Salt-tolerant domestication method of anaerobic bacteria in UASB (upflow anaerobic sludge blanket) reactor

Abstract

The invention discloses a salt-tolerant domestication method of anaerobic strains in a UASB reactor, and relates to the technical field of salt-tolerant domestication methods of strains. Comprising the following steps that landfill leachate is introduced into a UASB reactor, the concentration of inorganic salt in the landfill leachate introduced for the first time ranges from 20 g / L to 30 g / L, then the concentration of the inorganic salt when the landfill leachate is introduced is increased every 2-3 days, domestication is conducted for 45-60 days at the gradient of increasing 0.5 g / L every time till the concentration of the landfill leachate introduced into the UASB reactor reaches 40-50 g / L, and the salt-tolerant strain is obtained. According to the method, the landfill leachate to be treated is used as the domestication liquid, the structural characteristics of the UASB reactor are combined, and the domestication process is designed, so that good salt-tolerant domestication can be performed on anaerobic bacteria in a sludge bed, especially acid-producing bacteria and methanogens which play an important degradation role; the membrane system can better face a complex sewage environment, the treatment efficiency of the membrane system on high-salinity sewage is improved, and damage caused by too high salinity of the membrane system is avoided.

Description

Technical Field

[0001] The present invention relates to the field of microbial technology, in particular to the field of salt-tolerant acclimation methods for bacterial strains. Background Art

[0002] The main methods of treating domestic waste in my country are landfill and incineration, with landfill still occupying the main position. Landfilling usually involves stacking the garbage transported to the landfill in a certain order and layer. Each layer of garbage is compacted to reduce the volume and save space. It is then covered with a layer of soil to isolate the garbage from the environment and prevent odor and rainwater from directly seeping into the garbage layer. At the same time, a drainage system is set up to remove the infiltrated water and reduce the generation of leachate. Leachate is a highly concentrated liquid produced during the degradation of garbage. It contains a variety of harmful substances and needs to be collected and treated by a special leachate treatment system to prevent contamination of groundwater and the surrounding environment. The treated leachate is either discharged in compliance with standards or reused. The landfill will eventually form a closed garbage pile, which will be transformed into a relatively harmless state after a long period of natural degradation and stabilization. However, strict environmental monitoring and management are required throughout the process to ensure the safe operation of the landfill and minimize environmental impact.

[0003] Landfill leachate has characteristics that distinguish it from general municipal sewage: high BOD5 and COD concentrations, high metal content, significant variability in water quality and quantity, high ammonia and nitrogen content, and an imbalance in the ratio of microbial nutrients. Among leachate treatment methods, combining leachate with municipal sewage is the simplest approach. However, landfills are typically located far from towns, so combining their leachate with municipal sewage presents specific difficulties, often forcing them to be treated separately. Common treatment methods include physical and chemical methods and biological methods, which are further categorized into aerobic biological treatment, anaerobic biological treatment, and a combination of the two. Aerobic treatment includes activated sludge processes, aerated oxidation ponds, aerobic stabilization ponds, bio-rotating discs, and trickling filters; anaerobic treatment includes upflow sludge blankets, anaerobic immobilized bioreactors, hybrid reactors, and anaerobic stabilization ponds. Among them, the latter is mostly suitable for treating high-concentration organic wastewater. First, the sewage is introduced into the anaerobic reactor, and anaerobic microorganisms begin to decompose the complex organic matter in the water to form smaller molecules, such as volatile fatty acids and alcohol; then, these intermediates are further converted into hydrogen, carbon dioxide and acetic acid; finally, methanogens use hydrogen and carbon dioxide or directly use acetate to convert them into methane and more carbon dioxide. The methane gas is collected for energy recovery, and the remaining liquid can be further processed or safely discharged. Throughout the process, the operating parameters of the reactor, such as temperature, pH value and organic load, need to be precisely controlled to ensure the stability and efficiency of the anaerobic digestion process. In addition, regular monitoring and maintenance are required to prevent problems such as sludge accumulation, foam generation and odor to ensure the long-term stable operation of the system.

[0004] Physical and chemical methods mainly include activated carbon adsorption, chemical precipitation, density separation, chemical oxidation, chemical reduction, ion exchange, membrane dialysis, gas stripping and wet oxidation. When the COD is 2000-4000 mg / L, the COD removal rate of the physical and chemical method can reach 50-87%. Compared with biological treatment, physical and chemical treatment is not affected by changes in water quality and water volume, and the effluent water quality is relatively stable. In particular, it has a better treatment effect on landfill leachate with a low BOD5 / COD ratio (0.07-0.20) that is difficult to biologically treat. However, physical and chemical treatment methods are usually more expensive and are not suitable for the treatment of large amounts of landfill leachate. Therefore, biological methods are still the main treatment method for landfill leachate.

[0005] Among them, after using membrane technology to treat landfill leachate, a concentrate is produced. The conventional treatment method is re-injection, that is, reinjecting the concentrate into the landfill, and utilizing the biodegradation, physical, and chemical effects within the landfill to intercept pollutants. This method can reduce the volume of leachate and reduce the amount of filtrate through natural evaporation, while promoting waste degradation and landfill stability, and has a strong purification ability for organic matter. However, although leachate re-injection can reduce the content of organic components, ammonia, heavy metals and other inorganic substances still remain at a high level, so the concentrate after re-injection may require further treatment. In addition, the new version of the "Standard for Pollution Control of Municipal Waste Landfills" clearly requires that the concentrate produced by leachate treatment should be disposed of separately and must not be re-injected into municipal waste landfills or enter centralized sewage treatment facilities. This means that under the new standards, re-injection of concentrate is prohibited. Although the reinjection of concentrated liquid is simple to construct and low in cost, it may lead to the accumulation of difficult-to-degrade organic matter and salt circulation in the system over time, affecting the operation of the membrane treatment process of the leachate, causing excessive damage to the membrane system, greatly reducing its service life and increasing operating costs. In addition, reinjection will increase the moisture content of the landfill layer, which may cause groundwater pollution. In addition, since the reinjection area cannot be covered with HDPE membrane, serious odor problems will occur, affecting the surrounding environment.

[0006] The Chinese patent application number CN202110722306.8 discloses a high-temperature biochemical method and device for treating wastewater containing oligomers. The high-temperature biochemical method for treating wastewater containing oligomers simultaneously completes the domestication of anaerobic and aerobic bacteria in the anaerobic tank and aeration tank 1. After the domestication is completed, the wastewater is pretreated in the regulating preheating tank, and high-temperature anaerobic biochemical treatment is carried out in the anaerobic tank. The effluent from the anaerobic tank is subjected to high-temperature aerobic biochemical treatment in aeration tank 1 and aeration tank 2; the effluent from aeration tank 2 enters the inclined plate sedimentation tank for mud and water separation, and then undergoes deep mud and water separation through the MBR. Finally, the effluent is discharged to complete the high-temperature biochemical treatment of the wastewater. This invention can simultaneously heat up and domesticate anaerobic and aerobic microorganisms in a certain biochemical system, solve the problem of continuous polymerization and agglomeration of characteristic pollutants through high-temperature biochemical process research, and intercept sludge through the MBR for reflux to ensure that the high concentration of high-temperature biochemical sludge at the front end is not lost. In other words, the invention proposes to domesticate microorganisms so that they can better play a degradation role in certain specific scenarios. However, the high salt content of landfill leachate concentrate can easily cause microbial dehydration or poisoning. This is especially true for the UASB reactors commonly used in landfills, where the absorption of substances by anaerobic microorganisms is disrupted or blocked, ultimately inhibiting bacterial activity or even killing them. Therefore, simply acclimating microorganisms to the high-salinity wastewater environment is clearly insufficient, affecting their activity and reducing degradation effectiveness.

[0007] The Chinese patent application number CN201010292732.4 discloses a method for treating CH4 in a landfill by acclimating leachate to mineralized garbage, which comprises the following steps: (1) firstly lifting the leachate to an adsorption material layer, which is composed of an activated carbon layer and a macroporous resin layer; the water distribution load is 0.05 to 0.50 m 3 / (m 3 Mineralized garbage·d); (2) The effluent of the treated landfill leachate is lifted to the mineralized garbage filler layer for treatment, with a water distribution load of 0.05~0.30m 3 / (m 3 Mineralized garbage·d); (3) During the construction of the final cover layer of the municipal solid waste landfill, a mineralized garbage layer after the leachate obtained after the operation of step (2) is added between the drainage layer and the vegetation layer, or below the drainage layer. This invention proposes to use the ammonia nitrogen component in the landfill leachate to cultivate and enrich ammonium oxidizing bacteria in the mineralized garbage filler to oxidize CH4, so that the landfill leachate and methane can be well treated, reducing the total equivalent of greenhouse gas emissions from the landfill. However, this invention only specifically domesticates a strain of bacteria that can oxidize methane to reduce greenhouse gas emissions from the landfill, and does not solve the problem of membrane damage caused by excessive salt content in the leachate concentrate.

[0008] The Chinese patent application number CN201711058297.7 discloses a salt-tolerant anaerobic bacterium and its application. The salt-tolerant anaerobic bacterium was deposited in the China General Microbiological Culture Collection Center on July 8, 2016, with a deposit number of CGMCCNO.5503 and a deposit name of Pectinatus brassicae ZCTY. The salt-tolerant anaerobic bacterium provided by the present invention is obtained from salt-rich organic industrial wastewater and is isolated and purified. It is identified as a new strain. According to the results of morphological identification and ribosomal RNA sequence analysis, the salt-tolerant anaerobic bacterium is identified as Pectinatus brassicae, and the salt-tolerant anaerobic bacterium can grow itself under anaerobic conditions using organic matter in salt-rich organic industrial wastewater. The invention provides a salt-tolerant anaerobic bacterium that uses salt-rich organic industrial wastewater as a carbon, nitrogen source, and energy source for its own growth under anaerobic conditions to achieve the effect of cleaning wastewater and reducing the pollution of salt-rich organic industrial wastewater to the environment. According to the document's description, the invention involves the discovery and cultivation of an anaerobic, salt-tolerant bacterial species in salt-rich, organic industrial wastewater, thereby achieving the aforementioned microbial digestion of pollutants. However, the salt content (inorganic salts such as magnesium carbonate, calcium carbonate, and sodium chloride) of leachate concentrate from existing municipal solid waste landfills exceeds 60 g / L, and the presence of complex components such as ammonia and nitrogen strongly inhibits the activity of anaerobic microorganisms in UASB reactors. This makes it difficult and inefficient to specifically select and cultivate a specific salt-tolerant bacterial species.

[0009] In summary, since concentrated landfill leachate contains high salt concentrations, primarily NaCl, and also contains complex components such as ammonia and nitrogen, conventional recharge treatment in this situation can lead to cyclic accumulation of salt within the landfill, significantly damaging subsequent membrane treatment systems and significantly reducing the service life of membrane systems such as ultrafiltration, nanofiltration, STRO, and DTRO. Several prior art technologies have proposed the use of microorganisms to degrade wastewater. However, for landfill leachate concentrate, the complex composition, high organic matter concentration, and high salt content of the landfill concentrate inhibit the activity of anaerobic microorganisms in the UASB reactor, making the degradation effect unsuitable for landfill leachate concentrate. Therefore, overcoming the cyclic accumulation of salt in the concentrate caused by landfill recharge, the difficulty of UASB reactor treatment, the poor effluent quality, and the resulting damage and aging of the membrane system has become a technical problem that needs to be urgently addressed by those skilled in the art. Summary of the Invention

[0010] In the current landfill leachate treatment process, recirculation is often used, which leads to the circulation and accumulation of salt in the concentrated leachate, thereby damaging the membrane system. The purpose of the present invention is to provide a method for salt-tolerant acclimation of anaerobic bacteria in a UASB reactor. By controlling the inorganic salt content and acclimation period in the landfill leachate introduced into the UASB reactor, and adjusting relevant parameters such as the pH value and temperature of the leachate, the salt-tolerant bacteria capable of treating highly concentrated concentrates are successfully acclimated, thus solving the problems of difficult and expensive landfill concentrate treatment and membrane system damage caused by concentrated liquid recirculation.

[0011] The technical solution adopted by the present invention to solve its technical problem is:

[0012] A method for acclimating anaerobic bacteria to salt tolerance in a UASB reactor comprises the following steps:

[0013] Landfill leachate is introduced into the UASB reactor, wherein the inorganic salt concentration of the landfill leachate introduced for the first time is 20-30 g / L, and then the inorganic salt concentration of the landfill leachate is increased every 2-3 days, and the bacteria are acclimated for 45-60 days at a gradient increase of 0.5 g / L each time until the concentration of the landfill leachate introduced into the UASB reactor reaches 40-50 g / L, thereby obtaining a salt-tolerant bacterial strain.

[0014] The UASB reactor in this application refers to an anaerobic bioreactor, which is commonly used to treat high-concentration organic wastewater, such as landfill leachate. The wastewater to be treated enters the bottom of the UASB reactor and flows from bottom to top. At the bottom of the reactor, there is a high-concentration anaerobic sludge bed. This sludge contains a large number of anaerobic microorganisms, such as methanogens and acidogens. It is understood that the "acidogens" and "methanogens" referred to throughout this application refer to two major types of bacteria and are not specific. When the wastewater passes through the sludge bed, the organic matter therein is decomposed and metabolized by anaerobic microorganisms. First, the complex macromolecular organic matter is hydrolyzed and acidified into simple small-molecule organic matter, such as volatile fatty acids (VFAs) and alcohols, under the action of acidogens. Then, these small-molecule organic matter is further converted into gases such as methane and carbon dioxide under the action of methanogens. The biogas (mainly methane and carbon dioxide) produced during the decomposition of organic matter will rise in the form of bubbles. During the rising process, it will drive the mixing of sludge and wastewater, forming a good mass transfer effect.

[0015] However, as the concentration of inorganic salts in the landfill leachate gradually increases, the anaerobic bacteria in the UASB reactor are inhibited by the salt, affecting enzyme activity within the microbial cells and slowing their metabolic rate. The structure and function of the cell membrane are also damaged, impairing the transport of substances across the membrane and reducing the microbial ability to absorb nutrients and excrete metabolic waste. The activity of methanogens decreases significantly, inhibiting their growth and reproduction. The activity of acidogens decreases to a lesser extent, disrupting the balance between acidogenesis and methanogenesis and leading to the accumulation of VFAs. The accumulation of VFAs in the reactor causes the leachate pH to drop, further inhibiting the activity of methanogens, reducing COD and BOD removal rates, deteriorating effluent quality, and significantly degrading water treatment effectiveness. Furthermore, due to the reduced gas production, agitation and mixing within the reactor deteriorate, reducing the contact efficiency between the substrate and the microorganisms, further hindering the degradation of organic matter. As the concentration of inorganic salts in the leachate continues to rise, the activity of most anaerobic bacteria is severely inhibited or even lost. The osmotic pressure in the cells is severely unbalanced, a large number of cells lose water and die, and the structure of the microbial community changes dramatically. Almost all bacteria with weak salt tolerance die. Only a very small number of bacteria with extremely strong salt tolerance can survive, but their activity is also far below normal levels, and the metabolic function of the entire anaerobic microbial system almost stagnates. Because the microorganisms in the reactor cannot effectively decompose organic matter, a large amount of pollutants in the leachate accumulate, resulting in a basic loss of the reactor's processing capacity. Emergency measures (such as diluting the salt content of the influent, adding bacterial strain protectants, etc.) are needed to restore the activity of the system. Otherwise, the operation of the entire UASB reactor may collapse.

[0016] Typically, anaerobic microorganisms in the sludge bed have certain physiological regulatory mechanisms to adapt to environmental changes. For example, if the salt concentration in the environment gradually increases, the microbial cells will accumulate some compatible solutes, such as betaine and proline, through active transport and other means. These compatible solutes can regulate the osmotic pressure in the cells to balance it with the external high-salt environment, thereby preventing the cells from dying due to water loss. After investigation, the present application found that according to the different tolerance of the rich microbial flora in the sludge bed to salt concentration, the bacterial population can be acclimated to salt tolerance by gradually increasing the salt concentration, combining appropriate cycles, and increasing gradients. In a high-salt environment, the gene expression of the bacterial species will change. For example, certain genes related to osmotic pressure regulation, ion transport, etc. will be activated or upregulated, allowing the microorganisms to synthesize more osmotic pressure regulating substances or change the structure and function of the cell membrane to adapt to the high-salt environment. This genetic adaptive change enables the microorganisms to gradually possess stronger salt tolerance during the long-term salt tolerance acclimation process. As the acclimation progresses, the proportion of salt-tolerant microorganisms in the flora gradually increases, and the salt tolerance of the entire microbial community also increases accordingly. Among them, those microorganisms that are sensitive to salt will gradually be eliminated, while microorganisms with stronger salt tolerance will be able to survive and continue to reproduce, forming a stable colony.

[0017] The acclimation method of this application utilizes the "landfill leachate" to be degraded as the acclimation liquid, with an initial inorganic salt concentration generally around 25 g / L. Landfills and incinerators typically produce leachate, which is then treated by a membrane system to produce a waste concentrate. This application utilizes these two "liquids" for blending, producing the "landfill leachate" that enters the UASB reactor. Adjusting the ratio between the two liquids controls the concentration of the mixed liquid, or the inorganic salt concentration in the "landfill leachate" referred to herein, to acclimate the anaerobic bacteria in the UASB reactor sludge bed. The specific acclimation process involves increasing the inorganic salt concentration by 0.5 g / L every 2-3 days after the initial introduction of the landfill leachate, performing a gradient acclimation process. The acclimation period is 45-60 days. Firstly, the appropriate concentration gradient and increasing days prevent the bacteria from adapting to sudden and drastic changes in environmental conditions, reduce the likelihood of large-scale bacterial mortality, and ensure a sufficient number of bacteria for subsequent acclimation and treatment. A reasonable acclimation cycle should be set up to allow the bacteria enough time to gradually adapt to changes in salt concentration, adjust their own physiological metabolic mechanisms, and balance the osmotic pressure inside and outside the cells by synthesizing compatible solutes (such as betaine, proline, etc.), thereby enhancing tolerance to high-salt environments and reproducing to form stable and good colonies.

[0018] Secondly, unlike the traditional method of selecting strains and then acclimating them, this application proposes for the first time to acclimate the inoculated reactor using the wastewater to be treated, achieving good acclimation results for both methanogens and acidogens within the anaerobic strains. By increasing the inorganic salt concentration over 2-3 days, with the inorganic salt concentration in the landfill leachate increasing by a gradient of 0.5 g / L, the bacteria within the sludge bed have sufficient time to activate their stress mechanisms and adaptation strategies, gradually adjusting their physiological and metabolic functions, and gradually altering gene expression to synthesize more proteins and enzymes adapted to high-salt environments, thereby adapting to the increasing salinity. In this application, if the salt concentration is increased for too long, while providing the strains with ample time to adapt, it will prolong the acclimation process and reduce treatment efficiency. Furthermore, prolonged exposure to a relatively stable low-salinity gradient environment may slow the improvement of the strain's salt tolerance, preventing it from quickly adapting to the large fluctuations in salt concentration that may occur during actual treatment. Similarly, if the acclimation period of a gradient is too short, it will not be possible to ensure that all strains are effectively acclimated. The strains may even be damaged due to the concentration gradient increasing too quickly. Salt-tolerant bacteria will not have enough time to become the dominant strains, and a stable and efficient salt-tolerant microbial community cannot be formed.

[0019] Due to the appropriate incremental gradient setting, during the initial stages of acclimation, when inorganic salt concentrations are low, acidogenic bacteria are relatively salt-tolerant and adapt more quickly to environmental changes. Acidogenic bacteria adapt to increasing salt concentrations by regulating osmotic pressure, for example by actively absorbing or synthesizing compatible solutes such as betaine and proline, to balance osmotic pressure inside and outside the cell and prevent dehydration. Simultaneously, acidogenic bacteria may adjust the composition and structure of their cell membranes, increasing the content of unsaturated fatty acids, enhancing membrane fluidity and stability, and ensuring normal cell function. Methanogens, on the other hand, are more sensitive to changes in salt concentration. Although they are inhibited by rising salt concentrations, their intracellular stress response mechanisms are also activated. Methanogens alter gene expression and synthesize stress proteins, such as heat shock proteins, to help maintain proper protein folding and stability within the cell, protecting critical cellular functions from salt stress. They also reduce non-essential metabolic activities to focus energy on coping with salt stress.

[0020] As methanogen activity decreases, a slight increase in COD levels can be detected, marking the intermediate stage of acclimation. As salt concentrations continue to rise, acidogenic bacteria gradually adapt to the new saline environment, their metabolic activity stabilizes, and they continuously break down complex organic matter into simpler products such as organic acids, alcohols, and carbon dioxide, providing a rich substrate for methanogens. Furthermore, the acidogenic bacteria's metabolism creates an acidic environment that helps maintain a low redox potential in the system, creating a suitable anaerobic environment for methanogens and fostering their growth and metabolism. Thanks to a well-defined acclimation cycle and increasing gradient, methanogens have ample time and stages to continuously adapt under relatively favorable conditions, gradually improving their tolerance to salt concentrations, including adjusting their metabolic pathways and enhancing their adaptability to salt stress. Simultaneously, methanogens may develop a closer symbiotic relationship with acidogenic bacteria. Through synergistic interaction, methanogens obtain more nutrients and growth factors through direct and indirect exchange of metabolites with the acidogenic bacteria, promoting their mutual growth and reproduction.

[0021] In the later stage of acclimation, the inorganic salt concentration in the leachate reaches a relatively high level. This application sets the inorganic salt concentration at 40-50 g / L at the end of the acclimation stage. At this time, both acid-producing bacteria and methanogens have adapted to the higher salt concentration environment, and a new dynamic balance has been established between the two. Acid-producing bacteria can stably convert organic matter into substrates suitable for methanogens, and methanogens can also efficiently convert these substrates into end products such as methane and carbon dioxide. At this point, the entire anaerobic microbial community structure is more stable, the system's salt tolerance and treatment efficiency have reached a relatively high level, and the COD and volatile acid content of the reactor effluent can be better controlled. Some acid-producing bacteria and methanogen strains in the sludge bed that are more adaptable to high-salt environments will gradually become dominant populations. They may have some adaptive mutations at the genetic level, enabling them to survive and function better in high-salt environments. The increase in these dominant populations will help improve the resistance of the entire microbial community to salt stress, further enhance the stability and treatment effect of the system, better meet emission standards, and ultimately obtain a community structure that cooperates with each other and complements each other.

[0022] For reactors that rely on acid-producing bacteria and methanogens to degrade organic matter, if the acclimation period is less than 45 days, the bacteria will not have sufficient time to adapt to the increased salt concentration. In addition to causing the cells to die due to dehydration due to osmotic pressure imbalance, even if some bacteria survive, their metabolic function will be severely inhibited, the acclimation effect will be poor, and it will be impossible to achieve a balance between acid-producing bacteria and methanogens. Under the acclimation period of this application, with an increasing frequency of 2 to 3 days, the anaerobic bacteria can be exposed to the inorganic salt environment with gradually increasing concentration more frequently, thereby having more opportunities to gradually adapt to the changes, effectively avoiding the risk of acclimation failure due to the bacteria being unable to adapt to the large concentration mutation.

[0023] In addition, this application chooses to carry out bacterial strain domestication in a UASB reactor, and utilizes its unique three-phase separator. During the operation of the reactor, the generated biogas is collected and discharged through the gas collecting chamber, the treated wastewater flows out from the top, and the granular sludge is deposited at the bottom of the reactor, realizing the automatic reflux and retention of the sludge, thereby achieving effective separation of the three phases of gas, liquid and solid. After the anaerobic bacteria are domesticated for salt tolerance, the domesticated highly active anaerobic granular sludge can be stably retained in the reactor, avoiding the loss of sludge. Without the need for additional sludge return equipment or complex sludge separation processes, it is possible to ensure that the anaerobic bacteria maintain a high concentration and activity during the domestication process, providing a stable microbial basis for efficient wastewater treatment.

[0024] Secondly, the wastewater in the UASB reactor flows upward, allowing for good mixing and contact with anaerobic bacteria. Substrates are quickly transferred to the surface of microbial cells, while metabolites are promptly removed. This creates favorable material exchange conditions for microbial growth and metabolism, improves substrate utilization efficiency, and accelerates the acclimation process. Compared to some static or unevenly stirred acclimation methods, the uniform flow pattern and efficient mass transfer within the UASB reactor ensure that microorganisms are acclimated in a more stable and suitable environment, facilitating the screening and enrichment of anaerobic bacteria with good adaptability to specific substrates or environmental conditions, thereby achieving higher acclimation effects and treatment efficiency.

[0025] Finally, the unique granular sludge environment within the UASB reactor also provides suitable environmental conditions for the formation and growth of salt-tolerant bacterial strains. Unlike some other acclimation methods that may result in dispersed microbial growth, the microorganisms within the UASB reactor gradually aggregate to form granular sludge during the acclimation process. This granular sludge structure not only improves the microorganisms' resistance to shock and adaptability to the environment, but also enables anaerobic bacteria with different functions to form stable symbiotic relationships within the granular sludge. For example, acid-producing bacteria and methanogens can better cooperate with each other, further improving the treatment of organic matter and tolerance to complex environmental conditions.

[0026] Preferably, the pH value of the landfill leachate entering the UASB reactor is controlled to be 7-8.

[0027] Different types of microorganisms have different optimal growth pH ranges. For acid-producing bacteria, they are less affected by changes in salt concentration in the early stages. By maintaining the pH value of the leachate at a weakly alkaline environment of 7 to 8, their physiological states such as intracellular enzyme activity and cell membrane permeability are at a relatively ideal level, enabling them to better metabolize, absorb nutrients and reproduce, making it easier for them to gain a growth advantage in a high-salt environment and helping them adapt to salt stress more quickly. For methanogens, a stable weakly alkaline environment allows acid-producing bacteria to produce and accumulate organic acids in large quantities, which also continuously provides a rich and stable source of substrate for methanogens, promoting their growth and metabolism. The synergistic effect of the two is conducive to the formation of a better stable bacterial population.

[0028] Preferably, the temperature of the landfill leachate entering the UASB reactor is controlled to be 27-37°C.

[0029] The present application adopts the acclimation liquid temperature slightly higher than normal temperature as the growth environment of anaerobic strains. Usually, various metabolic activities in microbial cells all rely on the catalysis of enzymes. At this temperature, the enzymes in most strains are kept at a high activity, and the growth rate of microorganisms is usually moderate. Neither will the growth be too fast due to the high temperature, so that the cells do not have time to adapt to salt stress and metabolic disorders occur, nor will the growth be too slow due to the low temperature, which prolongs the acclimation period. Moderate growth rate helps strains to have enough time to carry out physiological adjustments and genetic adaptations in a gradually increasing salt concentration environment, and gradually improve salt tolerance. And controlling the acclimation liquid temperature at room temperature or slightly higher than room temperature can also save energy and cost to a certain extent, without consuming a large amount of energy for the operation of heating or cooling equipment, thereby improving the economy and feasibility of the whole acclimation process, and being conducive to large-scale strain salt tolerance acclimation operation and subsequent practical application.

[0030] Preferably, the hydraulic retention time of the landfill leachate entering the UASB reactor is controlled to be 262 to 284 hours.

[0031] Different hydraulic retention times (HRTs) will create different hydraulic environments and substrate concentration gradients, which will help screen out bacteria that are adapted to specific treatment conditions and have specific functions. Inappropriate HRTs will cause hydraulic scouring of certain unsuitable bacteria, making it difficult for them to stay and grow and reproduce in the reactor, and thus gradually be eliminated and screened out. During the anaerobic digestion process, the HRT set in this application is long enough for acid-producing bacteria to convert substrates into metabolites and accumulate them to a certain concentration, providing methanogens with suitable substrate concentrations and types, and achieving better connection between the acid-producing stage and the methanogenic stage in time and space. The two are better matched with each other in growth rate and metabolic activity, forming a stable microbial community structure, and improving the system's ability to degrade complex substrates and adapt to environmental changes.

[0032] The domestication method of the present application is used to obtain a salt-tolerant bacterial strain that is better at treating landfill leachate, has high biological activity and metabolic rate, and can maintain activity in a high-salt environment. Compared with ordinary bacterial strains, they can more efficiently decompose and remove organic matter in wastewater, converting it into harmless substances such as carbon dioxide and water, thereby reducing the discharge of chemical oxygen demand (COD) and biochemical oxygen demand (BOD), making it easier for wastewater to meet emission standards, improving wastewater treatment efficiency, shortening the residence time of wastewater in the treatment system, and increasing the wastewater treatment capacity of the treatment plant. The obtained salt-tolerant bacterial strain can maintain a high activity and metabolic capacity when the salinity changes, has strong stress resistance and adaptability, can quickly adapt to environmental changes, make the wastewater treatment system more stable, reduce the situation of reduced treatment efficiency or system collapse due to salinity shock, improve the overall operating efficiency of the treatment plant, and reduce overall operating costs.

[0033] Compared with the prior art, the technical solution of this application has at least the following beneficial effects:

[0034] 1. The present invention utilizes the landfill leachate to be treated as the acclimation liquid to acclimate the anaerobic bacteria in the UASB reactor to salt tolerance. This method effectively combines the structural characteristics of the UASB reactor and, through the design of the acclimation process, including the increasing gradient of inorganic salt concentration, the increasing days, and the acclimation period, can effectively acclimate the anaerobic bacteria in the sludge bed, especially the acid-producing bacteria and methanogens that play an important role in degradation, to salt tolerance. This allows the anaerobic bacteria to better cope with complex sewage environments, improves their treatment efficiency for high-salinity sewage, and avoids damage to the membrane system caused by excessive salt content.

[0035] 2. In addition to designing the acclimation process, the acclimation method of the present invention also controls the pH value, temperature, and hydraulic retention time of the acclimation liquid, i.e., the landfill leachate, in the reactor during the process, so that the acclimation process is more in line with the actual production scenario, and the resulting salt-tolerant bacteria can also be better used in subsequent applications.

[0036] 3. The domestication method of the present invention effectively achieves the simultaneous domestication of acid-producing bacteria and methanogens, breaking through the inhibitory effect of acid-producing bacteria on methanogens during the reproduction and metabolism process. In addition, the obtained salt-tolerant bacterial population not only has good salt tolerance, but also has good activity and can efficiently treat landfill leachate to meet emission standards. DETAILED DESCRIPTION

[0037] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, all are conventional products that can be purchased commercially.

[0038] A method for acclimating anaerobic bacteria to salt tolerance in a UASB reactor comprises the following steps:

[0039] Landfill leachate is introduced into a UASB reactor. The inorganic salt concentration of the initial leachate is 20-30 g / L. The inorganic salt concentration of the leachate is then increased incrementally every 2-3 days, by 0.5 g / L each time, for 45-60 days until the leachate concentration entering the UASB reactor reaches 40-50 g / L, thereby obtaining a salt-tolerant bacterial strain. During the acclimation period, the leachate entering the UASB reactor is maintained at a pH of 7-8, a temperature of 27-37°C, and a hydraulic retention time of 262-284 hours.

[0040] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments of the present invention can be combined with each other. The present invention will be described in detail below with reference to specific embodiments.

[0041] Examples 1 and 2

[0042] The embodiments of the present invention are implemented according to the technical solutions in the above specific embodiments. The specific implementations are shown in Tables 1 to 3.

[0043] Table 1: Inorganic salt concentration of landfill leachate entering UASB reactor in Examples 1 and 2

[0044]

[0045] Table 2: Anaerobic bacteria acclimation conditions of Examples 1 and 2

[0046]

[0047] Table 3: Water effluent from the UASB reactor in Examples 1 and 2

[0048]

[0049] It can be seen from Table 3 of the examples that in the salt-tolerance acclimation process of the technical solution of the present application, with each change in the salt concentration gradient, the COD removal rate will have a process of decreasing and then increasing with the change in salinity, and the removal effect can basically return to the previous high point, indicating that microorganisms, especially methanogens, are slowly adapting to environmental changes such as osmotic pressure. The content of volatile acid in the effluent shows a similar trend, which shows that during the acclimation process, acid-producing bacteria are constantly adjusting themselves to adapt to the high-salt environment, and the volatile acid produced at this time also helps the growth and reproduction of methanogens. Practice has shown that by maintaining the UASB reactor within an appropriate salinity range, keeping other water inlet conditions unchanged, and gradually increasing the salt concentration of the reactor inlet, anaerobic microorganisms can maintain their initial good activity, maintain the treatment state of the reactor at a good level, and achieve good removal effects for COD and volatile acid.

[0050] The embodiments described above are some embodiments of the present invention, rather than all embodiments. The detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed application, but merely represents selected embodiments of the present invention. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making creative efforts are within the scope of protection of the present invention.

Claims

1. A method for salt-tolerant acclimation of anaerobic bacteria in a UASB reactor, comprising: performing salt-tolerant gradient acclimation on the anaerobic bacteria, characterized in that: The anaerobic bacteria are located in the UASB reactor, and landfill leachate is introduced into the UASB reactor. The inorganic salt concentration of the landfill leachate introduced for the first time is 20 to 30 g / L. Thereafter, the inorganic salt concentration of the landfill leachate is increased every 2 to 3 days, and the bacteria are acclimated for 45 to 60 days at a gradient increase of 0.5 g / L each time until the concentration of the landfill leachate introduced into the UASB reactor reaches 40 to 50 g / L, thereby obtaining a salt-tolerant bacteria.

2. The method for salt-tolerant acclimation of anaerobic bacteria in a UASB reactor according to claim 1, characterized in that: The pH value of the landfill leachate entering the UASB reactor is controlled to be 7-8.

3. The method for salt-tolerant acclimation of anaerobic bacteria in a UASB reactor according to claim 2, characterized in that: The temperature of the landfill leachate entering the UASB reactor is controlled to be 27-37°C.

4. The method for salt-tolerant acclimation of anaerobic bacteria in a UASB reactor according to claim 1, characterized in that: The hydraulic retention time of the landfill leachate entering the UASB reactor is controlled to be 262 to 284 hours.

5. A salt-tolerant bacterial species, characterized in that The anaerobic bacteria are domesticated using the domestication method of an anaerobic bacteria in a UASB reactor as claimed in any one of claims 1 to 4.

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