16. For a water treatment plant having a flow rate of 432m³/hr, what is the required plan area of a Type I setting tank to remove 90% of the particles having a settling velocity of 0.12 cm/sec is

1. 1. 120 m²

   
   
   

   2. 111 m²

   
   
   

   3. 90 m²

   
   
   

   4. 100 m²

   
   
   

---

1. View Hint View Answer Discuss in Forum

   η =	Vs	× 100
   	Vd

   
   

   ∴ V0 =	Vs	× 100
   	η

   
   

   =	0.12 × 100	= 1.34 r10-3 m/s
   	0.9

   
   Q = AV₀
   

   ⇒ A = Q =	432	(60 × 60 to convert hour to second)
   	60 × 60 × 1.34 × 10-3

   
   = 90 m²

   Correct Option: C

   η =	Vs	× 100
   	Vd

   
   

   ∴ V0 =	Vs	× 100
   	η

   
   

   =	0.12 × 100	= 1.34 r10-3 m/s
   	0.9

   
   Q = AV₀
   

   ⇒ A = Q =	432	(60 × 60 to convert hour to second)
   	60 × 60 × 1.34 × 10-3

   
   = 90 m²

---

17. The theoretical oxygen dmenad of a 0.001 mol/L glucose solution is

1. 1. 180 mg/L

   
   
   

   2. 192 mg/L

   
   
   

   3. 90 mg/L

   
   
   

   4. 96 mg/L

   
   
   

---

1. View Hint View Answer Discuss in Forum

   Glucose: C₆H₁₂O₆
   
   0.001 mol/L of glucose = 180 × 0.001 g/litre
   = 180 mg/L glucose
   From the equation 180 parts glucose need 192 parts oxygen.
   ∴ 180 mg/L glucose need 192 mg/L oxygen

   Correct Option: B

   Glucose: C₆H₁₂O₆
   
   0.001 mol/L of glucose = 180 × 0.001 g/litre
   = 180 mg/L glucose
   From the equation 180 parts glucose need 192 parts oxygen.
   ∴ 180 mg/L glucose need 192 mg/L oxygen

---

---

18. Results of a water sample analysis are as follows:
    
    (milliequivalent weight of CaCO₃ = 50 mg/meq).
    Harness of the water sample in mg/L as CaCO₃ is

1. 1. 44.8

   
   
   

   2. 89.5

   
   
   

   3. 179

   
   
   

   4. 358

   
   
   

---

1. View Hint View Answer Discuss in Forum

   Hardness = Mg2+ ×	equivalent wt of CaCO3	+ Ca2+ ×	equivalent wt of CaCO3
   	equivalent wt of Mg2+		equivalent wt of Ca2+

   
   

   = 20 ×	50	+ 55 ×	50
   	12.2		20

   
   = 179 mg/l of CaCO₃.

   Correct Option: C

   Hardness = Mg2+ ×	equivalent wt of CaCO3	+ Ca2+ ×	equivalent wt of CaCO3
   	equivalent wt of Mg2+		equivalent wt of Ca2+

   
   

   = 20 ×	50	+ 55 ×	50
   	12.2		20

   
   = 179 mg/l of CaCO₃.

---

19. An ideal horizontal flow setting basin in 3m deep having surface area 900 m². Water flows at the rate of 8000 m³ /d, at water temperature 20°C (m = 10³ kg/m.s and p = 1000 kg/m³). Assuming Stokes law to be valid, the proportion (percentage) of spherical sand particles (0.01 mm in diameter with specific gravity 2.65), that will be removed is

1. 1. 32.5

   
   
   

   2. 67

   
   
   

   3. 87.5

   
   
   

   4. 95.5

   
   
   

---

1. View Hint View Answer Discuss in Forum

   NA

   Correct Option: C

   NA

---

---

20. The present population of a community is 28000 with an average water consumption of 4200m³/d. The existing water treatment plant has a design capacity of 6000 m³/d. It is expected that the population will increase to 44000 during the next 20 years. The number of years from now when the plant will react its design capacity, assuming an arithmetic rate of population growth, will be

1. 1. 5.5 years

   
   
   

   2. 8.6 years

   
   
   

   3. 15.0 years

   
   
   

   4. 16.5 years

   
   
   

---

1. View Hint View Answer Discuss in Forum

   Population growth rate =	44000 - 28000	= 800 persons/year
   	20

   
   

   Percapita water consumption =	4200	m²d/capita = 150 L/capita/d
   	28000

   
   

   For reacting design capacity, no. of popu required =	6000 - 4200	= 1200
   	0.15

   
   

   ∴ No. of years =	12000	= 15 years
   	800

   Correct Option: C

   Population growth rate =	44000 - 28000	= 800 persons/year
   	20

   
   

   Percapita water consumption =	4200	m²d/capita = 150 L/capita/d
   	28000

   
   

   For reacting design capacity, no. of popu required =	6000 - 4200	= 1200
   	0.15

   
   

   ∴ No. of years =	12000	= 15 years
   	800

---