# A settling tank in a water treatment plant is designed for a surface overflow rate of30 $\frac{m^{3}}{\text { day } \cdot m^{2}}$. Assumespecific gravity of sedimentparticles $=2.65,$ density of water $(\rho)=1000 \mathrm{~kg} / \mathrm{m}^{3},$ dynamic viscosity of water $(\mu)=0.001 \mathrm{~N} . \mathrm{s} / \mathrm{m}^{2},$ and Stokes' lawisvalid.The approximate minimum size of particles that would be completely removed is: (A) $0.01 \mathrm{~mm}$ $\begin{array}{llll}\text { (B) } 0.02 \mathrm{~mm}(\text { C }) & 0.03 \mathrm{~mm}(\mathrm{D}) & 0.04 \mathrm{~mm}\end{array}$

## Question ID - 155856 :- A settling tank in a water treatment plant is designed for a surface overflow rate of30 $\frac{m^{3}}{\text { day } \cdot m^{2}}$. Assumespecific gravity of sedimentparticles $=2.65,$ density of water $(\rho)=1000 \mathrm{~kg} / \mathrm{m}^{3},$ dynamic viscosity of water $(\mu)=0.001 \mathrm{~N} . \mathrm{s} / \mathrm{m}^{2},$ and Stokes' lawisvalid.The approximate minimum size of particles that would be completely removed is: (A) $0.01 \mathrm{~mm}$ $\begin{array}{llll}\text { (B) } 0.02 \mathrm{~mm}(\text { C }) & 0.03 \mathrm{~mm}(\mathrm{D}) & 0.04 \mathrm{~mm}\end{array}$

3537

0.02 mm

Next Question :

A student began experiment for determination of 5 -day, $20^{\circ} \mathrm{C} \mathrm{BOD}$ on Monday. Since the $5^{\text {th }}$ day fell on Saturday, the final DO readings were taken on next Monday. On calculation, BOD (i.e. 7 day, $20^{\circ} \mathrm{C}$ ) was found to be $150 \mathrm{mg} / \mathrm{L}$. What would be the5-day, $20^{\circ} \mathrm{C} \mathrm{BOD}$ (in $\left.\mathrm{mg} / \mathrm{L}\right)$ ? Assume value of $\mathrm{BOD}$ rate constant $(\mathrm{k})$ at standard temperature of $20^{\circ} \mathrm{C}$ as $0.23 /$ day $($ base $e) .$ 