Hong Kong Institute of Vocational Education Department of Construction CBE2029 Environmental Engineering

Assignment 1: Water & Noise

Instruction: Answer any TWO questions from each topic and any ONE question on A4-sized single lined paper.

Water & Wastewater Pollution

1. Define the following terms in relation to water engineering.

(a) Alkalinity

(b) Colour

2. The following test results were obtained from a wastewater sample taken at a

wastewater treatment plant.

Data:

Wastewater sample size = 300 mL

Weight of the filter paper = 1.2433 g

Test results:

Weight of residue and the filter paper after drying at 105oC = 1.267 g

Weight of residue and the filter paper after ignition at 550oC = 1.259 g

Determine the concentration in mg/L of suspended solids and suspendedvolatile

solids. All the samples used in the solids analyses were evaporated, dried or

ignited to constant weight.

3. A water sample has a BOD5 value of 800 mg/L at 25oC. Calculate theultimate

BOD (Lo) of the sample. Given that the reaction rate constant at20oC is 0.23 per

day.

4. A BOD analysis was carried out. A wastewater sample of 30mL with a DOof zero

was mixed with 270 mL of dilution water with a DO of 10 mg/L.The sample was

then put in the incubator for 5 days at 20oC. The final DOof the diluted sample

and the diluted water were 4.0 mg/L and 9.2 mg/Lrespectively. However, it was

discovered that the incubator was set at 30oCrather than at 20

oC. Determine the

5-days BOD of the sample at 20oC.Given that the rate constant, k20, is 0.2d

-1.

5. State the purpose of grit removal in wastewater treatment.

Noise Pollution:

1. Determine the Leq of the measured period from 0700 to 1900, i.e. the working

period of the construction site.

Time (hr.) Sound level (dBA)

0000 – 0700 45

0700 – 0800 63

0800 – 1000 78

1000 – 1200 65

1200 – 1300 60

1300 – 1600 74

1600 – 1900 77

1900 – 2100 55

2100 – 0000 51

2. Determine the un-weighted and A-weighted resultant SPL of the following sound

measurements.

F(Hz) 31.5 63 125 250 500 1k 2k 4k 8k

SPL(dB) 56 60 64 70 82 65 58 55 50

3. What are the differences of “Point Source” & “Line Source” of noise? Compare

the difference of noise level measurement between concrete ground and

vegetation ground.

4. Determine LN from the given data when N = 10, 50 & 90.

60 65 70 75 80 85

Sound Level dB(A)

20

10

2%

7%

14%

17%

22%

16%

10%

1.5%

0.5%

2dB

Freq

uen

cy o

f O

ccu

rren

ce (

%)

2.5%

8%

16%

20%

24%

18%

12%