CN101475931B - Preparation of embedding immobilized effective microorganism gel bead - Google Patents

Abstract

A preparation method for embedding and immobilizing effective microbial gel beads relates to a method for immobilizing microbial cells for sewage biological denitrification, in particular to a method using polyvinyl alcohol and sodium alginate as embedding agents to Calcium chloride and boric acid are used as cross-linking agents, and shell powder is used as an additive to entrap effective microorganisms. The invention provides a preparation method of the embedded and immobilized effective microbial gel beads which can not only effectively solve the shortcomings in the preparation and use of the gel beads, but also use the effective microorganisms as embedded bacteria to effectively improve the biological denitrification effect. Mix the embedding agent and additives evenly, dissolve them in water, dissolve completely and mix evenly, then cool down to below 40°C, mix with the centrifuged effective microbial concentrated bacterial solution, stir, and then add to the cross-linking agent to form gel beads .

Description

A preparation method for embedding and immobilizing effective microbial gel beads

technical field

The invention relates to a microbial cell immobilization method for biological denitrification of sewage, in particular to a method using polyvinyl alcohol and sodium alginate as embedding agents, calcium chloride and boric acid as crosslinking agents, and shell powder as embedding agents. Additives, the method of embedding effective microorganisms (Effective Microorganisms, referred to as EM).

Background technique

Microbe embedding and immobilization technology is a relatively new technology in the field of wastewater biological treatment. It encloses microorganisms in natural polymer polysaccharides or synthetic polymer gels, thereby immobilizing microorganisms. Compared with the ordinary activated sludge method, the embedding and immobilization technology has the following advantages: preventing microbial loss, high microbial concentration in the reactor, anti-toxin and impact load, good settling performance, and conducive to solid-liquid separation, etc.

The technical key of the embedding method is to choose a suitable embedding agent, mainly including agar, polyacrylamide (ACAM), gelatin, sodium alginate (CA), chitin and polyvinyl alcohol (PVA). Studies have shown that the strength of agar is poor, polyacrylamide gel is toxic to organisms, and the internal structure of gelatin is dense, but its mass transfer performance is poor ([1] Duan Mingfeng, Wu Weixia, Xiao Junxia, Li Lianghong. Using immobilized cell technology to treat wastewater Research progress [J]. Oil and gas field environmental protection, 2004, 14 (3): 17-20; [2] CarberyJB. Model of algalbacterial clay wastewater treatment system [J]. Water Science and Technology, 1992, 26 (7-8) ); In contrast, calcium alginate (CA) and polyvinyl alcohol (PVA) gels have better mechanical strength and mass transfer properties, are non-toxic to organisms, and have good resistance to biodegradation, so they are more suitable for immobilization. Cell carrier ([3] Jiang Yuhong, Huang Xia, Yu Yuxin. Comparison of several immobilized cell carriers [J]. Environmental Science, 2001, 14(2)).

Alginate is an intracellular product of brown algae, which consists of two different types of monosaccharides, namely 1,4-β-D-mannuronic acid (M) and 1,4-α-L-gulose Alkyd acid (G). Alginate cannot form thermoreversible gels, usually by adding divalent ions, such as Ca ²⁺ , to its sodium salt solution to form a gel network by replacing Na ⁺ with Ca ²⁺ . The properties of the gel are related to the type of divalent cations introduced and sodium alginate (mainly the composition ratio of two monosaccharides). Divalent cations have a great influence on the mechanical strength of the gel. The strength order of the gel formed by the metal ions of the second main group of the periodic table in the sodium alginate salt is as follows: Ba ²⁺ >Sr ²⁺ >Ca ^{2 +} >> Mg ²⁺ . Using sodium alginate gel to immobilize microorganisms is not only safe, fast, simple to prepare, mild in reaction conditions, and low in cost, but also suitable for the immobilization of most microorganisms ([4] Men Xuehu, Li Yanfeng, Zhou Lincheng. Polyvinyl alcohol carrier The preparation and application research progress of [J]. Gansu Science Journal, 2004, 16 (3): 30-35).

Compared with the polyvinyl alcohol-boric acid method, the alginate method has better physical strength and excellent mass transfer performance, but its adsorption performance is not as good as that of polyvinyl alcohol gel balls. The polyvinyl alcohol-boric acid method only uses polyvinyl alcohol and boric acid to crosslink It is difficult to form a ball, and it is easy to form a floc, and after forming a ball, the mechanical strength of the ball is poor. Although the survival time of polyvinyl alcohol gel is longer than that of alginate embedding method, sometimes due to incomplete cross-linking of polyvinyl alcohol gel, a small amount of organic carbon components are dissolved out, and it takes a long time for polyvinyl alcohol gel to harden and fix The conditions required for bio-immobilization are relatively complex ([5] Liu Lei. Embedded materials in bio-immobilization technology [J]. Water purification technology, 2005, 24 (1)).

Compared with other embedding and immobilization methods, the polyvinyl alcohol-boric acid embedding immobilization method has the advantages of high mechanical strength, high aeration resistance, good biodegradability, low cost and long service life, but it also appears in its application. some problems. Polyvinyl alcohol is a highly viscous substance, and it reacts slowly with boric acid. When the droplets collide, they will stick together and gradually dissolve into groups, that is, the polyvinyl alcohol pellets have a very strong tendency to agglomerate, so that It is difficult for polyvinyl alcohol gel to form a ball. When polyvinyl alcohol and boric acid are reacted and fixed, the three hydroxyl groups on the boric acid are only partially reacted, and hydrophilic -OH remains on the polymer gel formed after the reaction, making the immobilized beads There is a lot of water swelling in the application, and with the increase of the use time, the strength is greatly weakened, which is extremely unfavorable in practical application. There are also some problems in the alginate embedding process. When there are high concentrations of K ⁺ , Mg ²⁺ , phosphate and other monovalent metal ions, the structure of the calcium alginate gel will be destroyed. In addition, since the pore size of the calcium alginate gel network is too large, the enzyme may leak out of the network, so it is not suitable for enzyme immobilization.

In addition, adding an appropriate amount of activated carbon, CaCO ₃ powder, Ca(OH) ₂ powder, iron powder, and SiO ₂ powder as additives in the embedding agent can improve the properties of the gel beads and improve the strength of the immobilized beads. .

Biochemical denitrification includes three reaction processes: ammonification reaction, nitrification reaction and denitrification reaction. In the effluent of secondary treatment of urban sewage, nitrogen mainly exists in the form of ammonia nitrogen, while the tertiary treatment requires a denitrification process mainly including nitrification. In addition, due to the high concentration of ammonia nitrogen in the wastewater of many industries such as iron and steel, oil refining, chemical fertilizer, inorganic chemical industry, ferroalloy, glass manufacturing, meat processing and feed production. Therefore, nitrification, as an important step in the biochemical denitrification process, is of great significance for effectively removing ammonia nitrogen in wastewater and reducing the pollution of ammonia nitrogen emissions to water bodies.

The nitrification reaction is completed in two processes under the action of two autotrophic bacteria. First, ammonia nitrogen is converted into nitrite by nitrifying bacteria, and then nitrite is oxidized into nitrate by nitrifying bacteria. The reaction equation is as follows:

From the above reaction stoichiometry, it can be seen that under the condition of sufficient oxygen, every 1 mol of NH ₄ ⁺ -N removed produces 2 mol of H ⁺ , that is, every 1 g of NH ₄ ⁺ -N removed needs to consume 7.14 g of alkalinity (calculated as CaCO ₃ count).

Because the nitrification reaction needs to consume a large amount of alkalinity, when the alkalinity in the sewage is insufficient and the ammonia nitrogen load is relatively high, the pH value of the mixed solution in the treatment device will drop below 6.5, which will reduce the nitrification reaction rate and inhibit the nitrifying bacteria. Therefore, alkalinity calculation is required during engineering design. At present, the main way to supplement the alkalinity is to add NaHCO ₃ or NaOH, which will undoubtedly increase the operation cost and the difficulty of management.

As a kind of marine garbage, shells are produced in a huge amount in my country's coastal areas every year. As for the processing method of shells, the form of stacking in the open air is generally adopted, which has caused great pressure on the environment in coastal areas. Although there are many kinds of shells with different shapes and colors, their chemical composition is similar, mainly including calcium carbonate which accounts for 95% of the whole shell and a small amount of conchiin. According to reports, after the mussel shells produced in Yantai, Shandong were dried and crushed into powder, the elemental composition was measured with an atomic absorption spectrophotometer, and the mass fractions of the constant elements K, Na, Ca, and Mg were: 0.01%, 0.35%, and 15.1%, respectively. and 0.17%, the mass fractions of trace elements are (mg/kg): Fe 206.0, Zn 453.3, Se 0.85, I 2.3, Cu 10.7. Due to different sources, other shells have slightly different quality scores ([6] Li Jinzhi. Comprehensive Utilization of Shells [J]. Journal of Huaihai Institute of Technology. 2001, 10 (Special Issue): 22-23). Shell powder can gradually dissolve with the decrease of pH in wastewater, provide alkalinity for the biological denitrification process, and can effectively improve the effect of microbial denitrification.

The biological denitrification of wastewater has high requirements on process conditions in the actual operation process, but the setting of process conditions in many sewage treatment plants cannot meet the requirements of biological denitrification of sewage, especially some small industrial sewage treatment plants , due to its water quality characteristics and operating conditions do not meet the requirements, it is difficult to meet the discharge requirements for the degradation of pollutants. Too short and the pH value does not meet the denitrification requirements.

Effective microorganisms are a multifunctional biological agent developed by Professor Higa Teruo of the University of Ryukyu in Japan. It mainly includes 5 categories (photosynthetic bacteria, lactic acid bacteria, yeast bacteria, Gram-positive actinomycetes and filamentous bacteria of fermentation system) and 10 genera of more than 80 kinds of microorganisms, so that they can coexist and form A powerful functional group that enhances the physiological mobility of an object. Studies have shown that EM can effectively remove COD, nitrogen, phosphorus and other pollutants in wastewater, and is more efficient than traditional activated sludge methods. However, since the EM bacteria solution is a liquid, when it is directly added to treat sewage, the EM bacteria group lacks a carrier and is easy to be lost with the effluent, so that its removal rate of pollutants is not high. The age period of nitrifying bacteria is relatively long, which is not conducive to the enrichment and growth of denitrifying bacteria in EM, and is not conducive to the removal of nitrogen.

Contents of the invention

The purpose of the present invention is to overcome the difficulties in forming gel beads and slow hardening during the embedding process, as well as the defects of gel beads strength, service life, and easy water absorption and swelling after embedding, and the biological denitrification effect of wastewater is relatively low. To overcome the poor problem, provide an embedding immobilized effective microbial gel that can not only effectively solve the shortcomings of the preparation and use of gel beads, but also use effective microorganisms (EM) as embedded bacteria, which can effectively improve the effect of biological nitrogen removal. Preparation method of glue pellets.

The technical solution adopted by the present invention to solve its technical problems is:

Mix the embedding agent and additives evenly, dissolve them in water, dissolve completely and mix evenly, then cool down to below 40°C, mix with the centrifuged effective microorganism (EM) concentrated bacterial solution, stir, and then add to the cross-linking agent to form a coagulate Glue balls.

The embedding agent is polyvinyl alcohol and sodium alginate, the additive is shell powder, and the crosslinking agent is saturated boric acid solution containing calcium chloride.

The mass fraction of described polyvinyl alcohol is preferably 10% (W/V _{embedding agent} ), the mass fraction of sodium alginate is preferably 1% (W/V _{embedding agent} ), and the mass fraction of shell powder is preferably 0.2% (W/V _{embedding agent} ), the mass fraction of calcium chloride in the saturated boric acid solution containing calcium chloride is preferably 3% (W/V _{crosslinking agent} ).

The water temperature for dissolving in water is preferably 80-90°C.

The temperature of the cross-linking agent solution was lowered to 4°C before use, and stirred with a magnetic stirrer when making pellets. The mass fraction of polyvinyl alcohol and sodium alginate as embedding agent and the mass fraction of calcium chloride saturated boric acid solution as crosslinking agent can better solve the problem of agglomeration of gel beads and enhance the formation of gel. Ball ability, and maintain good mass transfer performance. Based on the principle of treating waste with waste, shell powder is added as an additive to the embedding agent, which can improve the strength, swelling, service life and other properties of the gel beads. In the process of biological denitrification of wastewater, the gel beads can also continuously provide alkalinity due to the dissolution of shell powder, and the gaps generated after dissolution also create favorable conditions for the beads to adsorb pollutants in wastewater; It also provides a way out for the treatment and disposal of marine shells. In order to solve the problem of poor biological denitrification effect, EM is used as the embedded bacteria to fix the microbial cells inside the gel beads to prevent their loss, and provide a relatively stable anaerobic area for the denitrification bacteria to play a role EM at its best.

The beneficial effect of the present invention is that it enhances the ball-forming ability of the gel ball during preparation, improves the strength and service life of the ball, and can significantly improve the biological denitrification effect of the waste water, and it is also a good solution for the treatment and disposal of shells. Provide a new way.

Description of drawings

Figure 1 The denitrification effect of PVA pellets embedded in EM. In Fig. 1, the abscissa is operation cycle/time, and the ordinate is NH ₄ ⁺ -N removal rate/%.

Fig. 2 The change curve of effluent NH ₃ -N concentration and turbidity with time. In Figure 2, the abscissa is time/h, the left ordinate is effluent NH ₃ -N concentration/mg·L ^-1 , the right ordinate is effluent turbidity/NTU; ▲ is the concentration curve, and ■ is the turbidity curve.

Figure 3 Comparison of denitrification effects of PVA pellets with different formulations. In Figure 3, the abscissa is the operation cycle/time, and the ordinate is the removal rate of NH ₃ -N/%; ▲ is the centrifuge with shells and EM; △ is the centrifuge without shells and EM; □ is the rejuvenation of EM without shells liquid.

Figure 4 Comparison of denitrification effects of PVA pellets with different embedding amounts of EM bacteria solution. In Fig. 4, the abscissa is operation cycle/time, and the ordinate is NH ₃ -N removal rate/%; ▲10, ◆30, ■50, ●80.

Detailed ways

1. Preparation of EM bacterial solution

Preparation of EM rejuvenation solution: prepare EM expansion solution according to volume ratio, EM-1:molasses:water=3:3:94. Sealed storage at room temperature, after the pH value drops below 3.5 and has a sweet and sour smell, the EM rejuvenation solution can be obtained.

Preparation of EM centrifugal liquid: Centrifuge the EM rejuvenation liquid prepared in the previous step at a speed of 5000 r/min for 20 min, discard the supernatant, and collect the concentrated EM cells enriched at the bottom of the centrifuge tube. The EM concentrated cells obtained after centrifugation per 10mL of EM rejuvenation liquid contain the amount of bacteria equivalent to 10mL of EM rejuvenation liquid.

2. Preparation of Shell Powder

Pulverize the oyster shells with a traditional Chinese medicine grinder and pass through an 80-mesh sieve to obtain shell powder.

3. Preparation of Immobilized Pellets

Preparation of embedding agent: mix polyvinyl alcohol, sodium alginate and shell powder evenly and dissolve in water at 80-90°C. During the dissolution process, cover the surface of the holding container and stir from time to time. After it is completely dissolved, cool to below 40°C, and mix with 30% (EM rejuvenation liquid/V _{embedding agent corresponding to the amount of V bacteria} ) EM concentrated cells to make the final concentrations of PVA, sodium alginate and shell powder respectively 10% (W/V _{embedding agent} ), 1% (W/V _{embedding agent} ) and 0.2% (W/V _{embedding agent} ).

Preparation of cross-linking agent: Dissolve CaCl ₂ with a concentration of 3% (W/V _{cross-linking agent} ) in saturated boric acid solution, and cool down to about 4°C.

Immobilization: Use a syringe to drop the well-mixed embedding agent into the cross-linking agent from a height of about 10cm, and stir the cross-linking agent with a magnetic stirrer. The embedding agent is cross-linked with the cross-linking agent to form small balls with a diameter of about 3 mm. The immobilized beads were immersed in the cross-linking agent and stored in a refrigerator at 4°C for about 24 hours to harden. Wash 3 times with normal saline before use.

Figure 1 shows the removal rate of ammonia nitrogen effluent of the SBR treatment system after 8 cycles of continuous operation.

After being treated with EM-embedded gel beads (hereinafter referred to as A beads), the removal rate of ammonia nitrogen showed an overall upward trend, and the removal rate of ammonia nitrogen rose from the initial 10.5% to 86.3% after 8 cycles of operation. After a period of recovery and adaptation, the buried microorganisms gradually showed the ability to degrade ammonia nitrogen.

The turbidity generated by the dissolution of gel beads will affect the removal effect of ammonia nitrogen. The relationship between the removal effect of the gel beads without any microorganisms on the removal of ammonia nitrogen and the change of effluent turbidity with time is shown in Figure 2.

After the gel beads were adsorbed in the simulated ammonia nitrogen wastewater for 0.5h, the concentration of ammonia nitrogen in the water sample decreased from 61.7mg/L to 38.4mg/L, and the turbidity increased from 1.43NTU to 43.47NTU. In the following 14 hours, the concentration of ammonia nitrogen in the water samples fluctuated within the range of 40-50mg/L; the turbidity generally showed an upward trend, but the rising speed was relatively slow, and the concentration of ammonia nitrogen remained in a relatively stable range. Before the turbidity affects the concentration of ammonia nitrogen in the effluent, the adsorption capacity of the gel beads to the ammonia nitrogen in the waste water is about 1-2 mg (NH ₃ -N)/g (gel beads). After 14 hours of shaking, the turbidity of the effluent began to increase significantly, and at 24 hours the turbidity rose to 128, and the concentration of ammonia nitrogen dropped to 2.77mg/L. It can be seen that the gel beads dissolve with the extension of the shaking time, the turbidity of the water sample gradually increases, and the concentration of ammonia nitrogen begins to decrease significantly. The concentration of ammonia nitrogen in the effluent has a close relationship with the turbidity. To sum up, the gel beads have a certain adsorption effect on ammonia nitrogen in wastewater, and the colloid produced by its dissolution also has an adsorption effect on ammonia nitrogen, so that the gel beads without embedding EM also have a significant effect on the removal of ammonia nitrogen.

Adding a certain amount of shell powder to the embedding agent to increase the strength of the gel beads and improve the denitrification effect is helpful; use EM centrifugation liquid and rejuvenation liquid (the amount is equivalent to 10mL EM rejuvenation liquid) for comparison, to determine The possible effects of molasses on the properties of gel beads and the activity of EM after embedding were compared. 4 different pellets were thus prepared, and the formulations of different gel pellets are shown in Table 1.

Table 1

During the preparation process of pellets, pellets A, C, and D can all be well formed into spherical shapes, and pellets B are extremely irregular in shape. After hardening for 24 hours, the hardness of A ball was significantly better than that of C and D balls, indicating that the shell powder was helpful to improve the hardness of the gel ball during preparation; the appearance of A and C balls was pure white, while B and D balls The appearance is light brown, indicating that the pellets embedded with EM rejuvenation fluid contain molasses. After 3 cycles of operation, the balls of B were all broken and lost with the effluent. After 6 cycles of continuous operation, the removal effects of three different pellets A, C, and D on ammonia nitrogen are shown in Figure 3.

In the first operation cycle, the removal effects of the three kinds of gel beads on ammonia nitrogen were not very good, and the adsorption effect of the beads was the main one. The beads of A were slightly better than those of C and D, and the beads of D did not Because it contains molasses, it shows better biological activity, which shows that molasses has no obvious help in protecting the activity of microorganisms in EM when the pellets are prepared, and will also introduce other nutrients into the water, and cause negative effects on the physical indicators such as the strength of the pellets. Impact. By the 6th cycle, the ammonia nitrogen removal rate of the A pellet with the best effect has reached 91.1%, indicating that adding shell powder to the embedding agent is beneficial to microbial denitrification; the denitrification effect of the C pellet also maintained a good Stability, indicating that embedding EM centrifugate is beneficial to improve the strength and denitrification performance of gel beads. The removal rates of ammonia nitrogen by the three kinds of pellets finally reached more than 75%.

During the running process, the three kinds of gel balls A, C, and D all dissolved and swelled to a certain extent, making the effluent water turbid; a large amount of foam was generated on the water surface of the reactor, and the volume of the balls expanded to twice the original, and the appearance changed from the initial The white and beige gradually become off-white. In the later stage of operation, the three kinds of pellets were slightly broken and lost with the effluent. The toughness of pellet A is better than that of pellets C and D, and the breakage rate is lower, indicating that shell powder can effectively improve the physical properties of gel pellets such as strength and toughness.

One of the advantages of the microbial embedding and immobilization method is that it can achieve a higher microbial concentration in the reactor. Make 4 kinds of gel pellets with different embedding amounts of EM bacteria, add 10mL EM centrifugation solution to each 100mL embedding agent, the bacteria amount is equivalent to 10, 30, 50, 80mL EM rejuvenation solution (hereinafter referred to as A, B, respectively). , C, D small ball). After nine cycles of continuous operation, the denitrification effects of the four pellets are shown in Figure 4.

In the first three cycles, the denitrification effect of pellet D is the best, pellets B and C are closer, and pellet A is less effective. The larger the amount of bacteria, the better the removal effect of ammonia nitrogen. With the increase of the operating cycle, the denitrification effects of the four pellets are gradually approaching, and the denitrification effect of the B pellets is equivalent to that of the D pellets. In the later stage of operation, the denitrification effect of pellet D gradually deteriorates, while the effect of pellet B is the best, because pellets with a large amount of bacteria will be broken due to the significant microbial activity after a period of use The higher the rate, the lower the concentration of microorganisms in the reactor after the loss, and the lower the removal rate. It can be seen that from the perspective of economy and treatment effect, the embedding amount of EM bacteria liquid is not the better, and 30mL (bacteria amount of EM rejuvenation liquid)/100mL (embedding agent) is the optimal ratio.

Claims (7)

1. A preparation method for embedding and immobilizing effective microbial gel beads, which is characterized in that the embedding agent and additives are mixed uniformly, dissolved in water, completely dissolved and mixed uniformly, then cooled to below 40°C, and mixed with centrifuged The effective microbial concentrated bacterial solution is mixed, stirred, and then added to the cross-linking agent to form gel beads; The embedding agent is polyvinyl alcohol and sodium alginate; The additive is shell powder. 2. a kind of preparation method of embedding and immobilizing effective microbial gel beads as claimed in claim 1, is characterized in that described cross-linking agent is the saturated boric acid solution containing calcium chloride. 3. A preparation method for embedding and immobilizing effective microbial gel beads as claimed in claim 1, wherein the mass fraction of said polyvinyl alcohol is 10% W/V _{embedding agent} . 4. A preparation method for embedding and immobilizing effective microbial gel beads as claimed in claim 1, wherein the mass fraction of sodium alginate is 1% W/V _{embedding agent} . 5. A preparation method for embedding and immobilizing effective microbial gel beads as claimed in claim 1, wherein the mass fraction of shell powder is 0.2% W/V _{embedding agent} . 6. a kind of preparation method of embedding and immobilizing effective microbial gel beads as claimed in claim 2, is characterized in that the massfraction of the calcium chloride in the saturated boric acid solution containing calcium chloride is 3%W/V _{crosslinking agent} . 7. The preparation method of a kind of embedded immobilized effective microbial gel beads as claimed in claim 1, characterized in that the water temperature for dissolving in water is 80-90°C. the

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