Abstract: The present invention relates to a method for oxidizing manganese species in a treatment device (10) comprising at least one anode unit (20) and at least one cathode (30), wherein said unit comprises at least one anode (21) and is confined by a housing (22), the housing defining a free inner volume (V), wherein (i) the housing comprises at least one permeable barrier (23) and the at least one cathode is located outside the anode unit, or (ii) the at least one anode unit comprises at least partly the at least one cathode, wherein the housing does not comprise a permeable barrier, characterized in that in (i) and (ii) the at least one anode and the at least one cathode have a distance (d) ranging from 0.5 mm to 100 mm. The invention furthermore refers to a respective treatment device (10).