About activate sludge / sludge drying

In most of sewage factories and sewage offices, activated sludge method is used for their effluent treatment. What does activated sludge suggest in the activated sludge method?

Activated sludge is microorganism such as bacteria and animalcule and living things found in various place such as river, water conduit, soil, etc. It also can be found in air and dusts with state of spores. These microorganisms appear to begin their activity when sewage is agitated by being air added. Then, number of the microorganisms gets more and more, and the sewage becomes activated sludge.
Activated sludge is aggregates of microorganisms and is stuff like soft mud whose state is like a few millimeters of fluff, and it can be observed while floating in water and is called floc. These flocs are aggregates of bacteria and microorganisms such as various kind of protozoa, and it propagates itself as decomposing waste and cleaning water when it is mixed with waste water/sewage followed by being air blown in and agitated. Activated sludge is settled out as sediment when agitation is stopped and treated clear water remains in the upper layer. In this way, activated sludge and clear water are separated in final settling tanks.

Bacteria cohering in activated sludge is called zoogloeal, and floc is formed in activated sludge when the zoogloeal get together because of their stickiness. Zoogloeal also has function to take particles that microorganism cannot decompose in so that these particles can be removed from sewage.
Substances that active sludge can decompose and use for their propagation are mainly organic matter, therefore, oils, poison, agricultural and other kind of chemicals cannot be decomposed and there are cases that the activated sludge extinct as well.
There are restrictions to drain off into sewage, and one of the reasons that detergents, insecticides, chemical agents are not allowed to drain off is that they cannot be treated by activated sludge method.
The treatment method using activated sludge is not used in effluent treatment for non-organic matters.

Removal of organic matter
Activated sludge decomposes organic matter and propagates themselves, and a part of the decomposed substance are changed into carbon dioxide gas. By mixing air during this process, oxygen in the air is used for the decomposition.
Dirt + Oxygen -> propagation of activated sludge + carbon dioxide gas

Removal of nitrogen and phosphorus
Although nitrogen and phosphorus can be used as components of fertilizer, they also cause a red tide in the sea. By applying activated sludge method, nitrogen and phosphorus can be removed.

Nitrogen treatment
1）Activated sludge changes nitrogen from ammonium ion into nitrate ion under aerobic state (state with air).
2）Under anaerobic state (state without air), it changes nitrate ion into nitrogen gas. (denitrification)
Nitrogen(nitrate ion) -> nitrogen gas

Phosphorus treatment
Activated sludge takes phosphorus under condition where oxygen exists, and releases phosphorus when there is no oxygen. By using this characteristic, phosphorus in waste water can be collected by being taken into activated sludge.

Source ： Aichi mizutomidorinokousya 

 Sludge drying 
In a method called conventional activated sludge process at effluent treatment plants, activated sludge propagate itself as breaking waste down and cleaning water though, activated sludge which is propagated excessively is deposited and need to be removed as excess sludge. Sediments generated when microorganisms are aggregated and settle out is called excess sludge and it is treated as waste after being condensed and dewatered.
Since it contains a lot of water even after the dewatering process, waste disposal cost can be reduced by drying and decreasing its weight with KENKI DRYER. Since excess sludge is organic matter, it also can be recycled by being dried with KENKI DRYER’s low-temperature drying function which does not change the components of materials being dried.

Sludge drying

Applications