 3-chloropropyltrimethylammonium chloride, tetramethylammonium chloride or tetraethylammonium chloride; the mass ratio of the addition amount of the organic nitrogen quaternary ammonium salt to the biochar material is 2-5:

1.

9. The sewage treatment process according to claim 5, characterized in that, In step c4), the temperature of the hydrothermal reaction is 70-80℃, and the reaction time is 4-8 h.

10. The sewage treatment process according to claim 5, characterized in that, ​

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