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
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.