Category: WASTE WATER Engineering Objective Questions

250+ TOP MCQs on Sludge Production and Process Control and Answers

Waste Water Engineering Multiple Choice Questions on “Sludge Production and Process Control”.

1. The Activated Sludge Process is a _______ wastewater treatment process.
a) Physical
b) Chemical
c) Biological
d) Biochemical
Answer: c
Clarification: The Activated Sludge Process is a biological wastewater treatment process. This means that treatment occurs as pollutants are used as a food source by many different types of micro-organisms.

2. The measure of pH is the ______ ion concentration.
a) Iron
b) Hydrogen
c) Aluminium
d) Sodium
Answer: b
Clarification: The measure of pH is the hydrogen ion concentration. pH is used to express the intensity of the acid or alkaline condition of a solution. The scale of pH ranges from 0 to 14, with 7 being neutral. The effluent limit for pH is typically 6 to 9.0.

3. Gravity thickening can achieve up to _____ solid fraction.
a) 5%
b) 10%
c) 15%
d) 20%
Answer: b
Clarification: Typical sludge comes at 1% solid fraction. Thickening it to 2% halves the volume, to 10% reduces the volume by a factor 10. [1% solid fraction ≈ 10,000 mg/L]. Gravity thickening can achieve up to 10% solid fraction.

4. ________ is oxidized by heterotypic micro-organisms.
a) Inorganic matter
b) Inert materials
c) Organic matter
d) Water
Answer: c
Clarification: Organic matter is oxidised by heterotrophic micro-organisms to produce water and carbon-dioxide in the process known as catabolism. This process requires the availability of an electron acceptor which may be oxygen or nitrate and lead to the production of energy as ATP.

5. What is autotrophic biomass made up of?
a) Inert particulate matter
b) Endogenous residue
c) Biodegradable particle
d) Nitrifying bacteria
Answer: d
Clarification: Inert particulate COD derives from the inert particulate COD present in the influent wastewater and entering the plant. Autotrophic biomass is made up of nitrifying bacteria.

6. What is the temperature at which sludge constituting biosolids are composted?
a) 55 degree Celsius
b) 45 degree Celsius
c) 65 degree Celsius
d) 75 degree Celsius
Answer: a
Clarification: The sludge constituting biosolids is composted at 55 degree Celsius. Composting is carried out in a vessel. This can also be subjected to static aerated composting.

7. For how many days the sludge constituting biosolids is subjected to composting?
a) 1 day
b) 2 days
c) 3 days
d) 5 days
Answer: c
Clarification: Sludge constituting biosolids are treated by composting. This is usually done for 3 days. This is one of the ways to treat sludge constituting biosolids.

8. What is the final water content of sludge after dewatering?
a) 5%
b) 2%
c) 10%
d) 1%
Answer: c
Clarification: After dewatering the moisture content of the sludge is reduced to 10 percent. Dewatering can be done by heat dryers. The biosolids are heated up to 80 degree Celsius.

9. To what temperature is a sludge constituting liquid biosolids heated in order to treat it?
a) 450 degree Celsius
b) 200 degree Celsius
c) 180 degree Celsius
d) 300 degree Celsius
Answer: c
Clarification: Sludge constituting liquid biosolids is heated to 180 degree Celsius. This sludge is mixed with oxygen in order to maintain aerobic conditions. The sludge is heated for at least 30 mins.

10. At what temperature the sludge constituting biosolids is heated, when it is treated by the pasteurization method?
a) 45 degree Celsius
b) 55 degree Celsius
c) 70 degree Celsius
d) 65 degree Celsius
Answer: c
Clarification: Other than heat treated sludge constituting biosolids can be treated by pasteurization also. In this method the sludge is heated at 70 degree Celsius. This treatment is carried out at least for 30 mins.

11. What is the solid retention time assumed when the sludge constituting biosolids is treated anaerobically?
a) 7 days
b) 4 days
c) 15 days
d) 10 days
Answer: c
Clarification: The sludge constituting biosolids can be treated anaerobically also. While carrying out anaerobic treatment, the solid retention time assumed is 15 days. The temperature is maintained at 15-20 degree celsius.

12. Which of the following methods is used in both dewatering and thickening?
a) Filter press
b) Centrifuge
c) Gravity belt
d) Rotary drum
Answer: b
Clarification: Centrifuge is used for dewatering the sludge. This is also used for thickening the sludge. The other methods for dewatering sludge are done by a filter press, lagoons, sludge drying bed, belt filter press and Reed bed.

13. For a return activated sludge pump what is the type of pump preferred?
a) Plunger
b) Peristaltic pump
c) Submersible
d) Non-clog
Answer: d
Clarification: For return activated sludge non-clog type pump is preferred. The return activated sludge is very dilute and also constitutes only fine particles. The non-clog pump should be operated at very low speed for this application.

14. For removing the digested biosolids which type of pump is preferred?
a) Submersible
b) Non-clog pumps
c) Vertical turbine pump
d) Plunger pump
Answer: d
Clarification: For the removal of digested biosolids a plunger pump is preferred. Well digested biosolids are homogeneous. These contain 5-8% solids.

15. Which type of pump is preferred to remove trickling filter humus?
a) Submersible cutter pump
b) Non-clog pump
c) Vertical turbine pumps
d) Diaphragm pump
Answer: d
Clarification: The pump which is used to remove trickling filter humus is usually a diaphragm type. Humus is usually homogeneous in nature. This can usually be pumped very easily.

250+ TOP MCQs on Effluent Disposal in Septic Tanks and Answers

Waste Water Engineering Multiple Choice Questions on “Effluent Disposal in Septic Tanks”.

1. Effluent sewer is also called as ______
a) Septic tank drainage
b) Drainage
c) Septic tank effluent drainage
d) Effluent drainage
Answer: c
Clarification: Effluent sewer system is also called as Septic Tank Effluent Drainage (STED) or solids-free sewer (SFS) systems. These have septic tanks that collect sewage from residences and businesses.

2. Gravity systems are preferred over pumping systems for the flow of wastewater.
a) True
b) False
Answer: b
Clarification: Most of the solids are removed by the septic tanks, so the treatment plant can be much smaller than a typical plant. A pumping system can be used to move the wastewater rather than a gravity system as there is a vast reduction in wastewater.

3. What is the function of two tanks provided in septic tank systems?
a) Divide solids and liquid
b) Divide wastewater and water
c) Divide black and grey water
d) Store large amount of effluent
Answer: c
Clarification: Septic systems are commonly used to treat waste water. There might be one tank that combines all black and grey water or two tanks that divide the black and grey water.

4. The longer the water is held in the tank, the better the treatment.
a) True
b) False
Answer: a
Clarification: Wastewater is treated by bacteria that live in the septic tank. The longer the water is held in the tank, the better the treatment. Crowded households may produce large quantities of grey water from the constant use of the washing machine, shower and bath.

5. Large amount of wastewater constantly produced _________ the treatment time of wastewater in a septic tank.
a) Increase
b) Shorten
c) Does not alter
d) Affects
Answer: b
Clarification: If a large amount of grey water is constantly produced, it will shorten the treatment time of wastewater in the septic tank. Leaking taps, valves and toilet cisterns also increase the amount of water entering the septic system and can further reduce treatment time.

6. ______ is called effluent.
a) Water
b) Untreated wastewater
c) Treated wastewater
d) Untreated water
Answer: c
Clarification: Treated wastewater is called ‘effluent’. In some communities, the effluent is piped from each house to a collection point for further treatment and disposal. This is called a Common Effluent Drain system (CED).

7. What is the common effluent pipe from each house to a collection point called?
a) CID
b) CED
c) CSD
d) CCD
Answer: b
Clarification: In some communities, the effluent is piped from each house to a collection point for further treatment and disposal. This is called a Common Effluent Drain system (CED). Effluent disposal can also occur at the house site through absorption trenches, which consist of underground trenches that allow the water to soak into the ground.

8. ______ allow the water to soak into the ground.
a) Septic tank
b) Trenches
c) Effluent pipe
d) Evapo-transpiration
Answer: b
Clarification: Effluent disposal can also occur at the house site through absorption trenches, which consist of underground trenches that allow the water to soak into the ground.

250+ TOP MCQs on Wet Air Oxidation & Electrocoagulation and Answers

Waste Water Engineering Multiple Choice Questions on “Wet Air Oxidation & Electrocoagulation”.

1. Wet air oxidation is a form of hydrothermal treatment.
a) True
b) False
Answer: a
Clarification: Wet oxidation is a form of hydrothermal treatment. It is the oxidation of dissolved or suspended components in water using oxygen as the oxidizer. It is referred to as “Wet Air Oxidation” (WAO) when air is used.

2. The oxidation process occurs above 374˚C.
a) True
b) False
Answer: b
Clarification: In superheated water at a temperature above the normal boiling point of water (100 °C), but below the critical point (374 °C), the oxidation reactions occur.

3. In a bubble column reactor, fresh water enters from the _________of the column.
a) Bottom
b) Top
c) Side
d) Top and side
Answer: a
Clarification: Commercial systems typically use a bubble column reactor, where the air is bubbled through a vertical column that is liquid full of the hot and pressurized wastewater. Fresh wastewater enters the bottom of the column and oxidized wastewater exits the top.

4. The heat released during the oxidation is_______
a) Released into the atmosphere
b) Cooled using cooling systems
c) Used to maintain an operating temperature
d) Used as energy to boil water
Answer: c
Clarification: The heat released during the oxidation is used to maintain the operating temperature. WAO is a liquid phase reaction using dissolved oxygen in the water to oxidize wastewater contaminants. The dissolved oxygen is typically supplied using pressurized air, but pure oxygen can also be used.

5. Which form of oxygen is used in the process of wet air oxidation?
a) Molecular oxygen
b) Dissolved oxygen
c) Pure oxygen
d) Atomic oxygen
Answer: b
Clarification: WAO is a liquid phase reaction using dissolved oxygen in the water to oxidize wastewater contaminants. The dissolved oxygen is typically supplied using pressurized air, but pure oxygen can also be used.

6. What is the minimum temperature required for WAO?
a) 30˚C
b) 50˚C
c) 90˚C
d) 150˚C
Answer: d
Clarification: The oxidation reaction generally occurs at moderate temperatures of 150°-320 °C and at pressures from 10 to 220 bars. The process converts organic contaminants to carbon dioxide, water and biodegradable short chain organic acids.

7. What is the percentage of dry solid slurry that can be processed in a WAO system?
a) 1%
b) 2%
c) 3%
d) 4%
Answer: d
Clarification: The thermal conditioning occurs at temperatures of 210 – 240 °C. 4% dry solid slurry can be processed in a WAO system where it is disinfected and the treated effluent can be dewatered to 55% dry solids using a filter press.

8. What is the maximum pressure below which oxidation reactions occur?
a) 110 bar
b) 150 bar
c) 220 bar
d) 250 bar
Answer: c
Clarification: The oxidation reactions occur at temperatures of 150°C to 320°C and at pressures from 10 bars to 220 bars. Higher temperatures require higher pressure to maintain a liquid phase in the system.

9. What is the minimum feed flow rate for industrial applications of WAO?
a) 1 m3/h
b) 5 m3/h
c) 10 m3/h
d) 50 m3/h
Answer: a
Clarification: Higher temperatures require higher pressure to maintain a liquid phase in the system. The feed flow rate must be 1m3/h to 50m3/h for industrial applications for the WAO.

10. Electro-coagulation process removes bacteria.
a) True
b) False
Answer: a
Clarification: Electrocoagulation process removes emulsified oils, total suspended solids (TSS), heavy metals, emulsified oils, bacteria and other contaminants from water.

11. The cathode material corrodes during the process.
a) True
b) False
Answer: b
Clarification: An electrocoagulation reactor is made up of an electrolytic cell with one anode and one cathode. The anode material will electrochemically corrode due to oxidation, while the cathode will be subjected to passivation.

12. What is the minimum number of electrodes required for the process?
a) 1
b) 2
c) 3
d) 4
Answer: b
Clarification: The minimum number of electrodes required for the process of electro-coagulation is 2. Minimum one anode and a cathode are required for the reaction to begin. A series of electrodes are connected for better results.

13. Which among the following corrodes due to oxidation?
a) Anode
b) Cathode
c) Anode and cathode
d) Only cathode
Answer: a
Clarification: The anode material will electrochemically corrode due to oxidation, while the cathode will be subjected to passivation when it is connected to an external source.

14. The conductive metal plates are placed in ________
a) Parallel
b) Perpendicular
c) Either parallel or perpendicular
d) Neither parallel or perpendicular
Answer: a
Clarification: An EC system essentially consists of pairs of conductive metal plates in parallel, which act as monopolar electrodes. It furthermore requires a direct current power source, a resistance box to regulate the current density and a multimeter to read the current values.

15. _________ results from the oxygen and hydrogen ions that bond into the water receptor sites of emulsified oil molecules.
a) Seeding
b) Emulsion breaking
c) Bleaching
d) Complexing
Answer: b
Clarification: The oxygen and hydrogen ions that bond into the water receptor sites of emulsified oil molecules creating a water-insoluble complex separating water from oil, driller’s mud, dyes, inks and fatty acids etc. causes emulsion breaking.

16. What is the common method used for mixing of wastewater in electrocoagulation process?
a) Mechanical mixing
b) Natural mixing
c) Electrical stirrer
d) Magnetic bar stirrer
Answer: d
Clarification: The common method used for mixing of wastewater in electrocoagulation process is through the use of magnetic bar stirrer. This is placed in the bottom of the jar at the centre.

250+ TOP MCQs on Removal of Iron, Manganese and Arsenic – 2 and Answers

Advanced Waste Water Engineering Questions and Answers on “Removal of Iron, Manganese and Arsenic – 2”.

1. If the water is brown in colour it indicates the presence of which of these?
a) Iron
b) Manganese
c) Arsenic
d) Barium
Answer: a
Clarification: The presence of iron in water is usually indicated by the colour of water. This is usually brown in colour. In some cases, this is usually reddish brown in colour.

2. How is Iron removed?
a) Oxidation
b) Clarifier
c) HRSCC
d) Ultrafiltration
Answer: a
Clarification: The Iron is removed by oxidation. The iron is usually present as a ferrous compound. This is usually oxidized to ferric compounds and is precipitated out.

3. What is the safe limit for iron in the water?
a) 0.3 ppm
b) 0.5 ppm
c) 5 ppm
d) 1 ppm
Answer: a
Clarification: The safe limit for iron in water is 0.3 ppm. Excessive iron in drinking water can lead to digestive problems. This can cause nausea, vomiting etc.

4. What is the safe limit for manganese in water?
a) 0.05
b) 0.15
c) 0.2
d) 0.25
Answer: a
Clarification: The safe limit for manganese in drinking water is 0.05 ppm. According to EPA, manganese concentration is not a concern unless and until it is 10 times the safe limit concentration. Presence of manganese can be found by an impairing colour, odour and taste to the water.

5. What is the method used to delay the precipitation of oxidized manganese and iron?
a) Addition of phosphate
b) Addition of nitrate
c) Addition of hydrogen
d) Addition of chloride
Answer: a
Clarification: The method used to delay the precipitation of oxidized manganese and iron is adding phosphate. This is effective when the water contains less than 0.3 ppm of iron. This is also effective when the water contains less than 0.1ppm of manganese.

6. What is the concentration of dissolved oxygen required to oxidize 1 ppm of iron?
a) 0.14 ppm
b) 0.12 ppm
c) 0.15 ppm
d) 0.20 ppm
Answer: a
Clarification: 0.14 ppm is required to oxidize 1 ppm of iron. Ferrous compounds are oxidized to ferric compounds. This is then precipitated out.

7. What is the concentration of dissolved oxygen required to oxidize 1 ppm of manganese?
a) 0.2 ppm
b) 0.23 ppm
c) 0.30 ppm
d) 0.27 ppm
Answer: d
Clarification: 0.27 ppm is required to oxidize 1 ppm of iron. Manganese can be oxidized by chloride. This can also be oxidized by permanganate.

8. Which of these methods is not used for the removal of arsenic?
a) Activated alumina
b) Green sand
c) Coagulation by Iron hydroxide
d) Activated carbon
Answer: d
Clarification: Activated carbon is not used in the removal of arsenic. Activated alumina is one of the methods to remove arsenic. Green sand and coagulation by Iron hydroxide is also one method to remove arsenic.

9. Considering the total cost which of these is the most expensive method to remove arsenic?
a) Green sand
b) Activated alumina
c) Coagulation by Iron hydroxide
d) Tehonoarz method
Answer: a
Clarification: The most expensive method to remove arsenic is green sand. The total cost includes capital cost. This total cost also includes operational and maintenance cost and waste disposal cost.

10. Which of these is the most efficient method to remove arsenic?
a) Green sand
b) Tehonoarz
c) Coagulation by Iron hydroxide
d) Activated alumina
Answer: b
Clarification: Tehonoarz is the most efficient method to remove arsenic. Activated alumina is the second most efficient method to remove arsenic. Green sand is the least efficient method to remove arsenic.

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250+ TOP MCQs on Eco-Friendly Toilets and Answers

Waste Water Engineering Multiple Choice Questions on “Eco-Friendly Toilets”.

1. What is the amount required to build a concrete septic tank?
a) Rs 30,000
b) Rs 60,000
c) Rs 80,000
d) Rs 1,00,000
Answer: a
Clarification: Low water table means pit toilets, constructed under the government’s sanitation programme, do not work. Water collected in the pit cannot percolate down because the soil is already saturated with water. Rs 30,000-40,000 is needed to build a concrete septic tank, where water flows out into a drain instead of percolating down.

2. What is the population that lacks access to sanitation in India?
a) 100 million
b) 200 million
c) 400 million
d) 600 million
Answer: d
Clarification: In India, nearly 600 million people lack access to adequate sanitation, increasing the risk of groundwater contamination. According to the World Bank, diseases like diarrhea can kill approximately 800,000 children, under age five, every year and leaves millions malnourished and stunted.

3. What is the expected year to achieve 100% sanitation?
a) 2010
b) 2015
c) 2020
d) 2022
Answer: d
Clarification: In an effort to address this absence of sanitation, which is especially acute in rural areas that lack access to water and sewage infrastructure, the Indian government has set the target of 100% sanitation by 2022 and is working to boost cleanliness and end open defecation in the country.

4. What is the power of solar panels used in glaciers?
a) 200 watt
b) 240 watt
c) 280 watt
d) 350 watt
Answer: b
Clarification: In glaciers, temperature is around -40°C. Toilets are fitted with solar panels of 240 watt to keep the excreta warm for processing.

5. What is the average amount of water required for normal flushing?
a) 6 litres
b) 9 litres
c) 12 litres
d) 15 litres
Answer: b
Clarification: The toilet flushes itself before and after every use, using a minimum amount of water that is determined through sensors: On an average, each flush uses 1.5 litres of water, compared to the 8-10 litres used by a normal flush.

6. What is the number of chambers in UDDT toilets?
a) 2
b) 4
c) 6
d) 8
Answer: a
Clarification: EcoSan or UDDT toilets make great individual toilets for areas where digging the ground is highly complicated. UDDT is built above the ground level using conventional bricks or hollow blocks. It has two chambers – the urine, faeces and cleansing water go into separate holes.

7. What is the duration of use of each UDDT chamber?
a) 10 months
b) 12 months
c) 14 months
d) 16 months
Answer: b
Clarification: UDDT has two chambers – the urine, faeces and cleansing water go into separate holes. The floor of the chamber is also paved with concrete to prevent water or soil coming into contact with the faeces. Each chamber will be used for about 12 months alternatively.

8. What is the maximum amount of water consumption per flush to certify toilets in North America?
a) 1.5 gallons
b) 1.6 gallons
c) 1.8 gallons
d) 2.0 gallons
Answer: b
Clarification: In Canada, there is the Canadian Standards Association (CSA) and the US has the American National Standards Institute (ANSI) as well as the American Society of Mechanical Engineers (ASME). These associations set the standard for water consumption in North America and will only certify toilets which meet their requirements of 6 Litres or 1.6 gallons of water per flush.

9. Flush toilets work well because of a part called “the S bend” or “the siphon”.
a) True
b) False
Answer: a
Clarification: There is a part in flush toilets called “the S bend” or “the siphon”. This part is located within the hole at the bottom of the toilet bowl. This tube is shaped like an S and connects to the sewer plumbing under the toilet.

10. Flush toilets are said to be more sanitary than squat toilets.
a) True
b) False
Answer: b
Clarification: Squat toilets are said to be more sanitary than flush toilets as there is no contact with the toilet and it is also said to be less expensive and easier to clean and maintain.

11. What is the percentage of the world lacking access to toilets?
a) 23 %
b) 35 %
c) 42 %
d) 56 %
Answer: b
Clarification: Infrastructure and cost of conventional toilets are high. Conventional toilets are not suitable for developing countries. 35% of the world’s population lacks access to toilets.

250+ TOP MCQs on Dry Weather Flow & Variations in Rate of Sewage and Answers

Waste Water Engineering Multiple Choice Questions on “Dry Weather Flow & Variations in Rate of Sewage”.

1. What is the wastewater flow in a sewer system during the periods of dry weather with minimum infiltration called?
a) Wet weather flow
b) Dry weather flow
c) Wet flow
d) Dry flow
Answer: a
Clarification: Summers are usually dry. Hence the rainfall is minimum and is called as dry weather flow in sewers. During the rainy season or periods of high rainfall or storm, the sewers will be full and are called wet weather flow.

2. In order to determine the section of the sewer, it is essential to know the total quantity of the sewage that would flow through the sewer.
a) True
b) False
Answer: a
Clarification: The quantity of sewage that would flow in dry weather is different from the quantity of the sewer that would flow in the wet weather. Hence peak conditions must be considered and sewer size should be determined.

3. The dry weather flow is also called as sanitary sewage.
a) True
b) False
Answer: a
Clarification: Dry weather flow mainly consists of domestic sewage and industrial wastewater as the rainfall or storm is absent or less in the times of summer of dry weather. Hence dry weather flow is also called as sanitary sewage.

4. Which of the following factors does the dry weather does not depend on?
a) Rate of water supply
b) Population growth
c) Infiltration of groundwater
d) Design of sewer system
Answer: d
Clarification: Dry weather flow depends on the type of area served, rate of water supply, population growth, infiltration of groundwater. Design of sewer system is to determine the size of a sewer system in peak conditions. It has nothing to do with the factors responsible for dry weather flow.

5. Which of the following common unit is used to express the rate of water supply to a city or town?
a) Litres/capita/second
b) Litres/capita/day
c) Millilitres/capita/day
d) Millilitres/capita/hour
Answer: b
Clarification: The common unit used to express the rate of water supply to a city or town is in terms of litres per person for a day. Capita refers to each person or an individual. Hence the unit is litres/capita/day.

6. The quantity of sanitary sewage entering the sewers would be ___________ the total quantity of water supplied.
a) Less than
b) Equal to
c) More than
d) Greater than
Answer: a
Clarification: The quantity of sanitary sewerage entering the sewers would be less than the total quantity of water supplied because the water is lost in domestic consumption, evaporation, lawn sprinkling, fire fighting and industrial consumption.

7. The quantity of sanitary sewage directly depends on ______
a) Rate of water supply
b) Area
c) Population
d) Precipitation
Answer: c
Clarification: As the population increases the rate of water consumption also increases which leads to the direct increase in sanitary sewage. This also increases water demand. Hence the quantity of sanitary sewage directly depends on the population.

8. The quantity of water supply is equal to the rate of supply multiplied by the ______
a) Population
b) Quantity of sewage
c) Area
d) Net usage
Answer: a
Clarification: The rate of usage of water varies from individual to individual and different sectors. Hence the total quantity of water supplied is equal to the rate of supply multiplied by population.

9. Wet weather flow is _________ than the dry weather flow.
a) Lower
b) Higher
c) Equal to
d) Not equal to
Answer: a
Clarification: Wet weather flow is higher than the dry weather flow because of the inflow and infiltration in the sewer system. Wet weather flow is the combination of stormwater and sanitary sewage but dry weather flow consists of only sanitary sewage.

10. Dry weather flow+ storm water=_________
a) Dry weather flow
b) Stormwater
c) Wet weather flow
d) Sanitary sewage
Answer: c
Clarification: Dry weather flow is the wastewater flow in sewers during dry weather. Dry weather flow in combination with stormwater is called as wet weather flow.

11. Sewage flow rates vary by source and with a time of the day, the season of the year and weather conditions.
a) True
b) False
Answer: a
Clarification: The rate of usage of water depends on the population of a city of a country. Sewage generation in terms depends on water usage. Different cities use the quantity of water based on their needs. Hence the sewage flow rates vary by source and with a time of the day, season of the year and so on.

12. A proper assessment should be made before sewers are sized or treatment plant capacities are set.
a) True
b) False
Answer: a
Clarification: Different treatment plants produce different quantities of wastewater depending upon the water needs and usage within the industry. The quantity of wastewater in sewer depends upon the population in that area and water usage. Hence proper assessment should be made considering both peak and normal conditions.

13. What is the lowest wastewater flow in hospitals?
a) 50 gpcd
b) 700 lpcd
c) 900 lpcd
d) 40 lpcd
Answer: b
Clarification: The unit lpcd stands for litres per capita per day and gpcd stands for gallons per capita per day. 40 lpcd indicates the minimum water usage for places like kids play home and schools. 700 lpcd is for hospitals.

14. __________ in residential areas resemble water usage patterns in those areas.
a) Hydrographs
b) Sewage flow patterns
c) Dry period patterns
d) Daily flow
Answer: b
Clarification: The water usage depends upon the population, number oh houses and the type of water usage in that area. Sewage flow in turn depends upon these activities. Hence sewage flow patterns in residential areas resemble water usage patterns in those areas.

15. A graph showing discharge versus time past a specific point in a conduit carrying flow is called?
a) Water flow graph
b) Precipitation graph
c) Hydrograph
d) Variation graph
Answer: c
Clarification: A graph showing discharge versus time at a specific point in a conduit carrying flow or river is called ‘hydrograph’. Hydrograph helps in understanding the flow characteristics of water at different time intervals.