Apparatus for separating grit from liquid sewage while retaining organic solids in suspension including inlet means for admitting liquid sewage into the apparatus, outlet means for removing liquid from which grit has been separated from the apparatus, and means for removing separated grit from the apparatus, the apparatus further comprising: - a cylindrical grit settling main chamber defining a bottom end portion, a top end and a peripheral wall; - a grit storage secondary chamber positioned below the main chamber bottom end portion such that grit settling out of the liquid will settle into said secondary chamber, said secondary chamber including a central grit settling access top mouth opening through said main chamber bottom end portion; - a vertical shaft positioned centrally in said main chamber and in said secondary chamber, said shaft having a longitudinal axis; - motorized means for causing rotation of said vertical shaft about said longitudinal axis; - a partition extending transversely through said main chamber intermediate said top end and said bottom end thereof spacedly therefrom wherein an upper subchamber is formed in said main chamber above said partition and a lower subchamber is formed in said main chamber below said partition, said liquid sewage inlet means in direct fluid communication with said lower sub-chamber, said liquid outlet means in direct fluid communication with said upper sub-chamber, said partition having a peripheral edge integrally mounted in substantially fluid tight fashion to said peripheral wall of said main chamber; said partition including a bottom central aperture housing said shaft, said partition bottom central aperture being spaced from said shaft to define an annular opening between said shaft and said partition to provide for upward flow of liquid from said lower subchamber to said upper subchamber; - and mechanical means positioned within said main chamber and enabling sustained rotational liquid sewage first fluid flow within said lower subchamber, enabling inducing upward liquid second fluid flow from said lower subchamber through said partition annular opening and into said upper subchamber, and enabling sustaining rotational liquid third fluid flow within said upper subchamber for escape through said outlet means, wherein the apparatus is arranged to provide a fluid flow speed gradient between said third fluid flow and said first fluid flow; and wherein the apparatus is arranged to provide said third fluid flow at substantially smaller speed than said first fluid flow, wherein said mechanical means for causing said second fluid flow and said third fluid flow includes a plurality of vanes fixed to said shaft and rotatable therewith, said vanes located within said lower subchamber; wherein the apparatus is arranged to provide said fluid flow speed gradient enabling omnidirectional radial and tangential escape flow of the liquid from which grit has been separated from said upper subchamber through said outlet means, and furthermore the apparatus is arranged to provide said fluid flow speed gradient accommodating differential fluid flow loads between said inlet means and said outlet means; wherein said partition is a downwardly convex cone, defining a diametrally larger top mouth and a diametrally smaller bottom mouth; and wherein said inlet means includes an access port made in said lower sub-chamber peripheral wall and opening into said lower subchamber, and a liquid sewage supply channel tangentially projecting from said lower subchamber, said supply channel having an angular slope ranging between 10° and 30° relative to a plane at right angle to said lower subchamber peripheral wall. - a cylindrical grit settling main chamber defining a bottom end portion, a top end and a peripheral wall; - a grit storage secondary chamber positioned below the main chamber bottom end portion such that grit settling out of the liquid will settle into said secondary chamber, said secondary chamber including a central grit settling access top mouth opening through said main chamber bottom end portion; - a vertical shaft positioned centrally in said main chamber and in said secondary chamber, said shaft having a longitudinal axis; - motorized means for causing rotation of said vertical shaft about said longitudinal axis; - a partition extending transversely through said main chamber intermediate said top end and said bottom end thereof spacedly therefrom wherein an upper subchamber is formed in said main chamber above said partition and a lower subchamber is formed in said main chamber below said partition, said liquid sewage inlet means in direct fluid communication with said lower sub-chamber, said liquid outlet means in direct fluid communication with said upper sub-chamber, said partition having a peripheral edge integrally mounted in substantially fluid tight fashion to said peripheral wall of said main chamber; said partition including a bottom central aperture housing said shaft, said partition bottom central aperture being spaced from said shaft to define an annular opening between said shaft and said partition to provide for upward flow of liquid from said lower subchamber to said upper subchamber; - and mechanical means positioned within said main chamber and enabling sustained rotational liquid sewage first fluid flow within said lower subchamber, enabling inducing upward liquid second fluid flow from said lower subchamber through said partition annular opening and into said upper subchamber, and enabling sustaining rotational liquid third fluid flow within said upper subchamber for escape through said outlet means,