Tribhuvan University · Institute of Engineering
Sanitary Engineering CE 656
Chapterwise Questions
10Chapters
15+Exam Papers
2070–2082Years Covered
Table of Contents
- Introduction [2 hrs]
- Quantity of Wastewater [4 hrs]
- Design and Construction of Sewers [4 hrs]
- Sewer Appurtenances [3 hrs]
- Characteristics and Examination of Wastewater [5 hrs]
- Wastewater Disposal [6 hrs]
- Wastewater Treatment [12 hrs]
- Sludge Treatment and Disposal [4 hrs]
- Disposal of Sewage from Isolated Buildings [3 hrs]
- Solid Waste Disposal [2 hrs]
Chapter 01
Introduction
2 Hours
1.
Define Sanitation. Justify the importance of sanitation system from public health and environment perspectives.
2.
Define sanitation system. Justify the importance of water-carriage sanitation system which is popular than the conservancy system.
3.
Define sanitation. Justify, why water-carriage sanitation system is popular than conservancy system nowadays.
4.
Define Sanitation system. And, justify the importance of wastewater management.
5.
Compare between separate and combined sewerage system.
6.
Describe the method used in the management of wastewater and solid waste produced from a community.
7.
Define Sanitary Sewage. Justify to adopt the separate system of sewage.
8.
What are positive and negative aspects of wastewater management practice in context of Nepal? What could be possible way outs for improvement?
9.
Briefly explain the methods of management of wastewater and solid waste produced in the society.
10.
Define sewerage system and recommend a suitable type of sewerage system for highly populated city with justifications.
11.
What is the major difference between conservancy and water carriage systems of sanitation? Why water carriage system is preferred in the disposal of sewage? Justify.
12.
Explain the relative merits and demerits of the combined and partially separate system of sewerage. Also state the conditions favorable for the adoption of each of them.
13.
Which type of sewerage system do you recommend in your locality? Discuss briefly with your justifications.
14.
What do you mean by sanitation? How it is related with our human life? Why water-carriage system of sanitation is popular than conservancy system nowadays.
15.
Why scientific management is necessary for wastewater and solid waste produced in community? Enlist the objectives of the sewage disposal.
16.
Describe the importance of wastewater and solid waste management for a community. What are the components of waste management methods?
17.
Which type of sewerage system do you recommend for urban area of Nepal? Discuss briefly with your justification.
18.
What is sewer and sewage? Why is the sewage disposal needed in today's civilizations?
19.
Describe briefly the conservancy and water carriage system of sanitation. When is it necessary and useful to employ separate system of sewerage?
20.
Compare between water carriage and conservancy methods of sewage disposal with merits and demerits of each method.
Chapter 02
Quantity of Wastewater
4 Hours
1.
Justify wet weather flow and dry weather flow are crucial design parameters.
2.
Why the wet weather flow and dry weather flow are considered as important parameters in designing a sewer line.
3.
With respect to designing a sewer line, discuss about the time of concentration with rainfall duration.
4.
Define dry and wet weather flow. Describe the factors affecting storm water.
5.
Define time of concentration and describe its significance in the design of sewers.
6.
Define dry weather flow (DWF) and wet weather flow (WWF). Discuss in brief about the quantity estimation of WWF.
7.
Define Dry Weather Flow (DWF) and discuss in brief about the key factors affecting DWF.
8.
As a designer for a highly populated urban area how would you determine quantity of storm water? Discuss in detail.
9.
Define dry and wet weather flow. Discuss the factors affecting storm water.
10.
List out potential sources of sanitary sewage and discuss briefly about key factors affecting quantity of sanitary sewage.
11.
State the factors influencing the discharge of sanitary sewage. What are the sources of sanitary sewage?
12.
If you are asked to determine discharge of storm water in a community designing sewer, how do you calculate? Mention with suitable example.
13.
Describe that time of concentration is an important while determining storm water discharge. Elaborate on time of concentration and time area graph.
14.
As a sanitation engineer how would you determine the quantity of storm water for a highly populated urban area? What type of limitations exists in storm water quantity determination for such area?
15.
What are various factors affecting the discharge of sanitary sewage? How do you calculate sanitary sewage discharge?
16.
What are the sources of sanitary sewage? Briefly describe its impact based on time and development activities of the city.
17.
How do you determine the quality of storm water for a locality?
18.
Differentiate dry weather flow and wet weather flow. Briefly describe various sources of sanitary sewage.
★ Numerical Problems — Quantity of Wastewater
N1.
A sewer carries a runoff water to its 0.6 depth at maximum flow which is entering from the catchment area of 200 hectare having overall coefficient of runoff as 0.45 and time of concentration of 55 minutes. The velocity in the sewer is to be maintained as 1.5 m/s at peak flow. Determine the diameter and slope of the cement concrete sewer with the Manning's coefficient as 0.013.
N2.
Propose the diameter and slope of a concrete sewer to carry runoff within its 0.7 depth at peak condition. The catchment area to be served is of 225 hectares with an overall coefficient of runoff of 0.35 and a time of concentration of 60 minutes. The velocity in the sewer is to be maintained as 1.3 m/s at peak flow. Assume Manning's coefficient as 0.013.
N3.
Calculate the design discharge for a combined sewer to convey sewage from an overall area of 300 hectares with a water supply rate of 100 lpcd and a peak factor of 2.5. The projected population of the area is 50000 numbers and only 85% of water supply contributes for the sewage. The 40% of the area has a runoff coefficient of 0.9, next 30% has 0.8 and remaining has 0.7. The time of concentration is assumed to be 90 minutes.
N4.
Calculate the design discharge for a sewer from the following data: Projected population = 75,000; Area = 8 km²; Rate of w/s = 100 lpcd; Permeability factor = 60%; Rainfall duration = 15 min; Time of flow = 15 min; Time of entry = 5 min. Assume that 80% supplied water converted as wastewater and maximum demand is 3 times average demand.
N5.
The catchment area of a city is 45 hectares. Assuming that the surface on which rain falls is classified with different surface types and runoff coefficients (Forest 10%/0.15; Open ground 10%/0.20; Parks 15%/0.15; Gravel 20%/0.25; Asphalt 20%/0.85; Roof 25%/0.90). Calculate the quantity of storm water if time of entry is 20 minutes and time of flow is 10 minutes.
Chapter 03
Design and Construction of Sewers
4 Hours
1.
Why is circular cross-sectional shape of sewer common in carrying wastewater? What will be the flow velocity and corresponding discharge in a circular sewer of diameter 0.9 m laid at a gradient of 1 in 500 running 0.7 full at maximum discharge? The Manning's coefficient is taken as 0.012.
2.
What are non-silting and non-scouring velocities? Calculate the velocity and discharge of flow if a circular concrete storm drain with 0.8 m diameter having 80% flow depth at maximum condition and laid at 1:200 slope. Consider Manning's coefficient of drain is 0.012.
3.
With the help of neat sketches, describe in detail the various steps of sewer construction.
4.
List the various types of pipe materials used in sewer line. Describe them with merits and demerits.
5.
State the steps involved in construction of sewers in urban area. Briefly describe the testing of sewer line.
★ Numerical Problems — Sewer Design
N1.
A circular sewer is designed to carry the maximum sewage while flowing 70% full at a velocity of 0.9 m/s. The ratio of maximum/average and average/minimum flows is 2.5 and 2 respectively. Find (i) proportionate depth of flow and (ii) velocities of flow generated at the time of average flow and minimum flow. Neglect the variation of n with depth of flow.
N2.
Design a sewer running 0.6 times full at maximum discharge for a town provided with the separate system serving a population of 250,000 persons. Water is from the water-work at a rate of 200 lpcd. Take a constant value of n = 0.013 at all depths of flow. The permissible slope is 1 in 600. Take peak factor of 2.25.
N3.
Determine the size of combined circular sewer for a discharge of 1.5 m³/s running half full. Assume a gradient of 1 in 2000 and Manning's rugosity coefficient N is 0.013. In the dry season if the flow drops to 0.5 m³/sec, does the flow maintain desired self-cleaning velocity of 0.60 m/s?
N4.
Design a sewer running 2/3rd full at maximum discharge for a town with a peak sewage flowrate of 0.6 m³/s. The sewer has Manning's coefficient of 0.014 and it is laid at a slope of 1 in 550. Also check velocity at peak and minimum flow conditions. Assume peak factor as 3 and a minimum flow as 1/3rd of average flow.
N5.
Calculate the diameter of a circular sewer laying at a slope of 1:150 when it is running just fall with a discharge of 1.6 m³/sec and Manning's coefficient 0.013. Also determine the discharge capacity if it is permitted to flow half full with the same gradient.
N6.
The population of a town is 80,000 persons with a water supply rate of 145 lpcd. Assuming 80% of water supply contributes for sewage flow, taking Manning's N as 0.013, average slope as 1:400 and peak factor as 3, determine the minimum diameter of sewer required to carry the maximum discharge at 0.75 depths.
N7.
Calculate the diameter of a sewer to serve an area of 2.5 sq. km with a population density of 400 persons per hectare. The average rate of water supply is 1101 pcd. Coefficient of runoff for 50% area is 0.5 and the remaining is 0.6. Time to reach by storm water = 18 min, storm duration = 21 min, Manning's n = 0.013, slope = 1 in 500, peak factor = 2.7. Sewer runs half full.
N8.
Calculate the diameter of a circular concrete sewer carrying 2/3rd depth at the peak discharge of 0.70 m³/s laid in a gradient of 1 in 1000. Also check whether it is safe for non-scouring velocity or not. Assume Manning's 'n' as 0.012.
Chapter 04
Sewer Appurtenances
3 Hours
1.
Justify the importance of manhole in sewer line. Describe briefly about the components of manhole.
2.
Define drop manhole. Explain the need of installing manhole along the sewer line.
3.
What are sewer appurtenances? Explain briefly the necessity of sewer appurtenances.
4.
Describe with neat sketches the working of any two sewer appurtenances that are usually provided on any sewer line.
5.
Describe about a drop manhole with a neat sketch.
6.
Why are manholes important in sewer lines? What are components of manholes? Draw neat sketches of manholes showing components in detail.
7.
Define sewer appurtenances. Justify the need of installation of sewer appurtenances with suitable examples.
8.
What are street inlets? Explain their types with neat sketches.
9.
Why flushing is necessary in sewers? With a neat sketch describe an automatic sewer flushing tank.
10.
Describe pollution removal mechanism and role of sun light in an oxidation pond. Also, discuss working mechanics of inverted siphon generally used as sewer appurtenances.
11.
Why sand, grease and oil traps are necessary in sewer lines? Describe them with neat sketches. Briefly discuss its operation and maintenance frequency and locations adopted in road network.
12.
What is an inverted siphon? In what circumstances such structure is provided? What are the purposes served by it? Describe briefly with neat sketch.
13.
Explain street inlets with neat sketch. Where are these located? Differentiate between a curb inlet and a gutter inlet.
14.
Describe street inlets and catch basins with neat sketches.
15.
With a neat sketch, describe the purpose, features and construction of Automatic flushing device used in sewerage system.
16.
Briefly describe drop-manhole with neat sketch mentioning its importance and discuss its alternative structural option with applicability.
Chapter 05
Characteristics and Examination of Wastewater
5 Hours
1.
Define first stage and second stage BOD. Also, discuss the significance of analyzing BOD and COD of wastewater sample.
2.
Describe the practical approach of determining settleable and non-settleable solids. Also, derive an expression for first-stage BOD.
3.
Derive the BOD equation, and discuss reaction rate, ultimate BOD with respect to temperature.
4.
Describe about significance of BOD and COD. If 3 days 25°C BOD of sewage sample is 250 mg/l, what will be its 5 days BOD at 30°C? Assume K₂₀=0.1 per day.
5.
The 5-day BOD at 20°C of a sewage sample was found to be 200 mg/l. Calculate 3 day BOD at 30°C for the same sample. Assume K₂₀= 0.1/day.
6.
Describe briefly about BOD and COD with their significance. The five days BOD of sewage was measured as 480 mg/l. If the base 'e' constant 'K' = 0.25 day, what is the ultimate BOD of the sewage? What proportion of BODu would remain un-oxidised or unsatisfied after 20 days?
7.
Discuss about BOD and COD with respect to its significance. Calculate the ultimate BOD if 5 day BOD of sewage sample at 25° is given as 500 mg/l.
8.
Explain BOD with its significance. How do you perform BOD test in laboratory from dilution method?
9.
Discuss first-stage and second-stage BOD with a suitable figure. Calculate ultimate BOD if 5 day BOD of sewage sample at 20°C is 400 mg/l.
10.
If 1 day BOD of sewage sample at 20°C is 300 mg/l, what will be its 5-day BOD at 30°C. Consider rate constant of 0.1/day (base 10) at 20°C.
11.
If a water sample have BOD₁,₂₀°C = 100 mg/l and BOD₅,₂₅°C = 210 mg/l; what will be the ultimate BOD and rate constant. Assume suitable data if necessary. Determine the BOD₄,₂₂°C of the same water sample.
12.
How do you determine the Total Solid, Total Volatile Solid, Total Fixed Solid, Settlable Solid and Non-settlable Solids contained in a sewage sample?
13.
How do you determine BOD of a sewage sample in laboratory from the dilution method? If 4 day BOD of a sewage sample at 20°C is 300 mg/l and K₂₀ = 0.1/day, what will be its 7 day BOD at 25°C?
14.
A wastewater sample was incubated at 25°C. 5 day BOD of sample was equal to 250 mg/l and 11 day BOD of sample was found to be 325 mg/L. Calculate the rate reaction constant and organic matter remaining in sample after 6 days at 30°C.
15.
BOD₁,₂₂°C of a sewage sample is 310 mg/l. What will be its BOD₅,₃₀°C? Assume reaction rate K₂₀ = 0.12 per day.
16.
5 ml of a sewage sample taken under the Thapathali bridge of Bagmati river was pipetted into a 300 ml capacity BOD bottle which was then completely filled with dilution water. The DO concentration of this mixture is tested and found to be 9.2 mg/l. Now it is kept in the incubator maintained at 25°C for a period of 7 days. The DO concentration after incubation is found to be 5.3 mg/l. Adopting base 10 value of K as 0.1/d, determine the 4 day BOD of sewage at 30°C in Bagmati river at that particular location.
17.
2.5 ml of raw sewage is diluted to 250 ml. DO concentration of the diluted sample at the beginning was 8.0 mg/l and 54.0 mg/l after 5 days of incubation at 20°C. Find 5-day B.O.D. of raw sewage and kg. B.O.D. contained in 5 million liters of sewage.
Chapter 06
Wastewater Disposal
6 Hours
1.
Define self-purification capacity of rivers. Discuss about factors affecting self-purification capacity of a river with example.
2.
Explain self purification of streams and indicate how sun-light helps in such purification.
3.
Discuss the process of self-purification of river and factors affecting the process. Draw the oxygen sag curve showing the zones of pollution along river.
4.
A city is discharging sewage of 50 l/s in the river having discharge of 500 l/s and a velocity of 48 km/day. The 5-day BOD of sewage and river water are 400 mg/l and 4mg/l respectively. The DO of sewage is zero. The DO in the river is 80% of saturation value. Saturation DO at 20°C is 9.17 mg/l. Consider deoxygenation constant (K) as 0.1/day (base 10) and reaeration constant (R) as 0.5/day. Calculate the time of critical DO deficit.
★ Numerical Problems — Self Purification / Oxygen Sag
N1.
115 m³/s of sewage of a city is discharged in a river which is fully saturated with oxygen and flows at a rate of 1600 m³/s with a minimum velocity of 0.12 m/s. If the 5-day BOD of the sewage is 300 mg/l, find out where the critical DO will occur in the river and calculate critical DO at the critical point. Assume reoxygenation and deoxygenation constants are 0.4 per day and 0.1 per day respectively, temperature throughout the river is 20°C. The ultimate BOD as 125% of 5-day BOD of the mixture of sewage and river water.
N2.
Determine the flow in river required per 1500 population for disposing off sewage from a residential town with the given data: average temperature of river water = 25°C; 5-day BOD of sewage at 25°C = 350 ppm; Average sewage flow = 200 lpcd; values of de-oxygenation and re-oxygenation constants of the river at 25°C are 0.15 day⁻¹ and 0.27 day⁻¹ respectively. Minimum DO concentration to be maintained in river water = 4 ppm and saturation DO of river water at 25°C = 8.38 ppm.
N3.
A town discharges 120 cumec of sewage into the river having rate of flow rate of 1600 cumec during lean period with velocity of 0.1 m/s. The 5-day BOD of sewage at the given temperature is 250 mg/l. Find the amount of Critical DO deficit, and when and where it will occur in the downstream portion of river. Deoxygenation coefficient K (base e) as 0.23/day and coefficient of self-purification fs as 3.5. Saturation DO at given temperature is 9.2 mg/l.
N4.
A stream saturated with DO has a flow of 1.9 m³/s, BOD of 2.5 mg/l and rate constant (K to base 10) of 0.1 per day. It receives an effluent discharge of 0.6 m³/s having BOD of 210 mg/l and DO of 1.8 mg/l. The average velocity of stream is 0.15 m/s. The average depth of stream is 1.4 m. Calculate DO deficit 50 km downstream of outfall. Assume temperature of 20°C throughout and saturation DO at 20°C is 9.17 mg/l.
N5.
The wastewater generated from a newly established town is proposed to dispose in the nearby river. Characteristics: Wastewater discharge = 300 l/s; BOD₅ of wastewater at 20°C = 450 mg/l; Sewage in putrefied state; Minimum river discharge = 5.5 m³/s; BOD₅ of river at 20°C = 0 mg/l; DO of river = 8.5 mg/l; Temperature in the river after mixing = 20°C; De-oxygenation constant = 0.1/day; Re-oxygenation constant = 0.4/day; Saturation DO = 9.1 mg/l; Allowable minimum DO deficit at d/s of disposal = 4.5 mg/l. Is treatment necessary? If so, what will be the required degree of treatment?
N6.
A city is discharging sewage at the rate of 1200 l/s, into a stream whose minimum flow is 5000 liters/sec, the temperature of both being 20°C. The 5 day BOD at 20°C for sewage is 160 mg/l and that of river water is 2 mg/l. The DO Content of sewage is zero while that of stream is 90% of the saturation DO. Find out the degree of treatment required if the minimum DO to be maintained in the stream is 4 mg/lit. Assume deoxygenation coefficient as 0.10 (base 10) and re-oxygenation coefficient as 0.30 (base 10). Given saturation DO at 20°C as 9.17 mg/lit.
N7.
In a town, the treated domestic sewage is to be discharged in a natural stream. Determine the percentage purification required in the treatment plant with following data: Population = 40,000; BOD contribution per capita = 0.075 kg/day; BOD at upstream side = 2 mg/l; DO to be maintained in downstream side = 5 mg/l; Domestic sewage production rate = 80 lpcd; Minimum discharge of stream = 0.3 m³/sec; Rate Constants K₁ = 0.1/day, K₂ = 0.5/day.
Chapter 07
Wastewater Treatment
12 Hours
7.1 Primary Treatment — Grit Chamber
1.
Define Grit chamber and justify the need of grit chamber in wastewater treatment plant. Also, describe about design considerations for a Grit chamber.
2.
Define grit chamber and outline its significance. Justify the need for incorporating grit chamber in wastewater treatment processes. Also, illustrate the design criteria of a grit chamber using clear and well-drawn sketches.
3.
Define unit operation and process in wastewater treatment system with examples. Describe the pollutants removal mechanism of intermittent sand, contact bed, and trickling filter.
4.
Design a grit chamber for a sewage treatment with 60 MLD of sewage flow at 25°C to remove 0.23 mm size of grit having specific gravity of 2.65. The specific gravity of organic matter is 1.02. Assume k = 0.06 and f = 0.03.
5.
Design a horizontal flow rectangular grit chamber operated at 25°C for an urban area of Nepal having 200000 population. Assume water supplied rate 112 lpcd, 80% of water supply contribute for sewage, peak factor = 3, size of grit and organic matters = 0.2 mm, specific gravity of grit = 2.65, specific gravity of organic matters = 1.2, value of K = 0.065 and f = 0.03.
6.
Design a grit chamber for wastewater flow of 190 liter/sec with surface overflow rate = 2 cm/s and detention time = 60 sec. Take specific gravity of organic and inorganic particles 1.2 and 2.65 respectively. Assume size of both organic and inorganic materials as 0.21 m. Take k = 0.06 and f = 0.03.
7.
Design a rectangular grit chamber for maximum wastewater flow for 10 Mld to remove particles up to 0.2 mm diameter having sp.gr. 2.65. Settling velocities of grits is found to be 0.02 m/s in average and maintain a flow velocity of 0.3 m/s constant through a flow weir.
8.
Design a grit chamber to remove grit size of diameter more than 0.2 mm present in 58 MLD of sewage at a temperature of 25°C. Assume specific gravity of grit and organic matters 2.65 and 1.2 respectively. Adopt k = 0.06 and f = 0.03 to calculate critical velocity.
9.
Calculate the size of grit chamber to treat wastewater with 20 MLD at 20°C to remove 0.2 mm size having specific gravity of 2.65.
7.2 Trickling Filter
1.
A wastewater flow rate of 6.5 MLD having BOD of 275 mg/l is primarily treated in PST. PST removes 30% of BOD. The effluent is then fed into a two-stage high-rate trickling filter. The volume of first and second filter is 800 and 600 m³ respectively. The recirculation ratio provided for the first and second filter are 1.8 and 1.2 respectively. What will be the effluent BOD from this high-rate trickling filter?
2.
Design a single stage high rate trickling filter for the sewage flow of 5 MLD with re-circulation ratio 1.3. The BOD of raw sewage is 250 mg/l. Primary sedimentation tank removes 30% of BOD and desired final BOD of the effluent is 30 mg/l.
3.
Calculate effluent BOD of two stage trickling filter for the following data: Sewage flow = 2.8 million liters per day, BOD of sewage after primary treatment = 310 mg/l, volume of both filters = 950 m³ and recirculation ratio for both filters = 1.5.
4.
Calculate the effluent BOD₅ of a two stage trickling filter with the following flows, BOD₅ and dimensions, using NRC formula: Q = 5000 m³/day, BOD₅ = 300 mg/l, volume of primary filter = 1200 m³, volume of secondary filter = 1000 m³, filters depth = 2 m, recirculation ratio for primary filter = 1.5 and recirculation ratio for secondary filter = 1.25.
5.
A sewage having BOD of 200 mg/l is fed to a two stage trickling filter with a flow of 4 million liters per day. The BOD required in the final effluent is ≤ 30 mg/l. The efficiency of the first stage trickling filter is 2 times the efficiency of the second stages trickling filter. If the depth and recirculation ratio of both the first stage and second stage trickling filters are 1.2 m and 2 respectively, determine the diameters of the first stage and second stage trickling filters.
6.
Determine the dimensions of high-rate trickling filter with sewage flow of 4 MLD, recirculation ratio 1.5, BOD of raw sewage 300 mg/l, BOD removal in primary settling tank 30% and final effluent BOD required is 25 mg/l.
7.
Calculate the depth and diameter of a secondary filter of a double stage trickling filter treating sewage of 2 MLD at a recirculation ratio of 2:1. The BOD₅ of the influent sewage to first filter is 170 mg/l and final effluent BOD₅ should be less than 30 mg/l. Take efficiency of first stage as 70%. Assume the organic loading in the filter as 8000 kg BOD₅/ha-m/day.
7.3 Activated Sludge Process
1.
Design a conventional activated sludge treatment plant to treat the domestic sewage with diffused air aeration with the following data. (Design up to dimensions of aeration tank only). Given data: Population = 1,50,000; Per capita sewage flow = 80 liters/day; Settled sewage BOD₅ = 280 mg/l; Food/micro-organisms = 0.3; Concentration of microorganism (MLSS) = 3000 mg/L.
2.
Design a conventional activated sludge plant to treat settled domestic sewage with diffused air aeration system for the given data: Sewage discharge = 0.104 m³/s; BOD 5 of settled sewage = 220 mg/l; Effluent BOD allowed = 30 mg/l; F/M ratio = 0.2; MLSS = 3000 mg/l.
3.
Design the aeration tank for a conventional activated sludge treatment plant to treat domestic sewage with an average flow of 15 MLD considering the following data: BOD of settled sewage = 200 mg/l; F/M = 0.25/d; MLSS = 3000 mg/l; ML VSS/MLSS = 0.8 and SVI = 100 ml/g.
4.
Design a conventional activated sludge treatment plant to treat the domestic sewage with diffused air aeration with the following data (Population = 1,26,000; Per capita sewage flow = 160 lpcd; Settled sewage BOD₅ = 200 mg/L; Effluent BOD₅ required = 15 mg/l; F/M = 0.2 and MLSS = 3000 mg/L). Also check for HRT, Volumetric Loading, Return Sludge ratio, Horizontal Velocity.
7.4 Oxidation Pond
1.
Define oxidation pond. Describe the pollutant removal mechanism of the pond with a neat sketch. Also, discuss the commissioning methods.
2.
Briefly illustrate about oxidation pond including role of algae. State the procedure to design it with an example.
3.
Design an oxidation pond to treat 300 m³/d of sewage from a community with permissible organic loading of 450 kg/ha/d. The influent BOD is 250 mg/l and the efficiency of the pond is maintained to be 90%.
4.
Calculate detention time and dimension of an oxidation pond for a town in Terai Region of Nepal with the following data: Population = 12,000; Sewage flow = 100 lpcd; BOD of incoming sewage = 250 mg/l; Assume operational depth at 1.1 m. Draw neat sketch with necessary components showing buffer zone and detail dimensions as designed.
5.
Design an oxidation pond for a domestic wastewater with a BOD of 250 mg/l generated from a community situated in the semi-urban area of Bhaktapur for a population of 25000 to obtain permissible BOD of 25 mg/l. The maximum and minimum operation temperature of the pond in the coldest month is 24 and 8°C respectively.
Chapter 08
Sludge Treatment and Disposal
4 Hours
1.
A sewage treatment plant produces 1000 kg of dry solids per day at a moisture content of 95%. The solids are 70% volatile with a specific gravity of 1.05 and 30% non-volatile with a specific gravity of 2.5. Determine the sludge volume: a) in raw sewage; b) after digestion which reduces volatile solids content by 50% and decreases the moisture content to 90%; c) after dewatering to 75% moisture; d) after drying to 10% moisture.
2.
Write down the aims of sludge treatment. A sewage treatment plant produces sludge having a moisture content of 94% with a dry solid of 500 kg/d in which 70% solids are volatile. The specific gravity of volatile and fixed solids are 1.02 and 2.65. Assuming parabolic digestion of 30 days and 12 days of monsoon storage, calculate the volume of conventional rate digester required to produce digested sludge with a moisture content of 90%.
3.
If Suspended Solids in raw sewage is 250 mg/lit. Design a sludge digestion tank to treat sludge of primary sedimentation tank if Primary sedimentation tank removes 55% of suspended solids and the Capacity of sedimentation tank is 812.5 m³. The detention time in sedimentation tank is 3 hrs. Water content in fresh sludge = 95%, digested sludge = 80%, Specific gravity of sludge = 1.02, Digestion period in digester = 2 months.
4.
Discuss about volume moisture content relationship in sludge. Calculate the specific gravity of sludge considering 25% of solid matter in a sludge containing 95% water is composed of fixed mineral solids with specific gravity 2.65 and 75% is composed of volatile solids with specific gravity 1.0.
5.
A PST sludge only containing fixed solids of 4000 kg/d having moisture content of 60% and specific gravity of 2.6 is mixed with SST sludge only containing volatile solids of 1500 kg/d having moisture content of 95% and specific gravity of 1.2. The mixture is then conveyed in an anaerobic digester for 35 days digestion. Determine the volume of digester. Assume linear digestion and neglect the monsoon requirements.
6.
A raw sewage having suspended solids content of 220 mg/lit is passed through primary sedimentation tank at a flow of 4 MLD. The PST removes 55% suspended solids. Determine the volume of sludge produced per day if moisture content and specific gravity of sludge are 95% and 1.02 respectively. What will be the volume if its moisture content reduces to 80% after digestion? Also design a digester for sludge digestion period of 80 days.
7.
Design a sludge digestion tank to treat sludge of primary sedimentation tank from the following data: Average flow of the sewage = 6.5 MLD; Total suspended solids in raw sewage = 250 mg/l; Water content of fresh sludge = 95%; Water content of digested sludge = 85%; Specific gravity of sludge = 1.02; Digestion period = 2 months; Primary settling tank removes 55% of suspended solids.
8.
Determine the sludge volume before and after digestion and percentage reduction for 600 kg (dry basis) of primary sludge having: Solids 6% (primary) → 12% (digested); Volatile Matter 65% (digested removes 65% of volatile matter). Take specific gravity of volatile and fixed solids 1.0 and 2.5 respectively for both primary and digested sludge.
9.
What is meant by thickening? List the various methods of sludge thickening. Describe with the help of neat sketch gravity-sludge thickener.
10.
Describe aerobic and anaerobic digestion of sludge. Design a sludge digestion tank for treating sludge: Water content of fresh sludge = 95%, Water content of digested sludge = 87%, Digestion period = 30 days, No monsoon requirements, Fresh sludge form PST and SST going to digestion tank is 90 m³/d.
Chapter 09
Disposal of Sewage from Isolated Buildings
3 Hours
1.
Define Soak pit and discuss its important. Also, describe with a neat sketch about a leaching cesspool.
2.
Describe about VIP latrine. Design a septic tank for 15 users. The rate if sewage flow is 80 lpcd. Assume sludge is cleaned from septic tank once in a three year.
3.
Design a septic tank for 10 users. The rate of sewage flow is 120 lpcd. Assume sludge is cleaned from septic tank on every 2-year interval. If soil percolation rate is 20 min/cm, design the drain field to dispose the effluent.
4.
Assuming 80% contribution of water supply for the sewage, design septic tank and dispersion trenches for a house having 12 persons with an average water supply rate of 70 lpcd. The desludging period of septic tank is 3 years. The infiltration capacity of soil is 30 l/m²/d.
5.
Calculate the internal dimension of a septic tank and numbers of soak pits for an isolated hotel situated at Eastern zone of Nepal having average 80 numbers of average users. Rate of sewage discharge is 210 lpcd. Cleaning period of septic tank is 3 years. Assume other necessary data if required.
6.
Design a septic tank and soak pit for 15 users of a house at a place where infiltration capacity of soil is 100 liters per square meter per day. The peak sewage flow rate 110 lpcd and the detention time in septic tank is 1 day and sludge is cleaned at an interval of 3 years. The ground water table lies 10 m below the ground level.
7.
Calculate size of septic tank and soak pit for a residential facility in an academic institution with 200 users. For septic tank, consider sludge digestion rate of 0.0425 m³/person and volume required for storage of digested sludge 0.0708 m³/person for 2 years cleaning period.
8.
What would be the internal dimension of a septic tank and numbers of soak pits for an isolated hotel situated at mid-southern zone of Nepal having average 80 numbers of average users? Rate of sewage discharge is 210 lpcd. Cleaning period of septic tank is 3 years.
9.
If you are asked to design septic tank and soak pit for a hostel with 400 users, calculate sizes. For septic tank, consider sludge digestion rate of 0.0425 m³/person and volume required for storage of digested sludge 0.085 m³/person for 3 years cleaning period.
10.
Design VIP latrine and septic tank for a family of 10 users. The detention time for septic tank is 24 hr. Sludge is cleaned in every three years.
11.
With neat sketches, describe the purpose and construction of a skimming tank.
12.
Design a double pit VIP latrine for a family of 15 users. Assume the necessary data suitably.
13.
A household having 22 persons produces 135 liter/person/day of sewage. Design a septic tank and drain field to dispose the sewage in a soil having infiltration rate of 35 liters/m²/day. Assume that the septic tank is cleaned once in three years.
14.
Design a septic tank and soak pit to dispose the sewage generated from a household of 80 persons. The sewage is generated at the rate of 120 lit/person/day. Assume that septic tank is cleaned once in 2 years and infiltration rate of soil is 80 lit/m²/day.
Chapter 10
Solid Waste Disposal
2 Hours
1.
Describe the methods of composting for solid waste disposal.
2.
Define open dumping, dumping and sanitary landfill with suitable examples, and discuss about their potential application in our context. Also, discuss about sludge grinding and blending process with its importance on subsequent sludge treatment units.
3.
Write short note on: Need of sludge treatment with examples; Aerobic and Anaerobic digestion process; Sanitary Landfill, Landfill and Open dumping; Sludge disposal methods (Dumping, Land filling, Lagooning).
4.
Describe the methods of composting for solid waste management and its merits and demerits.
5.
Describe briefly the various methods of solid waste disposal.
6.
Explain about the solid waste disposal by incineration along with its merits and demerits.
7.
Explain sanitary land filling method for disposal of solid waste.
8.
Describe briefly about sanitary landfill with some merits.
9.
Why is separation of organic part from solid waste necessary for composting? Describe open windrow composting method of solid waste disposal.
10.
Describe briefly about open dumping and sanitary landfill.
11.
Describe incineration of solid waste with its merits and demerits.
12.
Describe the incineration method of solid waste disposal.
13.
Discuss about the solid waste composting and its methods.
