A separator for separating solids from a liquid, the separator comprising: a hydrodynamic separator; a first filtration device (200, 600), the first filtration device (200, 600) comprising a first inlet (55, 655) at a first level for receiving at least a first portion of the liquid from the hydrodynamic separator and a first filter (48, 648) for filtering the first portion of the liquid received via the first inlet (55, 655), wherein during filtration of the first portion of the liquid, the first portion of the liquid passes through the first filter (48, 648) away from the first inlet (55, 655) and a first portion of solids is retained by the first filter (48, 648); a first backwash device (300, 900), wherein the first filter (48, 648) is located between the first inlet (55, 655) and the first backwash device (300, 900), wherein the first backwash device (300, 900) is configured to alternately prevent and allow the passage of the first portion of the liquid through the first backwash device (300, 900) such that, when the passage of the first portion of the liquid through the first backwash device (300, 900) is prevented, the first portion of the liquid that has passed through the first filter (48, 648) passes back through the first filter (48, 648) toward the first inlet (55, 655) so as to remove the first portion of solids from the first filter (48, 648); characterised in that the separator further comprises a second filtration device (400, 700), the second filtration device (400, 700) comprising a second inlet (455, 755) at a second level higher than the first level for receiving a second portion of the liquid from the hydrodynamic separator and a second filter (448, 748) for filtering the second portion of the liquid received via the second inlet (455, 755), wherein during filtration of the second portion of the liquid, the second portion of the liquid passes through the second filter (448, 748) away from the second inlet (455, 755) and a second portion of solids is retained by the second filter (448, 748); and a second backwash device (500, 800, 900, wherein the second filter (448, 748) is located between the second inlet (455, 755) and the second backwash device (500, 800, 900), wherein the second backwash device (500, 800, 900) is configured to alternately prevent and allow the passage of the second portion of the liquid through the second backwash device (500, 800, 900) such that, when the passage of the second portion of the liquid through the second backwash device (500, 800, 900) is prevented, the second portion of the liquid that has passed through the second filter (448, 748) passes back through the second filter (448, 748) toward the second inlet (455, 755) so as to remove the second portion of solids from the second filter (448, 748). a hydrodynamic separator; a first filtration device (200, 600), the first filtration device (200, 600) comprising a first inlet (55, 655) at a first level for receiving at least a first portion of the liquid from the hydrodynamic separator and a first filter (48, 648) for filtering the first portion of the liquid received via the first inlet (55, 655), wherein during filtration of the first portion of the liquid, the first portion of the liquid passes through the first filter (48, 648) away from the first inlet (55, 655) and a first portion of solids is retained by the first filter (48, 648); a first backwash device (300, 900), wherein the first filter (48, 648) is located between the first inlet (55, 655) and the first backwash device (300, 900), wherein the first backwash device (300, 900) is configured to alternately prevent and allow the passage of the first portion of the liquid through the first backwash device (300, 900) such that, when the passage of the first portion of the liquid through the first backwash device (300, 900) is prevented, the first portion of the liquid that has passed through the first filter (48, 648) passes back through the first filter (48, 648) toward the first inlet (55, 655) so as to remove the first portion of solids from the first filter (48, 648); characterised in that the separator further comprises a second filtration device (400, 700), the second filtration device (400, 700) comprising a second inlet (455, 755) at a second level higher than the first level for receiving a second portion of the liquid from the hydrodynamic separator and a second filter (448, 748) for filtering the second portion of the liquid received via the second inlet (455, 755), wherein during filtration of the second portion of the liquid, the second portion of the liquid passes through the second filter (448, 748) away from the second inlet (455, 755) and a second portion of solids is retained by the second filter (448, 748); and a second backwash device (500, 800, 900, wherein the second filter (448, 748) is located between the second inlet (455, 755) and the second backwash device (500, 800, 900), wherein the second backwash device (500, 800, 900) is configured to alternately prevent and allow the passage of the second portion of the liquid through the second backwash device (500, 800, 900) such that, when the passage of the second portion of the liquid through the second backwash device (500, 800, 900) is prevented, the second portion of the liquid that has passed through the second filter (448, 748) passes back through the second filter (448, 748) toward the second inlet (455, 755) so as to remove the second portion of solids from the second filter (448, 748).