subject: On several aerators in wastewater treatment - aeration, sewage treatment - water industries [print this page] On several aerators in wastewater treatment - aeration, sewage treatment - water industries
Water pollution problem is a worldwide environmental problem, both in developing and developed countries, this issue has drawn increasing attention. Now, all countries, especially developed countries spend each year enormous human and financial resources for industrial wastewater treatment. Since the 20th century, since 60 countries have a variety of research and development of new water pollution control technologies and new methods of pollution control have begun to enter a more advanced stage, that is, a new stage of comprehensive prevention and control of environmental pollution.
Elements as the diversity of industrial waste, often through a treatment system consisting of several ways to achieve the required emission standards. Sewage Means of handling classified according to the method used can be classified into physical, chemical, physical chemical and biological methods 4. Biological method is the use of wastewater in the metabolism of microbial decomposition of biodegradable organic matter in water method, as has the processing capacity, investment, economic and reliable by feature, which is the world's most common form of treatment Methods.
1 diffusers in Wastewater Treatment Biological treatment method according to the role of microorganisms involved in aerobic conditions, can be divided into aerobic and anaerobic methods into two categories. In general, more suitable for low aerobic effluent, such as ethylene plant effluent; and Anaerobic Sludge and more suitable for handling high concentrations of sewage. Aerobic biological treatment can be divided into activated sludge and biological Membrane Act two categories. Activated sludge process is to strengthen the artificial body of water purification method is to rely on the work of activated sludge removal of the main methods of organic matter in sewage. Present in activated sludge in the aerobic micro-organisms must have oxygen in the existence of conditions to work. Biochemical sewage treatment system in the aeration tank, oxygen transfer efficiency and aerobic microbial growth is positively correlated. Dissolved oxygen supply according to the number of aerobic microorganisms, physiological characteristics, the nature and concentration of substrate in consideration. In this way, activated sludge to the degradation of organic matter in the best condition. According to the trial showed that aeration tank dissolved oxygen maintained at 3 ~ 4mg / L is appropriate, if not getting enough oxygen, poor performance of activated sludge, resulting in waste water treatment down. To ensure adequate oxygen supply, we must rely on a device to complete, such as aerators.
1.1 Aeration Principle Aeration is to make strong contact with air and water as a means with the aim of the air in the oxygen dissolved in water, or water, gases and volatile substances do not exiled to the air. In other words, it is to promote the exchange of material between the gas and liquid as a means. It also has other important roles, such as mixing and stirring. Oxygen in the air passing into the water by aeration, the oxygen carried by the gas to liquid mass transfer, this mass transfer theory, the current applications are more Lewis and Whitman made the two-film theory.
Two-film theory that the "gas - water" interface, there are film and liquid film, film and liquid film outside the outside air and liquid flow is turbulent state; gas is a layer between the membrane and liquid film flow state, there is no convection occurs under certain conditions, the pressure gradient and concentration gradient. If the liquid oxygen concentration was lower than the saturation concentration of oxygen in water, air, continued inward diffusion of oxygen into water through the membrane, which will be the film and film oxygen transmission barrier , this is the two-film theory . Clearly, to overcome the membrane barrier most effective way to quickly transform "gas - liquid" interface. Aeration mixing is the case, the specific approach is to: reduce the size of the bubble, increasing the number of bubbles, increased turbulence of the liquid, increasing the depth of aeration the installation of the extension of the bubble and liquid contact time. Aeration equipment It is based on this approach in the treatment of wastewater has been widely used.
1.2 aerator aeration type and functions
Aeration type can be divided into two categories: one is diffused aeration, a class of mechanical aeration. Diffused aeration is used aerator diffuser or diffuser aeration air bubbles into the water way. General sewage treatment plant ethylene over this way. Mechanical aeration is the use of instruments such as the introduction of impeller bubble aeration.
All aeration equipment should meet the following three kinds of functions:
generate and maintain an effective gas - water contact, and oxygen consumption of bio-oxidation of the situation continued to maintain a certain concentration of dissolved oxygen in water;
generate sufficient aeration region mixed Cooperation Use and water flow ring;
to maintain sufficient liquid velocity, so that the water in a suspension of biological solids.
