Activated sludge  
In activated sludge plants the micro-organisms, which carry out the treatment process, are present in so-called sludge flocs. These flocs develop spontaneously when waste water is aerated. Wastewater and sludge flocs are mixed in the aeration tank. Most of the compounds present in the waste water are suitable nutrients for the bacteria in the flocs. They take up the nutrients in their cells and use them for growth and energy supply. When the treatment process is completed, sludge flocs and clean water are separated by settling of the flocs in the final clarifyer.










An activated sludge floc is a conglomerate of:

-        living and dead bacterial cells.                                                    

-        Protozoa and higher organisms                                                  

-        trapped inorganic particles (e.g. sand) and organic fibres           

-        precipitated salts and such like

It is held together by chemical forces and a slime matrix surrounding the cells. The composition of the floc is dynamic, not static, and can be changed through alterations in the process conditions.