A microbial flocculant and a method for treating heavy metal silver ions in sewage and preparing nano-silver

Abstract

The present application relates to the field of sewage treatment, in particular to a microbial flocculant and a method for treating heavy metal silver in sewage and preparing nano-silver, through the microbial flocculant, not only can the heavy metal in the sewage be adsorbed and removed, but also can be reduced under the condition of ultraviolet light, the heavy metal silver ions adsorbed can be reduced at the same time, nano-silver is prepared, and the problems of waste caused by the removal of heavy metals in the sewage and the unrecoverable precious metals are solved.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment, and in particular to a microbial flocculant and a method for treating heavy metal silver ions in wastewater and preparing nano-silver. Background Technology

[0002] Flocculants are widely used in wastewater treatment. Common flocculants include inorganic flocculants, organic synthetic flocculants, and bioflocculants. Among them, inorganic flocculants and organic synthetic flocculants are the two most common types, with good flocculation effects and low cost. However, inorganic flocculants and organic synthetic flocculants can cause environmental and health problems while treating wastewater. Compared with inorganic flocculants and organic synthetic flocculants, bioflocculants are non-toxic and biodegradable. As an environmentally friendly water treatment agent, they show good development prospects.

[0003] Microbial flocculants possess adsorption-enhancing functional groups in their structure, such as amino, carboxyl, and hydroxyl groups in monosaccharide residues, which play a crucial role in flocculation and adsorption. High uronic acid content, in particular, promotes the flocculation activity of microorganisms. Furthermore, the presence of polysaccharide structures imbues them with a large negative charge, resulting in effective flocculation of both suspended and dissolved pollutants in water, facilitating the sedimentation of dissolved pollutants during the flocculation process. Heavy metal pollutants in wastewater are highly stable, easily accumulate in the food chain, and are difficult to biodegrade. If not removed, they ultimately cause environmental pollution and harm human health. Simultaneously, the loss of precious metals is also a significant concern. Therefore, the treatment of heavy metal wastewater and the recovery and utilization of precious metals have become hot issues in ecological and environmental governance.

[0004] Patent CN 107686172 A discloses a method for preparing a composite metal ion adsorbent flocculant. It utilizes four strains of microbial flocculant-producing bacteria with the highest flocculation activity isolated and screened from river sludge. These strains are mixed and fermented to obtain a microbial flocculant, producing high molecular weight compounds such as glycoproteins, mucopolysaccharides, proteins, cellulose, and nucleic acids. When dissolved in water, these compounds can cause fine particles and natural colloids in the water to aggregate into large flocs, which are then removed from the water. Chitosan derivatives with high adsorption capacity are synthesized by modifying chitosan with α-ketoglutarate. The introduction of -NH2 and carbonyl groups, along with the introduction of carboxyl groups, effectively adsorbs heavy metal ions in wastewater. However, the adsorbed heavy metal ions cannot be properly treated and must be disposed of as pollutants, leaving the problem of precious metal loss unresolved.

[0005] Nano silver is a commonly used catalyst, especially in photocatalysis and electrocatalysis, where it has wide applications. In addition, nano silver can also be used as an antibacterial agent, exhibiting good antibacterial effects against a variety of pathogens. However, the synthesis process of nano silver is complex and requires the use of highly toxic reducing agents. Therefore, although nano silver has a wide range of applications, its preparation method limits its use.

[0006] In summary, although microbial flocculants have been used for the adsorption and removal of various heavy metals, there is a lack of microbial flocculants that can not only adsorb heavy metals in wastewater but also reduce them using their own properties to prepare nanomaterials and prevent heavy metal loss. Summary of the Invention

[0007] The purpose of this invention is to provide a microbial flocculant for removing heavy metal silver ions in wastewater treatment, and a method for obtaining nano-silver while treating heavy metal silver ions in wastewater using the microbial flocculant.

[0008] Experiments have shown that while commercially available microbial flocculants can all achieve the effect of flocculating heavy metals in wastewater, there is no suitable treatment method after the heavy metals are adsorbed. As a result, the heavy metals are difficult to recycle and reuse, and the problem of heavy metal enrichment and waste still has no reasonable solution.

[0009] In the biochemical treatment process of wastewater treatment, various substances rich in microorganisms, such as activated sludge, are used to treat the wastewater. Depending on the characteristics of different wastewater, the growth environment of microorganisms is changed by adding substances or other methods, thereby affecting the different characteristics of different microorganisms.

[0010] A microbial flocculant, said microbial flocculant including but not limited to: glucose monomer, galactose monomer, mannose monomer and rhamnose monomer and / or heteropolysaccharides composed of the above-mentioned sugar monomers.

[0011] Furthermore, the heteropolysaccharide composed of glucose monomer, galactose monomer, mannose monomer, and rhamnose monomer and / or the above-mentioned sugar monomers accounts for 65% or more of the molar mass of the extracellular polysaccharide.

[0012] Furthermore, the microbial flocculant contains sugar monomers in a molar ratio of glucose:mannose:rhamnose / galactose = 32-34:2-3:1-2:5-7.

[0013] Furthermore, a method is provided for using microbial flocculants to promote the microbial treatment of heavy metal silver in wastewater and to prepare nano-silver:

[0014] Currently, it is known that light can promote the production of reducing substances by microbial flocculants, which can promote the reduction of heavy metals. At the same time, light is also an effective auxiliary means in the synthesis of nanomaterials. In particular, ultraviolet light irradiation can promote the binding of polysaccharides and metals and promote the reduction of metal salts into nanoparticles.

[0015] First, adjust the pH of the wastewater to be treated to a slightly acidic or alkaline condition, using 60 mg / L Ag + To meet the standard, add 200 mg / L of the aforementioned microbial flocculant to the wastewater and use common wastewater treatment methods, such as introducing it into a biological treatment tank or an activated sludge tank, for water treatment under ultraviolet light irradiation.

[0016] The activated sludge is inoculated at a rate of 45%-55% of the effective volume of the biochemical treatment tank.

[0017] Furthermore, the pH value of the wastewater to be treated is adjusted to 6.0–10.0.

[0018] The addition of microbial flocculants alters the original living environment of the microbial community. Furthermore, the influx of wastewater allows the microbial flocculants to come into full contact with the microorganisms in the activated sludge, which is more conducive to the adsorption of heavy metals in the wastewater. Because microbial flocculants contain a large number of negative charges, they exhibit good decomposition and adsorption effects on pollutants in wastewater, enabling them to better settle dissolved pollutants, especially positively charged heavy metal ions, during the flocculation process.

[0019] After adsorption, the adsorbed Ag is collected. + The microbial flocculants, under ultraviolet light irradiation, will still adsorb Ag... + The microbial flocculants were placed on a shaker and thoroughly mixed. After thorough mixing, the solution was centrifuged for 10 minutes. After centrifugation, the supernatant was discarded, and the precipitate was washed with ultrapure water. After washing three times, the precipitate was freeze-dried to obtain the nano-silver material.

[0020] Microbial flocculants can not only adsorb metallic silver and encapsulate the adsorbed metallic silver using the flocculent material they produce, but they also have a polysaccharide structure that makes them rich in negative charges, which can reduce the encapsulated silver ions into nano-silver.

[0021] Compared with the prior art, the beneficial effects of the present invention are:

[0022] This application provides a microbial flocculant with a polysaccharide structure. This microbial flocculant is mainly used for the adsorption of heavy metals in wastewater, especially the adsorption and removal of silver ions. It utilizes the microbial flocculant to regulate the microbial living environment in the wastewater treatment process, enabling them to decompose and adsorb heavy metal silver ions in the wastewater. While adsorbing heavy metal silver ions in the wastewater, it further reduces the silver ions to zero-valent silver to prepare nano-silver materials. This not only solves the problem of heavy metal accumulation caused by the difficulty in removing heavy metals from wastewater, but also avoids the waste of precious metals. It also provides a new way to prepare nano-silver, expanding the application range of nano-silver without increasing costs. Attached Figure Description

[0023] Figure 1 The adsorption time of the microbial flocculant of this invention and its effect on Ag in wastewater + The amount of adsorption;

[0024] Figure 2 This is the ultraviolet-visible spectrum of the nano-silver material in this invention. Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0027] Example 1: Adsorption of heavy metal silver ions

[0028] A microbial flocculant, wherein the sugar content accounts for 70% of the molar mass of the microbial flocculant, and the remaining 30% is protein; specifically, the microbial flocculant contains the following molar fractions: glucose 75.40%, mannose 5.30%, rhamnose 2.30%, and galactose 13.70%.

[0029] Under laboratory conditions, silver nitrate was dissolved in ultrapure water to prepare Ag. + The stock solution with a concentration of 1 g / L was then diluted to 60 mg / L Ag. + The solution was used to simulate wastewater containing heavy metal silver ions.

[0030] After adjusting the initial pH of the simulated wastewater to 6.0 using 1 mol / L HNO3, a microbial flocculant was added to the simulated wastewater until its concentration reached 200 mg / L. The resulting mixture was then passed through a 5m³ tank pre-inoculated with activated sludge. 3 In the simulated wastewater treatment tank, the activated sludge inoculation amount was 55% of the volume of the simulated wastewater treatment tank; the simulated wastewater treatment tank was placed under ultraviolet light for irradiation, and wastewater was introduced for continuous adsorption for 0-24 hours.

[0031] Experimental results are as follows Figure 1 As shown, microbial flocculants affect Ag in solution. + Exhibiting good adsorption effects, the microbial flocculant continuously occupies its adsorption sites during the adsorption of pollutants until all adsorption sites are occupied, reaching adsorption saturation. Figure 1 It can be found that microbial flocculants have an effect on heavy metal Ag. + It can adsorb continuously for 24 hours before reaching saturation, which is sufficient to ensure the effective treatment of heavy metal Ag in wastewater. + Complete adsorption is achieved.

[0032] Example 2: Preparation of Nano Silver

[0033] The solution obtained in Example 1 was observed under ultraviolet light. When the colorless and transparent silver solution and the milky white microbial flocculant solution reacted and the solution color began to turn brown, the color change was related to the formation of nano-silver, which indicates that nano-silver was produced.

[0034] Adsorbed Ag + After the microbial flocculant solution was thoroughly mixed on a shaker, the solution was centrifuged at 8000 r / min for 10 min. After centrifugation, the supernatant was discarded, and the precipitate was washed with ultrapure water. After washing three times, the precipitate was freeze-dried to obtain the nano-silver material.

[0035] During this process, the nano-silver material was subjected to ultraviolet-visible spectroscopy detection, and the results are as follows: Figure 2 As shown.

[0036] pass Figure 2 It can be observed that the binding of microbial flocculants to Ag varies at different reaction times. + The change in the characteristic absorption peak after ultraviolet light irradiation, with Ag + With prolonged exposure time in the microbial flocculant, the intensity of the characteristic absorption peak of silver nanoparticles at 412 nm continuously increased, indicating that the size or number of silver nanoparticles increased during this process. Under the action of the microbial flocculant, the adsorbed Ag... + Reduced to Ag 0Silver element undergoes a nucleation and growth process to form silver nanoparticles, which are then loaded onto the surface of microbial flocculants to form silver nanomaterials.

[0037] The above description is only a preferred embodiment of the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for treating heavy metal silver in wastewater using microbial flocculants and preparing nano-silver, characterized in that, After adjusting the pH of the wastewater to a slightly acidic or alkaline state, activated sludge is inoculated into it, and a microbial flocculant is added. The mixture is then adsorbed under ultraviolet light. After a period of adsorption, the formed microbial flocculant is centrifuged, the precipitate is washed, and then freeze-dried to obtain nano-silver materials. The microbial flocculant includes, but is not limited to, glucose monomers, galactose monomers, mannose monomers, and rhamnose monomers, and / or heteropolysaccharides composed of the above-mentioned sugar monomers. The total molar mass of the glucose monomers, galactose monomers, mannose monomers, and rhamnose monomers, and / or heteropolysaccharides composed of the above-mentioned sugar monomers, accounts for 65% or more of the total molar mass of the microbial flocculant.

2. The method for treating heavy metal silver in wastewater using a microbial flocculant and preparing nano-silver as described in claim 1, characterized in that, The pH range of the wastewater is adjusted to 6.0~10.

0. The inoculation amount of the activated sludge is 45%-55% of the effective volume of the biological treatment tank, at a concentration of 60 mg / L Ag. + To meet the standard, 200 mg / L of the aforementioned microbial flocculant was added to the wastewater, followed by adsorption.

3. The method for treating heavy metal silver in wastewater using a microbial flocculant and preparing nano-silver as described in claim 1, characterized in that, The flocculant solution obtained after adsorption was placed under ultraviolet light to expose the adsorbed Ag to light. + The microbial flocculant was placed on a shaker and thoroughly mixed. The solution was then centrifuged for 10 minutes. After centrifugation, the supernatant was discarded, and the precipitate was washed with ultrapure water. After washing three times, the precipitate was freeze-dried to obtain the nano-silver material.

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