Microalgae harvesting method based on re-fried oil

Abstract

The invention relates to the technical field of microalgae harvesting, and provides a microalgae harvesting method based on refried oil, emulsified liquid is prepared by mixing the refried oil and Span80, the diameter of emulsified liquid microspheres formed by mixing Span80 serving as an emulsifier is about 20-40 microns, the emulsified liquid microspheres can collide and adhere to microalgae after being in contact with the microalgae, a floating bead-microalgae combination is formed on the outer surface of a floating bead, and the floating bead-microalgae combination is used for harvesting the microalgae. The formed floating bead-microalgae combination is suspended on the upper layer of the mixed liquid, collection of the floating bead-microalgae combination is completed, microalgae flotation is achieved, and the method has the advantages of being high in stability, high in recovery efficiency, low in input cost, low in recovery energy consumption and the like; the use amount of the emulsion is more accurate, the controllability of algae recovery is greatly improved, the use of the refrying oil provides a new thought for recycling waste resources, the problem of pollution caused by discharge of the refrying oil is effectively solved, the use of a chemical flocculant is effectively reduced by a floating bead flotation method based on the refrying oil emulsion, the possibility of secondary pollution of a water body is greatly reduced, and the method is suitable for industrial production. The environment-friendly requirement is met, and the commercialized industrial chain development is further perfected.

Description

Technical Field

[0001] The invention relates to the technical field of microalgae harvesting, and in particular to a microalgae harvesting method based on re-frying oil. Background Art

[0002] After being heated at high temperatures for many times, edible oil is formed into re-frying oil. During the heating process, peroxides and polar components are easily produced, such as free fatty acids, acrylamide and other harmful substances, which are very harmful to human health. Realizing the harmless treatment of re-frying oil has become one of the major problems that the catering industry urgently needs to solve. At the same time, these waste edible oils are difficult to degrade. If they are directly discharged into the water body, an oil film will form on the water surface, hindering the oxygen exchange between the gas and liquid phases on the water surface, causing aquatic organisms to die of lack of oxygen. Studies have shown that by using waste oil as a mixed fuel, not only can the possibility of adding gutter oil to food to harm human health be reduced, but it can also be recycled as a green fuel to reduce energy emissions.

[0003] Microalgae are considered to be a feasible and sustainable raw material for the production of low-carbon and renewable biofuels. They have the advantages of wide distribution, short growth cycle, and high fat content, while having almost no impact on the environment and food safety. The cultivation of microalgae does not require the occupation of arable land and a large amount of water resources, which saves arable land resources and water resources to a certain extent. In addition, microalgae are also used to produce other bio-based materials, such as nutritional products, medicines and cosmetics. However, as the research deepens, it is found that microalgae cells are small in size and carry negative charges on the surface. The high cost of cultivation has become the main factor restricting the preparation of biofuels from microalgae.

[0004] 20-30% of the production cost of microalgae-based bioproducts comes from the microalgae harvesting process. Traditional microalgae harvesting methods include centrifugation, filtration and flocculation, as shown in Table 1 below. These methods cannot simultaneously meet the requirements of low energy consumption, low cost and high efficiency. The centrifugation method has high operating and maintenance costs, high energy consumption, and the risk of cell damage. The filtration method has high operating and maintenance costs for harvesting microalgae. The flocculation method requires a large amount of flocculants, which contaminates subsequent products and is prone to secondary pollution to the environment. The direct air flotation method (DAF) requires the addition of a large amount of surfactants to enhance bubble stability, which causes great damage to microalgae cells and the environment.

[0005] The following table shows the energy consumption and harvesting efficiency of the traditional microalgae harvesting method and the bead flotation harvesting method used in the present invention:

[0006]

[0007]

[0008] Based on this, a new microalgae harvesting technology has emerged, namely bead flotation using low-density beads, which is considered to be a potential time-saving and energy-saving method to replace the traditional flotation process. Summary of the invention

[0009] The present invention aims to solve the deficiencies of the above-mentioned prior art and invents a novel floating bead flotation harvesting method. The method utilizes the re-explosion oil emulsion to adsorb the microalgae, thereby increasing the contact area between the floating beads and the microalgae, improving the adhesion efficiency of the microalgae, and thus improving the recovery rate of the microalgae. Compared with the air flotation method, no bubbles are generated during the harvesting process, which reduces equipment investment, reduces energy consumption generated during the harvesting process, and reduces the harvesting cost.

[0010] The technical solution of the present invention is as follows: a method for harvesting microalgae based on re-frying oil, the method comprising two parts, namely the preparation of re-frying oil emulsion and the flotation harvesting of microalgae.

[0011] Wherein the specific steps of the preparation of the re-frying oil emulsion are as follows:

[0012] The first step is to prepare double-frying oil using soybean oil, heat the soybean oil repeatedly at high temperature, and fry food, the fried food includes chicken, ham, eggs, mushrooms and other common fried foods;

[0013] Step 2: After cooling, filter the collected re-frying oil and then seal it in a beaker for subsequent use;

[0014] Step 3: Take 100 ml of the filtered re-frying oil and 2 ml of Span80, place them in a 1000 ml beaker, and mix them to form the oil phase;

[0015] Step 4: Add 100 ml of deionized water to the oil phase, place the oil-water mixture under a mechanical stirrer, lower the stirring paddle to the interface between the oil phase and the water phase and stir for 20 minutes, set the speed of the mechanical stirrer to 800-1000 r / min, until the re-frying oil is completely emulsified, let it stand for 12 hours, and wait for the emulsion to float;

[0016] Step 5. Draw out the emulsion into a beaker, add 100 ml of deionized water and stir to make it evenly distributed in the water system. Repeat 2-3 times to wash away the un-emulsified re-frying oil.

[0017] Step 6. Store the washed emulsion in ultrapure water.

[0018] In the above-mentioned preparation method of the re-frying oil emulsion, the re-frying oil is a waste. If it continues to be consumed, it will endanger human health. If it is not handled properly or directly discharged into the water, it will pollute the water environment and damage the ecological environment. The present invention uses the re-frying oil to prepare an emulsion that can float microalgae, which can achieve more efficient microalgae harvesting while realizing the recycling of waste.

[0019] The specific steps of flotation harvesting of microalgae are as follows:

[0020] Step 1: Add the original algae solution into the beaker at a ratio of 1:5 to make the pre-algae solution;

[0021] Step 2: Add a certain amount of flocculant to the pre-planned algae solution, and stir continuously with a magnetic stirrer at a stirring rate of 250 r / min until obvious flocs appear;

[0022] Step 3: extract a certain amount of re-frying oil emulsion and inject it into the beaker containing flocculent algae solution, stir for 2 minutes, let it stand for a certain period of time, and wait for the emulsion beads-microalgae aggregates to float up;

[0023] Step 4: harvest the floating emulsion beads-microalgae aggregates to achieve floatation of microalgae beads.

[0024] In the step 1, the flocculant includes a biological flocculant or a chemical flocculant. The biological flocculant is chitosan, and the chemical flocculant is one or a mixture of two or more of ferric chloride, ferric sulfate, aluminum chloride or aluminum sulfate.

[0025] The amount of the biological flocculant added is 20 mg / L to 50 mg / L based on the volume of the microalgae suspension, and the amount of the chemical flocculant added is 50 mg / L to 100 mg / L based on the volume of the microalgae suspension.

[0026] The re-frying oil emulsion used in the step three is obtained from the step six.

[0027] The floating bead particle size of the re-frying oil emulsion in the fifth step is 20-40 μm, and the density is 0.8-1.0 g / cm 3 In this state, the floating beads of the re-frying oil emulsion are uniform in size, stable in shape and have good adsorption properties with microalgae.

[0028] The concentration of the floating beads in the mixed suspension obtained in step 3 is 5 ml / L to 20 ml / L.

[0029] The beneficial effects of the present invention are:

[0030] 1. The present invention uses re-frying oil emulsion microbeads with a diameter of about 20-40 μm as carriers to harvest microalgae. First, the emulsion is fully mixed with the microalgae suspension. After the emulsion microbeads in the mixed liquid contact with the microalgae, collision and adhesion occur. The microalgae adhesion is concentrated on the outer surface of the floating beads to form a floating bead-microalgae combination. Since the floating beads have a relatively stable shape, a relatively uniform particle size, and a large spatial distance between the floating beads, the contact probability and contact area between the floating beads and the microalgae are increased, which greatly improves the adhesion efficiency of the microalgae. Since the density of the floating beads is much smaller than the density of the microalgae suspension, the formed floating bead-microalgae combination can still be suspended in the upper layer of the mixed liquid, so as to facilitate the collection of the floating bead-microalgae combination. Then, the density difference between the floating beads and the microalgae is used to make the microalgae adhered to the floating beads fall off, thereby achieving effective separation of the two, reducing the loss of microalgae cells, and improving the microalgae recovery rate.

[0031] 2. In the present invention, the microalgae suspension is pretreated before flotation, that is, a cationic flocculant is added to reduce the potential of the negatively charged microalgae suspension, which is in an unstable state, thereby increasing the adsorption surface area of ​​the microalgae and enhancing the adhesion ability, thereby promoting the combination between the floating beads and the microalgae, increasing the adsorption amount of the floating beads on the microalgae, and further improving the recovery rate of the microalgae;

[0032] 3. In the present invention, floating beads are used to flotate and harvest microalgae. The traditional flotation method requires complex and fragile bubble generation equipment and consumes a lot of energy, while the floating bead flotation does not need to generate bubbles during the microalgae harvesting process, which not only reduces equipment investment and saves costs, but also effectively reduces the harvesting energy consumption. At the same time, the shape of the emulsion microbeads is more stable than that of bubbles, and the dosage is more accurate, which effectively reduces the uncertainty in the harvesting process, improves the controllability of the microalgae flotation harvesting process, and is conducive to the realization of industrial promotion;

[0033] 4. The present invention uses floating beads to flotation-harvest microalgae, which effectively reduces the use of chemical flocculants to a certain extent and reduces the secondary pollution of the flocculants to the environment;

[0034] 5. The raw material of the emulsion used in the present invention is re-frying oil, which is the oil remaining after repeated frying 3 to 4 times. This provides a new idea for the reuse of re-frying oil, realizes the reuse of waste resources and reduces costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0036] Figure 1 The present invention is a schematic flow chart of a method for preparing a double-frying oil emulsion used in all embodiments of the present invention;

[0037] Figure 2 Schematic diagram of the microalgae harvesting process based on re-frying oil in all embodiments of the present invention. DETAILED DESCRIPTION

[0038] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0039] The present invention proposes 5 embodiments, among which the algae liquids used in Embodiment 1, Embodiment 2 and Experimental Example 3 are all taken from the moat of the ancient city wall of Shou County, Huainan, Shou County No. 1 Middle School and the pond water samples of Qinglian Village; the algae liquids used in Embodiment 4 and Embodiment 5 are all taken from Laoshan Island in Zhongmiao Town, Chaohu Lake and the water samples of the cyanobacteria treatment plant. The manufacturers of the photobioreactors used in Embodiments 1 to 5 of the present invention are all Shanghai Guangyu Biotechnology Co., Ltd.

[0040] See also Figure 1 Embodiments 1 to 5 of the present invention relate to a method for harvesting microalgae based on re-frying oil, the method comprising preparing a re-frying oil emulsion, and the specific steps are as follows:

[0041] The first step is to prepare the double frying oil;

[0042] Specifically, the preparation of the re-frying oil comprises:

[0043] 1. Use soybean oil to prepare double-frying oil, heat the soybean oil repeatedly at high temperature, and fry foods, including common fried foods such as chicken, ham, eggs, mushrooms, etc.;

[0044] 2. After the re-frying oil cools down, filter it and seal it for later use;

[0045] In the second step, the re-frying oil is placed in a beaker and Span80 is added to form the oil phase;

[0046] In this example, the amount of re-frying oil added is 98 ml, and the amount of Span80 added is 2 ml.

[0047] The third step is to add a certain amount of deionized water to the oil phase, lower the stirring paddle to the interface between the oil phase and the water phase, stir with a mechanical stirrer at a calibrated speed for a first calibrated time until the re-frying oil is completely emulsified, and then let it stand for a second calibrated time to wait for the emulsion to float up;

[0048] In this example, the amount of deionized water added is 100 ml, the calibrated speed is 800-1000 r / min, preferably, the calibrated speed is 800 r / min; the first calibration time is 20 min, and the second calibration time is 12 h.

[0049] In the fourth step, the emulsion is pumped out into a beaker, a certain amount of deionized water is added and stirred to make it evenly distributed in the water system, and the unemulsified re-frying oil is washed away according to the calibrated number of cycles.

[0050] In this example, the amount of deionized water added is 100 ml, and the number of calibration cycles is 2 to 3 times. Preferably, the number of calibration cycles is 3 times.

[0051] The fifth step is to store the washed re-frying oil emulsion in ultrapure water.

[0052] See also Figure 2 , a schematic diagram of the process of harvesting microalgae based on the re-frying oil emulsion in Examples 1 to 5 of the present invention, and a specific example is as follows:

[0053] Example 1 (Water sample of the moat of the ancient city wall of Shou County, Huainan)

[0054] This embodiment includes the following steps:

[0055] Step 1: Add 70 mg / L aluminum sulfate flocculant to 100 ml of microalgae suspension, and then stir at 250 rpm for 1 min to obtain a pretreated microalgae suspension; the absorbance of the microalgae suspension measured at a wavelength of 540 nm is 0.069-0.088.

[0056] Step 2: Use a pump to extract 10 ml / L of re-frying oil emulsion and add it to the pretreated microalgae suspension in step 1 to obtain a mixed suspension, stir the mixed suspension at a rate of 200 r / min for 2 minutes, let it stand at room temperature for 15 minutes, and then overflow to obtain an overflow liquid containing a floating bead-microalgae combination; wherein the emulsion raw material is prepared from the above-mentioned re-frying oil emulsion, and the particle size is 20-40 μm.

[0057] Step 3: The overflow liquid containing the emulsion-microalgae combination obtained in step 2 is centrifuged to collect the precipitate to obtain separated microalgae.

[0058] Example 2 (water sample from a middle school in Shou County, Huainan)

[0059] This embodiment includes the following steps:

[0060] Step 1: Add 70 mg / L aluminum sulfate flocculant to 100 ml of microalgae suspension, and then stir at 250 rpm for 1 min to obtain a pretreated microalgae suspension; the absorbance of the microalgae suspension measured at a wavelength of 540 nm is 0.057-0.078.

[0061] Step 2: Use a pump to extract 10 ml / L of emulsion and add it to the pretreated microalgae suspension in step 1 to obtain a mixed suspension, stir the mixed suspension at a rate of 200 r / min for 2 minutes, let it stand at room temperature for 15 minutes, and then overflow to obtain an overflow liquid containing a floating bead-microalgae combination; wherein the emulsion raw material is prepared from the above-mentioned double-frying oil emulsion, and the particle size is 20-40 μm.

[0062] Step 3: The overflow liquid containing the emulsion-microalgae combination obtained in step 2 is centrifuged to collect the precipitate to obtain separated microalgae.

[0063] Example 3 (Ordinary pond water sample from Qinglian Village, Shou County, Huainan)

[0064] This embodiment includes the following steps:

[0065] Step 1: Add 70 mg / L aluminum sulfate flocculant to 100 ml of microalgae suspension, and then stir at 250 rpm for 1 min to obtain a pretreated microalgae suspension; the absorbance of the microalgae suspension measured at a wavelength of 540 nm is 0.066-0.088.

[0066] Step 2: Use a pump to extract 10 ml / L of emulsion and add it to the pretreated microalgae suspension in step 1 to obtain a mixed suspension, stir the mixed suspension at a rate of 200 r / min for 2 minutes, let it stand at room temperature for 15 minutes, and then overflow to obtain an overflow liquid containing a floating bead-microalgae combination; wherein the emulsion raw material is prepared from the above-mentioned double-frying oil emulsion, and the particle size is 20-40 μm.

[0067] Step 3: The overflow liquid containing the emulsion-microalgae combination obtained in step 2 is centrifuged to collect the precipitate to obtain separated microalgae.

[0068] Embodiment 4 (Lukeshan Island, Zhongmiao Town, Chaohu Lake, Chaohu)

[0069] This embodiment includes the following steps:

[0070] Step 1: Add 70 mg / L aluminum sulfate flocculant to 100 ml of microalgae suspension, and then stir at 250 rpm for 1 min to obtain a pretreated microalgae suspension; the absorbance of the microalgae suspension measured at a wavelength of 540 nm is 0.061-0.083.

[0071] Step 2: Use a pump to extract 10 ml / L of emulsion and add it to the pretreated microalgae suspension in step 1 to obtain a mixed suspension, stir the mixed suspension at a rate of 200 r / min for 2 minutes, let it stand at room temperature for 15 minutes, and then overflow to obtain an overflow liquid containing a floating bead-microalgae combination; wherein the emulsion raw material is prepared from the above-mentioned double-frying oil emulsion, and the particle size is 20-40 μm.

[0072] Step 3: The overflow liquid containing the emulsion-microalgae combination obtained in step 2 is centrifuged to collect the precipitate to obtain separated microalgae.

[0073] Example 5 (Water sample from Chaohu blue algae treatment plant)

[0074] This embodiment includes the following steps:

[0075] Step 1: Add 70 mg / L aluminum sulfate flocculant to 100 ml of microalgae suspension, and stir continuously at a rate of 250 r / min for 1 min to obtain a pretreated microalgae suspension; the absorbance of the microalgae suspension measured at a wavelength of 540 nm is 0.087-0.261.

[0076] Step 2: Use a pump to extract 10 ml / L of emulsion and add it to the pretreated microalgae suspension in step 1 to obtain a mixed suspension, stir the mixed suspension at a rate of 200 r / min for 2 minutes, let it stand at room temperature for 15 minutes, and then overflow to obtain an overflow liquid containing a floating bead-microalgae combination; wherein the emulsion raw material is double frying oil with a particle size of 20-40 μm.

[0077] Step 3: The overflow liquid containing the emulsion-microalgae combination obtained in step 2 is centrifuged to collect the precipitate to obtain separated microalgae.

[0078] The harvesting efficiency of the microalgae obtained in Examples 1 to 5 was tested. The specific testing process was as follows: a 10 ml sample was slowly extracted from the bottom 5 cm of the harvested raw material microalgae suspension using a peristaltic pump, and then its absorbance was measured using an ultraviolet spectrophotometer, which was recorded as C0; a sample was extracted from the mixed suspension after overflow in the same way, and then its absorbance was measured using an ultraviolet spectrophotometer, which was recorded as C1; wherein the ultraviolet absorption wavelength of the samples in Examples 1 to 5 during measurement was 540 nm, and the microalgae harvesting efficiency of Examples 1 to 5 was calculated and recorded as H. The results are shown in Table 2 below.

[0079] in,

[0080] The following table shows the maximum recovery rate of microalgae in Examples 1 to 5.

[0081]

[0082] It can be seen from the above table that the microalgae recovery rates of Examples 1 to 5 of the present invention are all above 72.2%, among which the microalgae recovery rate of Example 2 is as high as 91.2%, indicating that the floating bead flotation recovery method of the present invention has a good recovery effect on microalgae, and the microalgae recovery rate is greatly improved.

[0083] According to calculations, the average energy consumption of the microalgae harvesting in Examples 1 to 5 of the present invention is 0.069 kWh / m3, which is less than the harvesting energy consumption of the traditional microalgae harvesting method and the air flotation method; in addition, the microalgae harvesting in Examples 1 to 5 of the present invention does not require equipment investment, and the floating beads used can be reused, and the average harvesting cost is 1.37 yuan / m 3 , which is far less than the cost of traditional microalgae harvesting methods. Therefore, the bead flotation harvesting method not only reduces the harvesting energy consumption, but also greatly reduces the harvesting cost of microalgae.

[0084] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for harvesting microalgae based on re-frying oil, characterized in that: include: Preparation of re-frying oil emulsion, the first step, using soybean oil to prepare re-frying oil, the soybean oil is repeatedly heated at high temperature, and fried food; Step 2: After cooling, filter the collected re-frying oil and then seal it in a beaker for subsequent use; Step 3: Take 100 ml of the filtered re-frying oil and 2 ml of Span 80, place them in a 1000 ml beaker, and mix them to form the oil phase; Step 4: Add 100 ml of deionized water to the oil phase, place the oil-water mixture under a mechanical stirrer, lower the stirring paddle to the interface between the oil phase and the water phase and stir for 20 minutes, set the speed of the mechanical stirrer to 800-1000 r / min, until the re-frying oil is completely emulsified, let it stand for 12 hours, and wait for the emulsion to float; Step 5: Draw out the emulsion into a beaker, add 100 ml of deionized water and stir to make it evenly distributed in the water system, repeat 2-3 times to wash away the unemulsified re-frying oil; Step 6: Store the washed emulsion in ultrapure water; Flotation harvesting of microalgae, step 1, adding the original algae solution into a beaker at a ratio of 1:5 between algae and water to prepare a pre-planned algae solution; Step 2: Add a certain amount of flocculant to the pre-planned algae solution, and stir continuously with a magnetic stirrer at a stirring rate of 250 r / min until obvious flocs appear; Step 3: extract a certain amount of re-frying oil emulsion and inject it into the beaker containing flocculent algae solution, stir for 2 minutes, let it stand for a certain period of time, and wait for the emulsion beads-microalgae aggregates to float up; Step 4: harvest the floating emulsion beads-microalgae aggregates to achieve floatation of microalgae beads.

2. The method for harvesting microalgae based on re-frying oil according to claim 1, characterized in that: In the step 1, the flocculant includes a biological flocculant or a chemical flocculant. The biological flocculant is chitosan, and the chemical flocculant is one or a mixture of two or more of ferric chloride, ferric sulfate, aluminum chloride or aluminum sulfate.

3. The method for harvesting microalgae based on re-frying oil according to claim 2, characterized in that: The amount of the biological flocculant added is 20 mg / L to 50 mg / L based on the volume of the microalgae suspension, and the amount of the chemical flocculant added is 50 mg / L to 100 mg / L based on the volume of the microalgae suspension.

4. The method for harvesting microalgae based on re-frying oil according to claim 1, characterized in that: The re-frying oil emulsion used in the step three is obtained from the step six.

5. The method for harvesting microalgae based on re-frying oil according to claim 1, characterized in that: The floating bead particle size of the re-frying oil emulsion in the fifth step is 20-40 μm, and the density is 0.8-1.0 g / cm 3 .

6. The method for harvesting microalgae based on re-frying oil according to claim 1, characterized in that: The concentration of the floating beads in the mixed suspension obtained in step 3 is 5 ml / L to 20 ml / L.

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