A method for detoxifying zinc-containing wastewater in the nylon 66 industry

Abstract

The present invention discloses a method for detoxifying zinc-containing wastewater in the nylon 66 industry. By using polyaluminum chloride and nano-hydroxyapatite to remove organic pollutants and strengthen zinc ion capture under acidic conditions, sodium carbonate-sodium hydroxide co-precipitation is used in the alkaline stage to form zinc hydroxide with zinc ions, and the flocculation effect of polyacrylamide is combined to achieve efficient solid-liquid separation. Citric acid is used to adjust to neutrality to ensure the stability of zinc precipitation. The multi-stage coagulation adsorption process synergistically removes organic matter, reduces the zinc ion concentration in the overall wastewater treatment system, can effectively eliminate the toxicity of zinc to microorganisms in the biochemical system, reduce the risk of zinc enrichment in sludge, can improve efficiency, improve water quality and restore microbial activity, ensure the stable operation of subsequent biochemical treatment, achieve effective detoxification, and solve the defect of poor detoxification effect in the existing zinc-containing wastewater detoxification method.

Description

Technical Field

[0001] The present invention relates to the technical field of wastewater treatment, and particularly to a method for detoxifying zinc-containing wastewater in the nylon 66 industry. Background Art

[0002] Nylon 66 is an important synthetic fiber of polyamide type, with the chemical name of polyhexamethylene adipamide, and is a semi-transparent or opaque milky white thermoplastic resin formed by polycondensation of adipic acid and hexamethylenediamine. In the nylon 66 industry, a certain amount of zinc-containing wastewater is discharged during the production process of cyclohexanol. Zinc ions are highly toxic to the denitrification and nitrogen removal system and the subsequent biochemical system, and can cause poisoning of the sludge and microorganisms in the biochemical system.

[0003] Too high zinc ion concentration in the sludge will affect the flocculation performance and sedimentation performance of the sludge, resulting in reduced sludge settling property and affecting the treatment effect. Sludge poisoning will damage the physiological functions and community structure of microorganisms. Excessive zinc ions will inhibit the activity of microbial enzymes, affect the growth and metabolism of microorganisms, and even cause the death of microorganisms, resulting in weakened ability of microorganisms to decompose organic matter in the wastewater and prolonged treatment time.

[0004] Currently, the main treatment methods for zinc-containing wastewater are ion exchange method and membrane separation method. The ion exchange method uses ion exchangers such as ion exchange resins to remove zinc ions in the wastewater, but the exchangers need to be regenerated or replaced regularly, increasing the operating cost. The membrane separation technology is prone to membrane fouling problems during operation, resulting in a decrease in membrane flux, and the membrane modules need to be cleaned or replaced regularly, increasing the operating cost and affecting the detoxification effect of zinc-containing wastewater. Especially when applied to nylon 66 wastewater containing a large amount of organic matter, the organic matter will exacerbate the blockage and make the detoxification effect of zinc-containing wastewater worse.

[0005] Therefore, it is necessary to improve the method for detoxifying zinc-containing wastewater in the prior art to solve the above problems. Summary of the Invention

[0006] The present invention overcomes the deficiencies of the prior art and provides a method for detoxifying zinc-containing wastewater in the nylon 66 industry, aiming to solve the defect of poor detoxification effect in the existing methods for detoxifying zinc-containing wastewater.

[0007] To achieve the above object, the technical solution adopted by the present invention is: a method for detoxifying zinc-containing wastewater in the nylon 66 industry, comprising the following steps:

[0008] S1: Adjust the pH of the zinc-containing wastewater to 5.5 - 6.5, and add polyaluminum chloride and stir for 5 - 10 min;

[0009] S2: Add sodium polyacrylate and nano-hydroxyapatite to the zinc-containing wastewater in S1 after adding polyaluminum chloride to obtain pretreated wastewater;

[0010] S3: Place sodium carbonate and caustic soda together in the pretreated wastewater in S2, adjust the pH of the wastewater to 8.8 - 9.2 and add polyacrylamide.

[0011] S4: Add citric acid to the zinc-containing wastewater with a pH of 8.8 - 9.2 in S3 and adjust the pH to 7.0 - 7.5. Filter the generated zinc hydroxide precipitate and sludge using a sieve, leaving the sludge.

[0012] In a preferred embodiment of the present invention, the ratio of the dosage value of sodium polyacrylate in S2 to the chemical oxygen demand is 0.003 - 0.005:1, and the unit of the dosage of sodium polyacrylate is mg / L.

[0013] In a preferred embodiment of the present invention, the particle size of the nano-hydroxyapatite is 80 - 150 nm, and the dosage of the nano-hydroxyapatite is 1% - 3% of the zinc ion concentration.

[0014] In a preferred embodiment of the present invention, the mass ratio between the polyaluminum chloride and the polyacrylamide is 100 - 200:1, and the total added mass is 6 - 6.5 times the mass of zinc ions per liter of wastewater.

[0015] In a preferred embodiment of the present invention, the mass ratio between the sodium carbonate and the caustic soda in S3 is 2 - 4:1.

[0016] In a preferred embodiment of the present invention, sodium alginate is added simultaneously with sodium carbonate and caustic soda in S3, and the dosage of sodium alginate is 30% - 80% of the zinc ion concentration.

[0017] In a preferred embodiment of the present invention, sodium sulfide is added simultaneously with sodium carbonate and caustic soda in S3, and the dosage of sodium sulfide is 150% - 250% of the sodium alginate concentration.

[0018] In a preferred embodiment of the present invention, ferrous sulfate is added when citric acid is added in S4, and the dosage of ferrous sulfate is 1.1 - 1.3 times the dosage of sodium sulfide.

[0019] In a preferred embodiment of the present invention, the dosage of citric acid in S4 is 1.1 - 1.3 times the zinc ion concentration, and after adding citric acid, the pH is adjusted to 7.0 - 7.5 using one of hydrochloric acid or sodium hydroxide.

[0020] In a preferred embodiment of the present invention, the aperture of the sieve in S4 is 50 - 100 μm.

[0021] The present invention solves the defects in the background technology and has the following beneficial effects:

[0022] (1) The present invention provides a method for detoxifying zinc-containing wastewater in the nylon 66 industry. By using polyaluminum chloride and nano-hydroxyapatite to remove organic pollutants and enhance zinc ion capture under acidic conditions, and using sodium carbonate-sodium hydroxide co-precipitation in the alkaline stage to form zinc hydroxide from zinc ions, and coordinating with the flocculation effect of polyacrylamide to achieve efficient solid-liquid separation, and adjusting to neutral with citric acid to ensure the stability of zinc precipitation. Compared with the zinc-containing wastewater detoxification methods in the prior art, the multi-stage coagulation adsorption process synergistically removes organic matter, reduces the zinc ion concentration in the overall wastewater treatment system, can effectively eliminate the toxicity of zinc to the microorganisms in the biochemical system, reduces the risk of zinc enrichment in the sludge, can improve the efficiency, improve the water quality and restore the microbial activity, ensures the stable operation of the subsequent biochemical treatment, realizes effective detoxification, and solves the defect of poor detoxification effect in the zinc-containing wastewater detoxification methods in the prior art.

[0023] (2) In the present invention, sodium alginate is added while adding sodium carbonate and sodium hydroxide. The addition of sodium alginate improves the structure of the sludge, making it more porous. Compared with the prior art, the porosity of the sludge is increased, which helps the distribution and growth of microorganisms in the sludge, improves the biodegradability of the sludge, and sodium alginate forms alginate under alkaline conditions, which can combine with zinc ions to form insoluble complexes, thereby more effectively removing zinc ions.

[0024] (3) In the present invention, sodium sulfide is added while adding sodium carbonate and sodium hydroxide, and ferrous sulfate is added when adding citric acid. Compared with the prior art, citric acid as a reducing agent can reduce refractory organic matter and convert it into a form more easily decomposed by microorganisms. The reducibility of Fe²⁺ can promote the reduction and degradation of organic matter and improve the degradation efficiency of organic matter.

[0025] (4) In the present invention, adding sodium carbonate and sodium hydroxide causes zinc ions to form zinc hydroxide, which is a compound insoluble in water and can be separated from the wastewater. Citric acid ensures the stability of zinc hydroxide and zinc carbonate while adjusting the wastewater to neutral. Compared with the prior art, it can effectively remove zinc ions from the wastewater and reduce the toxicity of zinc to microorganisms and sludge.

[0026] (5) In the present invention, sodium alginate has good gelling properties and can form a protective film on the surface of the sludge, which can reduce the direct contact between zinc ions and microorganisms. Compared with the prior art, it can reduce the toxicity of zinc ions to microorganisms, protect the activity of microorganisms, and the addition of sodium alginate improves the structure of the sludge, making it more porous, increasing the porosity of the sludge, which helps the distribution and growth of microorganisms in the sludge, and improves the biodegradability of the sludge. Brief Description of the Drawings

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art are briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative work.

[0028] Figure 1 It is a method step diagram of a preferred embodiment of the present invention. DETAILED DESCRIPTION

[0029] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein. Therefore, the protection scope of the present invention is not limited to the specific embodiments disclosed below.

[0031] If only the pH adjustment method is used to detoxify the zinc-containing wastewater in the nylon 66 industry, if the pH is too low, the zinc ions cannot be completely removed. If the pH is too high, the microorganisms will be damaged and the treatment effect of the wastewater will be seriously affected. Even after the zinc ions are removed, the microorganisms will not be able to completely treat the organic matter remaining in the nylon 66 wastewater. It is also found that there is a phenomenon of organic matter and zinc ions tightly combined in the sludge, such as the combination of hexamethylenediamine and zinc ions, which makes it impossible to remove the zinc ions in the sludge by only using the pH adjustment method.

[0032] The present invention has found that by adjusting the pH in stages and adding treatment substances at each pH level, the zinc content in sludge and wastewater can be effectively reduced, and the zinc poisoning of sludge can be alleviated. The zinc ions can be removed while effectively reducing the adipic acid and hexamethylenediamine content in wastewater and sludge, reducing the processing burden of the subsequent biochemical system and improving the detoxification effect.

[0033] like Figure 1 As shown, a method for detoxifying zinc-containing wastewater in the nylon 66 industry comprises the following steps:

[0034] S1: Adjust the pH of the zinc-containing wastewater to 5.5 - 6.5, and add polyaluminum chloride and stir for 5 - 10 min. The acidic condition helps to break the complexation bond between the organic matter and zinc ions, releasing free zinc ions. The electro-neutralization effect of polyaluminum chloride is used to break the complexation bond between organic matters such as hexamethylenediamine and zinc, releasing free zinc ions, laying the foundation for subsequent removal, removing part of the suspended organic matter, and reducing the subsequent zinc-organic matter complexation risk. Polyaluminum chloride hydrolyzes to form polynuclear hydroxy complexes, adsorbing colloidal organic matter and reducing the subsequent zinc recombination risk. Polyaluminum chloride can also capture the organic matter in the wastewater, including adipic acid, through flocculation, reducing the difficulty of subsequent treatment.

[0035] S2: Add sodium polyacrylate and nano-hydroxyapatite to the zinc-containing wastewater in S1 after adding polyaluminum chloride to obtain pretreated wastewater. Nano-hydroxyapatite, due to its high specific surface area and specific adsorption ability for zinc, preferentially captures free zinc ions, reducing the probability of its recombination with organic matters such as hexamethylenediamine. It disperses organic matter colloids through electrostatic repulsion, preventing them from wrapping zinc ions to form stable complexes and enhancing the exposure of zinc ions. Polyaluminum chloride releases zinc ions, and nano-hydroxyapatite quickly adsorbs zinc ions to form a stable zinc-hydroxyapatite complex, thus efficiently removing zinc ions. Sodium polyacrylate enhances the flocculation effect of nano-hydroxyapatite, simultaneously capturing zinc ions and organic pollutants, and further reducing the chemical oxygen demand of the wastewater. Nano-hydroxyapatite captures adipic acid in the wastewater through surface adsorption and chemical bonding, reducing its concentration in the wastewater.

[0036] S3: Place sodium carbonate and caustic soda together in the pretreated wastewater in S2, adjust the pH of the wastewater to 8.8 - 9.2 and add polyacrylamide. Stable zinc hydroxide precipitates are formed under weak alkaline conditions, avoiding the toxicity to microorganisms at too high pH. At the same time, sodium carbonate provides carbonate ions to strengthen the precipitation effect. The alkaline condition helps the hydrolysis and oxidation of some organic matters, further promoting the degradation of adipic acid.

[0037] S4: Add citric acid to the zinc-containing wastewater with a pH of 8.8 - 9.2 in S3 and adjust the pH to 7.0 - 7.5. Filter the generated zinc hydroxide precipitate and sludge using a sieve, leaving the sludge. Citric acid is adjusted to neutral to prevent the redissolution of zinc hydroxide in a strong acidic environment and avoid residual alkalinity from inhibiting the biochemical system.

[0038] By adjusting the pH step by step, a suitable reaction environment is provided for different materials, avoiding the contradictory problems under a single pH condition. The acidic stage breaks the complexation bond and releases zinc ions, the alkaline stage precipitates zinc ions, and the neutral stage stabilizes zinc ions, ensuring efficient removal. By gradually removing zinc ions and organic pollutants, the toxicity to microorganisms is reduced, their activity is restored, and the stable operation of the biochemical system is guaranteed.

[0039] By using polyaluminum chloride and nano-hydroxyapatite to remove organic pollutants and enhance zinc ion capture under acidic conditions, and adopting sodium carbonate-sodium hydroxide co-precipitation in the alkaline stage to form zinc hydroxide with zinc ions, and coordinating with the flocculation effect of polyacrylamide to achieve efficient solid-liquid separation, and adjusting to neutral with citric acid to ensure the stability of zinc precipitation. The multi-stage coagulation adsorption process synergistically removes organic substances, reduces the zinc ion concentration in the overall wastewater treatment system, can effectively eliminate the toxicity of zinc to the microorganisms in the biochemical system, reduces the risk of zinc enrichment in sludge, can improve efficiency, improve water quality and restore microbial activity, ensures the stable operation of subsequent biochemical treatment, realizes effective detoxification, and solves the defect of poor detoxification effect in the existing zinc-containing wastewater detoxification methods.

[0040] The ratio of the dosage value of sodium polyacrylate in S2 to the chemical oxygen demand is 0.003 - 0.005:1, and the dosage unit of sodium polyacrylate is mg / L. Sodium polyacrylate forms a composite flocculation system with nano-hydroxyapatite through electrostatic neutralization and bridging effects. The zinc ions adsorbed on the surface of the nanomaterial are wrapped and fixed by the polymer chains, effectively blocking the migration of zinc to the biochemical system. The flocculation effect of sodium polyacrylate can not only capture zinc ions, but also adsorb organic pollutants in the wastewater. Through the synergistic effect with polyaluminum chloride and nano-hydroxyapatite, sodium polyacrylate can further strengthen the capture and removal of organic substances.

[0041] The particle size of nano-hydroxyapatite is 80 - 150 nm, and the dosage of nano-hydroxyapatite is 1% - 3% of the zinc ion concentration. Nano-hydroxyapatite has a large specific surface area and high chemical activity, can capture zinc ions in the wastewater by surface adsorption and chemical combination, can quickly form a stable zinc-hydroxyapatite complex, thereby reducing the free concentration of zinc ions in the wastewater. Nano-hydroxyapatite can fix zinc ions on its surface or in its internal structure to form stable precipitates. These precipitates are removed in the subsequent filtration step, thereby reducing the risk of zinc enrichment in sludge and reducing the long-term toxicity of sludge to microorganisms. Under acidic conditions, nano-hydroxyapatite acts together with polyaluminum chloride and sodium polyacrylate to form composite flocs. This composite floc can more efficiently capture and remove organic substances in the wastewater, further reducing the chemical oxygen demand of the wastewater.

[0042] The mass ratio between sodium carbonate and caustic soda in S1 is 2 - 4:1. The combination of sodium carbonate and caustic soda adjusts the pH value of the wastewater to alkaline, enabling zinc ions to react with carbonate ions and hydroxide ions to form zinc hydroxide precipitation. The formation of zinc hydroxide can significantly reduce the zinc ion concentration in the wastewater, thereby alleviating the toxicity of zinc to sludge and microorganisms. High concentrations of zinc ions are toxic to microorganisms and inhibit their metabolic activity. Through the synergistic effect of sodium carbonate and caustic soda, zinc ions are rapidly precipitated and removed from the wastewater, thus reducing the direct contact of zinc ions with microorganisms and restoring the activity of microorganisms.

[0043] The combination of sodium carbonate and caustic soda not only promotes the precipitation of zinc ions but also, by increasing the pH value of the wastewater, makes other soluble pollutants in the wastewater more likely to precipitate or be adsorbed, thereby improving the removal efficiency of pollutants in nylon 66 wastewater. The removal of zinc ions and the adjustment of the pH value provide a more suitable living environment for microorganisms, enabling them to more effectively decompose complex organic substances in the wastewater. Meanwhile, the alkaline environment contributes to the hydrolysis and oxidation of some organic substances, further promoting their degradation. By removing zinc ions and other pollutants, the biodegradability of the wastewater is improved, and microorganisms can more efficiently decompose the remaining organic pollutants, thus enhancing the overall treatment efficiency.

[0044] The mass ratio between polyaluminum chloride and polyacrylamide is 100 - 200:1, and the total mass added is 6 - 6.5 times the mass of zinc ions per liter of wastewater. Polyaluminum chloride in the flocculant hydrolyzes under alkaline conditions to form positively charged complexes, which can adsorb negatively charged zinc ions in the wastewater to form flocs. Polyacrylamide further adsorbs and bridges these flocs through its long-chain structure, making them more stable and facilitating precipitation and filtration. In this way, zinc ions are effectively removed, reducing their toxicity to sludge and microorganisms. The synergistic effect of polyaluminum chloride and polyacrylamide not only targets zinc ions but also can adsorb and precipitate other pollutants in the wastewater, such as organic substances, suspended solids, and some heavy metals. These pollutants form larger flocs after being adsorbed by the flocculant, facilitating subsequent filtration and separation, thereby improving the removal efficiency of pollutants.

[0045] Sodium alginate is added simultaneously with sodium carbonate and caustic soda in S1, and the dosage of sodium alginate is 30 - 80% of the zinc ion concentration. Sodium carbonate and caustic soda adjust the pH of the wastewater to alkaline, causing zinc ions to form zinc hydroxide precipitation. The addition of sodium alginate further enhances the precipitation effect of zinc ions. Sodium alginate forms alginates under alkaline conditions, and these alginates can combine with zinc ions to form insoluble complexes, thus more effectively removing zinc ions.

[0046] Sodium alginate has good gelling properties and can form a protective film on the surface of sludge. This protective film can reduce the direct contact between zinc ions and microorganisms, thereby reducing the toxicity of zinc ions to microorganisms and protecting the activity of microorganisms. The addition of sodium alginate improves the structure of sludge, making it looser and increasing the porosity of sludge. This helps the distribution and growth of microorganisms in sludge and improves the biodegradability of sludge.

[0047] The flocs formed by sodium alginate provide more attachment sites for microorganisms, allowing them to decompose organic matter more effectively. At the same time, the adsorption of sodium alginate makes organic matter more concentrated, which is convenient for microorganisms to decompose and utilize. The combined action of sodium alginate and sodium sulfide not only removes zinc ions efficiently, but also reduces the toxicity of zinc ions to microorganisms by improving the sludge structure and redox environment.

[0048] Sodium alginate coordinates with zinc through its carboxyl group to form a three-dimensional network structure, effectively capturing organic complex zinc and effectively removing zinc ions combined with organic matter in sludge.

[0049] Sodium sulfide is added to S1 at the same time as sodium carbonate and caustic soda. The dosage of sodium sulfide is 150-250% of that of sodium alginate. Zinc sulfide is a water-insoluble compound that can effectively remove zinc ions in wastewater and reduce the toxicity of zinc to sludge and microorganisms. Sodium sulfide has reducing properties and can improve the redox environment of sludge. By reducing oxidative stress in sludge, sodium sulfide helps to reduce the toxicity of zinc ions and other heavy metals to microorganisms and restore the activity of microorganisms. Sodium sulfide can act as an electron donor to promote microbial growth and metabolic activity, help restore the activity of microorganisms in sludge, and improve their ability to decompose organic matter.

[0050] Sulfide ions gradually replace organic ligands with stronger coordination ability, combine with sulfur ions in sludge and produce precipitation, thereby removing sulfur ions in sludge. The generated precipitation surface is negatively charged, and positively charged organic zinc complexes are adsorbed through electrostatic action to form co-precipitation, which reduces the degree of zinc poisoning in sludge. The organic layer wrapped on the surface of zinc hydroxide will hinder the release of free zinc ions, while sulfur ions can directly attack the coordination bonds of organic zinc complexes through penetration. This process reduces the removal rate of bound zinc in sludge through the specific decomposition effect of sulfide on organic zinc.

[0051] When citric acid is added to S2, ferrous sulfate is added. The amount of ferrous sulfate added is 1.1-1.3 times the amount of sodium sulfide added. Citric acid forms a stable complex with zinc ions, while Fe in ferrous sulfate 2+It can form a more stable complex with citric acid, thereby further stabilizing zinc ions and preventing their re-dissolution. This synergistic effect helps to more effectively remove zinc ions from wastewater and reduce the toxicity of zinc to microorganisms. The Fe²⁺ in ferrous sulfate has reducibility and can improve the redox environment of the sludge. By reducing oxidative stress in the sludge, ferrous sulfate helps to reduce the toxicity of zinc ions and other heavy metals to microorganisms and restore the activity of microorganisms. Fe 2+ is an essential trace element for the growth of many microorganisms and can participate in the metabolic processes of microorganisms as a cofactor of enzymes. The addition of ferrous sulfate provides the necessary iron element for microorganisms, promotes their growth and metabolic activities, and improves the ability of microorganisms to decompose organic matter.

[0052] The synergistic effect of citric acid and ferrous sulfate helps the degradation of organic matter. As a reducing agent, citric acid can reduce refractory organic matter and convert it into a form more easily decomposed by microorganisms. At the same time, the reducibility of Fe²⁺ also contributes to the reductive degradation of organic matter and improves the degradation efficiency of organic matter. In the presence of zinc ions and ferrous salts, citric acid and adipic acid can form a complex through the synergistic coordination of carboxyl oxygen. This synergistic coordination effect enhances the stability of zinc ions, prevents zinc ions from being in a free state, and is better removed through adsorption.

[0053] In S2, the dosage of citric acid is 1.1 - 1.3 times the concentration of zinc ions. After adding citric acid, use either hydrochloric acid or sodium hydroxide to adjust the pH to 7.0 - 7.5. Citric acid is an organic acid with strong complexing ability and can form a stable complex with zinc ions. This complexing effect can effectively stabilize zinc ions and prevent them from re-dissolving into the wastewater, thereby reducing the toxicity of zinc to the sludge and microorganisms. The addition of citric acid and the adjustment of pH provide a more suitable living environment for microorganisms. A slightly alkaline pH value helps the growth and metabolic activities of microorganisms and restores their activity.

[0054] In S2, the mesh aperture of the sieve is 50 - 100 μm. The sieve separates the precipitated zinc hydroxide particles from the wastewater by physical interception, reducing the direct contact between zinc ions and microorganisms, thereby reducing the toxicity of zinc ions to microorganisms. Through the filtering effect of the sieve, larger particles in the sludge are intercepted, which helps to improve the structure of the sludge, make it more porous, and increase the porosity. This provides a better living environment for microorganisms and helps to restore the activity of microorganisms. The suspended solids and organic matter particles intercepted by the sieve can form larger flocs, which provide more attachment sites for microorganisms and enable microorganisms to decompose organic matter more effectively.

[0055] Example 1: This example provides a method for detoxifying zinc-containing wastewater in the nylon 66 industry, including the following steps:

[0056] S1: Adjust the pH of the zinc-containing wastewater to 6.0, and add polyaluminum chloride and stir for 8 min;

[0057] S2: Add sodium polyacrylate and nano-hydroxyapatite to the zinc-containing wastewater in S1 after adding polyaluminum chloride. The ratio of the dosage value of sodium polyacrylate to the chemical oxygen demand is 0.004:1. The unit of the dosage of sodium polyacrylate is mg / L. The particle size of nano-hydroxyapatite is 100 nm, and the dosage of nano-hydroxyapatite is 2% of the zinc ion concentration to obtain the pretreated wastewater.

[0058] S3: Place sodium carbonate and caustic soda together in the pretreatment. The mass ratio between sodium carbonate and caustic soda is 3:1. Adjust the pH of the wastewater to 8.6 and add polyacrylamide. The mass ratio between polyaluminum chloride and polyacrylamide is 150:1, and the total added mass is 6 times the mass of zinc ions per liter of wastewater; Add sodium alginate and sodium sulfide while adding sodium carbonate and caustic soda. The dosage of sodium alginate is 30% of the zinc ion concentration, and the dosage of sodium sulfide is 150% of that of sodium alginate.

[0059] S4: Add citric acid to the zinc-containing wastewater in S3 and adjust the pH to 7.5. Filter the generated zinc hydroxide precipitate and sludge with a sieve, and leave the sludge; Add ferrous sulfate when adding citric acid. The dosage of ferrous sulfate is 1.2 times the dosage of sodium sulfide added. The dosage of citric acid is 1.1 times the zinc ion concentration. After adding citric acid, adjust the pH to 7.3, and the sieve pore size is 50 μm.

[0060] Example 2: The difference between this example and Example 1 is that the pH of the wastewater is adjusted to 8.8 in S3, and the rest is the same.

[0061] Example 3: The difference between this example and Example 1 is that the pH of the wastewater is adjusted to 9.0 in S3, and the rest is the same.

[0062] Example 4: The difference between this example and Example 1 is that the pH of the wastewater is adjusted to 9.2 in S3, and the rest is the same.

[0063] Example 5: The difference between this example and Example 1 is that the pH of the wastewater is adjusted to 9.4 in S3, and the rest is the same.

[0064] Example 6: The difference between this example and Example 3 is that the dosage of sodium sulfide is 100% of that of sodium alginate in S3, and the rest is the same.

[0065] Example 7: The difference between this example and Example 3 is that the dosage of sodium sulfide is 200% of that of sodium alginate in S3, and the rest is the same.

[0066] Example 8: The difference between this example and Example 3 is that the dosage of sodium sulfide in S3 is 250% of sodium alginate, and the rest is the same.

[0067] Example 9: The difference between this example and Example 3 is that the dosage of sodium sulfide in S3 is 300% of sodium alginate, and the rest is the same.

[0068] Comparative Example 1: This comparative example provides zinc-containing wastewater from the nylon 66 industry in which untreated sludge and microorganisms are both zinc poisoned.

[0069] The COD value of the zinc-containing wastewater from the nylon 66 industry before treatment in Examples 1 to 9 and Comparative Example 1 is 3500 mg / L. Take the untreated wastewater and the wastewater after microbial treatment in Examples 1 to 9 and Comparative Example 1 for comparison, compare the organic matter content in the wastewater, calculate the reduction rate of the organic matter content, and test the zinc ion concentration of the wastewater after microbial treatment. The test data is shown in Table 1.

[0070] Table 1 Changes in organic matter content rate and zinc ion concentration in Examples 1 to 9 and Comparative Example 1

[0071]

[0072] As can be seen from Table 1, the reduction rates of the organic matter content in Examples 1 to 9 are all higher than those in Comparative Example 1, and the zinc ion concentrations in Examples 1 to 9 are all lower than those in Comparative Example 1. This application has superiority.

[0073] In Examples 1 to 5, as the pH of the wastewater is gradually increased, the reduction rate of the organic matter content first increases and then decreases, and the zinc ion concentration first decreases and then increases. This is because the pH of the wastewater is increased by adding sodium carbonate and caustic soda, which provides the best flocculation conditions for the flocculant. Through charge neutralization and enmeshment, the flocculant aggregates the organic matter and suspended particles in the wastewater to form larger flocs, making it easier to precipitate and remove. As the pH value increases, the flocculation effect is enhanced, and zinc ions react with hydroxide ions to form zinc hydroxide precipitation, promoting flocculation and microbial degradation, reducing the zinc poisoning symptoms for microorganisms, increasing the reduction rate of organic matter, and decreasing the zinc ion concentration. However, after the pH value is too high, the charge neutralization effect of the flocculant fails, resulting in a decline in the flocculation effect. The organic matter cannot be effectively precipitated, and the reduction rate begins to decline, leading to the failure of the flocculant and the decline of microbial activity. The reduction rate of organic matter begins to decline, the reduction rate of organic matter decreases, and the zinc ion concentration increases. The preferred example is Example 3.

[0074] In Example 3 and Examples 6 to 9, as the dosing ratio between sodium sulfide and sodium alginate increases, the reduction rate of organic matter content first increases and then decreases, and the zinc ion concentration first decreases and then increases. This is because the zinc sulfide precipitate formed by sodium sulfide can serve as the core for the flocculation of sodium alginate, further enhancing the flocculation effect, thus more effectively removing organic matter. The reaction between sodium sulfide and zinc ions generates zinc sulfide precipitate, increasing the reduction rate of organic matter and decreasing the zinc ion concentration. However, when the dosing ratio between sodium sulfide and sodium alginate is too high, it will have a toxic effect on microorganisms, inhibiting the growth and metabolic activities of microorganisms, leading to a decrease in the biodegradation efficiency of organic matter, thus reducing the reduction rate of organic matter content. Excessive sulfide ions will increase the solubility of zinc sulfide precipitate, decreasing the reduction rate of organic matter and increasing the zinc ion concentration. The preferred example is Example 7.

[0075] Based on the ideal embodiments of the present invention as inspiration, through the above description, relevant personnel can completely make various changes and modifications without departing from the technical idea of this invention. The technical scope of this invention is not limited to the content in the specification, and the technical scope must be determined according to the scope of the claims.

Claims

1. A method for detoxifying zinc-containing wastewater in the nylon 66 industry, characterized in that, It includes the following steps: S1: Adjust the pH of the zinc-containing wastewater to 5.5 - 6.5, and add polyaluminum chloride and stir for 5 - 10 min; S2: Add sodium polyacrylate and nano-hydroxyapatite to the zinc-containing wastewater in S1 after adding polyaluminum chloride to obtain pretreated wastewater; S3: Place sodium carbonate and caustic soda together in the pretreated wastewater in S2, adjust the pH of the wastewater to 8.8 - 9.2, add polyacrylamide, and add sodium alginate and sodium sulfide. The dosage of sodium alginate is 30 - 80% of the zinc ion concentration in the pretreated wastewater, and the dosage of sodium sulfide is 150 - 250% of the sodium alginate concentration; S4: Add citric acid to the zinc-containing wastewater with a pH of 8.8 - 9.2 in S3 and adjust the pH to 7.0 - 7.

5. Add ferrous sulfate when adding citric acid. The dosage of ferrous sulfate is 1.1 - 1.3 times the dosage of sodium sulfide. Filter the generated zinc hydroxide precipitate and sludge using a sieve, and leave the sludge.

2. The detoxification method of zinc-containing wastewater in the nylon 66 industry according to claim 1, characterized in that: The ratio of the dosage value of sodium polyacrylate in S2 to the chemical oxygen demand is 0.003 - 0.005:1, and the unit of the dosage of sodium polyacrylate is mg / L.

3. The detoxification method for zinc-containing wastewater in the nylon 66 industry according to claim 1, characterized in that: The particle size of the nano-hydroxyapatite is 80 - 150 nm, and the dosage of the nano-hydroxyapatite is 1% - 3% of the zinc ion concentration.

4. A detoxification method for zinc-containing wastewater in the nylon 66 industry according to claim 1, characterized in that: The mass ratio between the polyaluminum chloride and the polyacrylamide is 100 - 200:1, and the total added mass is 6 - 6.5 times the mass of zinc ions per liter of wastewater.

5. The detoxification method of zinc-containing wastewater in the nylon 66 industry according to claim 1, characterized in that: The mass ratio between sodium carbonate and caustic soda in S3 is 2 - 4:

1.

6. The detoxification method of zinc-containing wastewater in the nylon 66 industry according to claim 1, characterized in that: In S4, the dosage of citric acid is 1.1 - 1.3 times the zinc ion concentration. After adding citric acid, use one of hydrochloric acid or sodium hydroxide to adjust the pH to 7.0 - 7.

5.

7. A method for detoxifying zinc-containing wastewater in the nylon 66 industry according to claim 1, characterized in that: The sieve pore size in S4 is 50 - 100 μm.

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