Environmental Engineering–II (NCE-602 / ECE-602)
Complete Section-Wise Explanation – B.Tech Semester VI
Introduction to the Subject
Environmental Engineering–II mainly deals with water supply engineering and wastewater engineering. The subject explains how drinking water is treated, how wastewater is collected and treated, and how sludge is safely disposed of without harming the environment or public health.
This subject is very practical and directly connected to real-life public health engineering systems, such as:
Sewage treatment plants Water treatment plants
Sludge treatment and disposal systems Natural and advanced wastewater treatment methods
The paper is divided into three sections: A, B, and C, and students must attempt all sections as instructed.
SECTION A – Basic Concepts & Definitions
Pattern:
Attempt all questions
10 questions × 2 marks = 20 marks
Nature of Section A
Section A checks your basic conceptual clarity. Questions are short and definition-based, so answers should be brief, precise, and technically correct. This section is usually scoring if concepts are clear.
Explanation of Section A Questions
Impact of Oxygen Demanding Waste on Surface Water
Oxygen demanding waste consumes dissolved oxygen present in water bodies. This leads to depletion of DO, causing stress or death of aquatic life and resulting in foul odors and anaerobic conditions.
Theoretical Oxygen Demand (ThOD)
ThOD is the total amount of oxygen required to completely oxidize organic matter present in wastewater into carbon dioxide, water, and other stable products.
Objectives of Grit Removal
Grit removal aims to remove heavy inorganic particles like sand and gravel to prevent abrasion of pumps, clogging of pipes, and accumulation in treatment units.
Backwashing
Backwashing is the process of cleaning filters by reversing the flow of water to remove trapped impurities from the filter media.
Significance of GLSS in UASB
Gas–Liquid–Solid Separator (GLSS) separates biogas, treated effluent, and sludge, ensuring efficient anaerobic digestion and preventing washout of biomass.
Role of Acetogenic Bacteria
Acetogenic bacteria convert complex organic acids into acetic acid, hydrogen, and carbon dioxide, which are essential for methane formation.
Unit Operations vs Unit Processes
Unit operations involve physical treatment methods like screening and sedimentation, while unit processes involve chemical or biological reactions like coagulation and biological oxidation.
Solids Retention Time in Extended Aeration
SRT controls microbial population and ensures complete oxidation of organic matter with minimum sludge production.
Role of Algae in Aerobic Pond
Algae produce oxygen through photosynthesis, supporting aerobic bacteria in the oxidation of organic matter.
Factors Affecting Settling of Discrete Particles
Settling depends on particle size, shape, density, viscosity of fluid, and turbulence.
SECTION B – Descriptive & Design-Oriented Questions
Pattern:
Attempt any three questions
3 × 10 marks = 30 marks
Nature of Section B
This section tests your theoretical understanding and design ability. Answers must be written in paragraph form, with diagrams and calculations wherever required.
Explanation of Section B Questions
Indicator Organisms
Indicator organisms are used to assess the presence of pathogens in water. An ideal indicator should be present whenever pathogens exist, should not multiply in water, and should be easy to detect. Coliform bacteria, especially E. coli, most closely satisfy these characteristics.
Use of Coagulants in Sewage Treatment
Coagulants destabilize colloidal particles, allowing them to aggregate and settle. Common coagulants include alum, ferric chloride, and lime. Their effectiveness depends on dosage, pH, and mixing conditions.
Water Softening & Adsorption
The soda lime process is economical but produces sludge, while ion exchange gives high-quality water but is costly.
Adsorption is the accumulation of substances on a surface. Activated carbon is highly porous and treated to increase surface area, enhancing adsorption capacity.
Design of Grit Chamber
This design problem involves calculating dimensions based on flow velocity, detention time, and particle size. A schematic diagram of the grit chamber is essential to score full marks.
Design of Septic Tank and Dispersion Trench
This question tests wastewater treatment at small scale. Septic tank design involves volume calculation based on population, sewage flow, and desludging period. The dispersion trench size is designed to safely dispose effluent into soil.
SECTION C – Advanced Theory & Numericals
Pattern:
Attempt any one part from each question
5 questions × 10 marks = 50 marks
This section has the maximum weightage and strongly influences final scores.
Question 3
Carbonaceous BOD and Nitrogenous Oxygen Demand
Carbonaceous BOD represents oxygen required to oxidize organic carbon. Nitrogenous demand is inhibited using chemical inhibitors to ensure accurate BOD measurement.
First-Order BOD Reaction Numerical
This numerical applies first-order kinetics to calculate remaining organic matter after a given time using decay constant.
Question 4
Design of Plain Sedimentation Tank
This involves calculating surface overflow rate, settling velocity using Stoke’s law, and determining tank dimensions.
Design of Clariflocculator
Clariflocculator combines coagulation, flocculation, and sedimentation. Design includes flocculation time, tank diameter, and weir loading.
Question 5
Design of Rapid Sand Filter
This design problem involves determining number of filter units, area, backwash requirements, and layout of under-drainage system.
Head Loss Through Filter Bed
This numerical uses bed properties and hydraulic parameters to calculate head loss across the filter media.
Question 6
Anaerobic Digester Design & Sludge Drying Beds
This numerical involves calculating digester volume based on sludge quantity, digestion period, and storage requirements. Sludge drying beds are designed based on solids loading rate.
Trickling Filters
Trickling filters are classified based on loading rates. Biofilm formation and mass transfer are explained with a neat sketch.
Question 7
Natural Treatment Technologies
Duckweed ponds, vermiculture, and root zone technologies are eco-friendly wastewater treatment methods using natural biological processes.
Sludge Digestion and Disposal
Sludge digestion stabilizes organic matter. Aerobic and anaerobic digesters are explained, along with disposal methods like land application, incineration, and landfilling.
