A composite material, its preparation and use

Abstract

The application belongs to the technical field of wastewater treatment, and particularly relates to a composite material and a preparation method and application thereof. The composite material takes a blended hydrogel of sodium alginate and polyvinyl alcohol as a matrix, zeolite molecular sieves, activated biochar and zero-valent iron particles are embedded in the matrix to form microspheres, and sulfate-reducing bacteria are immobilized on the surface of the microspheres. The composite material is directly added into an anaerobic reactor of mine water, the removal rate of sulfate is more than 92%, and heavy metals such as Cu, Pb and Cr in the mine water can be simultaneously precipitated, and the treatment efficiency and stability of the anaerobic system are significantly improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of wastewater treatment, and particularly relates to a composite material and a preparation method and application thereof. BACKGROUND

[0002] As the associated wastewater in the process of coal mining, the high sulfate pollution of mine water is one of the key problems restricting the ecological restoration of the mining area. If such wastewater is directly discharged, it will cause water acidification, pipeline corrosion, downstream eutrophication and many other problems, and the hydrogen sulfide generated by sulfate reduction is more toxic and explosive. Therefore, developing efficient, economical and stable mine water treatment technology is an urgent task in the field of environmental engineering at present.

[0003] Although the traditional physical and chemical treatment technology such as lime precipitation method can remove part of the sulfate, it has defects such as large sludge yield, high operation cost per ton of water, and inability to simultaneously degrade organic pollutants; ion exchange and membrane separation technology are limited in large-scale application and have high treatment cost due to serious membrane pollution and accelerated resin failure caused by the characteristics of high hardness and high suspended solids of mine water. Among many mine water treatment technologies, biological method is considered as the preferred path for mine water treatment due to its low cost and environmental friendliness, which relies on the reduction of SO4 2- to S 2- by sulfate reducing bacteria (SRB) under anaerobic conditions. However, the special water quality of high sulfate mine water poses three challenges to biological treatment: first, SRB metabolism requires sufficient electron donors, but the biodegradable organic matter (BOD5) in mine water is usually less than 100 mg / L, the carbon-sulfur ratio (C / S) is seriously imbalanced, which suppresses the activity of SRB and reduces the reduction rate; second, the reduction product S 2- is easy to form metal sulfides with heavy metals such as Fe 2+ , Zn 2+ in the water body, which can wrap the bacteria and cause biological passivation; third, SRB and methanogens (MPB) compete for limited electron donors in anaerobic reactors, which can easily lead to system acidification and collapse. At present, in order to strengthen the activity of SRB, external electron donors such as lactic acid and ethanol are often added, but the addition of traditional organic electron donors increases the operation cost and increases the risk of secondary pollution, which seriously limits the engineering promotion and application.

[0004] To solve the problem of electron donor and transfer efficiency, zero-valent iron (ZVI) has been widely concerned in wastewater treatment field as a cheap, easy-to-obtain and reductive material. ZVI can provide electrons directly to promote the reduction metabolism of SRB, and is considered as an ideal electron donor for the treatment of high-sulfate wastewater with SRB. However, there are many inherent defects in the application of ZVI in wastewater treatment: first, ZVI particles have a large specific gravity, which is easy to precipitate in the reactor, resulting in a decrease in contact area with wastewater and low utilization rate; second, a passivation film such as iron hydroxide and iron sulfide is easily formed on the surface of ZVI, which hinders the release of electrons and significantly reduces its long-term activity; third, the direct electron transfer efficiency between ZVI particles and SRB is not high, and the synergistic effect needs to be improved by using media or optimizing the contact mode. In recent years, patent CN105903436A discloses a zero-valent iron / biochar composite material, which can alleviate the aggregation of ZVI, but the material density is high and cannot naturally suspend or float, which requires additional mechanical stirring to maintain suspension, resulting in increased operating energy consumption; at the same time, this design does not integrate the SRB biological function, SO4 2- Reduction depends on slow chemical reduction path, limited efficiency improvement.

[0005] Immobilized microbial technology provides a new way for SRB enrichment. By embedding or adsorbing microorganisms in carrier materials, microorganisms can be protected from environmental impact, biomass increased, and active life extended. Commonly used immobilized carrier materials include sodium alginate, polyvinyl alcohol, and polyacrylamide. However, single hydrogel carrier often has problems such as low mechanical strength, high breakage rate, and large mass transfer resistance. More importantly, the carrier lacks built-in electron donors, and SRB metabolism relies on external carbon sources, which does not fundamentally solve the C / S imbalance problem. Moreover, the carrier is not conductive, and after combining with ZVI, it cannot effectively utilize the electrons provided by ZVI to build an electron path, which greatly limits the synergistic potential between ZVI and SRB. In addition, biological treatment of high-sulfate mine water also faces the challenge of bacterial population balance. For example, in anaerobic treatment, SRB and methanogens compete for electron donors; if the conditions are not stable or the donor is insufficient, the dominance of methanogens will reduce the efficiency of sulfide generation and affect the removal of sulfate and heavy metals. Moreover, the formation of biofilm, granulation process and type selection in the reactor will affect the system performance and stability, such as UASB and EGSB.

[0006] The current design bottlenecks of composite materials can be summarized as three points: first, high ZVI content improves the electron supply capacity but leads to sedimentation, and light carriers are difficult to load sufficient ZVI, which exists the contradiction between material density and suspension; second, the spatial separation of ZVI and SRB hinders the direct transmission of electrons, and SRB cannot efficiently utilize ZVI corrosion electrons, which exists the problem of synergistic failure of biological and non-biological components; third, the microporous structure is beneficial to the fixation of bacteria but limits the mass transfer, and the macroporous structure improves the mass transfer but reduces the amount of bacteria, which exists the problem of mismatch between carrier structure and function. These defects are reflected in engineering practice, which is manifested in the long start-up period, weak resistance to load impact, and low simultaneous removal rate of heavy metals when the biological reactor treats high-sulfate mine water.

[0007] In summary, the existing composite materials cannot effectively fix SRB, provide a stable microenvironment, improve its mechanical strength and mass transfer efficiency; more importantly, they cannot efficiently integrate the electron donor function of ZVI, promote the electron transfer between ZVI and SRB by constructing a conductive network, and have good suspension to adapt to different biological reactors, so as to realize the simultaneous, efficient and stable removal of high-sulfate and heavy metals. SUMMARY

[0008] In order to solve the above technical problems, the present application provides a composite material and its preparation method and application.

[0009] In order to solve the above problems, the technical scheme adopted by the present application is as follows:

[0010] A composite material, the composite material takes a blended hydrogel of sodium alginate and polyvinyl alcohol as a matrix, zeolite molecular sieve, activated biochar and zero-valent iron particles are embedded in the interior of the matrix to form microspheres, and sulfate-reducing bacteria are immobilized on the surface of the microspheres;

[0011] The mass of the zeolite molecular sieve, activated biochar and zero-valent iron is 9% to 11%, 7% to 9% and 4% to 6% of the total mass of the blended hydrogel respectively;

[0012] The method for forming microspheres is that the zeolite molecular sieve, activated biochar and zero-valent iron particles are embedded in the interior of the matrix to obtain a mixed colloid, the mixed colloid is solidified in a crosslinking agent solution to form microspheres, and the volume ratio of the crosslinking agent solution to the mixed colloid is 10 to 20:1;

[0013] The crosslinking agent solution is obtained by mixing equal volumes of a 4% calcium chloride solution and a 2% boric acid solution.

[0014] Preferably, the mass of the zeolite molecular sieve, activated biochar and zero-valent iron is 10%, 8% and 5% of the total mass of the blended hydrogel respectively.

[0015] Preferably, the volume ratio of the bacterial solution of the sulfate-reducing bacteria to the microspheres is 3-5:1.

[0016] The OD600 value of the sulfate-reducing bacteria is greater than 1.0.

[0017] The present application provides a composite material, which is a zero-valent iron / sulfate-reducing bacteria composite microsphere, and is a novel self-suspending material.

[0018] Constructing a hydrogel matrix colloid: Dissolve sodium alginate and PVA in deionized water and heat and stir to form a homogeneous colloid.

[0019] Uniform dispersion of functional materials: Add nanoscale sieve zeolite, activated biochar and zero-valent iron particles to the colloid, and realize multiphase homogenization through ultrasonic dispersion to obtain a mixed colloid.

[0020] Microsphere forming and solidification: Drop the mixed colloid into a crosslinking agent containing calcium ions and boric acid to form solidified microspheres.

[0021] Microsphere mechanical strength reinforcement: Freeze-thaw cycle treatment of the solidified microspheres.

[0022] Microbial immobilization: Load SRB in the pores of the microspheres to obtain an active composite material.

[0023] The specific synthesis steps of the above composite material are as follows:

[0024] Preparation of hydrogel matrix colloid

[0025] Select sodium alginate and polyvinyl alcohol, and add them to anaerobic deionized water in a dry weight ratio of 1:1.2, stir at 300 rpm in a 85-90℃ water bath for more than 2h, until a transparent, particle-free blended hydrogel is formed. Then naturally cool to 25℃ at room temperature for standby.

[0026] Preferably, the sodium alginate used is medical grade or food grade, with a viscosity of ≥2000cP and a molecular weight of 100000-200000Da.

[0027] Preferably, the polyvinyl alcohol used is completely alcoholized, with an alcoholization degree of 98% and a polymerization degree of 1700±50.

[0028] Preferably, the added sodium alginate and PVA account for 4%-5% and 5%-7% of the total mass of the colloid, respectively. At this ratio, the colloid viscosity at 25℃ is 4500±500mPa·s, taking into account the drop forming property and mechanical strength.

[0029] Preferably, the prepared sodium alginate / PVA blended hydrogel is placed under a vacuum pump for 10-15 minutes to remove air bubbles that may be mixed in the solution, thereby improving the density and uniformity of the subsequent microspheres.

[0030] Functional material dispersion

[0031] The zeolite molecular sieve, activated biochar, zero-valent iron, and Tween 80 are added to the blended hydrogel, and an ultrasonic instrument is used for dispersion under the conditions of a power of 200 W and a frequency of 40 kHz for 20 min to ensure uniform dispersion of the solid powders, thereby obtaining a mixed colloid. The mass of the zeolite molecular sieve, activated biochar, and zero-valent iron is 10%, 8%, and 5% of the total mass of the blended hydrogel, respectively.

[0032] Tween 80 can be used as a dispersant to help the functional materials to be more uniformly dispersed. ZVI particles are prone to agglomeration, and the dispersion process needs to be sufficient, and the dispersion time can be appropriately extended. During the dispersion process, if it is too viscous, 1-2 mL of oxygen-free deionized water can be slowly added for dilution.

[0033] Preferably, the zeolite molecular sieve has an average particle size of about 1 μm and a pore size of 0.5-5 nm, and the surface is mostly microporous and mesoporous.

[0034] Preferably, the biochar used is rice husk-based biochar prepared by pyrolysis of rice husk at 800°C in a nitrogen atmosphere.

[0035] Preferably, the activation method of the rice husk-based biochar is as follows: the biochar is soaked in a 1 mol / L hydrochloric acid solution for 24 h, washed repeatedly with deionized water until neutral, and then pyrolyzed at 600-800°C under N2 protection for 2 h to improve the electrical conductivity of the biochar, thereby obtaining activated biochar powder.

[0036] Preferably, the zeolite molecular sieve and activated biochar powder are placed in a vacuum drying oven at 105°C for 2 hours before use to remove moisture.

[0037] Preferably, the activated biochar powder is sieved through a 100-mesh sieve after drying to ensure the fineness and uniformity of the powder.

[0038] Preferably, the zero-valent iron used is micron-sized, with a particle size of about 2-5 μm.

[0039] Preferably, the zero-valent iron is activated with 0.1 mol / L HCl for 5 min to remove surface oxides before use under N2 protection to improve the electron release activity of the zero-valent iron.

[0040] Microsphere forming and curing

[0041] The mixed crosslinking agent solution is prepared by mixing equal volumes of 4% CaCl2 solution and 2% H3BO3 solution, and needs to be prepared immediately before use. The prepared mixed crosslinking agent solution is placed in a crosslinking tank, and a constant temperature water bath is used to control the crosslinking temperature to maintain 25°C. The crosslinking tank is placed on a magnetic stirrer, and the stirring speed is maintained at 150 rpm to 200 rpm to maintain a slight vortex to avoid disturbing the liquid surface flatness.

[0042] The prepared mixed colloids are injected into a syringe pump, and are dropped into the crosslinking agent solution through a 22G needle at a rate of 10 mL / min. The droplet is about 10 cm away from the liquid level. The crosslinking tank temperature is maintained at 25°C. After the microspheres are solidified for 30 min to 60 min, they are fished out with a screen. First, they are horizontally shaken and rinsed with 0.9% NaCl solution to remove calcium ions. Then, they are washed with deionized water for 5 to 8 times until the pH value of the washing liquid is close to neutral, so as to completely remove the residual crosslinking agent and unreacted ions on the surface of the material, and obtain wet microspheres.

[0043] The crosslinking temperature is controlled below 25°C to avoid PVA precipitation caused by high temperature. The dropping speed is controlled below 10 mL / min to avoid deformation or adhesion of the microspheres caused by too fast dropping speed. The microsphere solidification time can be extended to 2 h to ensure that the sodium alginate is fully crosslinked and solidified. If the crosslinking time is too short, the strength of the microspheres will be insufficient.

[0044] Microsphere mechanical strength strengthening

[0045] The cleaned wet microspheres are placed in a sterile tray, and are balanced in a 4°C constant temperature box for 1 h to 2 h. Then, the wet microspheres are taken out, and are immersed in deionized water in a sterile container. The container is placed in a -20°C environment for freezing for 16 h to 24 h. After the microspheres are completely frozen, they are thawed in deionized water at 25°C for 2 h to 4 h. The freezing-thawing cycle is repeated for 3 times.

[0046] The microspheres are first balanced in a 4°C environment for 1 h to 2 h, which helps to eliminate the internal temperature gradient of the microspheres and avoid cracking of the microspheres caused by direct freezing.

[0047] Preferably, the freezing rate is controlled at 1°C / min to 2°C / min to avoid cracking of the microspheres caused by rapid freezing.

[0048] Microbial immobilization

[0049] The mechanically strength-enhanced microspheres are washed with sterile normal saline for 2-3 times to remove possible contaminants, 100 mL of the washed microspheres are transferred into a sterile anaerobic culture bottle or a bioreactor, 300 mL of activated SRB bacterial solution is added, and then 150 mL of sterile anaerobic culture medium is added, and the mixture is cultured at 37 DEG C under a strict anaerobic environment at a low-speed oscillation of 100 rpm for 48 h; after the culture is completed, the microspheres are repeatedly washed with sterile normal saline for 3-5 times to remove the non-immobilized SRB and residual culture medium; and the obtained composite material after washing can be immediately used for wastewater treatment experiments or stored under anaerobic conditions at 4 DEG C for standby use.

[0050] Preferably, the high-efficiency desulfurization SBR composite bacterial system is enriched from an anaerobic treatment tank of mine water, 50 mL of sludge in the anaerobic tank is diluted 20 times, and then added into 1 L of anaerobic culture medium, and the mixture is cultured in a constant-temperature incubator at 37 DEG C for several weeks; when the culture medium has a strong rotten egg smell and the wet lead acetate test paper turns black, it is proved that the SBR enrichment is successful, and the obtained is the SBR stock solution.

[0051] Preferably, the anaerobic culture medium adopts Postgate C liquid culture medium.

[0052] Preferably, the SBR stock solution is repeatedly transferred and cultured for enrichment to increase the density of bacterial cells, and the activated SBR bacterial solution satisfies OD600>1.0.

[0053] Preferably, high-throughput sequencing is used to detect the types of SBR in the SBR bacterial solution, and the enriched SBR bacteria mainly include Desulfovibrio vulgaris, Desulfovibrio piger, Desulfovibrio desulfuricans and Desulfovibrio alaskensis, and the relative abundances of the four types of bacteria in the enrichment solution are 79.8%, 16.3%, 3.1% and 0.8% respectively. Desulfomicrobium 、 Desulfococcus 、 Desulfovibrio and Desulfosporosinus

[0054] Preferably, during the oscillation culture process of the microspheres in the bacterial solution, the fresh culture medium is replaced after 12 h.

[0055] Preferably, the whole preparation process needs to strictly follow the aseptic operation specification.

[0056] Preferably, the composite material is stored in sterile SRB culture medium or normal saline and stored under anaerobic conditions at 4 DEG C for standby use.

[0057] Preferably, the storage liquid is replaced regularly during the storage period, and the activity of the SRB is checked.

[0058] Compared with the prior art, the present application has the beneficial effects that:

[0059] ​For mine water or general industrial wastewater, SO4²⁻ concentration > 1000 mg / L is generally considered to be high concentration, and a composite material and a use method thereof are disclosed, which can be applied to the treatment of high-concentration sulfate wastewater of 2000 mg / L. The composite material is a zero-valent iron / sulfate-reducing bacteria composite microsphere, which is based on a sodium alginate and PVA blended hydrogel, uniformly disperses and embeds nano-sieve zeolite powder, activated biochar powder and ZVI in the inside, and immobilizes SRB. The microsphere density is 1.06 g / cm 3 1.14 g / cm 3 , has a multi-level pore structure, and can realize self-suspension. The zeolite provides a colonization micropore for the SRB, the biochar constructs an electrically conductive network to promote the electron transfer between the ZVI and the SRB, enhances the SRB activity, the ZVI can provide an electron donor for the reduction of sulfate in the wastewater, and realizes efficient and synergistic removal of sulfate in mine water.

[0060] The microsphere is directly added to an anaerobic reactor of mine water, the sulfate removal rate is more than 92%, and can simultaneously precipitate heavy metals such as Cu, Pb and Cr in the mine water, the treatment efficiency and stability of the anaerobic system are significantly improved, and the operation cost of mine water treatment is obviously reduced. The microsphere is particularly suitable for anaerobic biological enhancement treatment of high-concentration sulfate wastewater and biological treatment of mine water, and specific advantages are as follows:

[0061] (1) The composite material of the application organically combines the hydrogel network, zeolite, biochar and ZVI, constructs a multi-level pore structure system from micropores to macropores, greatly increases the specific surface area of the material, and also provides a broad habitat space and an efficient material exchange channel for the SRB, which helps to solve the problem of SRB activity inhibition caused by limited mass transfer of traditional carriers.

[0062] (2) The composite material of the application directionally combines the conductive medium biochar and ZVI particles, builds an “electron bridge” between the ZVI and the SRB, promotes the direct or indirect transfer of electrons generated by ZVI corrosion to the SRB, solves the problem of ZVI surface passivation, improves the electron utilization rate, and thus significantly enhances the sulfate-reducing metabolic activity of the SRB.

[0063] (3) The composite material of the application precisely regulates the component ratio and the microsphere structure, so that the microsphere density is close to water, realizes self-suspension fluidization of the microsphere in the reactor, and effectively solves the problems of reaction dead zones and low carrier utilization rate caused by ZVI particle precipitation.

[0064] (4) The composite material of the present application can restore biological activity after deactivation through regeneration treatment, and the removal rate of SO4²⁻ of the regenerated microspheres can reach more than 85% of the initial efficiency. The high regeneration capacity significantly improves the service life and utilization rate of the microspheres, thereby effectively reducing the actual operation cost.

[0065] (5) The composite material of the present application can combine S²⁻ generated in situ by the ZVI / SRB system with the ion exchange capacity of zeolite and the adsorption capacity of biochar, realize the simultaneous removal of SO4²⁻ and Cu²⁺, Zn²⁺ and other heavy metal ions, and solve the problem that single functional materials are difficult to cooperatively remove multiple pollutants.

[0066] (6) The composite material of the present application combines the sodium alginate-PVA crosslinked network with the freeze-thaw strengthening process, which can enhance the compressive strength of the microspheres and help to solve the problem of crushing failure caused by the poor mechanical strength of traditional immobilized carriers.

[0067] (7) The composite material of the present application combines the continuous electron release function of ZVI with the electron transfer network of biochar and flora, realizes the improvement of the SO4²⁻ reduction rate of SRB, and helps to solve the problem of unstable efficiency of traditional biological methods in treating high-concentration sulfate.

[0068] (8) The composite material of the present application can provide a physical barrier for SRB, protect it from the impact of water quality fluctuations and toxic substances, and help to improve the operation stability and impact load resistance of the mine water biological treatment system.

[0069] (9) The composite material of the present application combines the pH buffering capacity of zeolite with the metabolic environment of SRB, which can improve the acid resistance of the anaerobic system and help to solve the problem of competition inhibition between SRB and methanogens caused by low pH in the treatment of high-sulfate mine water. BRIEF DESCRIPTION OF DRAWINGS

[0070] Figure 1 It is a digital photo of self-suspended zero-valent iron / sulfate-reducing bacteria composite microspheres before drying.

[0071] Figure 2 It is a sectional view of the self-suspended zero-valent iron / sulfate-reducing bacteria composite microspheres.

[0072] Figure 3 It is the influence of different doses of composite microspheres on the removal of sulfate in the UASB reactor in Example 2.

[0073] Figure 4 It is the influence of 10% composite microspheres on the removal of sulfate in the SBR reactor in Example 3.

[0074] Figure 5Example 4: Effect of composite microspheres on sulfate removal compared with other existing materials.

[0075] Figure 6 Example 5: Effect of composite microspheres and regenerated microspheres on sulfate removal. DETAILED DESCRIPTION

[0076] The specific embodiments of the present application are described in detail below, but it should be understood that the scope of the present application is not limited to the specific embodiments. Based on the examples in the present application, all other examples obtained by those of ordinary skill in the art without making creative efforts are within the scope of the present application. The experimental methods described in the embodiments of the present application are conventional methods unless otherwise specified.

[0077] Example 1

[0078] A preparation process of a self-suspending zero-valent iron / sulfate-reducing bacteria composite microsphere, specifically comprising:

[0079] Preparation of hydrogel matrix colloid: medical-grade sodium alginate and polyvinyl alcohol (PVA) with an alcoholysis degree of 98% and a polymerization degree of 1700±50 are added to deoxygenated deionized water in a dry weight ratio of 1:1.2 to obtain a mixed solution, so that the final mass concentrations of sodium alginate and PVA account for about 4.6% and 5.7% of the total mass of the colloid, respectively. The mixed solution is placed in a constant temperature water bath at 85°C and continuously stirred at a speed of 300 rpm for 2 hours until a transparent, homogeneous colloid without visible particles is formed. Then, the colloid is naturally cooled to 25°C at room temperature, and then the prepared colloid is placed under a vacuum pump to remove internal bubbles for 12 minutes to obtain a blended hydrogel of sodium alginate and polyvinyl alcohol.

[0080] Dispersion of functional materials: zeolite molecular sieves with an average particle size of about 1 μm, which are pre-dried in a vacuum drying oven at 105°C for 2 hours, activated biochar powder screened through a 100-mesh sieve, micron-sized ZVI particles with a particle size of 2 μm~5 μm activated in 0.1 mol / L hydrochloric acid solution for 5 minutes and dried under nitrogen protection, and Tween 80 are added to the blended hydrogel in small amounts and multiple times. The dosages of zeolite molecular sieves, activated biochar, zero-valent iron, and Tween 80 are 10%, 8%, 5%, and 0.1% of the total mass of the blended hydrogel, respectively. The activated biochar is prepared by immersing rice husk in 1 mol / L hydrochloric acid solution for 24 hours, washing to neutral, and then pyrolyzing at 800°C under nitrogen protection for 2 hours. After adding all the functional materials, an ultrasonic disperser with a power of 200 W and a frequency of 40 kHz is used to ultrasonically treat the mixed colloid for 20 minutes to ensure that all solid powders are homogeneously dispersed in the blended hydrogel to form a functionalized mixed colloid ready for dripping.

[0081] Molding and solidification of microspheres: A freshly prepared crosslinking agent solution made of equal volume of 4% calcium chloride solution and 2% boric acid solution was placed in a crosslinking tank, and the temperature in the tank was precisely controlled at 25°C by a constant temperature water bath, and magnetic stirring was carried out at a speed of 180 rpm. The functionalized mixed colloid prepared above was loaded into a syringe pump, and was added at a rate of 10 mL / min through a 22G needle into the crosslinking agent solution, the end of the needle was kept about 10 m above the liquid surface of the crosslinking agent, and after solidification in the crosslinking agent for 45 min, it was fished out with a screen, first shaken and rinsed with 0.9% sodium chloride solution on a horizontal shaking table, and then repeatedly washed with a large amount of deionized water for 6-8 times until the pH value of the washing liquid was neutral, to obtain wet microspheres. The volume of the crosslinking agent solution must be much larger than the volume of the mixed colloid added, to ensure that each droplet can instantaneously and fully contact the crosslinking agent to complete the solidification reaction, and to avoid adhesion between the microspheres. According to the performance of the finally prepared material, the volume ratio of the crosslinking agent solution to the functionalized mixed colloid is 10-20:1, and the ratio of 10:1 is the minimum requirement to ensure the continuity of production and the quality of the microspheres, and the material prepared at a ratio of 20:1 has the best performance.

[0082] Mechanical strength reinforcement of microspheres: The wet microspheres washed clean in the previous step were laid flat on a sterile tray, first placed in a 4°C constant temperature box for 1.5 hours, then immersed in deionized water and frozen in a -20°C environment for 20 hours, then moved to a 25°C environment for 3 hours, and the freezing-thawing cycle was repeated for a total of 3 times, to significantly strengthen the mechanical strength and porous structure of the microspheres.

[0083] Immobilization of microorganisms: The microspheres treated by three freezing-thawing cycles and washed with sterile physiological saline for 3 times were taken, and 100 mL of the microspheres were transferred to a sterile anaerobic culture bottle. 300 mL of SRB active bacteria solution with an optical density OD600 value greater than 1.0 after enrichment culture was added to the bottle, high-throughput sequencing was used to detect the types of SBR in the SBR bacteria solution, and the enriched SBR bacteria were mainly Desulfomicrobium , Desulfococcus , Desulfovibrio and Desulfosporosinus , and the relative abundance in the enrichment solution was 79.8%, 16.3%, 3.1% and 0.8% respectively; the volume of the bacteria solution was greater than 3 times the volume of the microspheres, and Postgate C sterile anaerobic culture medium was supplemented. The culture bottle was placed in a constant temperature shaking incubator at 37°C and 100 rpm, and was cultured under strict anaerobic environment and low speed vibration for 48 hours. After the culture was completed, the microspheres were repeatedly washed with sterile physiological saline for 4 times to completely remove the surface non-immobilized SRB bacteria and residual culture medium, to obtain composite microspheres, and the composite microspheres were self-suspended zero-valent iron / sulfate-reducing bacteria composite microspheres.

[0084] Figure 1 The digital image of the composite microspheres before drying is shown. The diameter of the microspheres is 2mm-3mm. Figure 2 The cross-sectional view of the composite microspheres under a scanning electron microscope is shown. Thus, the finished product, the self-suspended zero-valent iron / sulfate-reducing bacteria composite microspheres, is obtained. The microspheres can be used immediately or stored under anaerobic conditions at 4℃ for later use.

[0085] Example 2

[0086] The composite microspheres prepared in Example 1 were used to treat simulated high-sulfate mine well water in a laboratory-scale upflow anaerobic sludge bed (UASB) reactor as follows:

[0087] The simulated high-sulfate mine well water was prepared as follows: The SO4²⁻ concentration in the simulated high-sulfate mine well water was 2000mg / L, and the SO4²⁻ was provided by anhydrous sodium sulfate. Peptone was used as the electron donor and carbon source for the SRB. The peptone was added to provide a chemical oxygen demand (COD) of 6000mg / L, so that the C / S ratio of the simulated influent was 3:1. In addition, Cu²⁺, Zn²⁺, and Pb²⁺ were added to the influent at a concentration of 5mg / L each. The Cu²⁺ was provided by copper sulfate pentahydrate, the Zn²⁺ was provided by zinc sulfate heptahydrate, and the Pb²⁺ was provided by lead nitrate. The pH value of the influent was adjusted to 7.0 using sodium bicarbonate. The UASB reactor used in the experiment was made of organic glass, with a total effective volume of 15L and a height-diameter ratio of 12:1. The reactor was heated by wrapping heating tape around the outside, and the reaction temperature was accurately controlled at 37℃.

[0088] During the startup phase of the reactor, 0.75L, 1.5L, and 2.25L of the composite microspheres prepared in Example 1 were added to the bottom of the UASB reactor, respectively, so that the filling rate reached 5%, 10%, and 15% of the effective volume of the reactor. At the same time, to accelerate the startup of the system, 1L of high-activity anaerobic granular sludge taken from the anaerobic digester of a kitchen waste solid waste treatment plant was additionally inoculated into all of the UASB reactors. The specific methanogenic rate of the high-activity anaerobic granular sludge was 3860mL CH4 / (gVSS·d), -4720mL CH4 / (gVSS·d). The high-activity anaerobic granular sludge had a clear outline and was close to spherical in shape, with a black or dark brown color and a mechanical strength of about 80g / mm-120g / mm. It was not easily broken under moderate-strength stirring, and the settling velocity was 65m / h-80m / h.

[0089] Subsequently, the prepared simulated high sulfate mine water was continuously pumped from the bottom of the reactor by using a peristaltic pump, and the hydraulic retention time (HRT) of the reactor was controlled to be 24 hours. During the entire operation period, the pH value in the reactor was monitored in real time by using an online pH probe, and was maintained in the range of 7.0 to 7.5 by using an automatic acid and alkali adding system. During the continuous operation for 60 days, water samples were taken from the water outlet at the top of the reactor at a fixed time every day, and were analyzed. The sulfate concentration was determined by using ion chromatography, and the heavy ion concentration in the water sample was determined by using atomic absorption spectrophotometry.

[0090] After the reactor was operated for about 22 days, it entered a stable period, at which time the composite microspheres formed a uniform suspended fluidized layer in the reaction zone, the suspension rate was greater than 96%, and there was no cracking or deformation phenomenon; the sulfate concentration of the effluent was relatively stable, and the concentration was about 120 mg / L to 150 mg / L, the sulfate removal rate of the reactor after stabilization was always maintained to be more than 90%; at the same time, the heavy ion concentration in the effluent was less than 0.2 mg / L, and the removal rate was as high as more than 95%, the effluent was clear, and there was no black sulfide heavy metal suspended matter, and the precipitate was analyzed by XRD, which confirmed that all the precipitates in the reactor contained CuS, ZnS and PbS. During the entire operation period, there was no acidification phenomenon caused by the accumulation of volatile fatty acids in each reactor, and the effluent pH was stably maintained between 7.0 and 8.5; during the operation period, the biogas production of each reactor was relatively stable, indicating that the ecosystem in the reactor was relatively stable, the electron donor was sufficient, and there was no imbalance of the system caused by the competition of SRB and MPB for electron donors.

[0091] After the microspheres in each reactor were taken out, scanning electron microscope detection showed that the SRB formed a dense biofilm in the pores of the microspheres, and energy spectrum analysis showed that Fe 0 generated by oxidation 2+ / Fe 3+ signal, confirming that the electron transfer continued; the above results all indicated that the composite microspheres achieved efficient and stable purification of high sulfate and heavy metal contaminated mine water.

[0092] The results are shown in Table 1. Figure 3As shown, the removal rate of sulfate in the reactor with 15% composite microspheres was the highest, reaching 93.80%, and the sulfate concentration in the effluent was 124.03 mg / L. The removal rate of sulfate in the reactor with 10% composite microspheres was only slightly lower than that with 15%, reaching 93.25%. The removal rate of sulfate in the reactor with 5% composite microspheres was 91.02%. Considering the cost saving and sulfate removal effect, the optimal dosage of microspheres was 10%. The composite microspheres were recovered after the treatment, washed with sterile normal saline, and stored in an anaerobic environment at 4°C. The mechanical strength of the microspheres remained good, and they could be reused after regeneration.

[0093] Example 3

[0094] The composite microspheres prepared in Example 1 were used to treat simulated high-sulfate mine water in a laboratory-scale sequencing batch reactor (SBR). The specific process was as follows:

[0095] The simulated high-sulfate mine water was prepared with a SO42- concentration of 2000 mg / L and protein peptone as the electron donor and carbon source for SRB, with a COD of 6000 mg / L. In addition, Cu2+, Zn2+, and Pb2+ were added to the influent at a concentration of 5 mg / L, and sodium bicarbonate was used to adjust the pH of the influent to neutral. The SBR reactor used in the experiment was made of organic glass, with a total effective volume of 15 L and a height-diameter ratio of 4:1 to accommodate batch processing. The reactor was wrapped with heating tape to accurately control the reaction temperature at 37°C.

[0096] During the startup phase of the reactor, 1.5 L of composite microspheres prepared in Example 1 were added to the SBR reactor to achieve a filling rate of 10% of the effective volume of the reactor. At the same time, to accelerate system startup, 1 L of high-activity anaerobic granular sludge from the anaerobic digester of a kitchen waste solid waste treatment plant was inoculated into all SBR reactors, with a total solid concentration of about 20 g / L in the SBR reactor. Subsequently, the prepared simulated high-sulfate mine water was pumped into the reactor in batch mode using a peristaltic pump, with each operation cycle including a 0.5-hour influent phase, a 22-hour reaction phase, a 1-hour settling phase, a 0.5-hour drainage phase, and a 0-hour idle phase, with a controlled HRT of 24 hours. During the entire operation period, the pH value in the reactor was monitored in real time by an online pH probe, and an automatic acid and alkali addition system was used to maintain the pH value in the range of 7.0 to 7.5. The blank SBR reactor was identical to the other reactors except that no microspheres were added.

[0097] During the 60-day continuous operation, samples were taken from the effluent at the end of each day's drainage phase and analyzed. The results showed that the SBR reactor, limited by its own reactor conditions, had poor technical adaptability and was prone to sludge bulking and acidification, resulting in poor treatment performance, generally inferior to that of the UASB reactor. The control group without microspheres showed severe acidification on the 11th day of startup, with the pH dropping to around 5.2, requiring continuous addition of sodium bicarbonate to maintain system stability. In contrast, the experimental group with composite microspheres showed no significant acidification, maintaining a pH above 6.2. During the 60-day operation, the sulfate removal rate in the blank control group remained low, approximately 32-45%, with the effluent heavy metal concentration decreasing to 3.5 mg / L; the experimental group with composite microspheres achieved an effluent sulfate concentration of approximately 630 mg / L. Figure 4 As shown, the sulfate removal rate was approximately 66-74%; the heavy metal ion concentrations were all below 0.5 mg / L, with a removal rate >90%, and no obvious black sulfide heavy metal suspended solids were observed in the effluent; the composite microspheres formed a uniform suspended fluidized layer in the reaction zone, with a suspension rate >96%, and no obvious breakage or deformation. This example demonstrates that the composite microspheres in the SBR not only improved the sulfate treatment efficiency by approximately 40 percentage points compared to the control group, but also effectively alleviated acidification problems and shortened the start-up period.

[0098] Example 4

[0099] The effects of composite microspheres on enhancing the treatment of mine water are compared with those of several other existing materials, as detailed below:

[0100] To further verify the technical superiority of the composite microspheres used in Example 2, four additional UASB reactors identical to those used in Example 2 with a composite microsphere dosage of 10% were set up and designated as R2 group, R3 group, R4 group, and R5 group, respectively. The experimental group under the conditions of Example 2 was designated as R1 group. Parallel comparative experiments were conducted using identical simulated high-sulfate mine water and operating parameters, including basic sludge inoculum amount, temperature, pH, and HRT.

[0101] Among them, group R1 was the experimental group in which 10% of the composite microspheres were added to the UASB reactor;

[0102] Group R2 was a blank control group without the addition of composite microspheres;

[0103] Group R3 involved adding micron-sized zero-valent iron powder, in an amount equal to that contained in the R1 microspheres, to the UASB reactor at a dosage of approximately 10 g / L, to verify the independent role of ZVI.

[0104] R4 group is to UASB reactor daily dosing and R1 microspheres initial immobilization equal amount of activated in Postgate C medium SRB bacteria liquid, OD600 = 1.2, the amount of bacteria liquid is about 1.5L, to verify the role of free SRB;

[0105] R5 group is to UASB reactor 1.5L of blank microspheres carrier, the blank system is prepared according to the method of example 1, but the zero-valent iron particles are not added in the step, and the immobilization of microorganisms is not carried out at last, to verify the physical effect of the microsphere carrier.

[0106] After 60 days of continuous operation, the treatment effect of each control group is evaluated. Figure 5 And table 1 shows that for sulfate removal rate, R2 group is about 93.5%, R1 group is 67.2%, R3 group is 79.8%, R4 group is 74.2%, R5 group is 81.4%, R2 group is significantly higher than R1 group, R3 group, R4 group and R5 group; The removal rates of Cu²⁺, Zn²⁺ and Pb²⁺ in R2 group are all above 95%, and the removal rates of heavy metals in R1 group, R3 group, R4 group and R5 group are about 71%, 75%, 70% and 81%; The suspension rate of microspheres in R2 group is greater than 96%, the suspension rate of zero-valent iron in R3 group is only 46% due to precipitation, and it is extremely easy to lose in effluent, and additional supplement is needed to maintain the concentration of ZVI in the reactor during operation; The SRB loss rate in R4 group effluent is greater than 85%, and the SRB loss rate in R1 group effluent is only about 10%.

[0107] The sulfide production is calculated by iodometric method HJ / T 60-2000, the iron dissolution amount is calculated by o-phenanthroline spectrophotometry GB / T 5750.6-2006, the electron utilization rate of R1 group is about 86.7%, and the utilization rate of R3 group is increased by about 55%; The precipitate of R3 group is detected by XRD to show strong FeOOH characteristic peak, and the surface of R1 group microspheres is detected by XPS to show Fe 0 Peak, which indicates that the hydrogel carrier of the composite microspheres effectively prevents the direct contact of ZVI with water, so that the passivation rate of iron is significantly reduced; After SEM detection, it is shown that the SRB in R1 group forms a dense biofilm in the pores of the microspheres, and the SRB in R4 group is mostly lost with the effluent.

[0108] Comparing the results of each control group with the results of R1 group shows that the composite microspheres of the present application are significantly superior to the blank system, the system of adding functional components alone and the system of adding only physical carriers in terms of sulfate removal rate, heavy metal removal efficiency and long-term operation stability, which fully confirms the synergistic effect and superior technical performance among the components of the composite microspheres.

[0109] Example 5

[0110] Regeneration process of composite microspheres and determination of sulfate removal in mine water

[0111] Obtaining failed composite microspheres: select the composite microspheres in example 2 after running for 60 days, whose sulfate removal rate is reduced to less than 70% of the initial efficiency or whose heavy metal removal rate is significantly reduced, as failed microspheres. The failed microspheres are taken out of the UASB reactor, repeatedly washed with deionized water for 3 times to remove the loose sludge and residual wastewater attached to the surface, and then stored in an anaerobic environment at 4℃ for standby.

[0112] Acid washing and activation of microspheres: the washed failed composite microspheres are put into a sodium citrate solution at a solid-liquid ratio of 1:10 by wet weight. The concentration of the sodium citrate solution used is 0.3 mol / L, which needs to be prepared on site. The sodium citrate solution should be deoxygenated in advance to maintain an anaerobic environment. Subsequently, the mixture is placed in a constant temperature oscillator and oscillated at 30℃ and 120 rpm for 30 minutes to dissolve the metal sulfide precipitate accumulated on the surface and pores of the microspheres, expose the fresh ZVI surface, restore its chemical activity, and remove part of the passivation layer. After oscillation, the microspheres are separated from the sodium citrate solution and repeatedly washed with anaerobic deionized water for 5-8 times until the pH value of the washing liquid approaches neutral to completely remove the residual sodium citrate and dissolved metal ions.

[0113] Recovery of the biological activity of the composite microspheres: First, prepare a high-activity SRB bacterial solution, and then add the composite microspheres after acid washing and activation to the bacterial solution at a solid-liquid ratio of 1:5 by wet weight, and add sterile Postgate C liquid anaerobic culture medium to provide the nutrients required for the growth of SRB. Subsequently, the mixture of the composite microspheres and the SRB bacterial solution is placed in a strictly anaerobic environment at 37°C and 100 rpm, and is cultured for 48 hours with low-speed shaking. During the culture process, the fresh culture medium is replaced every 12 hours to ensure sufficient nutrients and remove metabolic products, thereby promoting the reattachment and reproduction of SRB inside and on the surface of the microspheres and recovering their biological activity. After the culture is completed, the microspheres are repeatedly rinsed with sterile normal saline for at least 3 to 6 times to remove the non-immobilized SRB and residual culture medium. The regenerated composite microspheres after cleaning are immediately used in subsequent performance determination experiments or are stored under anaerobic conditions at 4°C for standby use. The added sterile Postgate C liquid anaerobic culture medium needs to meet two requirements, one is to completely immerse the composite microspheres to ensure that all the composite microspheres are completely immersed in the liquid so that the SRB on the inner and outer surfaces of the microspheres can uniformly contact the nutrients, and the other is to leave enough headspace, generally 20% to 30% of the total volume, to maintain good gas-liquid exchange during shaking culture and prevent liquid from splashing out. In the present application, 100 mL of microspheres are treated, and a 1L anaerobic culture bottle is selected, and the volume of the microspheres and the bacterial solution is about 600 mL, and in order to reserve enough headspace, the volume of the added sterile Postgate C culture medium is about 150 mL.

[0114] Referring to the reactor conditions of Example 2, a separate 15L UASB reactor is set up. According to the conditions in Example 2, 1.5L of regenerated composite microspheres are added to the bottom of the reactor, and the same simulated high-sulfate mine well water as in Example 2 is used. The UASB reactor is started and continuously operated for about 30 days. The sulfate concentration, total sulfide concentration, COD, and heavy metal ion concentration of the effluent are monitored daily. The sulfate removal rate after treatment of the regenerated microspheres is compared with the sulfate removal rate of the initial microspheres in Example 2.

[0115] The results are shown in Table 1. Figure 6 As shown in Table 1, through the regeneration treatment, the chemical activity and biological activity of the composite microspheres can be significantly recovered. Through the regeneration treatment, it is expected that the chemical activity and biological activity of the composite microspheres can be significantly recovered. The sulfate removal rate of the regenerated composite microspheres in the treatment of the simulated high-sulfate mine well water can reach more than 90% of the initial efficiency. This will prove that the composite microspheres of the present application have good renewability, can reduce the operating cost, prolong the service life of the material, and provide a sustainable solution for practical engineering applications.

[0116] Table 1: Concentration values of heavy metals in the effluent of each experimental group in Examples 2-5

[0117]

[0118] It is to be understood that the numerical ranges recited in the claims are intended to include every integer value within the range and any fraction of the values within the range. In other words, the numerical ranges are intended to include every value from the lower limit to the upper limit, inclusive of the lower and upper limits, as well as any intervening incremental values. Preferred embodiments of the application are described herein.

[0119] Although preferred embodiments of the application have been described, those skilled in the art will recognize that additional modifications and variations can be made thereto without departing from the spirit and scope of the application. It is therefore intended that the appended claims encompass all such modifications and variations as fall within the scope of the application.

[0120] Obviously, many modifications and variations of the present application are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims and their equivalents, the application can be practiced otherwise than as specifically described.

Claims

1. A method of preparing a composite material, characterized by, The composite material takes a blended hydrogel of sodium alginate and polyvinyl alcohol as a matrix, and a microsphere formed by embedding a zeolite molecular sieve, activated biochar and zero-valent iron particles in the matrix, and a surface immobilized sulfate-reducing bacteria; The preparation method comprises the following steps: The zeolite molecular sieve, activated biochar and zero-valent iron particles are added into the blended hydrogel for dispersion to obtain a mixed colloid; the mass of the zeolite molecular sieve, activated biochar and zero-valent iron is 10%, 8% and 5% of the total mass of the blended hydrogel, respectively; The mixed colloid is added into a crosslinking agent solution for solidification to form the microsphere; after the microsphere is formed, mechanical strength of the microsphere is strengthened; during the strengthening, the microsphere is first placed at 4 DEG C for equilibrium, then immersed in deionized water and frozen, then thawed, and the freezing-thawing cycle is repeated for 3 times; the volume ratio of the crosslinking agent solution to the mixed colloid is 10-20:1; the crosslinking agent solution is obtained by mixing equal volumes of a 4% calcium chloride solution and a 2% boric acid solution; The sulfate-reducing bacteria are added into the microsphere; the volume ratio of a bacterial solution of the sulfate-reducing bacteria to the microsphere is 3-5:1; the OD600 value of the sulfate-reducing bacteria is greater than 1.0; the sulfate-reducing bacteria are cultured in an anaerobic environment for 48 h to obtain a composite microsphere, i.e. the composite material.

2. The production method according to claim 1, characterized by, The activated biochar is prepared by pyrolysis of rice husks at 600 DEG C-800 DEG C under nitrogen.

3. Use of the composite material produced by the method of claim 1 in wastewater treatment, characterized in that, The wastewater is sulfate wastewater.

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