4 Introduction to Process Analysis and Selection Treatment methods in which the application of physical forces predominate are known as physical unit operations Examples of physical unit operations include screening, mixing, sedimentation, gas transfer, filtration, and adsorption. Treatment methods in which the removal or conversion of constituents is brought about by the addition of chemicals or by other chemical reactions are known as chemical unit processes Examples of chemical unit processes include disinfection, oXidation, and precipitation Treatment methods in which the removal of constituents is brought about by biological activity are known as biological unit processes4 Introduction to Process Analysis and Selection Treatment methods in which the application of physical forces predominate are known as physical unit operations. Examples of physical unit operations include screening, mixing, sedimentation, gas transfer, filtration, and adsorption. Treatment methods in which the removal or conversion of constituents is brought about by the addition of chemicals or by other chemical reactions are known as chemical unit processes. Examples of chemical unit processes include disinfection, oxidation, and precipitation. Treatment methods in which the removal of constituents is brought about by biological activity are known as biological unit processes