NOVELTY - Bacterial composition for degradation of organic fatty substances comprises mainly bacterial strain Klebsiella Oxytoca and additionally Serratia Odorifera and/or Aeromonas Hydrophyla strains.    USE - In purification of aqueous effluents carrying organic fatty substances of animal or vegetable type, especially effluents from food and agriculture-food industry.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for:    (a) use of the bacterial composition for treatment/pre-treatment of effluents carrying fatty organic substances, especially effluents from food or agriculture-food industry; more specifically use of bacterial composition based on bacterial strain Klebsiella Oxytoca, and especially of the bacterial composition as claimed;    (b) a pre-treatment process for effluent containing organic fatty substances, such as effluent from food or agricultural-food industry, comprising direct pre-treatment of effluents containing fatty substances at the exit from the plant they have originated from, and consisting of:    (i) supplying effluent, as it is produced, to a homogenizing and/or conditioning tank (1), activating recycling circuit (2) between the latter and biological reactor (3), to obtain fatty substances dilution rate 0.400/h-1.500/h for their initial concentration 1 g/l;    (ii) decomposing fatty substances in biological reactor (3) using a bacterial composition composed mainly of Klebsiella Oxytoca bacterial strain, or as claimed; and    (iii) passing pretreated effluents containing practically no fatty substances to final treatment unit such as water purifying station; and    (c) an installation for conducting the claimed process, comprising at least one homogenizing and/or conditioning tank (1), at least one biological reactor (3) of capacity adapted to the daily yield of effluents and their fatty substances concentration, linked to (1) through the recycling circuit (2), at least one oxygen control device (7) disposed in biological reactor (s) (3) and at least one unit for evacuation pre-treated effluents, outside biological reactor(s) (3).    DESCRIPTION OF DRAWING(S) - The drawing represents scheme of technological process as claimed.    Homogenizing and/or conditioning tank (1)    Recycling circuit (2)    Biological reactor (3)    Sprinkling device (4)    Decanter (5)    Pump (6)    Oxygen control device (7)    Recycling circuit (8)    Coarse filtration/sieving unit (9)