Soybean protein wastewater resource recycling method

Abstract

The invention relates to the field of sewage treatment, in particular to a method for recycling soybean protein wastewater resources. The soybean protein wastewater recycling method provided by the invention comprises the following steps: 1) mixing soybean protein wastewater, activated carbon and quaternary ammonium salt modified chitosan, stirring, standing and precipitating to obtain a precipitate turbid solution; 2) mixing the precipitate turbid liquid with a fermentation inoculant, carrying out anaerobic acidogenic fermentation, and carrying out centrifugal separation to obtain a carbon source stock solution; 3) heating and denitrifying the carbon source stock solution, mixing with sodium alginate, dissolving, and spray-drying to prepare a sodium alginate-carbon source microcapsule; and 4) preparing a degradable porous suspended filler from polylactic acid, filling the sodium alginate-carbon source microcapsule into pores of the degradable porous suspended filler, and sealing to obtain the slow-release carbon source suspended filler. The method provided by the invention can improve the current soybean protein wastewater utilization rate, reduce resource waste, and solve the problem of final direction of the soybean protein wastewater.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of sewage treatment, in particular to a method for recycling soy protein wastewater. BACKGROUND

[0002] Soy protein wastewater is derived from the processes of alkali dissolution, acid precipitation and centrifugal separation in soy protein separation process, and has the characteristics of high COD concentration, high suspended solids and high nitrogen and phosphorus concentration. Studies have shown that the annual output of soy protein wastewater in China is about 10 million tons, with COD as high as 20,000 mg / L, including soy oligosaccharides (COD about 10,000-15,000 mg / L), soy protein isolate (COD about 2,000-3,000 mg / L), and soy whey protein (COD about 2,000-3,000 mg / L) and other high-value organic matter. However, the process of recycling these substances is basically difficult in technology, cumbersome in process, and high in cost, which is difficult to market. Therefore, at present, it is often treated by anaerobic digestion and then discharged into the AAO biochemical system of the sewage plant for treatment. This not only increases the environmental protection cost of soy protein production enterprises, but also wastes the rich organic resources in soy protein wastewater, so a more green and economic treatment method needs to be found.

[0003] The total nitrogen index of the effluent of the current sewage treatment plant is becoming more and more stringent, and many water plants are facing the risk of exceeding the total nitrogen of the effluent due to low C / N ratio of the influent and insufficient denitrification capacity of the anoxic tank. If the abundant organic matter in soy protein wastewater is used to prepare slow-release carbon source suspended filler, on the one hand, it can realize the resource recycling of soy protein wastewater, and on the other hand, it can be used as a biological carrier to enhance the biomass of the anoxic tank of the AAO process of the sewage plant. At the same time, with the thickening of the biological membrane of the filler, a relatively stable anoxic environment will be maintained inside the biological membrane, which is beneficial to improve the denitrification capacity of the process and reduce the influence of the internal reflux dissolved oxygen on the anoxic tank. In addition, with the degradation of microorganisms, the carbon source in the slow-release carbon source suspended filler is gradually released into the water body to supply denitrifying bacteria for denitrification, which can save the cost of additional carbon source such as methanol, sodium acetate and glucose for the water plant. SUMMARY

[0004] In order to solve the above technical problems, the present application provides a method for recycling soy protein wastewater, which can improve the utilization rate of current soy protein wastewater, reduce resource waste, and solve the problem of the final destination of soy protein wastewater.

[0005] In the first aspect, the present application provides a method for recycling soy protein wastewater, which comprises the following steps: 1) mixing soy protein wastewater, activated carbon and quaternary ammonium salt modified chitosan, stirring and then standing and precipitating to obtain a precipitated turbid liquid.

[0006] 2) mixing the precipitated turbid liquid with a fermentation agent to perform anaerobic acid fermentation, and centrifugally separating to obtain a carbon source stock solution.

[0007] 3) mixing and dissolving the carbon source stock solution with sodium alginate after heating and denitrification, and then preparing sodium alginate-carbon source microcapsules by a spray drying method.

[0008] 4) preparing a degradable porous suspended filler by polylactic acid, filling the sodium alginate-carbon source microcapsules into the pores of the degradable porous suspended filler and sealing to obtain a slow-release carbon source suspended filler.

[0009] Preferably, in step 1), the mass ratio of the activated carbon and the quaternary ammonium salt modified chitosan is 4-5:1. The activated carbon and the quaternary ammonium salt modified chitosan in a certain ratio are used for synergistic treatment in the present application, which can enhance the removal efficiency of protein pollutants and suspended particulate matters, achieve efficient removal of protein and suspended matters in soy protein wastewater, and reduce the organic matter content of the soy protein wastewater, thereby facilitating subsequent biological treatment.

[0010] Further preferably, the activated carbon is activated carbon passing through a 200-mesh sieve, which is beneficial to rapid adsorption and separation. The ton-water dosage of the activated carbon and the quaternary ammonium salt modified chitosan is 0-10 kg and 0-2 kg, respectively, and is preferably 4-10 kg and 1-2 kg, respectively.

[0011] Further preferably, the quaternary ammonium salt modified chitosan is prepared by a method comprising the following steps: adjusting the pH value of a chitosan solution to 9-10, adding trimethylammonium chloride, heating, washing, and drying. The modified chitosan has better water solubility and enhanced positive charge, which greatly enhances the mutual attraction with negatively charged proteins, thereby achieving efficient adsorption of proteins.

[0012] Preferably, the quaternary ammonium salt modified chitosan is prepared by a method comprising the following steps: mixing 1-2 parts by weight of chitosan and 8-9 parts by weight of isopropyl alcohol to obtain a chitosan solution with a mass concentration of 10%-20%, adjusting the pH value of the chitosan solution to 9-10 with sodium hydroxide, then adding 1-2 parts by weight of trimethylammonium chloride, heating at a temperature of 70-80℃ for 7-8 h, washing the obtained product with a mixture of acetone and ethanol 1-2 times, the volume ratio of the acetone and ethanol being preferably 4:1, and then vacuum drying at a temperature of 50-80℃ for 2-4 h.

[0013] Further preferably, in step 1), the stirring time is 3-7 min.

[0014] As preferred, in step 2), the fermentation agent is a mixed agent of Aspergillus niger and yeast. Aspergillus niger can produce various enzymes such as protease, amylase, pectinase, etc., and has strong adaptability, which can effectively decompose various organic matters in the precipitated turbid liquid, and the yeast can produce volatile fatty acids by using protein, amino acid, oligosaccharide, etc., and the utilization rate of protein and carbon source COD equivalent can be significantly improved by the cooperation of the two.

[0015] Preferably, the mass ratio of the Aspergillus niger and the yeast is 1-2:1-2, and the addition amount of the fermentation agent is 1-5 g / L. Under anaerobic conditions, the organic molecules enriched by the modified adsorption material are gradually hydrolyzed into small molecular organic matters such as alcohol and volatile fatty acid by microorganisms, and the activated carbon can accelerate the acid production fermentation process by enriching microorganisms. The fermentation time is 1-2 days, the acid production is efficient, the carbon source stock solution COD / content is stable, and the subsequent treatment and utilization are convenient. The COD of the obtained carbon source stock solution is 50000-100000 mg / L.

[0016] Further preferably, in step 2), the activated carbon in the residual mud phase is continuously used in step 1) after ultrasonic desorption, and the desorption product can be used as a fermentation agent in step 2), thereby saving treatment cost.

[0017] As preferred, in step 3), the addition amount of the sodium alginate is 20-30 g / L, and the sodium alginate-carbon source microcapsule is preferably prepared by spray drying. After spray drying, the sodium alginate forms a film wall with appropriate thickness to embed the carbon source material in the microcapsule. The film formed by the sodium alginate can effectively prevent the carbon source from contacting the external environment and deteriorating, and on the other hand, in the anoxic tank, the sodium alginate-carbon source microcapsule gradually releases the carbon source to supply the denitrifying bacteria, thereby improving the utilization rate of the carbon source.

[0018] As preferred, in step 4), the heated and molten polylactic acid is added to a porous mold for cooling and setting to obtain a degradable porous suspended filler. The polylactic acid filler has good mechanical strength and biodegradability, and after sealing the sodium alginate-carbon source microcapsule, stable carbon source slow release and microbial biofilm formation are achieved, which is beneficial to long-term operation, and the carbon source is supplied to the denitrifying bacteria inside the biofilm, thereby improving the utilization rate of the carbon source. Preferably, the molecular weight of the polylactic acid is 100000-200000, the heating and melting temperature is 170-180℃, and the density of the obtained suspended filler is 1.0-1.2 g / cm 3 . The filler has the advantages of convenient storage and transportation, high applicability, suspension in water by slight hydraulic stirring, direct addition without modification of the AAO biochemical process, and self-biodegradation without disposal of waste filler.

[0019] Further preferably, in step 4), a denitrifying bacteria agent is also added into the pores of the degradable porous suspended filler. The denitrifying bacteria agent is filled into the carbon source filling pores together with the sodium alginate-carbon source microcapsules to accelerate the biofilm formation of the denitrifying bacteria on the suspended filler and improve the denitrification effect of the anoxic tank.

[0020] In a preferred embodiment of the present application, a method for resource utilization of soy protein wastewater comprises the following steps: Figure 1 ), specifically comprising the following steps: 1) The soy protein wastewater is mixed with an appropriate amount of activated carbon and adsorbent, i.e., quaternary ammonium salt modified chitosan, to adsorb the organic matters such as proteins and oligosaccharides in the soy protein wastewater, and then the precipitated turbid liquid is separated.

[0021] 2) The flocculated precipitated turbid liquid obtained in step 1) is subjected to anaerobic acid fermentation with an appropriate amount of bacteria agent to obtain a fermentation liquid, and the supernatant is the carbon source stock solution, and the activated carbon in the remaining mud phase can be reused in step 1) after ultrasonic desorption, and the desorption product can be used as a fermentation bacteria agent in step 2).

[0022] 3) The carbon source stock solution obtained in step 2) is heated and boiled to kill the residual microbial activity in the carbon source stock solution and remove the excess ammonia nitrogen, then the heating is stopped, and while the carbon source stock solution still has residual heat, an appropriate amount of sodium alginate is added and stirred to dissolve, and then a sodium alginate-carbon source microcapsule is prepared by a spray dryer.

[0023] 4) A suitable amount of polylactic acid is heated and melted, added to a porous mold, and cooled to obtain a degradable porous suspended filler, and the sodium alginate-carbon source microcapsule obtained in step 3) is filled into the fixed pores and sealed to obtain a slow-release carbon source suspended filler, which is beneficial to improve the biomass in the anoxic tank and continuously and stably provide carbon source for the anoxic tank.

[0024] The present application provides a method for preparing a slow-release carbon source suspended filler from soy protein wastewater.

[0025] The present application has at least the following advantages: 1) The activated carbon and quaternary ammonium salt modified chitosan are used to adsorb and precipitate the organic matters in the soy protein wastewater, which can quickly reduce the content of pollutants in the soy protein wastewater, and the precipitate can be used to prepare carbon source by fermentation, and the activated carbon can be reused after desorption, realizing the comprehensive utilization of resources.

[0026] 2) The sodium alginate-carbon source microcapsule prepared in the present application can fix and slowly release carbon source, reducing the use of external carbon sources such as methanol, sodium acetate, and glucose, and increasing the utilization rate of carbon source.

[0027] 3、The prepared slow-release carbon source suspended filler material in the application is simple in raw material, and is a green biodegradable material, which only needs to be supplemented regularly after being added, and the waste filler material does not need to be treated, and the carbon source in the suspended filler material can be supplied to the filler biofilm microorganism nearby, which can provide carbon source for denitrifying bacteria, enhance the denitrification effect of the anoxic tank, and reduce the carbon source loss caused by the too high dissolved oxygen of the return liquid of the aerobic tank. BRIEF DESCRIPTION OF DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description are some embodiments of the application, and other drawings can be obtained by those skilled in the art without creative labor.

[0029] Figure 1 A resource recycling method of soybean protein wastewater is provided for the embodiments of the application.

[0030] Figure 2 A slow-release carbon source suspended filler structure diagram is provided for the embodiments of the application.

[0031] In the figure, 1 is a polylactic acid skeleton, 2 is a carbon source filling hole, and 3 is a hollow hole. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solutions and advantages of the application more clear, the technical solutions in the application will be clearly and completely described below. Obviously, the described embodiments are some embodiments of the application, but not all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor belong to the protection scope of the application.

[0033] The endpoints of the ranges and any values disclosed in the application are not limited to the precise values stated. The ranges or values should be interpreted as approximately between the stated values. For ranges, the endpoints are included between each respective range; the endpoints are included in the respective range or ranges; and each respective range is a separate and independent range. The various independent ranges can be combined.

[0034] In the embodiments of the application, the specific technology or condition not mentioned is carried out according to the technology or condition described in the literature in the field, or according to the product instruction. The used devices, instruments, reagents, etc. not mentioned the manufacturer are all conventional products that can be purchased through a regular channel. The experimental reagents and raw materials involved are commercially available, and the reagents are analytical pure products.

[0035] Example 1 The method for recycling soybean protein wastewater provided by the embodiment, and the specific steps are as follows: (1) Preparation of quaternary ammonium salt modified chitosan 10 g of chitosan (specification: degree of deacetylation > 79%; content > 95%) was dissolved in 90 g of isopropyl alcohol to obtain a 10% chitosan solution, 5 ml of 40% NaOH (pH value was adjusted to 9) was then added, and 10 g of trimethylammonium chloride was further added. The mixture was heated at 70°C for 8 h. After the reaction was completed, the obtained product was washed once with an acetone-ethanol mixed solution (volume ratio 4:1) and then dried at 50°C under vacuum for 4 h to obtain quaternary ammonium salt modified chitosan.

[0036] (2) Adsorption treatment of soybean protein wastewater The soybean protein wastewater was taken from a soybean protein production enterprise in Hebei, and the COD value was 15141 mg / L. 5 g of activated carbon (200 mesh sieve) was first added to 1 L of soybean protein wastewater, and then 1 g of quaternary ammonium salt modified chitosan was added. The mixture was continuously stirred for 5 min and then statically settled for 1 h. The COD value of the supernatant was 644.1 mg / L, and the COD removal rate was as high as 95.7%.

[0037] (3) Preparation of sodium alginate-carbon source microcapsules 200 ml of the adsorption and precipitation turbidity liquid obtained in the previous step was transferred into a conical flask, nitrogen was introduced to remove excess oxygen, 1 g of fermentation inoculum (Aspergillus niger: yeast = 1:1) and a magnetic rotor were further added, the mouth of the flask was sealed with a plastic film and a rubber band, and the mixture was continuously stirred at 45°C for 1 d. After centrifugal precipitation at 3600 r / min for 15 min, the COD equivalent of the obtained carbon source stock solution was 84000 mg / L. 100 ml of the supernatant was heated to boiling, 2 g of sodium alginate was added and stirred to dissolve, and finally sodium alginate-carbon source microcapsules were prepared by a spray dryer.

[0038] (4) Preparation of slow-release carbon source suspended filler Polylactic acid with a molecular weight of 100000 was heated and melted at 170°C, and then added into a customized 7-hole mold to cool and set into a polylactic acid skeleton 1, i.e., a cylindrical 7-hole filler (as shown in Figure 2 The filler has a height of 6 mm, a diameter of 10 mm, and an internal hole diameter of 3 mm. The carbon source filling hole 2 is closed on one side and is provided with a corresponding polylactic acid hole plug. The empty hole 3 is open on both sides, which is convenient for microorganisms to adhere. It is worth noting that the molten polylactic acid has good plasticity, so the size, shape, hole number and hole diameter of the filler can be changed according to the actual situation. After the sodium alginate-carbon source microcapsules are injected into the carbon source filling hole and the polylactic acid hole plug is plugged, a slow-release carbon source suspended filler is obtained. The density of the filler is 1.12 g / cm 3 .

[0039] Example 2 The method for recycling and reusing soybean protein wastewater provided in the embodiment uses the method of embodiment 1, except that the dosages of activated carbon and quaternary ammonium salt modified chitosan in step (2) are changed to 10 g and 2 g respectively, and other conditions remain unchanged. The COD removal rate of the soybean protein wastewater can reach 99.1%, and the COD equivalent of the carbon source stock solution prepared by fermentation is 81500 mg / L.

[0040] Embodiment 3 The method for recycling and reusing soybean protein wastewater provided in the embodiment uses the method of embodiment 1, except that the ratio of Aspergillus niger to yeast in step (2) is changed to 2:1, and the carbon source stock solution obtained by fermentation is 77800 mg / L.

[0041] Embodiment 4 The method for recycling and reusing soybean protein wastewater provided in the embodiment uses the method of embodiment 1, except that the porous suspended filler in step (4) is changed to a mixture of sodium alginate-carbon source microcapsules and denitrifying bacteria agent, and the mass ratio of the two is 2:1. The density of the slow-release carbon source suspended filler obtained is 1.14 g / cm 3 .

[0042] Experimental Example 1 The slow-release carbon source suspended filler prepared in embodiment 1 is used as the experimental object in this experimental example.

[0043] The influent of a certain domestic wastewater treatment plant in Beijing and the sludge-water at the end of the aerobic tank are used as the materials, and the influent is treated by using an SBR small-scale test device. Under the condition that other conditions are the same, the effluent COD and TN of the SBR small-scale test device with the addition of slow-release carbon source suspended filler, the addition of suspended filler (without the addition of sodium alginate-carbon source microcapsules in the filling hole), and the non-addition of slow-release carbon source suspended filler are compared and analyzed.

[0044] The specific operation is as follows: 1. Take 15 L of sludge-water sample at the end of the aerobic tank, and let it stand for 30-60 min. After skimming the supernatant of the sludge-water sample, add distilled water to 15 L and stir for 5 min. Repeat this process twice, and then add the influent of the wastewater plant (COD is 189 mg / L, TN is 56 mg / L) to 15 L. At this time, the MLSS of the treated sludge-water sample is 4100 mg / L. Divide the treated sludge-water sample into three equal parts, and place them in SBR reactors 1, 2 and 3 respectively. Among them, SBR reactor 1 does not add slow-release carbon source suspended filler, SBR reactor 2 adds 100 suspended fillers without the addition of carbon source, and SBR reactor 3 adds 100 slow-release carbon source suspended fillers.

[0045] 2、SBR reactor water, reaction, precipitation, decanting, five stages of time are set to 1h, 5h, 4h, 1h, 1h, the whole cycle is 12 hours, water and decanting are relied on peristaltic pump, single water volume is 2.5L, the dissolved oxygen concentration is controlled to 4~6mg / L in the reaction stage.

[0046] 3、Every two cycles take SBR reactor effluent to determine COD and TN, the results are shown in Table 1: Table 1

[0047] Finally, it should be noted that: the above examples are used to illustrate the technical solutions of the present application, rather than limit them; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for resource utilization of soybean protein wastewater, characterized in that, The method comprises the following steps: 1) mixing soybean protein wastewater, activated carbon and quaternary ammonium salt modified chitosan, stirring and then standing to obtain a precipitate turbid liquid; 2) mixing the precipitate turbid liquid with a fermentation inoculum, performing anaerobic acid fermentation, and centrifuging to obtain a carbon source stock solution; 3) mixing the carbon source stock solution with sodium alginate after heating denitrification, dissolving, and then spray drying to prepare sodium alginate-carbon source microcapsules; 4) preparing a degradable porous suspended filler with polylactic acid, filling the sodium alginate-carbon source microcapsules into the pores of the degradable porous suspended filler and sealing to obtain a slow-release carbon source suspended filler.

2. The method of soy protein wastewater valorization according to claim 1, characterized in that, In step 1), the mass ratio of the activated carbon to the quaternary ammonium salt modified chitosan is 4-5:

1.

3. The method of soy protein wastewater valorization according to claim 2, characterized in that, The activated carbon is activated carbon with a mesh size of 200.

4. The method of soy protein wastewater valorization according to claim 1, characterized in that, The quaternary ammonium salt modified chitosan is prepared by a method comprising the following steps: adjusting the pH value of a chitosan solution to 9-10, adding trimethylammonium chloride, and performing heating reaction.

5. The method of soy protein wastewater valorization according to any one of claims 1-4, characterized in that, In step 2), the fermentation inoculum is a mixed inoculum of Aspergillus niger and yeast; The mass ratio of the Aspergillus niger to the yeast is 1-2:1-2, the addition amount of the fermentation inoculum is 1-5 g / L, and the fermentation time is 1-2 days.

6. The method of soy protein wastewater valorization according to claim 5, characterized in that, In step 2), the activated carbon in the remaining mud phase is further used in step 1) after ultrasonic desorption.

7. The method of soy protein wastewater valorization according to any one of claims 1-4, characterized in that, In step 3), the addition amount of the sodium alginate is 20-30 g / L; and the sodium alginate-carbon source microcapsules are prepared by spray drying.

8. The method of soy protein wastewater valorization according to any one of claims 1-4, characterized in that, In step 4), the polylactic acid is added into a porous mold after heating and melting, and then cooled to obtain a degradable porous suspended filler; the molecular weight of the polylactic acid is 100000-200000, and the heating and melting temperature is 170-180℃.

9. The method of soy protein wastewater valorization according to any one of claims 1-4, characterized in that, In step 4), the degradable porous suspended filler is further added with a denitrifying inoculum.

10. A slow-release carbon source suspended filler, characterized by, The slow-release carbon source suspended filler is prepared by the method for resource utilization of soybean protein wastewater according to any one of claims 1-9.

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