Consider the following statements regarding the overflow rate of a sedimentation tank1. Temperature of water affects the overflow rate2. Size of particle intended to be removed does not affect the overflow rate3. Density of particle intended to be removed affects the overflow rateWhich of the above statements are correct?

Concept:Overflow Rate: It is assumed that the settlement of a particle at the bottom of tank does not depend on the depth of tank. But it depends on the surface area of the tank.i.e. \(T = \frac{C}{Q} = \frac{{L\; \times \;B\; \times \;D}}{Q}\) .....(1)and, also \(T = \frac{{Distance\;of\;descend}}{{Velocity\;of\;descend}} = \frac{D}{V}\) .....(2)Now, equating the above two equations,\(\frac{{L\; \times \;B\; \times \;D}}{Q} = \frac{D}{V}\)\(V = \frac{Q}{{L\; \times \;B}}\) .....(3)Where V = Velocity of DESCENT or surface overflow rate (S.O.R), T = Detention period, C = Capacity of the tank and Q = Disharge.From equation (3) it can be stated that the quantity of water passing per hour per unit area of settling tank is known as “surface overflow rate” (S.O.R.).1. For plain rectangular sedimentation tanks, the overflow rate is about 500-750 lit/hr/m2 and when coagulants are used, it is about 1000 to 1250 lits/hr/m2 of the plane area.2. It is further assumed that for 100% efficient sedimentation tank, overflow rate is NUMERICALLY equal to the settling velocity of particles. And we KNOW, settling velocity is given by \({V_s} = \frac{{\frac{g}{{18}}\left( {G - 1} \RIGHT){d^2}}}{\mu }\) m/secHere, G = Specific gravity of particle, d = Size of particle and μ = Viscosity of waterHence we can say that the overflow rate does depend upon the size and density of the particles to be removed.∴ We can also comment with the FACT of change in viscosity of water with change in temperature, that Overflow rate does depend on the temperature of water.