Abstract: A gravity clarifier for separating biological sludge from the water by gravity settling, which comprises a cylindrical tank having a closed bottom with a downwardly depending truncated conical shell attached at its large end to the upper portion of the tank wall, with a peripheral trough near the top end of the tank and a weir for the overflow of effluent liquid into the trough. The influent conduit enters the tank tangentially and flows the raw mixture into the tank in the space between the outside of the inverted conical shell and the tank wall. The sludge is removed from the tank bottom near the center of the tank.