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Dissolved Air Flotation Machine DAF Process Waste water Treatment System

I. Introduction of dissolved air flotation machine:

Dissolved air flotation machine is mainly used for solid - liquid or liquid - liquid separation. Through the gas dissolution and release system in the waste water to produce a large number of fine bubbles, so that it adheres to the density of solid or liquid particles close to the water in the wastewater, resulting in the overall density less than the state of water, and rely on buoyance to make it rise to the water surface, so as to achieve the purpose of solid-liquid or liquid-liquid separation.


Two, dissolved air flotation machine application scope:

1. Separation of fine suspended solids, algae and other microaggregates on the surface.

2. Recycle useful substances in industrial wastewater, such as pulp in papermaking wastewater.

3, instead of the secondary sedimentation tank and concentrated water sludge and other suspended matter.


Three, dissolved air flotation machine advantages:

Long-term stable performance, easy operation, easy maintenance, low noise;

The efficient adsorption of microbubbles and suspended particles in the dissolved air flotation machine improves the removal effect of SS;

Air flotation machine automatic control, simple maintenance;

The multi-phase flow pump of the dissolved air flotation machine can be carried with pressurized pump, air compressor, large dissolved gas tank, jet and release head, etc;

The dissolution efficiency of dissolved air water is 80-100%, 3 times higher than the traditional floating efficiency of dissolved air;

Multi-layer mud discharge to ensure water discharge effect;

    Project Introduction

    Dissolved Air Flotation Waste water Treatment System: 

    Dissolved air pump air flotation technology is a new type of air flotation technology developed in recent years, this technology overcomes the shortcomings of dissolved air flotation technology with more auxiliary equipment, high energy consumption and large bubbles produced by vortex concave air flotation technology, and has the characteristics of low energy consumption. The dissolved air pump uses vortex pump or gas-liquid multiphase pump. Its principle is that the air and water enter the pump shell together at the entrance of the pump. The impeller with high speed will cut the inhaled air into small bubbles for many times. The bubble diameter produced by the dissolved air pump is generally 20 ~ 40μm, the maximum solubility of the inhaled air reaches 100%, and the maximum air content of the dissolved air water reaches 30%. The performance of the pump can remain stable when the flow rate changes and the air volume fluctuations, which provides good operating conditions for the regulation of the pump and the control of the air flotation process.

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    Dissolved air pump air flotation waste water treatment equipment is composed of flocculation chamber, contact chamber, separation chamber, slag scraping device, dissolved air pump, release pipe and other parts. The basic air flotation waste water treatment principle is: Firstly, water is extracted by the dissolved air pump as reflux water to produce dissolved air water (the dissolved air water is full of a large number of fine bubbles at this time). The dissolved air water is released into the water of the contact chamber through the release pipe. The small bubbles slowly rise and stick to the impurity particles, forming a floating body with density less than water, floating on the water surface, forming scum, and slowly moving forward with the water flow into the separation chamber. The scum is then removed by a scrape device. Clear water is discharged by overflow regulation to complete the working process of air flotation.

    The technology of aeration equipment of dissolved air pump is mature, and the EDUR high efficiency aeration device is widely used. EDUR high efficiency air flotation device absorbs the advantages of vortex concave air flotation to cut bubbles and dissolved air flotation to stabilize dissolved air. The whole system is mainly composed of dissolved air system, air flotation equipment, slag scraper, control system and supporting equipment.

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    Pressure dissolved air flotation (DAF) is a relatively early application waste water treatment technology in air flotation technology, suitable for the treatment of low turbidity, high chrominance, high organic content, low oil content, low surfactant content or waste water rich in algae, widely used in papermaking, printing and dyeing, electroplating, chemical industry, food, oil refining and other industrial sewage water treatment. Compared with other air flotation methods, it has the advantages of high hydraulic load and compact pool. However, its complex process, large power consumption, air compressor noise, etc., limit its application.

    According to the types and properties of suspended solids contained in sewage, the purification degree of treated water and the different pressure methods, there are three basic methods: whole process dissolved gas float method, partial dissolved gas float method and partial reflux dissolved gas float method.

    (1) Whole process dissolved air float method
    The whole process of dissolved air float is to pressurize all sewage with a pump and inject air before or after the pump. In the dissolved gas tank, the air is dissolved in the sewage, and then the sewage is sent into the air floating tank through the pressure reducing valve. Many small bubbles are formed in sewage to adhere to the emulsified oil or suspended matter in sewage and escape from the water surface, forming scum on the water surface. The scum is discharged into the scum tank with a scraper, and the scum pipe is discharged out of the pool. The treated sewage is discharged through the overflow weir and the discharge pipe.

    The dissolved gas in the whole process is large, which increases the chance of contact between oil particles or suspended particles and bubbles. Under the condition of the same treatment water quantity, it is smaller than the air flotation tank required by the partial refluxion dissolved gas flotation method, thus reducing the infrastructure investment. However, because all the sewage passes through the pressure pump, the emulsification degree of oily sewage is increased, and the required pressure pump and dissolved gas tank are larger than the other two processes, so the investment and operation power consumption are larger.

    (2) Partially dissolved air float method
    Partial dissolved air float method is to take part of the sewage pressure and dissolved gas, the rest of the sewage directly into the air float tank and mixed with dissolved gas sewage in the air float tank. Its characteristics are: compared with the whole process of dissolved air float required pressure pump is small, so the power consumption is low.

    Recent advances in waste gas treatment represent significant progress in addressing environmental challenges while also providing opportunities for businesses to thrive in a sustainable, environmentally friendly manner. This innovative solution is bound to have a positive impact in the fields of waste gas treatment and environmental protection with its promise of high efficiency, low operating costs and zero secondary pollution.

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    (3) Partial reflux dissolved air float method

    Partial reflux dissolved gas air float method is to take a part of the oil removal after the effluent reflux for pressure and dissolved gas, after reduced pressure directly into the air float tank, mixed with the sewage from the flocculation tank and air float. The return flow is generally 25% ~ 100% of sewage. Its characteristics are: pressurized water, power consumption province; The process of air flotation does not promote emulsification; Alum flower formation is good, the flocculant in the effluent is less; The volume of the air flotation tank is larger than that of the previous two processes. In order to improve the treatment effect of air flotation, coagulant or air flotation agent is often added to sewage, and the dosage varies with water quality, which is generally determined by the test.

    According to the theory of air flotation, the partial reflux pressure dissolved gas flotation method can save energy, make full use of coagulant, and the treatment effect is better than that of the full pressure dissolved gas flotation process. The treatment effect is the best when the reflux ratio is 50%, so the partial reflux pressure dissolved air flotation process is the most commonly used air flotation method of waste water treatment.

    What are the requirements for the operation and control of pressurized dissolved air flotation?

    Pressurized dissolved air flotation (DAF) systems are widely used in the wastewater treatment process to effectively remove suspended solids, fats, oils, and other pollutants from industrial and municipal wastewater. However, to ensure the efficient operation and control of a pressurized DAF system, certain requirements need to be met.

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    1.operators need to closely monitor the coagulation process in the reaction tank and the quality of the effluent from the flotation tank in order to adjust the dosage of coagulants accordingly. It is crucial to prevent the clogging of the dosing tank, which can disrupt the entire treatment process.

    2.the condition of the surface of the flotation tank should be observed regularly. Any occurrence of large air bubbles in specific areas of the tank may indicate a problem with the releaser, which needs to be promptly inspected and resolved.

    3.operators must understand the pattern of sludge generation and determine the appropriate scraping cycle to remove the accumulated sludge from the DAF system. This is essential for maintaining the system's efficiency and preventing the buildup of solids.

    4.Proper control of the water level in the pressurized dissolved air tank is also crucial for the system's operation. This ensures stable and consistent air-to-water ratio, which is vital for the flotation process.

    5.adjustments to the air supply from the compressor should be made to maintain the stable working pressure of the dissolved air tank. This, in turn, guarantees the effectiveness of air dissolving in the water.

    6.Control of the water level in the flotation tank is equally important to maintain a stable treatment water flow. During winter, when water temperatures are low, it is crucial to increase the reflux water flow or the air pressure to ensure consistent effluent quality.

    7.maintaining detailed operational records is essential. This should include information on treatment water quantity, influent water quality, chemical dosages, air-to-water ratio, dissolved air tank pressure, water temperature, power consumption, sludge scraping cycles, sludge moisture content, and effluent water quality.

    In conclusion, by adhering to these requirements, operators can ensure the efficient and effective operation of pressurized dissolved air flotation systems in wastewater treatment facilities.

    Dissolved Air Tank

    What are the structural components of commonly used dissolved gas tanks? What are the specific forms of dissolved gas tanks?
    The dissolved gas tank can be welded with ordinary steel plate and anticorrosive treatment can be carried out in the tank. Its internal structure is relatively simple, no packing of the hollow dissolved gas tank in addition to the layout of the water pipe has certain requirements, is an ordinary empty tank. There are many specifications of dissolved gas tanks, and the ratio of height to diameter is generally 2 ~ 4. Some dissolved gas tanks are installed horizontally, and the length of the tank is divided into water inlet section, packing section and water outlet section along the length direction. The water inlet and outlet of the dissolved gas tank are stable, and the impurities in the inlet can be intercepted to avoid the blockage of the dissolved gas release device.

    The function of the pressure dissolved gas tank is to make water fully contact with the air and promote the dissolution of the air. Pressure dissolved gas tank is the key equipment affecting the efficiency of dissolved gas, its external structure is composed of water inlet, air inlet, exhaust safety valve interface, sight mirror, pressure gauge mouth, exhaust port, level gauge, water outlet, into the hole and so on.

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    There are many forms of dissolved gas tanks, which can be filled with baffle type, flower plate type, filling type, turbine type and so on. The filling filler in the tank can improve the efficiency of the dissolved gas tank. Because the packing can intensify the degree of turbulence, improve the dispersion degree of liquid phase, constantly update the interface between liquid phase and gas phase, so as to improve the efficiency of gas dissolution. There are various forms of fillers, and the study shows that the gas dissolving efficiency of the step ring is the highest, which can reach more than 90%, followed by the Rasi ring, and the corrugated sheet coil is the lowest, which is caused by the different geometric characteristics of the fillers.

    Dissolved gas release device
    What are the commonly used dissolved gas releasers?
    Dissolved gas releaser is the core equipment of air float method, its function is to release the gas in the dissolved gas water in the form of fine bubbles, so as to adhere well to the suspended impurities in the sewage to be treated. Commonly used releasers are TS type, TJ type and TV type.

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    What are the forms of air flotation tanks?
    There are many forms of air flotation tank. According to the waste water quality characteristics, treatment requirements and various specific conditions of the water to be treated, there have been a variety of forms of air flotation tank for use, including advection and vertical flow, square and round layout, and also a combination of air flotation and reaction, precipitation, filtration and other processes.

    (1) The horizontal air flotation tank is the most widely used type of tank, and the reaction tank and the air flotation tank are usually built together. After the reaction, the sewage enters the air flotation contact chamber from the bottom of the pool body, so that the bubbles and floc fully contact and then enter the air flotation separation chamber. The scum on the pool surface is scraped into the slag collection tank with a slag scraper, and the clean water is collected by the collection pipe at the bottom of the separation chamber.

    (2) The advantage of vertical flow flotation tank is that the contact chamber is in the center of the tank, and the water flow diffuses around. The hydraulic conditions are better than the horizontal flow unilateral outflow, and it is convenient to cooperate with the subsequent treatment structures. Its disadvantage is that the volume utilization rate of the tank body is low, and it is difficult to connect with the previous reaction tank.

    (3) The integrated air flotation tank can be divided into three forms: air floating-reaction-body type, air floating-precipitation-body type, air floating-filtration-body type.

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    What are the basic requirements of air flotation tank slag scraper?
    (1) Chain type slag scraper is usually used for small rectangular air flotation tank. Bridge type slag scraper can be used for large rectangular air flotation tank (span should be below 10m). For circular air flotation tank, planetary slag scraper (diameter is 2 ~ 10m) is used.

    (2) A large number of scum cannot be removed in time or the slag layer is disturbed greatly when scraping, the liquid level and slag scraping procedure are improper when scraping, and the slag scraping machine traveling too fast will affect the air flotation effect.

    (3) In order to make the moving speed of the scraper not greater than the speed of the scum overflow into the slag collecting tank, the moving speed of the scraper should be controlled at 50 ~ 100mm/s.

    (4)According to the amount of slag, set the running time of slag scraper.

    What should be paid attention to in the debugging of pressurized dissolved air flotation method?
    (1) Before commissioning water, first of all, the pipeline and dissolved gas tank should be repeatedly purged and cleaned with compressed air or high pressure water until there are no easily blocked particle impurities, and then install dissolved gas release.

    (2) Check valve should be installed on the inlet pipe to prevent pressure water from pouring back into the air compressor. Before commissioning, check whether the direction of the check valve on the pipeline connecting the dissolved gas tank and the air compressor points to the dissolved gas tank. In actual operation, the outlet pressure of the air compressor should be greater than the pressure of the dissolved gas tank, and then open the valve on the compressed air pipeline to inject air into the dissolved gas tank.

    (3) Debug the pressure dissolved gas system and dissolved gas release system with clean water first, and then inject sewage into the reaction tank after the system runs normally.

    (4) The outlet valve of the pressure dissolved gas tank must be completely open to prevent the water flow from being blocked at the outlet valve, so that the bubbles are released in advance and merged to become larger.

    (5) Control the water outlet adjustment valve or adjustable weir plate of the air floating pool, and stabilize the water level of the air floating pool at 5 ~ 10cm below the slag collection slot. After the water level is stable, adjust the treatment water quantity with the water inlet and outlet valve until the design water quantity is reached.

    (6) After the scum accumulates to the appropriate thickness (5 ~ 8cm), start the slag scraper for slag scraping, and check whether the slag scraping and slag discharge are normal, and whether the effluent water quality is affected.

    What are the matters needing attention in the daily operation and management of air flotation machine?

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    (1) During inspection, observe the water level in the dissolved air tank through the observation hole to ensure that the water level neither floods the packing layer and affects the dissolved gas effect, nor is it less than 0.6m to prevent a large amount of undissolved air from coming out of the water.

    (2) Pay attention to observe the waste water pool surface during inspection. If it is found that the scum surface in the contact area is uneven and the local water flow is churn violently, it may be that the individual release device is blocked or dropped off, and it needs timely maintenance and replacement. If it is found that the scum surface in the separation area is flat and the pool surface often has large bubbles, it indicates that the adhesion between the bubbles and the impurity flocs is not good, and it is necessary to adjust the dosage or change the type of coagulant.

    (3) When the low water temperature in winter affects the coagulation effect, in addition to taking measures to increase the dosage, the number of microbubbles and their adhesion to the floc can also be increased by increasing the backflow water or the dissolved gas pressure, so as to make up for the decrease of the floating performance of the floc with air due to the increase of the water viscosity and ensure the water quality.

    (4) In order not to affect the effluent water quality, the water level in the tank must be raised when scraping the slag, so we should pay attention to the accumulation of operation experience, summarize the best scum accumulation thickness and water content, regularly run the slag scraper to remove the scum, and establish a slag scraper system in line with the actual situation.

    (5) According to the flocculation of the reaction tank. The scum and effluent water quality in the separation area of the air flotation tank should be adjusted in time, and the operation of the dosing tube should be often checked to prevent blockage (especially in winter).

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