Treating and conditioning liquid sludge and a solidified sludge cake obtained thereby are disclosed. A first emulsion of sludge is formed in an in-line container fed at a first flow rate Q owing to the impact of the sludge with air injected into the container at a rate Q′, where Q′>5Q, in a first region which has a small volume of less than 0.05 m3. The first emulsion is then transferred into a second region of the container extending over a first length, and is then discharged via a component which generates a head loss in a chamber extending over a second length. A flocculant is injected in order to obtain a second coagulated emulsion, which is at least partially degasified. The matter in suspension in the second emulsion obtained in this way is then filtered or decanted.