DEPARTMENT OF CIVIL AND STRUCTURAL ENGINEERING
CIV61015 Water Quality Processes and Treatment
Autumn 2021-2022
Q1
a) Explain the differences between point source and non-point source pollution and provide examples. (6 marks)
b) Explain what is meant by eutrophication and the consequences that this process might have in aquatic ecosystems. (6 marks)
c) Describe the different types of hardness and the potential impact of this
parameter on the quality of water used to supply drinking water. Propose a process that a water utility can use to solve problems related to water hardness in a drinking water treatment plant (8 marks)
d) Explain which fractions are included in an estimate of total solids in a water sample and describe how each fraction is quantified. (6 marks)
Q2
a) Describe the main stages in the operation of a drinking water treatment plant, indicating the main aim of each stage. (14 marks)
b) How much power must be supplied to a flocculator to provide a velocity gradient of 80s-1 and a Camp Number of 60000 for an inflow of 0.26 m3/s? Assume that the water has a viscosity of 1 x 10-3 Pascals. (6 marks)
c) Calculate the terminal settling velocity for a sand particle that has a diameter of 100 μm and a density of 2,650 kg/m3 . The water temperature is 10°C. For water at 10°C, the density is 999.7 kg/m3, dynamic viscosity is 1.037x10-3 N- s/m2 and the kinematic viscosity is 1.036 x 10-6 m2/s. (8 marks)
d) In a water treatment plant rapid sand filters must be installed after the
sedimentation tanks. The design-loading rate is 200 m3 m-2 d-1 . Calculate the filter surface area required to achieve a design flow rate of 0.5 m3/s. If the surface area per filter box cannot exceed 50 m2 , how many filter boxes are required? (10 marks)
Q3
a) Describe the main types of urban sewer systems used in the UK and explain the main advantages and disadvantages of each. (6 marks)
b) Sedimentation is a key process in both primary and secondary clarifiers used in wastewater treatment plants. Explain the difference between Type I and Type II sedimentation processes. (6 marks)
c) A water company is planning to build a new wastewater treatment plant to treat waste from a small urban centre. The company must design a biological treatment system for a wastewater flow of 5000 m3/day. The influent BOD5 is 200 mg/L. The desired effluent BOD5 is 5 mg/L. Design an activated sludge aeration tank for this wastewater treatment using the design parameters given in Table 1.
Table 1: Values of design parameters for the wastewater treatment system
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Parameters
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|
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Yield coefficient Y mg VSS/mg BOD5
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0.6
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Decay rate of microbes kd, day-1
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0.05
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Conversion factor (f) for converting BOD5 to ultimate BODu,
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0.68
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Sludge Age θc, days
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10
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MLVSS, mg/L
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1700
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Sludge index volume, mg/L
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90
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Provide answers for the following:
1) The volume of the aeration tank (6 marks)
2) The food-microorganism ratio (6 marks)
3) The sludge production rate (6 marks)
4) The oxygen requirement (6 marks)