Method for comprehensive utilization of potato starch processing by-product resources

Abstract

The application discloses a kind of potato starch processing by-product resource comprehensive utilization method, belong to potato starch processing technical field.The resource comprehensive utilization method mainly includes double-effect pre-treatment of stacking screw, micro-nano bubble device processing, primary separation and primary concentration treatment, thermal flocculation, secondary separation and secondary concentration treatment, finally recover potato protein, the COD value of the filtrate obtained can reach discharge standard.The present application solves the problems of difficult sewage treatment of potato juice produced in the production process of potato starch and low recovery efficiency of by-products by precise process design and optimized process steps, realizes effective treatment of high-concentration organic wastewater, reduces environmental pollution, and can also recover high yield and high quality protein, effectively recycles waste liquid generated in potato starch production.

Description

Technical Field

[0001] This invention relates to the field of potato starch processing technology, and in particular to a method for the comprehensive utilization of potato processing by-products. Background Technology

[0002] In the production and processing of potato starch, the refining stage typically employs a multi-stage countercurrent washing process. This process generates a large amount of waste liquid, which contains a large amount of highly soluble, biodegradable organic matter, extremely high chemical oxygen demand (COD) and biological oxygen demand (BOD), high total nitrogen concentration, high suspended solids concentration, a certain amount of fine fiber, and is also rich in nutrients such as protein, free amino acids, and sugars. It is difficult to treat. If untreated potato starch waste liquid is directly discharged, it will cause serious water pollution and eutrophication, damaging aquatic ecosystems.

[0003] Therefore, potato starch wastewater generated during potato starch production is often first discharged into a transfer sedimentation tank for further treatment. Post-treatment mainly includes separating and purifying protein from the wastewater and direct wastewater treatment. However, existing methods for separating and purifying protein from potato starch wastewater have the following problems: the protein production process requires heating to above 90℃, but at this temperature, the wastewater still contains a large amount of fine cellulose, which easily undergoes gelatinization, resulting in a decrease in protein precipitation; the protein solution has a low solids content, and after centrifugation, the filtrate still contains a large amount of protein, with high ammonia nitrogen and total nitrogen values ​​after fermentation, making it difficult to process with centrifuge filters; furthermore, the stored potato starch wastewater ferments rapidly, and after rancidity, the yield and quality of protein decrease significantly.

[0004] If wastewater is to be treated directly, the current practice is to use an "anaerobic system + aerobic system". However, due to the high concentration of pollutants in potato starch wastewater, which are difficult to degrade, the required anaerobic treatment time will be longer, resulting in high input and operating costs. Moreover, potato starch production is highly seasonal, with an annual production cycle of only September to November, while wastewater treatment requires continuous operation and is difficult to adapt to the periodic working hours.

[0005] It can be seen that there has never been a good treatment solution for potato starch waste liquid. Therefore, it is of great significance to find a post-treatment process that combines seasonality, stability and rapid operation, so as to achieve effective resource utilization of potato starch waste liquid, reduce the load caused by organic matter such as starch and protein in sewage discharge. Summary of the Invention

[0006] This invention provides a method for the comprehensive utilization of potato starch processing by-products, which can solve the problems of protein separation difficulties and wastewater treatment difficulties in existing technologies for potato starch waste liquid.

[0007] In a first aspect, the present invention provides a method for the comprehensive utilization of potato starch processing by-products, comprising the following process steps:

[0008] S1. The potato residue filtrate and potato juice were pretreated together by a double-effect screw press to separate fine starch and filtrate. The fine starch was collected and recovered.

[0009] S2. The filtrate and overflow are mixed and then passed through a micro-nano bubble device to separate the upper foam and the middle clear liquid.

[0010] S3. The intermediate layer clear liquid undergoes primary separation and primary concentration processes to obtain primary concentrate and primary filtrate;

[0011] S4. After the upper layer of foam is defoamed, it is mixed with the primary concentrate and then subjected to hot flocculation treatment to produce potato protein.

[0012] S5. The centrifugal waste liquid generated in step S4 is further subjected to secondary separation and secondary concentration treatment to obtain secondary concentrate and secondary filtrate;

[0013] S6. Potato protein is produced by drying the secondary concentrate;

[0014] S7. The primary and secondary filtrates can be reused and / or discharged, and the primary and secondary filtrates can be reused in the primary separation process and / or the secondary separation process.

[0015] Preferably, the potato residue filtrate is obtained by using a filter press device to filter the potato residue produced during the pre-refining of potato starch.

[0016] The potato residue is processed through a filter press and then a drying unit for recycling.

[0017] Preferably, the potato juice is wastewater generated during the pre-refining of potato starch production.

[0018] Preferably, the overflow liquid is the liquid stored in the buffer tank during the double-effect pretreatment process of the screw press in step S1.

[0019] More preferably, the pretreatment of the screw press in step S1 is carried out by a screw press double-effect pretreatment device; the screw press double-effect pretreatment device includes a screw shaft and a densely woven screen.

[0020] More preferably, the aperture of the finely woven screen is 10–30 μm.

[0021] By adopting the above technical solution, the potato residue produced in the pre-refined potato starch production process has a high moisture content. The residue filtrate is separated by a filter press, which also contains rich fine starch and protein, thereby improving the overall recovery rate.

[0022] The potato residue filtrate and potato juice are first pretreated by a screw press double-effect pretreatment. Specifically, in the screw press double-effect pretreatment device, the mixed liquid first enters the spiral shaft area composed of fixed rings and floating rings stacked on top of each other. Driven by the slow rotation of the spiral shaft, the mixed liquid moves forward, and the pitch of the spiral shaft gradually decreases. The rings are subjected to progressive pressure, and the spatial pressure on the mixed liquid gradually increases. During this process, free water is filtered out through the gaps between the rings, and fine starch is gradually enriched.

[0023] The device also includes a finely woven screen. When the liquid containing fine starch, after being enriched by the spiral shaft, flows through, the fine starch particles are directly trapped on the screen surface, thus achieving more efficient separation. Moreover, the movement of the spiral shaft during the entire separation process continuously pushes and discharges the trapped solids forward, finally conveying them to the filtration interface of the finely woven screen, thereby effectively preventing equipment clogging and ensuring long-term stable operation.

[0024] Because the specific gravity of fine starch particles in potato juice and pulp filtrate is similar to that of water, traditional natural sedimentation is inefficient. However, the dual-effect pretreatment device using a screw press with a spiral shaft and a finely woven screen allows for forced separation of fine starch through mechanical action. This results in a significantly higher capture efficiency for fine particles compared to natural sedimentation or other pressure filtration and centrifugation methods. This not only enables continuous and efficient recovery of fine starch byproducts but also produces a low-turbidity filtrate, removing solid impurities that hinder subsequent protein enrichment. This not only improves the quality of the recovered protein but also reduces the adverse effects of solid impurities on the protein recovery process.

[0025] Preferably, step S2 specifically includes:

[0026] S201. The filtrate and overflow are mixed to obtain a mixture;

[0027] S202. The mixture is pressurized by a water pump and flows into a pressure dissolved air tank. An air compressor is used to pressurize air into the pressure vessel tank, and the air and mixture are thoroughly mixed.

[0028] S203. By suddenly depressurizing the pressure through the release device, the gas is released from the mixture in the form of micro-nano bubbles and forms upper foam. The upper foam and the middle clear liquid are separated by a foam scraper and the upper foam is collected.

[0029] By employing the above technical solution, the filtrate obtained after the double-effect pretreatment by the screw press and the overflow liquid in the buffer tank during the process are passed through a micro-nano bubble generator to selectively adsorb and flotate the proteins in the mixed liquid. Specifically:

[0030] In micro-nano bubble generators, the solubility of a gas in a mixed liquid is altered by changing the gas pressure. A sudden pressure release then causes the dissolved gas to precipitate as micro-nano bubbles. Ordinary bubbles, due to their large size, experience buoyancy in water that far exceeds their weight, causing them to rise rapidly to the surface and burst. Micro-nano bubbles, on the other hand, are small and experience relatively less buoyancy in water, allowing them to rise slowly.

[0031] Meanwhile, the surface of micro- and nano-bubbles has a significant double-layer structure, which can adsorb soluble proteins in the mixed liquid through electrostatic interaction. The slow rising speed and huge specific surface area of ​​micro- and nano-bubbles provide sufficient contact and reaction time for protein adsorption.

[0032] Finally, the bubbles that rise to the surface accumulate densely, forming a stable foam layer, which is then collected by a skimmer. This foam layer contains a large amount of soluble protein, which is enriched and concentrated. After defoaming, thermal flocculation yields a protein product with higher purity. Meanwhile, the concentration of organic impurities in the intermediate clear liquid is significantly reduced, which can greatly alleviate the membrane fouling pressure in subsequent separation processes and is also beneficial for the deep purification of potato juice.

[0033] Preferably, the primary separation process and the secondary separation process are performed using an ultrafiltration membrane; the pore size of the ultrafiltration membrane is 10–20 nm.

[0034] More preferably, the ultrafiltration membrane includes a polyvinylidene fluoride ultrafiltration membrane.

[0035] Preferably, the primary concentration treatment and the secondary concentration treatment are separated using a reverse osmosis membrane; the pore size of the reverse osmosis membrane is 0.1 to 0.15 nm.

[0036] More preferably, the reverse osmosis membrane is a polyamide composite reverse osmosis membrane.

[0037] The intermediate clarified liquid obtained after treatment with the micro-nano bubble device and the centrifugal waste liquid generated after protein thermal flocculation, obtained by adopting the above technical solution, need to be further treated to achieve pollution-free discharge of wastewater. Specifically, both first undergo separation treatment, in which an ultrafiltration membrane is used as the separation membrane element. Under pressure, substances larger than the membrane pore size, including residual proteins and polysaccharide macromolecules, are effectively retained on the membrane surface, thus being concentrated on the feed side to form a concentrate. This yields a highly clear filtrate free of suspended solids, which is then further concentrated. Simultaneously, polyvinylidene fluoride (PVDF) ultrafiltration membranes are preferentially selected during the separation process. PVDF ultrafiltration membranes have extremely strong chemical stability, which can reduce the irreversible adsorption of organic matter in the filtrate while ensuring flux, ensuring complete retention of all residual suspended particles or colloids.

[0038] After separation, the filtrate undergoes further treatment via reverse osmosis. Using reverse osmosis membrane elements, water molecules preferentially dissolve and diffuse through the dense reverse osmosis membrane under high pressure. Soluble impurities in the filtrate are efficiently retained due to differences in solubility and diffusion rate, forming a concentrate. The resulting primary and secondary filtrates have significantly reduced organic matter content, with COD values ​​reduced to ≤50mg / L. This allows for closed-loop circulation or safe direct discharge, effectively reducing wastewater pollution and achieving efficient recovery of valuable byproducts.

[0039] Preferably, step S4 specifically includes:

[0040] S401. After the upper layer of foam is defoamed, it is mixed with the first-stage concentrate. Then the temperature of the mixed solution is raised to 85-110℃ and maintained for 10-30 minutes. Then it is naturally cooled to room temperature and the flocculent and centrifugal waste liquid are obtained by centrifugation.

[0041] S402. Potato protein is obtained by drying the flocculent at 140-200℃.

[0042] By adopting the above technical solution, the upper foam and concentrate are enriched with a large amount of soluble protein. First, they are heated, which destroys the molecular interaction forces that maintain the higher structure of the protein, causing the protein to denature and gradually transform into insoluble protein. The denatured protein molecules collide and combine to form small aggregates. Then, through centrifugation, the dense flocs are enriched, achieving efficient solid-liquid separation. Finally, the flocs are treated at high temperature, dried, and sterilized to obtain a potato protein product with stable properties and excellent quality.

[0043] Compared to the conventional process of directly recovering protein from potato juice, the feed of the flocculated protein in this invention is a high-concentration protein solution that has been enriched by micro-nano bubbles and concentrated in multiple stages by membrane elements. The protein concentration is higher, the volume of liquid to be processed is greatly reduced, the protein recovery rate is significantly increased, and the processing difficulty is greatly reduced.

[0044] The beneficial effects of this invention are:

[0045] 1. The method for comprehensive utilization of potato starch processing by-products provided by this invention can reduce wastewater pollution at the source. Through the double-effect pretreatment of the screw press and the separation of micro-nano bubbles, most of the suspended solids such as fine starch in potato juice can be efficiently removed and recovered at the front end of the process, as well as a large amount of soluble protein can be separated, reducing the load of subsequent processing.

[0046] Through multi-stage separation and concentration, the potato starch wastewater is deeply purified. The resulting filtrate can be directly used for production or discharged externally, eliminating the problem of high-concentration organic wastewater discharge, reducing environmental pollution, and avoiding the problems of traditional sewage treatment, such as difficulty in adapting to periodic production and difficulty in disposing of large amounts of biochemical sludge.

[0047] 2. The resource recovery efficiency of the comprehensive utilization method of potato starch processing by-products provided by this invention is high, which can maximize the value of the product. It can not only effectively recover the residual fine starch in potato juice, but also obtain a filtrate containing high concentration of protein through micro-nano bubble separation and concentration. Then, through efficient precipitation and solidification, high yield and high quality protein are recovered.

[0048] 3. The method for comprehensive utilization of potato starch processing by-products provided by this invention solves the problems of difficult wastewater treatment and low efficiency of by-product resource recovery in potato juice generated during potato starch production through precise process design and optimized process steps, achieving zero wastewater discharge and effectively protecting the environment. Attached Figure Description

[0049] Figure 1 This is a schematic diagram of the process flow of Embodiment 1 of the present invention. Detailed Implementation

[0050] The specific embodiments of the present invention will be described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0051] Example

[0052] Example 1, a method for the comprehensive utilization of potato starch processing by-products, is carried out according to the following process steps:

[0053] S1. After the pre-refining of potato starch production, the potato residue generated in the process is filtered to obtain potato residue filtrate, which is then combined with the generated wastewater, i.e. potato juice, through a double-effect screw press pretreatment to separate fine starch and filtrate. Both the fine starch and potato residue are collected and recycled.

[0054] S2. The filtrate is mixed with the overflow liquid stored in the buffer tank of the double-effect pretreatment device of the screw press, and then passed through a micro-nano bubble device to separate the upper foam and the middle clear liquid, specifically including:

[0055] S201. The filtrate and overflow are mixed to obtain a mixture;

[0056] S202. The mixture is pressurized by a water pump and flows into a pressure dissolved air tank. An air compressor is used to pressurize air into the pressure vessel tank, and the air and mixture are thoroughly mixed.

[0057] S203. By suddenly depressurizing the pressure through the release device, the gas is released from the mixture in the form of micro-nano bubbles and forms upper foam. The upper foam and the middle clear liquid are separated by a foam scraper and the upper foam is collected.

[0058] S3. The intermediate layer clear liquid undergoes primary separation and primary concentration treatment. The primary separation process uses a polyvinylidene fluoride ultrafiltration membrane with a pore size of 10 nm, and the primary concentration process uses a polyamide composite reverse osmosis membrane with a pore size of 0.1 nm to obtain primary concentrate and primary filtrate.

[0059] S4. After the upper layer of foam is defoamed, it is mixed with the primary concentrate and subjected to thermal flocculation treatment to produce potato protein, specifically including:

[0060] S401. After the upper layer of foam is defoamed, it is mixed with the primary concentrate. Then the temperature of the mixed solution is raised to 95°C and maintained for 20 minutes. Then it is naturally cooled to room temperature. The flocculent and centrifugal waste liquid are obtained by centrifugation.

[0061] S402. Potato protein is obtained by drying the flocculants at 180℃.

[0062] S5. The centrifuged waste liquid generated in step S4 is further subjected to secondary separation and secondary concentration treatment. In the secondary separation treatment, a polyvinylidene fluoride ultrafiltration membrane with a pore size of 15 nm is used for separation, and in the secondary concentration treatment, a polyamide composite reverse osmosis membrane with a pore size of 0.1 nm is used for separation, to obtain secondary concentrate and secondary filtrate.

[0063] S6. Potato protein is produced by drying the secondary concentrate;

[0064] S7. The primary and secondary filtrates are discharged externally.

[0065] Comparative Example

[0066] Comparative Example 1: A method for the comprehensive utilization of potato starch processing by-products, carried out according to the following technological steps:

[0067] S1. After the pre-refining of potato starch production, the potato residue generated in the process is filtered to obtain potato residue filtrate, which is then combined with the generated wastewater, i.e. potato juice, through a double-effect screw press pretreatment to separate fine starch and filtrate. Both the fine starch and potato residue are collected and recycled.

[0068] S2. The filtrate and the overflow liquid stored in the buffer tank of the double-effect pretreatment device of the screw press are respectively subjected to primary separation treatment and primary concentration treatment. The primary separation treatment uses a polyvinylidene fluoride ultrafiltration membrane with a pore size of 10 nm, and the primary concentration treatment uses a polyamide composite reverse osmosis membrane with a pore size of 0.1 nm to obtain primary concentrate and primary filtrate.

[0069] S3. Potato protein is produced from the primary concentrate through thermal flocculation treatment, specifically including:

[0070] S301. Raise the temperature of the primary concentrate to 75°C, maintain for 20 minutes, then allow it to cool naturally to room temperature, and obtain flocculents and centrifugal waste liquid by centrifugation.

[0071] S302. Potato protein is obtained by drying the flocculant at 200℃.

[0072] S4. The centrifuged waste liquid generated in step S3 is further subjected to secondary separation and secondary concentration treatment. In the secondary separation treatment, a polyvinylidene fluoride ultrafiltration membrane with a pore size of 15 nm is used for separation, and in the secondary concentration treatment, a polyamide composite reverse osmosis membrane with a pore size of 0.1 nm is used for separation, to obtain secondary concentrate and secondary filtrate.

[0073] S5. Potato protein is produced by drying the secondary concentrate;

[0074] S6. The primary and secondary filtrates are discharged externally.

[0075] Comparative Example 2, a method for recovering protein from potato starch processing by-products, was prepared according to the following method:

[0076] After the pre-refining of potato starch production, the potato residue produced in the process is filtered to obtain potato residue filtrate, which is then mixed with the generated wastewater, i.e. potato juice, to obtain a mixed liquid.

[0077] The mixture is pumped into a heating tank, the temperature is raised to 95°C, maintained for 30 minutes, and then centrifuged to obtain flocculent material and centrifugal waste liquid.

[0078] Potato protein was obtained by drying the flocculent at 180°C.

[0079] Performance testing:

[0080] 1. Potato protein recovery rate: The potato protein recovery rate was calculated by testing the protein content in the mixture of potato juice and potato residue filtrate, and then testing the final potato protein content. The experimental results are shown in Table 1.

[0081] 2. Environmental performance: The COD values ​​of potato juice and potato residue filtrate in the examples and comparative examples were tested by the dichromate reflux method. The COD values ​​of the primary and secondary filtrates of Example 1 and Comparative Example 1, as well as the COD value of the centrifuged waste liquid of Comparative Example 3, were also tested. The test results are shown in Table 2.

[0082] Table 1 Results of Potato Protein Recovery Test

[0083]

[0084] Table 2 COD Value Test Results

[0085]

[0086] Based on Tables 1 and 2, and in conjunction with Example 1, Comparative Example 1, and Comparative Example 2, it can be seen that the comprehensive utilization method for potato starch processing by-products provided by this invention significantly improves the recovery rate of potato protein compared to traditional protein extraction and separation processes. Furthermore, the COD value of the filtrate produced using the method provided by this invention is extremely low, allowing for direct discharge without the need for an additional wastewater treatment system, achieving zero wastewater discharge and protecting the environment. In Comparative Example 2, a traditional protein extraction and separation process was used. In the untreated potato juice and residue filtrate, a large amount of protein exists in its natural soluble state. Direct thermal coagulation can only recover a small portion of the heat-sensitive proteins; many other small-molecule soluble proteins cannot be precipitated by simple heating. Moreover, some large-molecule impurities and suspended impurities gelatinize during the process, affecting the yield. Furthermore, the COD value of the generated wastewater remains high, and some unrecovered proteins, as well as soluble impurities such as sugars and organic acids, are not effectively removed or recovered. Direct discharge would cause serious environmental pollution, and the water pollution problem remains unresolved.

[0087] In Comparative Example 1, the micro-nano bubble device treatment step was missing compared to Example 1. This allowed the initial potato juice, including the potato residue filtrate, to directly enter the primary separation and concentration processes. During the separation and concentration process, a large amount of untreated protein in the potato juice would form a dense layer on the surface of the membrane element. Some soluble small molecule proteins were also difficult to retain, resulting in a decrease in the overall protein recovery rate. Furthermore, the unretained small molecule impurities caused the COD value in the filtrate to be too high, making it impossible to meet the standards for direct discharge.

[0088] The above-disclosed embodiments are merely a few specific examples of the present invention. However, the embodiments of the present invention are not limited thereto, and any variations that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A method for the comprehensive utilization of potato starch processing by-products, characterized in that, The process includes the following steps: S1. The potato residue filtrate and potato juice were pretreated together by a double-effect screw press to separate fine starch and filtrate. The fine starch was collected and recovered. S2. The filtrate and overflow are mixed and then passed through a micro-nano bubble device to separate the upper foam and the middle clear liquid. S3. The intermediate layer clear liquid undergoes primary separation and primary concentration processes to obtain primary concentrate and primary filtrate; S4. After the upper layer of foam is defoamed, it is mixed with the primary concentrate and then subjected to hot flocculation treatment to produce potato protein. S5. The centrifugal waste liquid generated in step S4 is further subjected to secondary separation and secondary concentration treatment to obtain secondary concentrate and secondary filtrate; S6. Potato protein is produced by drying the secondary concentrate; S7. The primary filtrate and secondary filtrate can be reused and / or discharged, and the primary filtrate and secondary filtrate can be reused in the primary separation treatment and / or secondary separation treatment process; In step S1, the double-effect pretreatment by the screw press is carried out by a double-effect pretreatment device; the double-effect pretreatment device includes a screw shaft and a densely woven screen. The aperture of the densely woven screen is 10–30 μm; The S4 step specifically includes: S401. After the upper layer of foam is defoamed, it is mixed with the first-stage concentrate. Then the temperature of the mixed solution is raised to 85-110℃ and maintained for 10-30 minutes. Then it is naturally cooled to room temperature and the flocculent and centrifugal waste liquid are obtained by centrifugation. S402. Potato protein is obtained by drying the flocculent at 140-200℃.

2. The method for comprehensive utilization of potato starch processing by-products according to claim 1, characterized in that, The potato residue filtrate is obtained by filtering potato residue produced during the pre-refining process of potato starch through a pressure filter. The potato residue is processed by a filter press and then by a drying device for recycling.

3. The method for comprehensive utilization of potato starch processing by-products according to claim 1, characterized in that, The potato juice is wastewater generated during the pre-refining of potato starch.

4. The method for comprehensive utilization of potato starch processing by-products according to claim 1, characterized in that, The overflow liquid is the liquid stored in the buffer tank during the double-effect pretreatment process of the stacked screw press in step S1.

5. The method for comprehensive utilization of potato starch processing by-products according to claim 1, characterized in that, The S2 step specifically includes: S201. The filtrate and overflow are mixed to obtain a mixture; S202. The mixture is pressurized by a water pump and flows into a pressure dissolved air tank. An air compressor is used to pressurize air into the pressure vessel tank, and the air and mixture are thoroughly mixed. S203. By suddenly depressurizing the pressure through the release device, the gas is released from the mixture in the form of micro-nano bubbles and forms upper foam. The upper foam and the middle clear liquid are separated by a foam scraper and the upper foam is collected.

6. The method for comprehensive utilization of potato starch processing by-products according to claim 1, characterized in that, The primary and secondary separation processes are performed using an ultrafiltration membrane; the pore size of the ultrafiltration membrane is 10–20 nm.

7. The method for comprehensive utilization of potato starch processing by-products according to claim 6, characterized in that, The ultrafiltration membrane includes a polyvinylidene fluoride ultrafiltration membrane.

8. The method for comprehensive utilization of potato starch processing by-products according to claim 1, characterized in that, The primary and secondary concentration processes are separated using a reverse osmosis membrane; the pore size of the reverse osmosis membrane is 0.1–0.15 nm.

9. The method for comprehensive utilization of potato starch processing by-products according to claim 8, characterized in that, The reverse osmosis membrane is a polyamide composite reverse osmosis membrane.

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