GATE Environmental Engineering Water & Wastewater Treatment and Management Syllabus

Water & Wastewater Treatment and Management syllabus — full chapter and topic list

Expand any chapter to see its topics and sub-topics. This is the whole examinable outline for Water & Wastewater Treatment and Management in GATE Environmental Engineering, not a summary of it.

1. 1

   Water and Wastewater Quality Parameters

   2 topics

   • Eutrophication and Thermal Stratification in Lakes
   • River Pollution - Oxygen Sag Curve
2. 2

   Water Treatment Methods

   6 topics

   • Screening
   • Sedimentation with and without Coagulation
   • Filtration
   • Desalination
   • Disinfection
   • Water Distribution and Storage
3. 3

   Wastewater Management

   10 topics

   • Point and Non-point Sources of Wastewater
   • Population Forecasting Methods
   • Design of Sewer and Storm Water Sewers
   • Sewer Appurtenances
   • Preliminary Sewage Treatment
   • Primary Sewage Treatment
   • Secondary Sewage Treatment
   • Tertiary Sewage Treatment
   • Sludge Generation, Processing, and Disposal Methods
   • Sewage Farming
4. 4

   Industrial Effluents

   3 topics

   • Sources and Characteristics of Industrial Effluents
   • Concept of Common Effluent Treatment Plants (CETP)
   • Wastewater Recycling and Zero Liquid Discharge
5. 5

   Kinetics and Reactor Design

   5 topics

   • Mass and Energy Balance
   • Order and Rate of Reactions
   • Batch Reactors
   • Completely Mixed Flow Reactors
   • Plug Flow Reactors

Water & Wastewater Treatment and Management flashcards for GATE Environmental Engineering

19 of 61 cards from the Water & Wastewater Treatment and Management deck — real questions with worked answers.

1. What is eutrophication of a lake?

   The process by which a water body becomes enriched with nutrients (mainly nitrogen and phosphorus), stimulating excessive growth of algae and aquatic plants, leading to algal blooms, oxygen depletion on decay, and degradation of water quality. Phosphorus is usually the limiting nutrient.

2. During summer thermal stratification of a deep lake, name the three layers from top to bottom and the transition zone.

   Epilimnion (warm, well-mixed, less dense top layer), Metalimnion containing the thermocline (zone of rapid temperature decrease), and Hypolimnion (cold, dense, stagnant bottom layer).

3. What is the thermocline in a stratified lake?

   The transition layer (within the metalimnion) where temperature drops sharply with depth, typically taken as a temperature gradient greater than $1^{\circ}\text{C}$ per metre. It acts as a barrier preventing mixing between the epilimnion and hypolimnion.

4. When do lake overturns (complete mixing) typically occur in temperate lakes?

   During spring and autumn (fall turnover), when surface and bottom water temperatures equalize (water density is maximum near $4^{\circ}\text{C}$), destroying stratification and allowing wind-driven complete vertical mixing of the lake.

5. In the Streeter–Phelps oxygen sag analysis, what does the dissolved oxygen deficit $D$ represent?

   The difference between the saturation DO concentration and the actual DO concentration at a point: $D = DO_{sat} - DO_{actual}$.

6. State the Streeter–Phelps equation for the DO deficit $D_t$ at time $t$ downstream.

   $$D_t = \frac{k_d L_0}{k_r - k_d}\left(e^{-k_d t} - e^{-k_r t}\right) + D_0\, e^{-k_r t}$$ where $k_d$ is deoxygenation rate, $k_r$ is reaeration rate, $L_0$ is initial BOD, and $D_0$ is initial deficit.

7. Give the expression for the critical time $t_c$ at which the maximum DO deficit occurs on the oxygen sag curve.

   $$t_c = \frac{1}{k_r - k_d}\ln\left[\frac{k_r}{k_d}\left(1 - \frac{D_0(k_r - k_d)}{k_d L_0}\right)\right]$$

8. At the critical point of the oxygen sag curve, what is the relationship between rate of deoxygenation and rate of reaeration?

   They are equal in magnitude. The DO is minimum, so $\frac{dD}{dt}=0$, giving $k_d L_t = k_r D_c$, i.e. the critical deficit $D_c = \frac{k_d}{k_r}L_t = \frac{k_d}{k_r}L_0 e^{-k_d t_c}$.

9. What is the self-purification of a river?

   The natural process by which a polluted stream recovers its quality through dilution, sedimentation, sunlight, reaeration (atmospheric oxygen transfer), and biological oxidation of organic matter, restoring dissolved oxygen and reducing pollutant load downstream.

10. What is the purpose of screening in water/wastewater treatment, and name the screen types by bar spacing?

    Screening removes large floating and suspended solids to protect downstream equipment. Coarse screens (bar racks) have openings of $50$–$100\,\text{mm}$; medium screens $20$–$50\,\text{mm}$; fine screens $6$–$20\,\text{mm}$ (or microscreens $<6\,\text{mm}$).

11. Differentiate the four classes (Types I–IV) of sedimentation.

    Type I: discrete particle settling (dilute, no interaction, e.g. grit chambers). Type II: flocculant settling (particles aggregate, e.g. coagulation tanks, primary clarifiers). Type III: hindered/zone settling (concentrated suspension settles as a mass). Type IV: compression settling (sludge thickening at the bottom).

12. State Stokes' law for the terminal settling velocity of a discrete spherical particle in the laminar (Type I) regime.

    $$v_s = \frac{g\,(\rho_s - \rho_w)\,d^{2}}{18\,\mu}$$ where $d$ is particle diameter, $\rho_s$ and $\rho_w$ are particle and water densities, $\mu$ is dynamic viscosity, and $g$ is gravitational acceleration.

13. What is the surface overflow rate (SOR) of a settling tank and its significance?

    $$SOR = \frac{Q}{A_{surface}}$$ It equals the settling velocity of the smallest particle that is 100% removed in an ideal tank. Particles with $v_s \geq SOR$ are fully removed; removal is independent of tank depth (ideal Type I).

14. In an ideal sedimentation tank, what fraction of particles with settling velocity $v_p < v_s$ (overflow rate) is removed?

    The removal fraction equals the ratio $\dfrac{v_p}{v_s}$ (where $v_s = Q/A$), assuming uniform distribution of particles at the inlet.

15. Why is coagulation used before sedimentation, and what does a coagulant do?

    Coagulation destabilizes fine colloidal particles (which have very low settling velocities) by neutralizing their negative surface charges using a coagulant (e.g. alum), allowing them to aggregate during flocculation into larger, heavier flocs that settle rapidly in Type II sedimentation.

16. Write the simplified reaction of alum with the natural alkalinity of water during coagulation.

    $$\ce{Al2(SO4)3\cdot 14H2O + 3Ca(HCO3)2 -> 2Al(OH)3(v) + 3CaSO4 + 6CO2 + 14H2O}$$ The insoluble $\ce{Al(OH)3}$ floc enmeshes colloidal particles. Each mole of alum consumes alkalinity and produces $\ce{CO2}$.

17. Compare slow sand filters and rapid sand filters on filtration rate and pretreatment.

    Slow sand filters: rate $0.1$–$0.4\,\text{m}^3/\text{m}^2/\text{h}$ (i.e. $\sim2$–$5\,\text{m/day}$), no coagulation needed, cleaned by scraping top layer. Rapid sand filters: rate $\sim 4$–$6\,\text{m}^3/\text{m}^2/\text{h}$ ($\sim100$–$150\,\text{m/day}$), require prior coagulation–sedimentation, cleaned by backwashing.

18. What is the schmutzdecke in a slow sand filter?

    A biologically active gelatinous layer of algae, bacteria, plankton and organic matter that forms on the top surface of the sand bed. It is largely responsible for the high purification efficiency (including pathogen removal) of slow sand filters and is removed during scraping for cleaning.

19. What is the purpose of backwashing a rapid sand filter and how does the bed behave?

    Backwashing reverses clean water flow upward at high velocity to fluidize and expand the sand bed, dislodging trapped impurities (turbidity) which are washed out. It is triggered when head loss becomes excessive or effluent quality deteriorates. Air scour may assist.

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