CN113999839A

CN113999839A - Immobilization method of microalgae and application thereof

Info

Publication number: CN113999839A
Application number: CN202111497568.5A
Authority: CN
Inventors: 王勇; 于枭燕; 赵国群
Original assignee: Hebei University of Science and Technology
Current assignee: Hebei University of Science and Technology
Priority date: 2021-12-09
Filing date: 2021-12-09
Publication date: 2022-02-01

Abstract

The invention discloses a microalgae immobilization method and application thereof, wherein a freeze-thaw technology is adopted to embed microalgae cells in a PVA carrier for immobilization, the pores of immobilized microspheres are utilized for material exchange, nutrient substances in starch wastewater are absorbed and utilized by chlorella through the pores, and the immobilization of magnetic ferroferric oxide nanoparticles by the carrier is realized. The microalgae immobilization method can achieve the purpose of efficiently removing organic matters in the starch wastewater, and simultaneously realize the rapid online separation of the microalgae in the starch wastewater fermentation system under the drive of magnetic force. The method is suitable for immobilizing the microalgae, and the immobilized microalgae can be further applied to removing organic matters in the starch wastewater.

Description

Immobilization method of microalgae and application thereof

Technical Field

The invention belongs to the technical field of microorganisms, and relates to a microbial agent, in particular to a microalgae immobilization method and application thereof.

Background

The starch wastewater is produced in the process of producing starch or starch sugar, glucose, starch derivatives and other substances of starch deep-processing products by using agricultural products such as corn, potato, wheat, rice and the like as raw materials, belongs to high-concentration organic wastewater, contains a large amount of soluble starch, a small amount of protein and other substances, has high chemical oxygen demand and total nitrogen discharge, causes environmental pollution problems such as water eutrophication, serious spoilage and the like if the starch wastewater is directly discharged into environmental water, cannot effectively utilize organic matters in the wastewater, causes serious waste of resources, and can be discharged after being treated. However, the treatment process of starch wastewater is difficult and high in cost, so that people have conducted extensive research on the treatment of pollutants such as ammonia nitrogen, phosphorus, total nitrogen and the like.

Microalgae is a kind of microorganism widely distributed in fresh water areas, has high growth and propagation speed, belongs to photoautotrophic organisms, and is widely applied to the fields of food, medicine, genetic engineering, liquid fuel and the like due to polysaccharide, protein, pigment and the like generated by the metabolism of microalgae cells. Chlorella has been used as a good food and animal feed additive for over 30 years in the united states and japan, and furthermore, energy-based microalgae offer a potential solution to current energy crisis and environmental problems due to their low risk and high productivity.

In recent years, China also pays attention to the development and utilization of microalgae, wherein the culture of the microalgae by utilizing the microalgae to absorb nutrient substances in starch wastewater is always a hotspot in the research field, a large amount of nutrient substances such as water resources, carbon sources, nitrogen sources, phosphorus nutrient salts and the like are needed in the growth process of the microalgae, rich carbon, nitrogen and phosphorus resources in the starch wastewater can be used as nutrient sources required by the growth of the microalgae, and the culture of the microalgae by utilizing the starch wastewater is a good bridge for realizing low-cost industrial production of biomass and resource discharge of wastewater; research on water quality treatment by using microalgae is a new water quality treatment technology and method which are started in recent decades, and the immobilization of the microalgae is a key link in the utilization process of the microalgae.

Currently, immobilized microalgae technologies mainly include adsorption, cross-linking and embedding methods: the adsorption method is to fix microalgae cells on a carrier in a physical adsorption, chemical adsorption or ion combination mode, is a microalgae immobilization method which is mild, simple to operate and low in price, but the quantity of microalgae fixed by the adsorption method is limited, and the fixed microalgae cells are easy to fall off, so that the stability of a microalgae system in the actual wastewater treatment process is poor, and the problem of immobilized microalgae cell leakage is caused; the principle of the cross-linking method is that a plurality of active groups with the same function existing in a cross-linking agent interact with inherent active groups on the surfaces of microalgae cells to form a network structure, so that the aim of immobilizing the microalgae is fulfilled, however, the cross-linking method has the problems that reaction conditions are complex and changeable, the killing power on the microalgae cells is strong, the microalgae cells are partially inactivated, and experimental conditions are difficult to control; the embedding method has the unique advantages of high microalgae cell retention rate, small damage to microalgae cells so as to retain high proportion of living cells, high immobilization strength, difficult shedding of microalgae cells and the like, and for the embedding method, common reagents comprise: alginate, agar, carrageenan, pectin, polyvinyl amide, poly-carrageenan, collagen, etc. are not well developed in the immobilized cell technology, and thus are not sufficient in the toxicity of the immobilized embedding material, the strength of the immobilized cells, and the sterility thereof.

Disclosure of Invention

The invention aims to provide a microalgae immobilization method for effectively removing nutrient substances in starch wastewater;

another object of the present invention is to provide an application of the immobilized microalgae.

In order to achieve the purpose, the invention adopts the technical scheme that:

a microalgae immobilization method comprises the following steps which are carried out in sequence:

s1, culturing microalgae

Carrying out high-density culture on microalgae to logarithmic phase to obtain microalgae solution A;

s2, immobilized microalgae

And (3) taking the algae solution A, centrifuging and removing supernatant to obtain bacterial sludge F, adding the bacterial sludge F and the ferroferric oxide nanoparticles into the sterilized PVA aqueous solution, uniformly mixing, placing in a 96-well plate, and sequentially freezing, thawing and cleaning to obtain the immobilized microalgae.

As one limitation, in step S1, the microalgae are chlorella pyrenoidosa, anabaena, and bifidobacterium minutissima;

the high-density culture is carried out by subjecting the sterile algae cells to high-density culture at a temperature of 23-30 ℃, an illumination intensity of 2000-2800 lux and an illumination period of 24 h: culturing in BG11 liquid culture medium under 0h light-dark ratio to logarithmic phase to obtain microalgae solution A.

By way of further limitation, the BG11 liquid medium comprises the following components in parts by weight: 100-200 parts of sodium nitrate, 3-5 parts of dipotassium hydrogen phosphate, 6-9 parts of magnesium sulfate, 3-4 parts of calcium chloride, 0.5-0.7 part of ammonium citrate, 0.5-0.7 part of ferric ammonium citrate, 0.1-0.2 part of disodium ethylene diamine tetraacetate, 1-3 parts of sodium carbonate and 100-300 parts of A5 culture solution.

As a further limitation, the a5 culture solution comprises, in parts by weight: 2-3 parts of boric acid, 1.5-2 parts of manganese chloride, 0.2-0.3 part of zinc sulfate, 0.3-0.5 part of sodium molybdate, 0.05-0.1 part of copper sulfate and 0.03-0.09 part of cobalt nitrate.

As a second limitation, in step S2, the preparation method of the ferroferric oxide nanoparticles is sequentially performed according to the following steps:

dissolving sodium acetate in ethylene glycol, and heating in a water bath to obtain a dispersion liquid B;

s II, FeCl₃·6H₂Dissolving O and trisodium citrate in ethylene glycol to obtain a solution C;

s III, injecting the solution C into the dispersion liquid B, and heating in a water bath to obtain a solution D;

and S IV, heating, pressurizing and cooling the solution D to obtain a solid E, and cleaning and drying the solid E to obtain the ferroferric oxide nano-particles.

In the step S I, the weight volume ratio of the sodium acetate to the glycol is 2-3 g:20 mL;

heating in a water bath at 35-45 ℃ for 20-40 min;

in the step SII, the trisodium citrate and FeCl₃·6H₂The weight ratio of O is 1: 1.5-2.

In a further limitation, in the step S III, the water bath is heated at 35-45 ℃ for 25-40 min.

In a further limitation, in the step S IV, the heating and the pressurizing are carried out in a stainless steel high-temperature high-pressure reaction kettle with a polytetrafluoroethylene lining, and the temperature is 180-230 ℃;

the temperature after cooling is 20-30 ℃;

and the cleaning is carried out by sequentially using ethanol and deionized water, and the cleaning is repeated for 3-5 times.

As a third limitation, in step S2, centrifuging at 3000-6000 rpm for 3-8 min;

sterilizing at 115-130 ℃ for 10-20 min;

the concentration of the PVA aqueous solution is 5-15%;

the radius of the small ball is 2-4 mm, and the height of the small ball is 6-8 mm;

freezing at the temperature of-25 to-15 ℃ for 10 to 15 hours;

the unfreezing is carried out at the temperature of 3-6 ℃;

and the cleaning is carried out by washing with sterile water for 3-5 times.

The invention also provides an application of the immobilized microalgae, and the immobilized microalgae is used for removing organic matters in starch wastewater.

Due to the adoption of the technical scheme, compared with the prior art, the invention has the technical progress that:

firstly, in the microalgae immobilization method, the PVA carrier is adopted to immobilize the microalgae, and the method has the beneficial effects of high fermentation rate, good repeatability, low fermentation cost and less pollution;

and secondly, in the microalgae immobilization method, ferroferric oxide nanoparticles are added, so that microalgae can be quickly and effectively separated from starch wastewater by using an external magnetic field.

The method is suitable for immobilizing the microalgae, and the prepared immobilized microalgae is suitable for removing organic matters in the starch wastewater.

Drawings

The invention is described in further detail below with reference to the figures and the embodiments.

FIG. 1 shows the reaction time vs. Fe in example 7 of the present invention₃O₄Schematic representation of the effect of the appearance of the nanoparticles;

FIG. 2 shows the removal rate of organic matters in starch wastewater by PVA immobilized microalgae with different concentrations in example 14 of the present invention;

FIG. 3 shows the results of measuring the mechanical properties of the immobilized chlorella in example 20 of the present invention;

FIG. 4 shows the removal rate of organic matters in starch wastewater by immobilized microalgae with different freezing and thawing times in example 21 of the present invention.

Detailed Description

The present invention is further illustrated by the following specific examples, which are to be construed as merely illustrative, and not limitative of the remainder of the disclosure.

Biological material:

chlorella: from Alger Biotechnology Ltd.

Example 1 culture method of microalgae

The present example was carried out according to the following steps:

the density of the algae is 1 × 10⁶10mL of cfu/mL sterile chlorella pyrenoidosa, culturing in BG11 liquid culture medium at 28 ℃, with the illumination intensity of 2400lux and the illumination period of 24 h: culturing to logarithmic growth phase with light-dark ratio of 0h to obtain sterile Chlorella beta culture solution, centrifuging the sterile Chlorella beta culture solution at 8000rpm for 10min, and resuspending with ultrapure water for three times to obtain Chlorella pyrenoidosa mud, i.e. microalgae mud X₁；

Wherein, the content of each component in the BG11 liquid culture medium is shown in Table 1:

TABLE 1BG11 liquid Medium formulation

Principal Components	Concentration value
		Sodium nitrate (g/L)	1.5
Dipotassium hydrogen phosphate (g/L)	0.04
		Magnesium sulfate (g/L)	0.075
Calcium chloride (g/L)	0.036
		Ammonium citrate (g/L)	0.006
Ferric ammonium citrate (g/L)	0.006
		Ethylene diamine tetraacetic acid disodium (g/L)	0.001
Sodium carbonate (g/L)	0.02
		Microelement A5 solution (mL/L)	1

The contents of the components in the trace element a5 solution are shown in table 2.

TABLE 2 formulation of microelement A5 solution

Examples 2-6 culture method of microalgae

Examples 2 to 6 are methods for culturing microalgae, which are substantially the same as example 1 except for the differences in the amounts of raw materials and process parameters, and are detailed in table 3:

TABLE 3 summary of the process parameters of examples 2-6

Wherein, the content of each component in BG11 liquid culture medium in examples 2-6 is shown in Table 4:

TABLE 4 BG11 liquid Medium formulation in examples 2-6

Wherein, the contents of the components in the trace element A5 solution in the examples 2-6 are shown in Table 5:

TABLE 5 formulation of trace element A5 solution in examples 2-6

Examples 2-6 preparation of microalgae algal sludge X, respectively₂-X₆。

Example 7A Fe₃O₄Method for preparing nanoparticles

This example is Fe₃O₄The preparation method of the nano-particles comprises the following steps which are carried out in sequence:

s1, weighing 240g of CH₃Dissolving COONa in 2L ethylene glycol, and heating in water bath at 40 deg.C for 30min to obtain CH₃COONa is uniformly dispersed in the glycol to obtain dispersion liquid B;

s2, weighing 108gFeCl₃·6H₂Dissolving O in 2L of ethylene glycol, adding 60g of trisodium citrate, and violently stirring until the particles in the solution are completely dissolved to obtain a solution C;

s3, injecting the solution C into the dispersion liquid B, and stirring for 30min under the water bath condition of 40 ℃ to obtain a solution D;

s4, transferring the solution D into a stainless steel high-temperature high-pressure reaction kettle with polytetrafluoroethylene as a lining, heating to 200 ℃, cooling to 25 ℃ after the reaction is finished, collecting a black product at the bottom of the reaction kettle, repeatedly cleaning the black product with ethanol and deionized water for three times, and drying to obtain Fe₃O₄Nanoparticles, measured Fe₃O₄The particle size of the nano particles is 200 nm;

the invention adopts a solvent method to prepare Fe₃O₄In the course of nanoparticles, Fe₃O₄The appearance of the nanoparticles is closely related to the reaction time, and as the reaction time is prolonged, Fe₃O₄The particle size of the nanoparticles gradually decreases, the appearance of the sample approaches to spherical shape, the surface gradually becomes smooth, and the sample presents complete spherical shape, as shown in fig. 1, wherein fig. 1a is Fe when the reaction time is 4h₃O₄Appearance of the nanoparticles, FIG. 1b Fe at 6h reaction time₃O₄The appearance of the nanoparticles, FIG. 1c Fe at a reaction time of 8h₃O₄The appearance of the nanoparticles, FIG. 1d is Fe at 10h reaction time₃O₄The appearance of the nanoparticles; this is because when the surfactant concentration and the reaction temperature in the reaction system are constant and the reaction time is short, the reaction is incomplete, resulting in Fe₃O₄The particle diameter of the nano particles is not uniform, and FeCl in a liquid phase system is generated along with the extension of reaction time₃·6H₂O and CH₃COONa is sufficient waterRelease a large amount of OH^－Promotion of Fe (OH)₃Generation of (2) and Fe³⁺Reduction of (2); meanwhile, the viscosity of the dispersion medium EG is higher, and Fe is reduced₃O₄Growth rate of nanoparticles, and thus, Fe prepared by solvent method with prolonged reaction time₃O₄The particle size of the nanoparticles is greatly reduced.

Examples 8 to 12 Fe₃O₄Method for preparing nanoparticles

Examples 8 to 12 are each Fe₃O₄The preparation method of the nano-particles has the same steps as the preparation method of the nano-particles in example 6, and the differences only lie in the differences of the raw material dosage and the process parameters, and the details are shown in the table 6:

TABLE 6 summary of the process parameters of examples 8-12

Example 13 pretreatment method of corn starch wastewater

Standing the corn steep liquor starch wastewater for 4h, removing precipitates, adjusting the pH of the corn steep liquor starch wastewater to 7 by using HCl and NaOH to obtain a solution I to be treated, and detecting the water quality of the solution I to be treated, wherein the results are shown in Table 7.

TABLE 7 ingredient Table of starch wastewater

Index (I)	COD(mg/L)	Total nitrogen (mg/L)	Total phosphorus (mg/L)	Ammonia nitrogen (mg/L)
					Content (wt.)	8098.83	531.86	164.15	600.82

Example 14 method for immobilizing Chlorella in PVA Carrier

The embodiment provides a method for fixing chlorella in a PVA carrier, which comprises the following steps in sequence:

taking the algae solution A, centrifuging and removing supernatant to obtain bacterial sludge F, adding the bacterial sludge F and ferroferric oxide nanoparticles into a sterilized PVA (polyvinyl alcohol) aqueous solution, uniformly mixing, placing in a 96-hole plate, and sequentially freezing, thawing and cleaning to obtain the immobilized microalgae particles;

s1, respectively dissolving 5g, 10g and 15g of PVA in 100mL of distilled water to prepare 5%, 10% and 15% PVA aqueous solutions in weight-volume ratio, completely dissolving the PVA aqueous solutions at 80 ℃, and sterilizing the PVA aqueous solutions for 15min at 121 ℃ to obtain PVA aqueous solutions I-III;

s2, centrifuging chlorella solution A at a rotating speed of 3500r/min for 3min, concentrating, discarding supernatant to obtain chlorella mud, adding 10g of chlorella mud and 2g of ferroferric oxide nanoparticles into PVA aqueous solutions I-III respectively, mixing uniformly, extruding through a stainless steel needle with the inner diameter of 1.2mm, extruding into a 200-mu L mold container (96 pore plate), freezing at-20 ℃ for 12 hours, slowly thawing at 4 ℃, and washing with sterile water to obtain immobilized chlorella I-III;

s3, respectively putting 10g of immobilized chlorella I-III into a conical flask containing 100mL of corn starch wastewater, marking the conical flask as a conical flask I-III, placing the conical flask I-III into a magnetic field illumination incubator for culture, wherein the culture temperature is 30 ℃, the illumination intensity is 2400lux, and the light-dark ratio is 24 h: 0h, rotating speed of 140rpm and culture time of 8 days;

s4, respectively detecting the removal rates of COD, total nitrogen, total phosphorus and ammonia nitrogen in the conical flasks I-III, wherein the results are shown in figure 2, wherein figure 2a shows the removal rate of COD, figure 2b shows the removal rate of total nitrogen, figure 2c shows the removal rate of total phosphorus, and figure 2d shows the removal rate of ammonia nitrogen; specific data are shown in table 8;

TABLE 8 removal rate of organic matter in starch wastewater by PVA immobilized microalgae with different concentrations

As is clear from Table 8, when the PVA concentration was 10%, the effect of removing starch wastewater by the immobilized chlorella was the best.

Example 15-19 method for immobilizing Chlorella in PVA Carrier

Examples 15 to 19 are methods for immobilizing chlorella on a PVA carrier, and the procedures are substantially the same as in example 14 except for the differences in the amounts of the raw materials and the process parameters, as detailed in Table 9.

TABLE 9 summary of the process parameters of examples 15-19

Example 20 analysis of mechanical Properties of immobilized Chlorella

The embodiment is used for testing the mechanical property of the immobilized chlorella;

the principle of the experiment is as follows: the storage modulus (G ') reflects the elastic component of the rheological behaviour and can be regarded as an index for measuring the degree of formation of the gel network, the loss modulus (G ") reflects the viscous component of the rheological behaviour, and their ratio (G'/G") represents the strength of the gel;

the method comprises the following specific steps: 197.82 mu L of PVA (polyvinyl alcohol) carrier with the radius of 3.0mm and the height of 7.0mm is taken, and the storage modulus and the loss modulus of the PVA carrier are respectively measured, and the results are shown in figure 3, wherein figure 3a is the loss modulus before and after fermentation with different PVA concentrations, figure 3b is the storage modulus before and after fermentation with different PVA concentrations, figure 3c is the storage modulus before and after fermentation with different freeze-thaw times, and figure 3d is the loss modulus before and after fermentation with different freeze-thaw times;

as can be seen from fig. 3:

the storage modulus (G ') of the PVA carriers prepared is almost independent of frequency, and has obvious solid-state behavior (G ' > G ') in the whole frequency range, which indicates that the PVA carriers can be described as ' strong gel ';

the storage modulus (G ') and the loss modulus (G') depend on the concentration and the freeze-thaw times of the PVA, the storage modulus and the loss modulus increase along with the increase of the concentration of the PVA, the increase range from 5% to 10% is smaller than the increase range from 10% to 15%, and the loss modulus has larger range; along with the increase of the number of times of freezing and thawing, G 'and G' are gradually increased, and when the number of times of freezing and thawing reaches four times, the storage modulus is slowly increased;

comparing before and after fermentation, the storage modulus and the loss modulus of the fermented carrier are increased on the whole, and the phenomenon is supposed to be related to the increase of the density of thalli on the surface of the carrier, so that the fermented carrier becomes harder and firmer on the whole.

Example 21 Freeze-thaw cycle analysis of immobilized Chlorella

The method is used for verifying the influence of the number of freeze-thaw cycles on the chlorella immobilization effect, and comprises the following steps in sequence:

taking quartered 10% PVA-immobilized chlorella, respectively performing freeze thawing I, freeze thawing II, freeze thawing III and freeze thawing IV to obtain 10% PVA-immobilized chlorella I-IV, respectively inoculating 100g of 10% PVA-immobilized chlorella I-IV into 1L of corn starch wastewater, performing a fermentation experiment at 25 ℃, observing the removal rate of each group of chlorella on organic matters in the corn starch wastewater after 240h, wherein the result is shown in figure 4, figure 4a shows the influence of different freeze thawing times on the COD removal rate, figure 4b shows the influence of different freeze thawing times on the total nitrogen removal rate, figure 4c shows the influence of different freeze thawing times on the total phosphorus removal rate, figure 4d shows the influence of different freeze thawing times on the ammonia nitrogen removal rate, and the specific data are shown in table 10;

wherein, the specific process of freezing and thawing for the first time comprises freezing for 12 hours at-20 ℃, then slowly thawing for 8 hours at 4 ℃, and washing with sterile water; the second freeze thawing process includes freezing at-20 deg.c for 12 hr, slow thawing at 4 deg.c for 8 hr, washing with sterile water and repeating the operation once; the third freeze thawing process includes freezing at-20 deg.c for 12 hr, slow thawing at 4 deg.c for 8 hr, washing with sterile water and repeating the operation twice; the specific process of the IV times of freezing and thawing comprises freezing for 12 hours at the temperature of-20 ℃, then slowly thawing for 8 hours at the temperature of 4 ℃, washing with sterile water, and repeating the operation for three times;

TABLE 10 removal rate of organic matter from starch wastewater by immobilized microalgae with different freezing and thawing times

As can be seen from table 10, the removal effect of the immobilized microalgae frozen and thawed for the first time on organic matters in the starch wastewater is the best, because after one to four times of cyclic freezing and thawing, the compression modulus and the relative crystallinity of the 10% PVA hydrogel are changed, the mechanical properties are changed, meanwhile, part of thalli are damaged to a certain extent by multiple times of cyclic freezing and thawing under a low-temperature condition, the integral biomass of the thalli is reduced, and the removal rate of the organic matters in the starch wastewater is not obviously reduced in three times of freezing and thawing of the immobilized microalgae, which indicates that the immobilized microalgae can be repeatedly used after multiple times of freezing and thawing, but the fermentation efficiency is obviously reduced from the four times of cyclic freezing and thawing, so the number of times of the freezing and thawing can reach three times.

Claims

1. A microalgae immobilization method is characterized by comprising the following steps of:

s1, culturing microalgae

s2, immobilized microalgae

2. The method of immobilizing microalgae according to claim 1, wherein in step S1, the microalgae is chlorella pyrenoidosa, anabaena, and bifidobacterium minutissima;

3. The microalgae immobilization method according to claim 2, wherein the BG11 liquid medium comprises, in parts by weight: 100-200 parts of sodium nitrate, 3-5 parts of dipotassium hydrogen phosphate, 6-9 parts of magnesium sulfate, 3-4 parts of calcium chloride, 0.5-0.7 part of ammonium citrate, 0.5-0.7 part of ferric ammonium citrate, 0.1-0.2 part of disodium ethylene diamine tetraacetate, 1-3 parts of sodium carbonate and 100-300 parts of A5 culture solution.

4. The microalgae immobilization method according to claim 3, wherein the A5 culture solution comprises, in parts by weight: 2-3 parts of boric acid, 1.5-2 parts of manganese chloride, 0.2-0.3 part of zinc sulfate, 0.3-0.5 part of sodium molybdate, 0.05-0.1 part of copper sulfate and 0.03-0.09 part of cobalt nitrate.

5. The microalgae immobilization method according to claim 1, wherein in step S2, the preparation method of the ferroferric oxide nanoparticles is sequentially performed according to the following steps:

6. The microalgae immobilization method according to claim 5, wherein in step SI, the weight-to-volume ratio of sodium acetate to ethylene glycol is 2-3 g:20 mL;

heating in a water bath at the temperature of 35-45 ℃ for 20-40 min;

7. The method of claim 5, wherein in step S III,

and heating in a water bath at the temperature of 35-45 ℃ for 25-40 min.

8. The method for immobilizing microalgae according to any one of claims 5 to 7, wherein the heating and pressurizing are performed in a stainless steel high-temperature high-pressure reaction kettle with a polytetrafluoroethylene lining at a temperature of 180 to 230 ℃ in step SIV;