Consider a primary sedimentation tank (PST) in a water treatment plant with Surface Overflow Rate (SOR) of 40 m³/m²/d. The diameter of the spherical particle which will have 90 percent theoretical removal efficiency in this tank is ________ mm. Assume that settling velocity of the particles in water is described by stokes’s Law. Given: Density of water = 1000 kg/m³; density of particle = 2650 kg/m³; g = 9.81 m/s²; Kinematic viscosity of water (v) = 1.10 × 10^–6m²/s