<prompt> Aerobic digestion of sludge takes place in -Trickling filterBroad irrigationActivated sludgeSeptic tank  <response>: Parks 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. 