NOVELTY - The method comprises subjecting effluents to a first aerobic activated sludge treatment followed by a second treatment with filtration by membranes (8a, 8b), where the first treatment is a treatment in mixed cultures with mobile bacteria supports (4) under a weak mass load and with maintenance of a sludge age. The mass load is lower than 0.3 kg biochemical oxygen demand after 5 days of incubation (BOD5)/kg MES.day. The sludge age in the first treatment, is higher than 10 days of free biomass and 20 days of fixed biomass.    USE - The method is useful for treating biodegradable waste such as industrial or urban effluents (claimed) and effluents from agri-foodstuffs, pharmaceutical, chemical, petrochemical and paper industries.    ADVANTAGE - The method is capable of achieving higher treatment efficiency of 98% of carbonaceous pollution removal, flexibly and rapidly treating the waste, and eliminating the risks of swelling of sludge.    DETAILED DESCRIPTION - The method comprises subjecting effluents to a first aerobic activated sludge treatment followed by a second treatment with filtration by membranes (8a, 8b), where the first aerobic treatment is a treatment in mixed cultures with mobile bacteria supports (4) under a weak mass load and with maintenance of a sludge age. The mass load is lower than 0.3 kg biochemical oxygen demand after 5 days of incubation (BOD5)/kg MES.day. The sludge age in the first treatment, is higher than 10 days of free biomass and 20 days of fixed biomass. The membranes are external with a first reactor (2) ensuring the first treatment. The two treatments are carried out in separate reactors, where the effluent having undergone the first treatment is sent to a second reactor for the second treatment. The membranes are immersed in the second reactor carrying out the second treatment. The first treatment in mixed cultures is carried out in a reactor of type Meteor (RTM: Compact integrated fixed-film activated sludge biological process). The reactor of the type Meteor (RTM: Compact integrated fixed-film activated sludge biological process) is coupled with an organic membrane bioreactor of type Ultrafor (RTM: Biological wastewater treatment process-combining ultra filtration membrane purification and clarification). An INDEPENDENT CLAIM is included for an installation for the application of a method of waste treating.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of an installation implementing a method for treating biodegradable waste.    First reactor (2)    Mobile bacteria supports (4)    Strainer (5)    Pumps (7)    Membranes. (8a, 8b)