(1) Expanded sludge
The performance of activated sludge settling and flocculation can be understood by measuring the sludge volume index (SVI). Generally, the sludge volume index (SVI) is above 200mL/g, and the concentration of the sludge layer in the graduated cylinder changes from 5g/L to pressure. The dense phase sludge is called bulking sludge, one is formed by filamentous bacteria and the other is formed by non-filamentous bacteria.
If you observe the expanded sludge under a microscope, you can see broken thread-like filamentous microorganisms entangled with each other.
(2) Rising sludge
During the measurement time of the 30-minute sedimentation experiment, the sludge settled well but rose again within a few hours. If the rising sludge was destroyed by stirring with a rod, it would settle again immediately.
This phenomenon is caused by the denitrification of the sludge mixture that has undergone nitrification into the sedimentation tank, and the nitrogen generated during the denitrification process adheres to the sludge and causes it to float.
When this phenomenon occurs, just reduce the concentration of dissolved oxygen and control the nitrification process.
