Detoxification method for zinc-containing wastewater in nylon 66 industry

Abstract

The invention discloses a detoxification method for zinc-containing wastewater in the nylon 66 industry, which comprises the following steps: removing organic pollutants and strengthening zinc ion trapping by using polyaluminum chloride and nano-hydroxyapatite under an acidic condition, and carrying out sodium carbonate-caustic soda synergistic precipitation at an alkaline stage to enable zinc ions to form zinc hydroxide; the efficient solid-liquid separation is achieved through cooperation with the flocculation effect of polyacrylamide, citric acid is adjusted to be neutral to ensure the stability of zinc precipitation, organic matter is synergistically removed in the multi-stage coagulation and adsorption process, the zinc ion concentration in the whole wastewater treatment system is reduced, the toxicity of zinc to microorganisms in a biochemical system can be effectively eliminated, the enrichment risk of zinc in sludge is reduced, and the wastewater treatment effect is improved. The efficiency can be improved, the water quality can be improved, the microbial activity can be recovered, stable operation of subsequent biochemical treatment is guaranteed, effective detoxification is realized, and the defect of poor detoxification effect in a zinc-containing wastewater detoxification method in the prior art is overcome.

Description

Technical Field

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

[0002] Nylon 66 is an important polyamide synthetic fiber, with the chemical name of polyhexamethylene adipamide. It is a translucent or opaque milky white thermoplastic resin formed by the polycondensation of adipic acid and hexamethylenediamine. The cyclohexanol production process in the nylon 66 industry will discharge a certain amount of zinc-containing wastewater. Zinc ions are highly toxic to the denitrification and denitrification system and subsequent biochemical systems, which will poison the sludge and microorganisms in the biochemical system.

[0003] Too high zinc ion concentration in sludge will affect the flocculation and sedimentation properties of sludge, resulting in reduced sludge sedimentation and affecting the treatment effect. Sludge poisoning will destroy 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 a weakened ability of microorganisms to decompose organic matter in wastewater and a prolonged treatment time.

[0004] At present, the treatment methods for zinc-containing wastewater mainly use ion exchange and membrane separation. The ion exchange method uses ion exchange resins and other exchange agents to remove zinc ions in wastewater, but the exchange agents need to be regenerated or replaced regularly, which increases the operating cost. Membrane separation technology is prone to membrane contamination during operation, resulting in a decrease in membrane flux. The membrane components need to be cleaned or replaced regularly, which increases the operating cost and affects 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 aggravate the blockage, making the detoxification effect of zinc-containing wastewater worse.

[0005] Therefore, it is necessary to improve the detoxification method of 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 prior art method 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 nylon 66 industry, comprising the following steps: S1: Adjust the pH of zinc-containing wastewater to 5.5-6.5, add polyaluminium chloride and stir for 5-10 minutes; S2: adding sodium polyacrylate and nano-hydroxyapatite to the zinc-containing wastewater in S1 after adding polyaluminium chloride to obtain pretreated wastewater; S3: placing sodium carbonate and caustic soda together in the pretreated wastewater in S2, adjusting the pH of the wastewater to 8.8-9.2 and adding polyacrylamide; S4: adding citric acid to the zinc-containing wastewater with a pH of 8.8-9.2 in S3 and adjusting the pH to 7.0-7.5, filtering the generated zinc hydroxide precipitate and sludge using a sieve, and leaving the sludge.

[0008] In a preferred embodiment of the present invention, the ratio between the dosage of the sodium polyacrylate in S2 and the chemical oxygen demand is 0.003-0.005:1, and the dosage unit of the sodium polyacrylate is mg / L.

[0009] 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.

[0010] In a preferred embodiment of the present invention, the mass ratio between the polyaluminium chloride and the polyacrylamide is 100-200:1, and the total mass added is 6-6.5 times the mass of zinc ions in each liter of wastewater.

[0011] 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.

[0012] In a preferred embodiment of the present invention, sodium alginate is added to S3 at the same time as sodium carbonate and caustic soda, and the amount of sodium alginate added is 30-80% of the zinc ion concentration.

[0013] In a preferred embodiment of the present invention, sodium sulfide is added to S3 at the same time as sodium carbonate and caustic soda, and the amount of sodium sulfide added is 150-250% of the concentration of sodium alginate.

[0014] In a preferred embodiment of the present invention, ferrous sulfate is added when citric acid is added to S4, and the amount of ferrous sulfate added is 1.1-1.3 times the amount of sodium sulfide added.

[0015] In a preferred embodiment of the present invention, the dosage of citric acid in S4 is 1.1-1.3 times the concentration of zinc ions, and after adding citric acid, one of hydrochloric acid or sodium hydroxide is used to adjust the pH to 7.0-7.5.

[0016] In a preferred embodiment of the present invention, the mesh size of the S4 is 50-100 μm.

[0017] The present invention solves the defects existing in the background technology and has the following beneficial effects: (1) The present invention provides a method for detoxifying zinc-containing wastewater in the nylon 66 industry, which uses polyaluminium chloride and nano-hydroxyapatite under acidic conditions to remove organic pollutants and enhance zinc ion capture, uses sodium carbonate-caustic soda synergistic precipitation in the alkaline stage to convert zinc ions into zinc hydroxide, cooperates with the flocculation effect of polyacrylamide to achieve efficient solid-liquid separation, and adjusts to neutral with citric acid to ensure the stability of zinc precipitation. Compared with the zinc-containing wastewater detoxification method in the prior art, the multi-stage coagulation and 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, 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, achieves effective detoxification, and solves the defect of poor detoxification effect in the zinc-containing wastewater detoxification method in the prior art.

[0018] (2) In the present invention, sodium alginate is added at the same time as sodium carbonate and caustic soda. The addition of sodium alginate improves the structure of the sludge, making it looser. Compared with the prior art, the porosity of the sludge is increased, which helps the distribution and growth of microorganisms in the sludge and improves the biodegradability of the sludge. Sodium alginate forms alginate under alkaline conditions and can combine with zinc ions to form an insoluble complex, thereby more effectively removing zinc ions.

[0019] (3) In the present invention, sodium sulfide is added at the same time as sodium carbonate and caustic soda, and ferrous sulfate is added when citric acid is added. Compared with the prior art, citric acid as a reducing agent can reduce difficult-to-degrade organic matter and convert it into a form that is more easily decomposed by microorganisms. The reducing property of Fe²+ can promote the reduction and degradation of organic matter and improve the degradation efficiency of organic matter.

[0020] (4) In the present invention, sodium carbonate and caustic soda are added to form zinc hydroxide from zinc ions. Zinc hydroxide is a compound that is insoluble in water and can be separated from wastewater. Citric acid ensures the stability of zinc hydroxide and zinc carbonate while adjusting the wastewater to neutral. Compared with the prior art, the present invention can effectively remove zinc ions in wastewater and reduce the toxicity of zinc to microorganisms and sludge.

[0021] (5) In the present invention, sodium alginate has good gelling properties and can form a protective film on the surface of 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 and protect the activity of microorganisms. The addition of sodium alginate improves the structure of the sludge, making it looser, increases the porosity of the sludge, helps the distribution and growth of microorganisms in the sludge, and improves the biodegradability of the sludge. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] 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. Figure 1 It is a method step diagram of a preferred embodiment of the present invention. DETAILED DESCRIPTION

[0023] 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.

[0024] 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.

[0025] If only the pH adjustment method is used to detoxify 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 zinc ions in the sludge by only using the pH adjustment method.

[0026] 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.

[0027] like Figure 1 As shown, a method for detoxifying zinc-containing wastewater in the nylon 66 industry comprises the following steps: S1: Adjust the pH of zinc-containing wastewater to 5.5-6.5, and add polyaluminium chloride and stir for 5-10 minutes; acidic conditions help to destroy the complex bonds between organic matter and zinc ions and release free zinc ions. Use the electrical neutralization effect of polyaluminium chloride to destroy the complex bonds between organic matter such as hexamethylenediamine and zinc, release free zinc ions, lay the foundation for subsequent removal, and remove some suspended organic matter, reducing the risk of subsequent zinc-organic complexation. Polyaluminium chloride hydrolyzes to form multinuclear hydroxyl complexes, adsorbs colloidal organic matter, and reduces the risk of subsequent zinc recombination. Polyaluminium chloride can also capture organic matter in wastewater, including adipic acid, through flocculation, reducing the difficulty of subsequent treatment.

[0028] S2: Sodium polyacrylate and nano-hydroxyapatite are added to the zinc-containing wastewater in S1 after adding polyaluminium chloride to obtain pretreated wastewater; nano-hydroxyapatite, with its high specific surface area and specific adsorption capacity for zinc, preferentially captures free zinc ions and reduces the probability of its recombination with organic matter such as hexamethylenediamine. Organic colloids are dispersed by electrostatic repulsion to prevent them from wrapping zinc ions to form stable complexes, thereby increasing the exposure of zinc ions. Polyaluminium chloride releases zinc ions, and nano-hydroxyapatite quickly adsorbs zinc ions to form a stable zinc-hydroxyapatite complex, thereby efficiently removing zinc ions. Sodium polyacrylate enhances the flocculation effect of nano-hydroxyapatite, while capturing zinc ions and organic pollutants, further reducing the chemical oxygen demand of the wastewater. Nano-hydroxyapatite captures adipic acid in the wastewater by surface adsorption and chemical bonding, reducing its concentration in the wastewater.

[0029] S3: Sodium carbonate and caustic soda are placed together in the pretreated wastewater in S2, the pH of the wastewater is adjusted to 8.8-9.2 and polyacrylamide is added; stable zinc hydroxide precipitation is generated under weak alkaline conditions to avoid the toxicity of excessively high pH to microorganisms, while sodium carbonate provides carbonate to enhance the precipitation effect. Alkaline conditions are conducive to the hydrolysis and oxidation of some organic matter, further promoting the degradation of adipic acid.

[0030] 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. Use a sieve to filter the generated zinc hydroxide precipitate and sludge, leaving the sludge. The citric acid is adjusted to neutral to prevent zinc hydroxide from re-dissolving in a strong acidic environment and to avoid residual alkalinity from inhibiting the biochemical system.

[0031] By adjusting pH in stages, we can provide a suitable reaction environment for different materials and avoid the contradictions under a single pH condition. The acidic stage destroys the complex bond and releases zinc ions, the alkaline stage precipitates zinc ions, and the neutral stage stabilizes zinc ions to ensure 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.

[0032] The invention utilizes polyaluminium chloride and nano-hydroxyapatite to remove organic pollutants and strengthen zinc ion capture under acidic conditions, adopts sodium carbonate-caustic soda synergistic precipitation in the alkaline stage to convert zinc ions into zinc hydroxide, cooperates with the flocculation effect of polyacrylamide to realize efficient solid-liquid separation, and adjusts to neutral with citric acid to ensure the stability of zinc precipitation. The multi-stage coagulation and 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, 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 detoxification method of zinc-containing wastewater in the prior art.

[0033] The ratio between the dosage of sodium polyacrylate in S2 and 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. The zinc ions adsorbed on the surface of the nanomaterial are wrapped and fixed by the polymer chain, 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 wastewater. Through the synergistic effect with polyaluminium chloride and nano-hydroxyapatite, sodium polyacrylate can further enhance the capture and removal of organic matter.

[0034] The particle size of nanohydroxyapatite is 80-150nm, and the dosage of nanohydroxyapatite is 1%-3% of the zinc ion concentration. Nanohydroxyapatite has a large specific surface area and high chemical activity. It can capture zinc ions in wastewater by surface adsorption and chemical bonding, and can quickly form a stable zinc-hydroxyapatite complex, thereby reducing the free concentration of zinc ions in wastewater. Nanohydroxyapatite can fix zinc ions on its surface or internal structure to form stable precipitates. These precipitates are removed in the subsequent filtration steps, thereby reducing the risk of zinc enrichment in sludge and reducing the long-term toxicity of sludge to microorganisms. Under acidic conditions, nanohydroxyapatite works together with polyaluminum chloride and sodium polyacrylate to form composite flocs. This composite floc can more efficiently capture and remove organic matter in wastewater, further reducing the chemical oxygen demand of wastewater.

[0035] The mass ratio between sodium carbonate and caustic soda in S1 is 2-4:1. The combination of sodium carbonate and caustic soda reacts with carbonate and hydroxide to form zinc hydroxide precipitation by adjusting the pH value of the wastewater to alkaline. The formation of zinc hydroxide can significantly reduce the zinc ion concentration in the wastewater, thereby reducing 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 quickly precipitated and removed from the wastewater, thereby reducing the direct contact of zinc ions with microorganisms and restoring the activity of microorganisms.

[0036] The combination of sodium carbonate and caustic soda not only promotes the precipitation of zinc ions, but also improves the removal efficiency of pollutants in nylon 66 wastewater by increasing the pH value of the wastewater, making it easier for other soluble pollutants in the wastewater to precipitate or be adsorbed. The removal of zinc ions and the adjustment of pH provide a more suitable living environment for microorganisms, enabling them to more effectively decompose complex organic matter in wastewater. At the same time, the alkaline environment facilitates the hydrolysis and oxidation of some organic matter, further promoting its degradation. By removing zinc ions and other pollutants, the biodegradability of the wastewater is improved, and microorganisms are able to more efficiently decompose the remaining organic pollutants, thereby improving the overall treatment efficiency.

[0037] The mass ratio between polyaluminium chloride and polyacrylamide is 100-200:1, and the total mass added is 6-6.5 times the mass of zinc ions in each liter of wastewater. The polyaluminium chloride in the flocculant is hydrolyzed 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 easy to precipitate and filter. In this way, zinc ions are effectively removed, reducing their toxicity to sludge and microorganisms. The synergistic effect of polyaluminium chloride and polyacrylamide not only targets zinc ions, but also adsorbs and precipitates other pollutants in wastewater, such as organic matter, suspended matter and some heavy metals. These pollutants are adsorbed by the flocculant to form larger flocs, which are convenient for subsequent filtration and separation, thereby improving the removal efficiency of pollutants.

[0038] Sodium alginate is added to S1 at the same time as sodium carbonate and caustic soda, and the amount of sodium alginate added is 30-80% of the zinc ion concentration. Sodium carbonate and caustic soda adjust the pH of the wastewater to alkaline, so that the zinc ions 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, thereby more effectively removing zinc ions.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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 them from re-dissolving. 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 is reducing and can improve the redox environment of sludge. By reducing oxidative stress in 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+ It is a trace element necessary for the growth of many microorganisms and can participate in the metabolic process of microorganisms as an enzyme cofactor. 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.

[0045] The synergistic effect of citric acid and ferrous sulfate helps to degrade organic matter. Citric acid, as a reducing agent, can reduce refractory organic matter and convert it into a form that is more easily decomposed by microorganisms. At the same time, the reducing property of Fe²+ also helps to reduce and degrade organic matter, improving 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 carboxylic acid oxygen. This synergistic coordination effect enhances the stability of zinc ions, prevents zinc ions from being in a free state, and removes them better through adsorption.

[0046] The dosage of citric acid in S2 is 1.1-1.3 times the concentration of zinc ions. After adding citric acid, use 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 can effectively stabilize zinc ions and prevent them from re-dissolving into wastewater, thereby reducing the toxicity of zinc to sludge and microorganisms. The addition of citric acid and the adjustment of pH provide a more suitable living environment for microorganisms. The neutral to slightly alkaline pH value is conducive to the growth and metabolic activities of microorganisms and restores their activity.

[0047] The mesh aperture of S2 is 50-100μm. The mesh 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. The larger particles in the sludge are intercepted by the filtering action of the mesh, which helps to improve the structure of the sludge, making it looser and increasing the porosity. This provides a better living environment for microorganisms and helps to restore the activity of microorganisms. The suspended matter and organic matter particles intercepted by the mesh can form larger flocs, which provide more attachment sites for microorganisms, allowing microorganisms to decompose organic matter more effectively.

[0048] Embodiment 1: This embodiment provides a method for detoxifying zinc-containing wastewater in the nylon 66 industry, comprising the following steps: S1: Adjust the pH of zinc-containing wastewater to 6.0, add polyaluminium chloride and stir for 8 minutes; S2: Sodium polyacrylate and nano-hydroxyapatite are added to the zinc-containing wastewater in S1 after adding polyaluminium chloride. The ratio between the dosage of sodium polyacrylate and the chemical oxygen demand is 0.004:1. The dosage unit of sodium polyacrylate is mg / L. The particle size of nano-hydroxyapatite is 100nm. The dosage of nano-hydroxyapatite is 2% of the zinc ion concentration to obtain pretreated wastewater.

[0049] S3: Sodium carbonate and caustic soda are placed together in pretreatment, the mass ratio between sodium carbonate and caustic soda is 3:1, the pH of the wastewater is adjusted to 8.6 and polyacrylamide is added, the mass ratio between polyaluminum chloride and polyacrylamide is 150:1, and the total mass added is 6 times the mass of zinc ions per liter of wastewater; sodium alginate and sodium sulfide are added at the same time as sodium carbonate and caustic soda, the addition amount of sodium alginate is 30% of the zinc ion concentration, and the addition amount of sodium sulfide is 150% of the sodium alginate.

[0050] S4: Add citric acid to the zinc-containing wastewater in S3 and adjust the pH to 7.5. Use a sieve to filter the generated zinc hydroxide precipitate and sludge, leaving the sludge. Add ferrous sulfate when adding citric acid. The amount of ferrous sulfate added is 1.2 times the amount of sodium sulfide added, and the amount of citric acid added is 1.1 times the zinc ion concentration. After adding citric acid, adjust the pH to 7.3 and the mesh aperture is 50μm.

[0051] Embodiment 2: The difference between this embodiment and embodiment 1 is that the pH value of the wastewater is adjusted to 8.8 in S3, and the rest is the same.

[0052] Embodiment 3: This embodiment differs from Embodiment 1 in that the pH value of the wastewater is adjusted to 9.0 in S3, and the rest are the same.

[0053] Embodiment 4: This embodiment differs from Embodiment 1 in that the pH value of the wastewater is adjusted to 9.2 in S3, and the rest are the same.

[0054] Embodiment 5: This embodiment differs from Embodiment 1 in that the pH value of the wastewater is adjusted to 9.4 in S3, and the rest are the same.

[0055] Example 6: The difference between this example and Example 3 is that the dosage of sodium sulfide in S3 is 100% of that of sodium alginate, and the rest are the same.

[0056] Embodiment 7: This embodiment differs from Embodiment 3 in that the dosage of sodium sulfide in S3 is 200% of that of sodium alginate, and the rest are the same.

[0057] Embodiment 8: The difference between this embodiment and embodiment 3 is that the dosage of sodium sulfide in S3 is 250% of that of sodium alginate, and the rest are the same.

[0058] Embodiment 9: The difference between this embodiment and embodiment 3 is that the dosage of sodium sulfide in S3 is 300% of that of sodium alginate, and the rest are the same.

[0059] Comparative Example 1: This comparative example provides zinc-containing wastewater from the nylon 66 industry in which both untreated sludge and microorganisms are poisoned by zinc.

[0060] The COD value of the zinc-containing wastewater in the nylon 66 industry before treatment in Examples 1 to 9 and Comparative Example 1 is 3500 mg / L. The untreated wastewater in Examples 1 to 9 and Comparative Example 1 is compared with the wastewater after microbial treatment, the organic matter content in the wastewater is compared, the reduction rate of the organic matter content is calculated, and the zinc ion concentration of the wastewater after microbial treatment is tested. The test data are shown in Table 1.

[0061] Table 1 Organic matter content change rate and zinc ion concentration of Examples 1 to 9 and Comparative Example 1

[0062] It can be seen from Table 1 that the reduction rates of organic matter content in Examples 1 to 9 are all higher than that in Comparative Example 1, and the zinc ion concentrations in Examples 1 to 9 are all lower than that in Comparative Example 1, and the present application has superiority.

[0063] In Examples 1 to 5, as the pH of the wastewater is gradually increased, the organic matter content decreases, first increases and then decreases, and the zinc ion concentration 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. The flocculant aggregates the organic matter and suspended particles in the wastewater to form larger flocs through charge neutralization and net capture, which makes 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 precipitates, which promotes flocculation and microbial degradation, reduces the symptoms of zinc poisoning to microorganisms, increases the reduction rate of organic matter, and reduces the zinc ion concentration; but when the pH value is too high, the charge neutralization effect of the flocculant fails, resulting in a decrease in the flocculation effect. The organic matter cannot be effectively precipitated, the reduction rate begins to decrease, resulting in the failure of the flocculant and the decrease in microbial activity, the organic matter reduction rate begins to decrease, the organic matter reduction rate decreases, and the zinc ion concentration increases. The preferred embodiment is Example 3.

[0064] In Example 3 and Examples 6 to 9, as the ratio of the dosage of sodium sulfide to sodium alginate increases, the organic matter content decreases first and then decreases, and the zinc ion concentration decreases first and then increases. This is because the zinc sulfide precipitate generated by sodium sulfide can serve as the core of sodium alginate flocculation, further enhancing the flocculation effect, thereby more effectively removing organic matter. Sodium sulfide reacts with zinc ions to generate zinc sulfide precipitate, which increases the organic matter reduction rate and reduces the zinc ion concentration; however, when the dosage ratio of sodium sulfide to sodium alginate is too high, it will have a toxic effect on microorganisms, inhibit the growth and metabolic activity of microorganisms, and cause the biodegradation efficiency of organic matter to decrease, thereby reducing the organic matter content reduction rate. Excessive sulfur ions will increase the solubility of zinc sulfide precipitate, which reduces the organic matter reduction rate and increases the zinc ion concentration. The preferred embodiment is Example 7.

[0065] The above is based on the ideal embodiment of the present invention. Through the above description, relevant personnel can make various changes and modifications without departing from the technical concept of the present invention. The technical scope of the present 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 nylon 66 industry, characterized in that: The following steps are involved: S1: Adjust the pH of zinc-containing wastewater to 5.5-6.5, add polyaluminium chloride and stir for 5-10 minutes; S2: adding sodium polyacrylate and nano-hydroxyapatite to the zinc-containing wastewater in S1 after adding polyaluminium chloride to obtain pretreated wastewater; S3: placing sodium carbonate and caustic soda together in the pretreated wastewater in S2, adjusting the pH of the wastewater to 8.8-9.2 and adding polyacrylamide; S4: adding citric acid to the zinc-containing wastewater with a pH of 8.8-9.2 in S3 and adjusting the pH to 7.0-7.5, filtering the generated zinc hydroxide precipitate and sludge using a sieve, and leaving the sludge.

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

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

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

1.

6. The method for detoxifying zinc-containing wastewater in nylon 66 industry according to claim 1, characterized in that: Sodium alginate is added to S3 at the same time as sodium carbonate and caustic soda, and the amount of sodium alginate added is 30-80% of the zinc ion concentration.

7. A method for detoxifying zinc-containing wastewater in nylon 66 industry according to claim 6, characterized in that: Sodium sulfide is added to S3 at the same time as sodium carbonate and caustic soda, and the amount of sodium sulfide added is 150-250% of the concentration of sodium alginate.

8. The method for detoxifying zinc-containing wastewater in nylon 66 industry according to claim 7, characterized in that: When citric acid is added to S4, ferrous sulfate is added, and the amount of ferrous sulfate added is 1.1-1.3 times the amount of sodium sulfide added.

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

5.

10. The method for detoxifying zinc-containing wastewater in nylon 66 industry according to claim 1, characterized in that: The mesh size of S4 is 50-100 μm.

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