Sulfur autotrophic denitrification deep nitrogen removal method for wastewater

Abstract

The invention belongs to the field of sewage treatment, and particularly relates to a wastewater sulfur autotrophic denitrification deep nitrogen removal method. Modified sulfur and sodium thiosulfate are adopted as electron donors, and an adsorbent is adopted to adsorb sulfate ions; taking a sulfur solution as a solvent phase; dissolving glucose oligosaccharide and polyethylene glycol in water to serve as an anti-solvent phase; mixing the anti-solvent phase with the solvent phase, performing ultrasonic dispersion, and drying to obtain modified sulfur; silicon dioxide is loaded on the surface of hydrotalcite, organic acid is used for corrosion, and the adsorbent is obtained after heat treatment. According to the method, the elemental sulfur is higher in solubility, high in dispersity and not prone to loss, sulfate ions can be effectively adsorbed, the good denitrification effect can be achieved within the short hydraulic retention time, and the denitrification cost is low.

Description

Technical Field

[0001] The present invention belongs to the field of sewage treatment, and particularly relates to a method for deep denitrification of wastewater by sulfur autotrophic denitrification. Background Art

[0002] Sulfur autotrophic denitrification is a process in which sulfur autotrophic denitrifying bacteria (such as Thiobacillus denitrificans) use reduced sulfides such as elemental sulfur or sulfur compounds as electron donors under anaerobic or anoxic conditions to reduce NO 3- and NO 2- to N2, thereby achieving denitrification. S0 has been widely studied because of its advantages such as low price, good denitrification effect and relatively less sulfate produced. However, the solubility of S0 in water is too low, and S0 is soft and will become caked after being soaked in water for a long time, which easily leads to reactor blockage and affects the denitrification efficiency of the denitrification system. At the same time, the consumed reduced sulfur will generate sulfate ions during the reaction process. Excessive sulfate ions will affect the denitrification rate and effluent quality, and also cause waste of sulfur elements. Summary of the Invention

[0003] In order to solve the problems in the prior art that elemental sulfur is not easily soluble in water, is easy to cake, and there are more sulfate ions in the effluent, the present invention mainly provides a method for deep denitrification of wastewater by sulfur autotrophic denitrification that can efficiently utilize elemental sulfur and has less sulfate ions in the effluent. The technical solution is as follows: A method for deep denitrification of wastewater by sulfur autotrophic denitrification 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.

[0004] Further, the preparation of the modified sulfur includes the following steps: Weigh sulfur and dissolve it in toluene at 60 - 85°C, and magnetically stir at room temperature until completely dissolved to obtain a sulfur solution as the solvent phase; take low molecular weight glucose and polyethylene glycol and dissolve them in water as the anti-solvent phase; mix the anti-solvent phase and the solvent phase at a volume ratio of 5 - 10:1, ultrasonically disperse, and obtain modified sulfur after drying.

[0005] Further, the concentration of the sulfur solution is 20 - 40 g / L; the concentration of low molecular weight glucose in the anti-solvent phase is 2 - 4 g / L, and the concentration of polyethylene glycol is 0.5 - 1.5 g / L.

[0006] Further, ultrasonically disperse for 30 - 60 min; during the ultrasonic dispersion process, cool down to 15 - 30°C at a rate of 5 - 10°C / min.

[0007] Further, the preparation of the adsorbent includes the following steps: Load silica on the surface of hydrotalcite, dissolve it with organic acid, and obtain the adsorbent after heat treatment.

[0008] Further, the organic acid includes one or more of citric acid, acetic acid, lactic acid, benzoic acid or acrylic acid.

[0009] Further, it includes the following steps: a. Place the hydrotalcite in an aqueous solution of ethanol, and mix well; add ammonia water to make the solution alkaline, add tetraethyl orthosilicate, and after the reaction is complete, wash and dry to obtain a precursor; b. Prepare a diluted organic acid solution, place the precursor in an aqueous solution of ethanol, and continuously dropwise add the diluted organic acid solution while stirring within 0.3 - 1 h, and keep the pH of the system weakly acidic, then let it stand for 3 - 5 h; collect the precipitate, wash and dry it, and perform heat treatment to remove the residual acid to obtain an adsorbent.

[0010] Further, the concentration of the aqueous solution of ethanol in step a is 75 - 90% v / v; the mass ratio of tetraethyl orthosilicate to hydrotalcite in step a is 1:2 - 5; the reaction in step a is carried out at 40 - 65 °C for 3 - 5 h.

[0011] Further, the concentration of the aqueous solution of ethanol in step b is 15 - 40% v / v; the heat treatment in step b is carried out at 200 - 250 °C for 4 - 6 h.

[0012] Further, the dosing ratio is C / N = 3 - 1; the operating temperature is 15 - 35 °C; the hydraulic retention time is 6 - 24 h.

[0013] Adopting the above - mentioned scheme, the method of the present invention has the following advantages: In the method for deep denitrification of wastewater sulfur autotrophic denitrification of the present invention, the directly - available sodium thiosulfate and elemental sulfur with a slow - release effect are combined, which can make the change of the reduced sulfur content in the system more stable and is conducive to the full progress of sulfur autotrophy. In the method of the present invention, the solubility of elemental sulfur is higher, the dispersion degree is high, it is not easy to be lost, and it can effectively adsorb sulfate ions, and a good denitrification effect can be achieved with a shorter hydraulic retention time, and the denitrification cost is low.

[0014] The present invention refines sulfur particles to improve their dispersion degree and solubility in water. The combination of oligo - glucose and polyethylene glycol can improve the affinity between sulfur and oligo - glucose, reduce the aggregation of sulfur particles, and the network structure formed by oligo - glucose and polyethylene glycol can stabilize sulfur particles during the denitrification process, reduce the movement and aggregation of sulfur, and reduce the loss of sulfur and its influence on equipment and denitrification efficiency.

[0015] The glucooligosaccharide and polyethylene glycol of the present invention are biocompatible and biodegradable. During the denitrification process, as the reaction proceeds, the glucooligosaccharide and polyethylene glycol on the surface layer are gradually degraded, exposing sulfur particles, achieving control of the sulfur dosage and making the sulfur content in the system more stable.

[0016] The present invention uses glucooligosaccharide and polyethylene glycol to modify sulfur particles. The presence of sulfur particles also facilitates the colonization of bacterial cells on the framework of glucooligosaccharide and polyethylene glycol, facilitating the reproduction of sulfur autotrophic bacteria.

[0017] The adsorbent of the present invention has strong selective adsorption ability for sulfate ions and a stable structure. It does not participate in the reaction during the denitrification process, causing the sulfate ions to aggregate, which is beneficial for the colonization of reducing microorganisms and the reduction of sulfate, thereby reducing the dosage of electron donors in the system. At the same time, it can also reduce the concentration of sulfate ions in the effluent and improve the effluent quality.

[0018] The present invention loads silica on the surface of hydrotalcite, uses the stability of silica to ensure the stability of the hydrotalcite structure, and reduces the damage to the hydrotalcite structure and pores during the denitrification process; then uses mild organic acids for corrosion to increase the surface area of the material, improve the adsorption performance, and reduce the influence of hydrotalcite on the pH of the system.

[0019] The present invention performs heat treatment on the corroded hydrotalcite to remove residual organic acids and activate the material, improving the activity and loading stability of the material.

[0020] The sulfur autotrophic denitrification deep denitrification method of the present invention can be applied to the deep denitrification of nitrate wastewater with different concentrations. The raw materials are easily obtained, the preparation method is simple, the wastewater treatment cost is low, and the practicability is strong. Description of the Drawings

[0021] Figure 1 It is a graph showing the change in the nitrate nitrogen concentration of the effluent in Example 1; Figure 2 It is a graph showing the change in the nitrate nitrogen concentration of the effluent in Example 2; Figure 3 It is a graph showing the change in the nitrate nitrogen concentration of the effluent in Example 3; Figure 4 It is a graph showing the change in the nitrate nitrogen concentration of the effluent in Example 4. Detailed Embodiments

[0022] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0023] Example 1: (1) Weigh sulfur and dissolve it in toluene at 70°C. Stir magnetically at room temperature until completely dissolved to obtain a sulfur solution with a concentration of 40 g / L as the solvent phase. Dissolve oligoglucose and polyethylene glycol in water to obtain an antisolvent phase with an oligoglucose concentration of 3 g / L and a polyethylene glycol concentration of 1 g / L. Mix the antisolvent phase and the solvent phase at a volume ratio of 10:1, ultrasonically disperse for 60 min, and cool down to 20°C at a rate of 5°C / min during the ultrasonic dispersion process. After drying, the modified sulfur is obtained.

[0024] (2) Place 3 parts by mass of hydrotalcite in an aqueous solution of ethanol with a concentration of 80% v / v and mix well. Add ammonia water to make the solution alkaline, add 1 part by mass of tetraethyl orthosilicate, and react at 60°C for 4 h. After washing and drying, a precursor is obtained. (3) Prepare a citric acid dilution solution. Place the precursor in an aqueous solution of ethanol with a concentration of 30% v / v. While stirring, continuously dropwise add the citric acid dilution solution within 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 then perform heat treatment at 220°C for 6 h to obtain the adsorbent.

[0025] Example 2: The difference from Example 1 is as follows: (1) Weigh sulfur and dissolve it in toluene at 70°C. Stir magnetically at room temperature until completely dissolved to obtain a sulfur solution with a concentration of 20 g / L as the solvent phase. Dissolve oligoglucose and polyethylene glycol in water to obtain an antisolvent phase with an oligoglucose concentration of 3 g / L and a polyethylene glycol concentration of 1 g / L. Mix the antisolvent phase and the solvent phase at a volume ratio of 10:1, ultrasonically disperse for 30 min, and cool down to 20°C at a rate of 5°C / min during the ultrasonic dispersion process. After drying, the modified sulfur is obtained.

[0026] Example 3: The difference from Example 1 is as follows: (1) Weigh sulfur and dissolve it in toluene at 70°C. Stir magnetically at room temperature until completely dissolved to obtain a sulfur solution with a concentration of 40 g / L as the solvent phase. Dissolve oligoglucose and polyethylene glycol in water to obtain an antisolvent phase with an oligoglucose concentration of 3 g / L and a polyethylene glycol concentration of 1 g / L. Mix the antisolvent phase and the solvent phase at a volume ratio of 5:1, ultrasonically disperse for 30 min, and cool down to 20°C at a rate of 5°C / min during the ultrasonic dispersion process. After drying, the modified sulfur is obtained.

[0027] Example 4: The difference from Example 1 is as follows: (1) Weigh sulfur and dissolve it in toluene at 70 °C. Stir magnetically at room temperature until completely dissolved to obtain a sulfur solution with a concentration of 40 g / L as the solvent phase; take oligosaccharides and polyethylene glycol and dissolve them in water to obtain an anti-solvent phase with a concentration of 3 g / L for oligosaccharides and 1 g / L for polyethylene glycol; mix the anti-solvent phase and the solvent phase at a volume ratio of 10:1, disperse ultrasonically for 30 min, and cool down to 20 °C at a rate of 10 °C / min during the ultrasonic dispersion process. After drying, the modified sulfur is obtained.

[0028] Example 5: The difference from Example 1 is as follows: (2) Place 2 parts by mass of hydrotalcite in an aqueous solution of ethanol with a concentration of 80% v / v, and mix well; add ammonia water to make the solution alkaline, add 1 part by mass of tetraethyl orthosilicate, and react at 60 °C for 4 h. After washing and drying, the precursor is obtained.

[0029] Example 6: The difference from Example 1 is as follows: (3) Prepare a citric acid dilution solution. Place the precursor in an aqueous solution of ethanol with a concentration of 30% v / v, and continuously dropwise add the citric acid dilution solution while stirring within 1 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 then perform heat treatment at 220 °C for 6 h to obtain the adsorbent.

[0030] Example 7: The difference from Example 1 is as follows: (3) Prepare a citric acid dilution solution. Place the precursor in an aqueous solution of ethanol with a concentration of 30% v / v, and continuously dropwise add the citric acid dilution solution while stirring within 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 then perform heat treatment at 250 °C for 6 h to obtain the adsorbent.

[0031] Example 8: The difference from Example 1 is as follows: (3) Prepare a citric acid dilution solution. Place the precursor in an aqueous solution of ethanol with a concentration of 30% v / v, and continuously dropwise add the citric acid dilution solution while stirring within 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 then perform heat treatment at 220 °C for 4 h to obtain the adsorbent.

[0032] Test Example: Weigh sodium thiosulfate and the modified sulfur prepared in the example, and the adsorbent accounting for 5% of the total mass, respectively, according to a mass ratio of 1:5. Then add 5% of the total weight of gelatinized starch and 10% of the total mass of limestone, mix evenly, and then add 10% of the solid mass of water, mix evenly and granulate; dry the obtained particles in a vacuum drying oven at 180 - 190 °C for 2 h to obtain the filler.

[0033] The sulfur autotrophic denitrification fillers with different formulations in each example were respectively loaded into an upflow reactor with a volume of 1 L, inoculated with activated sludge with a concentration of about 3000 mg / L MLVSS, with an influent nitrate nitrogen concentration of 200 mg / L, an ammonia nitrogen concentration of 5 mg / L, a total phosphorus of 1 mg / L, and a hydraulic retention time of 12 h. The effluent nitrate nitrogen was measured to evaluate the denitrification effect. The results are as Figures 1 to 4 shown.

[0034] It can be seen from Figure 1 that the average effluent nitrate nitrogen of the filler in Example 1 after running for 30 days was 30.1 mg / L. Compared with Example 1, the sulfur concentration in the solvent phase of Example 2 was smaller and the sulfur dispersion was larger. It can be seen from Figure 2 that the average effluent nitrate nitrogen of the filler in Example 2 was 27.5 mg / L. Comparing the influent and effluent data, the average effluent nitrate nitrogen of Example 2 was slightly less than that of Example 1, indicating that the denitrification ability of the wastewater sulfur autotrophic denitrification deep nitrogen removal method in Example 2 was slightly stronger than that in Example 1, probably because the sulfur particle size was smaller, which was more conducive to the utilization by microorganisms. However, during the preparation process, the sulfur yield of Example 2 was significantly lower than that of Example 1, and the improvement ratio of its denitrification ability was not as large as the decrease in the sulfur yield.

[0035] Compared with Example 1, the amount of antisolvent added in Example 3 was less than that in Example 1. Figure 3 In it, the average effluent nitrate nitrogen was 31.3 mg / L. The nitrate nitrogen load and total nitrogen load at the initial stage of Example 3 did not change significantly compared with those of Example 1, but the denitrification effect was significantly improved in the later stage, indicating that more antisolvent was beneficial to the refinement of sulfur particles, but it was also easy to cause excessive contents of dextrin and polyethylene glycol, affecting the release of sulfur at the initial stage.

[0036] Compared with Example 1, during the preparation of modified sulfur in Example 4, the cooling rate was faster. Figure 4 In it, the average effluent nitrate nitrogen was 35 mg / L. It can be seen from this that the denitrification ability of Example 4 was inferior to that of Example 1, indicating that too fast a cooling rate was not conducive to the refinement of sulfur particles, thus affecting the solubility and bioavailability of modified sulfur.

[0037] The contents of sulfate ions in the effluents of Example 1 and Examples 5 to 8 were tested, and the results are shown in the following table: Table 1

[0038] As can be seen from the above table, compared with Example 1, the silicon addition amount in Example 5 is relatively higher, but the sulfate ion concentration in the effluent increases instead. It may be that the loading and coating of more silicon easily affect the adsorption pores of the hydrotalcite, weakening the selective adsorption ability of the adsorbent for sulfate ions. The acid dissolution time in Example 6 is longer than that in Example 1. In theory, more adsorption channels should be generated, but the sulfate ion concentration increases slightly instead. It may be that the too long acid dissolution time affects the structure of the hydrotalcite, thus affecting the adsorption of sulfate ions. The heat treatment temperature in Example 7 is higher and the sulfate ion concentration in the effluent is low; the heat treatment time in Example 8 is shorter and the sulfate ion concentration in the effluent is high, indicating that higher temperature and time are beneficial to improving the adsorption of sulfate ions by the adsorbent or beneficial to the reduction of sulfate ions by the reducing bacteria.

[0039] For those skilled in the art, various corresponding changes and deformations can be made according to the technical solutions and concepts described above, and all such changes and deformations should fall within the protection scope of the claims of the present invention.

Claims

1. A method for deep denitrification of wastewater by sulfur autotrophic denitrification, characterized in that, Using 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.

2. The method for deep denitrification of wastewater by sulfur autotrophic denitrification according to claim 1, characterized in that, The preparation of the modified sulfur includes the following steps: Weigh sulfur and dissolve it in toluene at 60 - 85°C, and magnetically stir at room temperature until completely dissolved to obtain a sulfur solution as the solvent phase; take oligosaccharide and polyethylene glycol and dissolve them in water as the anti-solvent phase; mix the anti-solvent phase and the solvent phase at a volume ratio of 5 - 10:1, ultrasonically disperse, and obtain modified sulfur after drying.

3. The method for deep denitrification of sulfur autotrophic denitrification of wastewater according to claim 2, characterized in that, The concentration of the sulfur solution is 20 - 40 g / L; the concentration of oligosaccharide in the anti-solvent phase is 2 - 4 g / L, and the concentration of polyethylene glycol is 0.5 - 1.5 g / L.

4. The method for deep denitrification of wastewater sulfur autotrophic denitrification according to claim 2, characterized in that, Ultrasonically disperse for 30 - 60 min; during the ultrasonic dispersion process, cool down to 15 - 30°C at a rate of 5 - 10°C / min.

5. The method for deep denitrification of sulfur autotrophic denitrification of wastewater according to claim 1, characterized in that, The preparation of the adsorbent includes the following steps: Load silica on the surface of hydrotalcite, erode it with an organic acid, and obtain the adsorbent after heat treatment.

6. The method for deep denitrification of wastewater by sulfur autotrophic denitrification according to claim 5, wherein, The organic acid includes one or several of citric acid, acetic acid, lactic acid, benzoic acid, or acrylic acid.

7. The method for deep denitrification of sulfur autotrophic denitrification of wastewater according to claim 5, characterized in that, Includes the following steps: a. Place hydrotalcite in an aqueous solution of ethanol, mix well; add ammonia water to make the solution alkaline, add tetraethyl orthosilicate, wash and dry after the reaction is complete to obtain a precursor; b. Prepare a diluted solution of the organic acid, place the precursor in an aqueous solution of ethanol, continuously dropwise add the diluted solution of the organic acid while stirring within 0.3 - 1 h, and keep the pH of the system weakly acidic, then let it stand for 3 - 5 h; collect the precipitate, wash and dry, and remove the residual acid by heat treatment to obtain the adsorbent.

8. The method for deep denitrification of wastewater by sulfur autotrophic denitrification according to claim 7, characterized in that, The concentration of the aqueous solution of ethanol in step a is 75 - 90% v / v; the mass ratio of tetraethyl orthosilicate to hydrotalcite in step a is 1:2 - 5; the reaction in step a is carried out at 40 - 65°C for 3 - 5 h.

9. The method for deep denitrification of wastewater sulfur autotrophic denitrification according to claim 7, characterized in that, The concentration of the aqueous solution of ethanol in step b is 15 - 40% v / v; the heat treatment in step b is carried out at 200 - 250°C for 4 - 6 h.

10. The method for deep denitrification of wastewater by sulfur autotrophic denitrification according to any one of claims 1 to 8, characterized in that, The dosing ratio of carbon to nitrogen is 3 - 1; the operating temperature is 15 - 35°C; the hydraulic retention time is 6 - 24 h.

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