The biological treatment techniques used can be classified into attached growth processes and suspended growth processes. Which of the following treatments is classified under attached growth processes?
- AAerated lagoon
- BSludge digestion system
- CActivated sludge process
- DRotating biological contactorCorrect
Solution
Concept
In attached growth processes, microorganisms grow as a biofilm on a fixed or moving surface (media).
Step-by-step solution
1. Attached growth means microbes stick to a medium as a biofilm. 2. RBC: rotating discs carry the biofilm, so it is attached growth. 3. Activated sludge and aerated lagoon: microbes stay suspended in the liquid, so they are suspended growth. 4. Sludge digestion is also a suspended (mixed) process. 5. Answer: D.
Explanation
A rotating biological contactor has large discs that rotate slowly in the wastewater. Microorganisms grow as a film on the disc surface, so it is an attached growth process. Trickling filters are another example of attached growth.
Why the other options are wrong
A: Aerated lagoon is suspended growth. B: Sludge digestion is a suspended growth (mixed) process. C: Activated sludge process is the classic suspended growth process.
Shortcut
If there is a fixed or rotating media (filter, disc), it is attached growth.
Common mistake
Confusing the activated sludge process with trickling filters or RBC.
Correct answer: D) Rotating biological contactor