A method for simultaneously harvesting algal bodies and producing oil by using microalgae to treat dye wastewater

Abstract

The application relates to a method for treating dye wastewater by using microalgae to simultaneously collect algal bodies and produce oil, and belongs to the wastewater treatment field, in particular to a method for treating dye wastewater by using microalgae to simultaneously collect algal bodies and produce oil. The method comprises the following steps: using simulated dye wastewater as a culture medium of microalgae, using various substances in the wastewater, such as dyes, to promote the increase of the biomass of the microalgae and the efficient accumulation of oil, reduce the cost of the culture of the microalgae and the production of biological energy, make the dyes be efficiently removed, reduce environmental pollution, and strengthen the sedimentation of the microalgae and reduce the difficulty of the collection of the microalgae. The method realizes low-cost wastewater treatment and biological energy production, and is an ideal method for treating dye wastewater.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of wastewater treatment, in particular to a method for treating dye wastewater by using microalgae to simultaneously harvest algal bodies and produce oil. BACKGROUND

[0002] As a kind of wastewater with large water volume, high content of organic pollutants, deep color, strong alkalinity and strong toxicity, dye wastewater is difficult to be degraded, which, if directly discharged into water environment, not only destroys the appearance of water body, but also has toxic effects on aquatic organisms, and is one of the serious threats to water environmental safety.

[0003] Currently, physical, chemical and biological methods are usually used to treat dye wastewater, such as adsorption, membrane separation and magnetic separation, coagulation, electrochemistry, chemical oxidation and photocatalytic oxidation. However, the physical and chemical methods generally have the disadvantages of high cost, high sludge treatment requirement, low dye removal rate and generation of toxic degradation products. In the biological method, fungi and bacteria are often used to treat dye wastewater, but these systems generally need to supplement carbon source, which will cause additional treatment cost. SUMMARY

[0004] The present application can realize low-cost dye wastewater treatment and bioenergy production. Thus, a method for treating dye wastewater by using microalgae to simultaneously harvest algal bodies and produce oil is provided.

[0005] The method for treating dye wastewater by using microalgae to simultaneously harvest algal bodies and produce oil is specifically performed according to the following steps:

[0006] I. Prepare simulated dye wastewater, adjust pH, sterilize and obtain microalgae culture medium;

[0007] II. Inoculate microalgae into the microalgae culture medium, anaerobically culture to the stationary phase, take algal liquid and stand, and simultaneously harvest algal bodies and produce oil.

[0008] Advantages of the present application:

[0009] The present application first prepares simulated dye wastewater, which is used as the culture medium of oil-producing microalgae, not only achieves good dye removal effect, but also realizes the recycling of resources in wastewater, promotes the efficient accumulation of microalgae oil, and reduces the cost of microalgae culture and bioenergy production. At the same time, the sedimentation of microalgae is significantly enhanced under the action of dye, which reduces the difficulty of microalgae harvesting. BRIEF DESCRIPTION OF DRAWINGS

[0010] Figure 1 The microalgae growth comparison curves in the examples and comparative examples;

[0011] Figure 2 The removal rate change comparison chart of microalgae on dye in the examples and comparative examples;

[0012] Figure 3 Figure 1 shows the settling rate of microalgae in the examples and comparative examples;

[0013] Figure 4 Figure 2 shows the lipid production and lipid content of microalgae in the examples and comparative examples. DETAILED DESCRIPTION

[0014] Specific embodiment one: the method of the present embodiment for treating dye wastewater with microalgae to simultaneously harvest algal bodies and produce lipids is carried out according to the following steps:

[0015] I. Prepare simulated dye wastewater, adjust pH, sterilize, and obtain a microalgae culture medium;

[0016] II. Inoculate microalgae into the microalgae culture medium, anaerobically culture to the stationary phase, take the algal liquid and stand, and simultaneously harvest algal bodies and produce lipids.

[0017] The present embodiment adopts anaerobic conditions to improve the effect of dye removal.

[0018] The bioreactor used for culture in the present embodiment is not particularly limited and can be any of various culture conditions and bioreactors commonly used in the art.

[0019] The present embodiment has many advantages for treating dye wastewater with microalgae. Microalgae have a large surface area and affinity and can remove many pollutants at a high rate. Microalgae can proliferate under mixed nutrient conditions and can use carbon dioxide and organic carbon in wastewater as carbon sources, so there is no need to supplement external organic carbon sources. Compared with heterotrophic organisms, microalgae are a more cost-effective and environmentally sustainable choice. Microalgae cells can produce lipids, proteins, polysaccharides, pigments, and other substances, which are widely used in the fields of chemical industry and biomass energy and have great economic value and environmental benefits. Therefore, combining microalgae culture with dye wastewater treatment is a promising method for low-cost wastewater treatment and bioenergy production.

[0020] Specific embodiment two: the difference between the present embodiment and specific embodiment one is that the concentration of Congo red in the simulated dye wastewater in step one is 20-100 mg / L. The other steps are the same as in specific embodiment one.

[0021] The present embodiment comprehensively considers the effects of dye removal, microalgae growth, and lipid production.

[0022] Specific embodiment three: the difference between the present embodiment and specific embodiment two is that the pH is adjusted to 6.8-7.0 in step one. The other steps are the same as in specific embodiment two.

[0023] Specific embodiment four: the difference between this embodiment and specific embodiment one is that the sterilization temperature in step one is 115-120℃, and the time is 20-30 min. The others are the same as specific embodiment one.

[0024] Specific embodiment five: the difference between this embodiment and specific embodiment one is that the microalgae in step two is Asterarcys quadricellulare R-56. The others are the same as specific embodiment one.

[0025] The microalgae Asterarcys quadricellulare R-56 in this embodiment is known to the public and can be obtained by purchase or other means.

[0026] Specific embodiment six: the difference between this embodiment and specific embodiment five is that the inoculation amount of microalgae in step two is 5-15%. The others are the same as specific embodiment five.

[0027] Specific embodiment seven: the difference between this embodiment and specific embodiment one is that the method of simultaneous extraction of oil and harvesting of algal cells in step two is as follows: the algal liquid is left to stand, the Asterarcys quadricellulare R-56 in the algal liquid is separated and settled, the algal cells are collected, washed with distilled water for 2-3 times, placed in a refrigerator at a temperature of -80℃ for 12 h, then vacuum freeze-dried for 48 h, the freeze-dried algal powder is collected and weighed, the freeze-dried algal powder is added into a chloroform-methanol solution, and ultrasonic crushing is performed under the condition of power 200 W until the algal cells turn white, the organic phase is collected by centrifugation and dried to obtain microalgae oil. The others are the same as specific embodiment one.

[0028] Specific embodiment eight: the difference between this embodiment and specific embodiment seven is that the mass ratio of freeze-dried algal powder to chloroform-methanol solution is 0.1 g:10 mL. The others are the same as specific embodiment seven.

[0029] Specific embodiment nine: the difference between this embodiment and specific embodiment eight is that the volume ratio of chloroform to methanol in the chloroform-methanol solution is 2:1. The others are the same as specific embodiment eight.

[0030] Specific embodiment ten: the difference between this embodiment and specific embodiment seven is that the method for determining and analyzing the fatty acid composition in the microalgae oil is as follows: 40 mg of microalgae oil is taken in a 10 mL culture tube, 1 mL of saponification reagent is added, mixed and placed in a boiling water bath for 5 min, then taken out, cooled and shaken for 5-10 s, and then continuously reacted in the boiling water bath for 25 min; after the culture tube is cooled, 2 mL of methylation reagent is added, mixed, and heated at a water bath temperature of 79-81 °C for 9-11 min; after the culture tube is cooled, 1.25 mL of extraction reagent is added, and the culture tube is inverted for 10 min; the water phase part at the bottom of the tube is discarded, and the upper liquid phase is retained; 3 mL of washing reagent is added to the remaining organic phase in the culture tube, which is sealed and inverted for 5 min; NaCl saturated aqueous solution is added to the fatty acid methyl ester in the organic phase until it is clear; after the cover is opened, 2 / 3 of the clear organic phase is added to a sealed gas chromatography bottle for determination of the composition of the fatty acids on a GC-MS. The rest is the same as specific embodiment seven.

[0031] The effect of the present application is verified by the following examples:

[0032] The composition of the simulated dye wastewater in this example is shown in Table 1:

[0033] Table 1 Composition of simulated dye wastewater

[0034]

[0035]

[0036] Example 1: A method for treating dye wastewater with microalgae to simultaneously harvest algal bodies and produce oil is carried out according to the following steps:

[0037] I. Prepare simulated dye wastewater, adjust the pH to 6.8-7.0, sterilize, and obtain a microalgae culture medium;

[0038] II. Inoculate microalgae Asterarcys quadricellulare R-56 into simulated wastewater with a Congo red dye concentration of 25 mg / L, with an inoculation volume of 10%, and control the culture conditions as follows: full light 3500 lux, temperature 23-27 °C, light cycle L:D = 24:0, take a certain amount of algal liquid every 24 h to measure the absorbance of the algal liquid, and draw a growth curve. The dry weight change of the algal liquid at different stages is shown in Figure 1 . Another amount of algal liquid is centrifuged at 5000 rpm for 10 min, the supernatant is taken, distilled water is used as a reference, the absorbance of the supernatant is measured at the maximum absorption wavelength of Congo red dye using a spectrophotometer, and the dye removal rate is calculated. The change in the dye removal rate is shown in Figure 2 .

[0039] The microalgae is cultured to the stable phase, and the algal liquid is taken and left to stand. The Asterarcys quadricellulare R-56 in the culture solution is layered and settled, and after 2 hours, the settling rate of the algae is measured to be 40.0%; after 12 hours, the settling rate of the algae is measured to be 99.0%, the algal cells are collected, the oil in the algal cells is extracted, and the production is completed.

[0040] The method for extracting the oil in the microalgae is as follows: the algal cells are collected, washed with distilled water for 2-3 times, placed in a refrigerator with a temperature of -80℃ for 12 hours, and then vacuum freeze-dried for 48 hours. The freeze-dried algal powder is collected and weighed, added into a chloroform-methanol solution, and the addition amount ratio of the freeze-dried algal powder to the chloroform-methanol solution is controlled to be 0.1g:10mL. The algal body is white after ultrasonic crushing for 10 minutes under the condition of a power of 200W. The organic phase is collected by centrifugation and dried to obtain the microalgae oil.

[0041] The method for measuring the content of fatty acids is as follows: 40mg of the microalgae oil is taken in a 10mL culture tube, 1mL of a saponification reagent is added, mixed, placed in a boiling water bath for reaction for 5 minutes, taken out, cooled, and shaken for 5-10 seconds. The boiling water bath reaction is continued for 25 minutes. After the culture tube is cooled, 2mL of a methylation reagent is added, mixed, and heated for 9-11 minutes under the condition that the water bath temperature is 79-81℃. After the culture tube is cooled, 1.25mL of an extraction reagent is added, and the culture tube is turned up and down for 10 minutes. The water phase part at the bottom of the culture tube is discarded, and the upper liquid phase is reserved. 3mL of a washing reagent is added into the remaining organic phase in the culture tube, the culture tube is sealed, and turned up and down for 5 minutes. NaCl saturated aqueous solution is added until the fatty acid methyl ester in the organic phase is clear. After the culture tube is opened, 2 / 3 of the clear organic phase is added into a sealed gas chromatography bottle, and the composition of the fatty acids is measured on a GC-MS.

[0042] It is tested that, under the condition that the culture is carried out at a Congo red dye concentration of 25mg / L, the biomass of the microalgae is 0.30g / L, the dye removal rate is 96.22%, the oil content is 61.92%, and the fatty acid composition of the oil is shown in Table 2.

[0043] In Example 2, the microalgae Asterarcys quadricellulare R-56 is inoculated into simulated wastewater with a Congo red dye concentration of 50mg / L, and the inoculation amount is 10% of the volume. The culture conditions are controlled as follows: full light 3500lux, temperature 23-27℃, light cycle L:D=24:0. A certain amount of algal liquid is taken every 24 hours to measure the absorbance of the algal liquid, and the growth curve is drawn. The dry weight change of the algae at different stages is shown in Figure 1 In addition, a certain amount of algal liquid is centrifuged at 5000rpm for 10 minutes, the supernatant is taken, distilled water is used as a reference, the absorbance of the supernatant is measured at the maximum absorption wavelength of the Congo red dye by using a spectrophotometer, the dye removal rate is calculated, and the change of the dye removal rate is shown in Figure 2 .

[0044] The microalgae is cultured to the stable phase, and the algal liquid is taken and left to stand. The Asterarcys quadricellulare R-56 in the culture solution is stratified and settled. After 2 hours, the settling rate of the algae is measured to be 34.3%. After 12 hours, the settling rate of the algae is measured to be 98.0%. The algal cells are collected, and the oil and fat of the algal cells is extracted, and the production is completed.

[0045] It is tested that, under the condition of culturing at the Congo red dye concentration of 50 mg / L, the biomass of the microalgae is 0.34 g / L, the dye removal rate is 95.06%, the oil and fat content is 50.59%, and the oil and fat fatty acid composition is shown in Table 2.

[0046] In Example 3, the microalgae Asterarcys quadricellulare R-56 is inoculated into the simulated wastewater with the Congo red dye concentration of 75 mg / L, and the inoculation amount is 10% of the volume. The culture conditions are controlled as follows: full light 3500 lux, temperature 23-27℃, light cycle L:D = 24:0. Every 24 hours, a certain amount of algal liquid is taken to measure the absorbance of the algal liquid, and the growth curve is drawn. The dry weight change of the algae at different stages is shown in Table 3. Figure 1 Another certain amount of algal liquid is centrifuged at 5000 rpm for 10 min. The supernatant is taken, distilled water is used as the reference, the absorbance of the supernatant is measured at the maximum absorption wavelength of the Congo red dye by using a spectrophotometer, and the dye removal rate is calculated. The change of the dye removal rate is shown in Table 4. Figure 2

[0047] The microalgae is cultured to the stable phase, and the algal liquid is taken and left to stand. The Asterarcys quadricellulare R-56 in the culture solution is stratified and settled. After 2 hours, the settling rate of the algae is measured to be 34.3%. After 12 hours, the settling rate of the algae is measured to be 98.0%. The algal cells are collected, and the oil and fat of the algal cells is extracted, and the production is completed.

[0048] It is tested that, under the condition of culturing at the Congo red dye concentration of 75 mg / L, the biomass of the microalgae is 0.36 g / L, the dye removal rate is 91.98%, the oil and fat content is 47.56%, and the oil and fat fatty acid composition is shown in Table 2.

[0049] In Example 4, the microalgae Asterarcys quadricellulare R-56 is inoculated into the simulated wastewater with the Congo red dye concentration of 100 mg / L, and the inoculation amount is 10% of the volume. The culture conditions are controlled as follows: full light 3500 lux, temperature 23-27℃, light cycle L:D = 24:0. Every 24 hours, a certain amount of algal liquid is taken to measure the absorbance of the algal liquid, and the growth curve is drawn. The dry weight change of the algae at different stages is shown in Table 5. Figure 1 ​The absorbance of the supernatant was measured at the maximum absorption wavelength of the Congo red dye by using a spectrophotometer with distilled water as a reference. The dye removal rate was calculated, and the change in the dye removal rate is shown in Table 1. Figure 2

[0050] The microalgae were cultured to the stable phase, and the algal liquid was allowed to stand. The Asterarcys quadricellulare R-56 in the culture solution was stratified and settled. After 2 hours, the settling rate of the algae was measured to be 28.4%. After 12 hours, the settling rate of the algae was measured to be 98.0%. The algal cells were collected, and the oil in the algal cells was extracted, thus completing the production.

[0051] It was tested that, under the condition of culturing at a Congo red dye concentration of 100 mg / L, the biomass of the microalgae was 0.41 g / L, the dye removal rate was 87.75%, and the oil content was 41.62%. The fatty acid composition of the oil is shown in Table 2.

[0052] In the comparative example, the microalgae Asterarcys quadricellulare R-56 were cultured in the BG11 culture medium, and the inoculation amount was 10% by volume. The culture conditions were controlled as follows: full light of 3500 lux, temperature of 23-27°C, and light cycle of L:D = 24:0. Every 24 hours, a certain amount of algal liquid was taken to measure the absorbance of the algal liquid, and a growth curve was drawn. The dry weight change of the algae at different stages is shown in Table 1. The microalgae were cultured to the stable phase, and the algal liquid was allowed to stand. The Asterarcys quadricellulare R-56 in the culture solution was stratified and settled. The algal cells were collected, and the oil in the algal cells was extracted, thus completing the production. Figure 1

[0053] Table 2 Oil fatty acid composition

[0054]

[0055]

[0056] It can be known by comparing the comparative example 1 with the examples 1, 2, 3, and 4 that, by using the simulated dye wastewater as the culture medium of the microalgae, the settling rate of the microalgae can be improved, which is conducive to the aggregation and harvesting of the microalgae.

[0057] It can be known by comparing the comparative example 1 with the examples 1, 2, 3, and 4 that, by using the simulated dye wastewater as the culture medium of the microalgae, the growth rate of the microalgae can be improved, which is more conducive to the biomass accumulation of the microalgae.

[0058] ​​Comparing Example 1, 2, 3, 4 with Comparative Example 1, it can be seen that, using simulated dye wastewater as the culture medium of microalgae, the fatty acid components in the microalgae oil produced, such as palmitic acid (C16:0), palmitoleic acid (C16:1), stearic acid (C18:0), oleic acid (C18:1) and linoleic acid (C18:2), are much higher than those in Comparative Example 1, proving that the simulated Congo red dye wastewater as the culture medium of microalgae is conducive to the accumulation of microalgae oil and the production of bioenergy.

[0059] By Figures 1 to 4 From the results of the biomass, dye removal rate, oil production, oil content and oil fatty acid composition of microalgae R-56 in Table 2, it can be seen that using simulated dye wastewater to culture microalgae not only achieves good dye removal effect, but also realizes the recycling of resources in wastewater, promotes the efficient accumulation of microalgae oil, and reduces the cost of microalgae culture and bioenergy production. At the same time, the sedimentation of microalgae is significantly enhanced under the action of dye, which reduces the difficulty of microalgae harvesting. Therefore, the method of using microalgae to treat dye wastewater to simultaneously produce oil and harvest algae is a feasible, economic, environmentally friendly and effective method, which meets the basic needs of efficient treatment of dye wastewater and production of bioenergy by microalgae.

Claims

1. A method for simultaneous harvesting of algal biomass and production of lipid using microalgae for treating dye wastewater, the method comprising: The method for simultaneously harvesting microalgae and producing oil by treating dye wastewater with microalgae comprises the following steps: ​ I. Preparing simulated dye wastewater, adjusting pH to 6.8-7.0, sterilizing to obtain microalgae culture medium; the concentration of Congo red in the simulated dye wastewater is 20-100 mg / L; the sterilization temperature is 115-120 ℃, and the sterilization time is 20-30 min; II. Inoculating microalgae into the microalgae culture medium, anaerobically culturing to the stable phase, and taking the algal liquid to stand, thereby simultaneously harvesting microalgae and producing oil; the microalgae is Asterarcys quadricellulare R-56; the inoculation amount of the microalgae is 5-15%.

2. A method for simultaneous harvesting of algal biomass and production of lipid from dye wastewater using microalgae as claimed in claim 1, wherein The method for simultaneously extracting oil and harvesting microalgae in step II is as follows: taking the algal liquid to stand, and after the Asterarcys quadricellulare R-56 in the algal liquid is separated and settled, collecting the algal cells, washing the algal cells with distilled water for 2-3 times, placing the algal cells in a refrigerator with a temperature of-80 ℃ for 12 h, and then vacuum freeze-drying the algal cells for 48 h, collecting the freeze-dried algal powder, weighing the freeze-dried algal powder, adding the freeze-dried algal powder into a chloroform-methanol solution, and ultrasonically crushing the freeze-dried algal powder until the algal cells turn white under the condition that the power is 200 W, and then centrifugally collecting the organic phase to obtain microalgae oil.

3. A method for simultaneous harvesting of algal biomass and production of lipid using microalgae for treatment of dye wastewater as claimed in claim 2, wherein the microalgae is selected from the group consisting of Chlorella sp., Scenedesmus sp., Spirulina sp., and combinations thereof. The mass ratio of the freeze-dried algal powder to the volume of the chloroform-methanol solution is 0.1 g:10 mL.

4. The method for simultaneous harvesting of algal biomass and production of lipid from dye wastewater using microalgae according to claim 3, wherein The volume ratio of chloroform to methanol in the chloroform-methanol solution is 2:

1.

5. The method for simultaneous harvesting of algal biomass and production of lipid from dye wastewater using microalgae according to claim 2, wherein The method for determining and analyzing the fatty acid composition in the microalgae oil is as follows: taking 40 mg of the microalgae oil into a 10 mL culture tube, adding 1 mL of saponification reagent, mixing, placing in a boiling water bath for 5 min, taking out, and after cooling, shaking for 5-10 s, and continuing to react in the boiling water bath for 25 min; after the culture tube is cooled, adding 2 mL of methylation reagent, mixing, and heating at a water bath temperature of 79-81 ℃ for 9-11 min; after the culture tube is cooled, adding 1.25 mL of extraction reagent, and inverting for 10 min, discarding the water phase at the bottom of the tube, and retaining the upper liquid phase; taking 3 mL of washing reagent and adding into the remaining organic phase in the culture tube, sealing, and inverting for 5 min; adding NaCl saturated aqueous solution until the fatty acid methyl ester in the organic phase is clear; after opening the cover, adding 2 / 3 of the clear organic phase into a sealed gas chromatography bottle, and determining the composition of the fatty acid on a GC-MS.

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