(SEM VI) THEORY EXAMINATION 2021-22 ENVIRONMENTAL ENGINEERING

ENVIRONMENTAL ENGINEERING (KCE603)

Section-wise Detailed Answers – As per B.Tech Semester VI Examination Pattern

SECTION A

(Attempt all questions – descriptive answers)

Q1(a) Define “per capita demand”

Per capita demand is the average quantity of water required per person per day for all purposes such as domestic use, industrial use, commercial activities, public services, fire demand, and losses. It is usually expressed in litres per capita per day (lpcd). This value forms the basis for designing water supply schemes, as it helps estimate the total water requirement of a community.

Q1(b) Define “Design Period”

Design period refers to the future time span for which a water supply or wastewater system is planned to serve adequately without major modification. It depends on factors such as population growth, economic development, life of structures, and ease of expansion. Different components of a system may have different design periods based on their durability and cost.

Q1(c) Explain the function of distribution reservoir

A distribution reservoir is a storage structure located near the area of consumption. Its primary function is to balance variations between water supply and demand. During low-demand hours, excess water is stored, and during peak demand, water is supplied from the reservoir. It also helps maintain adequate pressure in the distribution system and provides emergency storage during power failure or breakdowns.

Q1(d) What is ‘Reservoir yield’?

Reservoir yield is the maximum quantity of water that can be supplied continuously from a reservoir during a specific period under given conditions. It depends on factors such as rainfall, catchment characteristics, storage capacity, evaporation losses, and sedimentation. Yield analysis ensures that the reservoir can meet water demands even during dry periods.

Q1(e) What guidelines EPA has set for suspended solids?

The Environmental Protection Agency (EPA) has prescribed limits for suspended solids in water and wastewater to protect public health and the environment. Suspended solids should be maintained within permissible limits to prevent turbidity, clogging of filters, and harm to aquatic life. Excess suspended solids reduce light penetration in water bodies and interfere with biological treatment processes.

Q1(f) Define ‘dissolved material’

Dissolved material refers to substances present in water in molecular or ionic form that cannot be removed by simple filtration. These materials include salts, minerals, and organic compounds. Dissolved materials affect taste, hardness, conductivity, and chemical quality of water.

Q1(g) Differentiate between Unit Operation and Unit Process

Unit operations involve physical treatment methods such as screening, sedimentation, filtration, and aeration where no chemical or biological reactions occur. Unit processes involve chemical or biological reactions, such as coagulation, disinfection, and biological oxidation. Both are combined in treatment plants to achieve effective purification.

Q1(h) Difference between “Disinfection” and “Sterilization”

Disinfection is the process of destroying harmful microorganisms to a safe level but not necessarily eliminating all organisms. It is commonly used in water treatment using chlorine. Sterilization, on the other hand, is the complete destruction of all forms of life, including spores. Sterilization is not generally required for water supply systems.

Q1(i) Explain aerobic decomposition

Aerobic decomposition is the biological breakdown of organic matter in the presence of oxygen. Microorganisms oxidize organic substances into stable end products such as carbon dioxide, water, and nitrates. This process releases energy and is widely used in wastewater treatment methods like activated sludge and trickling filters.

Q1(j) Define wastewater treatment
 

Wastewater treatment is the process of removing physical, chemical, and biological contaminants from sewage or industrial effluents to make it safe for disposal or reuse. It involves preliminary, primary, secondary, and sometimes tertiary treatment stages to protect public health and the environment.

SECTION B

(Attempt any three – detailed explanations)
 

Q2(a) Explain the suitability of population forecasting methods
 

Population forecasting is essential for planning water supply systems. Different methods are suitable for different conditions. The arithmetic increase method is suitable for cities with uniform growth. The geometric increase method applies where population growth is proportional to existing population. The incremental increase method considers changing growth rates and is suitable for moderately growing cities. The logistic curve method is applicable for cities approaching saturation. Selection depends on past growth trends and future development prospects.
 

Q2(b) Explain with neat sketch any one type of surface reservoir
 

A gravity surface reservoir is formed by constructing a dam across a river valley. Water is stored upstream of the dam and flows by gravity to the treatment plant. Such reservoirs are economical, reliable, and suitable for large water supply schemes. They also provide flood control and irrigation benefits. The dam, spillway, and storage zone together ensure regulated water supply throughout the year.
 

Q2(c) Explain in detail about organics in wastewater
 

Organic matter in wastewater originates from domestic sewage, food waste, industrial effluents, and agricultural runoff. It includes carbohydrates, proteins, fats, oils, and other biodegradable substances. Organic content is measured in terms of Biochemical Oxygen Demand (BOD) and Chemical Oxygen Demand (COD). High organic content depletes dissolved oxygen in receiving waters, causing harm to aquatic life. Hence, biological treatment is essential to remove organics.
 

Q2(d) Design of rectangular settling tank (numerical explanation)
 

In a rectangular settling tank, raw water flow rate, detention time, flow velocity, and depth are used to determine tank dimensions. The given data allows calculation of surface area and volume required. Using detention period and flow velocity, the length and width of the basin are determined so that sedimentation occurs efficiently. Allowance for sludge accumulation ensures uninterrupted operation.

Q2(e) Working of Trickling Filter
 

A trickling filter is a biological treatment unit where wastewater is sprayed over a bed of stones or plastic media. A biofilm develops on the media surface, consisting of microorganisms that oxidize organic matter as wastewater trickles down. Oxygen is supplied through natural ventilation. The treated effluent is collected at the bottom and sent for further treatment. Trickling filters are simple, reliable, and energy-efficient.
 

SECTION C

(Attempt any one – detailed solution)
 

Q3(a) Population forecasting by different methods
 

Using the census data provided, population for the year 2030 is calculated by arithmetic increase, geometric increase, and incremental increase methods. The arithmetic method assumes constant growth per decade, the geometric method assumes percentage growth, and the incremental method considers increasing growth rate. These calculations help determine future water demand accurately for planning purposes.
 

Q3(b) Estimation of hydraulic gradient in pipe
 

Hydraulic gradient represents the head loss per unit length of pipe. Using Darcy-Weisbach formula, friction factor, velocity, and pipe diameter are considered. Hazen-Williams formula estimates head loss based on empirical constants and flow rate. Both methods help in designing efficient water transmission systems.
 

Q4(a) Layouts of water distribution systems
 

Water distribution systems may follow dead-end, gridiron, ring, or radial layouts. Each layout has advantages based on city planning, pressure maintenance, and reliability. Proper layout selection ensures uniform supply and ease of maintenance.
 

Q4(b) Gravity vs pressure conduits
 

Gravity conduits rely on elevation difference and are economical, while pressure conduits use pumps to convey water over long distances or uneven terrain. Pressure conduits are commonly used for distant sources due to flexibility in alignment and assured supply.
 

Q5(a) BOD reaction constant determination
 

BOD reaction follows first-order kinetics. Given percentage BOD exerted in four days, the reaction constant is calculated using standard BOD equations. This constant indicates the rate of organic matter decomposition.
 

Q5(b) BOD variation with temperature
 

BOD reaction rate increases with temperature. Using temperature correction factors, BOD at higher temperature and different duration is calculated to understand treatment efficiency.
 

Q6(a) Alum requirement and CO₂ release
 

Alum dosage and daily water quantity determine the total alum requirement. CO₂ released during coagulation is calculated using chemical reaction relationships. This helps design chemical treatment units accurately.
 

Q6(b) Bleaching powder requirement
 

Annual bleaching powder requirement is calculated based on population, per capita demand, chlorine dose, and percentage of available chlorine. This ensures effective disinfection of water supply.
 

Q7(a) Activated Sludge Process
 

The activated sludge process is a secondary treatment method where wastewater is aerated in the presence of microorganisms. These organisms form flocs that consume organic matter. The mixture is settled in a secondary clarifier, and part of the sludge is recycled to maintain microbial concentration. This process achieves high removal efficiency.
 

Q7(b) Vermicomposting and its advantages
 

Vermicomposting is a biological process where earthworms convert organic waste into nutrient-rich compost. It improves soil fertility, reduces waste volume, and is environmentally friendly. Vermicomposting is simple, cost-effective, and sustainable.