A deep denitrification method for sulfur autotrophic denitrification in wastewater

Abstract

This invention belongs to the field of wastewater treatment, specifically relating to a method for deep denitrification of wastewater via autotrophic denitrification. Modified sulfur and sodium thiosulfate are used as electron donors, and an adsorbent is used to adsorb sulfate ions. A sulfur solution is used as the solvent phase; oligodextrose and polyethylene glycol are dissolved in water as the antisolvent phase; the antisolvent phase and solvent phase are mixed, ultrasonically dispersed, and dried to obtain modified sulfur; silica is loaded onto the surface of hydrotalcite, etched with organic acid, and heat-treated to obtain the adsorbent. The method of this invention yields elemental sulfur with higher solubility and dispersion, less loss, and effective adsorption of sulfate ions. It achieves good denitrification effect with a shorter hydraulic retention time and low denitrification cost.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment, specifically relating to a method for deep denitrification of sulfur through autotrophic denitrification in wastewater. Background Technology

[0002] Sulfate autotrophic denitrification utilizes sulfur autotrophic denitrifying bacteria (such as Thiobacillus denitrificans) under anaerobic or anoxic conditions, using elemental sulfur or sulfur compounds as electron donors to convert NO into nitrogen. 3- and NO 2- The process of reducing sulfur to nitrogen (N2) to achieve denitrification is widely studied due to its advantages such as low cost, good denitrification effect, and relatively low sulfate production. However, SO has very low solubility in water, and its soft texture causes it to clump after prolonged immersion in water, easily leading to reactor blockage and affecting the denitrification efficiency of the denitrification system. Simultaneously, the consumed reducing sulfur generates sulfate ions during the reaction; excessive sulfate ions can affect the denitrification rate and effluent quality, and also result in sulfur waste. Summary of the Invention

[0003] To address the problems in existing technologies where elemental sulfur is poorly soluble in water, prone to caking, and produces high levels of sulfate ions in the effluent, this invention provides a wastewater sulfur autotrophic denitrification deep denitrification method that efficiently utilizes elemental sulfur and produces effluent with low sulfate ion levels. The technical solution is as follows:

[0004] A deep denitrification method for sulfur autotrophic denitrification in wastewater uses modified sulfur and sodium thiosulfate as electron donors and an adsorbent to adsorb sulfate ions; the mass ratio of modified sulfur to sodium thiosulfate is 1:0.1~5.

[0005] Furthermore, the preparation of the modified sulfur includes the following steps: weighing sulfur and dissolving it in toluene at 60~85℃, stirring magnetically at room temperature until completely dissolved, and using the resulting sulfur solution as the solvent phase; taking oligodextrose and polyethylene glycol dissolved in water as the antisolvent phase; mixing the antisolvent phase and the solvent phase at a volume ratio of 5~10:1, ultrasonically dispersing, and drying to obtain the modified sulfur.

[0006] Furthermore, the concentration of the sulfur solution is 20-40 g / L; the concentration of oligodextrose in the antisolvent phase is 2-4 g / L, and the concentration of polyethylene glycol is 0.5-1.5 g / L.

[0007] Furthermore, ultrasonic dispersion is carried out for 30-60 minutes; during ultrasonic dispersion, the temperature is reduced to 15-30℃ at a rate of 5-10℃ / min.

[0008] Furthermore, the preparation of the adsorbent includes the following steps: loading silica onto the surface of hydrotalcite, dissolving it with an organic acid, and then heat-treating it to obtain the adsorbent.

[0009] Furthermore, the organic acid includes one or more of citric acid, acetic acid, lactic acid, benzoic acid, or acrylic acid.

[0010] Furthermore, this includes the following steps:

[0011] a. Place hydrotalcite in an aqueous solution of ethanol and mix thoroughly; add ammonia to make the solution alkaline, add tetraethyl silicate, and after the reaction is complete, wash and dry to obtain the precursor;

[0012] b. Prepare an organic acid dilution solution by placing the precursor in an aqueous ethanol solution and continuously adding the organic acid dilution solution dropwise over 0.3 to 1 hour while stirring, maintaining the pH of the system at a weakly acidic level. Then, let it stand for 3 to 5 hours. Collect the precipitate, wash and dry it, and then heat-treat it to remove residual acid to obtain the adsorbent.

[0013] Furthermore, the concentration of the aqueous ethanol solution in step a is 75-90% v / v; the mass ratio of tetraethyl silicate to hydrotalcite in step a is 1:2-5; and the reaction in step a is carried out at 40-65°C for 3-5 hours.

[0014] Furthermore, the concentration of the aqueous ethanol solution in step b is 15-40% v / v; the heat treatment in step b is performed at 200-250°C for 4-6 hours.

[0015] Furthermore, the dosage ratio is C / N = 3~1; the operating temperature is 15~35℃; and the hydraulic retention time is 6~24h.

[0016] By adopting the above scheme, the method of the present invention has the following advantages:

[0017] The wastewater sulfur autotrophic denitrification deep denitrification method of the present invention combines directly usable sodium thiosulfate with elemental sulfur that produces a slow-release effect, which makes the change in reduced sulfur content in the system more stable and is conducive to the full occurrence of sulfur autotrophy. The elemental sulfur in the method of the present invention has higher solubility and dispersion, is less prone to loss, and can effectively adsorb sulfate ions, achieving good denitrification effect with a shorter hydraulic retention time and low denitrification cost.

[0018] This invention refines sulfur particles, improving their dispersibility and solubility in water. The combination of oligodextrose and polyethylene glycol enhances the affinity between sulfur and oligodextrose, reducing sulfur particle aggregation. Furthermore, the network structure formed by oligodextrose and polyethylene glycol stabilizes sulfur particles during denitrification, reducing sulfur movement and aggregation, minimizing sulfur loss, and minimizing the impact on equipment and denitrification efficiency.

[0019] The oligosaccharides and polyethylene glycol of this invention are bio-friendly and biodegradable. During the denitrification process, as the reaction proceeds, the surface oligosaccharides and polyethylene glycol are gradually degraded, exposing sulfur particles, thus enabling control over the amount of sulfur added and making the sulfur content in the system more stable.

[0020] This invention uses oligodextrose and polyethylene glycol to modify sulfur particles. The presence of sulfur particles also facilitates the colonization of bacteria on the oligodextrose and polyethylene glycol framework, which is conducive to the reproduction of sulfur autotrophic bacteria.

[0021] The adsorbent of this invention exhibits strong selective adsorption capacity for sulfate ions and has a stable structure. It does not participate in the reaction during the denitrification process, causing sulfate ions to aggregate, which is beneficial for the colonization of reductive microorganisms and the reduction of sulfate ions, thereby reducing the amount of electron donors required in the system. Simultaneously, it can also reduce the concentration of sulfate ions in the effluent, improving effluent quality.

[0022] This invention loads silica onto the surface of hydrotalcite, utilizing the stability of silica to ensure the stability of the hydrotalcite structure and reduce the damage to the hydrotalcite structure and pores caused by the denitrification process; then, a mild organic acid is used for dissolution, increasing the surface area of ​​the material, improving adsorption performance, and reducing the influence of hydrotalcite on the pH of the system.

[0023] This invention involves heat-treating the dissolved hydrotalcite to remove residual organic acids and to activate the material, thereby improving its activity and load stability.

[0024] The sulfur autotrophic denitrification deep denitrification method of the present invention is applicable to the deep denitrification of nitrate wastewater with different concentrations. The raw materials are easy to obtain, the preparation method is simple, the wastewater treatment cost is low, and it is highly practical. Attached Figure Description

[0025] Figure 1 This is a graph showing the change in nitrate nitrogen concentration in the effluent of Example 1;

[0026] Figure 2 This is a graph showing the change in nitrate nitrogen concentration in the effluent of Example 2;

[0027] Figure 3 This is a graph showing the change in nitrate nitrogen concentration in the effluent of Example 3;

[0028] Figure 4 This is a graph showing the change in nitrate nitrogen concentration in the effluent of Example 4. Detailed Implementation

[0029] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] Example 1: (1) Sulfur was weighed and dissolved in toluene at 70°C. The solution was magnetically stirred at room temperature until completely dissolved, and the resulting sulfur solution with a concentration of 40 g / L was used as the solvent phase. Oligosaccharides and polyethylene glycol were dissolved in water to form an antisolvent phase with a concentration of 3 g / L for oligosaccharides and a concentration of 1 g / L for polyethylene glycol. The antisolvent phase and the solvent phase were mixed at a volume ratio of 10:1 and ultrasonically dispersed for 60 min. During the ultrasonic dispersion process, the temperature was lowered to 20°C at a rate of 5°C / min. After drying, modified sulfur was obtained.

[0031] (2) Place 3 parts by mass of hydrotalcite in an aqueous solution of 80% v / v ethanol and mix thoroughly; add ammonia to make the solution alkaline, add 1 part by mass of tetraethyl silicate, react at 60°C for 4 hours, wash and dry to obtain the precursor;

[0032] (3) Prepare citric acid dilution solution. Place the precursor in an aqueous solution of ethanol with a concentration of 30% v / v. Add citric acid dilution solution dropwise while stirring over 0.5 h, and keep the pH of the system weakly acidic. Then let it stand for 5 h. Collect the precipitate, wash and dry it, and heat treat it at 220℃ for 6 h to obtain the adsorbent.

[0033] Example 2: The difference from Example 1 is that: (1) Sulfur was weighed and dissolved in toluene at 70°C, and magnetically stirred at room temperature until completely dissolved. The resulting sulfur solution with a concentration of 20 g / L was used as the solvent phase. Oligosaccharides and polyethylene glycol were dissolved in water to form an antisolvent phase with a concentration of 3 g / L for oligosaccharides and a concentration of 1 g / L for polyethylene glycol. The antisolvent phase and the solvent phase were mixed at a volume ratio of 10:1 and ultrasonically dispersed for 30 min. During the ultrasonic dispersion process, the temperature was lowered to 20°C at a rate of 5°C / min. After drying, modified sulfur was obtained.

[0034] Example 3: The difference from Example 1 is that: (1) Sulfur was weighed and dissolved in toluene at 70°C, and magnetically stirred at room temperature until completely dissolved. The resulting sulfur solution with a concentration of 40 g / L was used as the solvent phase. Oligosaccharides and polyethylene glycol were dissolved in water to form an antisolvent phase with a concentration of 3 g / L for oligosaccharides and a concentration of 1 g / L for polyethylene glycol. The antisolvent phase and the solvent phase were mixed at a volume ratio of 5:1 and ultrasonically dispersed for 30 min. During the ultrasonic dispersion process, the temperature was lowered to 20°C at a rate of 5°C / min. After drying, the modified sulfur was obtained.

[0035] Example 4: The difference from Example 1 is that: (1) Sulfur was weighed and dissolved in toluene at 70°C, and magnetically stirred at room temperature until completely dissolved. The resulting sulfur solution with a concentration of 40 g / L was used as the solvent phase. Oligosaccharides and polyethylene glycol were dissolved in water to form an antisolvent phase with a concentration of 3 g / L for oligosaccharides and 1 g / L for polyethylene glycol. The antisolvent phase and the solvent phase were mixed at a volume ratio of 10:1 and ultrasonically dispersed for 30 min. During the ultrasonic dispersion process, the temperature was lowered to 20°C at a rate of 10°C / min. After drying, the modified sulfur was obtained.

[0036] Example 5: The difference from Example 1 is that: (2) 2 parts by mass of hydrotalcite were placed in an aqueous solution of ethanol with a concentration of 80% v / v and mixed thoroughly; ammonia was added to make the solution alkaline, 1 part by mass of tetraethyl silicate was added, and the reaction was carried out at 60°C for 4 hours. After washing and drying, the precursor was obtained.

[0037] Example 6: The difference from Example 1 is that: (3) a citric acid dilution was prepared by placing the precursor in an aqueous solution of ethanol with a concentration of 30% v / v, continuously adding the citric acid dilution while stirring for 1 hour, and keeping the pH of the system weakly acidic, and then letting it stand for 5 hours; the precipitate was collected, washed and dried, and then heat-treated at 220°C for 6 hours to obtain the adsorbent.

[0038] Example 7: The difference from Example 1 is that: (3) a citric acid dilution was prepared by placing the precursor in an aqueous solution of ethanol with a concentration of 30% v / v, continuously adding the citric acid dilution while stirring for 0.5 h, and keeping the pH of the system weakly acidic, and then letting it stand for 5 h; the precipitate was collected, washed and dried, and then heat-treated at 250°C for 6 h to obtain the adsorbent.

[0039] Example 8: The difference from Example 1 is that: (3) a citric acid dilution was prepared by placing the precursor in an aqueous solution of ethanol with a concentration of 30% v / v, continuously adding the citric acid dilution while stirring for 0.5 h, and keeping the pH of the system weakly acidic, and then letting it stand for 5 h; the precipitate was collected, washed and dried, and then heat-treated at 220°C for 4 h to obtain the adsorbent.

[0040] Test example: Sodium thiosulfate and modified sulfur prepared in the example were weighed at a mass ratio of 1:5, along with 5% of the total mass of adsorbent. Then, 5% of the total mass of gelatinized starch and 10% of the total mass of limestone were added. After mixing evenly, 10% of the solid mass of water was added and mixed evenly. The mixture was then granulated. The resulting granules were dried in a vacuum oven at 180~190℃ for 2 hours to obtain the filler.

[0041] Different formulations of sulfur-autotrophic denitrification packing materials from each embodiment were loaded into 1L upflow reactors. Activated sludge with an inoculum concentration of approximately 3000 mg / L LMLVSS was inoculated. The influent nitrate nitrogen concentration was 200 mg / L, ammonia nitrogen concentration was 5 mg / L, total phosphorus concentration was 1 mg / L, and the hydraulic retention time was 12 h. Effluent nitrate nitrogen was measured to evaluate the denitrification effect. Results are as follows: Figures 1-4 As shown.

[0042] Depend on Figure 1 It can be seen that the average effluent nitrate nitrogen using the packing material of Example 1 after 30 days of operation was 30.1 mg / L. Compared with Example 1, the sulfur concentration in the solvent phase of Example 2 was lower, and the sulfur dispersion was greater. Figure 2 It can be seen that the average effluent nitrate nitrogen using the packing material in Example 2 was 27.5 mg / L. Comparing the influent and effluent data, the average effluent nitrate nitrogen in Example 2 was slightly lower than that in Example 1, indicating that the denitrification capacity of the wastewater sulfur autotrophic denitrification deep denitrification method in Example 2 was slightly stronger than that in Example 1. This may be because the sulfur particle size is smaller, which is more conducive to microbial utilization. However, during the preparation process, the sulfur yield in Example 2 was significantly lower than that in Example 1, and the increase in denitrification capacity was less than the decrease in sulfur yield.

[0043] Compared to Example 1, the amount of antisolvent added in Example 3 is less than that in Example 1. Figure 3 In Example 3, the average nitrate nitrogen content in the effluent was 31.3 mg / L. The initial nitrate nitrogen load and total nitrogen load in Example 3 did not change significantly compared to Example 1, but the denitrification effect was significantly improved in the later stages. This indicates that more desolvents are beneficial for the refinement of sulfur particles, but they can also easily lead to excessive content of oligosaccharides and polyethylene glycol, affecting the initial sulfur release.

[0044] Compared to Example 1, Example 4 exhibits a faster cooling rate during the preparation of modified sulfur. Figure 4 In this study, the average effluent nitrate nitrogen content was 35 mg / L. This indicates that the denitrification capacity of Example 4 was not as good as that of Example 1, suggesting that excessively rapid cooling is detrimental to the refinement of sulfur particles, thus affecting the solubility and bioavailability of modified sulfur.

[0045] The sulfate ion content in the effluent of Examples 1 and 5-8 was tested, and the results are shown in the table below:

[0046] Table 1

[0047]

[0048] As shown in the table above, compared to Example 1, Example 5 had a relatively higher silicon content, but the sulfate ion concentration in the effluent actually increased. This may be because the increased silicon loading and coating can affect the adsorption channels of the hydrotalcite, weakening the selective adsorption capacity of the adsorbent for sulfate ions. Example 6 had a longer acid dissolution time than Example 1, which theoretically should have generated more adsorption channels, but the sulfate ion concentration increased slightly. This may be because the excessively long acid dissolution time affected the structure of the hydrotalcite, thus affecting the adsorption of sulfate ions. Example 7 had a higher heat treatment temperature and a lower sulfate ion concentration in the effluent; Example 8 had a shorter heat treatment time and a higher sulfate ion concentration in the effluent. This indicates that higher temperatures and times are beneficial for improving the adsorbent's adsorption of sulfate ions, or for the reduction of sulfate ions by reducing bacteria.

[0049] For those skilled in the art, various other corresponding changes and modifications can be made based on the technical solutions and concepts described above, and all such changes and modifications should fall within the protection scope of the claims of this invention.

Claims

1. A method for advanced denitrification of wastewater by sulfur autotrophic denitrification, characterized in that, The modified sulfur and sodium thiosulfate are used as electron donors, and an adsorbent is used to adsorb sulfate ions; the mass ratio of the modified sulfur to the sodium thiosulfate is 1:0.1-5; The preparation of the modified sulfur comprises the following steps: weighing sulfur and dissolving the sulfur in toluene at 60-85°C, magnetically stirring at room temperature until complete dissolution, and taking the obtained sulfur solution as a solvent phase; taking oligomeric glucose and polyethylene glycol dissolved in water as an anti-solvent phase; mixing the anti-solvent phase and the solvent phase at a volume ratio of 5-10:1, ultrasonic dispersion, and drying to obtain the modified sulfur.

2. The process for wastewater sulfur autotrophic denitrification advanced nitrogen removal according to claim 1, characterized in that, The concentration of the sulfur solution is 20-40g / L; the concentration of the oligomeric glucose in the anti-solvent phase is 2-4g / L, and the concentration of the polyethylene glycol is 0.5-1.5g / L.

3. The process for wastewater sulfur autotrophic denitrification advanced nitrogen removal according to claim 1, characterized in that, Ultrasonic dispersion is performed for 30-60min; during the ultrasonic dispersion, the temperature is lowered to 15-30°C at a rate of 5-10°C / min.

4. The process for wastewater sulfur autotrophic denitrification advanced nitrogen removal according to claim 1, characterized in that, The preparation of the adsorbent comprises the following steps: The hydrotalcite is loaded with silica, and an organic acid is used for dissolution, and the adsorbent is obtained after heat treatment.

5. The process for wastewater sulfur autotrophic denitrification advanced nitrogen removal according to claim 4, characterized in that, The organic acid comprises one or more of citric acid, acetic acid, lactic acid, benzoic acid or acrylic acid.

6. The process for wastewater sulfur autotrophic denitrification advanced nitrogen removal according to claim 4, characterized in that, The preparation comprises the following steps: a. The hydrotalcite is placed in an aqueous ethanol solution, and mixed thoroughly; ammonia water is added to make the solution alkaline, and tetraethyl silicate is added, and the precursor is obtained after washing and drying after complete reaction; b. An organic acid diluent is prepared, the precursor is placed in an aqueous ethanol solution, the organic acid diluent is continuously added while stirring within 0.3-1h, the pH of the system is kept weakly acidic, and then the system is left to stand for 3-5h; the precipitate is collected, washed and dried, and the adsorbent is obtained after heat treatment to remove residual acid.

7. The process for wastewater sulfur autotrophic denitrification advanced nitrogen removal according to claim 6, characterized in that, The concentration of the aqueous ethanol solution in step a is 75-90%v / v; the mass ratio of the tetraethyl silicate to the hydrotalcite in step a is 1:2-5; and the reaction in step a is performed at 40-65°C for 3-5h.

8. The process for wastewater sulfur autotrophic denitrification advanced nitrogen removal according to claim 6, characterized in that, The concentration of the aqueous ethanol solution in step b is 15-40%v / v; and the heat treatment in step b is performed at 200-250°C for 4-6h.

9. The process for advanced denitrification of wastewater by sulfur autotrophic denitrification according to any one of claims 1 to 7, characterized in that, The operating temperature is 15-35°C; and the hydraulic retention time is 6-24h.

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