Civil Engineering 2023 Paper II 50 marks Discuss

Q7

(a) Discuss the following operational difficulties encountered in the operation of Activated Sludge process : (i) Rising Sludge or Floating Sludge (ii) Sludge Bulking What kind of impact these are having in the operation of Activated Sludge process ? 20 (b) Explain the following : (i) Specific capacity of a well (ii) Specific yield of an aquifer (iii) Perched water table (iv) Intrinsic permeability (v) Bulk pore velocity 15 (c) (i) Define Delta, Duty and Base Period, and derive the relationship among them. 7 (ii) Discuss the factors influencing the selection of site for a proposed dam. 8

हिंदी में प्रश्न पढ़ें

(a) सक्रिय अवपंक प्रक्रिया के संचालन में आने वाली निम्नलिखित कठिनाइयों की चर्चा कीजिए : (i) आरोही अवपंक या प्लवी अवपंक (ii) अवपंक का फूलना सक्रिय अवपंक प्रक्रिया के संचालन में इनका किस प्रकार का प्रभाव होता है ? 20 (b) निम्नलिखित की व्याख्या कीजिए : (i) कुएँ की विशिष्ट क्षमता (ii) जलभृत का विशिष्ट उत्सर्जन (iii) अध्यासीन भौम जल स्तर (iv) नैज पारगम्यता (v) पुंज छिद्र गति 15 (c) (i) कृति (ड्यूटी), डेल्टा और आधार काल को परिभाषित कीजिए और उनके बीच के सम्बन्ध को व्युत्पन्न कीजिए । 7 (ii) एक प्रस्तावित बांध के स्थान के चुनाव को प्रभावित करने वाले कारकों की चर्चा कीजिए । 8

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Directive word: Discuss

This question asks you to discuss. The directive word signals the depth of analysis expected, the structure of your answer, and the weight of evidence you must bring.

See our UPSC directive words guide for a full breakdown of how to respond to each command word.

How this answer will be evaluated

Approach

The directive 'discuss' in part (a) demands critical examination with causes, effects and remedies; parts (b) and (c) require 'explain' and 'define/derive' respectively. Allocate approximately 40% time/words to part (a) given its 20 marks weightage, 30% to part (b) for 15 marks, and 30% to part (c) for 15 marks. Structure: brief introduction on activated sludge process relevance → systematic treatment of each sub-part with definitions, mechanisms, impacts/diagrams → concluding synthesis on operational challenges in Indian STPs.

Key points expected

  • Part (a)(i): Rising/floating sludge — denitrification mechanism (NO₃⁻ → N₂ gas bubbles), sludge density reduction, identification by sludge volume index, remedies like increasing sludge wasting or reducing MLSS
  • Part (a)(ii): Sludge bulking — filamentous bacteria (Sphaerotilus, Thiothrix) vs. floc-forming bacteria competition, low DO/high F/M ratio causes, SVI>150 mL/g indicator, control by chlorination or selector basins
  • Part (b): Specific capacity (Q/s, m³/day/m), specific yield (Sy = ΔV/Δh·A, dimensionless), perched water table (localized saturated zone above main aquitard), intrinsic permeability (k, m², fluid-independent), bulk pore velocity (v = K·i/n, actual interstitial velocity)
  • Part (c)(i): Delta (Δ, depth of water required), Duty (D, area irrigated per cumec), Base Period (B, crop duration); derivation: Δ = 8.64·B/D in cm, with unit consistency demonstration
  • Part (c)(ii): Dam site factors — narrow gorge with wide upstream valley, sound foundation rock, adequate catchment, sediment-free water, proximity to demand, seismic stability, environmental/social acceptability (cite Tehri or Sardar Sarovar context)

Evaluation rubric

DimensionWeightMax marksExcellentAveragePoor
Concept correctness25%12.5Precise definitions across all sub-parts: correctly identifies denitrification for rising sludge, filamentous bacteria dominance for bulking, distinguishes specific capacity from specific yield, and accurately describes perched water table as discontinuous saturation; dam site factors include geological and hydrological considerations with Indian examplesGenerally correct definitions with minor errors (e.g., conflating specific capacity with specific yield, or describing rising sludge only as 'gas formation' without specifying denitrification); misses perched water table's discontinuous natureFundamental conceptual errors: describes sludge bulking as 'excess sludge production', confuses intrinsic permeability with hydraulic conductivity, or defines delta/duty/base period incorrectly; dam factors limited to vague 'strong foundation'
Numerical accuracy15%7.5Correct unit handling in Δ = 8.64·B/D derivation with proper conversion (cumec to m³/day, hectares to m²); accurate numerical relationships in specific capacity calculations; dimensionless treatment of specific yieldCorrect final formula for delta-duty-base period but missing intermediate unit conversion steps; acceptable numerical treatment but lacks explicit demonstration of 8.64 factor derivationIncorrect numerical derivation (e.g., Δ = B/D without 8.64), wrong units (specific yield with units of m/day), or arithmetic errors in any quantitative expression; omits numerical treatment entirely
Diagram quality20%10Clear labeled diagrams: activated sludge process schematic showing sludge blanket for (a); perched water table cross-section with main water table, aquitard, and localized saturation for (b)(iii); dam site geological cross-section showing narrow gorge, abutments, and foundation for (c)(ii)Adequate diagrams with most labels present but missing critical elements (e.g., perched water table without clear aquitard indication, or dam site without foundation detail); hand-drawn acceptable but less preciseMissing essential diagrams (particularly for perched water table and dam site), or diagrams present without labels; diagrams confused (e.g., showing confined aquifer instead of perched water table)
Step-by-step derivation20%10Systematic derivation for Δ = 8.64·B/D: starting from volume balance (Δ·A = Q·B), substituting Q = D·A/8.64×10⁴ with proper unit conversions (1 cumec = 86400 m³/day, 1 ha = 10⁴ m²), clear algebraic manipulation to final dimensionally consistent formulaPresents final formula with partial derivation steps; shows volume balance concept but skips explicit unit conversion demonstration or has condensed algebraic stepsStates formula without derivation, or incorrect derivation with unit inconsistencies; derivation attempted but logically flawed (e.g., incorrect volume balance setup, missing base period incorporation)
Practical interpretation20%10Contextualizes activated sludge operational difficulties with Indian STP experiences (e.g., bulking in tropical climates, power failure impacts on DO); relates specific capacity to well design in alluvial aquifers of Indo-Gangetic plains; dam site selection references specific projects (Tehri, Bhakra, Sardar Sarovar) with lessons on seismicity and rehabilitationGeneric practical mentions without specific Indian context; acknowledges operational impacts but limited to textbook statements; dam factors listed without project-based illustrationNo practical interpretation; purely theoretical treatment; or irrelevant examples (non-Indian, non-civil engineering contexts); fails to connect perched water table to drilling hazards or specific yield to groundwater sustainability

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