CN108251459B

CN108251459B - Method for recovering struvite from wastewater

Info

Publication number: CN108251459B
Application number: CN201810296839.2A
Authority: CN
Inventors: 周根陶; 罗毅; 姚奇志; 李涵
Original assignee: University of Science and Technology of China USTC
Current assignee: University of Science and Technology of China USTC
Priority date: 2018-04-03
Filing date: 2018-04-03
Publication date: 2020-10-27
Anticipated expiration: 2038-04-03
Also published as: CN108251459A

Abstract

The invention belongs to the field of environmental protection, and particularly relates to a method for recovering struvite from wastewater. The method provided by the invention comprises the following steps: a) activating the Shewanella onadatuma to obtain activated bacterial liquid; b) mixing the activated bacterium liquid, magnesium oxide and wastewater, and carrying out aerobic culture to obtain struvite; the wastewater contains phosphorus and nitrogen. According to the method, magnesium oxide with low price is used as a magnesium source for synthesizing struvite, the metabolic activity of the Shewanella onadatumi is utilized to promote the magnesium oxide to be dissolved in water, necessary environmental conditions are provided for the synthesis of struvite, and an alkali source does not need to be additionally added, so that the cost for recovering the struvite from wastewater is greatly reduced. Experimental results show that the method provided by the invention can realize high-efficiency utilization of magnesium oxide, and the conversion rate of the magnesium oxide can reach 97.6% at most.

Description

Method for recovering struvite from wastewater

Technical Field

The invention belongs to the field of environmental protection, and particularly relates to a method for recovering struvite from wastewater.

Background

Phosphorus is an indispensable element for all organisms and plays an irreplaceable role in the growth, development and reproduction of organisms. Phosphate rock is a non-renewable resource as the main form of phosphorus occurring in nature. Meanwhile, excessive input of phosphorus into the water body causes eutrophication of the water body, affects water quality and threatens human health. In the past half century, about 5 million tons of phosphorus ore are input into a water ring under human intervention, and the problem of water pollution caused by the input of the phosphorus ore needs to be solved urgently. With the continuous improvement of the discharge standard of nutrient substances in sewage and the increasing urgent need of resource recycling under the strategy of sustainable development, the sewage treatment technology begins to develop towards the direction of removing nitrogen and phosphorus and recovering nitrogen and phosphorus. It is in this context that the struvite crystallization recovery process is produced.

Struvite, also known as magnesium ammonium phosphate (MgNH)₄PO₄·6H₂O), is a white crystal that is poorly soluble in water. The struvite contains three nutrient elements of nitrogen, phosphorus and magnesium, and is an ideal slow-release fertilizer. The struvite crystallization recovery process is implemented by precipitating struvite under controlled conditions to simultaneously remove nitrogen and phosphorus in sewage and recovering the product struvite as fertilizer. Therefore, the process has potential environmental benefits and economic benefits and becomes a hot spot of current water treatment research. Related patent applications are continuously emerging, for example, Chinese patent application 201210145002 "a process for recovering phosphorus using struvite productionA method for phosphorus in chemical wastewater, a Chinese patent application 201410012829 'a process method for treating ammonia nitrogen wastewater by a struvite precipitation method', a Chinese patent application 201610084036 'a method and a system for recovering struvite from sludge', and the like. However, the sewage is often rich in nitrogen and phosphorus but short of magnesium, and the struvite crystal precipitate needs a higher pH value, and the ideal range is 8.5-9.5. Therefore, the struvite crystallization process requires the addition of a magnesium source to nitrogen and phosphorus containing wastewater and the addition of an alkali source to adjust the pH to a suitable range to promote struvite precipitation. Wherein the magnesium reagent (e.g. MgCl)₂、MgSO₄) And the addition of the alkali reagent greatly increases the recovery cost of struvite crystals, thereby reducing the economic feasibility of recovering nitrogen and phosphorus by a struvite crystallization method.

Disclosure of Invention

In view of the above, the present invention aims to provide a method for recovering struvite from wastewater, which is low in cost.

The invention provides a method for recovering struvite from wastewater, which comprises the following steps:

a) activating the Shewanella onadatuma to obtain activated bacterial liquid;

b) mixing the activated bacterium liquid, magnesium oxide and wastewater, and carrying out aerobic culture to obtain struvite;

the wastewater contains phosphorus and nitrogen.

Preferably, in step a), the density of bacteria in the activated bacterial liquid is 1 × 10⁹～15×10⁹CFU/mL。

Preferably, the step a) specifically comprises:

inoculating the Shewanella onadatumi preserved on the solid culture medium into a liquid culture medium, and performing aerobic culture to obtain an activated bacterial liquid.

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

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

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

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

preferably, in the step b), the temperature of the aerobic culture is 25-35 ℃; the aerobic culture time is 48-96 h.

Preferably, in the 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 the step b), the content of organic phosphorus in 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 invention provides a method for recovering struvite from wastewater. The method provided by the invention comprises the following steps: a) activating the Shewanella onadatuma to obtain activated bacterial liquid; b) mixing the activated bacterium liquid, magnesium oxide and wastewater, and carrying out aerobic culture to obtain struvite; the wastewater contains phosphorus and nitrogen. According to the method, magnesium oxide with low price is used as a magnesium source for synthesizing struvite, the metabolic activity of the Shewanella onadatumi is utilized to promote the magnesium oxide to be dissolved in water, necessary environmental conditions are provided for the synthesis of struvite, and an alkali source does not need to be additionally added, so that the cost for recovering the struvite from wastewater is greatly reduced. Experimental results show that the method provided by the invention can realize high-efficiency utilization of magnesium oxide, and the conversion rate of the magnesium oxide can reach 97.6% at most.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.

FIG. 1 is an XRD pattern of struvite prepared in examples 1-3 provided by the present invention;

FIG. 2 is a FESEM image of struvite provided in example 1 of the present invention;

FIG. 3 is a FESEM image of struvite provided in example 2 of the present invention;

FIG. 4 is a FESEM image of struvite provided in example 3 of the present invention;

FIG. 5 is an XRD pattern of struvite provided in example 4 of the present invention;

FIG. 6 is a FESEM image of struvite prepared at an addition of 0.16g/L magnesium oxide provided in example 4 of the present invention;

FIG. 7 is an FESEM image of struvite prepared at an addition of 0.64g/L magnesium oxide provided in example 4 of the present invention;

FIG. 8 is a FESEM image of struvite prepared at a magnesium oxide addition level of 0.96g/L provided in example 4 of the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention are clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

a) activating the Shewanella onadatuma to obtain activated bacterial liquid;

the wastewater contains phosphorus and nitrogen.

In the method provided by the invention, the Shewanella onadatumi is activated to obtain activated bacteria liquid. Wherein said Shewanella oneidensis MR-1, ATCC 700550 is a rod-shaped gram-negative facultative anaerobe, widely existing in freshwater sediments, gulf sediments and other various environments; the density of bacteria in the activated bacterial liquid is preferably 1X 10⁹～15×10⁹CFU/mL, specifically 6X 10⁹CFU/mL. In the present invention, the activation is preferably performed by:

In the above activation mode provided by the invention, the liquid culture medium is preferably an LB culture medium, the LB culture medium is composed of tryptone, yeast extract, NaCl and water, the content of the tryptone in the LB culture medium is 10g/L, the content of the yeast extract is 5g/L, and the content of the NaCl is 5 g/L; the inoculation amount of the Shewanella onadatumi is preferably 1-3 colonies in terms of the number of colonies preserved on a solid culture medium; the aerobic culture temperature is preferably 25-35 ℃, and specifically can be 30 ℃; the aerobic culture time is preferably 8-16 h, and specifically can be 12 h; the aerobic culture is preferably carried out on a shaking table, and the rotation speed of the shaking table is preferably 100-300 rpm, and specifically can be 200 rpm.

And (3) after obtaining the activated bacterial liquid, mixing the activated bacterial liquid, magnesium oxide and wastewater, and carrying out aerobic culture. Wherein the wastewater contains phosphorus and nitrogen. In one embodiment provided by the invention, the total phosphorus content of the wastewater is preferably 100-500 mg/L, more preferably 170-425 mg/L, and specifically may be 170mg/L, 340mg/L or 425 mg/L; the total nitrogen content of the wastewater is preferably 500-1700 mg/L, more preferably 625-1560 mg/L, and specifically 625mg/L, 1250mg/L or 1560 mg/L. In one embodiment provided by the invention, the organic phosphorus content of the wastewater is preferably 50-300 mg/L, more preferably 100-250 mg/L, and specifically may be 100mg/L, 200mg/L or 250 mg/L; the organic nitrogen content of the wastewater is preferably 400-1500 mg/L, more preferably 560-1400 mg/L, and specifically 560mg/L, 1120mg/L or 1400 mg/L. In one embodiment provided by the invention, the wastewater further contains sodium chloride, and the content of the sodium chloride is preferably 1-10 g/L, and specifically can be 5 g/L. In one embodiment provided by the invention, the pH value of the wastewater is 6-8, and specifically can be 7. In one embodiment provided by the invention, an LB culture medium or an improved LB culture medium is used as simulated wastewater, the improved LB culture medium is composed of tryptone, yeast extract, NaCl and water, and the content of the tryptone in the improved LB culture medium is preferably 10-25 g/L, and specifically can be 10g/L, 20g/L or 25 g/L; the content of the yeast extract in the improved LB culture medium is preferably 5-12.5 g/L, and specifically can be 5g/L, 10g/L or 12.5 g/L; the content of NaCl in the modified LB medium is preferably 5 g/L. In the invention, the dosage ratio of the magnesium oxide to the wastewater is preferably (0.1-1.2) g: 1L, specifically 0.16 g: 1L, 0.32 g: 1L, 0.64 g: 1L or 0.96 g: 1L; the volume ratio of the activated bacterial liquid to the wastewater is preferably (0.1-5): 100, specifically 1: 10; the aerobic culture temperature is preferably 25-35 ℃, and specifically can be 30 ℃; the aerobic culture time is preferably 48-96 h, and specifically 72 h.

And after the aerobic culture is finished, separating a product in the culture solution to obtain a struvite crude product. And washing and drying the crude struvite product to obtain a pure struvite product. Wherein the washing reagent is preferably absolute ethyl alcohol; the drying temperature is preferably 20-30 ℃, and specifically can be 25 ℃; the drying time is preferably 24-72 hours, and specifically can be 48 hours.

According to the method, magnesium oxide with low price is used as a magnesium source for synthesizing struvite, the metabolic activity of the Shewanella onadatumi is utilized to promote the magnesium oxide to be dissolved in water, necessary environmental conditions are provided for the synthesis of struvite, and an alkali source does not need to be additionally added, so that the cost for recovering the struvite from wastewater is greatly reduced. Specifically, the method provided by the invention can achieve the following positive effects:

1) the magnesium oxide is low in price, and the cost of recovering struvite from sewage can be obviously reduced.

2) Although the magnesium oxide is low in solubility in water as a magnesium source, the Shewanella onadatumi and the metabolite thereof can promote the dissolution of the magnesium oxide, so that sufficient magnesium ions are provided for struvite synthesis, and the efficient utilization of the magnesium oxide resource is realized.

3) The magnesium oxide can release hydroxide ions in water solution to promote the pH value of the solution to rise, and the pH value is improved by combining the effect of the self metabolism of the Shewanella onadatumi, so that the addition of an additional alkali source can be avoided, and the production cost of the struvite is further reduced.

4) The metabolic activity of the Shewanella onadatumi can also convert organic phosphorus and organic nitrogen in the wastewater into inorganic nitrogen and phosphorus, so that struvite precipitation is promoted, and the traditional struvite crystallization process can only treat inorganic nitrogen and phosphorus, so that the method provided by the invention is beneficial to promoting the combination of a sewage nitrogen and phosphorus removal process and a struvite crystallization process, realizes more effective and low-cost nitrogen and phosphorus removal and struvite recovery, and is expected to greatly reduce the sludge amount generated in the sewage treatment process.

5) The method provided by the 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 way for industrial production of struvite with different specifications.

For the sake of clarity, the following examples are given in detail.

The activated bacterial suspension referred to in the following examples was obtained by the following method:

scraping 1 colony of Shewanella onadatumi stored on slant culture medium with inoculating loop, inoculating into culture bottle containing 100mLLB culture medium (10g/L tryptone, 5g/L yeast extract, 5g/L sodium chloride), and aerobically culturing for 12 hr on shaking table with temperature of 30 deg.C and rotation speed of 200rpm to make final bacterial density reach 6 × 10⁹And (5) CFU/mL, namely obtaining the activated bacterial liquid.

Example 1

100mL of LB medium (10g/L tryptone, 5g/L yeast extract, 5g/L sodium chloride) was added as a model wastewater to a 250mL flask, and autoclaved at 121 ℃ for 20 minutes. Wherein the total phosphorus content of the simulated wastewater is 170mg/L, and the total nitrogen content is 625 mg/L; the content of organic phosphorus is 100mg/L, and the content of organic nitrogen is 560 mg/L. Meanwhile, 0.032g of magnesium oxide powder was placed in an electric heating constant temperature forced air drying oven and sterilized by dry heat at 170 ℃ for 2 hours. Then, 1mL of the activated bacterial liquid was inoculated into a flask containing magnesium oxide sterilized by dry heat and 100mL of LB medium, and aerobic culture was carried out on a shaker at a rotation speed of 200rpm and a temperature of 30 ℃. After 72h of culture, the pH of the culture solution is measured, the product is subjected to sedimentation separation, and then the product is washed three times with absolute ethyl alcohol and placed in a vacuum drying oven to be dried for 48 hours at room temperature. The product was analyzed by X-ray diffraction and scanning electron microscopy, and as shown in FIGS. 1 and 2, FIG. 1 is an XRD pattern of struvite prepared in examples 1 to 3 provided by the present invention, S-1 in FIG. 1 represents struvite prepared in example 1, S-2 represents struvite prepared in example 2, S-3 represents struvite prepared in example 3, JCPDS-77-2303 represents an International Standard X-ray diffraction data card for struvite, and FIG. 2 is a FESEM pattern of struvite provided in example 1 of the present invention. As can be seen from fig. 2, the product produced in this example is a mass of pseudo-tetragonal pyramid struvite.

Three parallel experiments were performed and it was determined that an average yield of struvite of 121.0mg was obtained, corresponding to a conversion of 61.8% of magnesium oxide.

Example 2

100mL of modified LB medium (20g/L tryptone, 10g/L yeast extract, 5g/L sodium chloride) was added as a model wastewater to a 250mL flask and autoclaved at 121 ℃ for 20 minutes. Wherein, the total phosphorus content of the simulated wastewater is 340mg/L, and the total nitrogen content is 1250 mg/L; the content of organic phosphorus is 200mg/L, and the content of organic nitrogen is 1120 mg/L. Meanwhile, 0.032g of magnesium oxide powder was placed in an electric heating constant temperature forced air drying oven and sterilized by dry heat at 170 ℃ for 2 hours. Then, 1mL of the activated bacterial liquid was inoculated into a culture flask containing magnesium oxide sterilized by dry heat and 100mL of a medium, and aerobic culture was carried out on a shaker at a rotation speed of 200rpm at a temperature of 30 ℃. After 72h of culture, the pH of the culture solution is measured, the product is subjected to sedimentation separation, and then the product is washed three times with absolute ethyl alcohol and placed in a vacuum drying oven to be dried for 48 hours at room temperature. The product was analyzed by X-ray diffraction (XRD) and scanning electron microscopy, as shown in fig. 1 and 3, and fig. 3 is a FESEM image of struvite provided in example 2 of the present invention. As can be seen from FIG. 3, the products prepared in this example were all pseudo-tetragonal pyramid struvite.

Three parallel experiments were performed and it was determined that an average yield of struvite of 173.3mg was obtained, corresponding to a conversion of 88.4% of magnesium oxide.

Example 3

100mL of modified LB medium (25g/L tryptone, 12.5g/L yeast extract, 5g/L sodium chloride) was added to each of 250mL flasks as a model wastewater, and autoclaved at 121 ℃ for 20 minutes. Wherein, the total phosphorus content of the simulated wastewater is 425mg/L, and the total nitrogen content is 1560 mg/L; 0.032g of magnesium oxide powder is put into an electric heating constant temperature blast drying oven and is sterilized for 2 hours by dry heat at 170 ℃ while the content of organic phosphorus and organic nitrogen are 250mg/L and 1400 mg/L. Then, 1mL of the activated bacterial liquid was inoculated into a culture flask containing magnesium oxide sterilized by dry heat and 100mL of a culture medium, and aerobic culture was carried out on a shaker at a rotation speed of 200rpm at a temperature of 30 ℃. After 72h of culture, the pH of the culture solution is measured, the product is subjected to sedimentation separation, and then the product is washed three times with absolute ethyl alcohol and placed in a vacuum drying oven to be dried for 48 hours at room temperature. The product was analyzed by X-ray diffraction (XRD) and scanning electron microscopy, as shown in fig. 1 and 4, and fig. 4 is a FESEM image of struvite provided in example 3 of the present invention. As can be seen from FIG. 4, the products prepared in this example were all pseudo-tetragonal pyramid struvite.

Three parallel experiments were performed and it was determined that an average yield of struvite of 192.2mg was obtained, corresponding to a conversion of 97.6% of magnesium oxide.

Example 4

100mL of LB medium (10g/L tryptone, 5g/L yeast extract, 5g/L sodium chloride) was added as a model wastewater to a 250mL flask, and autoclaved at 121 ℃ for 20 minutes. Wherein the total phosphorus content of the simulated wastewater is 170mg/L, and the total nitrogen content is 625 mg/L; the content of organic phosphorus is 100mg/L, and the content of organic nitrogen is 560 mg/L. Meanwhile, magnesium oxide powders with different masses (0.016g, 0.064g and 0.096g) are placed in an electric heating constant temperature blast drying oven and are sterilized for 2 hours by dry heat at 170 ℃. Then, 1mL of the activated bacterial liquid was inoculated into a culture flask containing magnesium oxide sterilized by dry heat and 100mL of a medium, and aerobic culture was carried out on a shaker at a rotation speed of 200rpm at a temperature of 30 ℃. After 72h of culture, the pH of the culture solution is measured, the product is subjected to sedimentation separation, and then the product is washed three times with absolute ethyl alcohol and placed in a vacuum drying oven to be dried for 48 hours at room temperature. The product is analyzed by X-ray diffraction (XRD) and scanning electron microscopy, and as shown in fig. 5 to 8, fig. 5 is an XRD pattern of struvite provided in example 4 of the present invention, fig. 6 is an FESEM pattern of struvite prepared when the amount of magnesium oxide added provided in example 4 of the present invention is 0.16g/L, fig. 7 is an FESEM pattern of struvite prepared when the amount of magnesium oxide added provided in example 4 of the present invention is 0.64g/L, and fig. 8 is an FESEM pattern of struvite prepared when the amount of magnesium oxide added provided in example 4 of the present invention is 0.96 g/L. As can be seen from the graphs in FIGS. 5 to 8, the Shewanella onadatumi can specifically mineralize struvite by using MgO as a magnesium source, and the added MgO has no influence on the purity of the struvite; when the addition amount of the magnesium oxide is low, the particle size of the struvite is large, and conversely, the particle size is small; when the addition amount of the magnesium oxide is different, the struvite presents different appearances.

Three parallel experiments were performed to determine that the average yields of struvite obtained at the addition of magnesium oxide of 0.16g/L, 0.64g/L and 0.96g/L were 79.9mg, 122.3mg and 124.6mg, respectively, and the conversion of magnesium oxide was 81.5%, 31.3% and 21.2%, respectively.

To facilitate comparison of experimental conditions and results differences for different examples, the feed composition and yield data for examples 1-4 are integrated into table 1:

TABLE 1 Material composition and yields for the different examples

As can be seen from Table 1, as the concentration of organic nitrogen and phosphorus in the culture medium increases, the struvite yield and the conversion rate of magnesium oxide are greatly improved, and the conversion rate of magnesium oxide can reach 97.6 percent, which shows that the method can be suitable for sewage treatment containing organic nitrogen and phosphorus with different concentrations, and has the potential of economically and efficiently treating high-concentration organic nitrogen and phosphorus and recovering struvite.

The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.

Claims

1. A method for recovering struvite from wastewater, comprising the steps of:

a) activating the Shewanella onadatuma to obtain activated bacterial liquid;

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 wastewater is (0.1-1.2) g: 1L of the compound.

2. The method according to claim 1, wherein the density of bacteria in the activated bacterial liquid in step a) is 1 x 10⁹～15×10⁹CFU/mL。

3. The method according to claim 1, characterized in that said step a) comprises in particular:

4. The method according to claim 3, wherein in step a), the liquid medium is LB medium.

5. The method according to claim 3, wherein the temperature of the aerobic culture in the step a) is 25-35 ℃; the aerobic culture time is 8-16 h.

6. The method according to claim 1, wherein in the step b), the volume ratio of the activated bacterium liquid to the wastewater is (0.1-5): 100.

7. the method according to claim 1, wherein in the step b), the temperature of the aerobic culture is 25-35 ℃; the aerobic culture time is 48-96 h.

8. The method of claim 1, wherein in the 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.