The present invention relates to methods and apparatus for separation of solids from liquids and separation of liquids from liquids (such as oil from water) by dissolved gas floatation. A dissolved gas floatation clarifier is described as is a liquid-gas mixer, a liquid-liquid mixer, and solid-liquid chemical feeders. The methods and apparatus of the present invention are particularly suitable for supplying dissolved air and mixing of chemicals for use in separation of solids in dissolved air floatation clarifiers.