Model essay on food processing 1: application of foam separation technology in food industry
Foam separation, also known as foam adsorption separation technology, is a separation method that uses bubbles as the medium and uses the difference of surface activity between components to achieve the purpose of separation or concentration [1]. At the beginning of the 20th century, foam separation technology was first applied to mineral flotation, and then to the recovery of surfactants from industrial wastewater. It was not until 1970s that people began to apply foam separation technology to the separation and extraction of protein and enzymes [2-3]. At present, in the food industry, foam separation technology has been applied to the separation and extraction of protein, enzymes, sugars, saponins and other effective components. Because most food raw materials are foam, foam separation technology will be more and more widely used in food industry.
Principle and characteristics of 1 foam separation technology
1. 1 Principle of foam separation technology
Foam separation technology is based on the principle of surface adsorption and the difference of surface activity between solutes or particles in liquid phase. The substances with strong surface activity are firstly adsorbed on the interface between the dispersed phase and the continuous phase, and a foam layer is formed by bubbling, so that the foam layer is separated from the liquid phase main body, and the surface active substances are enriched in the foam layer, thereby achieving the purpose of concentrating solute or purifying the liquid phase main body.
1.2 characteristics of foam separation technology
Advantages of 1.2. 1
(1) Compared with the traditional method of separating dilute concentration products, foam separation technology has simple equipment and convenient operation, and is more suitable for the separation of dilute concentration products. (2) The foam separation technology has a high resolution, and a higher enrichment ratio can be obtained for substances with large differences in surface activity between components. (3) Foam separation technology does not need a large number of organic solvent eluents and extractive solutions, and has low cost and little environmental pollution, which is beneficial to industrial production.
1.2.2 Disadvantages
Most of the surface active substances are high molecular compounds, which have large digestion and are difficult to recover. In addition, the concentration of surfactant in the solution is not easy to control, and the back mixing phenomenon in the foam tower will affect the separation effect [4].
Application of foam separation technology in food industry
2. Separation of1protein
In the process of separating protein, the adsorption effect of protein with little difference in surface activity is influenced by the adsorption structure of gas-liquid interface, so the intensity of surface activity of protein is the main index to investigate the separation effect of foam. Tan et al. [5] studied the adsorption of bovine serum albumin and casein at the gas-liquid interface, and found that casein had a significant effect on the adsorption of bovine serum albumin at the gas-liquid interface. After that, Hossain et al. [6] separated and enriched β -lactoglobulin and bovine serum albumin by foam separation technology, and obtained 96% β -lactoglobulin and bovine serum albumin. Brown et al. [7] used continuous foam separation technology to separate bovine serum albumin and casein from mixed solution, and the results showed that the recovery rate of casein was very high. However, most bovine serum albumin remains in solution. Saleh et al. [8] studied the separation of lactoferrin from the mixed solution of lactoferrin, bovine serum albumin and α -lactalbumin by foam separation, adding lactoferrin with different concentrations into the mixed solution of bovine serum albumin and α -lactalbumin, constantly changing the gas flow rate, and optimizing the optimal process conditions. The results showed that under the optimum conditions, 87% of lactoferrin remained in the solution, 98% of bovine serum albumin and 9 1% of α -lactalbumin existed in the foam entrainment solution. The foam separation method can effectively separate lactoferrin from three protein mixtures. Chen et al [9] used foam separation technology to extract immunoglobulin from milk. The effects of initial pH value, initial immunoglobulin concentration, nitrogen flow rate, column height and foaming time on the reaction were investigated. The results show that the foam separation method can effectively separate immunoglobulin from milk. Liu et al. [10] concentrated and enriched soybean protein from industrial soybean wastewater. The optimum technological conditions are: temperature 50℃, pH 5.0, air flow 100mL? Min- 1, liquid filling height 400mm, soybean protein enrichment ratio 3.68. Li et al. [1 1] In order to improve foam drainage, a new type of foam separation tower filled with barbed wire was developed. Bovine serum protein was separated by foam separation in a fully packed tower with barbed wire. Taking BSA aqueous solution as reference, the effects of fillers on bubble size, liquid holdup, enrichment ratio and effective collection rate under different conditions were studied. The results show that the filler can accelerate the bubble burst, reduce the liquid holdup, improve the foam drainage and increase the enrichment rate of bovine serum albumin. The research shows that when the liquid storage volume is 490 ml and the air velocity is 300 ml? Min- 1, and the initial concentration of bovine serum protein was 0. 10g? Under the conditions of L- 1, packed bed height of 300mm and initial pH value of 6.2, the optimum enrichment multiple of bovine serum protein is 2 1.78, which is 2.44 times that of the control tower. Liu Haibin et al [12] used mulberry leaves as raw materials to separate mulberry leaf proteins by foam separation, and analyzed the main factors affecting the separation effect. Results The recovery rate of mulberry leaf protein was 92.50%, and the enrichment multiple was 7.63. Therefore, high content of mulberry leaf protein can be obtained by foam separation. Compared with traditional leaf protein separation methods such as acid (alkali) thermal method and organic solvent method [13- 14], foam separation method has better separation effect. Protein denaturation caused by heating and environmental pollution caused by organic solvents are avoided. Li et al. [15] optimized the technological conditions of flax protein separation from degummed flax cake foam by response surface methodology with flax protein concentration, NaCl concentration, pH value of raw material solution and liquid content as main factors. Under the optimum conditions, the yield of flax protein was 95.8% and the loss of polysaccharide was only 6.7%.
2.2 Separation of enzymes
Protein is a biosurfactant, which contains polar and nonpolar groups and can be selectively adsorbed on the gas-liquid interface in solution. Therefore, substances such as enzyme and protein can be separated from low concentration solution by foam. Kelin et al. [16] studied the foam separation of extracellular lipase in fermentation broth, and investigated the effects of main factors such as aeration time, pH value and gas flow rate on the recovery rate. The results showed that the recovery rate of enzyme protein was 95% when aeration time was 50min, pH value was 7.0 and gas velocity was 60mL/min. Mohan et al [17] separated yeast and malt from beer foam. The results showed that yeast and malt took different time to separate, and it was easier to enrich at low concentration. Holmstr[ 18] foam was separated from low concentration solution. It was found that the amylase activity in the foam entrainment solution was 4 times higher than that in the original solution by bubbling at the isoelectric point. Lambert et al. [19] studied the relationship between pH value and surface tension of β -glucosidase by foam separation technology. The results showed that the optimum foaming pH values of cellulose disaccharidase and cellulase were 10.5 and 6 ~ 9, respectively. Brown et al. [7] studied the separation and purification of bovine serum protein and lysozyme and the mixed system of casein and lysozyme by foam separation technology. The results showed that the recovery rate of lysozyme was very low whether it was mixed with bovine serum protein or casein, but the recovery rate of bovine serum protein and lysozyme was improved because lysozyme could improve the stability of foam. Samita et al. [20] studied two binary systems of bovine serum albumin and casein, and found that in the protein binary system of bovine serum albumin and casein, the adsorption of casein at the gas-liquid interface accounted for most of the gas-liquid interface, thus preventing the adsorption of bovine serum albumin at the gas-liquid interface. In the binary system of bovine serum protein and lysozyme, the research shows that lysozyme improves the recovery rate of bovine serum protein and the stability of foam. In view of this phenomenon, Noble et al. [2 1] also separated the binary system of bovine serum protein and lysozyme by foam separation. It was found that there was a small amount of lysozyme in the entrainment liquid of foam, which improved the stability of foam, and bovine serum albumin solution could not produce stable foam at low concentration. The existence of lysozyme enables it to produce stable foam. These studies show that protein with surface activity can be separated by foam separation technology at low concentration, which opens up a new field for the application of foam separation technology in protein separation. Domestic foam separation technology has been applied to the separation of enzymes, and Fan Ming et al. [22] designed a foam separation device. The simulated lipase solution was separated from the aqueous lipase solution for biodiesel production by foam separation technology, and the aqueous lipase solution was recovered and enriched. The effects of main factors such as ventilation, feed enzyme concentration and pH value of lipase aqueous solution on separation efficiency were investigated. When the ventilation rate is 10L/(LH), the feed enzyme concentration is 0.2g/L and the pH value is 7.0, the recovery rate of protein and enzyme activity is close to 100%, and the enrichment ratio is 3.67. The results show that the initial lipase concentration has a significant effect on the enrichment ratio and protein recovery rate of foam separation, while the pH value has no significant effect on the enrichment ratio, protein and enzyme recovery rate, while the gas velocity is an important factor affecting the protein recovery rate. There is no loss of enzyme activity during the recovery of aqueous lipase. It can be seen that foam separation is an effective method to recover liquid lipase [22]
2.3 Separation of sugar
Sugar generally exists in plants and microorganisms. According to the difference of surface activity between sugar and protein or other substances, sugar can be separated and extracted by foam separation technology [23]. Fu et al. [24] separated and extracted soluble sugar and protein from sweet potato blocks produced in Keelung by centrifugation, and the recovery rates were 4.8% and 33.8% respectively. By foam separation, the recovery rates of soluble sugar and protein were 98.8% and 74.65438 0% respectively. Sarachat et al. [25] used foam separation method to enrich rhamnolipid produced by Pseudomonas, and the enrichment ratio was 4. _ _ Zhou [26] The boletus polysaccharide was separated from the water extract of Boletus edulis by intermittent foam separation. The effects of pH value, concentration of raw material solution, wind speed, surfactant dosage and flotation time on the separation effect were investigated, and the separation effect was evaluated with the recovery rate as the index, and the separation process conditions of boletus polysaccharide were optimized. Under the optimum conditions, the recovery rate of boletus polysaccharide was 83.65438 0%. The extraction of polysaccharide from edible fungi in China generally adopts the method of water extraction and alcohol precipitation, but this method needs a lot of ethanol and has a long operation period. The energy consumption is high [27-28], and the foam separation method has the advantages of fast separation speed, simple equipment, continuous operation, no need of high temperature and high pressure, and is suitable for separating low-concentration components, so the intermittent foam separation method is an effective method for extracting edible mushroom polysaccharides.
2.4 Separation of effective components of saponins
Saponins contain hydrophilic sugars and hydrophobic sapogenins, which have good foaming properties. They are excellent natural nonionic surfactants, so they can be separated from natural plants by foam separation [29]. Foam separation method has been widely used to separate effective components such as soybean isoflavone aglycone, ginsenoside, soapberry saponin, panax japonicus saponin and Xanthoceras sorbifolia Bunge saponin.
2.4. 1 separation of soybean isoflavone aglycone Liu et al. [10]
Soybean isoflavone aglycone was separated from soybean whey wastewater by foam separation and acidolysis. It is pointed out that isoflavone aglycone extracted from industrial soybean whey wastewater mainly exists in the form of β-aglycone, and Fourier transform infrared spectrum analysis shows that soybean isoflavone and soybean protein exist in the form of complex. The results show that the foam separation technology can effectively enrich soybean isoflavone and β -aglycone in soybean whey wastewater.
2.4.2 Isolation of Saponins Wei et al. from Sapindus mukoraiensis [30]
The soapberry saponin was separated and purified by intermittent foam separation and continuous foam separation respectively. The effects of raw material concentration, gas flow rate, temperature and pH value on the recovery rate of soapberry saponin were investigated by orthogonal test, and the optimum technological conditions of foam separation were determined. Brigitte Lin et al. [3 1] used foam separation technology to separate and purify soapberry saponin, and determined the content of soapberry saponin by ultraviolet spectrophotometer. The effect of separation and purification is judged by enrichment ratio, purity and recovery rate. When the feed concentration is 2.0g/L, the feed rate is 150mL, the gas velocity is 32L/h, the temperature is 30℃ and the pH value is 4.3, the enrichment ratio is 2. 153, and the purity and recovery rate are 74.68% and 79. 19, respectively. The enrichment ratio decreases with the increase of feed concentration, gas velocity and feed rate, and pH value has little effect on the enrichment ratio. The purity decreases with the increase of feed concentration and gas velocity, and the feed velocity and pH value have little effect on the purity.
2.4.3 Separation of Total Saponins from Panax japonicus
Saponins, the main component of Panax japonicus, are excellent natural surfactants, while Panax japonicus polysaccharides, inorganic salts and amino acids in Panax japonicus are non-surfactants, which can be separated and purified by foam separation technology according to different surface activities [32-34]. Zhang Haibin et al. [35] investigated the effects of main factors such as bubble size, pH value of raw material solution, temperature, amount and concentration of electrolyte on the foam separation of panax japonicus saponins. The effect of separation and purification was analyzed with the indexes of enrichment ratio, purity ratio and recovery rate, and the optimum technological conditions were obtained as follows: bubble diameter 0.4~0.5mm, pH value 5.5, temperature 65℃, electrolyte NaCl concentration 0.0 15mol? L- 1。 Under the optimum conditions, the enrichment ratio of total saponins was 2. 1, the purity ratio was 2.6, and the recovery rate was 98.33%, which obtained a good separation. Zhang Changcheng et al [36] studied the methods and conditions of separating and purifying saponins from Panax japonicus by foam separation technology, and pointed out that foam separation technology has high product recovery rate, simple process and low energy consumption.
2.4.4 Separation of Saponins from Xanthoceras sorbifolia Bunge Peel
Xanthoceras sorbifolia Bunge seed oil is a high-quality edible oil with an oil content of 35% ~ 40% [37], which can be used as a raw material for biodiesel. Xanthoceras sorbifolia peel contains 1.5% ~ 2.4% saponins. Saponins in Xanthoceras sorbifolia peel have anti-tumor, anti-oxidation and anti-fatigue effects [38]. The added value brought by the development and utilization of saponins from Xanthoceras sorbifolia Bunge can effectively reduce the production cost of biodiesel. In the process of producing biodiesel, a large number of peels need to be treated, so it is necessary to find a simple and feasible method for separating saponins with low cost, high yield and little environmental pollution. Wu Weijie et al. [39] used a self-made foaming device. The feasibility and optimum reaction conditions of separating total saponins from Xanthoceras sorbifolia peel by foam separation technology were studied. The optimum technological conditions for foam separation of saponins from Xanthoceras sorbifolia Bunge are as follows: the gas velocity of feed liquid is 2.5L? Min- 1, initial concentration 2mg? ML- 1, temperature 20℃, pH 5. Compared with the gas flow rate of separating saponins such as ginseng and notoginseng by foam, the gas flow rate of Xanthoceras sorbifolia peel is lower, which can minimize energy consumption and save costs. At the same time, the foam separation of saponins from Xanthoceras sorbifolia peel can be carried out at room temperature, which reduces the energy consumption required for heating. In addition, because the pH value of the aqueous solution of Xanthoceras sorbifolia Bunge saponin is about 5. There is no need to adjust pH value during foam separation. Under the optimum conditions, the enrichment ratio is 3.05, the recovery rate is 60.02% and the purity is 63.35%. The research shows that the separation of saponin from Xanthoceras sorbifolia Bunge by foam can achieve high enrichment ratio, recovery rate and purity, which is of great significance for vigorously developing and utilizing bioenergy, comprehensively utilizing Xanthoceras sorbifolia Bunge and reducing the cost of biodiesel.
3 outlook
Foam separation technology is a promising new separation technology, which will be more and more widely used in food industry, and will be more widely used in the separation and extraction of natural products and rare substances in the future. At the same time, foam separation technology also has some limitations. In order to promote the application and development of foam separation technology in food industry, the following aspects should be studied in depth: (1) establish a theoretical model of foam formation in the actual separation process of complex substances, establish a standard database for the separation and extraction of standard surfactants, and establish a fingerprint for the separation of standard surfactants and non-surfactant substances; (2) How to reduce the amount of surfactant when using foam to separate non-surfactant substances; (3) How to solve the problem of low recovery rate of foam separation of high concentration products; (4) At present, there are limitations in foam separation equipment, so we should research and develop new foam separation equipment suitable for food industry separation to improve the effect of foam separation [40].
Study on energy saving of wastewater treatment in food industry
The food industry includes sugar making, brewing, meat and dairy products processing, etc. The wastewater from food industry mainly comes from the treatment, washing, dehydration, filtration, deacidification, deodorization and cooking of raw materials. These wastewaters contain a lot of organic matter, protein, organic acids and carbohydrates, and have strong oxygen consumption. If discharged directly into the water without treatment, it will consume a lot of dissolved oxygen in the water, resulting in hypoxia in the water and the death of aquatic organisms. The wastewater from food industry has a high oil content, which is often accompanied by a large number of suspended solids discharged with the wastewater. Wastewater discharged from animal food processing may also contain germs. In addition, these wastewater also contain metal ions such as copper, manganese and chromium. In recent years, with the rapid development of food processing industry, the amount of wastewater produced by it is also increasing rapidly year by year. Many wastewater is discharged directly without effective treatment, which has caused very serious damage to the environment. Therefore, it is of great practical significance to discuss the treatment of food industry wastewater for ecological environment protection.
1 Present situation of wastewater treatment process in food industry
At present, domestic and foreign food industry wastewater treatment mainly adopts biological treatment technology, including aerobic biological treatment technology, anaerobic biological treatment technology and the combination of aerobic biological treatment technology and anaerobic biological treatment technology. In the aspect of aerobic biological treatment process, there are mainly activated sludge process (SBR process is widely used in practice at present) and biofilm process (represented by biological aerated filter). Compared with aerobic biological treatment process, anaerobic biological treatment process has great advantages in both late operation and management costs and early capital investment costs. Among them, the typical treatment processes are anaerobic granular sludge expanded bed (EGSB) process and the third generation anaerobic treatment process-anaerobic internal circulation reactor (ic) which is widely used in food industry wastewater treatment. In addition, anaerobic biological treatment process has a good treatment effect in food industry wastewater treatment [1].
2 process characteristics and application effect analysis
At present, the treatment of food industry wastewater at home and abroad is mainly biological treatment [2]. Mature technologies widely used in practice mainly include anaerobic contact method, anaerobic sludge bed method, shallow aeration method, extended aeration method and aeration sedimentation tank method.
2. 1 aerobic biological treatment process
Aerobic biological treatment is the oxidation of organic matter by aerobic microorganisms under the condition of continuous oxygen supply. In the aerobic process, microorganisms decompose complex organic matters, some of which are transformed into stable inorganic matters such as CO2, H2O and NH3, and some of which are synthesized into new cells by microorganisms, and finally the organic matters in sewage are removed.
2. 1. 1SBR process, that is, intermittent activated sludge system (also known as sequencing batch intermittent activated sludge process). At present, SBR method is widely used at home and abroad. The biological reaction tank integrates the functions of biodegradation, sedimentation and sludge return. This process is relatively simple. It is a new process developed on the basis of the previous intermittent activated sludge process. The operation process of SBR wastewater treatment generally includes five steps: water intake, oxygenation, static precipitation, drainage and sludge discharge. Compared with the continuous activated sludge process, this process has the following advantages: the aeration tank has the function of secondary sedimentation tank, and there is no secondary sedimentation tank or sludge reflux equipment, so the system structure is simple and easy to manage; Anti-impact load, generally do not need to set up a regulating pool; The reaction driving force is large, and high-quality effluent quality can be simply obtained; The sludge has good settling performance and low SVI value, which is convenient for automatic operation and later maintenance management. Juhua [3] Through the application research of SBR method in the treatment of soy sauce and pickle food wastewater, it is concluded that the CODcr of the original wastewater is in the range of 2000 mg/L ~ 4000 mg/L, and the effluent quality after SBR treatment reaches the second-class standard, with a removal rate of over 96%, no sludge bulking, convenient operation and management, small floor space and low operating cost.
2. 1.2BAF method, that is, biological aerated filter method. This process can be traced back to the 1980s, and it has been applied and developed in Europe and America. Dalian Malanhe Sewage Treatment Plant is the first sewage treatment plant adopting BAF process in China. Based on the biological contact process, the filter is filled with granular fillers such as ceramsite and quartz sand, and the filler and its attached biofilm are used as the medium to exert the metabolic function of organisms. Through physical filtration and the interception and adsorption of membranes and fillers, the efficient treatment of pollutants is realized. Liao Yan and others used coagulation -—ABR combined biological aerated filter (BAF) to study the removal of chemical oxygen demand (COD) and ammonia nitrogen in high concentration wastewater from a slaughterhouse in a city. It is found that the removal efficiency of chemical oxygen demand and ammonia nitrogen in raw water is 65,438 0,500 mg/L to 4,500 mg/L, and the treated effluent is 30mg/L to 85 mg/L.. 100 mg/l, ammonia nitrogen
2. 1.3MBR method, namely membrane bioreactor method. It is a wastewater treatment technology developed gradually in 1990s. This technology replaces the traditional secondary sedimentation tank with membrane module to realize solid-liquid separation. Its essence is to attach bacteria and microorganisms to the solid surface in the form of biofilm, and metabolize, grow and reproduce the organic matter in sewage as nutrients, thus achieving the effect of purifying sewage. The process has strong impact resistance and adaptability to the change of water quality and quantity; Low sludge yield, good sedimentation performance and easy solid-liquid separation; Low concentration sewage can also be treated. During normal operation, BOD5 in raw water can be increased or decreased from 20mg/L to 30mg/L to 5mg/L to10mg/L; The operation cost is not high and the management is convenient. Zhang Liangping, Wang Feng [5] Taking the application of MBR- in wastewater treatment of a food factory in Hubei as an example, it was found that the removal rate of COD and BOD in effluent reached over 99% with low energy consumption and stable operation.
2.2 Anaerobic biological treatment process
In the process of food wastewater treatment, compared with aerobic treatment, anaerobic treatment is gradually widely respected in the high-concentration organic wastewater industry-food industry because of its less sludge, less power flow consumption and simple management, which can save energy and reduce costs.
2.2. 1UASB process, namely the upflow anaerobic sludge bed process. This process is granular sludge composed of highly active anaerobic bacteria, which flows upward with the updraft in UASB device. High treatment efficiency, reliable performance, low energy consumption, no need for fillers and carriers, low operating cost, etc., and can treat high-load wastewater without clogging. It is also one of the most widely used high-speed reactors. Wang Wei, how [6] found that after food wastewater was treated by+contact oxidation process, CODcr, BOD5, ss and vegetable oil were reduced from raw water concentration of 1 170mg/L, 570mg/L, 600mg/L, 150mg/L, and the effect after treatment.
2.2.2EGSB reactor, namely expanded granular sludge bed reactor. This process is a new anaerobic process developed on the basis of UASB. Compared with UASB process, EGSB increased the effluent reflux, and increased the water flow velocity in the reactor, reaching 5 m/h ~ 10 m/h, which was nearly 10 times higher than that of UASB's 0.6 m/h ~ 0.9 m/h ... Li Kexun and others took a starch factory in Tianjin as an example. The removal rate of COD in EGSB anaerobic reactor exceeded 85%, and the effluent quality reached the national first-class discharge standard, which removed a lot of organic matter and reduced the treatment pressure of subsequent units. In addition, the intervention of anaerobic reactor can produce biogas as energy for secondary utilization, reducing the operating cost (the total operating cost is 0.73 yuan /m3? It has good environmental and social benefits.
2. 2. 3 SBR process, namely anaerobic sequencing batch activated sludge process. ASBR anaerobic sequencing batch activated sludge process was first born in the United States in 1990s, and it was developed on the basis of SBR. The remarkable feature of this process is that it runs intermittently in sequencing batch, which is divided into four steps: water inlet, reaction, precipitation and drainage. Compared with the continuous flow anaerobic reactor, this process does not need a large resistance water distribution system, which greatly reduces the energy consumption of the system, does not produce cut-off and short flow, and has flexible operation and strong resistance.
3 Analysis of the advantages of anaerobic biological treatment process
Compared with aerobic biological treatment process, anaerobic biological treatment process has many advantages in food industry wastewater treatment: the amount of excess sludge is very small during process operation, which reduces the operation and management cost because no additional oxygen source is needed; The concentration of organic matter in food industry wastewater is high, and anaerobic biological treatment process has the good advantage of resisting the impact load of high concentration organic matter, and can realize indirect discharge; In addition, anaerobic biological treatment process can produce biogas, realize the secondary utilization of resources, truly turn waste into treasure and reduce energy consumption. Therefore, anaerobic treatment process is an energy-saving wastewater treatment process in food industry wastewater treatment. As a process with low energy consumption and capable of generating secondary energy, anaerobic biological treatment will surely become the mainstream direction of wastewater treatment in food industry [8].