Air flotation treatment method is to pass air to the wastewater, and in the form of tiny bubbles precipitated from the water to become a carrier, so that the emulsified oil in the wastewater, tiny suspended particles and other pollutants adhering to the bubbles, with the bubbles up to the surface of the water to form a bubble a three-phase mixture of gas, water, particles (oil), through the collection of bubbles or flotsam to achieve the separation of impurities, purification of wastewater Purpose. Flotation method is mainly used to deal with wastewater by natural sedimentation or upward flotation is difficult to remove the emulsified oil or relative density close to 1 of the tiny suspended particles.
(B) the basic principles of air flotation
1. The flotation of the floc particles with air and the relationship between the surface load of air flotation
adherent bubbles of floc particles in the water when floating in the macroscopic will be subjected to gravity G buoyancy F and other external forces. The speed of floc floating with gas can be derived from Newton's second law, the floating speed depends on the difference in density between the water and the floc with gas, the diameter of the floc with gas (or characteristic diameter) and the temperature of the water, the flow state. If the band with gas floc particles in the proportion of bubbles in the larger the density of the floc particles with gas is smaller; and its characteristic diameter is increased accordingly, both of this change can make the floating speed greatly increased.
However, the actual water flow; with gas flocs of different sizes, and the resistance caused by the constant change, while in the air flotation of the external force also changes, so that the bubble formation body and floating speed is also changing. The specific floating speed can be determined according to the experiment. According to the value of the floating speed can determine the surface load of the air flotation. And the determination of the floating speed shall be determined according to the requirements of the water.
2. Adhesion of floc particles in the water to the bubble
As mentioned earlier, the main separation of pollutants in the water flotation method, there are two types of flocs and particles of the coagulation reaction monomer. The combination of air bubbles on coagulation flocs and particles in the process of air flotation can be three ways, namely, bubble top support, bubble wrap and air particle adsorption. Obviously, the strength of the wrap and adhesion between them, that is, gas, particle (including floc waste) combined with the degree of firmness or not, not only with the particles, the shape of the floc, more importantly, by the three-phase interface between the water, gas, particles and the nature of the impact. The content of active agent in the water, the hardness of the water, the concentration of suspended solids, and the viscous flotation strength of the bubbles have a close relationship. Good or bad operation of air flotation and this is fundamentally related. In the actual application of quality must be adjusted water quality.
3. The formation of bubbles in the water and its characteristics
The formation of bubbles depends on the size and strength of the release of air when the various uses of conditions and the size of the surface tension of the water. (Surface tension is equal in size and opposite in direction, respectively, on the surface layer of the mutually contacting parts of a pair of forces, which always acts in the direction tangent to the liquid surface.)
(1) the smaller the radius of the bubble, the greater the additional pressure inside the bubble, the bubble air molecules on the bubble film collision chances are also more and more intense. Therefore to obtain a stable micro bubble, bubble film strength should be ensured.
(2) The bubble is small, the floating speed is fast, the disturbance to the water body is small, and it won't smash the floc. And can increase the bubble and floc collision rate. But it is not the finer the bubble the better, the bubble is too fine to affect the floating speed, and thus the size of the air flotation tank and the cost of the project. In addition to adding a certain amount of surfactant, can effectively reduce the surface tension coefficient of water, strengthen the bubble film fastness, r also become smaller.
(3)Adding highly soluble inorganic salts to the water can weaken the bubble film fastness, and make the bubbles easy to rupture or and large.
4, surfactants and coagulants in the separation of the role and impact of air flotation
(1) surface-active substances affect
such as the lack of surface-active substances in the water, small bubbles will always have a tendency to break through the bubble wall and large bubbles and merge to undermine the stability of the air flotation body. At this time it is necessary to add foaming agent to the water to ensure the stability of the bubbles in the air flotation operation. The so-called foaming agent, most of which is composed of polar and non-polar molecules of surfactants, surfactants, the molecular structure of the symbols are generally used to indicate 0, rounded end of the polar base, soluble in water, reaching out to the water (because the water is a strong polar molecules); end of the nonpolar base, hydrophobic, reaching out to the air bubble. Due to the same number of charge repulsive effect, thus preventing the annexation and bursting of bubbles, enhanced foam stability, and thus most surfactants are also foaming agent.
Organic pollutants content of wastewater flotation treatment, bubble dispersion and foam stability may be necessary (such as drinking water flotation filtration). But when its concentration exceeds a certain limit due to the increase in surface-active substances, so that the surface tension of the water is reduced, the water pollution particles serious emulsification, the surface potential increases, at this time the role of the water contains the same charge with the polluted particles of the role of the surface-active material is turned to the opposite side, then despite the bubble phenomenon is strong, the bubble formation is stable; but the gas a particle of adhesion is not good, the effect of air flotation becomes low. Therefore, how to grasp the best content of surface-active substances in the water has become one of the important topics to be explored in the air flotation treatment.
(2) coagulant addition of charged floc
The industrial wastewater containing finely dispersed hydrophilic particles of impurities (such as pulp, coal sludge, etc.), the use of air flotation treatment, in addition to the application of the application of the previously mentioned addition of electrolytic coagulant for the surface of the electrical neutralization method, but also to the water to the water (or the presence of water) flotation agent, but also to the particles of hydrophilic surface changes to the hydrophobicity and can adhere to the air bubbles. capable of adhering to air bubbles. When the polar end of the flotation agent (which is also a surface-active substance composed of diphilic molecules) is adsorbed on the surface of the hydrophilic particles, the nonpolar end of the flotation agent is oriented toward the water, so that the substance having a hydrophilic surface is changed to hydrophobicity, and thus is able to adhere with the air bubbles and float to the surface of the water with them.
There are many kinds of flotation agent, the use of whether it can play a role, first of all, whether its polar end can be attached to the surface of the hydrophilic pollutants, and the strength of its bonding force with the bubble depends on the length of its nonpolar end of the chain.
Such as the separation of coal washing wastewater in the coal dust flotation agent used for de-phenolization of light oil, oil, diesel oil, kerosene or pine oil, etc..
(C), the form of air flotation process
Air flotation water purification process has developed a variety of forms. According to the way it produces bubbles can be divided into: cloth gas method of air flotation (including the rotor broken gas method, microporous cloth gas method, impeller diffusion flotation method, etc.) electrolytic air flotation; biochemical air flotation (including biological gas flotation, chemical gas flotation); dissolved air air flotation (including the real air flotation, pressure air flotation method of the whole dissolved air, part of the dissolved air and part of the reflux dissolved air type).
1. Cloth air flotation
Cloth air flotation is the use of mechanical shear, will be mixed in the water of the air into tiny bubbles, in order to carry out the method of air flotation. According to the different methods of crushing bubbles, cloth air flotation is divided into: pump suction pipe suction air flotation, jet air flotation, diffusion plate aeration flotation and impeller air flotation and other four.
(1) pump suction pipe suction air flotation
This is the simplest method of air flotation. Due to the limitations of the pump's operating characteristics, the amount of suction air should not be too much, generally not greater than 10% of the suction volume (by volume), otherwise it will destroy the pump suction pipe negative pressure work. In addition, the air bubbles in the water pump is not broken enough completely, particle size, air flotation effect is not good, this method is used to deal with oil-containing wastewater after passing through the de-oiling pool, the oil removal efficiency is generally 50% ~ 65%.
(2)Jet air flotation
The water with air jets to the wastewater mixed with air flotation method. Jet from the nozzle shot out of the high-speed water so that the suction chamber to form a negative pressure, and from the suction pipe suction air, in the water and gas mixture into the throat section of the intense energy exchange, the air is crushed into tiny bubbles, and then straight into the diffusion section, kinetic energy into potential energy, further compression of bubbles, increasing the solubility of air in the water, and ultimately into the air flotation tank for gas-water separation. The size of each part of the ejector and related parameters, generally through the test to determine its optimal size.
(3) diffusion plate aeration air flotation
This cloth air flotation is more traditional, compressed air through the diffusion plate with microporous or diffusion tube, so that the air in the form of fine bubbles into the water, but due to the diffusion of the device's microscopic holes are too small easy to clog. If the pore size of the microporous plate is too large, must be injected with surfactant, can be used to form tiny bubbles, which leads to the use of this method is limited. But in recent years, the development of the elastic membrane microporous aerator, to overcome the diffusion device microporous easily blocked or large aperture and other shortcomings, with microporous elastic material made of microporous disk to play the role of expansion, closure.
(4) impeller air flotation
Impeller in the motor drive high-speed rotation, the formation of negative pressure under the cover to inhale air, wastewater from the cover of the small holes into the impeller stirring, the air is crushed into tiny bubbles, and fully mixed with water into a water-gas mixture by the rectifier plate to stabilize the flow, the pool in the body of the smooth vertical rise, air flotation. The foam formed is continuously scraped out of the tank by the slowly rotating scraper.
The diameter of the impeller is generally 200~400mm, and the maximum diameter is not more than 600~700mm. The rotational speed of the impeller is 900~1500r/min, and the circumferential linear velocity is 10~15m/s. The depth of the air-floating pool is generally 1.5~2.0m, but it is not more than 3m, and the spacing between the impeller and the guiding blades can also affect the size of the suction volume. Size, practice has proved that this pitch more than 8mm will make the air intake greatly reduced.
This kind of air flotation equipment is suitable for treating wastewater with small water volume and high concentration of pollutants. Degreasing effect is generally up to about 80%, the advantages of cloth air flotation is simple equipment, easy to realize. But its main disadvantage is that the air is not enough to be crushed, the formation of the bubble particle size is larger, generally not less than 0.1mm. so that, in the supply of a certain amount of air under the conditions of the surface area of the bubble is small, and due to the large diameter of the bubble, the movement of the bubble and the removal of pollutants in contact with a short period of time, all of these factors make the cloth air flotation to reach the high efficiency of the removal of the effect.
2. Dissolved air flotation
Based on the type of suspended solids contained in the wastewater, the nature of the degree of purification of the treated water and the different ways of pressurization, the basic process there are the following three.
(1) the whole process of dissolved air flotation method
The whole process of dissolved air flotation method is to pressurize all the wastewater with a pump and inject air before or after the pump. In the dissolved air tank, the air is dissolved in the wastewater, and then the wastewater is sent to the air flotation tank through the pressure reducing valve. Wastewater formed in many small bubbles adhering to the emulsified oil in the wastewater or suspended matter and escape from the water surface, the formation of slag on the water surface. The scum will be discharged into the scum tank by scraper, and discharged out of the tank through scum pipe, and the treated wastewater will be discharged through overflow weir and outlet pipe.
The advantages of the whole process dissolved air flotation method: ① dissolved gas volume, increasing the oil or suspended particles and bubble contact opportunities; ② in the same conditions of the water treatment, it is part of the return flow of dissolved air flotation method of the air flotation tank is small, thus reducing the infrastructure investment. However, because all the wastewater through the pressure pump, so increase the degree of emulsification of oily wastewater, and the required pressure pump and dissolved air tank are larger than the other two processes, so the investment and operation of power consumption is larger.
(2)Part of the dissolved air flotation method
Part of the dissolved air flotation method is to take part of the wastewater pressurization and dissolved air, the rest of the wastewater directly into the air flotation tank and in the air flotation tank and dissolved air wastewater mixing. Its characteristics are: ① than the full-flow dissolved air flotation method requires a small pressure pump, so the power consumption is low; ② pressure pump caused by the amount of emulsified oil than the full-flow dissolved air flotation method is low: ③ the size of the air flotation tank with the full-flow dissolved air flotation method is the same, but part of the reflux of dissolved air flotation method is small.
(3)Partial reflux dissolved air flotation method
Partial reflux dissolved air flotation method is to take a part of the return flow after oil removal for pressurization and dissolved air, decompression and then directly into the flotation tank, and the oily wastewater from the flocculation tank mixing and flotation. The return flow is generally 25% to 100% of the oily wastewater. It is characterized by: ① less pressurized water, power consumption; ② air flotation process does not promote emulsification; ③ alumina formation is good, the flocculation in the effluent water is also less; ④ the volume of the air flotation tank is larger than the first two processes. In order to improve the treatment effect of air flotation, often added to the wastewater coagulant or air flotation agent, dosage varies depending on the water quality, generally determined by the test.
(D), pressurized dissolved air flotation method of the main equipment.
Air intake method of pressurized dissolved air method has two air intake methods, namely, pump forward air and pump back air intake. Pump forward air intake, which is led by the pump pressure water pipe out of a pipe back to the suction pipe, installed on the branch pipe hydrojet, eliminating the need for air compressors. Wastewater through the hydraulic injector caused by negative pressure, the air sucked and wastewater mixing, through the suction pipe, the pump to send people dissolved gas tank. This method is relatively simple, water and gas mixed evenly, but the pump must be self-priming water intake, and to maintain a head of more than 1m. In addition, its maximum suction volume can not be greater than 10% of the water pump suction, otherwise, the pump work is not stable, will produce cavitation. Pump after the air intake, generally in the pressure water pipe through the compressed air. This method makes the pump work stable, and do not have to require working under positive pressure, but need to be supplied by the air compressor air.
There are two main technical performance indicators for evaluating the gas dissolution system, namely, gas dissolution efficiency and unit energy consumption. So far the double membrane theory explains the gas mass transfer in liquid or closer to the actual. According to the double membrane theory, for insoluble gases to determine the main resistance of the mass transfer process from the liquid membrane, while the gas membrane in the mass transfer resistance can be negligible compared to it. That is, to strengthen the dissolved gas process, in addition to should have enough mass transfer driving force, the key is to expand the liquid phase interface or thin liquid film thickness. But in fact, in the turbulence of the free interface is difficult to exist in a stable laminar flow film. Therefore, the emergence of random surface renewal theory, this theory increases the surface renewal rate, that is, in the consideration of gas-liquid contact interface mass transfer, the introduction of the gas phase, the liquid phase in the unit of time due to eddy diffusion into the gas, the liquid renewal interface of the mass transfer factors, so that the theory and the actual closer.
(E) pressurized dissolved air flotation process
Pressurized dissolved air flotation method is most widely used at home and abroad. At present, the pressurized gas flotation method is most widely used. Compared with other methods, it has the following advantages:
Under pressurized conditions, the solubility of air is large, and the number of bubbles used for flotation is large, which ensures the effect of flotation;
The dissolved gas is released by the sudden decompression, and the bubbles produced are not only micro-fine, uniform in particle size, large in density, but also float stably, and the perturbation of the liquid is tiny, which makes it particularly suitable for solid-liquid separation of loose flocs and fine particles;
This method is also widely used in the separation of solid-liquid, and the separation of solid-liquid, and the separation of solid-liquid and fine particles. Solid-liquid separation of loose flocculent, fine particles;
The process and equipment is relatively simple, easy to manage, maintenance; especially part of the reflux type, the treatment effect is significant, stable, and can save energy consumption.
The pump lifts the raw water to the reaction tank from the regulating tank. The flocculant is put into the suction pipe (before the pump) and mixed by the impeller for flocculation in the reaction pool, and the intensity and reaction time of the reaction pool should be adjusted according to the nature of different wastewater. After the reaction, the flocculated water enters the contact area of the air flotation tank and mixes with the dissolved gas water released from the dissolved gas releaser. At this time, the floc particles and micro-bubbles in the water collide and adhere with each other, forming floc particles with gas and floating, and solid-liquid separation in the separation area, and the mud and slag floating on the surface of the water are scraped by the scraper to the slag discharge tank and discharged. The clean water is collected by perforated collecting pipe to the collecting tank and then discharged. Part of the fresh water is pressurized by the return pump and enters into the dissolved air tank, where it is dissolved in contact with the compressed air from the air compressor, and the saturated dissolved air water is piped from the bottom of the tank to the releaser.
Pressure dissolved air flotation process is mainly composed of three parts, namely, pressure dissolved gas system, dissolved gas release system and air flotation separation system.
1. Pressure dissolved gas system. It includes water pump, air compressor, pressure dissolved gas tank and other ancillary equipment. The pressure dissolved gas tank is the key equipment affecting the effect of dissolved gas.
The dissolved air system using air compressor air supply is currently the most widely used pressure dissolved air system. Air flotation method requires less air, can choose the power of small air compressor, and take the intermittent operation. In addition, air compressor air supply can also ensure that the pressure of the pump does not have a large loss of Zhu. General pump to the dissolved air tank pressure of about 0.5MPa, so you can save energy.
2. Dissolved gas release system. It is generally composed of the releaser (or perforated pipe, pressure reducing valve) and dissolved gas water piping. Dissolved gas releaser function is the pressure of dissolved gas water through the dissipation of energy, decompression, so that the gas dissolved in the water in the form of micro-bubbles released, and can be quickly and uniformly with the water impurities adhering to the phase.
The specific requirements of the dissolved gas releaser are:
sufficient depressurization, to ensure that the dissolved gas in water can be fully released; the depressurization should be in line with the law of gas release, to ensure that the micro-fine degree of bubbles to increase the number of bubbles, increase the surface area of the adhesion of the impurities with the micro-bubbles to prevent the collision between the bubbles to make the expansion of bubbles; to create a gas release water and flocculants in the water to be treated. Create good adhesion conditions between the air release water and the flocculating body in the water, avoid the impact of the water flow, ensure that the bubbles can be quickly and evenly mixed with the water to be treated, and improve the "capture" rate; In order to quickly dissipate the energy, it is necessary to narrow the water flow channel, so it is necessary to prevent the water flow channel clogging measures; Strive to be simple in construction, the material should be strong, corrosion-resistant, and at the same time should be easy to process, manufacture and dismantle to reduce the number of moving parts to ensure stable and reliable operation; Ensure that the air release water and the impurities to be treated. Ensure stable and reliable operation; The main process parameters of the dissolved gas releaser are: the pipeline flow rate before the releaser: 1m/s or less, the outlet flow rate of the releaser to 0.4 ~ 0.5m / s is appropriate; flushing when the narrow gap opening degree of 5mm; the role of each releaser range of 30 ~ 100cm.3. Air flotation separation system. It can generally be divided into three types namely advection, vertical flow and integrated. Its function is to ensure a certain volume and the surface area of the pool, so that the micro-bubble group and the flocculent in the water fully mixed, contact, adhesion, in order to ensure that the flocculent with gas and clear water separation.
The following is an example of advective air flotation tank to analyze the movement of the floc with air separation process.
The air floc particles in the contact chamber through the buoyancy, gravity and water resistance of the balance of the role of the water flow resistance, made the upward speed U. After entering the separation zone, it is subjected to the two floc flocs and clear water separation. After entering the separation zone, it is subjected to two forces: one is the horizontal flow velocity U pushed by the horizontal thrust produced by the diffusion of water flow; the other is the downward flow velocity U down produced by the bottom outflow. The size and direction of the combined velocity of these two types of flow determines whether the flocs with air are removed by upward floating, or held out with the water flow. The rate of rise or fall depends on the magnitude of the combined velocity U projected on the longitudinal axis. This velocity affects the treatment effect of air flotation. The size of the flocculent, the size of the bubble, the downward speed of the water in the air flotation tank body three directly affect the synthesis of upward velocity. Synthesized upward speed, the greater the removal efficiency of air flotation, air flotation tank body of the smaller, the lower the cost of the whole project. To make the upward floating effect is good, first in the pool body to minimize the U under. It can be used to expand the bottom of the outflow area or improve the uniformity of the water to achieve, with the bottom of the uniform set of flow, outflow, water flow to the pool at the end of the U flat is about zero, which is conducive to the separation of air flocs with less buoyancy; such as to achieve the removal of the floating in advance, should try to reduce the U flat, which can be used to expand the cross-section of the air-float pool way to achieve. Then we should deal with the size of flocculent, through the addition of drug mixing, and flocculation reaction to complete, should pay attention to the control of the following points, the varieties of chemicals, the amount of drugs, chemicals and sewage mixing time and mixing intensity, the addition of chemicals, chemicals and sewage reaction time and reaction intensity, the size of the resulting flocculent. In addition to control the size of the bubble in the dissolved air system.
Vertical flow air flotation tank separation zone in the movement of particles similar to the advection type. But its horizontal velocity is much smaller, and with the increase of radial distance, the section is rapidly expanding, u flat quickly become smaller. In particular, the flow direction of the vertical flow type is not changed much, the floc is mainly driven by the inertia of the upward current, the upward velocity of the particles increases, so that the separation conditions of the floc with gas and the water body are much better than the advection type. But exactly what form needs to be used in all aspects of the conditions of a comprehensive evaluation to determine.
(F) electrolytic flotation flotation process
Electrolytic flotation method of electrolysis of wastewater, this time in the cathode produces a large number of hydrogen bubbles, hydrogen bubbles of a very small diameter of only 20 ~ 100 microns, they play the role of the flotation agent. Suspended particles in the wastewater adhere to the hydrogen bubbles, with its upward floating, thus achieving the purpose of purifying wastewater. At the same time, the hydroxide formed on the anode ionization plays the role of coagulant, which helps the sludge in the wastewater to float or sink.
The advantages of the electrolytic air flotation method are: it can produce a large number of small bubbles; when utilizing the soluble anode, the air flotation process and the coagulation process are carried out in conjunction with each other; and the device is simple in construction, which makes it a new method of wastewater purification.
This is the last few years in the field of water treatment only appeared in the two processes, because this method has simple equipment; management is convenient; operating conditions are easy to control, the device is compact, the effect is good, and therefore the development of rapid.
(VII) dissolved air flotation design and calculation
1. Design points and considerations
(1) to fully study and explore the water quality of the water to be treated to analyze the reasonableness and applicability of the use of air flotation process;
(2) in the conditions of the wastewater to be processed should be necessary to carry out a small-scale test of the air flotation or model test. And according to the results of the test to select the appropriate dissolved air pressure and reflux ratio (refers to the dissolved air volume of water and the ratio of water to be treated). Usually dissolved gas pressure of 0.2 ~ 0.4MPa, reflux ratio of 5% to 100% of a between the determination of reflux ratio needs to be linked to the concentration of suspended solids. Concentration of high reflux ratio, concentration of small reflux ratio is small.
(3) according to the test selected coagulant type, dosage, flocculation time, the degree of reaction, etc., to determine the form of reaction and reaction time, the general precipitation reaction time is shorter to 2-30 minutes appropriate;
(4) determine the type of air-float pool pool should be based on the treatment of water quality requirements, the water purification process with the connection between the front and rear treatment structures, the surrounding topography and structures, the degree of construction ease and cost coordination. Construction, ease of construction and cost and other factors to be considered comprehensively. Reaction pool should be built together with air flotation pool. In order to avoid breaking up the flocculent, attention should be paid to the structure of the articulation form. Into the air flotation pool contact chamber flow rate should be controlled within 0.1m / s;
(5) contact chamber must be on the bubble and flocculent to provide good contact conditions, while the width should be considered installation and maintenance requirements. The rising flow rate of water is generally taken as 10~20mm/s:, the residence time of water flow in the chamber should not be less than 60 seconds.
(6) contact with the indoor dissolved gas releaser, need to determine the return flow, dissolved gas pressure and the role of various types of releasers to be selected according to the following table:
(7) air flotation separation room needs to be based on the degree of separation of flocs with the ease of flotation and the water quality of the treatment requirements. Selection of water flow (downward) flow rate, generally take 1.5 ~ 3.0mm / s, that is, the separation chamber of the surface loading rate of 5.4 ~ 10.8m3 / (m2.h);
(8) the effective depth of the air flotation tank is generally taken as 2.0 ~ 2.5m, the pool of water flow retention time is generally 10 ~ 20min;
(9) the air flotation tank length and width of the pool without strict requirements; Generally, the width of a single cell does not exceed 10m, the length of the pool does not exceed 15m is appropriate;
(10) air flotation pool slagging is generally used to scrape the slag machine regularly excluded. Slag collection tank can be set at one end or both ends of the pool. The scraper's traveling speed should be controlled within 5m/min;
(11) air-floatation pool water collection should strive for uniformity, generally use perforated collection pipe, collection pipe maximum flow rate should be controlled at about 0.5m/s;
2. Design procedures
(1) laboratory or field tests
Because of the many types of wastewater, even the same type of wastewater, its water quality varies. of wastewater, its water quality varies greatly. The usual design parameters are only empirical statistical values. Therefore, a reliable method is best to use the results obtained from the laboratory or field small-scale test as the basis for design.
(2) Determine the design program in the site survey and comprehensive analysis of a variety of information on the basis of determining the main design program.
① dissolved gas mode using full dissolved gas or part of the reflux type;
② air flotation tank type selection of advection or vertical flow, take the round, square or rectangular;
③ in the air flotation before or after the need for pre-treatment or after-treatment structures, the form of how to how to connect?
④Slag treatment and disposal pathway;
⑤Preliminary determination and rationalization of process flow and layout analysis.
(3) Design calculations (excluding conventional calculations for general treatment structures)
(4) Provide the nature of wastewater, see the attached table for details.
(H) dissolved air flotation method of the design of the main equipment
1. dissolved gas releaser
(1) complete release of gas, in the 0.15MPa above the amount of dissolved gas can be released about 99%;
(2) can be working at a lower pressure, in the 0.2MPa above the water purification can be achieved when a good effect, saving electricity:
(3) The released bubbles are micro-fine, the average diameter of bubbles is 20-40 microns, the bubbles are dense and have good adhesion performance.
2. Pressure dissolved gas tank
Dissolved gas efficiency of more than 80%
(IX) technical and economic analysis
Since the water purification process in the precipitation method has been used for many years, the people choose the air flotation method naturally want to be compared with the precipitation method. In fact, the two methods have their own characteristics, for light floating impurities should be used dissolved air flotation method; for dense heavy impurities should be used precipitation method. Usually through the dosing, mixing and reaction after the formation of flocs, when the floating speed is faster than the precipitation, then choose the air flotation method is good. Because the air flotation method covers an area of small (only 1 / 8 for the precipitation method of 1 / 2), the pool volume is small (only 1 / 8 for the precipitation method of 1 / 1 / 4), good quality of treated effluent, not only turbidity and SS low and high dissolved oxygen, discharged flotsam water content is much lower than the sludge discharged by the precipitation method. General sludge volume ratio of 1/10-1/2, which gives the further treatment and disposal of sludge has brought greater convenience and cost savings.
Some wastewater containing sinkable and floatable impurities, the use of air flotation or precipitation alone is not ideal. At this time the combination of precipitation and air flotation, to give play to their respective advantages, will not only improve the treatment effect, but also save investment and operating costs.
Production practice shows that the air flotation pool is not only better than the sedimentation tank in the removal of color, turbidity, and in the reduction of polluted water COD, lignin and extraction of oxygen and so on show extremely unique advantages, its cost is also lower than the advection sedimentation tank, inclined tube sedimentation tank, hydraulic or mechanical acceleration of clarification tank, and its operating costs are also slightly lower.
Although the air-float method of water purification due to its unique advantages of the day, but to give full play to its characteristics, should also focus on the following three aspects of research and development.
1. Bubbles further refinement.
It is well known that, under the condition of equal air release, the micro bubble produced by the finer, the more dense the number of bubbles, the smaller the floc particles adhered to, the better the effect of water purification, and the formation of flotsam is also more stable. Therefore. The study of dissolved air releaser with smaller average bubble diameter is a way to improve the current air flotation water purification technology. It can not only improve the removal effect of existing water purification objects, but also open up the scope of application of air flotation water purification.
2. Direct cutting gas to create micro-bubbles
Pressure dissolved gas flotation method of water purification there are two problems: the first is the pressure of dissolved gas relative energy consumption; the second is the addition of dissolved gas water volume increases the hydraulic load in the flotation tank, to the separation of difficulties. The ideal solution to these two problems is to develop a direct generation of micro-bubble gas distribution device, through which the gas will be cut into a stable, fine, dense micro-bubble group, thus greatly reducing energy consumption, and will not increase the volume of the air flotation tank. Despite the difficulty of the direct gas distribution method, it is the most attractive research direction.
3. Solid and liquid separation technology.
In order to improve the solid-liquid separation technology, give full play to the advantages of air flotation water purification, in addition to the further refinement of the bubble and the use of direct air distribution method, to improve the solid-liquid separation effect is also an important aspect. Because the ultimate purpose of air flotation water purification is still reflected in the improvement of separation effect. If you try to coagulate air flotation bubble, flocculation at the same time the formation and cohesion of the concept of the introduction of pressure dissolved air flotation method is likely to greatly improve its separation effect. This concept can be called *** cohesive air flotation. In order to adapt to the *** cohesive flotation, should develop a new type of dissolved air release device, it should be delayed release of highly dense ultra-micro bubbles, in the mixing of the primary reaction with the drug injection (precisely, the micro-flocculated particles have not yet formed when the water) fully mixed, the two at the same time, that is, the ultra-micro bubbles and micro-flocculated particles formed at the same time and combined with the *** with the growth of flocculated with the gas particles. So that the formation of air flocs in the floating process, not only will not be affected by the shear force and make the bubbles fall off, and even sinking, and floating fast, stable slag, the least amount of gas consumption. Therefore, *** cohesive air flotation is a very promising research direction.
4, how to properly solve the problem of adhesion fastness is also a current problem to be solved.
Air flotation as a physical method, not only to improve the quality of bubbles (such as fineness, density, stability, etc.), but also to pay great attention to improve the performance of flocs. If we can get the monk water, adsorption of floc particles, it will greatly help to improve the effect of air flotation water purification. For this reason, the study of flocculants and coagulants for air flotation is also a pressing issue.
Just as the development of sedimentation technology is inseparable from the study of sedimentation theory, the development of air flotation technology also needs the guidance of air flotation theory. What's more, the object of air flotation research is liquid, solid, gas three-phase system, more complex than precipitation. For the structure and characteristics of the bubble, the bubble size of the correct choice and control, bubble and floc adhesion conditions, all must be studied in depth. Some theoretical new concepts and assumptions must be further verified and confirmed one by one through experiments. Therefore, the air flotation water purification technology is far from perfect, many problems waiting for us to research breakthroughs.
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