This is about anaerobic-anoxic-aerobic (A2O) method which is one of various activated sludge methods in wastewater treatment process. This method is a wastewater treatment method whose main purpose is to remove nitrogen and phosphorus from wastewater, and a method improved from conventional activated sludge process.
Also, this method is one of advanced wastewater treatment method which remove nitrogen and phosphorus. Red Tide in sea is caused by eutrophication that nutrient salts such as phosphorus and nitrogen flow into the sea.
|■ About Anaerobic-anoxic-aerobic method (A2O method)|
Anaerobic-anoxic-aerobic method (A2O method) is a wastewater treatment method whose main purpose is to remove nitrogen and phosphorus from wastewater, and reaction tank is configured by three tanks which are called anaerobic tank, anoxic tank, and aerobic tank.
Since no air is sent into anaerobic tanks and there is no oxygen, microorganism and activated sludge become less active and release phosphorus. Sewage in anaerobic tanks is sent to anoxic tank after releasing phosphorus, then sent to aerobic tank. Agitators are settled in anaerobic tanks and activated sludge in the tanks are kept being agitated. Similar to anaerobic tank, anoxic tank is tank with no air sent into and no oxygen melt in water in the tank. Since microorganism (denitrifier) which prefer anaerobic state consume oxygen, nitrate ion in nitrate containing liquid pumped from aerobic tank is decomposed in the anoxic tank. During this decomposed process, nitrogen is released to air as nitrogen gas by being removed its oxygen with nitrate ion. Inside of aerobic tank is in the state that aeration is done and oxygen are added into water. Activated sludge and microorganisms (Nitrifying bacteria : Nitrosomonas bacteria, Nitrobacter bacteria) which is active in aerobic tank decompose ammoniacal nitrogen sent from anoxic tank and change into nitrate ion. Nitrate containing liquid with the nitrate ion is circulated to anoxic tank with pumps.
Also, in aerobic tank, activated sludge and microorganisms which have taken in phosphorus are sent to final settling tank and sedimented. Clarified water in the final settling tank is discharged after passing through disinfection apparatus and some of settled activated sludge is returned to reaction tank as returned sludge, then remained stuffs are sent to sludge thickening tank as waste sludge. Sludge thickened in thickening tank are dehydrated and treated as dehydrated sludge such as being dried.
This method of removing nitrogen is also called recirculating denitrification system since nitrification and denitrification is took place while nitrate containing liquid is circulated. In case that only nitrogen is aimed to be removed, reaction tank is configured with only anoxic tank and aerobic tank and anaerobic tank is not used.
■ Difference between anaerobic tank and anoxic tank.
It is the same for anaerobic tank and anoxic tank that air is not sent into the tanks. Their difference is that nitrate ion exits or not.
■ Nitrate containing liquid
Mixture of activated sludge which containing abundant nitrate ion (NO3-) generated by nitrification of ammonia contained in waste water.
Water in the sludge thickened in the sludge thickener tank are removed at dehydration process to a certain degree.
However, moisture content is normally more than 80% and the sludge still has adhesiveness and stickiness. Also, latter processes are not easy because of influence of flocculants. Our drying apparatus of KENKI DRYER with international patented technology can surely dry any sticky, adhesive and viscus sludge, and also materials in liquid state like slurry, without clogging inside of the dryer. Also, because of its simple structure, its price is low and apparatus cost of the dryer can be retrieved by reducing industrial waste disposal cost within 3 years. Dried materials can be recycled as fuel, bacterial fertilizer, soil conditioner, etc. since component of the material is hardly changed because of its low-temperature drying method.
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