NOVELTY - The process comprises supplying a liquid charge to be treated to a first tank containing an aqueous phase and first bacterial population, solubilizing the liquid charge by enzymatic hydrolysis with the first bacterial population, extracting a first reaction product from the first tank, filtering the biomass contained in the first reaction product to give a first effluent, supplying the first effluent to a second tank containing an aqueous phase and a second bacterial population, and biodegrading the first effluent into the second tank by biological digestion.    USE - The process is useful for treating a liquid feedstock comprising an organic toxic liquid dispersible and digestible in an oil or toxic solvent using a biological unit.    ADVANTAGE - The process allows economical, reliable and rapid treatment of liquid feedstock comprising an organic toxic liquid at industrial scale with high efficiency, and avoids the risk of producing toxic volatile compounds during incineration.    DETAILED DESCRIPTION - The process comprises supplying a liquid charge to be treated to a first tank containing an aqueous phase and first bacterial population, solubilizing the liquid charge by enzymatic hydrolysis with the first bacterial population, extracting a first reaction product from the first tank, filtering the biomass contained in the first reaction product to give a first effluent, supplying the first effluent to a second tank containing an aqueous phase and a second bacterial population, biodegrading the first effluent into the second tank by biological digestion with the second bacterial population, extracting a second liquid reaction product from the second tank, filtering the biomass contained in the second reaction product to give a second effluent, supplying the first effluent to a third tank containing an aqueous phase and a third bacterial population, reducing residual bacterial components of the second effluent in the third tank by biological action of the third bacterial population, extracting a third liquid reaction product from the third tank, and separately recycling the biomass to the tank, which extracts the reaction product subjected to filtration. A chemical oxidation is carried out in the second effluent after filtration and/or excess biomass from the filter. An INDEPENDENT CLAIM is included for an installation for treating a liquid feedstock comprising an organic toxic liquid dispersible and digestible in an oil or toxic solvent using a biological unit.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of an installation for treating a liquid feedstock.    Reaction tank (100)    Measuring pump (102)    Aqueous phase (104)    Oil passage pump (106)    Tangential filter (108)    Conduit. (110)