Dissolved Air Flotation (DAF) Unit

fully automaticDissolved Air Flotation (DAF) UnitManufacturer's Price 1

fully automaticDissolved Air Flotation (DAF) UnitManufacturer's Price 1

Air flotation methods can be divided into dispersed air flotation, dissolved air flotation (including true air flotation), and electrolytic air flotation. Currently, it has applications in water supply, industrial wastewater, and urban sewage treatment. Compared to other solid equipment, air flotation equipment-Liquid separation equipment has the characteristics of low investment, minimal footprint, high degree of automation, and convenient operation and management. In practice, targeted selection and use should be made based on the characteristics of wastewater treatment processes, wastewater quality and quantity. Based on years of practical experience, this article introduces the application of several types of air flotation equipment for reference by peers and users in design, renovation, and selection.

1 Electrolytic air flotation equipment

　　Electrolytic air flotation equipment directly electrolyzes wastewater using inert anodes and cathodes. The tiny bubbles of hydrogen and oxygen generated by electrolysis carry the flocculated suspension to the surface of the water. Reaching a solid state-The purpose of liquid separation. The bubble size generated by electrolysis is much smaller than that generated by dissolved air flotation and dispersed air flotation, and does not generate turbulence. The device removes a wide range of pollutants and reduces the removal of organic wastewaterBODIn addition, it also has oxidation, decolorization, and sterilization effects, with strong adaptability to changes in wastewater load, less sludge generation, less land occupation, and no noise generation. In recent years, it has developed rapidly. At present, electrolytic air flotation equipment still faces problems such as high energy consumption and plate loss, as well as high operating costs, which limit the promotion and use of this equipment.

2 Scattered air flotation equipment

The air flotation equipment relies on the vacuum negative pressure state caused by the centrifugal force of the high-speed rotating impeller to suck in air, which becomes fine air bubbles and diffuses in the water. Bubbles rise from the bottom of the pool to the water surface and adhere to suspended solids in the water, bringing them to the surface. Reaching a solid state-The purpose of liquid separation. The formed floating slag is continuously scraped out of the pool by a slowly rotating scraper plate. The mechanical shear force of water flow and the large bubbles generated by the diffuser plate (with a diameter of)1mmOn the left and right sides, it is not easy to adsorb with small particles and flocs, and instead tends to break the flocs. Therefore, air flotation is not suitable for treating wastewater containing small particles and flocs. The air flotation time of the dispersed air flotation equipment is about30nim,Dissolved gas reaches0.51m3/m3(Qi)/Water). The linear velocity around the rotating impeller is approximately12.5m/s.

The application scope of this equipment includes small-scale sewage treatment projects such as painting, leather making, oil refining, printing and dyeing, chemistry, dairy processing, fiber production, papermaking, food and beverage, slaughtering, textile, mechanical processing, municipal sewage, etc. The operating conditions in some industries are shown in the table1.

fromdata analysisCOD（BOD）After processing, its removal rate is43.38%-89.1%，SSGo handle it90%-99.8%The removal rate of oil is78%-99.3%The processing capacity is25-163m3/hFrom this, it can be seen that this air flotation equipment has limited water treatment capacity for wastewater, but its treatment effect on insoluble substances and suspended solids is more obvious. The oil removal effect can generally reach80%about. The removal rate of oil, gel and suspended solids in wastewater treatment is95%Above, adding appropriate chemical agents can make the wastewaterCODandBODThe removal rate is60%The above.

3 Dissolved air vacuum flotation equipment

　　The supersaturated air in water can be released in the form of fine bubbles during decompression, causing impurities particles in the water to adhere and float up. Reaching a solid state-The purpose of liquid separation. If air is first pressurized to dissolve in water to form an air supersaturated solution, and then reduced to atmospheric pressure to allow air to precipitate, it is called pressurized dissolved air flotation; If wastewater is aerated under normal pressure and then induced to release dissolved air under vacuum conditions, it is called vacuum air flotation.

Dissolved air vacuum flotation equipment is an air flotation device that dissolves air in water under normal pressure or pressure, and precipitates it under negative pressure. The advantage of vacuum air flotation equipment is that the formation of bubbles, their adhesion to particles, and the upward flotation of bubbles and particle flocs all occur in a stable environment, with a low possibility of floc damage and low energy consumption required for the entire air flotation process. Its disadvantage is that the amount of dissolved gas in water is limited and it is not suitable for concentrations greater than250-300mg/LWastewater containing suspended solids; Another disadvantage is the requirement for sealed containers, which also require the installation of scraper machinery inside. The structure is complex, so it is less commonly used in engineering practice. The amount of air that the device may obtain is affected by the achievable vacuum level (usually operating vacuum level)40kPa）Due to its limited amount of precipitated microbubbles, complex structure, and inconvenient operation and maintenance, it has been gradually phased out.

4 Pressure dissolved air flotation equipment

The pressurized dissolved air flotation equipment pressurizes clean water to（3-4）×105PaAt the same time, air is added to dissolve the air in water, and then suddenly reduced to atmospheric pressure. The air dissolved in water forms tiny bubbles (with a diameter of approximately)20-100μmLeft and right), precipitate from the water and float suspended particles on the surface of the water. Thus achieving solidification-Liquid separation. Pressure dissolved air flotation equipment is currently a widely used type of air flotation equipment. This device can be widely used for various types of wastewater treatment (especially oily wastewater treatment), sludge concentration, and water supply treatment.

The pressurized dissolved air flotation equipment mainly includes air saturation equipment, equipment for air release and mixing with wastewater, and solid-Liquid or liquid-The liquid separation equipment consists of three parts. According to the types, properties, and treatment efficiency of suspended solids in raw water, it can be divided into three types: fully pressurized dissolved air flotation, partially pressurized dissolved air flotation, and reflux pressurized dissolved air flotation.

At present, pressurized gas flotation is widely used. Compared with other air flotation equipment, it has the following characteristics:

⑴Under pressurized conditions, the air solubility is high, and the number of bubbles used for gas flotation is large, which can ensure the effectiveness of air flotation;
⑵The dissolved gas is suddenly released under reduced pressure, producing bubbles that are not only fine, uniform in size, and dense, but also stable and have little disturbance to the liquid. Therefore, it is particularly suitable for solid-liquid separation of loose flocs and small particles;
⑶The process and equipment are relatively simple, easy to manage and maintain;
⑷Especially for partial reflux type, it can handle *, stabilize, and greatly save energy consumption.

4.1Combination air flotation equipment　　

This type of equipment belongs to pressurized dissolved air flotation. It is widely used in the treatment of industrial wastewater such as papermaking, printing and dyeing, electroplating, chemical industry, food, and oil refining. The application situation in some enterprises is shown in the table2.

from the table2The data shows that the pressurized dissolved air combined air flotation equipment is effective in treating wastewaterCODTheSSThe removal rate is78%-95%Between them, the processing ability is30-150 m3/h左右。

4.2Efficient shallow pool air flotation equipment　　

The emergence of efficient shallow pool air flotation equipment is a major breakthrough in air flotation water purification technology. It replaces the traditional static inlet and dynamic outlet of air flotation with dynamic inlet and static outlet“Zero speed principle”Make the flotation body float vertically to the water surface in a relatively static environment, achieving solidification-Liquid separation.“Zero speed principle”Reduce the floating distance to a minimum and not be affected by the outflow velocity. The floating velocity reaches or approaches the theoretical value, and the residence time of sewage in the purification tank is reduced by traditional air flotation30－40Minutes reduced to just needed3－5In minutes, the processing efficiency is greatly improved, and the equipment volume is significantly reduced. It can be elevated, stacked, or installed on buildings, occupying less or no land. With the rotation of the water distribution device, the bubbles that have been uniformly mixed with the sewage in advance can fill the entire purification tank very evenly, without any dead zone of air flotation or uneven bubble zone, thus greatly improving the purification efficiency.

Shallow tank air flotation equipment is a rotary machine that rotates around the center of the air flotation tank, with the inlet, outlet, and air flotation scraper installed on it. The rotary frame and scraper bucket are both driven by motors and can be infinitely variable in speed. Rotate at the same speed as the inlet flow rate *. Wastewater is fed into the rotating inlet at the center of the pool and distributed through the inlet water distributor, which can move at the same speed as the inlet flow rate. Make the raw water enter the pool to generate zero velocity, follow this“Zero speed principle”The inflow of water will not disrupt the flow of water in the pool. The settling and floating of particles in the pool are carried out in an ultra static state, greatly improving the efficiency of the air flotation tank. The spiral shaped mud scraping device causes minimal disturbance to the water body and only blows up fully separated floating slag, with a high solid content. Compared with other air flotation equipment, it has the following characteristics:

⑴adopt“Shallow pool theory”、“Zero speed principle”、“New gas dissolution mechanism”design
⑵The hydraulic retention time is short, only3-5Minutes, pool depth not exceeding700mm；
⑶Microbubbles are extremely small and have a density of *, so there is no need to agglomerate them into large alum flowers beforehand. This can greatly reduce the amount of medication added and greatly lower operating costs;
⑷The adhesion between fine bubbles and flocs occurs throughout the entire air flotation separation process, including the contact zone;
⑸Forced water distribution, with static inflow and outflow of water;
⑹The discharge of clean water is carried out after solid-liquid separation, with instantaneous isolation and removal of floating slag, resulting in minimal disturbance to the water body;
⑺The solid content of the slag is as high as3%-5%The removal rate of suspended solids reaches99.5%The bottom of the pool is equipped with a scraper plate, which automatically scrapes away settled sludge;
⑻The adopted gas dissolution tube design * has a small volume, high gas dissolution efficiency, easy operation, and small footprint;
⑼The equipment has high operating efficiency, good stability, large processing capacity, and low one-time investment;
⑽Reasonable selection of dissolved water and agent addition points to ensure the achievement of co air flotation;
⑾It has multiple adjustment functions and can change with the variation of treated water quality and quantity.

Shallow pool air flotation is a new and efficient air flotation treatment equipment in the physical and chemical treatment of industrial wastewater, widely used in fields such as paper white water recovery, leather making, textile, soap making, food, carbon black, fiber products, oil extraction, beer, and municipal wastewater reuse. Reasonable configuration of auxiliary equipment such as dosing equipment, gas dissolution equipment, and pumps can reduce the total amount of suspended solids in wastewater90%The above. And the hydraulic retention time of air flotation is only3-5nimThe use of this equipment can significantly reduce investment and operating costs, save a lot of arable land, and is particularly significant when used to treat large-scale sewage.

4 Conclusion

⑴The water treatment capacity of the air flotation equipment is25-163m3/hThe amount of wastewater treated is relatively small, and the treatment effect on insoluble substances and suspended solids is more obvious. The oil removal effect can generally reach80%about. The removal rate of oil, gel and suspended solids in wastewater treatment is95%Above, adding appropriate chemical agents can make the wastewaterCODandBODThe removal rate is60%The above.

⑵The processing capacity of pressure dissolved air flotation equipment is also limited, and the processing capacity is30-150m3/habout. After adding appropriate chemical agents, treat wastewaterCODTheSSThe removal rates are all within80%左右。

⑶The processing capacity of shallow pool air flotation equipment is300-850m3/hAbove, the removal rate of suspended solids reaches92.8%AboveCODThe removal rate is65.3%Above, the equipment is correctSSThe removal effect is quite obvious. At the same time, the hydraulic retention time of the equipment is only3-5Minutes, occupying less space than other air flotation equipment, with high technical content and convenient operation and management. The treated water meets the requirements of process reuse, saving water resources and having considerable economic benefits.

⑷For the application and comparison of several types of air flotation equipment, it is recommended that when selecting air flotation equipment for wastewater treatment processes, comprehensive consideration should be given to factors such as the water quality and quantity of the wastewater, the recyclability value of the wastewater, the footprint, and equipment investment. Under the premise of ensuring process requirements, the wastewater treatment capacity should be less than300m3/hAt this time, one can choose between dispersed air flotation or pressure dissolved air flotation equipment. The scale of wastewater treatment exceeds300m3/hWhen selecting shallow pool air flotation equipment, consideration should be given.