This type of plant has replaced many submerged aerated filter models.
Activated Sludge Technology use two stages of dealing with commerical and residential sewage / waste water:
- They have no primary settlement tanks.
- Secondary Treatment The sewage flows straight to the digestion chamber or 'Biozone', where the organic material in the sewage is digested. The Activated Sludge process is a natural biological treatment process, involving many different sorts of bugs. In the Activated Sludge Plant (ASP) bacteria produce sticky substances that coat the bits of organic material in the sewage. The particles stick together to form lumps or 'flocs', creating a structure within which the bugs live. The milk chocolate coloured activated sludge is aerated to dissolve oxygen in the sewage liqor, which allows the bacteria to breathe and the organic matter (BOD) to be digested by the bugs.
- Final Settlement / Clarification The sewage effluent then flows to a clarification chamber, where the flocs sink to the bottom and are transferred back to the digestion chamber.
The tank should be big enough to allow sufficient contact time (retention time) between the sewage and the activated sludge for all the digestion to take place.