Quality Control of Water · Environmental Engineering · GATE CE
Marks 1
Free residual chlorine concentration in water was measured to be $2 \mathrm{mg} / \mathrm{l}$ (as $\mathrm{Cl}_2$ ). The pH of water is 8.5. By using the chemical equation given below, the HOCl concentration (in $\mu$ moles $/ \mathrm{l}$ ) in water is $\qquad$ (round off to one decimal place).
$$ \mathrm{HOCl} \rightleftharpoons \mathrm{H}^{+}+\mathrm{OCl}^{-}, \mathrm{pK}=7.50 $$
Atomic weight: Cl(35.5)
The following table gives various components of Municipal Solid Waste (MSW) and a list of treatment/separation techniques.
Component of MSW | Treatment/separation technique |
---|---|
P - Ferrous metals | i - Incineration |
Q - Aluminum and copper | ii - Rapid composting |
R - Food waste | iii - Eddy current separator |
S - Cardboard | iv - Magnetic separator |
The CORRECT match is
A 100 mg of HNO3 (strong acid) is added to water, bringing the final volume to 1.0 liter. Consider the atomic weights of H, N, and O, as 1 g/mol. 14 g mol. and 16 g/mol, respectively. The final pH of this water is (Ignore the dissociation of water.)
The total hardness in raw water is 500 milligram per liter as CaCO3. The total hardness of this raw water, expressed in milligram equivalent per liter, is (Consider the atomic weights of Ca, C, and O as 40 g/mol, 12 g/mol, and 16 g/mol, respectively.)
In a water sample, the concentrations of Ca2+, Mg2+ and HCO$$_3^ - $$ are 100 mg/L, 36 mg/L and 122 mg/L, respectively. The atomic masses of various elements are : Ca = 40, Mg = 24, H = 1, C = 12, O = 16. The total hardness and the temporary hardness in the water sample (in mg/L as CaCO3) will be
Marks 2
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.
$\mathrm{MgCl}_2$ and $\mathrm{CaSO}_4$ salts are added to 1 litre of distilled deionized water and mixed until completely dissolved. Total Dissolved Solids (TDS) concentration is $500 \mathrm{mg} / \mathrm{l}$, and Total Hardness (TH) is $400 \mathrm{mg} / \mathrm{l}$ (as $\mathrm{CaCO}_3$ ). The amounts of $\mathrm{MgCl}_2$ and $\mathrm{CaSO}_4$ added are calculated (rounded off to the nearest integer). Which of the following options is/are true:
Atomic weights: $\mathrm{Ca}(40), \mathrm{Mg}(24), \mathrm{S}(32), \mathrm{O}(16), \mathrm{Cl}(35.5), \mathrm{C}(12)$
Activated carbon is used to remove a pollutant from wastewater in a mixed batch reactor, which follows first-order reaction kinetics.
At a reaction rate of 0.38 /day, the time (in days) required to remove the pollutant by 95% is _______________ (rounded off to 1 decimal place).
A water treatment plant treats 25 MLD water with a natural alkalinity of 4.0 mg/L (as CaCO3). It is estimated that, during the coagulation of this water, 450 kg/day of calcium bicarbonate (Ca(HCO3)2) is required based on the alum dosage.
Consider the atomic weights as: Ca-40, H-1, C-12, O-16.
The quantity of pure quick lime, CaO (in kg) required for this process per day is _______ (rounded off to 2 decimal places).



Ion | $$Ca^{2+}$$ | $$Mg^{2+}$$ | $$Na^+$$ | $$HCO_3^-$$ | $$SO_4^{2-}$$ | $$Cl^{-}$$ |
---|---|---|---|---|---|---|
Ionconcentration(mg/L) | 100 | 6 | 15 | 250 | 45 | 39 |
Atomic Weight | Ca=40 | Mg=24 | Na=23 | H=1,C=12,O=16 | S=32,O=16 | Cl=35.5 |
Carbonate hardness (mg/L as $$CaCO_3$$) present in the above water sample is
Ion | $$Ca^{2+}$$ | $$Mg^{2+}$$ | $$Na^+$$ | $$HCO_3^-$$ | $$SO_4^{2-}$$ | $$Cl^{-}$$ |
---|---|---|---|---|---|---|
Ionconcentration(mg/L) | 100 | 6 | 15 | 250 | 45 | 39 |
Atomic Weight | Ca=40 | Mg=24 | Na=23 | H=1,C=12,O=16 | S=32,O=16 | Cl=35.5 |
Total hardness (mg/L as $$CaCO_3$$) present in the above water sample is