Composite material as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of wastewater treatment, and particularly relates to a composite material as well as a preparation method and application thereof. According to the composite material, blended hydrogel of sodium alginate and polyvinyl alcohol is used as a matrix, zeolite molecular sieves, activated charcoal and zero-valent iron particles are embedded into the matrix to form microspheres, sulfate reducing bacteria are immobilized on the surfaces of the microspheres, the composite material is directly added into a mine water anaerobic reactor, the sulfate radical removal rate exceeds 92%, and the sulfate radical removal rate exceeds 92%. Heavy metals such as Cu, Pb and Cr in the mine water can be synchronously precipitated, and the treatment efficiency and stability of the anaerobic system are remarkably 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. The concentration of sulfate in typical mine water generally reaches 2000 mg / L to 5000 mg / L, far exceeding the limit value of 600 mg / L specified in the Coal Industry Pollutant Discharge Standard (GB 20426-2006). 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.

[0003] Although the traditional physicochemical treatment technology such as lime precipitation method can remove part of the sulfate, it has defects such as large sludge production, 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, and its core 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 easily wrap the bacteria and cause biological passivation; third, SRB and methanogens (MPB) compete for limited electron donors in the anaerobic reactor, 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 ability 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 transfer 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: A composite material, 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 interior of the matrix to form microspheres, and sulfate-reducing bacteria are immobilized on the surface of the microspheres; The mass of the zeolite molecular sieves, 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; The method for forming the microspheres is that the zeolite molecular sieves, 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 the microspheres, and the volume ratio of the crosslinking agent solution to the mixed colloid is 10 to 20:1; The crosslinking agent solution is obtained by mixing equal volumes of a 4% calcium chloride solution and a 2% boric acid solution.

[0010] Preferably, the mass of the zeolite molecular sieves, activated biochar and zero-valent iron is 10%, 8% and 5% of the total mass of the blended hydrogel respectively.

[0011] Preferably, the volume ratio of the bacterial solution of the sulfate-reducing bacteria to the microspheres is 3 to 5:1.

[0012] The sulfate-reducing bacteria have an OD600 value greater than 1.0.

[0013] This invention provides a composite material, which is a novel self-suspending material consisting of zero-valent iron / sulfate-reducing bacteria composite microspheres. The preparation method of the composite material is as follows: Constructing the hydrogel matrix colloid: Sodium alginate and PVA were dissolved in deionized water and heated and stirred to form a homogeneous colloid.

[0014] Uniform dispersion of functional materials: Nano-sieve zeolite, activated biochar and zero-valent iron particles are added to the colloid, and multiphase homogenization is achieved by ultrasonic dispersion to obtain a mixed colloid.

[0015] Microsphere molding and curing: The mixed colloid is dripped into a crosslinking agent containing calcium ions and boric acid, and cured to form cured microspheres.

[0016] Mechanical strength enhancement of microspheres: The solidified microspheres are subjected to a freeze-thaw cycle treatment.

[0017] Microbial immobilization: SRB is loaded into the pores of microspheres to obtain an active composite material.

[0018] The specific synthesis steps of the above composite material are as follows: Preparation of hydrogel matrix colloids Sodium alginate and polyvinyl alcohol were selected and added to deionized water at a dry weight ratio of 1:1.2. The mixture was placed in a water bath at 85-90℃ and stirred continuously at 300 rpm for more than 2 hours until a transparent, particle-free blended hydrogel was formed. Then, it was allowed to cool naturally to 25℃ at room temperature for later use.

[0019] Preferably, the sodium alginate used is medical grade or food grade, with a viscosity ≥2000 cP and a molecular weight of 100,000-200,000 Da.

[0020] Preferably, the polyvinyl alcohol used is a fully hydrolyzed type with a degree of hydrolysis of 98% and a degree of polymerization of 1700±50.

[0021] 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°C is 4500±500mPa·s, which balances drop-forming properties and mechanical strength.

[0022] Preferably, the prepared sodium alginate / PVA blend hydrogel is placed under a vacuum pump and evacuated for 10 to 15 minutes to remove any air bubbles that may be mixed in the solution, thereby improving the density and uniformity of the subsequent microspheres.

[0023] Functional material dispersion The zeolite molecular sieve, activated biochar, zero-valent iron and Tween 80 are added into the blending hydrogel, and an ultrasonic instrument disperser is used to ultrasonically treat for 20 min under the condition of power 200 W and frequency 40 kHz to ensure uniform dispersion of the solid powder, to obtain a mixed colloid, and the mass of the zeolite molecular sieve, activated biochar and zero-valent iron is respectively 10%, 8% and 5% of the total mass of the blending hydrogel.

[0024] The Tween 80 can be used as a dispersant to help the functional materials to be more uniformly dispersed. The ZVI particles are prone to agglomeration, and the dispersion process needs to be sufficient, and the dispersion time can be appropriately prolonged. During the dispersion process, if it is too thick, 1 mL-2 mL of oxygen-free deionized water is slowly added for dilution.

[0025] Preferably, the zeolite molecular sieve has an average particle size of about 1 μm, a pore size of 0.5 nm-5 nm, and a surface mainly composed of micropores and mesopores.

[0026] Preferably, the biochar used is a rice husk-based biochar prepared by pyrolysis of rice husk at 800 ℃ under nitrogen atmosphere.

[0027] Preferably, the activation method of the rice husk-based biochar is as follows: soaking in 1 mol / L hydrochloric acid solution for 24 h, washing repeatedly with deionized water until neutral after removing most of the ash, and then pyrolyzing at 600 ℃-800 ℃ under N2 protection for 2 h to improve the electrical conductivity of the biochar, so that the obtained biochar is the activated biochar powder.

[0028] Preferably, the zeolite molecular sieve and the activated biochar powder are placed in a vacuum drying oven at 105 ℃ for 2 hours before use to remove water.

[0029] Preferably, the activated biochar powder is sieved through a 100-mesh sieve after drying to ensure the fineness and uniformity of the powder.

[0030] Preferably, the zero-valent iron used is micron-sized, and has a particle size of about 2 μm-5 μm.

[0031] 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.

[0032] Microsphere forming and curing The mixed crosslinking agent solution is prepared by mixing equal volumes of 4% CaCl2 solution and 2% H3BO3 solution, and needs to be prepared on site 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 be maintained at 25 ℃. The crosslinking tank is placed on a magnetic stirrer, and the stirring speed is maintained at 150 rpm-200 rpm to maintain a slight vortex to avoid disturbing the liquid surface flatness.

[0033] The prepared mixed colloid is injected into a syringe pump and dropped into the crosslinking agent solution through a 22G needle at a rate of 10 mL / min, with the liquid drop being about 10 cm from the liquid level, and the crosslinking tank temperature being maintained at 25°C. The microspheres are solidified for 30-60 min and then fished out with a screen. First, they are horizontally shaken and rinsed with 0.9% NaCl solution to remove calcium ions, and then they are washed with deionized water for 5-8 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, thereby obtaining wet microspheres.

[0034] The crosslinking temperature is controlled below 25°C to avoid PVA precipitation caused by excessively high temperature. The dropping speed is controlled below 10 mL / min to avoid deformation or adhesion of the microspheres caused by excessively fast dropping speed. The solidification time of the microspheres can be extended to 2 h to ensure sufficient crosslinking and solidification of sodium alginate, and excessively short crosslinking time will result in insufficient strength of the microspheres.

[0035] Mechanical strength reinforcement of microspheres The cleaned wet microspheres are laid flat in a sterile tray, taken out after being balanced in a 4°C constant temperature box for 1-2 h, then placed in a sterile container and immersed in deionized water, and frozen at -20°C for 16-24 h to ensure complete freezing of the microspheres, and then thawed in deionized water at 25°C for 2-4 h. The freezing-thawing cycle is repeated for 3 times.

[0036] The microspheres are first balanced in a 4°C environment for 1-2 h, which helps to eliminate the internal temperature gradient of the microspheres and avoid cracking of the microspheres caused by direct freezing.

[0037] Preferably, the freezing rate is controlled at 1-2°C / min to avoid cracking of the microspheres caused by rapid freezing.

[0038] Microbial immobilization The mechanically reinforced microspheres are washed with sterile normal saline for 2-3 times to remove possible contaminants; 100 mL of the washed microspheres are transferred to 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. The culture is carried out at 37°C, 100 rpm, and strict anaerobic environment, with low-speed oscillation 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. The obtained composite material can be immediately used for wastewater treatment experiment or stored under 4°C anaerobic conditions for standby use.

[0039] Preferably, the SBR composite bacteria system for efficient desulfurization is enriched from the anaerobic treatment tank of mine water, 50 mL of sludge diluted 20 times from the anaerobic tank is added into 1 L of anaerobic culture medium, and 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.

[0040] Preferably, the anaerobic culture medium adopts Postgate C liquid medium.

[0041] Preferably, the SBR stock solution is repeatedly transferred and cultured for enrichment, so that the density of the bacteria is increased, and the activated SBR bacterial solution satisfies OD600>1.0.

[0042] Preferably, high-throughput sequencing is used to detect the types of SBR in the SBR bacterial solution, and the enriched SBR bacteria are mainly Desulfomicrobium 、 Desulfococcus 、 Desulfovibrio and Desulfosporosinus , and the relative abundance in the enrichment solution is 79.8%, 16.3%, 3.1% and 0.8% respectively.

[0043] Preferably, the microspheres are subjected to oscillation culture in the bacterial solution, and the fresh culture medium is replaced after 12 hours.

[0044] Preferably, the whole preparation process needs to strictly follow the aseptic operation specification.

[0045] Preferably, the composite material is stored in sterile SRB culture medium or physiological saline, and stored at 4 DEG C under anaerobic conditions for standby.

[0046] Preferably, the storage solution is replaced regularly during the storage period, and the activity of SRB is checked.

[0047] Compared with the prior art, the beneficial effects of the present application are: For mine water or general industrial wastewater, SO4 2- Concentration > 1000 mg / L is usually considered as high concentration, and the present application discloses a preparation and use method of a composite material, 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 takes sodium alginate and PVA blended hydrogel as the matrix, uniformly disperses and embeds nano-sieve zeolite powder, activated biochar powder and ZVI in the inside, and immobilizes SRB. The density of the microsphere is 1.06 g / cm 3 ~1.14 g / cm 3, with a multi-level pore structure, can realize self-suspension. Among them, the zeolite provides a micro-pore for the SRB to settle, the biochar constructs an electrically conductive network to promote the electron transfer between the ZVI and the SRB, and the ZVI can provide an electron donor for the reduction of sulfate in wastewater, thereby realizing the efficient and synergistic removal of sulfate in the mine water.

[0048] The microspheres can be directly added to the anaerobic reactor of the mine water, and the removal rate of sulfate is more than 92%, and the heavy metals such as Cu, Pb and Cr in the mine water can be simultaneously precipitated, the treatment efficiency and stability of the anaerobic system are significantly improved, and the operation cost of the mine water treatment is obviously reduced. The microspheres are particularly suitable for the anaerobic biological enhancement treatment of high-concentration sulfate wastewater and the biological treatment of mine water, and the specific advantages are as follows: (1) The composite material of the application organically combines the hydrogel network, zeolite, biochar and ZVI, constructs a multi-level pore structure system from micro-pore to macro-pore, greatly increases the specific surface area of the material, and provides a broad habitat and 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.

[0049] (2) The composite material of the application directionally combines the conductive medium biochar with the ZVI particles, builds an "electron bridge" between the ZVI and the SRB, promotes the direct or indirect transfer of the electrons generated by the corrosion of the ZVI to the SRB, solves the problem of passivation of the ZVI surface, improves the electron utilization rate, and thereby significantly enhances the sulfate reduction metabolic activity of the SRB.

[0050] (3) The composite material of the application precisely regulates the component ratio and the microsphere structure, so that the density of the microspheres is close to that of water, the microspheres realize self-suspension fluidization in the reactor, and the problems of reaction dead zone and low carrier utilization rate caused by the precipitation of ZVI particles can be effectively solved.

[0051] (4) The composite material of the application can restore the biological activity through regeneration treatment after deactivation, and the removal rate of SO4 2- by the regenerated microspheres can be 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.

[0052] (5) The composite material of the application can combine the ion exchange capacity of the zeolite and the adsorption capacity of the biochar with the S 2- generated in situ by the ZVI / SRB system, realize the simultaneous removal of SO4 2- and heavy metal ions such as Cu 2+ and Zn 2+ , and solve the problem that a single functional material is difficult to synergistically remove multiple pollutants.

[0053] (6) The composite material of the present application combines the sodium alginate-PVA cross-linked network with the freeze-thaw strengthening process, which can enhance the compression strength of the microspheres and help to solve the problem of breakage and failure of traditional immobilized carriers caused by poor mechanical strength.

[0054] (7) The composite material of the present application combines the continuous electron release function of ZVI with the electron transfer network of biochar and microbial flora, realizes the reduction of SO4 2- by SRB, and helps to solve the problem of unstable efficiency of traditional biological methods in treating high-concentration sulfate.

[0055] (8) The composite material of the present application provides a physical barrier for SRB, protects them from the impact of water quality fluctuations and toxic substances, and helps to improve the operation stability and impact load capacity of the mine water biological treatment system.

[0056] (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 helps to solve the problem of competition and inhibition of SRB and methanogens caused by low pH in the treatment of high-sulfate mine water. BRIEF DESCRIPTION OF DRAWINGS

[0057] Figure 1 It is a digital photo of self-suspended zero-valent iron / sulfate-reducing bacteria composite microspheres before drying.

[0058] Figure 2 It is a sectional view of self-suspended zero-valent iron / sulfate-reducing bacteria composite microspheres.

[0059] Figure 3 It is the effect of adding different doses of composite microspheres on the removal of sulfate in the UASB reactor in Example 2.

[0060] Figure 4 It is the effect of adding 10% composite microspheres on the removal of sulfate in the SBR reactor in Example 3.

[0061] Figure 5 It is the effect of composite microspheres and other existing materials on the removal of sulfate in Example 4.

[0062] Figure 6 It is the effect of composite microspheres and regenerated microspheres on the removal of sulfate in Example 5. DETAILED DESCRIPTION

[0063] 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 creative labor 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.

[0064] Example 1 A preparation process of a self-suspending zero-valent iron / sulfate-reducing bacteria composite microsphere, specifically comprising: 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 and 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 are 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.

[0065] Dispersion of functional materials: zeolite molecular sieves with an average particle size of about 1 μm, which have been 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 uniformly dispersed in the blended hydrogel to form a functionalized mixed colloid ready for dripping.

[0066] Molding and solidification of microspheres: A crosslinking agent solution prepared by mixing equal volumes of a 4% by mass calcium chloride solution and a 2% by mass 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 performed at a speed of 180 rpm. The functionalized mixed colloid prepared above was loaded into a syringe pump, and was added dropwise to the crosslinking agent solution at a rate of 10 mL / min through a 22G needle, with the end of the needle being kept about 10 m above the liquid surface of the crosslinking agent. After solidification in the crosslinking agent for 45 min, the microspheres were fished out with a screen, and were first rinsed with a 0.9% sodium chloride solution on a horizontal shaker, and then were repeatedly washed with a large amount of deionized water for 6 to 8 times until the pH 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 to be 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 10:1 to 20:1, and a ratio of 10:1 is the minimum requirement to ensure the continuity of production and the quality of the microspheres, and a ratio of 20:1 is optimal for the performance of the prepared material.

[0067] Mechanical strength reinforcement of microspheres: The wet microspheres cleaned in the previous step were laid flat on a sterile tray, and were first placed in a 4°C constant-temperature box for 1.5 hours, and then were immersed in deionized water and frozen in a -20°C environment for 20 hours, and were then moved to a 25°C environment for thawing for 3 hours, and the freezing-thawing cycle was repeated for a total of 3 times, to significantly reinforce the mechanical strength and porous structure of the microspheres.

[0068] Immobilization of microorganisms: The microspheres that had been 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 an 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 abundances in the enrichment solution were 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 a strict anaerobic environment with low-speed shaking 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.

[0069] Figure 1The digital image shown is the composite microspheres before drying, the diameter of the microspheres is 2mm~3mm. Figure 2 The cross-sectional view of the composite microspheres prepared under the scanning electron microscope. Thus, the finished product, the self-suspended zero-valent iron / sulfate-reducing bacteria composite microspheres, is obtained, which can be used immediately or stored under anaerobic conditions at 4℃ for future use.

[0070] Example 2 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 reactor, abbreviated as UASB, as follows: Preparation of simulated high-sulfate mine well water: The SO4 2- concentration in the simulated high-sulfate mine well water was 2000mg / L, and the SO4 2- was provided by anhydrous sodium sulfate, and peptone was used as the electron donor and carbon source for SRB. The addition of peptone provided a chemical oxygen demand (COD) of 6000mg / L, resulting in a C / S ratio of 3:1 in the simulated influent. In addition, Cu 2+ , Zn 2+ , Pb 2+ , Cu 2+ was provided by copper sulfate pentahydrate, Zn 2+ was provided by zinc sulfate heptahydrate, and Pb 2+ was provided by lead nitrate. Sodium bicarbonate was used to adjust the pH of the influent to 7.0. 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 wrapped with heating tape to heat and accurately control the reaction temperature at 37℃.

[0071] 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, to achieve a filling rate of 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 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 stirring, with a settling velocity of 65m / h~80m / h.

[0072] Subsequently, a peristaltic pump continuously pumped the prepared simulated high-sulfate mine water into the reactor from the bottom, controlling the hydraulic residence time (HRT) to be 24 hours. Throughout the operation, the pH value within the reactor was monitored in real time using an online pH probe and maintained within the range of 7.0 to 7.5 using an automatic acid and alkali addition system. During the 60-day continuous operation, samples were taken daily from the effluent outlet at the top of the reactor and analyzed. The sulfate concentration was determined using ion chromatography, and the concentration of heavy ions in the water samples was determined using atomic absorption spectrophotometry.

[0073] After approximately 22 days of operation, the reactors entered a stable phase. At this point, the composite microspheres formed a uniform suspended fluidized layer in the reaction zone, with a suspension rate greater than 96%, and no cracking or deformation was observed. The effluent sulfate concentration was relatively stable, ranging from approximately 120 mg / L to 150 mg / L, and the sulfate removal rate remained above 90% after reactor stabilization. Simultaneously, the heavy ion concentration in the effluent was below 0.2 mg / L, with a removal rate exceeding 95%. The effluent was clear, free of black sulfide heavy metal suspensions. XRD analysis of the precipitates confirmed the presence of CuS, ZnS, and PbS in all reactors. Throughout the operation, no acidification due to the accumulation of volatile fatty acids occurred in any reactor, and the effluent pH remained stable between 7.0 and 8.5. During operation, the biogas production in each reactor was relatively stable, indicating a stable ecosystem within the reactors, sufficient electron donors, and no system imbalance caused by competition for electron donors between SRB and MPB.

[0074] After the microspheres were removed from each reactor, scanning electron microscopy revealed that SRB formed a dense biofilm within the pores of the microspheres. Energy dispersive spectroscopy analysis showed that Fe2+ was present on the microspheres. 0 Fe generated by oxidation 2+ / Fe 3+ The signal confirms that electron transfer continues; all the above results indicate that the composite microspheres achieve efficient and stable purification of mine water contaminated with high sulfate and heavy metals.

[0075] The results are as follows Figure 3As shown, the removal rate of sulfate in the reactor with 15% composite microspheres is the highest, reaching 93.80%, and the sulfate concentration in the effluent is 124.03 mg / L. The removal rate of sulfate in the reactor with 10% composite microspheres is only slightly lower than that with 15%, reaching 93.25%. The removal rate of sulfate in the reactor with 5% composite microspheres is 91.02%. Considering the cost saving and sulfate removal effect, the optimal dosage of microspheres is 10%. The composite microspheres are recovered after treatment, washed with sterile normal saline, and stored in an anaerobic environment at 4°C. The mechanical strength of the microspheres remains good, and they can be reused after regeneration.

[0076] Example 3 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 is as follows: Preparation of simulated high-sulfate mine water: The SO4 2- concentration in the simulated high-sulfate mine water was 2000 mg / L, and proteose peptone was used as the electron donor and carbon source for SRB, with a COD of 6000 mg / L. In addition, Cu 2+ , Zn 2+ , and Pb 2+ 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.

[0077] 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 taken 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 consisting of a 0.5-hour influent stage, a 22-hour reaction stage, a 1-hour settling stage, a 0.5-hour drainage stage, and a 0-hour idle stage, 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.

[0078] 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.

[0079] Example 4 The effects of composite microspheres on enhancing the treatment of mine water are compared with those of several other existing materials, as detailed below: 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.

[0080] Among them, group R1 was the experimental group in which 10% of the composite microspheres were added to the UASB reactor; Group R2 was a blank control group without the addition of composite microspheres; 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. Group R4 involved adding an equal amount of SRB culture activated in Postgate C medium to the UASB reactor daily, with an OD600 of 1.2 and a culture volume of approximately 1.5 L, to verify the role of free SRB. R5 group is to add 1.5 L of blank microspheres carrier into the UASB reactor, the carrier is prepared according to the method of Example 1, but no zero-valent iron particles are added in the step, and no immobilization of microorganisms is performed at last, so as to verify the physical effect of the microspheres carrier.

[0081] After 60 days of continuous operation, the treatment effect of each control group is evaluated. The results are shown in Table 2. Figure 5 and Table 1 show that, for the sulfate removal rate, the R2 group is about 93.5%, the R1 group is 67.2%, the R3 group is 79.8%, the R4 group is 74.2%, and the R5 group is 81.4%, and the R2 group is significantly higher than the R1 group, the R3 group, the R4 group and the R5 group; the removal rates of Cu 2+ , Zn 2+ , Pb 2+ of the R2 group are all above 95%, and the removal rates of heavy metals of the R1 group, the R3 group, the R4 group and the R5 group are about 71%, 75%, 70% and 81% respectively; the microsphere suspension rate of the R2 group is greater than 96%, the suspension rate of the zero-valent iron in the R3 group is only 46% due to precipitation, and the zero-valent iron is extremely easy to be lost in the effluent, and additional supplement needs to be added to maintain the ZVI concentration in the reactor during the operation; the SRB loss rate in the effluent of the R4 group is greater than 85%, and the SRB loss rate in the effluent of the R1 group is only about 10%.

[0082] 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 the R1 group is about 86.7%, and the utilization rate of the R3 group is increased by about 55%; the precipitate of the R3 group is detected by XRD to show a strong FeOOH characteristic peak, and the surface of the microspheres of the R1 group is detected by XPS to show a Fe 0 peak, which indicates that the hydrogel carrier of the composite microspheres effectively prevents the direct contact between ZVI and water, and significantly reduces the passivation rate of iron; after SEM detection, it is shown that the SRB in the R1 group forms a dense biofilm in the pores of the microspheres, and the SRB in the R4 group is mostly lost with the effluent.

[0083] Comparing the results of each control group with the results of the 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.

[0084] Example 5 Regeneration preparation process of composite microspheres and determination of sulfate removal in mine water by regenerated material Obtaining the failed composite microspheres: The composite microspheres with the sulfate removal rate decreased to less than 70% of the initial efficiency or the heavy metal removal rate significantly reduced after running for 60 days in Example 2 were selected as the failed microspheres. The failed microspheres were 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 of the microspheres, and then stored in an anaerobic environment at 4°C for standby.

[0085] Acid washing and activation of the microspheres: The washed failed composite microspheres were 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 was 0.3 mol / L, which was prepared on site. The sodium citrate solution was pre-deoxidized to maintain an anaerobic environment. Subsequently, the mixture was placed in a constant temperature shaker and shaken at 30°C and 120 rpm for 30 minutes to dissolve the metal sulfide precipitates 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 the shaking was completed, the microspheres were separated from the sodium citrate solution and repeatedly washed with deoxygenated deionized water for 5-8 times until the pH value of the washing liquid was close to neutral to completely remove the residual sodium citrate and dissolved metal ions.

[0086] Restoration of the biological activity of the composite microspheres: First, a high-activity SRB bacterial solution was prepared. The acid-washed and activated composite microspheres were put into the above bacterial solution at a solid-liquid ratio of 1:5 by wet weight, and sterile Postgate C liquid anaerobic medium was added to provide the nutrients required for the growth of SRB. Subsequently, the mixture of composite microspheres and SRB bacterial solution was placed in a strictly anaerobic environment at 37°C and 100 rpm, and low-speed shaking culture was carried out for 48 hours. During the culture process, the fresh medium was 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 restoring their biological activity. After the culture was completed, the microspheres were repeatedly washed with sterile physiological saline for at least 3-6 times to remove the non-immobilized SRB and residual medium. The washed regenerated composite microspheres were immediately used for subsequent performance determination experiments or stored under anaerobic conditions at 4°C for standby. The added sterile Postgate C liquid anaerobic medium met two requirements. One was to completely immerse the composite microspheres to ensure that all the composite microspheres were completely immersed in the liquid so that the SRB on the inner and outer surfaces of the microspheres could uniformly contact the nutrients. The other was to leave enough headspace, generally 20%-30% of the total volume, to maintain good gas-liquid exchange during shaking culture and prevent liquid from splashing out. In this invention, 100 mL of microspheres were treated, and a 1 L anaerobic culture bottle was selected. The volume of the microspheres and the bacterial solution was about 600 mL, and the volume of the sterile Postgate C medium added was about 150 mL to reserve enough headspace.

[0087] Referring to the reactor conditions of Example 2, a separate 15L UASB reactor was set up. According to the conditions in Example 2, 1.5L of regenerated composite microspheres were added to the bottom of the reactor, and the same simulated high-sulfate mine water as in Example 2 was used. The UASB reactor was started and continuously operated for about 30 days. The effluent sulfate concentration, total sulfide concentration, COD, and heavy metal ion concentration were monitored daily. The sulfate removal rate of the regenerated microspheres was compared with the sulfate removal rate of the initial microspheres in Example 2.

[0088] The results, as shown in Figure 6 The chemical activity and biological activity of the composite microspheres can be significantly restored through the regeneration process. Through the regeneration process, the chemical activity and biological activity of the composite microspheres are expected to be significantly restored. The sulfate removal rate of the regenerated composite microspheres in treating simulated high-sulfate mine 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 operating costs, prolong the service life of the material, and provide a sustainable solution for practical engineering applications.

[0089] Table 1: Concentration values of heavy metals in the effluent of each experimental group in Examples 2-5

[0090] It should be noted that when the present application claims involving numerical ranges, both endpoints of each numerical range and any number between the two endpoints can be selected. In order to prevent repetition, the present application describes preferred embodiments.

[0091] Although preferred embodiments of the present application have been described, those skilled in the art, once aware of the basic inventive concept, can make additional changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications falling within the scope of the present application.

[0092] Obviously, those skilled in the art can make various modifications and variations to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalents, the present application is also intended to include these modifications and variations.

Claims

1. 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 zeolite molecular sieve, activated biochar and zero-valent iron particles in the matrix and immobilizing sulfate-reducing bacteria on the surface of the microsphere; The mass of the zeolite molecular sieve, activated biochar and zero-valent iron is 9-11%, 7-9% and 4-6% of the total mass of the blended hydrogel, respectively. The method for forming the microsphere includes embedding the zeolite molecular sieve, activated biochar and zero-valent iron particles in the matrix to obtain a mixed colloid, and solidifying the mixed colloid in a crosslinking agent solution to form the microsphere, wherein 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.

2. The composite material of claim 1, wherein, 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.

3. The composite material of claim 1, wherein, The volume ratio of the 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.

4. A method of producing the composite material of claim 1, characterized by, The method includes the following steps: The zeolite molecular sieve, activated biochar and zero-valent iron are added to the blended hydrogel to obtain a mixed colloid, wherein 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 to a crosslinking agent solution to solidify and form the microsphere; The sulfate-reducing bacteria are added to the microsphere, the volume ratio of the bacterial solution of the sulfate-reducing bacteria to the microsphere is 3-5:1, and the composite microsphere, i.e., the composite material, is obtained after anaerobic culture for 48 h.

5. The preparation method according to claim 4, characterized in that, The mechanical strength of the microsphere is strengthened after solidification.

6. The preparation method according to claim 5, characterized in that, When the mechanical strength of the microsphere is strengthened, the microsphere is first equilibrated at 4°C, then immersed in deionized water and frozen, then thawed, and the freezing-thawing cycle is repeated for 3 times.

7. The preparation method according to claim 4, characterized in that, The crosslinking agent solution is obtained by mixing equal volumes of a 4% calcium chloride solution and a 2% boric acid solution.

8. The preparation method according to claim 4, characterized in that, The activated biochar is prepared by pyrolyzing rice husks at 600-800°C in a nitrogen atmosphere.

9. Use of the composite material according to claim 1 in waste water treatment, characterized in that, The wastewater is sulfate wastewater.

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