Example of environmental treatment exam

3.0 pts This problem is related to the schematic below which shows a flow diagram of a domestic wastewater treatment plant.. The type of particle settling encountered in the grit chambe

United Arab Emirates University Name

College of Engineering

Dept Civil & Env Eng Student ID#

CIVL375: Water and Wastewater Technology

2 nd Semester 05-06

Section 1

1 (3.0 pts) This problem is related to the schematic below which shows a flow

diagram of a domestic wastewater treatment plant Select the correct answer

a The type of particle settling encountered in the grit chamber is (are)

(i) Type I settling (ii) Type II settling

(iii) Type III settling (iv) Type III and IV settling

b The type of particle settling encountered in the primary settling tank is (are)

(i) Type I settling (ii) Type II settling

(iii) Type III settling (iv) Type III and IV settling

c The type of particle settling encountered in the secondary settling tank is (are)

(i) Type I settling (ii) Type II settling

(iii) Type III settling (iv) Type III and IV settling

d The objective of aeration in the aeration tank is to

(i) increase dissolved oxygen (ii) reduce the pH

(iii) remove undesirable gases (iv) increase the pH

e The activated carbon reactor shown is designed as a

(iii) continuous-stirred tank reactor (iv) packed bed reactor

f If the primary settling tank of this treatment plant is 12-ft deep and the tank receives

a flow rate of 2 million gallon per day The minimum weir length that should be

provided for this tank is:

BS=bar screen TS= traveling screen GC= grit chamber PS=primary settling tank AT=aeration tank SS= secondary settling tank F= filtration AC= activated carbon CT= contact tank

GC Wastewater BS

CT Chlorine

TS

Treated wastewater

AC F

2 (1.5 pts.) In the design of a wastewater treatment plant, the quality of the effluent

and the capacity of the plant are basic requirements for the design On what basis each

of these two requirements is determined?

3 (2.0 pts.) The US EPA states that “bacterial quality criteria for drinking water from

public supplies require not more than 1 total coliform/100 ml as the arithmetic mean

of all water samples examined per month, with no more than 4 coliforms/100 ml in any sample if the number of samples is ≤ 20/month or no more than 4 coliforms/100

ml in 5% of the samples if the number of samples exceeds 20/month"

The effluent of a water treatment plant that serves 15,000 people was sampled at regular intervals over a month period for coliform testing and the results are shown in the table below:

Sample number 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Coliforms/100 ml 1 0 3 0 0 0 5 0 2 1 0 1 1 0 0 0 Based on the above results, are the number of samples tested and the effluent bacterial quality acceptable? Explain

4 (3.0 pts) The cumulative volume of water consumption of a residential town that

has 90,000 is presented below An elevated water tank is to be built so that water is

pumped from a water treatment plant at a constant rate to the tank and is then transferred by gravity to the residents

0

2

4

6

8

Time, hr

a (2.0 pts) What is the design capacity of the storage tank?

b (0.5 pts) What is the pumping rate from the water treatment plant into the tank?

c (0.5 pts) Based on the given data, what is the average daily per capita water

consumption in the town?

5 (2.5 pts) What detention time is needed to remove 99% of a contaminant in a plug

flow reactor with a reaction rate constant of 1.5 per day?

6 (3 pts) A sedimentation tank 3.5-m deep has a flow-through velocity of 4 m/hr and

an over-flow rate of 0.92 m3/(hr.m2) What is the length of the tank?

7 (2.0 pts) A secondary settling tank is 4-m deep and receives a flow rate of 7400

m3/day with suspended solids concentration of 2,200 mg/l

a (1 pts) What would be the sludge depth in the tank for a settled sludge with a

suspended solids concentration of 12,000 mg/l?

b ( 1 pts) If the detention time required to reach the solids concentration in part a is 1

hr, what is the surface area needed to achieve this?

8 (3.0 pts) Using settling trajectories determined by the settling column analysis

shown in the figure below, find the overall percent removal for a settling basin 3.0-m deep with a settling time of 30 minutes Note that solid lines indicate percent removal

of suspended solids

10

2.5

Depth (m)

2.0

1.5

1.0

0.5

0

60%

75%

3.0

Time (min)

POTENTIALLY USEFUL INFORMATION

GLUMRB Recommendations

Rapid mixing: Detention time≤ 30 sec

Slow mixing (flocculation): Detention time > 30 min

Velocity through tank= 0.5-1.5 ft/min Paddle velocity= 0.5-3 ft/sec

Sedimentation: Detention time ≥ 4 hrs

Velocity through tank ≤ 0.5 ft/min Weir loading≤ 20,000 gpd/ft Over-flow rate= 500-800 gpd/ft2

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Number of samples taken for coliform testing based on population served by treatment facility

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