Part IX — Environmental Engineering

Chapter 9: Water Supply, Sewerage & Pollution Control

9.1 Water Supply Engineering

Water treatment for public supply typically follows the sequence: screening (removing large debris), aeration, coagulation and flocculation (using chemicals like alum to clump fine suspended particles into larger, settleable flocs), sedimentation (allowing flocculated particles to settle), filtration (commonly through slow sand or rapid sand filters, removing remaining fine particles and pathogens), and disinfection (commonly chlorination, killing remaining pathogens before distribution). Per-capita water demand estimates for Indian towns/cities are typically standardised in litres per capita per day (lpcd), varying by city size/class per CPHEEO (Central Public Health and Environmental Engineering Organisation) manual guidelines.

9.2 Sewerage Systems

A sewerage system collects and conveys used/waste water; systems are classified as combined (sanitary sewage and stormwater in one pipe network), separate (sanitary sewage and stormwater in separate networks), or partially separate. Biochemical Oxygen Demand (BOD) measures the amount of dissolved oxygen consumed by microorganisms decomposing organic matter in water over a standard period (conventionally 5 days at 20°C, hence "BOD5"), a key indicator of organic pollution load — higher BOD indicates more organic pollution and greater oxygen depletion risk for aquatic life. Chemical Oxygen Demand (COD) measures the total oxygen required to chemically oxidise both biodegradable and non-biodegradable organic matter, and is generally higher than BOD for the same sample.

9.3 Pollution and Environmental Concepts

Air pollution sources include vehicular emissions, industrial emissions, and construction dust; common pollutants include particulate matter (PM2.5, PM10), sulphur dioxide (SO2), nitrogen oxides (NOx), and carbon monoxide (CO). Global warming results from increased concentrations of greenhouse gases (notably carbon dioxide, methane, and water vapour) trapping heat in the atmosphere. Ozone layer depletion, distinct from global warming, is primarily caused by chlorofluorocarbons (CFCs) and related compounds breaking down stratospheric ozone (O3), reducing protection from harmful ultraviolet (UV) radiation. Acid rain results from sulphur dioxide and nitrogen oxide emissions reacting with atmospheric moisture to form sulphuric and nitric acids, which fall as precipitation, damaging structures, soil, and water bodies.

9.4 Practice Set — Environmental Engineering (14 MCQs)

1. In water treatment, coagulation and flocculation primarily use chemicals like alum to:
   (a) Kill pathogens directly (b) Clump fine suspended particles into larger, settleable flocs (c) Add colour to the water (d) Increase dissolved oxygen
2. The final disinfection step in water treatment is most commonly achieved through:
   (a) Sedimentation (b) Chlorination (c) Aeration only (d) Screening
3. A combined sewerage system carries:
   (a) Only sanitary sewage (b) Only stormwater (c) Both sanitary sewage and stormwater in one network (d) Neither sewage nor stormwater
4. Biochemical Oxygen Demand (BOD) is conventionally measured over a standard period of:
   (a) 1 day at 20°C (b) 5 days at 20°C (c) 10 days at 20°C (d) 30 days at 20°C
5. A higher BOD value in water generally indicates:
   (a) Lower organic pollution (b) Higher organic pollution and greater oxygen depletion risk (c) Higher dissolved oxygen availability (d) No relation to pollution levels
6. Chemical Oxygen Demand (COD), compared to BOD for the same sample, is generally:
   (a) Lower than BOD (b) Higher than BOD (c) Always exactly equal to BOD (d) Unrelated to BOD
7. CPHEEO manual guidelines are primarily used in India for standardising:
   (a) Highway pavement thickness (b) Per-capita water demand estimates (lpcd) (c) Railway gauge width (d) Concrete mix grades
8. Ozone layer depletion is primarily caused by:
   (a) Carbon dioxide emissions (b) Chlorofluorocarbons (CFCs) (c) Sulphur dioxide emissions (d) Methane emissions
9. Acid rain results from which pollutants reacting with atmospheric moisture?
   (a) Carbon dioxide and methane (b) Sulphur dioxide and nitrogen oxides (c) CFCs alone (d) Particulate matter alone
10. Global warming is primarily attributed to increased concentrations of:
    (a) Greenhouse gases (CO2, methane, etc.) trapping heat (b) Ozone in the stratosphere (c) Particulate matter alone (d) Groundwater depletion
11. Rapid sand filters and slow sand filters are used in water treatment primarily for:
    (a) Coagulation (b) Filtration, removing fine particles and pathogens (c) Disinfection only (d) Aeration only
12. PM2.5 and PM10 refer to categories of:
    (a) Dissolved oxygen levels (b) Particulate matter, classified by particle size (c) Water hardness levels (d) Sewage flow rates
13. A separate sewerage system, as distinct from a combined system, carries sanitary sewage and stormwater:
    (a) In the same single network (b) In separate networks (c) Neither is collected (d) Only stormwater is collected
14. Ozone layer depletion primarily reduces atmospheric protection from:
    (a) Visible light (b) Harmful ultraviolet (UV) radiation (c) Infrared radiation only (d) Radio waves

Answer Key

1.(b)

2.(b)

3.(c)

4.(b)

5.(b)

6.(b)

7.(b)

8.(b)

9.(b)

10.(a)

11.(b)

12.(b)

13.(b) 14.(b)