A Sterilization and Drying System for Spirulina Slurry Based on Low-Temperature Plasma Technology

Abstract

This invention provides a spirulina slurry sterilization and drying system based on low-temperature plasma technology, belonging to the field of microalgae product processing technology. It includes an air compressor, a plasma generator, a plasma jet head, a microalgae sterilization tank, a microalgae discharge device, a microalgae feeding device, a first adjustable pump, a second adjustable pump, a detection and sampling device, and a tail gas collection and treatment device. This system is simple to operate, highly efficient in sterilization, and addresses consumer concerns about irradiation sterilization and the high energy consumption of other sterilization methods. Utilizing a high-flow-rate plasma jet to simultaneously sterilize and dry at low temperatures significantly shortens the processing time for microalgae production, reduces the loss of heat-sensitive nutrients in microalgae, and improves product quality.

Description

Technical Field

[0001] This invention relates to the field of microalgae product processing technology, specifically to a spirulina slurry sterilization and drying system based on low-temperature plasma technology. Background Technology

[0002] Spirulina and its extracts possess a range of physiological functions in maintaining human health, including antioxidant, anti-inflammatory, anti-tumor, immune-boosting, and fatty liver prevention. This gives spirulina significant market potential in the food, biological, and medical fields. Currently, my country ranks first in the world in spirulina production. However, due to the rich nutrients in spirulina and the reuse of its culture medium, the culture medium has become a breeding ground for microorganisms such as bacteria, yeast, and mold. Furthermore, the basic production process cannot guarantee against microbial contamination, resulting in a high total bacterial count in spirulina powder, reaching as high as (4-5) × 10⁻⁶. 4 The cfu / g level far exceeds the national standard for edible spirulina powder (≤1×10⁻⁶). 4 The low concentration of cfu / g of spirulina has severely hampered the development and application of spirulina in food and biology, as well as the export of spirulina powder, thus restricting economic development in this field.

[0003] Phycocyanin in spirulina is a heat-sensitive substance, and its content decreases significantly at temperatures above 60℃, with temperature being the main factor in its degradation. Table 1 shows the main sterilization methods for heat-sensitive substances both domestically and internationally, along with their characteristics. These sterilization methods are not only inefficient and prone to safety hazards, but also cause significant loss of heat-sensitive nutrients in microalgae.

[0004] Table 1. Main sterilization methods for heat-sensitive substances at home and abroad

[0005] Summary of the Invention

[0006] In view of the shortcomings and difficulties in the existing technology, the purpose of this invention is to provide a high-efficiency, fast, safe and low-energy-consumption spirulina slurry sterilization and drying system based on low-temperature plasma technology.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A spirulina slurry sterilization and drying system based on low-temperature plasma technology includes an air compressor, a plasma generator, a plasma jet head, a microalgae sterilization tank, a microalgae discharge device, a microalgae feeding device, a first adjustable pump, a second adjustable pump, a detection and sampling device, and a tail gas collection and treatment device.

[0009] The air compressor, plasma generator, and plasma nozzle are connected sequentially via pipes. The plasma nozzle is embedded in the top side of the microalgae sterilization tank and is inclined. A microalgae discharge device is connected to one side of the microalgae sterilization tank via a pipe. A second adjustable pump is installed on the pipe between the microalgae sterilization tank and the microalgae discharge device. A first three-way valve is installed on the pipe between the second adjustable pump and the microalgae discharge device. A microalgae feeding device is installed on one side of the microalgae discharge device. The microalgae feeding device is connected to the top center of the microalgae sterilization tank via a pipe. A first adjustable pump is installed on the pipeline between the feeding device and the microalgae sterilization tank. A second three-way valve is installed on the pipeline between the first adjustable pump and the microalgae feeding device. The second three-way valve is connected to the first three-way valve through a pipeline. A third three-way valve is installed on the pipeline between the first adjustable pump and the microalgae sterilization tank. The other end of the third three-way valve is connected to a detection and sampling device through a pipeline. One side of the exhaust gas collection and treatment device is connected to the top of the microalgae sterilization tank, the microalgae discharge device, and the detection and sampling device through a pipeline. The other side of the exhaust gas collection and treatment device is connected to an air compressor through a pipeline.

[0010] Furthermore, an air inlet is provided on one side of the air compressor.

[0011] Furthermore, a stirring paddle is provided at the center of the bottom of the microalgae sterilization tank.

[0012] Furthermore, a temperature detector is provided on the side of the microalgae sterilization tank, and a temperature probe is provided on the inside of the microalgae sterilization tank. The temperature detector and the temperature probe are electrically connected.

[0013] Furthermore, the top of the microalgae sterilization tank, the microalgae discharge device, and the detection and sampling device are respectively equipped with a first air filter, a second air filter, and a third air filter at the end of the pipe connecting the exhaust gas collection and treatment device.

[0014] Furthermore, the plasma generator has a power of 600-1000W.

[0015] Furthermore, the tilt angle of the plasma jet head is adjustable.

[0016] Compared with the prior art, the beneficial effects of the present invention are:

[0017] This invention utilizes active particles in a low-temperature plasma jet to kill microorganisms. The plasma flow reduces spray drying time, minimizes heat loss, and improves drying efficiency. Circulation extends the algae treatment time, increasing contact time with hot air and further enhancing drying efficiency. Circulation and sample stirring ensure uniform sample processing while avoiding localized scorching that occurs in microwave or irradiation drying processes, effectively guaranteeing the quality of algae products. It possesses advantages such as continuous operation, speed, low energy consumption, rational process, and wide applicability, making it an ideal drying and sterilization device for heat-sensitive and easily oxidized materials.

[0018] This invention is stable in operation, simple in structure, convenient to use, and has controllable temperature. It can achieve dynamic and high-speed drying while simultaneously achieving sterilization, thus meeting the needs of actual production. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the system of the present invention.

[0020] Diagram Description: 1. Air Inlet; 2. Air Compressor; 3. Plasma Generator; 4. Exhaust Gas Collection and Treatment Device; 5. Plasma Jet Head; 6. Temperature Detector; 7. Temperature Probe; 8. Microalgae Sterilization Tank; 9. Stirring Paddle; 10. First Air Filter; 11. Discharge Pipe; 12. Feed Pipe; 13. First Three-Way Valve; 14. Second Air Filter; 15. Third Three-Way Valve; 16. Microalgae Discharge Device; 17. Third Air Filter; 18. Detection and Sampling Device; 19. Second Three-Way Valve; 20. Microalgae Feeding Device; 21. First Adjustable Pump; 22. Second Adjustable Pump. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. The specific embodiments described herein are only for explaining the technical solutions of this invention and are not intended to limit the invention.

[0022] like Figure 1 As shown, a spirulina slurry sterilization and drying system based on low-temperature plasma technology includes an air compressor 2, a plasma generator 3, a plasma jet head 5, a microalgae sterilization tank 8, a microalgae discharge device 16, a microalgae feeding device 20, a first adjustable pump 21, a second adjustable pump 22, a detection and sampling device 18, and a tail gas collection and treatment device 4.

[0023] An air inlet 1 is provided on one side of the air compressor 2. The air compressor 2, plasma generator 3, and plasma jet head 5 are connected in sequence through a pipe. The plasma jet head 5 is embedded in the top side of the microalgae sterilization tank 8 and is inclined. A stirring paddle 9 is provided at the center of the bottom of the microalgae sterilization tank 8. A temperature detector 6 is provided on the side of the microalgae sterilization tank 8, and a temperature probe 7 is provided on the inner side of the microalgae sterilization tank 8. The temperature detector 6 and the temperature probe 7 are electrically connected. A microalgae discharge device 16 is connected to one side of the microalgae sterilization tank 8 through a pipe. A second adjustable pump 22 is provided on the pipe between the microalgae sterilization tank 8 and the microalgae discharge device 16. A first three-way valve 13 is provided on the pipe between the second adjustable pump 22 and the microalgae discharge device 16. The microalgae discharge device 16... A microalgae feeding device 20 is provided on one side. The microalgae feeding device 20 is connected to the top center of the microalgae sterilization tank 8 through a pipe. A first adjustable pump 21 is provided on the pipe between the microalgae feeding device 20 and the microalgae sterilization tank 8. A second three-way valve 19 is provided on the pipe between the first adjustable pump 21 and the microalgae feeding device 20. The second three-way valve 19 is connected to the first three-way valve 13 through a pipe. A third three-way valve 15 is provided on the pipe between the first adjustable pump 21 and the microalgae sterilization tank 8. The other end of the third three-way valve 15 is connected to a detection and sampling device 18 through a pipe. One side of the exhaust gas collection and treatment device 4 is connected to the top of the microalgae sterilization tank 8, the microalgae discharge device 16, and the detection and sampling device 18 through pipes. The other side of the exhaust gas collection and treatment device 4 is connected to the air compressor 2 through a pipe. The top of the microalgae sterilization tank 8, the microalgae discharge device 16, the detection and sampling device 18, and the end of the pipe connected to the exhaust gas collection and treatment device 4 are respectively provided with a first air filter 10, a second air filter 14, and a third air filter 17.

[0024] The entire system operates as follows during a single operation: After the air compressor 2, plasma generator 3, and plasma jet head 5 are running stably, microalgae slurry to be sterilized is added from the microalgae feeding device 20. The second three-way valve 19 is opened to connect the microalgae feeding device 20 with the first adjustable pump 21, and the first three-way valve 13 is opened to connect the discharge pipe 11 with the microalgae discharge device 16. Under the action of the first adjustable pump 21, the microalgae slurry is transported to the microalgae sterilization tank 8 through the feeding pipe 12. At the end of the pipe, it comes into contact with the plasma jet ejected by the plasma jet head 5 and reacts. Under the action of gravity and the plasma jet, it gathers at the bottom of the microalgae sterilization tank 8. After being fully homogenized by the stirring paddle 9, it is collected through the discharge pipe 11 and enters the microalgae discharge device 16 under the action of the second adjustable pump 22. The single operation is completed when the sample in the microalgae feeding device 20 is processed.

[0025] The entire system operates as follows: After the air compressor 2, plasma generator 3, and plasma jet head 5 are running stably, microalgae slurry to be sterilized is added from the microalgae feeding device 20. The second three-way valve 19 is opened to connect the microalgae feeding device 20 with the first adjustable pump 21, and the second adjustable pump 22 is closed, so that the microalgae slurry is transported to the microalgae sterilization tank 8 through the feeding pipe 12 under the action of the first adjustable pump 21. At the end of the pipeline, the microalgae slurry comes into contact with the plasma jet ejected by the plasma jet head 5. Under the action of gravity and the plasma jet, after all the microalgae samples have collected at the bottom of the microalgae sterilization tank 8, they are thoroughly homogenized by the stirring paddle 9. Then, the first three-way valve 13 is changed to connect the discharge pipeline 11 and the first adjustable pump 21, and the second three-way valve 19 is changed to connect the discharge pipeline 11 and the first adjustable pump 21. The second adjustable pump 22 is opened, and under the action of the second adjustable pump 22 and the first adjustable pump 21, the slurry is transported to the microalgae sterilization tank 8 through the feed pipeline 12, realizing the circulation treatment of the microalgae slurry. After the circulation work is completed, the first adjustable pump 21 is closed, and the microalgae slurry is collected through the discharge pipeline 11 and enters the microalgae discharge device 16. The operation is completed when the treatment is finished.

[0026] Throughout the process, the temperature of the homogenized microalgae slurry in the microalgae sterilization tank 8 is monitored by temperature detector 6 and temperature probe 7, thereby adjusting the required working conditions for the sample to achieve low-temperature control during sterilization. If sampling is required for observation and monitoring during operation, the third three-way valve 15 can be opened to collect a portion of the microalgae slurry sample to the detection and sampling device 18. A first air filter 10, a second air filter 14, and a third air filter 17 are respectively installed at the top of the microalgae sterilization tank 8, the microalgae discharge device 16, and the detection and sampling device 18. The gas passes through the air filters and enters the exhaust gas collection and treatment device 4 for unified treatment, then is circulated back to the air compressor 2 for recycling. When the circulating air pressure is insufficient, the air compressor 2 can maintain system operation through the air inlet 1. The entire gas path maintains the pressure balance of each device while fully utilizing the active substances generated by the plasma device.

[0027] Preferably, the concentration of microalgae slurry is 5% to 25%.

[0028] Preferably, the plasma generator 3 has a power of 600-1000W.

[0029] Preferably, the plasma jet temperature is controlled at 25–50°C.

[0030] Preferably, the working angle between the plasma jet head 5 and the sample discharge point is adjustable.

[0031] The system has controllable cycle count, speed, flow rate, and temperature. Parameters can be adjusted according to the concentration of each harvested microalgae slurry, the volume of the slurry to be sterilized, and the characteristics of microalgae samples with different initial bacterial counts, in order to meet various sterilization requirements and technical standards in production and achieve high-efficiency sterilization with minimal energy consumption.

[0032] Example 1:

[0033] According to the adjustable power range of the plasma generator 3, 200 mL of 15% Spirulina slurry was treated with power of 600, 700, 800, 900 and 1000 W, and the bacterial content of the slurry was measured at 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10 min. The sterilization effect under different time and power parameters was investigated by comparing the initial bacterial content of Spirulina slurry with the results.

[0034] Studies have found that within the treatment power range of 600-1000W, the sterilization rate gradually increases with time, and the sterilization effect of 1000W power is significantly better than that of 600-900W. Except for the 600W group, the algal slurry in the 700-1000W power group can achieve a sterilization rate of 90% or higher after 10 minutes of low-temperature plasma treatment. The sterilization rate of Spirulina slurry reaches 99.9% within 1 minute of treatment at 1000W power. When the algal slurry concentration is 15% and the sample size is 200g, the total bacterial count is reduced by 0.556, 1.951, 1.636, 7.760, and 8.091lg CFU / g, respectively, after 10 minutes of treatment at 600, 700, 800, 900, and 1000W power.

[0035] The higher the processing power in plasma treatment, the more significant the weight reduction of spirulina slurry. After treatment with 1000W power for 10 minutes, the weight decreased by nearly 67g, and the total sample weight decreased by 33.5%. This demonstrates that low-temperature plasma technology can not only effectively sterilize but also help to heat up and dry spirulina slurry, providing pretreatment for subsequent spray drying into spirulina powder, improving the drying rate, and shortening the drying time.

[0036] Example 2:

[0037] The harvested spirulina slurry was centrifuged, and the precipitated spirulina sludge was retained. 100 mL of spirulina slurry with a mass fraction of 5%, 10%, 15%, 20%, and 25% was prepared using the recovered liquid. The slurry was treated with 800W plasma power for 5 min to observe the effect of slurry concentration on sterilization efficiency during low-temperature plasma sterilization.

[0038] The results showed that the sterilization effect of spirulina slurry was better within the range of 5%-20% mass fraction. However, when the mass fraction of spirulina slurry increased to 25%, the sterilization effect was poor under the same treatment conditions. Under the same treatment power and treatment time, the degree of weight reduction was inversely proportional to the mass fraction of spirulina slurry, that is, directly proportional to the water content of spirulina slurry. The higher the water content of spirulina slurry, the more water evaporates. Therefore, when using low-temperature plasma to sterilize turbid samples, appropriate process parameters should be selected to ensure sterilization effect while retaining as much nutrition as possible.

[0039] Example 3:

[0040] Take 20, 50, 100, 200 and 500 mL of 15% Spirulina slurry, place them in round-bottom beakers with the same bottom area and seal them with a membrane cap. Treat with 800W plasma power for 5 min and observe the effect of sample volume on sterilization efficiency in low-temperature plasma sterilization.

[0041] Algal slurry volumes ranging from 50-200 mL showed sterilization effects after treatment at 800 W for 5 minutes, with sterilization rates between 10-25%. The best sterilization effect, reaching 63%, was observed with a sample volume of 500 mL. Under the same low-temperature plasma treatment conditions, the total water content of the sample was positively correlated with the weight reduction before and after treatment, indicating that higher total water content meant greater water evaporation. The degree of temperature increase in the algal slurry was positively correlated with the treatment volume and water content.

[0042] The above description merely illustrates preferred embodiments of the present invention, and while the description is relatively specific and detailed, it should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications, improvements, and substitutions without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this patent should be determined by the appended claims.

Claims

1. A system for sterilizing and drying spirulina paste based on low temperature plasma technology, characterized by: The air compressor (2), the plasma generating device (3), the plasma jet head (5), the microalgae sterilization tank (8), the microalgae discharging device (16), the microalgae feeding device (20), the first adjustable pump (21), the second adjustable pump (22), the detection sampling device (18) and the tail gas collection and treatment device (4) are sequentially communicated through pipelines. The air compressor (2), the plasma generating device (3), the plasma jet head (5) are sequentially communicated through pipelines, the plasma jet head (5) is embedded on one side of the top of the microalgae sterilization tank (8) and is arranged in an inclined manner, one side of the microalgae sterilization tank (8) is communicated with the microalgae discharging device (16) through a pipeline, a second adjustable pump (22) is arranged on the pipeline between the microalgae sterilization tank (8) and the microalgae discharging device (16), a first three-way valve (13) is arranged on the pipeline between the second adjustable pump (22) and the microalgae discharging device (16), one side of the microalgae discharging device (16) is provided with the microalgae feeding device (20), the microalgae feeding device (20) is communicated to the top center of the microalgae sterilization tank (8) through a pipeline, a first adjustable pump (21) is arranged on the pipeline between the microalgae feeding device (20) and the microalgae sterilization tank (8), a second three-way valve (19) is arranged on the pipeline between the first adjustable pump (21) and the microalgae feeding device (20), the second three-way valve (19) and the first three-way valve (13) are communicated through pipelines, a third three-way valve (15) is arranged on the pipeline between the first adjustable pump (21) and the microalgae sterilization tank (8), the other end of the third three-way valve (15) is communicated with the detection sampling device (18) through a pipeline, one side of the tail gas collection and treatment device (4) is communicated to the top of the microalgae sterilization tank (8), the microalgae discharging device (16) and the detection sampling device (18) through pipelines, and the other side of the tail gas collection and treatment device (4) is communicated to the air compressor (2) through a pipeline.

2. A system for sterilization and drying of spirulina paste based on low temperature plasma technology as claimed in claim 1, wherein: One side of the air compressor (2) is provided with an air inlet (1).

3. The system for sterilization and drying of spirulina paste based on low-temperature plasma technology according to claim 1, characterized in that: A stirring paddle (9) is arranged at the bottom center of the microalgae sterilization tank (8).

4. The system for sterilization and drying of spirulina paste based on low-temperature plasma technology according to claim 1, characterized in that: A temperature detector (6) is arranged on the side of the microalgae sterilization tank (8), and a temperature probe (7) is arranged on the inner side of the microalgae sterilization tank (8), and the temperature detector (6) and the temperature probe (7) are electrically connected.

5. The system for sterilization and drying of spirulina paste based on low temperature plasma technology as claimed in claim 1 wherein: First, second and third air filter screens (10), (14) and (17) are respectively arranged at the pipeline ends of the top of the microalgae sterilization tank (8), the microalgae discharging device (16) and the detection sampling device (18) and the tail gas collection and treatment device (4).

6. A system for sterilization and drying of spirulina paste based on low temperature plasma technology as claimed in claim 1, wherein: The power of the plasma generating device (3) is 600-1000W.

7. A system for sterilizing and drying spirulina paste based on low-temperature plasma technology according to claim 1, characterized in that: The inclination angle of the plasma jet head (5) is adjustable.

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