Activated Sludge Process and IFAS: Design Rules and Guidelines
Published on by Karl-Uwe Schmitz, President at Aqua Equip Technologies LLC (AET LLC) in Technology
Activated sludge is worldwide the most used suspended growth process in wastewater treatment. The treatment process can include different steps, but most commonly are:
- Screening and grit removal to filter out debris
- Primary clarifier for particle sedimentation
- Biological treatment with activated sludge consisting of an aeration basin, secondary clarifier and recycle stream
- Disinfection for final removal of germs and bacteria
Wastewater entering the aeration basin still contains organic matter such as food waste and fecal. Microorganisms in the raw water influent will colonize in the aeration tank and metabolize organic waste to ATP for further cell growth as well as CO2 and water. As the microorganisms need oxygen to survive, the tank is aerated for example with diffuser systems. The amount of oxygen needed for biochemical processes is also known as the BOD value. BOD is a very important indicator of the level of wastewater pollution.
To keep a good balance between the number of microorganisms, organic waste and oxygen, some microorganisms are settled down in the secondary clarifier. Adding flocculants will cause that microorganisms clump together with particles and settle down as activated sludge. Some of the activated sludge is then recycled back to the aeration basin whereas the rest is removed as waste sludge, thickened and then for example used as fertilizers. By recycling the activated sludge back into the aeration basin, the amount of microorganisms can be increased significantly – e.g. 30 times compared to the raw water influent. This is exactly the principle of activated sludge: To accelerate biological degradation significantly in a confined space.
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Taxonomy
- fixed-bed technology
- Activated Sludge
- Fixed bed