I. Overview The water resources in most areas of China, especially in the north, are relatively scarce. With the development of the economy and the improvement of people's living standards, the demand for industrial, agricultural and domestic water has increased year by year, and the development and utilization of water resources has become more and more important. Among the water resources in China, groundwater is being widely developed and applied due to its wide distribution, good water quality and low pollution. But due to the natural state of the rock itself And destruction of vegetation, the concentration of Fe 2+ and Mn 2+ groundwater significantly exceeds requirements, thus reducing the groundwater Fe 2+ and Mn 2+ concentration to drinking water standards, it has become a hot research in recent years. Groundwater iron and manganese removal methods mainly include: alkali adjustment pH value, strong oxidant oxidation method, ion exchange method, ozone oxidation method, magnetic separation method, etc. China's research on groundwater iron removal technology is relatively early, and the research on manganese removal is relatively rare. The theory and application have experienced natural oxidation, contact oxidation and biological oxidation. (1) Natural oxidation method Natural oxidation methods include a series of complex processes such as aeration, oxidation, precipitation, and filtration. Aeration is to make the iron-containing groundwater fully contact with the air, so that the oxygen in the air dissolves in the water, and at the same time, the CO 2 in the groundwater is dispersed in a large amount, and the pH value is increased to facilitate the chemical oxidation of the iron-manganese. After aeration of groundwater, the pH is generally between 6.0 and 7.5. Fe 2+ is oxidized to Fe 3+ and precipitated as Fe(OH) 3 , which is removed by precipitation and filtration. However, the removal of Mn 2+ can not be achieved only by simple aeration, because the natural oxidation rate of Mn 2+ is significantly accelerated at pH greater than 9.0, while the groundwater is mostly neutral, under the same pH conditions. The oxidation of Mn 2+ is much slower than that of Fe 2+ and it is difficult to be removed by the oxidation of dissolved oxygen into a precipitate. Therefore, it is necessary to add alkali (such as lime) to the groundwater to raise the pH to oxidize Mn 2+ . It can be seen that the natural oxidation method requires further acidification after manganese removal, which complicates the process and increases operating costs. Secondly, in the actual operation, due to the fine Fe(OH) 3 floc particles, it is easy to penetrate the filter layer, and the iron removal effect sometimes fails to meet the requirements. The oxidation and precipitation process requires that the treated water stays in the sedimentation tank for a long time, about 2 to 3 hours. Therefore, the process equipment is large and the investment is high. In addition, the formation of a ferrosilicon complex with dissolved silicic acid in water and Fe(OH) 3 makes it difficult to agglomerate Fe(OH) 3 colloid, which affects the separation of Fe(OH) 3 from water by flocculation. The existence of the above questions limits the extensive application of this method in engineering practice, and does not reach the fundamental goal of efficient iron and manganese removal. (2) Contact oxidation method In the 1960s, Li Guibai and others developed the groundwater iron removal technology, successfully experimented with the natural manganese sand contact oxidation and iron removal process and established the theory of contact oxidation and iron removal in the 1970s. In the early 1980s, contact oxidation was developed. Manganese process and rapid promotion. After simple aeration, the groundwater directly enters the filter tank. Under the action of the catalyst on the surface of the filter material, Fe 2+ and Mn 2+ are directly oxidized and then removed by the filter layer. The mechanism of this method is autocatalytic oxidation reaction, the catalyzed by the iron and manganese active filter membrane on the surface of the filter. The iron active filter adsorbs Fe in water, and the adsorbed Fe 2+ is rapidly oxidized to Fe 3+ under the catalytic action of the active filter membrane, and the product acts as a catalyst and participates in the new catalytic reaction. Similarly, Mn2+ is oxidized to MnO by dissolved oxygen in water under the action of manganese active membrane on the surface of the filter material, and adsorbed on the surface of the filter material, so that the filter membrane is continuously updated. The autocatalytic action of the active membrane achieves the removal of Mn 2+ at pH > 7.5, which reduces the difficulty of removing manganese and solves the complicated process of natural oxidation process. The residence time of water in the system is only 2 ~ 30 min, the equipment is small, greatly reducing the operating costs. At the same time, the removal of iron is not affected by the dissolved silicic acid, and the total iron concentration of the effluent is also reduced as the filtration time increases, and the water quality is getting better during the filtration cycle. However, since the redox potential of iron is lower than that of manganese, the rate of oxidation of Mn 2+ to MnO 2 in the filter layer is slow, and the maturation period of the manganese active filter membrane is long. In addition, the manganese active filter sometimes cannot be formed due to frequent backwashing, which makes the manganese removal effect unstable. In addition, the use of first-stage aeration, filtration, iron removal and manganese removal will increase the thickness of the iron removal filter layer on the filter bed, and the thickness of the lower manganese removal filter layer will decrease, which will affect the manganese removal effect. When the iron or manganese concentration is high, the first-stage aeration, filtration and iron removal, secondary aeration, and filtration and manganese removal are generally used. However, the process tends to be complicated and the operation cost is high. Practice has shown that this method of removing iron and manganese from groundwater is not sufficiently rigorous and requires more effective methods and techniques. (3) Microbial oxidation method Previous research has shown that some microorganisms capable of producing extracellular polymers such as polysaccharides, glycoproteins, lipopolysaccharides, etc. groups having a large number of anions, complexed with metal ions. Microorganisms can also change the valence state of metals through methylation, hydration, absorption, oxidation and reduction. Some microorganisms can also change metals from highly toxic to low toxic through biotransformation or physiological metabolic activities. . In the late 1980s, Academician Zhang Jie of China conducted in-depth research on the manganese removal filter and found that there was a large amount of microbial growth on the surface of the sand filter. This proposed a new idea of ​​biocatalytic oxidation and iron removal, and took the lead in China in the 1990s. The theory and application research of new technologies for groundwater biological manganese removal were carried out. 1. Biological method for removing manganese The early mechanism of manganese removal from groundwater was derived from the high-efficiency iron removal process and the similar chemical structures and properties of iron and manganese. After in-depth research, it is found that the biological manganese removal method is not a manganese oxide but a microorganism, and the main body of oxidation is iron-manganese bacteria. Therefore, the researchers re-examined the mechanism of microbial manganese removal by microscopic analysis. It is believed that the primary oxidation of biooxidation and manganese removal is achieved by the enzymatic reaction in the intracellular phase of manganese oxidizing bacteria, and Mn 2+ is adsorbed in negatively charged On the extracellular polymer on the surface of the cell membrane of manganese oxidizing bacteria, an enzymatic reaction is produced. The biopolymer secreted near the oxidizing bacteria produces an alkaline microenvironment, resulting in a simple catalytic reaction. 2. Biological method for removing manganese The process of biological manganese removal includes three stages of diffusion, adsorption and oxidation. In the diffusion phase, Mn 2+ diffuses from the water to the surface of the biofilm; in the adsorption phase, Mn 2+ diffused to the surface of the biofilm is adsorbed onto the surface of the biofilm by van der Waals attraction and bacterial extracellular secretion; during the oxidation phase, it is adsorbed Mn 2+ is oxidized to MnO 2 . The process may include two aspects. One is to form an alkaline microenvironment around and inside the microorganism. Mn 2+ is diffused into the surface of the microorganism and enters the interior of the biofilm. Dissolved oxygen is rapidly oxidized. Second, Mn 2+ adsorbed on the surface of the biofilm is oxidized to MnO 2 under the catalysis of microbial extracellular enzymes. The iron-manganese oxidizing bacteria are inoculated in the filter tank, and after cultivation, a complex microbial ecosystem is formed on the surface of the clinker, and a large number of bacteria having manganese oxidizing ability exist in the system. The activity of the filter layer is derived from the activity of the attached manganese oxidizing bacteria. The bacteria regenerate a new adsorption surface on the carrier, thereby making the adsorption, oxidation and regeneration in a dynamic equilibrium. 3. Advantages of biological method for removing manganese and problems still to be solved The biological method is a new method proposed by microbial technology, which improves the manganese removal effect and reduces engineering investment and operating costs. It is the latest development direction in the field. However, in engineering practice, due to the difference in water quality, the biological manganese removal filter column lacks standardized debugging operation methods, such as backwashing time, period and strength, filtration rate, dissolved oxygen amount, filter layer thickness, filter material size, etc. There is no uniform standard on the selection. How to shorten the maturity time of the filter material and reduce the head loss under the premise of ensuring the qualified water is still a subject that should be continuously studied. The solution of these problems will have greater practical significance for reducing operating costs and improving the removal of iron and manganese ions. (4) Other methods of iron and manganese removal Other groundwater iron and manganese removal technologies such as chlorine oxidation, ozone oxidation, potassium permanganate oxidation and ion exchange, although sometimes can achieve better manganese removal, but the process is complex, costly, and debugging It is difficult to operate, and some methods (such as treatment with ozone) have the risk of bacterial growth. The treatment process will produce a large amount of sludge, which is rarely used in large and medium-sized groundwater plants in China. Second, the factors affecting the efficient removal of manganese by microorganisms Compared with the traditional method, microbial solid manganese and manganese removal have obvious advantages. In order to efficiently remove manganese on the basis of microbial manganese removal, it is necessary to explore economical and effective methods and conditions for improving biological manganese removal. Based on the research situation in recent years, several factors affecting the high-efficiency manganese removal technology of microorganisms are found. (1) Nutritional conditions such as carbon, nitrogen and phosphorus The iron-manganese bacteria usually separated from groundwater are facultative oligotrophic microorganisms. Therefore, the nutrient content of the medium should not be too high, otherwise it will cause contamination of the bacteria, destroy the original micro-ecological balance, and change the original filter material. The surface structure causes the manganese removal rate to decrease or the leakage of manganese to occur, which seriously damages the water quality. Studies have shown that the growth of such microorganisms and the maturity of the filter material only require some essential nutrients such as carbon, nitrogen and phosphorus. The carbon source material becomes a microbial cell material and metabolite after a series of complicated chemical changes during microbial growth. The carbon source that microbes can utilize is divided into inorganic carbon source and organic carbon source. Studies have shown that the presence or absence of organic carbon has almost no effect on the filter layer. Simply relying on CO 2 dissolved in water can ensure the carbon demand of the filter layer. This is because the dominant bacteria in the biological iron and manganese removal filter layer is mainly iron-manganese bacteria. Most of these bacteria belong to the chemical autotrophic bacteria. CO 2 is the carbon source of their cell metabolism, so it relies solely on dissolution. The CO 2 in the water ensures the carbon demand of the filter layer. Nitrogen sources are generally not used as energy sources and are mainly used to synthesize nitrogenous substances in cells. It has been pointed out in the literature that extremely small amounts of nitrogen can ensure the demand for nitrogen sources in mature biological iron and manganese removal filters. The content of ammonia nitrogen in groundwater generally provides sufficient nitrogen source to ensure efficient and stable operation of biological iron and manganese removal filter. Phosphorus is an essential element for the growth of microorganisms. The content of phosphorus in the medium only needs to ensure that the ferromanganese bacteria can grow normally and play a role. The proper carbon-phosphorus ratio in the medium has a significant effect on the biological manganese removal. When the mass ratio is reduced to 20:1, the manganese removal effect is improved, but if the carbon-phosphorus mass ratio is further reduced, the manganese removal effect is not obvious. In addition, calcium and magnesium ions have a great influence on microorganisms. Calcium has the functions of regulating pH value and reducing cell membrane permeability, and is an important cofactor for some enzymes. Magnesium is also a cofactor for many enzyme reactions. The distribution of calcium and magnesium ions in groundwater is extensive, and almost all groundwater can meet the nutritional requirements of calcium and magnesium ions in biological iron and manganese removal filters. (2) dissolved oxygen Biological oxidation and manganese removal requires a certain amount of dissolved oxygen for the growth of bacteria in the influent, but the oxygen content also has a certain standard, because the high oxygen content will accelerate the chemical oxidation of Fe 2+ , which is not conducive to the oxidation of manganese. Studies have shown that when the water contains a certain amount of dissolved oxygen, the biological manganese removal effect is basically not affected by the amount of dissolved oxygen. At this time, if the aeration intensity is increased to increase the oxidation rate of Mn 2+ in the filter column, it is not only unnecessary, but also increases the treatment cost. In biological methods, simple aeration (such as water drop, jet aeration, etc.) can meet the demand for dissolved oxygen in iron and manganese oxidation. (C) the choice of several filter materials Du Juhong et al.'s research shows that the filter material mainly has two functions: first, as a carrier, an active filter membrane is formed on the surface to catalytically oxidize Fe 2+ and Mn 2+ in water; secondly, it is filtered to intercept water. Iron manganese oxidation product. Different filter materials have different maturity times due to differences in physical properties, etc., and the effect of removing manganese is also different. There are quartz sand, manganese sand and anthracite filter media. Quartz sand filter material is a hard, wear-resistant, chemically stable silicate mineral. The main component is SiO 2 . The filter material has high density, high mechanical strength and long service life. Quartz sand is used as a filter medium. Under the pressure, it can effectively intercept and remove some heavy metal ions in water. Manganese sand filter material is made of manganese ore as raw material, crushed, sieved, etc. It is a special filter material for treating water. It is often used in iron and manganese removal filter devices. The effect is good. It is worth noting that when manganese is used When the mass fraction of MnO 2 in the sand filter is more than 35%, both iron and manganese can be removed, and the manganese sand filter with a mass fraction of less than 30% can only be used for groundwater removal. Anthracite filter material is selected from deep well minerals, with high carbon content, high mechanical strength, stable chemical properties, no toxic and harmful substances, and is insoluble in general acidic, alkaline and neutral water. Comparing several kinds of filter materials, it is found that the manganese sand filter material has large adsorption capacity, but its mechanical strength is low, the relative volume and mass are large, and the price is high. Although the quartz sand filter material has less adsorption strength than manganese sand, it has high mechanical strength, relative volumetric quality and moderate price. Anthracite filter material has high porosity, relatively small volume and low price, and can be used as a carrier of iron-manganese bacteria from physical properties. Because the higher porosity can increase the biomass in the filter layer, save the water consumption of the backwash, and at the same time, make the microbial system and Fe 2+ and Mn 2+ penetrate deeper into the filter layer with the raw water, and play the whole filter. The manganese removal capacity of the layer. The porosity is large, avoiding excessive clogging of the surface layer, delaying the increase of the full-layer resistance and prolonging the backwashing cycle. Light weight can reduce backwashing strength. In addition, compared with quartz sand and manganese sand filter materials, anthracite filter material significantly accelerates the maturity of the filter pool and greatly shortens the maturity time of the filter pool. Third, the technical process to shorten the filter maturity time The increase in filter column activity is not due to the proliferation of bacteria on the surface of the filter material, but the growth of bacteria in the iron mud. The maturity of the filter column requires a period of time to immobilize the bacteria on the filter material. In general, the maturity of the filter column can be divided into four periods: 0-15d is the adaptation period. At this stage, the filter layer has almost no obvious manganese removal effect; 15-30d is the first active growth period, at this time with the microbial Continuous reproduction, the manganese removal rate of the filter layer is continuously improved; 30-50d is the second active growth period, at which time the microbial quantity is relatively stable, the effluent manganese gradually reaches the standard; after 50d, it reaches the stable period, at which time the filter layer is fully mature and stable. . It can be seen that the formation and maturation of the active membrane in the groundwater treatment filter of a large water plant takes a long time, so shortening the maturity of the membrane is of great significance for reducing production cost and improving manganese removal efficiency. (1) Complete oxidation time The complete oxidation time of Fe 2+ in groundwater varies greatly from region to region, which is mainly affected by dissolved oxygen, soluble silicic acid, water acidity and alkalinity in water. In some areas, groundwater can be oxidized to Fe 2+ colloidal particles in a short period of time after exposure to air, and some can not be completely oxidized for a longer period of time. After complete oxidation of Fe 2+ , the groundwater changes from clear and transparent to turbid yellow-brown, forming a thin layer of iron mud on the surface of the filter layer. These iron muds will affect the growth of biofilm and lead to prolongation of maturity. (B) the adhesion efficiency of the bacteria In engineering practice, only bacteria with strong oxidizing ability are not enough. It is also necessary to have better adhesion of bacteria and filter materials. Studies have shown that appropriate immobilization methods can be used. Chitin as an immobilized carrier can effectively promote the maturity of the filter material. First of all, due to the very loose structure of chitin itself, it has a strong affinity for proteins and is positively charged in a slightly acidic medium, so it has a strong adsorption effect on microorganisms, especially negatively charged bacteria. Secondly, chitin is extracted from organisms, has good biocompatibility, is harmless to microorganisms and can maintain microbial activity at a high level. The literature indicates that chitin retains 90% of the activity of enzymes when immobilized amylase and lysozyme. In addition, the optimum pH range for the adsorption and chelation of heavy metal ions by chitin is 6.5-8.0, which is in the range of pH value of microbial solid manganese and manganese, and the optimal pH range of microorganisms is also consistent. Protects microorganisms from heavy metal ions. (3) The influence of Fe 2+ Practice has proved that, in the process of biological removal of manganese, Fe 2+ plays a significant role, the presence of Fe 2+ in addition to promoting the secretion of extracellular enzymes and microorganisms to stimulate their activity, but also can transfer the electronic value by varying Fe 2+, Mn catalyst 2+ oxidation reaction. In addition, it may also act as an enzyme activator. When Fe 2+ is combined with an enzyme, Mn 2+ is more favorable to combine with the catalytic site and binding site of the enzyme to accelerate the oxidation of Mn shake. If Fe 2+ is absent in the influent water, the filter column has only physical adsorption to Mn 2+ and cannot achieve the purpose of biological solid manganese removal. The reason is that when Fe 2+ is not present or the mass concentration is too low, the filter layer is extremely oligotrophic environment, and the oxidation rate of the substrate to the substrate is affected by the substrate concentration, the substrate concentration is too low, and the metabolism of iron-manganese bacteria is Reproduction is limited and the maturity period is extended accordingly. However, excessive Fe 2+ will compress the manganese removal space of the filter layer, affecting the removal of Mn 2+ , and hindering the oxidation of Mn 2+ due to the reduction, which also leads to frequent backwashing, which is disadvantageous for the culture of the filter. (4) Filtration speed The size of the filtration rate during the culture period directly affects the maturity of the filter layer, which is mainly due to the environmental requirements of the iron-manganese bacteria. After the iron-manganese bacteria are in contact with the carrier, they cannot be firmly attached to the surface immediately. If the filtration rate is large at this time, the corresponding water flow shearing force is also large, and the bacteria just attached to the surface of the filter material are washed away. Therefore, a relatively stable environment is required after the iron-manganese bacteria are in contact with the surface of the carrier, so that they can have a certain residence time on the surface of the carrier, so that the iron and manganese oxidizing bacteria adhere firmly on the surface of the carrier. Create conditions for future growth and reproduction. As the number of microorganisms in the filter layer increases, the amount of microorganisms attached to and fixed on the surface of the filter sand increases, and the filtration rate can be gradually increased. Therefore, adopting a low filtration rate is beneficial to the rapid maturation of the biofilter layer. (5) Backwashing time and strength It is extremely important for the biological iron and manganese removal filter to maintain the biomass and its activity in the sand filter surface and the pores of the filter layer. Therefore, the backwashing operating parameters are particularly important during the cultivation. The backwashing intensity is weak and the time is short, which will cause the accumulation of iron mud, bacterial metabolites and aging cells, increase the head loss of the filter layer, affect the biological activity, and even occur when the filter layer is formed, affecting the normal operation of the filter tank and reducing the manganese removal. rate. For groundwater of different water quality, the backwashing parameters of the filter are different. A number of factors should be considered comprehensively and determined according to the production status. In general, the determination of the backwashing parameters should follow the following principle: During the culture period, the backwashing intensity is gradually increased from weak to strong, the time is gradually extended, and the working cycle of the filtration is correspondingly shortened. After the filter layer is matured, the treatment capacity and impact load resistance of the filter layer are greatly improved. At this time, the backwashing strength should be improved to ensure smooth biological metabolism. Appropriately increase the backwashing intensity, so that the bacteria can adapt to the strong hydraulic impact, which is beneficial to maintain the stability of the filter layer and promote the quick start of the filter. Therefore, it is necessary to determine a reasonable backwashing intensity from the actual situation. (6) How the filter operates The operation mode of the filter tank is also one of the factors affecting the maturity of the filter tank. The operation mode of the traditional filter tank is the downflow filtration of the graded filter material. The graded filter layer is characterized by the small particle size of the upper filter material and the lower layer particle. The large diameter, for the hydraulic conditions of the downward flow filtration, will cause a large amount of iron-manganese oxide to be quickly deposited on the upper part of the filter layer, which not only reduces the adsorption capacity, but also causes the head loss to grow faster. Moreover, since the clogging of the upper filter layer hinders the penetration of the bacteria into the lower layer, the bacterial growth of the entire filtration space is hindered, and the filter layer culture period is relatively long. In the homogeneous filter layer (the so-called homogeneous filter material means that the filter material composition and the average particle size are uniform on any cross-section along the depth direction of the entire filter layer), and the increase of the particle size of the upper filter material makes the iron-manganese impurity have More opportunities to enter the lower filter layer, provide conditions for the propagation of iron-manganese oxidizing bacteria deep in the filter layer, slowing the head loss and prolonging the filtration cycle. Under the same experimental conditions, the penetration depth of iron in the homogeneous filter layer is twice that of the graded filter layer. In the distribution of the number of bacteria, the homogeneous filter layer significantly increases the effective biolayer thickness and improves the thickness. The effective biological amount of the filtration space greatly enhances the processing capacity of the biological filter layer, and at the same time, when the filter layer is backwashed, a part of the bacteria in the lower layer space can be carried into the upper filter material, thereby promoting the proliferation of the whole filter layer bacteria and improving the filter layer space. The number of bacteria inside, thereby shortening the filter culture period. Fourth, the impact of strains The latest research shows that the adaptability of mixed bacteria is stronger than that of a single strain, and the complementary effect between mixed bacteria makes the oxidation stronger than a single strain. Although each single strain has a certain adaptation to the growth period, in general, when the bacteria coexist with other bacteria, the growth and development is much better than when they grow alone, so the bacteria adapt to the growth period is very short, does not affect the entire system. Variety. In addition, the research process also shows that the oxidation process of manganese by mixed bacteria is relatively stable. V. Conclusion This paper summarizes the groundwater iron and manganese removal technology commonly used in China, and compares the main methods of natural oxidation, contact oxidation and biological oxidation. At the same time, it introduces the biological application widely used in northern China. Manganese manganese removal method, the development of microbial manganese removal technology was discussed and the existing problems were discussed. Various processes have their own advantages and disadvantages. In order to choose the most suitable treatment method, various factors should be considered and the methods should be comprehensively applied. Achieve effective and economical treatment. Taper Roller,Carrying Roller,Large Conveyor Rollers,Nylon Conveyor Rollers Qufu Zhuoyue Heavy Industry Science&Technology Co., Ltd , https://www.zhuoyueindustry.com