An apparatus comprising; a) one or more mixing sectors, wherein the mixing sectors is placed on top of the apparatus as a whole and further comprises at least 4 or more plates or weirs,,....,, that are tilted at an angle of of about 5° to about 20°, b) one or more liquid distribution sectors, wherein the liquid distribution sector is placed between the one or more mixing sectors and one or more liquid retention sectors, c) the one or more liquid retention sector, wherein the liquid retention sector is placed at the bottom of the apparatus and further divided in subsectors (i)-(iii) in fluid connection with one another, wherein the subsectors are chambers or pipes, wherein the liquid retention sector is further equipped with vertical pipes, characterized in that the liquid distribution sector comprises at least three or more trays or plates -, or such as e.g. at least four or more trays, or plates, wherein one tray is positioned at the lower part of the liquid distribution sector and placed in a horizontal position and may be regarded as a liquid distributor, and wherein the liquid distribution sector comprises a second additional plate, which may be denoted as a third plate, which is placed in between the said liquid distributor and said trays or plates and wherein the third plate or tray is placed between the lower and upper plates or trays and tilted to an angle of about 5° to about 20°, and wherein the liquid distribution sector comprises a plate or tray positioned above the liquid distributor and wherein the plate or tray is horizontal and further characterized in that the liquid retention sector is in fluid connection with at least the liquid distribution sector and placed downstream of both the liquid distribution sector and the mixing sector. a) one or more mixing sectors, wherein the mixing sectors is placed on top of the apparatus as a whole and further comprises at least 4 or more plates or weirs,,....,, that are tilted at an angle of of about 5° to about 20°, b) one or more liquid distribution sectors, wherein the liquid distribution sector is placed between the one or more mixing sectors and one or more liquid retention sectors, c) the one or more liquid retention sector, wherein the liquid retention sector is placed at the bottom of the apparatus and further divided in subsectors (i)-(iii) in fluid connection with one another, wherein the subsectors are chambers or pipes, wherein the liquid retention sector is further equipped with vertical pipes, characterized in that the liquid distribution sector comprises at least three or more trays or plates -, or such as e.g. at least four or more trays, or plates, wherein one tray is positioned at the lower part of the liquid distribution sector and placed in a horizontal position and may be regarded as a liquid distributor, and wherein the liquid distribution sector comprises a second additional plate, which may be denoted as a third plate, which is placed in between the said liquid distributor and said trays or plates and wherein the third plate or tray is placed between the lower and upper plates or trays and tilted to an angle of about 5° to about 20°, and wherein the liquid distribution sector comprises a plate or tray positioned above the liquid distributor and wherein the plate or tray is horizontal and further characterized in that the liquid retention sector is in fluid connection with at least the liquid distribution sector and placed downstream of both the liquid distribution sector and the mixing sector.