A method for treating a fluid stream by a fluid treatment system comprising: inputting a fluid stream to an input section of the fluid treatment system; receiving the fluid stream by a spiral mixer-conditioner in form of a single spiral and being positioned in operative association with the input section, wherein the fluid stream enters the spiral mixer-conditioner at an inlet at a center of the spiral, the spiral mixer-conditioner including a mixer section and an conditioner section, wherein the mixer section includes at least the first two turns of the spiral mixer-conditioner, controlling the shear rate in the spiral mixer-conditioner, by use of the width of the channels in the spiral mixer-conditioner and the velocity of the input stream into the spiral mixer-conditioner such that the flow of the input stream in the mixer section is at or above the critical Dean number of 150 and the flow of the input stream in the conditioner section is less than the critical Dean number of 150; receiving the mixed and conditioned fluid stream at a spiral separator; separating the mixed and conditioned fluid stream received by the spiral separator into at least two fluid streams, a first fluid stream having particulates in the input fluid stream removed and the second fluid stream having the particulates in the input fluid stream concentrated; and outputting the two fluid streams from the spiral separator, wherein the Dean number D e is defined as: D e = ρVD μ ⁢ D 2 ⁢ R 1 / wherein p is the density of the fluid; μ is the dynamic viscosity; V is the axial velocity; D is the hydraulic diameter; and R is the radius of curvature of the path of the channel. inputting a fluid stream to an input section of the fluid treatment system; receiving the fluid stream by a spiral mixer-conditioner in form of a single spiral and being positioned in operative association with the input section, wherein the fluid stream enters the spiral mixer-conditioner at an inlet at a center of the spiral, the spiral mixer-conditioner including a mixer section and an conditioner section, wherein the mixer section includes at least the first two turns of the spiral mixer-conditioner, controlling the shear rate in the spiral mixer-conditioner, by use of the width of the channels in the spiral mixer-conditioner and the velocity of the input stream into the spiral mixer-conditioner such that the flow of the input stream in the mixer section is at or above the critical Dean number of 150 and the flow of the input stream in the conditioner section is less than the critical Dean number of 150; receiving the mixed and conditioned fluid stream at a spiral separator; separating the mixed and conditioned fluid stream received by the spiral separator into at least two fluid streams, a first fluid stream having particulates in the input fluid stream removed and the second fluid stream having the particulates in the input fluid stream concentrated; and outputting the two fluid streams from the spiral separator, wherein the Dean number D e is defined as: D e = ρVD μ ⁢ D 2 ⁢ R 1 / wherein p is the density of the fluid; μ is the dynamic viscosity; V is the axial velocity; D is the hydraulic diameter; and R is the radius of curvature of the path of the channel.