be submerged in a "sludge blanket" which can, depending on the applications, be formed by activated sludge (see Ultrafor) or by hydroxides and, occasionally, by PAC (surface water or aquifer containing Fe, Mn ... Clarification, Ultrafor, Cristal, Pulsator, Densadeg, Membrane separation, aquasource® ... Clarification Ultrafor Cristal Pulsator Densadeg Membrane separation aquasource®...