isomer(1. Two or more compounds having the same molecular formula, but a different arrangement of atoms within the molecule. 2. One of two or more chemical substances having the same elementary percentage composition and molecular weight but differing in structure, and therefore in properties; there are many ways in which such structural differences occur)
thickening(Any process beyond gravity sedimentation that increases the concentration of solids in sludge with or without the use of chemical flocculants)