Questions
5 questions on average
Difficulty
Medium
Importance
High yield for NTPC/ONGC/IOCL
Overview
Environmental Engineering covers the treatment of water and wastewater, air quality management, and solid waste disposal protocols. It is a high-yield area in Indian PSU exams because it combines chemistry and biology with civil engineering design principles. Aspirants must master the specific treatment process sequences and the biological kinetics governing pollutant removal.
Water Treatment Processes
Water treatment involves removing contaminants through physical, chemical, and biological stages. Coagulation and flocculation are crucial for turbidity removal using chemicals like Alum.
- Optimum pH for Alum is 6.5 to 8.5
- Stokes Law defines terminal settling velocity
- Types of sedimentation tanks: Type I, II, III, and IV
- Chlorination efficiency depends on contact time and residual concentration
- Breakpoint chlorination occurs after satisfying chlorine demand
Sewage Treatment and Kinetics
Sewage treatment focuses on stabilizing organic matter measured by BOD and COD. The Activated Sludge Process (ASP) remains the most common biological treatment method for domestic sewage.
- BOD5 = Lo * (1 - 10^(-k1*t))
- COD represents chemically oxidizable organic matter
- Sludge Volume Index (SVI) indicates settling characteristics
- F/M ratio is a critical operational parameter for ASP
- Aerobic processes generally require higher oxygen transfer rates than anaerobic
Air Pollution Control
Air pollution control focuses on particulate matter (PM) removal and gas control devices. Understanding the efficiency of these devices is essential for solving numerical problems.
- Gravity settlers are effective for large particles (>50 microns)
- Cyclones use centrifugal force for particle separation
- Electrostatic Precipitators (ESP) offer high efficiency for fine particles
- Wet scrubbers remove both particulate matter and gaseous pollutants
- Lapse rate and inversion determine the stability of the atmosphere
Solid Waste Management
This subtopic deals with the collection, treatment, and disposal of solid waste including hazardous materials. Landfilling is the most prevalent disposal technique in India.
- Pyrolysis involves thermal decomposition in the absence of oxygen
- Incineration is used for volume reduction of medical and industrial waste
- Composting utilizes aerobic decomposition of organic matter
- Leachate management is the primary challenge for landfill design
- Typical Indian solid waste has high organic content and moisture
Formula Sheet
BOD5 = Lo(1 - 10^(-kt))
SVI = (Volume of sludge in ml/L) / (MLSS in mg/L) * 1000
Stokes Law: Vs = (g * (ps - pw) * d^2) / (18 * mu)
F/M = Q * So / (V * X)
Exam Tip
Memorize the treatment sequence and the specific chemical coagulants used at different pH levels, as these are the most frequently asked memory-based questions.
Common Mistakes
- Confusing the purpose of rapid sand filters versus slow sand filters regarding grain size and backwashing capability.
- Neglecting temperature corrections in BOD calculations (k_T = k_20 * theta^(T-20)).
- Mixing up the definitions of BOD5 and ultimate BOD, leading to errors in stoichiometry problems.
More Revision Notes
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