activated-sludge process [`ak·tǝ´vād·ǝd ´slǝj `prä´sǝs] CIVIL ENGINEERING A sewage treatment process in which the sludge in the secondary stage is put into aeration tanks to facilitate aerobic decomposition by microorganisms; the sludge and supernatant liquor are separated in a settling tank; the supernatant liquor or effluent is further treated by chlorination or oxidation. |