Views: 218 Author: Site Editor Publish Time: 2024-09-08 Origin: Site
This article will continue the "2024 Dissolved Air Flotation (DAF) Knowledge Encyclopedia Part 1" article and continue to introduce the relevant knowledge points of dissolved air flotation, including dissolved air flotation design and construction, installation and operation, precautions and routine maintenance, fault diagnosis and troubleshooting, etc.
Table of contents（Click to go to where you want to see）
Design and construction of dissolved air flotation
1.1 Demand Analysis
1.2 Process Design
1.3 Equipment selection and procurement
1.5 Debug and run
1.6 Maintenance and management
Dissolved Air Flotation (DAF) is a water treatment process involving dissolving air under pressure to create tiny bubbles. These bubbles then attach to suspended particles, causing them to float to the surface for separation from the liquid. Below are the steps for designing and building a dissolved air flotation system:
Conduct a comprehensive analysis of the influent water quality, including the concentration of suspended solids, distribution of particle size, and content of organic matter, to ensure optimization of the designed system for the specific water quality.
Process parameter optimization: Through laboratory-scale experiments or simulation software, optimize process parameters such as dissolved gas pressure, release time, bubble size, etc. to find the best balance between processing efficiency and cost.
Equipment selection and scale: Choose cost-effective equipment and consider the scale effect. Bulk purchase or selection of standardized equipment can reduce the cost of a single device.
Modular design: Modular design allows the system to be expanded or reduced according to actual processing needs, avoiding cost waste caused by over-design.
Energy efficiency considerations: Choose energy-efficient equipment, such as high-efficiency air compressors and dissolved air pumps. Although the initial investment is higher, the long-term operating costs are lower.
Control system optimization: Design intelligent control systems to achieve automatic adjustment and optimized operation of the system, reducing labor costs and energy consumption.
Ease of maintenance and operation: Design systems that are easy to maintain and operate to reduce long-term maintenance costs and operational difficulties.
Life Cycle Cost Analysis: Perform a life cycle cost analysis that considers not only the initial investment cost, but also factors such as operating costs, maintenance costs, and equipment life to find the solution with the lowest total cost.
Supplier and contractor management: Select reliable suppliers and contractors and reduce procurement and construction costs through competitive bidding and other means.
Technological innovation and application: Pay attention to the development of new technologies, such as new materials, efficient dissolved gas technology, etc., which may reduce equipment costs and improve processing efficiency.
Analyzing the properties and concentration of suspended solids in water is a key step in water treatment design, which directly affects the design parameters and treatment effects of the dissolved air flotation (DAF) system. The following are the detailed steps for analyzing the properties and concentration of suspended solids in water:
First, representative water samples need to be collected from the water source. Sampling points should be selected at different locations and depths of the water source to ensure the representativeness of the water samples.
The collected water samples are sent to the laboratory for analysis. The following are commonly used analysis methods
Suspended solids (SS) determination: The concentration of suspended solids is determined by filtering the water sample, drying and weighing the residue on the filter paper.
Turbidity determination: The turbidity of the water sample is determined using a turbidimeter. Turbidity is an indirect indicator of the concentration of suspended solids.
Microscope observation: The shape and size of the suspended solids are observed under a microscope to understand the type and distribution of the suspended solids.
Particle size analysis: The particle size distribution of the suspended solids is determined using equipment such as a laser particle size analyzer.
（3） Data recording and analysis
record the data obtained from laboratory analysis and conduct statistical analysis. Including the following key analyses
Suspended matter concentration: calculate the average concentration and standard deviation of suspended solids to understand the fluctuation range of suspended matter concentration.
Particle size distribution: analyze the particle size distribution of suspended matter to determine the main particle size range and particle size composition.
Suspended matter morphology: record the morphological characteristics of suspended matter, such as whether there are organic matter, inorganic matter, biological particles, etc.
Based on the analysis results, evaluate the nature and concentration of suspended matter to provide a basis for the design of the dissolved air flotation system. The evaluation should include the following key points:
Difficulty of treatment: Suspended solids with high concentration or small particle size may require higher dissolved air pressure and longer release time.
Equipment selection: Select the appropriate releaser and flotation tank size according to the properties of the suspended solids.
Process parameters: Determine the optimal dissolved air pressure, release time bubble size, and other process parameters.
Based on the evaluation results, the design of the dissolved air flotation system is optimized. This may include adjusting the size of the flotation tank, changing the pressure and flow of the dissolved air system, selecting a suitable scraper, etc.
During the design optimization process, economic factors also need to be considered to ensure that the system design can meet the processing requirements while controlling costs.
Determining treatment objectives and effluent standards is a key step in designing and constructing a dissolved air flotation (DAF) system. The following are the specific steps and methods.
Regulatory research: Study local environmental regulations and emission standards to understand the water quality requirements for treated water.
Standard comparison: Compare with national or local discharge standards to determine the effluent water quality standards that must be achieved.
Suspended solids removal: Determine the target concentration for suspended solids removal based on water quality analysis results.
Organic matter removal: Determine the goal of organic matter removal based on indicators such as chemical oxygen demand (COD) and biochemical oxygen demand (BOD).
Nutrient control: Determine the control targets for nutrients such as total nitrogen (TN) and total phosphorus (TP).
Microbiological indicators: Determine the control targets for microbial indicators such as total bacteria count and E. coli.
What is chemical oxygen demand (COD)
What is chemical oxygen demand (BOD)
Suspended solids (SS): Set the maximum allowable concentration of suspended solids in the effluent.
Turbidity: Set the maximum allowable value of effluent turbidity.
COD/BOD: Set the maximum allowable concentration of COD and BOD in the effluent.
TN/TP: Set the maximum allowable concentration of total nitrogen and total phosphorus in the effluent.
Microbial indicators: Set the maximum allowable values of microbial indicators such as total bacteria and E. coli in the effluent.
Process optimization: According to the treatment objectives and effluent standards, adjust the design parameters of the dissolved air flotation system, such as the size of the flotation tank, dissolved air pressure, release time, etc.
Equipment selection: Select appropriate equipment, such as high-efficiency releasers, scrapers, etc., to ensure that the treatment objectives are achieved.
Cost-benefit analysis: Evaluate the cost-effectiveness under different treatment objectives and effluent standards, and select the most cost-effective solution.
Long-term operating costs: Consider the long-term operating costs of the system, including energy consumption, maintenance costs, etc.
System debugging: After the system is built, it is debugged to ensure that all equipment is operating normally.
Water quality monitoring: Regularly monitor the effluent quality to ensure that the set effluent standards are met.
Data collection: Continuously collect water quality data to evaluate the system's treatment effect.
Process adjustment: Adjust and optimize process parameters based on monitoring results and operating experience.
Designing the size and shape of the flotation tank is a critical step in the design of a dissolved air flotation (DAF) system, which directly affects the system's treatment efficiency and operating parameters. The following are the specific steps and considerations for designing the size and shape of the flotation tank:
A detailed introduction to dissolved air flotation is available in "2024 Dissolved Air Flotation (DAF) Knowledge Encyclopedia Part 1". This article introduces electrolysis, diffused air, impeller, dissolved air flotation, the whole dissolved air process, partial dissolved air process, and reflux pressurized dissolved air process in detail. You can jump to the next chapter in the article.
Design flow: Determine the design flow of the system based on the demand analysis, that is, the amount of water the system needs to treat.
Residence time: Determine the residence time of the water sample in the flotation tank, which usually depends on the nature and concentration of the suspended matter.
Volume calculation: Calculate the volume of the flotation tank based on the design flow and residence time.
Rectangular flotation tank: Suitable for large flow and high load applications, easy to construct and stable operation.
Circular flotation tank: Suitable for small and medium flow, small footprint, but relatively difficult to construct.
Square flotation tank: Suitable for special site restrictions, but the operating stability may be better than rectangular or circular flotation tanks.
Length and width: Determine the flotation tank's height and width based on the flotation tank's volume and the selected shape.
Depth: The depth of the flotation tank usually depends on the hydraulic design and the sedimentation characteristics of the suspended matter.
Water flow stability: Ensure that the water flow in the flotation tank is stable to avoid short-circuit and vortex phenomena.
Bubble distribution: Design the position and type of the releaser to ensure that the bubbles are evenly distributed throughout the flotation tank.
Water inlet system: Design the position and size of the water inlet pipe to ensure that the water sample enters the flotation tank evenly.
Water outlet system: Design the position and size of the water outlet pipe to ensure that the treated water sample can be discharged smoothly.
Sludge discharge: Design the sludge discharge system, including the scraper and sludge collection device, to ensure that the suspended matter can be effectively removed.
Site conditions: Adjust the size and shape of the flotation tank according to the actual site conditions and space limitations.
Cost-benefit analysis: Evaluate the cost-effectiveness of flotation tanks of different sizes and shapes and select the most cost-effective solution.
Construction difficulty: Evaluate the construction difficulty and feasibility of different design solutions.
Design and working pressure of the dissolved gas tank：The design working pressure of the dissolved gas tank is generally 0.3 to 0.5 MPa. Dissolved gas tanks usually use stepped ring packing. The height of the packing layer should be 1/2 of the tank height and not less than 0.8 m. The liquid level control height should be 1/4 to 1/28 of the tank height.
Determination of dissolved gas efficiency：The level of dissolved gas efficiency directly affects the amount of return water, which in turn affects operating costs. The method for measuring the dissolved gas efficiency includes a system connected in parallel with an air flotation tank to measure the amount of gas released per unit volume of water produced by the dissolved gas device.
Influence of dissolved gas pressure:Dissolved gas pressure has a significant impact on bubble size. At pressures below about 350-400 kPa, dissolved air pressure significantly affects bubble size.
(2) Determine the flow rate of the dissolved gas system
Reflux ratio:The reflux ratio refers to the volume of dissolved gas water to the water to be treated. If possible, necessary small-scale air flotation tests or model tests should be carried out on the wastewater to be treated, and the appropriate dissolved air pressure and reflux ratio should be selected based on the test results.
Dissolved gas efficiency:The level of dissolved gas efficiency directly affects the amount of return water, which determines the operating cost level. Achieving and maintaining high dissolved gas efficiency is a priority.
Bubble formation and release:The formation and release of bubbles depend on the conditions at which the air is released and the surface tension of the water. The smaller the bubble radius, the greater the additional pressure inside the bubble, and the more likely the air molecules in the bubble will collide with the bubble film, and the more violent it will be. Therefore, to obtain stable microbubbles, the strength of the bubble film must be guaranteed.
Design dissolved gas tank:The design of the dissolved gas tank should consider its working pressure and the height of the filling layer to ensure the efficiency of dissolved gas and the formation of bubbles.
Choose the appropriate dissolved air pump and air compressor:Choose the dissolved air pump and compressor to ensure adequate pressure and flow. The selection of dissolved air pumps and air compressors should be based on the design flow rate and dissolved air pressure of the system.
Design and Installation of Dissolved Air Release Systems:The design and installation of the dissolved air release system should ensure that bubbles can be released evenly and avoid short flows and eddy currents. The location and type of release should be selected based on the size and shape of the flotation tank.
Conduct pilot and model tests:During the design and manufacturing process, pilot and model tests should be conducted to verify whether the pressure and flow settings of the dissolved gas system are reasonable. Based on the test results, adjustments should be made to ensure the system can achieve the expected processing effect.
In the design and construction process of dissolved air flotation (DAF) system, designing the water inlet, water outlet and sludge discharge system of the flotation tank is one of the key steps.
Partial reflux dissolved air flotation method: take a part of the deoiled effluent backflow for pressurization and dissolved air, and then directly enter the flotation tank after decompression, mix and float with the wastewater from the flocculation tank. The return volume is generally 25% to 100% of the wastewater.
Pipeline material: Choose corrosion-resistant and pressure-resistant pipe materials, such as stainless steel or plastic pipes.
Pipeline diameter: Select the appropriate pipe diameter according to the design flow to ensure stable water flow.
Pipeline layout: The pipeline should be arranged above the flotation tank to avoid the water flow directly impacting the bottom of the flotation tank and affecting the formation and distribution of bubbles.
Water level control: The flotation tank should be equipped with a water level control room, and a regulating valve (or water level controller) should be used to adjust the water level to prevent the effluent from carrying mud or scum layer.
Outlet weir: Control the outlet regulating pipe or weir of the flotation tank to stabilize the water level of the flotation tank 5 to 10 cm below the slag collection slot. After the water level stabilizes, measure the amount of treated water and adjust it with the water inlet gate until the designed flow rate is reached.
Outlet SS: The effluent SS of the flotation tank can generally be less than 20 to 30 mg/L. When the effluent is directly discharged, it should meet the requirements of national or local emission standards; when it is discharged into the next level treatment system, it should meet the inlet water quality requirements of the next level treatment system.
Scraper: The flotation tank should be equipped with a scraper to ensure that suspended matter can be effectively removed. The scraper should be cleaned regularly to avoid clogging.
Slag collection tank: The flotation tank should be equipped with a slag collection tank to collect slag and suspended matter. The slag collection tank should be cleaned regularly to avoid affecting the flotation effect.
Sludge discharge pipeline: The sludge discharge pipeline should be designed at the bottom of the flotation tank to ensure that the sludge can be discharged smoothly. The pipeline should be made of corrosion-resistant and pressure-resistant materials, such as stainless steel or plastic pipes.
Sludge treatment: The sludge should be further treated, such as concentration and dehydration, to meet the discharge standards.
Foundation compaction: Before installing the equipment, the foundation needs to be compacted to ensure the stability of the equipment.
Level adjustment: After the equipment is in place, the level needs to be adjusted to ensure stable operation of the equipment.
Cleaning sewer: The equipment needs to be equipped with a cleaning sewer, which can be dug an open channel or directly connected to the regulating tank by a pipeline so that the water used to flush the flotation tank can be discharged.
Choose the right air compressor and dissolved air pump.
Purchase the main equipment such as flotation tank(Knowledge about dissolved air tank), dissolved air tank, releaser, scraper, etc.
Determine the control system and instrumentation requirements.
Construction and Building1
Construction and Building 2
Before installing the equipment, a practical foundation must be laid. The equipment can be raised by 100-150mm with concrete mortar. It can also be installed overhead, but the foundation must be able to bear the weight of the equipment.
The equipment needs to be leveled after it is in place.
The equipment needs to be equipped with a cleaning sewer. An open channel can be dug, or it can be directly connected to the regulating tank by pipes to facilitate the discharge of water from the flotation tank.
The connecting pipe between the sewage inlet and the reaction tank is required to be as short as possible to prevent the flocculants from being destroyed in the pipe.
The clean water outlet can be connected to the sewer for discharge. If it needs to enter the sewer treatment process, it can be directly connected to the sewer treatment equipment.
The sludge outlet can be directly connected to the sludge tank or the sewage treatment equipment.
The electrical box should generally be placed on the side of the escalator, and the environment should be clean and tidy.
Clean all the dirt and debris in the pool.
Lubricate the parts that need lubrication, such as the water pump and air compressor.
Turn on the power, start the water pump, and check whether the direction is consistent with the direction indicated by the arrow. Use hydraulic control to start the air compressor, check whether the air compressor is operating normally, and find out the cause in time if any abnormality is found.
Press the scraper switch to make it move toward one end of the dissolved air system. After running to the end, under the action of the stroke block, the scraper moves in the opposite direction until it reaches the sludge tank. The stroke block flips up the scraper, and the stop button is pressed to stop scraping.
The pressure gauge reading of the dissolved air tank should not exceed 0.6MPa
Lubricants should be added regularly to the clean water pump, air compressor and scraper. Generally, the air compressor should be lubricated once every two months and the oil should be changed once every six months.
The sewage entering the flotation machine must be added with medicine, otherwise the effect will be unsatisfactory.
Check the safety valve of the dissolved air tank regularly to see if it is working properly.
When the releaser is blocked, open the vacuum valve to open the tongue of the releaser, clean it with clean water, flush the blockage, and then close the valve.
