Mid-Semester Examination PES-104: Unit Processes and Operations -1 (Physico-chemical) M.Tech. – Environmental Science and Technology Instructor: Dr. Akepati S. Reddy Date: 20-09-2011 Time: 2 hours (01-00 - 03-00 Hrs.) Max. Marks: 50
Note:
Please assume if any requisite data is not given Please attempt all the subparts of a question at one place
Q.1
Answer any 6 of the following:
1.1
Differentiate perielectric coagulation from orthokinetic coagulation?
1.2
Write note on vortex type grit chambers?
1.3
Find the number of bars of a bar screen provided across a channel of 0.4 m width? Thickness and depth of the bars is 8 mm and 42 mm respectively. Spacing between the bars is 10 mm.
1.4
Differentiate the terms ‘prevention, control and abatement’?
1.5
List the objectives of pre-treatment?
1.6
List the alternatives available for the stabilization of the sludge generated at a wastewater treatment plant?
1.7
What alternate techniques can be employed for the removal of Total Dissolved Solids (TDS) from water/wastewater? Marks: 2 x 6 = 12
Q.2
Answer any 4 of the following:
2.1
Differentiate the Weir Loading Rate from the Overflow Rate, indicate units for both of these, and find out the Weir Loading Rate for a primary clarifier of 20 m diameter with peripheral overflow weir when its overflow rate 1.5 m/hour?
2.2
Write note on Zeta potential?
2.3
Write note on Stoke’s law?
2.4
Differentiate inline equalization from the offline equalization and discuss which is preferred when and why?
2.5
Write note on the provisions made in the circular primary clarifier for the removal of solids (both floating and settled)? Marks: 4 x 4 = 16
Q.3
Answer any 2 of the following:
3.1
Draw schematic diagram of a conventional Sewage Treatment Plant, show all the inputs and outputs and label, and discuss the designed purpose(s) served by each of the treatment units employed therein?
3.2
Wastewater flow rates from an industrial unit are as given below: Time of the day
08-00
11-00
14-00
17-00
20-00
23-00
02-00
05-00
Flow rate (in L/min.)
180
240
210
170
150
120
80
130
For equalizing this flow, find the volume of the equalization tank required? 3.3
120 m3/hour of wastewater is being treated by coagulation-flocculation-settling process. Lime and
Page 1 of 20
alum are dosed as 5% slurry/solution and the dosing is at 100 mg/L and 150 mg/L rates respectively. The wastewater, after the flocculation, is having 350 mg/L suspended solids and the clari-flocculator is reducing the suspended solids level to 100 mg/L. If consistency is 4%, find the sludge generation rate (in m3/day) at the clari-flocculator. If purity of the lime and the alum are 85% and 96% respectively, find daily volume requirements of the alum solution and the lime slutty? Marks: 6 x 2 = 12 Q.4
Answer any 1 of the following?
4.1
Describe the method used for the construction of a settling profile graph for the results obtained from the laboratory scale settling column test? Further, also describe the use of a settling profile graph for obtaining information on HRT and Overflow Rate for the design of a primary clarifier?
4.2
Find width and length of a grit channel that removes 0.15 mm size and 1.6 specific gravity grit with 100% efficiency for 120 m3/hour wastewater flow rate? If the horizontal flow velocity and depth of flow desired in the grit channel are 0.4 m/sec. and half the width of the channel respectively, find the slope of the grit channel required? Marks: 10 x 1 = 10
Page 2 of 20
Mid-semester Examination PES 103: Unit processes and operations -1 (physic-chemical) M.Tech. – Environmental Science and Technology Instructor: Dr. Akepati S. Reddy Date: 25-09-2010 Time: 2 hours (8-00 - 10-00 Hrs.) Max. Marks: 30 Note:- Please assume if any requisite data is not given Q.1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 Q.2 2.1 2.2 2.3 2.4
2.5 Q.3 3.1
3.2 3.3
Answer any eight (8) of the following? Indicate the location of a degassifier in a DM water plant and state the purpose served by the degassifier? A secondary clarifier of 200 m2 area is receiving 170 m3/hour of mixed liquor. If the underflow sludge withdrawal rate is 70 m3/hour find overflow rate for the secondary clarifier? What is scour velocity? In the design of which treatment unit the scour velocity should be taken into account? What is psi potential and state how it is different from zeta potential? State what is restabilization of colloids and indicate when it can occur? Differentiate microflocculation from macroflocculation? On settling for 30 minutes of one liter of mixed liquor, the sludge was found to occupy 0.3 L volume. If MLSS of the mixed liquor is 2250 mg/L find sludge volume index for the mixed liquor? State the purposes served by the central rotating equipment of a primary clarifier? Write note on weir loading? Marks: 8x1.5=12 Answer any four (4) of the following? Indicate the objectives of wastewater treatment and wastewater pre-treatment? And state the purposes served by primary treatment, secondary treatment and tertiary treatment? Comprehensively list the technologies that can be used for the removal suspended solids from wastewater? Design rectangular approach channel for a bar screen for a peak flow of 142 m3/hour? Effective volume of a strength equalization tank is 400 m3. Wastewater enters into this tank gets completely mixed with the tank contents and gets out without flow equalization. If flow rates and strengths of the wastewater entering the tank are as given below find the level of strength equalization that can occur because of this strength equalization tank? Time of the day Flow rate (m3/hour) Strength (mg/L) 03-00 AM 15 100 06-00 AM 30 450 09-00 AM 175 200 12-00 Noon 100 300 03-00 PM 125 320 06-00 PM 80 150 09-00 PM 70 250 12-00 mid night 25 130 Nnn Draw a schematic process flow diagram of a typical process water treatment plant and properly label it? Marks: 4x3=12 Answer any two (2) of the following? Find theoretically required grit channel length for the removal of grit particles of 0.15 mm size and 2.25 specific gravity with 100% efficiency. Assume flow rate as 150 m3/hour and assume if any additional information is required. Write note on how a settling profile graph is constructed and how a settling graph can be used for finding out HRT and overflow rate for a primary clarifier? Using the settling test results given below find the area required for thickening and for clarification for a 3 secondary clarifier. Take flow rate of the mixed liquor as 300 m /hour, MLSS is 2500 mg/L and underflow sludge concentration as 10500 mg/L.
Time (in minutes)
Sludge-liquid interface Height (in mm) Page 3 of 20
0 5 10 20 30 45 60 80 100 125 150
1000 820 690 600 520 447 388 350 325 310 295 Marks: 2x6=12
Page 4 of 20
Mid-semester Examination Water and Wastewater Treatment–I (Physico-chemical) M.Tech. – Environmental Science and Technology Instructor: Dr. Akepati S. Reddy Date: 22-09-2009 Time: 2 hours (08-00 - 10-00 AM) Max. Marks: 48 Note: Please assume if any requisite data is not given Q.1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 Q.2 2.1 2.2
2.3 2.4 2.5
Q.3 3.1 3.2 3.3
3.4
Q.4 4.1
4.2
Answer any 6 of the following: Differentiate the in-line flow equalization from the off-line flow equalization? List the primary and secondary objectives of wastewater treatment? What is weir loading and what are its units? Indicate the technologies that can be used for the removal of dissolved solids from water or wastewater? What conditions favour the use of aerated grit chambers in place of grit channels? Write note on Reynolds Number? List any four advanced wastewater treatment technologies? Marks: 1.5 x 6 = 9 Answer any 4 of the following: Write note on density current and list the factors that contribute to it? A water sample’s total alkalinity and phenolphthalene alkalinity are reported as 210 and 120 mg/L respectively. Find the sample’s carbonate, bicarbonate and hydroxide alkalinities? Write note on Psi potential and differentiate it from Zeta potential? Discuss the advantages and disadvantages of using tube settlers? 1 N HCl solution is prepared from 33% HCl with specific gravity 1.36. For preparing 3 m3 of 1 N HCl find the volume of 33% HCl required? Marks: 3 x 4 = 12 Answer any 3 of the following: Draw a properly labeled and comprehensive process flow diagram for a conventional sewage treatment plant? Write note on limiting solids flux? A drain is carrying 300 m3/hour of wastewater at 0.3 m/sec. approach velocity. On this drain a bar screen with 8 mm thick and 50 mm depth bars and with a bar spacing of 12 mm is provided. If depth of wastewater flow in the drain is 0.4 m, find the number of bars provided in the bar screen? At 9-00 AM an equalization tank was found to have 275 m3 of wastewater and its BOD was 170 mg/L. During 9-00 to 10-00 AM and 10-00 to 11-00 AM the equalization tank has received 80 m3 and 110 m3 of wastewater respectively. These wastewaters were having 230 and 100 mg/L of BOD. If outflow rate of wastewater from the equalization tank is 75 m3/day find BOD of the wastewater present in the equalization tank at 11-00 AM? Marks: 3 x 5 = 15 Answer any 2 of the following In a settling column test the following results were obtained: Time (min.) 0 5 10 20 30 45 60 80 100 Interface height 1000 950 895 770 640 447 388 350 325 (mm) Find the area required for thickening, if the wastewater flow rate is 475 m3/hour and TSS is 3,000 mg/L, and the underflow sludge concentration is 12,000 mg/L? A grit chamber is designed to remove grit of 0.21 mm size and 2.45 specific gravity with 100% efficiency. Find the efficiency with which grit of 2.65 specific gravity and 0.17 0.21 mm size range will be removed in the grit chamber?
Page 5 of 20
4.3
Describe how a settling profile graph is constructed and also how this graph is used in the design of a primary clarifier? Marks: 2 x 6 = 12
Page 6 of 20
Mid-term (House) Test Unit Processes and Operations –I (physico-chemical) M.Tech. – Environmental Science and Technology Instructor: Dr. Akepati S. Reddy Date:23-09-2008 Time: Max. Marks: 60 Note:Please assume if any requisite data is not given Q.1
Answer any three of the following?
15
1.1
Draw schematic diagram of the UASB based sewage treatment plant installed in Ludhiana, Phagwara, Jalandhar and Kapurthala under the Satluj River Action Plan?
5
1.2
Find out terminal settling velocity of grit particles of 0.15 mm size and 3.25 specific gravity? Assume viscosity as …
5
1.3
Wastewater of 400 mg/L of TSS and 600 mg/L of ultimate BOD is clarified in a primary clarifier with 70% and 40% removal efficiencies respectively. Find out biodegradable fraction of the primary sludge generated at the primary clarifier?
5
1.4
Find equalization tank volume for the wastewater showing the following flow variations?
5
Time (hrs.)
4
8
12
16
20
24
Flow rate (m3/hr.)
68
132
151
105
88
92
Q.2
Answer any four of the following?
16
2.1
List the technologies that can be used to remove suspended solids from wastewater and indicate which technology is appropriate under what conditions?
4
2.2
Describe how will you construct a Settling Profile Graph from the data obtained from a Settling Column Test?
4
2.3
For a bar screen, if approach velocity is 0.4 m/sec. find the velocity through the screen? Assume the bar width as 10 mm and spacing between the bars as 15 mm.
4
2.4
Write note on zeta potential?
4
2.5
List and classify the techniques used for the handling of the ETP sludges?
4
Q.3
Answer any five of the following?
15
3.1
A primary clarifier of 15 m diameter has peripheral clarified effluent overflow weir. if overflow rate of the clarifier is 1.25m3/m2.hour find weir loading for the primary clarifier?
3
3.2
If T-alkalinity and P-alkalinity of a wastewater sample are 210 mg/L and 60 mg/L find out carbonate, bicarbonate and hydroxide alkalinities?
3
3.3
Mixed liquor entering a secondary clarifier has 3400 mg/L MLSS. After settling for 30 minutes the MLSS present in one liter of the mixed liquor occupied 0.5 Liters. Find sludge volume index (SVI) for the mixed liquor?
3
3.4
Write note on continuous belt screen?
3
3.5
Write note on break point chlorination?
3
3.6
Write note on the MPN test?
3
Q.4
Answer any seven of the following?
14
4.1
Indicate advantages and disadvantages of the off-line equalization when compared with the inline equalization?
2
4.2
Indicate the technologies that can be used for the removal of dissolved solids from water or wastewater?
2
Page 7 of 20
4.3
Indicate the advantages of using aerated grit chambers over horizontal flow grit channels?
2
4.4
Find overflow rate for a primary clarifier of 2.5 hours HRT and 2.5 m side wall liquid depth?
2
4.5
Differentiate microflocculation from the macroflocculation?
2
4.6
Define buffer intensity?
2
4.7
Differentiate sewage from sewerage and sewer?
2
4.8
What is operating point of a pump?
2
Page 8 of 20
End semester Examination PES-104: Unit Processes and Operations –I (Physico-chemical) M.Tech. – Environmental Science and Technology Instructor: Dr. Akepati S. Reddy Date: 07-12-2011 Time: 3 hours (9-00 AM to 12-00 Noon) Max. Marks: 100 Note: Please assume if any requisite data is not given. Q.1
Answer any two (2) of the following?
1.1
Ion exchange capacity of a synthetic cation exchange resin is 4.7 eq/L. Using this resin a DM water plant of 80 m3/hour DM water generation capacity is to be designed. The resin bed is to be regenerated daily once after 20 hours of running. Cation strength and TDS of the input water are 4.6 meq/L and 420 mg/L respectively. Resin bed depth is 1.25 m. Internal consumption of the DM water is 250 m3/day. 33% hydrochloric acid is to be used for the resin bed regeneration. Use efficiency of the acid in the regeneration process is 42%. 5% acid solution is to be used in the resin bed regeneration. Water consumption during displacement rinsing and rapid rinsing are 15% and 35% respectively of the total internally consumed DM water. Backwashing of the resin bed will be with input water for 10 min at 50 m/hour rate. Find the quantity of resin required? Estimate monthly 33% HCl consumption? Estimate TDS level in the combined stream of regeneration wastewater?
1.2
A settling column test on the mixed liquor entering into a secondary clarifier gave the following results: Time (in minutes) Sludge blanket depth (in mm)
0
10
20
30
40
55
75
100
130
1000
700
505
380
300
248
215
195
180
Using this information, design a secondary clarifier for 500 m3/hour mixed liquor flow rate? MLSS of the mixed liquor is 2000 mg/L and the secondary clarifier underflow sludge concentration is 7000 mg/L. If diameter of the central well is 25% of the clarifier diameter, find weir loading rate for the secondary clarifier. 1.3
A grit channel is designed for 100% removal of 0.2 mm size grit particles. If the grit particle size distribution in the sewage is as given below, find out overall grit removal efficiency of the grit channel? Size (in mm)
>0.2
>0.15-0.20
>0.1-0.15
>0.05-0.1
<0.05
Fraction of the total grit
35%
30%
20%
10%
5%
The grit channel is designed for 0.3 m/sec. horizontal velocity during an average flow of 225 m3/hour. What will be the horizontal flow velocity in the grit channel during peak flow if the peak factor is 2.5? Marks: 2 x 10 =20
Page 9 of 20
Q.2
Answer any three (3) of the following?
2.1
Wastewater flows from an industry and BOD levels in the wastewater are as given below: Time of the day
3 AM
6 AM
9AM
12 Noon
3 PM
6 PM
9 PM
Mig night
Flow rate (m /min.)
2
4
9
7
4
6
5
1
BOD (mg/L)
80
300
150
200
120
170
140
50
3
For these flows find the flow equalization volume? If residual volume of the equalization tank is 30% of the flow equalization volume, determine the influence of the flow equalization on the BOD of the equalized flow? 2.2
A rapid gravity filter of 0.9 m filter media layer thickness is backwashed. The filter medium used has D10, D60 and D90 values as 0.4 mm, 0.7 mm and 0.9 mm respectively. Shape factor, porosity and specific gravity of the filter medium are 0.76, 0.4 and 2.4 respectively. If the filter bed is expanding 1.5 times, during the backwashing, find the backwash velocity required?
2.3
Describe chemical precipitation of wastewater by ferrous sulfate (FeSO4.7H2O). 400 m3/day of wastewater with 60 mg/L of alkalinity from a textile processing industry is given chemical precipitation treatment with ferrous sulfate at 300 mg/L dose. Find the lime and oxygen dosing required for the precipitation and estimate daily ferric hydroxide sludge generate rate?
2.4
Describe the procedure for finding out optimum pH, and optimum dose of coagulant and coagulant aid for the coagulation-flocculation-settling treatment of wastewater? Marks: 3 x 8 = 24
Q.3
Answer any four (4) of the following?
3.1
Draw a schematic process and material flow diagram for a DM water plant and show the key inputs and wastes from each of the units?
3.2
Design an approach channel for a bar screen for 3500 m3/day average flow and a peaking factor of 2? If spacing between bars is 12 mm and thickness of the bars is 10 mm, find the number of bars to be provided in the bar screen? Flow velocity in the approach channel for a clean bar screen should 0.4 m/sec. to 0.6 m/sec.
3.3
Head loss across a clean multi-grade filter is 0.25 m. Profile of the filter is as given below: Depth from the top Thickness of the medium layer
Effective size of the medium particles
0.00-0.25 m
Standing water column
----
0.25-0.50 m
0.25 m
0.5 mm
0.50-0.75 m
0.25 m
1.0 mm
0.75-1.00 m
0.25 m
2.0 mm
1.00-1.25 m
0.25 m
4.0 mm
1.25-1.50 m
0.25 m
8.0 mm
If specific gravity of the filter media is 2.5 and if porosity for all the layers is 40%, find filtration rate through the filter?
Page 10 of 20
3.4
List the water disinfection technology alternatives and discuss the merits and demerits of each of the alternate techniques?
3.5
A primary clarifier is treating 450 m3/hour of municipal sewage and removing TSS and BOD5 at 20°C by 65% and 40% efficiencies. The sewage received is having 250 mg/L of BOD and 320 mg/L of TSS. Find the primary sludge generation rate and the biodegradable fraction of the primary sludge generated? Marks: 4 x 6 = 24
Q.4
Answer any five (5) of the following?
4.1
Indicate the technology alternatives for the removal of suspended solids (and flocs) from water and wastewater, and state when what technology is preferred?
4.2
Write note on the characteristics of granular filter media?
4.3
Write note on adsorption isotherms?
4.4
Write note on ion-selectivity coefficient?
4.5
Write note on break point chlorination?
4.6
Discuss how chromium can be removed from wastewater through chemical precipitation? Marks: 5 x 4 = 20
Q.5
Answer any six (6) of the following?
5.1
Define and differentiate ‘unit process’ from ‘unit operation’?
5.2
Primary and secondary objectives of wastewater treatment
5.3
Catenary screen
5.4
Exhaust point
5.5
Sludge volume index
5.6
MPN
5.7
Chelating resins Marks: 6x2 = 12
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End semester Examination PES-104: Unit Processes and Operations –I (Physico-chemical) M.Tech. – Environmental Science and Technology Instructor: Dr. Akepati S. Reddy Date: 05-12-2010 Time: 3 hours (9-00 AM to 12-00 Noon) Max. Marks: 100 Note: Please assume if any requisite data is not given.
Q.1
Answer any two (2) of the following?
1.1
Find the filter backwash velocity when the filter bed depth is 80 cm and expansion of the bed is 1.5 times? Assume the following filter medium characteristics: porosity of 0.4, specific gravity of 2.65 and D90 = 0.75 mm.
1.2
Adsorption studies were carried out with powdered activated carbon on the treated wastewater for the removal of colour imparting substance. Concentration of the colour imparting substance in the wastewater is 0.6 mg/L. Results obtained from the adsorption studies are as given below: Activated carbon used (g/L)
1.00
1.25
1.75
2.50
3.50
4.25
Residual colour in equilibrium with activated carbon (mg/L)
0.125
0.1
0.08
0.065
0.053
0.044
Using these results construct Langmuir adsorption isotherm? Estimate daily requirement of the powdered activated carbon for treating 2400 m3/day of wastewater to reduce the concentration of the colour imparting substance to 0.05 mg/L? 1.3
Using the following settling column test results find HRT of a primary clarifier required for achieving 70% TSS removal efficiency? Time (min.)
Percent TSS removal at following depths 0.5 m
1.0 m
1.5 m
2.0 m
2.5 m
20
61
---
---
---
---
30
71
63
65
---
---
40
81
72
63
61
57
50
90
81
73
67
63
60
---
90
80
74
68
70
---
---
86
80
75
80
---
---
---
86
81 Marks: 2 x 10 =20
Page 12 of 20
Q.2
Answer any three (3) of the following?
2.1
A DM water plant of 200 m3/day capacity is using input water with 0.04 eq/m3 cation strength. The cation exchange resin bed is assembled using a resin with 6 eq/L cation exchange capacity. For the regeneration of the resin bed 33% hydrochloric acid with 1.165 specific gravity is used. If the resin bed is to be regenerated daily once find the volume of resin required. If the regeneration chemical use efficiency is 38%, find daily (33%) HCl requirement of the DM water plant?
2.2
Draw a line diagram of a rapid sand filter and describe the sequence of steps involved in the filter run and backwash cycle? If air is to be used in backwashing, discuss in what alternative ways it can be used?
2.3
Describe the method used for finding optimum pH, coagulant dose and coagulant aid dose for the coagulation-flocculation-settling treatment of wastewater?
2.4
Design a bar screen for a sewage flow of 1000 m3/day and peaking factor of 3.0. Spacing between the bars should be 10 mm and thickness of the bars should be 8 mm? Approach velocity should be between 0.4 and 0.6 m/sec. Free board during peak flow for a clean screen should be 0.3 m. Marks: 3 x 8 = 24
Q.3
Answer any four (4) of the following?
3.1
Write the expression used for the estimation of Actual Oxygen Transfer Rate/Efficiency from the Standard Oxygen Transfer Rate/Efficiency for a diffused aeration system? Discuss how this expression differs from the expression for a surface aeration system?
3.2
Write note on the safety provisions made and precautions to be taken at a chlorine storage facility?
3.3
Write note on (ion) selectivity coefficient?
3.4
Find surface area of a secondary clarifier needed for the clarification of 250 m3/hr flow of mixed liquor? The mixed liquor is having 2500 mg/L of MLSS and 145 mL/g of sludge volume index (SVI). Assume underflow sludge concentration as 10,000 mg/L and consider 2.0 as the safety factor.
3.5
A primary clarifier of 30 m diameter, 2.25 m settling zone depth, and 9 m central well diameter, and a peripheral overflow weir is used to clarify 325 m3/hour flow of wastewater. Find the overflow rate, settling time and weir loading rate for the primary clarifier in question? Marks: 4 x 6 = 24
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Q.4
Answer any five (5) of the following?
4.1
100 m3/hr. flow of wastewater is mixed with acid/alkali in a neutralization tank whose HRT is 1.5 minutes. If the velocity gradient required for proper mixing is 7000, find the power input required for mixing the acid/alkali in the wastewater?
4.2
Write note on log probability plot and indicate where and for what purpose it is used?
4.3
A blower was found to supply 600 m3/hour flow of air at 0.65 kg/cm2 pressure and 110C. Express the blower air supply in kg/hour units?
4.4
Write note on Reynolds number?
4.5
Discuss how aerated grit chambers differ from grit channels, and state when aerated grit chambers are preferred over grit channels?
4.6
Indicate the modifications you suggest for a flow equalization tank for achieving the desired level strength equalization also? Marks: 5 x 4 = 20
Q.5 Answer any six (6) of the following? 5.1 Differentiate break through point from exhaust point? 5.2 List the factors that influence disinfection during chlorination? 5.3 Write note on limiting solids flux? 5.4 Differentiate in-line equalization from off-line equalization? 5.5 Write note on velocity gradient? 5.6 Define and differentiate unit processes from unit operations? 5.7 List the technologies that can be used for improving the biological quality of water? Marks: 6x2 = 12
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End semester Examination Unit Processes and Operations –I (physico-chemical) M.Tech. – Environmental Science and Technology Instructor: Dr. Akepati S. Reddy Date: 02-12-2009 Time: 3 hours (9-00 AM to 12-00 Noon) Max. Marks: 100 Note: Assume if any requisite data is not given. Q.1
Answer any three (3) of the following?
1.1
A flow equalization tank has been designed for wastewater with the following flow and BOD variations: Time 3 AM 6 AM 9 AM Noon
Flow (L/Sec.) 10 40 100 75
BOD (mg/L) 100 280 310 200
Time 3 PM 6 PM 9 PM Mid- night
Flow (L/Sec.) 30 80 70 12
BOD (mg/L) 150 140 210 110
The equalization tank included 20% residual volume. Find the equalization tank volume and the minimum and maximum BOD values of the equalized flow? 1.2
A primary clarifier is found removing TSS from the wastewater by 65%. For increasing the TSS removal efficiency to 85% dosing of alum at the rate of 240 mg/L is found needed. If the wastewater is having 275 mg/L of TSS and 150 mg/L alkalinity find the dosing of lime required and the percent increase in the primary sludge generation because of alum dosing? The reaction involved in the alum treatment is shown below:
3Ca ( HCO3 ) 2 Al 2 ( SO4 )3 .18 H 2O 2 Al (OH )3 3CaSO4 6CO2 18 H 2O 1.3
An ion exchange resin bed based soft water plant is treating groundwater with 300 mg/L of hardness. The ion exchange resin used has 10 equivalents per liter ion exchange capacity. 3 If the softwater plant has to be regenerated after producing 100 m of softwater find the volume of resin required to assemble the resin bed? If only 30% of the dosed salt is actually used in the ion exchange resin regeneration find per regeneration salt requirement
1.4
Write the expression used for finding out the actual oxygen transfer efficiency from standard oxygen transfer efficiency for diffused aeration systems and explain all the terms of the expression? State how this expression will change if it is used for surface aerators? Marks: 3 x 5 =15
Q.2
Answer any four (4) of the following?
2.1
Using the settling profile diagram given below find the design overflow rate and the design hydraulic retention time for the removal of TSS by 70% efficiency in a primary clarifier?
Page 15 of 20
2.2
D90 of the filter medium used in a rapid sand filter is 1.6 mm. If specific gravity of the medium is 2.65 and porosity of the expanded bed is 0.7 find backwash velocity required?
2.3
Write note on power number and flow number and indicate where and for what purpose these are needed?
2.4
Coagulation-flocculation treatment of a wastewater required 150 mg/L as CaCO 3 and 70 3 mg/L of lime and alum respectively. If the wastewater flow rate is 6000 m /day find monthly quick lime and alum requirements when their purity is 82% and 95% respectively. If 5% slurries of both the chemicals are to be used find daily water requirement for the lime slurry and alum solution preparation?
2.5
Draw a schematic diagram of a rapid sand filter and properly label it? And, systematically describe running and backwashing of a rapid sand filter? Marks: 4 x 4 = 16
Q.3
Answer any five (5) of the following?
3.1
A bar screen of 6 mm thick bars with 8 mm bar spacing is provided across a drain of 0.7 m width. During peak flow, if depth of flow is 0.35 m find head loss across the clean screen?
3.2
Draw line diagram of a primary clarifier and label all the important parts?
3.3
Describe how tu (of the expression for area for thickening) can be found from the settling column test results? Also show the method of finding tu on the settling curve?
3.4
Discuss the method followed for the removal of chromium from the wastewater through chemical precipitation?
3.5
Weir loading for a secondary clarifier has to be 125 m /day. For a secondary clarifier of 60 m diameter, 3.7 m settling zone depth and 2.5 hours HRT, find the weir length required? Indicate how will you accommodate this weir length on the clarifier?
3.6
VOC concentration of a treated effluent has to be reduced from 4 mg/L to 0.2 mg/L through powdered activated carbon adsorption process. Freundlich isotherm was found to explain the adsorption process appropriately. Laboratory experimentation has shown the capacity factor (K) and intensity parameter (n) as 1.5 and 4 respectively. If the effluent to be treated 3 is 100 m /hour find daily powdered activated carbon requirement of the treatment process?
2
Marks: 5 x 3 = 15 Q.4 4.1 4.2 4.3
Answer any seven (7) of the following? Indicate the main purpose of pre-treatment, primary treatment, secondary treatment and tertiary treatment? Write note on vortex type grit chambers? What is restabilization of colloids and state when it occurs? Further, state what should be done for achieving the orthrokinetic coagulation?
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4.4 4.5 4.6 4.7 4.8
Write note on the five parameters used for the characterization of the filter media used in water filters? List the provisions made and precautions taken at the chlorine storage facilities? Write note on selectivity coefficient? Draw a comprehensive schematic diagram of a conventional water treatment plant and properly label it? Write note on the multiple tube fermentation technique? Marks: 7 x 2 = 14
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End semester Examination Unit Processes and Operations –I (physico-chemical) M.Tech. – Environmental Science and Technology Instructor: Dr. Akepati S. Reddy Date: 03-12-2008 Time: 3 hours (9-00 AM to 12-00 Noon) Max. Marks: 60 Note:Please assume if any requisite data is not given Q.1
Answer any three of the following?
15
1.1
Design a grit chamber for the 100% removal of 0.225 mm size grit particles? Assume sewage flow rate as 400 m3/hour. Take specific gravity of the grit as 2.65 and dynamic viscosity of the sewage being treated as 1.003x10-3 If grit particle size distribution in the sewage is as given below find out overall grit removal efficiency of the grit chamber:
5
1.2
Size (in mm)
>0.2-0.25
>0.15-0.20
>0.1-0.15
>0.05-0.1
<0.05
Fraction of the total grit
35%
30%
20%
10%
5%
Adsorption studies were carried out with powdered activated carbon on the treated wastewater for colour removal. Colour intensity of the untreated effluent was 600 PCU. Results obtained from the adsorption studies are as given below: Activated carbon used (g/L)
1.00
1.25
1.75
2.50
3.50
4.25
Residual colour in equilibrium with activated carbon (in PCU)
125
100
80
65
53
44
5
Using these results construct Langmuir adsorption isotherm? 1.3
Standard oxygen transfer efficiency for a diffused aeration system is 30%. Find the actual oxygen transfer efficiency of the system when temperature is 30C, and wastewater depth upto the diffuser is 4.5 m. Take Beta correction factor as 0.95, saturation DO in clean water at 30C and at the altitude in question as 7.54 mg/L, saturation DO in clean water at 20C as 9.08 mg/L, operating DO of the tank as 1.0 mg/L, Alpha correction factor as 0.6 and fouling factor as 0.7.
5
1.4
A settling column test on the mixed liquor entering into a secondary clarifier gave the following results:
5
Time (in minutes) Sludge blanket depth (in mm)
0
10
20
30
40
55
75
100
130
1000
700
505
380
300
248
215
195
180
Find the area required for thickening and the area for clarification if the mixed liquor flow rate is 400 m3/hour and mixed liquor suspended solids concentration is 2000 mg/L? Assume suspended solids concentration in the underflow line is 9000 mg/L.
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Q.2
Answer any four of the following?
16
2.1
Draw a properly labeled line diagram of a rapid sand filter and describe step by step procedure for the rapid sand filter backwashing?
4
2.2
Describe the laboratory procedure for finding the optimum pH, optimum coagulant dose and optimum coagulant aid dose?
4
2.3
Write note on note on the functional groups of ion exchange resins and on the selectivity coefficient?
4
2.4
A primary clarifier of 24 m diameter, 2.5 m settling zone depth, and having a 8 m diameter central well and a peripheral overflow weir is used to clarify 200 m3/hour flow of wastewater. Find the overflow rate, settling time and weir loading rate for the primary clarifier in question?
4
2.5
Cation exchange resin of 8 equivalents per kg capacity is used for softening water at 80 m3/hour rate. Bulk density of the resin is 1100 kg/m3. Hardness of the input water is 170 mg/L (as CaCO3). Two resin beds, each of 1.25 m height resin column, are to be used. Run time of the resin bed is 12 hours per regeneration cycle. Only 90% of the ion exchange capacity of the resin is used in the water softening process. Find the amount of cation exchange resin required and also find the diameter of the resin bed?
4
Q.3
Answer any five of the following?
15
3.1
Write note on Carmen-Kozeny equation?
3
3.2
In a chemical precipitation experiment alum dose applied is 250 mg/L. The water sample experimented has enough alkalinity in it for the chemical precipitation. Stoichiometrically find the precipitate concentration resulting from the chemical precipitation? Assume that the calcium sulfate formed is also insoluble?
3
3.3
Draw schematic diagram of the water treatment plant you have visited and label all its input and output streams?
3
3.4
A secondary clarifier is loaded with mixed liquor with 3000 mg/L of TSS at 400 m3/hour rate. TSS of the clarified overflow and consistency of the underflow sludge are 50 mg/L and 0.9% respectively. Find the flow rate of the clarifier effluent from the secondary clarifier?
3
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3.5
Using the following break point chlorination diagram find the break point chlorination dose? Estimate the amount of chlorine required for treating 2500 m3/day of water for supplying the chlorinated water with 0.6 mg/L of residual chlorine?
3
3.6
A blower was found to supply 720 m3/hour flow of air at 0.5 kg/cm2 pressure and 90C. Express the blower air supply in Nm3/hour units and in kg/hour units?
3
Q.4
Answer any seven of the following?
14
4.1
2
4.2
Write note on uniformity coefficient? Differentiate Psi (y) potential from Zeta (z) potential?
4.3
Write note on sludge blanket unit?
2
4.4
Discuss how hexavalent chromium is removed from wastewater by chemical precipitation technique?
2
4.5
Differentiate in-line equalization from off-line equalization?
2
4.6
List the technologies that can be employed for the removal of volatile matter from the wastewater?
2
4.7
From a reverse osmosis unit 65% of the input water is recovered as RO water. If the input water and the RO water have 405 mg/L and 20 mg/L of TDS respectively, find the TDS level in the reject stream of the reverse osmosis unit?
2
4.8
Find the number of bars of a bar screen designed for screening 540 m3/hour flow of wastewater? Assume depth of flow as 0.4 m, approach velocity as 0.4 m, bar thickness as 6 mm and spacing between the bars as 8 mm.
2
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