NOVELTY - A reactor (21) containing an oxygen-permeable membrane (28) separating an oxygen supply compartment (30) from a fermentation compartment (31), and a biofilm, is used. Strain(s) of aerobic microorganism is supplied with oxygen through the membrane. In the fermentation compartment, enzymes for enzymatic degradation of organic feedstock are produced by aerobic microorganisms. Enzymatic degradation of the organic feedstock to fermentable sugars is carried out, and the sugars are fermented by the anaerobic microorganism in the anaerobic zone.    USE - Microbial production of fermentation products from organic feedstock, in particular lignocellulosic biomass such as wood, straw, miscanthus, switch grass, or municipal solid waste. The fermentation products include acetone, diethyl ketone, methyl ethyl ketone, methyl/ethyl/propyl long chain alkanoate, methane, ethane, propane, propionic acid, lactic acid, butyric acid, ethanol, methanol, propanol, and biodiesel.    ADVANTAGE - The method can be run in batch mode as well as in a continuous mode. The method is less complex and more economical by integrating several process steps.    DETAILED DESCRIPTION - A reactor containing an oxygen-permeable membrane separating an oxygen supply compartment from a fermentation compartment, and containing a surface facing the fermentation compartment and on which a biofilm is located, and a biofilm containing at least one strain of an aerobic microorganism in an aerobic zone of the fermentation compartment for the production of enzymes and the fermentation compartment further contains at least one strain of an anaerobic microorganism in an anaerobic zone of the fermentation compartment for the fermentation of fermentable sugars, is used. At least one strain of aerobic microorganism is supplied with oxygen through the membrane. In the fermentation compartment, enzymes for the enzymatic degradation of organic feedstock are produced by the aerobic microorganisms in the aerobic zone. Enzymatic degradation of the organic feedstock to fermentable sugars is carried out, and the fermentable sugars are fermented to fermentation products by the anaerobic microorganism in the anaerobic zone. An INDEPENDENT CLAIM is included for reactor consisting of an oxygen supply compartment for accommodating a fluid containing oxygen, and a fermentation compartment for accommodating a base material mixture (22) containing organic feedstock.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of the biofilm reactor.    Reactor (21)    Base material mixture (22)    Oxygen permeable membrane (28)    Oxygen supply compartment (30)    Fermentation compartment (31)