This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Environment and health, Subject name: Social & Preventive Medicine
Aerobic digestion of sludge takes place in - 
Select and explain. 
A. Trickling filter, B. Broad irrigation, C. Activated sludge, D. Septic tank
A: Trickling filter
Answer: A: Trickling filter 
Explanation: Park's textbook of preventive and social medicine 23rd edition. *The effluent from the primary sedimentation tank still contains a propoion of organic matter in solution or colloidal state and numerous living organisms.it is subjected to fuher treatment by filter method activated sludge process.