Air blowers have already become necessary equipment in the sewage treatment of various industries in the rapid progress of society and the rapid development of modern industry.
First: Aeration oxygen supply of Air blowers in sewage treatment
In the activated sludge method of wastewater treatment, aerobic microorganisms need to absorb organic matter in the water, and oxidize and decompose to form carbon dioxide and water, Same-time they proliferate, which requires sufficient dissolved oxygen to provide microorganisms in the activated sludge, and aeration is the key-link.
Oxygen supply: Air blower provides oxygen for microbial growth and metabolism by transporting air to the aeration tank. Air blower continuously supplies air, transferring oxygen from the air to the water through air-water contact to meet the oxygen needs of microbial growth and metabolic processes. Its main role is to introduce air into the wastewater in order to provide enough oxygen to supply microorganisms and promote the degradation of organic matter.
Enhanced biodegradation: Adequate oxygen provided by Air blower can promote the decomposition of organic matter in the wastewater, and the purpose of aeration is to provide enough dissolved oxygen to the sewage to maintain the metabolism of microorganisms so that they can effectively decompose organic matter in the sewage. Helps to remove contaminants from wastewater and improve water quality.
Improve wastewater treatment efficiency: An oxygen-sufficient environment helps to reduce chemical and biological oxygen demand in wastewater and improve treatment efficiency. According to the amount of sewage treatment, water quality (especially organic content, such as chemical oxygen demand COD, biochemical oxygen demand BOD) different stages and actual oxygen demand to determine the required aeration. Air blower can flexibly adjust the air supply to ensure that the oxygen supply meets the demand and avoids oversupply, thereby improving the efficiency and quality of sewage treatment.
For example, for an urban sewage treatment plant with a capacity of 10,000 cubic meters/day, if the inlet BOD is 200mg/L, and the effluent BOD is required to be controlled below 20mg/L, the aeration rate required per cubic meter of sewage can be calculated according to empirical data such as the aerobic coefficient of microorganisms.
Second: Air Blower wastewater agitation and dissolution treatment
Air blower is also used to stir sewage. Its main purpose is to ensure that the substances in the wastewater are evenly mixed, avoid precipitation and deposition, and improve the treatment effect. Stirring can make the microorganisms, nutrients and dissolved oxygen in the sewage fully mixed to improve the treatment efficiency.
Air blower with stirring effect
Improve the mixing efficiency: the substances in the wastewater are fully stirred through the air bubbles to ensure that the pollutants in the wastewater are evenly mixed with the treatment agent, thereby improving the treatment effect.
Preventing deposition: Agitation prevents the precipitation of solid substances in the wastewater, maintaining the suspended state and contributing to the efficiency of the subsequent treatment stage.
Promote chemical reaction: In some wastewater treatment processes, stirring can promote the chemical reaction and improve the reaction efficiency of the treatment agent.
For example, in the oxidation ditch process, certain hydraulic conditions are required to ensure the suspension and mixing of activated sludge, which requires the blower to provide suitable air flow to achieve. The activated sludge is suspended in the aeration tank, in full contact with the sewage, to enhance the mass transfer conditions of pollutants in the water treatment system, so that the organic matter, microorganisms and oxygen in the sewage can fully contact and react, and improve the treatment effect. Provide good conditions for the diffusion and transfer of oxygen in the liquid phase, promote the oxygen to dissolve into the water faster and more evenly, and further improve the aeration efficiency.
Third : Air blower system design considerations
The successful design of a air blower system in wastewater treatment depends on several considerations:
Flow rate, pressure, site conditions (ambient pressure, operating ambient temperature, available space, indoor or outdoor, climate, etc.), range ratio (the change between real-time flow and maximum flow), redundancy requirements (a critical nature of the wastewater treatment process), economic cost (initial capital investment and long-term operating costs).
Flow rate and pressure
Theoretical calculation method: According to the amount of sewage treatment, inlet and effluent water quality indicators (such as BOD, ammonia nitrogen, etc.) and the treatment process adopted, theoretical oxygen demand is calculated according to the chemical reaction formula and microbial metabolism oxygen demand. Taking activated sludge method as an example, the empirical formula Lawrence-McCarty equation is usually used to calculate the oxygen demand of microorganisms.
For example, for removing 1 kg of BOD, approximately 1-1.4 kg of oxygen is required. Then convert the oxygen demand into the air demand, considering the oxygen content in the air (about 21%), you can calculate the theoretical air volume.
The flow rate is a function of the oxygen demand of the aerobic microorganisms used in the treatment process. Wastewater treatment actually involves two separate processes, both of which require oxygen: the metabolism of bioorganic materials,
Examples include organisms in municipal wastewater treatment plants, waste, food particles in food and beverage processing, wood in paper mills or fiber waste in textile mills + aerobic microbes +O2=CO2+NH3+ other bad energy.
Notably, taking samples of wastewater and calculating biological oxygen demand and ammonia levels helps technicians determine the system's air demand, which is a mass flow rate that varies with ambient temperature because warmer air has less oxygen.
Air blower mainly provides flow rather than pressure. Its rated pressure indicates the maximum back pressure that can be overcome. The relationship between the flow rate generated by the blower and the pressure needs to be adjusted according to the specific needs. Screw blowers use screw compressor technology to extend the pressure range up to 22psi for moderate pressure requirements.
Actual correction
In practical applications, due to the oxygen transfer efficiency of aeration equipment, temperature and pressure changes of sewage and other factors, the theoretical air volume needs to be corrected. For example, the oxygen transfer efficiency of aeration equipment is generally between 5%-30%, and according to the performance parameters of the selected aeration equipment, such as the oxygen transfer efficiency of the microporous aeration head is 20%, it is necessary to multiply the theoretical air volume by a certain coefficient (such as 1/0.2 = 5) to obtain the actual required air volume.
Air pressure calculation
Range ratio refers to the range of change between real-time flow and maximum flow. When designing the blower system, it is necessary to consider the variation range of the flow rate during the wastewater treatment process to ensure that the system can operate normally under different working conditions.
Static pressure calculation
Static pressure refers to the pressure of a gas at rest. In sewage treatment, static pressure mainly considers the resistance of aeration system, including pipe resistance and aeration head resistance. Pipe resistance can be calculated by Darcy-Weisbach formula, which is related to pipe length, pipe diameter, roughness and gas flow rate. The resistance of the aerator head is obtained according to the product manual of the aerator head. For example, for an aeration pipe with a length of 100 meters, a pipe diameter of 100 mm and a gas flow rate of 10 meters/s, the static pressure requirement is obtained by calculating the sum of the resistance of the pipe and the resistance of the aeration head.
Dynamic pressure calculation
Dynamic pressure is related to the flow rate of the gas, according to the Bernoulli equation, the dynamic pressure calculation formula is, where is the gas density, is the gas flow rate. In the sewage treatment aeration system, it is necessary to consider the dynamic pressure when the gas enters the aeration head to ensure that the gas can enter the sewage through the aeration head normally.
Total pressure calculation
Total pressure is the sum of static pressure and dynamic pressure. In the selection, the rated air pressure of the blower should be greater than or equal to the total pressure to ensure that the pressure needs of the aeration system can be met.
Fourth: Site conditions
Site conditions include ambient pressure, operating ambient temperature, site contaminants (dust, methane, hydrogen sulfide, or other harmful gases), available space, indoor or outdoor, and climate. These factors will affect the selection and installation of the blower system, and need to be reasonably considered and designed according to the actual situation.
Fifth: Redundancy requirements
Redundancy requirements refer to key properties in the sewage treatment process, such as the reliability of oxygen supply and system stability. When designing the blower system, it is necessary to consider whether backup equipment is needed to cope with emergencies and ensure the stability and reliability of the system. Aeration levels in wastewater treatment are typically five to seven times higher than naturally occurring aeration levels. If a system suddenly doesn't have that high oxygen content, the aerobic microbes will quickly begin to die. Sewage treatment systems can take days or weeks to reach equilibrium, so system operators cannot take that risk. As a result, sewage treatment systems often have multiple blowers to provide a degree of redundancy so that treatment can continue in the event that the blowers require maintenance or repair.
Sixth: Economic Cost
Cost is an important factor to consider when designing a waste water treatment blower system, including initial capital investment and long-term operating costs. The system costs, including equipment procurement costs, energy consumption costs, and maintenance costs, must be minimized on the premise of meeting processing requirements.
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