- A A free-floating cluster of photosynthetic algal cells
- B Masses of bacteria held together by fungal filaments
- C A perforated filter bed used in the primary settling tank
- D Activated sludge specifically recycled from secondary settling tanks
Correct answer: B. Masses of bacteria held together by fungal filaments
Explanation: Flocs are masses of bacteria held together by fungal filaments (mycelia) that form during secondary sewage treatment and help in biological degradation of organic matter.
Concept context
Microorganisms in food, medicine, sewage treatment, biocontrol, and biofertilizers