A compound has a general formula $\mathrm{C}_{\mathrm{a}} \mathrm{H}_{\mathrm{b}} \mathrm{O}_{\mathrm{c}} \mathrm{N}_{\mathrm{d}}$ and molecular weight 187. A $935 \mathrm{mg} / \mathrm{l}$ solution of the compound is prepared in distilled deionized water. The Total Organic Carbon (TOC) is measured as $360 \mathrm{mg} / \mathrm{l}$ (as C). The Chemical Oxygen Demand (COD) and the Total Kjeldahl Nitrogen (TKN) are determined as $600 \mathrm{mg} / \mathrm{l}$ (as $\mathrm{O}_2$ ) and $140 \mathrm{mg} /$ I (as N), respectively (as per the chemical equation given below). Which of the following ptions is/are CORRECT?

$$ \mathrm{C}_{\mathrm{a}} \mathrm{H}_{\mathrm{b}} \mathrm{O}_{\mathrm{c}} \mathrm{~N}_{\mathrm{d}}+\frac{(4 \mathrm{a}+\mathrm{b}-2 \mathrm{c}-3 \mathrm{~d})}{4} \mathrm{O}_2 \rightarrow \mathrm{aCO}_2+\frac{\mathrm{b}-3 \mathrm{~d}}{2} \mathrm{H}_2 \mathrm{O}+\mathrm{dNH}_3 $$

Atomic weight : $\mathrm{C}(12), \mathrm{H}(1), \mathrm{O}(16), \mathrm{N}(14)$

The analyses results of a water sample are given below. The non-carbonate hardness of the water (in $\mathrm{mg} / \mathrm{L}$ ) as $\mathrm{CaCO}_3$ is __________ (in integer).

$$ \begin{aligned} & \mathrm{Ca}^{2+}=150 \mathrm{mg} / \mathrm{L} \text { as } \mathrm{CaCO}_3 \\ & \mathrm{Mg}^{2+}=40 \mathrm{mg} / \mathrm{L} \text { as } \mathrm{CaCO}_3 \\ & \mathrm{Fe}^{2+}=10 \mathrm{mg} / \mathrm{L} \text { as } \mathrm{CaCO}_3 \\ & \mathrm{Na}^{+}=50 \mathrm{mg} / \mathrm{L} \text { as } \mathrm{CaCO}_3 \\ & \mathrm{~K}^{+}=10 \mathrm{mg} / \mathrm{L} \text { as } \mathrm{CaCO}_3 \\ & \mathrm{CO}_3{ }^{2-}=120 \mathrm{mg} / \mathrm{L} \text { as } \mathrm{CaCO}_3 \\ & \mathrm{HCO}_3{ }^{-}=30 \mathrm{mg} / \mathrm{L} \text { as } \mathrm{CaCO}_3 \end{aligned} $$

$\mathrm{Cl}^{-}=50 \mathrm{mg} / \mathrm{L}$ as $\mathrm{CaCO}_3$; Other anions were not analysed.

A community generates 1 million litres/day (MLD) of wastewater. This wastewater is treated using activated sludge process (ASP). The working volume of the aeration tank of the ASP is $250 \mathrm{~m}^3$, and the biomass concentration in the tank is $3000 \mathrm{mg} / \mathrm{L}$. Analyses results showed that a biomass concentration of $10 \mathrm{mg} / \mathrm{L}$ is present in the treated effluent from the secondary sedimentation tank of the ASP. Sludge wastage from the system is at a rate of $5000 \mathrm{~L} /$ day with a biomass concentration of $10000 \mathrm{mg} / \mathrm{L}$. The system is in steady state condition.

The biological sludge residence time (BSRT) of the system (in days) is _________ (round off to one decimal place).

A settling chamber is used for the removal of discrete particulate matter from air with following conditions. Horizontal velocity of air $=0.2 \mathrm{~m} / \mathrm{s}$; Temperature of air stream $=77^{\circ} \mathrm{C}$; Specific gravity of particle to be removed $=2.65$; Chamber length $=12 \mathrm{~m}$; Chamber height = 2 m ;

Viscosity of air at $77^{\circ} \mathrm{C}=2.1 \times 10^{-5} \mathrm{~kg} / \mathrm{m} . \mathrm{s}$;

Acceleration due to gravity $(\mathrm{g})=9.81 \mathrm{~m} / \mathrm{s}^2$; Density of air at $77^{\circ} \mathrm{C}=1.0 \mathrm{~kg} / \mathrm{m}^3$;

Assume the density of water as $1000 \mathrm{~kg} / \mathrm{m}^3$ and Laminar condition exists in the chamber.

The minimum size of particle that will be removed with 100\% efficiency in the settling chamber (in $\mu \mathrm{m}$ ) is ___________ (round off to one decimal place).