Method of biologically purifying liquids contaminated with impurities

A method of biologically purifying liquids that are heavily contaminated with organic or inorganic impurities, by using bacteria in the presence of a solid support on which bacteria can be fixed, comprising the steps of:

• (A) continuously injecting the liquid to be purified without prior filtering into an aerobic medium reactor, the reactor providing a solid support having grain size lying in the range 1 mm to 5 mm and density lying in the range 1.01 g/cm.sup.3 to 1.3 g/cm.sup.3, the solid support having been put into turbulent motion by blowing in gas in the presence of bacteria, and while satisfying the conditions required by the metabolism of the bacteria;
• use being made in the reactor both of nitrogen bacteria that are autotrophic and that fix on the support, and of carbon bacteria that are heterotrophic and that reproduce essentially in the liquid by forming flocculation;
• and
• (B) continuously taking the treated liquid from the reactor after a transit time that is long enough to ensure purification of the impurities contained in the liquid to be purified.