Process for treating an aqueous-alcoholic feedstock comprising water, ethanol and butanol in order to produce an ethanol-rich effluent, a water-rich effluent and a butanol-rich effluent, comprising: a) a water-ethanol separation step, comprising a water-ethanol separation section comprising a distillation column comprising at least 14 theoretical plates and having a reflux ratio of less than or equal to 1.2, said water-ethanol separation section comprising: o a feed of said aqueous-alcoholic feedstock, located at the level of or downstream of the third theoretical plate, o the side withdrawal of an aqueous-alcoholic solution comprising butanol in the butanol accumulation zone of the distillation column located downstream of the feed, o an injection of the heavy phase resulting from step b), located downstream and in a zone between the side withdrawal and the third theoretical plate downstream of the side withdrawal, o an injection of the ethanol-water distillate resulting from step c), located upstream of the feed and in a zone of the distillation column between the theoretical plate at the top of the column at which the reflux returns and the third theoretical plate, said water-ethanol separation section producing, at the top of the column, an ethanol-rich effluent and, at the bottom of the column, a water-rich effluent; b) a demixing step comprising o a section for mixing said aqueous-alcoholic solution withdrawn in step a) with the water/butanol/ethanol fraction withdrawn in step c); o a section for decanting the previous mixture, comprising a decantation tank in which the pressure is less than or equal to 6 bar absolute, said decanting section producing a heavy phase (15, 17) mainly containing water and a light phase; c) a butanol separation step, comprising a butanol distillation section comprising at least one distillation column fed with the light phase resulting from step b) and comprising a side withdrawal, located on said column in a zone between the feed and the bottom of the column, of a water/butanol/ethanol fraction, said butanol distillation section producing, at the bottom of the column, a butanol-rich effluent and, at the top of the column, an ethanol-water distillate. a) a water-ethanol separation step, comprising a water-ethanol separation section comprising a distillation column comprising at least 14 theoretical plates and having a reflux ratio of less than or equal to 1.2, said water-ethanol separation section comprising: o a feed of said aqueous-alcoholic feedstock, located at the level of or downstream of the third theoretical plate, o the side withdrawal of an aqueous-alcoholic solution comprising butanol in the butanol accumulation zone of the distillation column located downstream of the feed, o an injection of the heavy phase resulting from step b), located downstream and in a zone between the side withdrawal and the third theoretical plate downstream of the side withdrawal, o an injection of the ethanol-water distillate resulting from step c), located upstream of the feed and in a zone of the distillation column between the theoretical plate at the top of the column at which the reflux returns and the third theoretical plate, said water-ethanol separation section producing, at the top of the column, an ethanol-rich effluent and, at the bottom of the column, a water-rich effluent; o a feed of said aqueous-alcoholic feedstock, located at the level of or downstream of the third theoretical plate, o the side withdrawal of an aqueous-alcoholic solution comprising butanol in the butanol accumulation zone of the distillation column located downstream of the feed, o an injection of the heavy phase resulting from step b), located downstream and in a zone between the side withdrawal and the third theoretical plate downstream of the side withdrawal, o an injection of the ethanol-water distillate resulting from step c), located upstream of the feed and in a zone of the distillation column between the theoretical plate at the top of the column at which the reflux returns and the third theoretical plate, b) a demixing step comprising o a section for mixing said aqueous-alcoholic solution withdrawn in step a) with the water/butanol/ethanol fraction withdrawn in step c); o a section for decanting the previous mixture, comprising a decantation tank in which the pressure is less than or equal to 6 bar absolute, said decanting section producing a heavy phase (15, 17) mainly containing water and a light phase; o a section for mixing said aqueous-alcoholic solution withdrawn in step a) with the water/butanol/ethanol fraction withdrawn in step c); o a section for decanting the previous mixture, comprising a decantation tank in which the pressure is less than or equal to 6 bar absolute, said decanting section producing a heavy phase (15, 17) mainly containing water and a light phase; c) a butanol separation step, comprising a butanol distillation section comprising at least one distillation column fed with the light phase resulting from step b) and comprising a side withdrawal, located on said column in a zone between the feed and the bottom of the column, of a water/butanol/ethanol fraction, said butanol distillation section producing, at the bottom of the column, a butanol-rich effluent and, at the top of the column, an ethanol-water distillate.