Course: Wastewater Management Prof. M. M. Ghangrekar Questions 1
1. Describe advantages and disadvantages offered by the water carriage system. 2. What are the possible adverse effects when untreated or partially treated sewage is discharged to the environment? 3. Why it is necessary to treat wastewater before disposal? What is the objective of the sewerage works? 4. Define sewage, sullage, sewer, and sewerage. 2
1. Describe in brief various types of water carriage systems. 2. Describe merits and drawback of separate system, partially separate system and combined system. 3. What are the considerations while finalizing the type of sewerage system? 4. Write about various patterns of collection system. 3
1. What should be properties of the material to be used for sewer construction? 2. Write a note on different materials used for sewer construction. 3. With schematic describe various shapes used for sewer section. 4. What are the advantages and drawback of the circular section sewers? 4
1. Write about evaluation of design discharge for sanitary sewage. 2. What is dry weather flow? 3. Describe variation in sewage flow. How design of different component of sewerage scheme will be affected due to this variation? 4. What is design period? It depends on what parameters? Provide design period for different components of the sewerage scheme. 5
1. Explain different methods of population forecasting. 2. The population data for a town is given below. Find out the population in the year 2021, 2031 and 2041 by (a) arithmetical (b) geometric (c) incremental increase methods. Year 1971 1981 1991 2001 2011 Population 84,000 1, 15,000 1, 60,000 2, 05,000 2, 50,000 3. In three consecutive decades the population of a town is 40,000; 100,000 and 130,000. Determine: (a) Saturation population; (b) Equation for logistic curve; (c) Expected population in next decade. 6
1. Explain the factors affecting the storm water discharge. 2. What is time of concentration? What is its role in determination of the storm water runoff? 3. Explain critical rainfall duration. Why rainfall of this duration will generate maximum runoff? 4. Write short notes on the estimation of storm water runoff. 5. What is coefficient of runoff? 6. A catchment is having total area of 60 hectares. The rainfall intensity relation with duration for this catchment is given by the relation I = 100/(t+20), where I is in cm/h and t is duration of rain in min. (a) Draw the graph of rainfall intensity relation with duration at 10 min interval? (b) What will be the storm water runoff from this catchment if the average imperviousness factor is 0.63, and time of concentration is 35 min? (c) If population density of the area is 350 persons per hectare and water consumption is 170 LPCD, what will be the design discharge for separate system and combined system? 7
1. A 900 m long storm sewer collects water from a catchment area of 40 hectares, where 35% area is covered by roof (C=0.9), 20% area by pavements (C=0.8) and 45% area is covered by open plots (C=0.15). Determine the average intensity of rainfall and diameter of storm water drain. Assume the time of entry = 3 min; velocity at full flow = 1.45 m/sec; gradient of sewer = 0.001, and roughness coefficient = 0.013. The intensity of rainfall, cm/h = 75/(t + 5). 2. Explain the importance of considering minimum and maximum velocity while designing the sewers. 3. Explain Self-cleansing velocity. 4. Explain important consideration while finalizing alignment and bed line of storm water drain. 5. Find the gradient required in sewer of 0.5 m diameter to maintain self cleansing velocity at flow full condition. 6. Write short notes on laying of sewer pipes. What hydraulic tests are conducted on the sewers? 7. Prepare notes on sewer maintenance. 8
1. Define sewer appurtenances. What are the appurtenances used in sewerage? 2. Describe different types of Manholes used in collection system. 3. When the drop manhole is used in sewers? 4. Describe different types of storm water inlets used in collection system. 5. Why flow regulator device is used in sewers? Describe different types of regulators used. 9
1. Describe when pumping station will be required in sewerage scheme. 2. How pumping of sewage is different than pumping fresh water? 3. Write short notes on pumps used in sewage pumping and capacity of pumps required to be installed at pumping stations. 4. Prepare short notes on specific speed of the centrifugal pumps. 5. Describe the criteria for selection of site for pumping station. What are the facilities/accessories required in the pumping station? 6. Describe different types of pumping stations and the types of pumps used in each. What is the basis for deciding the capacity of the wet well? 10
1. Explain different types of water pollutants. 2. What are the adverse effects on the receiving water body when these pollutants are discharged in water along with effluents? 3. Describe thermal pollution. How it is caused? 11
1. Explain objectives of conducting BOD test. 2. Explain BOD reaction rate constant and parameters on which it is dependent. 3. Draw a curve for BOD exerted and remaining with respect to time for organic wastewater and derive mathematical expression for both. 4. Why only about 60% BOD is satisfied during BOD test determination, whereas during actual wastewater treatment in aerobic process more than 90% of BOD can be removed during 5 to 6 hours of retention time in biological reactor? 5. BOD of a sewage incubated for 3 days at 27oC was measured 110 mg/l. Calculate BOD5 at 20oC. Consider k = 0.23 per day (base e) and temperature coefficient =1.047. 6. Describe nitrification during BOD test. 7. Explain correlation between BOD, BODu and COD for sewage. 12
1. Explain factors affecting self purification of natural streams. 2. What is reoxygenation? What are the factors that affect reoxygenation? 3. Derive Streeter-Phelps equation for oxygen sag analysis. 4. A river is having discharge of 22 m3/s receives wastewater discharge of 0.5 m3/s. The initial DO of the river water is 6.3 mg/l, and DO content in the wastewater is 0.6 mg/l. The five day BOD in the river water is 3 mg/l, and the wastewater added to river has five day BOD of 130 mg/l. Consider saturation DO of 8.22 mg/l and deoxygenation and reoygenation constant values of 0.1 and 0.3 per day, respectively. Find critical DO deficit and DO in the river after one day. The average velocity of flow in the stream after mixing of wastewater is 0.18 m/sec. 4. A municipal wastewater treatment plant discharges secondary effluent to a river. The worst condition occurs in the summer when the treated wastewater in summer is found to have a maximum flow rate of 10000 m3/day, a BOD5 of 30 mg/l, dissolved oxygen concentration of 1.5 mg/l and temperature of 25oC. At upstream of the disposal point the minimum flow in the stream is 0.65 m3/sec with BOD5 of 3.0 mg/l, dissolved oxygen concentration of 7.0 mg/l and temperature of 22oC. The mixing of wastewater and stream is almost instantaneous at the point of disposal and velocity of the mixture is 0.2 m/sec. The reaeration constant is estimated to be 0.4 per day at 20oC temperature. Determine the critical DO deficit and distance at which it will occur. Also draw the dissolve oxygen profile for 100 km downstream of the river from the point of discharge. 13
1. Describe broad characteristics of the untreated sewage. 2. What are the factors that are responsible for changing characteristics of sewage from place to place? 3. What are the pollutants that should be removed before the sewage is considered safe for discharging back to water body? 4. Describe the classification of the water treatment methods. 5. Describe different reactor types used in biological treatment of wastewaters. 6. What is the objective of primary and secondary treatment of sewage? 7. What is secondary treatment of sewage? What types of reactors are used to facilitate this treatment? 8. What is excess sludge generation in secondary treatment? How this sludge is disposed off? 14
1. Describe types of screens used in wastewater treatment. 2. Discuss classification of screens and state application of each class. 3. With schematic describe how double chamber bar screen channels can be arranged? For what discharge each of them will be designed? 4. Describe design guidelines for the bar racks. 5. Determine head loss through a bar screen when it is 50% clogged. The approach velocity of wastewater in the channel is 0.6 m/sec, velocity of flow through the clear rack is 0.8 m/sec. Clear opening area in the screen is 0.2 m2. Consider flow coefficient for clogged bar rack as 0.6. 15
1. Why separate grit chamber is provided before primary sedimentation tank in sewage treatment plant? 2. Describe different types of grit chambers. 3. Describe square grit chamber. 4. Design a rectangular grit chamber and square grit chamber for treatment of sewage with average flow of 8.5 MLD and peak flow factor of 2.25. 5. Prepare notes on vortex type grit chamber. 16
1. Describe flocculant settling. 2. What is the purpose of providing primary sedimentation tank in wastewater treatment? What is the expected BOD and SS removal is primary sedimentation tank? 3. What are the parameters which will govern performance of PSTs? 4. Describe design guidelines for primary sedimentation facilities. 5. Design circular and rectangular PST for treatment of 4 MLD of average sewage flow with peaking factor of 2. 17
1. Describe equalization. Under what circumstances this is provided? How the volume of the equalization basin is estimated? 2. What will be ideal location for the equalization basin in wastewater treatment plant? Give justification for suggested location. 3. Draw schematic of the skimming tank and explain the purpose of providing it and how removal of pollutant occurs in this tank. 4. What are the advantages of providing flocculation and pre-aeration to wastewater? 18
1. Why aerobic processes produce more sludge as compared to anaerobic process? 2. With the help of figure explain how the rate of metabolism and hence the growth phase will vary with changes in food to microorganisms ratio in case of continuously feed biological reactor. 3. Explain nutritional requirements for bacterial metabolism. 4. Describe the types of microbial metabolism used in wastewater treatment. 19
1. Describe different types of settling. 2. Explain hindered settling. How the area required for sedimentation is worked out on the single batch test result? 3. Prepare notes on different types of settling occurring in treatment of wastewaters. 4. Explain the purpose of providing secondary sedimentation. 5. Design secondary sedimentation tank for the industrial effluent treatment plant employing completely mixed ASP. The MLVSS in aeration tank is 3500 mg/l and average annual wastewater flow rate is 500 m3/d. However in summer the wastewater generation is 1.5 times the annual average. Consider MLVSS/MLSS = 0.8. 20
1. What are the means by which the nuisance conditions associated with untreated sludge can be eliminated? 2. Describe advantages of sludge thickening and explain gravity thickening. 3. Describe sludge thickening by air floatation unit. 4. Why it is necessary to digest the sludge generated from sewage treatment plant before disposal? 5. Explain anaerobic and aerobic digestion of the sludge. 6. Stating necessity, describe sludge conditioning. 7. With the help of sketch, explain two stage digester. 8. What are different types of anaerobic digesters? Describe it with sketch. 9. Design a low rate digester for waste sewage sludge generated from aerobic secondary treatment of sewage generated from 40000 persons. The fresh sludge has 0.13 kg dry solids/capita.day (VS = 70 % of ds). The dry solids (ds) is 5% of the sludge and specific gravity is 1.01. During digestion 2/3 of VS are destroyed and fixed solids are remaining unchanged. The digested sludge has 6% ds and a wet specific gravity is 1.03. Operating temperature of digester is 320C for which the digestion time of 25 days is required. Consider sludge storage time of 50 days. Determine the digester volume required. 10. Design a sludge drying bed for drying 400 m3/d of sewage sludge. Provide detail specifications for the bed. 11. Describe various options available for final disposal of the dewatered sludge. 12. Design high rate digester for ASP for a city of total population of 30000 generating sewage. The feed to the digester (primary and secondary sludge) is 56.1 m3/day for the operating temperature of 34oC. Determine the volume of the digester. 21
1. Explain the precautions to be taken for environmentally safe onsite sanitation. 2. Design a septic tank for the group housing scheme of total population of 300 persons. The probable peak discharge will be 720 L/min. Also design a soil absorption system for the disposal of septic tank effluent considering the average percolation rate of 6 mm/min. 3. Describe septic tank. State advantages and disadvantages of the septic tank. 4. Describe pit privy and aqua privy. Under what circumstances they will be used? 5. Where bore hole latrines will be used? Explain the construction features of these types of latrines. 22