Ece 2313 Public Health Engineering Ii

W1-2-60-1-6
JOMO KENYATTA UNIVERSITY OF AGRICULTURE AND TECHNOLOGY

UNIVERSITY EXAMINATIONS 2014/2015
EXAMINATION FOR THE MASTER OF BACHELOR OF SCIENCE IN CIVIL
ENGINEERING
ECE 2313: PUBLIC HEALTH ENGINEERING II
DATE: APRIL, 2015 TIME: 2 HOURS
INSTRUCTIONS: Answer Question Any THREE Questions

All questions carry equal marks
Question One (20 Marks)
a) State conditions that should be fulfilled in a waster water collection and conveyance
design system. [5 marks]
b) A PVC sewer pipe is required to carry a design capacity of 0.15 m3/s through the length
of 500 m. The minimum earth cover is 1.5 m. The ground level elevations of the upper
and lower parts are 90 m and 87.5 m respectively. Determine the pipe diameter, slope and
invert elevations at the upper and lower ends . Take the pipe Manning’s n=0.01. the pipes
are available in multiples of 50 mm and the partial flow design diagram is attached.
[15 marks]
Question Two (20 Marks)
a) Micro organisms that are important in waste water treatment are bacteria, algae and
protozoa.
i. State two systems where algae plays significance role and why. [5 marks]
ii. Micro organisms growth depends on environmental conditions and food
(substrate). Bacterial culture growth on a substrate was monitored over a period
and the data given was obtained.
Biomass 2500 2800 3210 3515 3900
(mg/l)
Time (hr) 1.5 2.9 4.3 5.6 7.1
Determine the specific growth rate of the bacteria culture. [8 marks]
1
b) The 5-day BOD at 20oc of a waste water is found to be 200 mg/l. Taking k=0.15 per day
(base 10) estimate the ultimate BOD. Also determine the 8-day BOD value of the waste
water at 15oC. [7 marks]
Question Three (20 Marks)
a) Design a grit chamber of rectangular cross section. Following information is provided:

Flow (Q) = 50 x 106 l/d
Minimum particle diameter to be completely removed (d)=0.20mm
Specific gravity of particles (ss) =2.65
Horizontal mean flow of velocity (v) =0.30 m/s
Theoretical depth (D ) =1.0 m
Calculate the dimensions and slope of the grit chamber. While designing the actual grit
chamber, add 25% to the depth for grit collection and 0.25 m free board. Also add 50% to
the theoretical calculated length. Sketch the plan and sectional elevation of the grit
chamber.
  dynamic viscosity = 1.002 x10 3 Ns 2
m
n- Manning’s coefficient =0.02 [12 marks]
b) Design Q sedimentation tank for a flow of waste water Q=1000 m3/d. determine the
dimensions of the tank and the outflow weir length. Take an overflow rate (OFR) of
20m3/m2.d, detention time 2 hours, width to length ratio. 1:3 and weir loading rate of 160
m3/m.d. [8 marks]
Question Four (20 Marks)
a) BOD and COD are both common parameters of organic content measurements of waste
water.
i. Explain the differences/similarities and why COD is usually the preferred method
in lab analysis.
ii. Explain the three factors on which the BOD reaction rate depends. [8 marks]
b) The treated domestic sewage of the town is to be discharged in a natural stream.

Determine the maximum permissible effluent BOD and the percentage purification
required in the treatment plant with the following particulars.
Population of town 30000

minimum flow of stream 0.13 m3/s
BOD of stream 3 mg/L
DWF (Dry weather flow) of sewage 140L/c/d
BOD contribution per capital 0.07 kg/day
Maximum BOD of stream on down stream 5 mg/L
[12 marks]
2
Question Five (20 Marks)
a) Compare the merits and demerits of the activated sludged treatment process and trickling
filters and state the conditions under which one is suitable to the other. [6 marks]
b) A 2-m deep trickling filter with a diameter of 18 m is operated with recirculation ratio of
1.5. The raw waste water flow is 2.5x106 L/d and BOD5 of the raw sewage is 210 mg/l.
Assuming that the primary tank BOD removed efficiency is 30%, determine the
hydraulic loading and organic load on the trickling filer. [6 marks]
c) Briefly state four advantages of waste stabilization ponds. Also discuss briefly how
facultative ponds operate. [8 marks]

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W1-2-60-1-6

JOMO KENYATTA UNIVERSITY OF AGRICULTURE AND TECHNOLOGY

ECE 2313: PUBLIC HEALTH ENGINEERING II

DATE: APRIL, 2015 TIME: 2 HOURS

INSTRUCTIONS: Answer Question Any THREE Questions

Question One (20 Marks)

Question Two (20 Marks)

Determine the specific growth rate of the bacteria culture. [8 marks]

Question Three (20 Marks)

a) Design a grit chamber of rectangular cross section. Following information is provided:

Question Four (20 Marks)

b) The treated domestic sewage of the town is to be discharged in a natural stream.

Population of town 30000

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