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
[{'content': 'Trickling filter is used in: \nSelect and explain. \nA. Primary treatment of sewage, B. Secondary treatment of sewage, C. Oxygen ponds, D. Sewage farming', 'role': 'user'}, {'content': "Answer: B \nExplanation: Ans. is 'b' ie secondary t/t of sewage Modern Sewage treatmentThe treatment of sewage may be divided into 2 stages primary t/t & - secondary t/t Primary t/t - in primary t/t the solids are separated from the sewage partly by screening and partly by sedimentation and subjected to anaerobic digestion Secondary t/t - the effluent is subjected to aerobic oxidation.* Secondary treatment is done by one of the following methodsTrickling filter methodActivated sludge process.", 'role': 'assistant'}]