Because of the diversity of industrial wastewater components, treatment systems often require several methods to achieve the required emission standards. Sewage treatment methods used by the means of classification can be divided into physical, chemical, physical and biological methods 4. The biological method is a method of decomposing degradable organic matter in the water by using the metabolic action of microorganisms in waste water. Because of its large processing capacity, economical investment and economic reliability, it is the most common water treatment method in the world today.
1 aerator in the sewage treatment applications
Biological treatment According to the aerobic conditions involved in the role of microorganisms can be divided into aerobic and anaerobic two categories.
In general, aerobic method is more suitable for lower concentrations of sewage, such as ethylene plant wastewater; and anaerobic method is more suitable for the treatment of sludge and higher concentrations of sewage.
Aerobic biological treatment can be divided into activated sludge and biofilm two categories. Activated sludge method is artificial self-purification of water body is a method of relying on the main body of activated sludge removal of organic matter in sewage. Aerobic microorganisms present in activated sludge must be effective in the presence of oxygen. In the sewage treatment biochemical aeration tank, oxygenation efficiency and aerobic microbial growth is positively correlated. Dissolved oxygen supply according to the number of aerobic microorganisms, physiological characteristics, matrix properties and concentrations to consider. In this way, activated sludge can be in the best state of organic matter degradation.
According to the test shows that the dissolved oxygen in the aeration tank maintained at 3 ~ 4mg / L is appropriate, if insufficient oxygen, activated sludge performance is poor, resulting in decreased wastewater treatment. To ensure adequate oxygen supply, one must rely on a single device, such as an aerator.
2 aeration principle
Aeration is a means of bringing air into strong contact with water and is designed to dissolve the oxygen in the air in the water or to expel unwanted gases and volatiles from the water to the air. In other words, it is a means of promoting the exchange of matter between gases and liquids. It also has other important functions, such as mixing and mixing. Oxygen in the air is diffused into the water by aeration. Oxygen is transferred from the gas phase to the liquid phase. The theory of mass transfer and diffusion is currently being applied to the double-membrane theory proposed by Lewis and Whitman.
The double-membrane theory holds that there are gas and liquid membranes at the gas-water interface, and the air and liquid flow outside the gas and liquid membranes are in turbulent flow state. The laminar flow state between the gas and liquid membranes is not Convection exists, under certain conditions there will be pressure gradient and concentration gradient. If the concentration of oxygen in the liquid film is lower than the saturation concentration of oxygen in the water, the oxygen in the air continues to diffuse inward through the liquid film into the body of water, so that the liquid film and the gas film become barriers to oxygen transfer, which is the double film theory.
Obviously, the most effective way to overcome the fluid barrier is to quickly change the "gas-liquid" interface. Aeration agitation is the case, the specific approach is to reduce the size of the bubble to increase the number of bubbles to improve the degree of turbulence of the liquid to increase the installation depth of the aerator to extend the contact time bubbles and liquid. It is based on this practice that aeration equipment is widely used in sewage treatment.
3 aeration type and aerator function
Aeration types generally fall into two categories: one is blast aeration, one is mechanical aeration. Blast aeration is the use of aeration diffuser or diffuser in the water bubbles into the way of aeration. General ethylene plant wastewater treatment in this way. Mechanical aeration refers to the use of impeller and other instruments to introduce air bubbles aeration.
All aeration equipment, should meet the following three kinds of functions:
â‘ produce and maintain an effective gas-water contact, and in the case of biological oxygen consumption continue to consume oxygen to maintain a certain concentration of dissolved oxygen in water;
â‘¡ in the aeration zone to produce adequate mixing and water circulation;
â‘¢ maintain enough liquid speed, so that the biological solids in water in suspension.
Aeration aeration equipment
Blast aeration system by the blower, aerator and a series of connected pipelines. Blowers deliver the air through a series of ducts to an aerator mounted on the bottom of the tank, through which aerators create bubbles of different sizes. Bubbles are formed at the outlet of the aerator, the size of which depends on the form of the air diffuser, the bubbles rise and follow the water ring, and finally rupture at the liquid surface. This produces oxygen transfer to the effluent. Aeration aerator blast system is divided into micro-bubbles, bubbles, bubbles, hydraulic shear, hydraulic impact and air lifts and other types.
The main technical performance indicators of aeration aeration equipment are: Power efficiency (Ep), that is, the amount of oxygen transferred to the mixture per 1kW of electricity consumed; the oxygen utilization efficiency (EA), which is transferred to the mixture by aeration Of oxygen, the percentage of total oxygen (%).
Micro-bubble aerator
Micro-bubble aerator, also known as microporous aerator, the use of porous materials such as ceramsite, coarse porcelain doped with a suitable class of adhesives such as phenolic resin, sintered at high temperatures to become a diffusion plate, diffusion tube and diffusion cover form. According to the type of installation, can be divided into lifting microporous aerator and fixed microporous aerator.
Lifting microporous aerator is mainly composed of microporous aeration pipe, movable rocker, hoist and other 3 parts: â‘ microporous aeration pipe is composed of microporous tube, front cover, back cover and connecting bolts; â‘¡ activities Rocker arm is to enhance the pipe, microporous aeration pipe installed in the bronchus, into a grid-like, the base is fixed to the pool wall, the activities of riser into the pool, the branch pipe fell on the bottom of the pool, and the support bracket at the bottom of the pool ; â‘¢ aerator hoist, electric hoist for the activities, lifting the car can be free to move, the rocker lift.
Its working principle is: air from the micro-bubble aeration tube back cover vent into the aeration tube, aeration tube wall densely packed many small pores, the air pressure in the tube under the effect of the pressure from the tube wall pores In the proliferation of sewage in the formation of many tiny bubbles, and cause water turbulence, so as to achieve the purpose of the oxygen in the air into the water.
There are many forms of microporous aeration tube, there are two more commonly used:
One is from coarse porcelain or corundum sintered ordinary aeration tube, this tube wall in the sintering process to produce many tiny pores, its main feature is the ability to produce tiny bubbles, the bubble diameter of about 0.1 to 0.2 mm, gas and liquid contact area, high oxygen utilization, generally up to 20 to 25%; its disadvantage is the larger pressure loss, easy to plug, the air to be filtered, easy to damage, once damaged, the use of oxygen Rate began to decline rapidly.
The other is a tube membrane microporous aeration tube. This type of aeration pipe is installed in the same way as the previous one, but its structure is very different. It consists of a pipe made of ABS or UPVC as the gas pipe, and the pipe wall is provided with ventilation holes The outer circumference of the trachea is covered with a diaphragm made of synthetic rubber. The diaphragm is fixed to the pipe by a metal clip. In the synthetic rubber diaphragm with laser and other methods to make uniform distribution of holes.
Aeration, the air through the wall of the vent into the membrane between the wall and the tube, under the action of compressed air, so that the membrane slightly bulging, open the hole to achieve the purpose of the proliferation of cloth gas. Stop the gas supply, the pressure disappears, the diaphragm itself under the elastic action of the eyelet automatically closed, due to water pressure, the diaphragm compacted in the pipe wall. Therefore, the sewage will not flow back and plug the hole. However, since the diameter of the opening of the membrane directly affects the utilization of oxygen, the opening diameter should be appropriate. Orifice diameter is too large, oxygen utilization is low, the opening diameter is too small, high oxygen utilization, but the resistance increases. Rubber diaphragm should be used anti-aging, high-strength plastic, so as to avoid tearing diaphragm, resulting in damage to the aerator.
Dynamic Aerator
Dynamic aerator is a new type of aerator, which belongs to the fixed-mounted microbubble aerator. It consists of a circular cover, a rotary mixer, a swirling ring, a sleeve hoop and a gas distribution pipe.