CN108251459B - A method of recovering struvite from wastewater - Google Patents

Abstract

The invention belongs to the field of environmental protection, and in particular relates to a method for recovering struvite from waste water. The method provided by the invention comprises the following steps: a) activating Oneida Shewanella to obtain an activated bacterial solution; b) mixing the activated bacterial solution, magnesium oxide and waste water, and aerobic cultivation to obtain struvite ; The wastewater contains phosphorus and nitrogen elements. The invention uses low-cost magnesium oxide as the magnesium source for synthesizing struvite, utilizes the metabolic activity of Oneida Shewanella to promote the dissolution of magnesium oxide in water, provides necessary environmental conditions for the synthesis of struvite, and does not need to An additional source of alkalinity is added, thereby significantly reducing the cost of recovering struvite from wastewater. The experimental results show that the method provided by the invention can realize the efficient utilization of magnesium oxide, and the conversion rate of magnesium oxide can reach up to 97.6%.

Description

A method of recovering struvite from wastewater

technical field

The invention belongs to the field of environmental protection, and in particular relates to a method for recovering struvite from waste water.

Background technique

Phosphorus is an indispensable element for all organisms and plays an irreplaceable role in the growth, development and reproduction of organisms. As the main form of phosphorus in nature, phosphate rock is a non-renewable resource. At the same time, excessive phosphorus input into water bodies will cause eutrophication of water bodies, affecting water quality and posing a threat to human health. In the past half century, about 500 million tons of phosphate rock have been imported into the hydrosphere under human intervention, and the resulting water pollution problem needs to be solved urgently. With the continuous improvement of sewage nutrient discharge standards and the increasingly urgent need for resource recycling under the sustainable development strategy, sewage treatment technology has begun to develop in the direction of removing nitrogen and phosphorus while recovering nitrogen and phosphorus. It is against this background that the struvite crystallization recovery process is produced.

Struvite, also known as magnesium ammonium phosphate (MgNH ₄ PO ₄ ·6H ₂ O), is a white crystal that is poorly soluble in water. Struvite contains three nutrients, nitrogen, phosphorus and magnesium, and is an ideal slow-release fertilizer. The struvite crystallization recovery process is to simultaneously remove nitrogen and phosphorus from sewage by precipitating struvite under controlled conditions, and recycling the product struvite as fertilizer. Therefore, this process has potential environmental and economic benefits, and has become a hot spot in current water treatment research. Patent applications related to it continue to appear, such as Chinese patent application 201210145002 "A method for recovering phosphorus in phosphorous chemical wastewater by struvite production process", Chinese patent application 201410012829 "A kind of struvite precipitation process for ammonia nitrogen wastewater treatment process"Method" and Chinese patent application 201610084036 "A method and system for recovering struvite from sludge", etc. However, sewage is often rich in nitrogen and phosphorus but lacks magnesium, and struvite crystal precipitation also requires a high pH, the ideal range is 8.5-9.5. Therefore, the struvite crystallization process needs to add a magnesium source to the sewage containing nitrogen and phosphorus, and adjust the pH to an appropriate range by adding an alkali source, thereby promoting struvite precipitation. Among them, the addition of magnesium reagents (such as MgCl ₂ , MgSO ₄ ) and alkali reagents will greatly increase the cost of struvite crystallization recovery, thereby reducing the economic feasibility of struvite crystallization to recover nitrogen and phosphorus.

SUMMARY OF THE INVENTION

In view of this, the object of the present invention is to provide a method for recovering struvite from waste water, and the method is low in cost.

The invention provides a method for reclaiming struvite from waste water, comprising the following steps:

a) activating Oneida Shewanella to obtain an activated bacterial solution;

b) mixing described activated bacterial liquid, magnesium oxide and waste water, and aerobic cultivation to obtain struvite;

The wastewater contains phosphorus and nitrogen.

Preferably, in step a), the bacterial density in the activated bacterial solution is 1×10 ⁹ to 15×10 ⁹ CFU/mL.

Preferably, the step a) specifically includes:

Shewanella Oneida stored on the solid medium is inoculated into the liquid medium and cultured aerobically to obtain an activated bacterial liquid.

Preferably, in step a), the liquid medium is LB medium.

Preferably, in step a), the temperature of the aerobic cultivation is 25-35° C.; the time of the aerobic cultivation is 8-16 h.

Preferably, in step b), the dosage ratio of the magnesium oxide to the waste water is (0.1-1.2) g: 1L.

Preferably, in step b), the volume ratio of the activated bacterial solution to the waste water is (0.1-5):100.

Preferably, in step b), the temperature of the aerobic cultivation is 25-35° C.; the time of the aerobic cultivation is 48-96 h.

Preferably, in step b), the total phosphorus content of the wastewater is 170-425 mg/L; the total nitrogen content of the wastewater is 625-1560 mg/L.

Preferably, in step b), the organic phosphorus content of the wastewater is 100-250 mg/L; the organic nitrogen content of the wastewater is 560-1400 mg/L.

Compared with the prior art, the present invention provides a method for recovering struvite from wastewater. The method provided by the invention comprises the following steps: a) activating Oneida Shewanella to obtain an activated bacterial solution; b) mixing the activated bacterial solution, magnesium oxide and waste water, and aerobic cultivation to obtain struvite ; The wastewater contains phosphorus and nitrogen elements. The invention uses low-cost magnesium oxide as the magnesium source for synthesizing struvite, utilizes the metabolic activity of Oneida Shewanella to promote the dissolution of magnesium oxide in water, provides necessary environmental conditions for the synthesis of struvite, and does not need to An additional source of alkalinity is added, thereby significantly reducing the cost of recovering struvite from wastewater. The experimental results show that the method provided by the invention can realize the efficient utilization of magnesium oxide, and the conversion rate of magnesium oxide can reach up to 97.6%.

Description of drawings

In order to explain the embodiments of the present invention or the technical solutions in the prior art more clearly, the following briefly introduces the accompanying drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only It is an embodiment of the present invention. For those of ordinary skill in the art, other drawings can also be obtained according to the provided drawings without creative work.

Fig. 1 is the XRD figure of the struvite prepared by embodiment 1～3 provided by the invention;

Fig. 2 is the struvite FESEM figure that the embodiment of the present invention 1 provides;

Fig. 3 is the struvite FESEM figure that the embodiment of the present invention 2 provides;

Fig. 4 is the struvite FESEM figure that the embodiment of the present invention 3 provides;

Fig. 5 is the XRD figure of the struvite provided by the embodiment of the present invention 4;

Fig. 6 is the FESEM image of the struvite prepared when the magnesium oxide addition amount that the embodiment of the present invention 4 provides is 0.16g/L;

Fig. 7 is the FESEM image of the struvite prepared when the magnesium oxide addition amount that the embodiment of the present invention 4 provides is 0.64g/L;

Fig. 8 is the FESEM image of the struvite prepared when the addition amount of magnesium oxide provided in Example 4 of the present invention is 0.96 g/L.

Detailed ways

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

The invention provides a method for reclaiming struvite from waste water, comprising the following steps:

a) activating Oneida Shewanella to obtain an activated bacterial solution;

b) mixing described activated bacterial liquid, magnesium oxide and waste water, and aerobic cultivation to obtain struvite;

The wastewater contains phosphorus and nitrogen.

In the method provided by the present invention, the Oneida Shewanella is first activated to obtain an activated bacterial solution. Among them, the Shewanella oneidensis MR-1 (ATCC 700550) is a rod-shaped gram-negative facultative anaerobic bacteria, which is widely found in freshwater sediments, bay sediments and other various environments exists; the bacterial density in the activated bacterial solution is preferably 1×10 ⁹ to 15×10 ⁹ CFU/mL, specifically 6×10 ⁹ CFU/mL. In the present invention, the activation mode is preferably:

Shewanella Oneida stored on the solid medium is inoculated into the liquid medium and cultured aerobically to obtain an activated bacterial liquid.

In the above-mentioned activation method provided by the present invention, the liquid medium is preferably LB medium, and the LB medium is composed of tryptone, yeast extract, NaCl and water, and the content of tryptone in the LB medium is 10 g/ L, the content of the yeast extract is 5g/L, and the content of NaCl is 5g/L; the inoculum of the Oneida Shewanella is preferably 1 to 3 colonies in terms of the number of colonies preserved on the solid medium The temperature of the aerobic cultivation is preferably 25-35°C, specifically 30°C; the aerobic cultivation time is preferably 8-16h, specifically 12h; the aerobic cultivation is preferably carried out on a shaking table, The rotating speed of the shaker is preferably 100-300 rpm, specifically 200 rpm.

After the activated bacterial solution is obtained, the activated bacterial solution, magnesium oxide and waste water are mixed for aerobic cultivation. Wherein, the waste water contains phosphorus element and nitrogen element. In an embodiment provided by the present invention, the total phosphorus content of the wastewater is preferably 100-500 mg/L, more preferably 170-425 mg/L, specifically 170 mg/L, 340 mg/L or 425 mg/L; The total nitrogen content of the wastewater is preferably 500-1700 mg/L, more preferably 625-1560 mg/L, specifically 625 mg/L, 1250 mg/L or 1560 mg/L. In an embodiment provided by the present invention, the organic phosphorus content of the wastewater is preferably 50-300 mg/L, more preferably 100-250 mg/L, specifically 100 mg/L, 200 mg/L or 250 mg/L; The organic nitrogen content of the wastewater is preferably 400-1500 mg/L, more preferably 560-1400 mg/L, specifically 560 mg/L, 1120 mg/L or 1400 mg/L. In an embodiment provided by the present invention, the wastewater also contains sodium chloride, and the content of the sodium chloride is preferably 1-10 g/L, specifically 5 g/L. In an embodiment provided by the present invention, the pH value of the wastewater is 6-8, specifically 7. In an embodiment provided by the present invention, LB medium or improved LB medium is used as simulated wastewater, and the improved LB medium is composed of tryptone, yeast extract, NaCl and water, and the content of tryptone in the improved LB medium is The content is preferably 10-25g/L, specifically 10g/L, 20g/L or 25g/L; the content of yeast extract in the improved LB medium is preferably 5-12.5g/L, specifically 5g/L, 10g/L or 12.5g/L; the content of NaCl in the modified LB medium is preferably 5g/L. In the present invention, the dosage ratio of the magnesium oxide to the waste water is preferably (0.1-1.2) g:1L, specifically 0.16g:1L, 0.32g:1L, 0.64g:1L or 0.96g:1L; The volume ratio of the activated bacterial solution and the waste water is preferably (0.1-5):100, specifically 1:10; the temperature of the aerobic cultivation is preferably 25-35°C, specifically 30°C; The oxygen culture time is preferably 48-96 hours, specifically 72 hours.

After the aerobic culture is completed, the products in the culture solution are separated to obtain crude struvite. The crude struvite product is washed and dried to obtain a pure struvite product. Wherein, the washing reagent is preferably absolute ethanol; the drying temperature is preferably 20-30°C, specifically 25°C; the drying time is preferably 24-72h, specifically 48h.

The invention uses low-cost magnesium oxide as the magnesium source for synthesizing struvite, utilizes the metabolic activity of Oneida Shewanella to promote the dissolution of magnesium oxide in water, provides necessary environmental conditions for the synthesis of struvite, and does not need to An additional source of alkalinity is added, thereby significantly reducing the cost of recovering struvite from wastewater. Specifically, the method provided by the invention can achieve the following positive effects:

1) Magnesium oxide is cheap and can significantly reduce the cost of recovering struvite from sewage.

2) Magnesium oxide as a magnesium source has low solubility in water, but Oneida Shewanella and its metabolites can promote the dissolution of magnesium oxide, thereby providing sufficient magnesium ions for struvite synthesis and realizing magnesium oxide resources. efficient use.

3) The dissolved solution of magnesium oxide in water can release hydroxide ions, which promotes the increase of pH of the solution, combined with the effect of Oneida Shewanella's own metabolism on raising pH, so the addition of additional alkali sources can be avoided and further reduced Production cost of struvite.

4) The metabolic activity of Shewanella Oneida can also convert organic phosphorus and organic nitrogen in wastewater into inorganic nitrogen and phosphorus, and promote struvite precipitation, while the traditional struvite crystallization process can only process inorganic nitrogen and phosphorus, Therefore, the method provided by the present invention helps to promote the combination of the nitrogen and phosphorus removal process of sewage and the struvite crystallization process, realizes more effective and low-cost nitrogen and phosphorus removal and struvite recovery, and is expected to greatly reduce the amount of nitrogen and phosphorus generated in the sewage treatment process. amount of sludge.

5) The method provided by the present invention can obtain struvite with different shapes and particle sizes by controlling different addition amounts of magnesium oxide, and is expected to provide a new approach for industrial production of struvite with different specifications.

For the sake of clarity, detailed description will be given below through the following examples.

The activated bacterial liquid involved in the following examples is obtained according to the following methods:

One colony of Oneida Shewanella preserved on the slant medium was scraped with an inoculation loop, and inoculated into 100 mL of LB medium (10 g/L tryptone, 5 g/L yeast extract, 5 g/L sodium chloride) ) in a culture bottle with a temperature of 30°C and a rotating speed of 200rpm for 12 hours aerobic cultivation, so that the final bacterial density reaches 6×10 ⁹ CFU/mL, that is, the activated bacterial liquid is obtained.

Example 1

100 mL of LB medium (10 g/L tryptone, 5 g/L yeast extract, 5 g/L sodium chloride) was added to a 250 mL culture flask as simulated wastewater, and autoclaved at 121 °C for 20 minutes. Among them, the total phosphorus content of the simulated wastewater was 170 mg/L, and the total nitrogen content was 625 mg/L; the organic phosphorus content was 100 mg/L, and the organic nitrogen content was 560 mg/L. At the same time, 0.032 g of magnesium oxide powder was placed in an electric heating constant temperature blast drying oven, and sterilized by dry heat at 170° C. for 2 hours. Then, 1 mL of the activated bacterial liquid was inoculated into a culture flask containing dry-heat sterilized magnesium oxide and 100 mL of LB medium, and aerobic cultivation was performed on a shaking table with a rotation speed of 200 rpm and a temperature of 30 °C. After culturing for 72 hours, the pH of the culture solution was measured, the product was separated by sedimentation, and then the product was washed three times with absolute ethanol, and dried in a vacuum drying box at room temperature for 48 hours. The product is analyzed by X-ray diffraction and scanning electron microscope, as shown in Figure 1 and Figure 2, Figure 1 is the XRD pattern of the struvite prepared in Examples 1 to 3 provided by the present invention, and S-1 in Figure 1 represents the implementation of The struvite prepared in Example 1, S-2 represents the struvite prepared in Example 2, S-3 represents the struvite prepared in Example 3, and JCPDS-77-2303 represents the international standard X-ray diffraction data of struvite Card, Figure 2 is the FESEM image of struvite provided in Example 1 of the present invention. It can be seen from FIG. 2 that the product prepared in this example is a large number of false square conical struvite.

Three parallel experiments were carried out, and it was determined that the average yield of struvite was 121.0 mg, corresponding to a conversion rate of magnesium oxide of 61.8%.

Example 2

100 mL of modified LB medium (20 g/L tryptone, 10 g/L yeast extract, 5 g/L sodium chloride) was added to a 250 mL culture flask as simulated wastewater, and autoclaved at 121 °C for 20 minutes. Among them, the total phosphorus content of the simulated wastewater was 340 mg/L, and the total nitrogen content was 1250 mg/L; the organic phosphorus content was 200 mg/L, and the organic nitrogen content was 1120 mg/L. At the same time, 0.032 g of magnesium oxide powder was placed in an electric heating constant temperature blast drying oven, and sterilized by dry heat at 170° C. for 2 hours. Then, 1 mL of the activated bacterial liquid was inoculated into a culture flask containing dry-heat sterilized magnesium oxide and 100 mL of culture medium, and aerobic culture was performed on a shaking table with a rotating speed of 200 rpm and a temperature of 30 °C. After culturing for 72 hours, the pH of the culture solution was measured, the product was separated by sedimentation, and then the product was washed three times with absolute ethanol, and dried in a vacuum drying box at room temperature for 48 hours. The product is analyzed by X-ray diffraction (XRD) and scanning electron microscope, as shown in Figures 1 and 3, and Figure 3 is a FESEM image of struvite provided in Example 2 of the present invention. It can be seen from Fig. 3 that the products prepared in this example are all pseudo-square conical struvite.

Three parallel experiments were carried out, and it was determined that the average yield of struvite was 173.3 mg, corresponding to a conversion rate of magnesium oxide of 88.4%.

Example 3

100 mL of modified LB medium (25 g/L tryptone, 12.5 g/L yeast extract, 5 g/L sodium chloride) was added to a 250 mL culture flask as simulated wastewater, and autoclaved at 121 °C for 20 minutes. Among them, the total phosphorus content of the simulated wastewater was 425 mg/L, and the total nitrogen content was 1560 mg/L; the organic phosphorus content was 250 mg/L, and the organic nitrogen content was 1400 mg/L. At the same time, 0.032 g of magnesium oxide powder was placed in an electric heating constant temperature blast drying Dry heat sterilization at 170°C for 2 hours. Afterwards, 1 mL of the activated bacterial liquid was inoculated into culture flasks containing dry-heat sterilized magnesium oxide and 100 mL of culture medium, respectively, and aerobically cultivated on a shaking table with a rotational speed of 200 rpm and a temperature of 30°C. After culturing for 72 hours, the pH of the culture solution was measured, the product was separated by sedimentation, and then the product was washed three times with absolute ethanol, and dried in a vacuum drying box at room temperature for 48 hours. The product was analyzed by X-ray diffraction (XRD) and scanning electron microscope, as shown in FIG. 1 and FIG. 4 , and FIG. 4 is the FESEM image of struvite provided in Example 3 of the present invention. It can be seen from FIG. 4 that the products prepared in this example are all pseudo-square conical struvite.

Three parallel experiments were carried out, and it was determined that the average yield of struvite was 192.2 mg, corresponding to a conversion rate of 97.6% of magnesium oxide.

Example 4

100 mL of LB medium (10 g/L tryptone, 5 g/L yeast extract, 5 g/L sodium chloride) was added to a 250 mL culture flask as simulated wastewater, and autoclaved at 121 °C for 20 minutes. Among them, the total phosphorus content of the simulated wastewater was 170 mg/L, and the total nitrogen content was 625 mg/L; the organic phosphorus content was 100 mg/L, and the organic nitrogen content was 560 mg/L. At the same time, magnesium oxide powders of different masses (0.016g, 0.064g, 0.096g) were placed in an electric heating constant temperature blast drying oven, and sterilized by dry heat at 170° C. for 2 hours. Then, 1 mL of the activated bacterial liquid was inoculated into a culture flask containing dry-heat sterilized magnesium oxide and 100 mL of culture medium, and aerobic culture was performed on a shaking table with a rotating speed of 200 rpm and a temperature of 30 °C. After culturing for 72 hours, the pH of the culture solution was measured, the product was separated by sedimentation, and then the product was washed three times with absolute ethanol, and dried in a vacuum drying box at room temperature for 48 hours. The product is analyzed by X-ray diffraction (XRD) and scanning electron microscope, as shown in Figures 5 to 8, Figure 5 is the XRD pattern of the struvite provided by Example 4 of the present invention, and Figure 6 is provided by Example 4 of the present invention. The FESEM image of the struvite prepared when the addition amount of magnesium oxide is 0.16g/L, Fig. 7 is the FESEM image of the struvite prepared when the addition amount of magnesium oxide provided in Example 4 of the present invention is 0.64g/L, Fig. 8 It is the FESEM image of the struvite prepared when the magnesium oxide addition amount provided in Example 4 of the present invention is 0.96 g/L. It can be seen from Figures 5 to 8 that Oneida Shewanella can use MgO as a magnesium source to exclusively mineralize struvite, and the added MgO has no effect on the purity of struvite; the amount of magnesium oxide added is relatively low When the particle size of struvite is large, on the contrary, the particle size is small; when the addition amount of magnesium oxide is different, the struvite has different appearances.

Three parallel experiments were carried out to determine that the average yields of struvite obtained when the amount of magnesium oxide was 0.16g/L, 0.64g/L and 0.96g/L were 79.9mg, 122.3mg and 124.6mg, respectively. The conversion rates of magnesium oxide were were 81.5%, 31.3% and 21.2%.

For the convenience of comparing the experimental conditions and results of different embodiments, the material composition and yield data of Examples 1 to 4 are integrated into Table 1:

The material composition and output of different embodiments of table 1

It can be seen from Table 1 that with the increase of the concentration of organic nitrogen and phosphorus in the medium, the yield of struvite and the conversion rate of magnesium oxide are greatly improved, and the conversion rate of magnesium oxide can be as high as 97.6%. Nitrogen and phosphorus wastewater treatment has the potential to economically and efficiently treat high concentrations of organic nitrogen and phosphorus and recover struvite.

The above are only the preferred embodiments of the present invention. It should be pointed out that for those skilled in the art, without departing from the principles of the present invention, several improvements and modifications can be made. It should be regarded as the protection scope of the present invention.

Claims (8)

1. a method for reclaiming struvite from waste water, comprising the following steps: a) activating Oneida Shewanella to obtain an activated bacterial solution; b) mixing described activated bacterial liquid, magnesium oxide and waste water, and aerobic cultivation to obtain struvite; The total phosphorus content of the wastewater is 170-425 mg/L, and the total nitrogen content is 625-1560 mg/L; The dosage ratio of the magnesium oxide to the waste water is (0.1-1.2) g: 1L. 2 . The method according to claim 1 , wherein in step a), the bacterial density in the activated bacterial solution is 1×10 ⁹ to 15×10 ⁹ CFU/mL. 3 . 3. The method according to claim 1, wherein the step a) specifically comprises: Shewanella Oneida stored on the solid medium is inoculated into the liquid medium and cultured aerobically to obtain an activated bacterial liquid. 4. method according to claim 3, is characterized in that, in step a), described liquid medium is LB medium. 5 . The method according to claim 3 , wherein, in step a), the temperature of the aerobic cultivation is 25-35° C.; the time of the aerobic cultivation is 8-16 h. 6 . 6 . The method according to claim 1 , wherein in step b), the volume ratio of the activated bacterial solution to the waste water is (0.1-5):100. 7 . 7 . The method according to claim 1 , wherein, in step b), the temperature of the aerobic cultivation is 25-35° C.; the time of the aerobic cultivation is 48-96 h. 8 . The method according to claim 1, wherein in step b), the organic phosphorus content of the wastewater is 100-250 mg/L; the organic nitrogen content of the wastewater is 560-1400 mg/L.

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