2 kg bod5 kg vms d preferably the use according to the invention is carried out under conditions where the applied load al is greater than 0 2 kg bod5 kg vms d in a yet more preferred manner greater than 0 5 kg bod5 kg vms d according to a preferred embodiment of the use according to the invention no external carbonaceous source is added to the wastewater for treatment one of the preferred characteristics of the use according to the invention is that the combined treatments of the kjeldahl nitrogen ammoniacal nitrogen and or nitrogen oxides and carbonaceous matter contained in the wastewater take place in a single free activated sludge tank alternatively the use according to the invention is characterized by the fact that the combined treatments of the kjeldahl nitrogen ammoniacal nitrogen and or nitrogen oxides and carbonaceous matter contained in the wastewater take place in a culture device fixed onto a support according to another aspect the invention relates to the use of a microorganism as described previously produced by continuous culture beforehand preferably said continuous culture is carried out under sterile conditions in a yet more preferred manner said continuous culture is carried out under a selective pressure and for indefinite periods another subject of the invention relates to a wastewater treatment method characterized in that it utilizes a microorganism as described previously according to.