Water Resources and Environmental Engineering — Quiz 7

Questions in this quiz (10)

1. Three wastewater flows combine in a sewer. Source 1: $$4.0\times10^6\ \mathrm{L/day}$$, $$200\ \mathrm{mg/L}$$ Source 2: $$0.8\times10^6\ \mathrm{L/day}$$, $$300\ \mathrm{mg/L}$$ Source 3: $$0.2\times10^6\ \mathrm{L/day}$$, $$500\ \mathrm{mg/L}$$ If infiltration with zero BOD is $$10\%$$ of the total wastewater flow, determine the resulting BOD concentration.

   • 76
   • 207
   • 228
   • 333

2. An unseeded domestic wastewater BOD test is performed. A $$6$$-mL sample of wastewater is diluted in a $$300$$-mL test bottle. Initially, the dissolved oxygen is $$8.0\ \mathrm{mg/L}$$. After $$5$$ days, the dissolved oxygen is $$4.0\ \mathrm{mg/L}$$. If the decay rate constant is $$0.30\ \mathrm{day^{-1}}$$, determine the ultimate BOD in $$\mathrm{mg/L}$$.

   • 150
   • 207
   • 76
   • 257
   • 207
   • 300
   • 228
   • 333

3. Water is flowing in a rectangular channel at the rate of $$30\ \mathrm{ft^3/s}$$. The channel is $$5$$-ft wide. Determine the critical depth.

   • 1
   • 2
   • 150
   • 4
   • 207
   • 6
   • 257
   • 300

4. A $$12$$-in diameter, $$1{,}000$$-ft long, new cast iron pipe connects two reservoirs. The water velocity in the pipe is $$11$$ ft/s. Neglect all minor losses. Using the Hazen-Williams method, determine the difference in elevations of the water tables between the reservoirs.

   • 25
   • 30
   • 1
   • 35
   • 2
   • 65
   • 4
   • 6

5. A circular culvert with a diameter of $$1.2\ \mathrm{m}$$ operates under inlet control conditions. The headwater depth above the culvert invert is $$1.8\ \mathrm{m}$$. Using a discharge coefficient of $$0.6$$ and the orifice equation $$Q=C_d\times A\times\sqrt{2gH}$$, estimate the flow capacity. Use $$g=9.81\ \mathrm{m/s^2}$$.

   • $$6.72$$ $$m^3/s$$
   • $$2.85$$ $$m^3/s$$
   • 25
   • $$4.03$$ $$m^3/s$$
   • 30
   • $$5.15$$ $$m^3/s$$
   • 35
   • 65

6. A pumping well fully penetrates an unconfined aquifer with an initial saturated thickness of $$30\ \mathrm{m}$$. The well pumps at $$0.025\ \mathrm{m^3/s}$$, the hydraulic conductivity is $$18\ \mathrm{m/day}$$, and the radius of influence is $$450\ \mathrm{m}$$. Using the Dupuit equation, calculate the drawdown at a distance of $$120\ \mathrm{m}$$ from the well.

   • 1.18 m
   • 0.74 m
   • 1.42 m
   • 2.05 m

7. An activated sludge aeration tank has a volume of $$2{,}000\ \mathrm{m^3}$$ and receives $$6{,}000\ \mathrm{m^3/day}$$ of wastewater with an influent BOD of $$250\ \mathrm{mg/L}$$. Calculate the volumetric organic loading rate.

   • 0.75 kg BOD/(m^3·day)
   • 0.50 kg BOD/(m^3·day)
   • 0.65 kg BOD/(m^3·day)
   • 0.85 kg BOD/(m^3·day)

8. A Venturi meter has a pipe diameter of $$0.25\ \mathrm{m}$$ and a throat diameter of $$0.12\ \mathrm{m}$$. The discharge coefficient is $$0.97$$ and the measured differential head is $$0.65\ \mathrm{m}$$. Using the Venturi equation with the velocity-of-approach correction factor, calculate the flow rate. Use $$g=9.81\ \mathrm{m/s^2}$$.

   • 0.046 m^3/s
   • 0.052 m^3/s
   • 0.061 m^3/s
   • 0.038 m^3/s

9. A centrifugal pump operating at $$1{,}650$$ rpm delivers $$0.10\ \mathrm{m^3/s}$$ against a head of $$28\ \mathrm{m}$$. If the pump speed is reduced to $$1{,}350$$ rpm, what is the new head using the pump affinity laws?

   • 18.7 m
   • 21.6 m
   • 24.1 m
   • 20.2 m

10. An aeration tank has a volume of $$650\ \mathrm{m^3}$$. The oxygen transfer coefficient $$K_La$$ is $$3.8\ \mathrm{hr^{-1}}$$, the saturation dissolved oxygen is $$9.0\ \mathrm{mg/L}$$, and the actual dissolved oxygen in the tank is $$2.5\ \mathrm{mg/L}$$. Calculate the oxygen transfer rate.

    • 16.1 kg/hr
    • 14.8 kg/hr
    • 12.6 kg/hr
    • 10.9 kg/hr