UGC NET Environmental Science Unit-VI: Environmental Pollution and Control Syllabus

What is a catalytic converter and what reactions does a three-way catalytic converter perform?

A catalytic converter (Pt, Pd, Rh catalysts) reduces vehicular emissions: it oxidizes CO to CO2, oxidizes unburned hydrocarbons to CO2 and H2O, and reduces NOx to N2 and O2 (three-way action).

What is the Air Quality Index (AQI), and how many categories does India's National AQI use?

AQI is a number used to communicate how polluted air is and associated health effects. India's National AQI (2015) has 6 categories: Good (0-50), Satisfactory (51-100), Moderate (101-200), Poor (201-300), Very Poor (301-400), and Severe (401-500).

List the major sources of noise pollution.

Industrial (machines, generators), Transportation (road traffic, railways, aircraft), Construction activities, Domestic/community sources (loudspeakers, appliances), and commercial/social events. Transportation is the largest contributor in urban areas.

What is the decibel (dB) and the dB(A) scale used for measuring noise?

The decibel is a logarithmic unit expressing sound pressure level relative to a reference (20 micropascal). dB(A) is the A-weighted scale that adjusts the measured sound to approximate the frequency response of the human ear, used for environmental noise standards.

Define Leq, L10, L50, and L90 noise indices.

Leq = equivalent continuous sound level (constant level with same energy as the fluctuating noise). L10 = level exceeded 10% of the time (peak/intrusive noise). L50 = median level (50%). L90 = level exceeded 90% of the time (background/ambient noise).

What is the Noise Pollution Level (LNP) formula?

LNP = Leq + (L10 - L90), where (L10 - L90) is the noise climate that accounts for the fluctuation/variability of the noise. Units are in dB(A).

Define noise dose and how it relates to permissible occupational exposure.

Noise dose is the percentage of the permissible daily noise exposure received by a worker. 100% dose corresponds to the limit (e.g., 90 dB(A) for 8 hours). For every 5 dB increase (exchange rate), permissible exposure time is halved (e.g., 95 dB for 4 hr, 100 dB for 2 hr).

State the ambient noise standards (day/night) in India for the four area categories.

Industrial: 75/70 dB(A); Commercial: 65/55 dB(A); Residential: 55/45 dB(A); Silence zone: 50/40 dB(A). Day is 6 AM-10 PM; night is 10 PM-6 AM. Silence zones are areas within 100 m of hospitals, schools, courts.

Describe three categories of noise control measures.

Control at source (quieter machines, mufflers, maintenance, enclosures), Control along the path (barriers, sound-absorbing materials, distance, green belts), and Control at receiver (ear plugs, ear muffs, limiting exposure time/rotation).

What are the health and physiological impacts of noise pollution and vibration?

Auditory effects: temporary/permanent hearing loss (NIHL), tinnitus. Non-auditory: hypertension, increased heart rate, sleep disturbance, stress, annoyance, reduced work efficiency. Whole-body vibration causes fatigue and musculoskeletal disorders; hand-arm vibration causes white finger syndrome.

Classify the types and sources of water pollution.

Point sources (discrete, e.g., industrial discharge pipes, sewage outfalls) and non-point sources (diffuse, e.g., agricultural runoff, urban runoff). Types: organic, inorganic, thermal, radioactive, pathogenic, sediment, and nutrient pollution.

What is eutrophication and which nutrients primarily cause it?

Eutrophication is the nutrient enrichment of water bodies, mainly by nitrogen and phosphorus, leading to excessive algal growth (algal blooms), oxygen depletion on decay, fish kills, and degradation of water quality.

What is biomagnification, and give a classic example of its impact.

Biomagnification is the increasing concentration of a persistent toxic substance at each higher trophic level of a food chain. Classic example: mercury in Minamata disease (Japan) and DDT accumulation causing eggshell thinning in birds of prey.

Define BOD and COD and explain the key difference between them.

BOD (Biochemical Oxygen Demand) is the oxygen consumed by microorganisms to biologically oxidize organic matter (measured over 5 days at 20 deg C). COD (Chemical Oxygen Demand) is the oxygen equivalent to chemically oxidize organic matter using a strong oxidant. COD is always greater than or equal to BOD.

What is Dissolved Oxygen (DO) and what is the method used to measure it?

DO is the amount of oxygen dissolved in water (mg/L), essential for aquatic life. It is measured by Winkler's iodometric titration method or with a DO meter/membrane electrode. Healthy water typically has DO > 5 mg/L.

What is the Most Probable Number (MPN) test used for in water quality analysis?

The MPN test is a statistical microbiological method to estimate the density of coliform bacteria (indicator of fecal contamination) in water using multiple-tube fermentation, expressed as MPN per 100 mL.

Why are coliform bacteria (especially E. coli) used as indicator organisms for drinking water safety?

Coliforms, especially fecal coliform E. coli, indicate fecal contamination and the potential presence of pathogens. They are easy to detect, present in large numbers in feces, and survive in water similarly to pathogens. Drinking water standard: zero coliforms per 100 mL.

List the conventional sequence of unit operations in a drinking (surface) water treatment plant.

Screening, Aeration, Coagulation-Flocculation (alum), Sedimentation (clarification), Filtration (rapid sand filter), and Disinfection (chlorination), then storage and distribution.

What is the role of coagulation-flocculation in water treatment, and which coagulant is commonly used?

Coagulation neutralizes the charges on fine colloidal particles allowing them to destabilize; flocculation aggregates them into larger settleable flocs. Alum (aluminium sulfate) is the most common coagulant; ferric chloride and PAC are also used.

What is breakpoint chlorination?

Breakpoint chlorination is adding chlorine until the demand from reducing agents and ammonia (forming chloramines) is satisfied; beyond the breakpoint, all chloramines are destroyed and free residual chlorine appears, ensuring effective disinfection.

Differentiate between primary, secondary, and tertiary wastewater treatment.

Primary: physical removal of solids (screening, grit removal, sedimentation). Secondary: biological removal of dissolved/colloidal organic matter (activated sludge, trickling filter). Tertiary/advanced: removal of nutrients, pathogens, and residual pollutants (filtration, disinfection, nutrient removal).

Describe the activated sludge process.

It is an aerobic secondary treatment where wastewater is mixed with a microbial floc (activated sludge) in an aeration tank; microbes oxidize organic matter. The mixture goes to a secondary clarifier where sludge settles; part is recycled (return activated sludge) and excess is wasted.

What is the F/M ratio in the activated sludge process?

The Food-to-Microorganism ratio is the rate of organic load (BOD) applied per unit mass of microorganisms (MLSS) per day. It controls process efficiency and sludge settleability; typical range is 0.2-0.5 kg BOD/kg MLSS/day.

What is a Common Effluent Treatment Plant (CETP) and what is its main advantage?

A CETP is a centralized facility that collects and treats combined wastewater from a cluster of small and medium industries (often in an industrial estate). Advantages: economy of scale, makes treatment affordable for small units, professional operation, and better pollution control.

Define soil texture, soil structure, and cation exchange capacity (CEC).

Soil texture = relative proportion of sand, silt, and clay particles. Soil structure = arrangement of soil particles into aggregates. CEC = the capacity of soil to hold and exchange cations (measured in cmol(+)/kg), governed mainly by clay and organic matter content.

What does soil pH indicate and what is the optimum range for most crops?

Soil pH indicates acidity/alkalinity, affecting nutrient availability and microbial activity. Most crops grow best in slightly acidic to neutral soils (pH 6.0-7.5). Acidic soils are limed; alkaline/sodic soils are treated with gypsum.

List major causes of soil pollution and three control measures.

Causes: excessive use of fertilizers/pesticides, industrial effluents, solid waste/leachate, mining, and oil spills. Control: bioremediation/phytoremediation, proper waste disposal and landfilling, reduced agrochemical use, reclamation, and soil washing/excavation.

How do industrial effluents interact with soil components and affect soil quality?

Industrial effluents add heavy metals, acids/alkalis, salts, and organics. They alter soil pH, increase salinity/sodicity, get adsorbed onto clay and organic matter (CEC), disrupt soil microbial communities, reduce fertility, and heavy metals can leach to groundwater or be taken up by plants.

Name four important functions of soil microorganisms.

Decomposition of organic matter and nutrient cycling (C, N, S, P), nitrogen fixation (Rhizobium, Azotobacter), mineralization and humus formation, and biodegradation of pollutants. They also aid in nitrification/denitrification and soil structure formation.

What are the main sources of thermal pollution and its primary impact on aquatic ecosystems?

Sources: discharge of heated water from thermal/nuclear power plants (cooling water), industries, and deforestation along banks. Impact: raised water temperature lowers dissolved oxygen (DO), increases metabolic rate of organisms, causes thermal shock, and disrupts aquatic life and breeding.

What are the major sources and impacts of marine pollution, and what is the major international convention controlling ship pollution?

Sources: oil spills, industrial and sewage discharge, plastics, agricultural runoff, and ocean dumping. Impacts: oil slicks reduce oxygen and kill marine life, eutrophication, bioaccumulation, and damage to coral reefs. MARPOL is the key international convention preventing pollution from ships.

What are the sources of radioactive pollution and the units used to measure radiation dose?

Sources: nuclear power plants, nuclear weapon tests, mining/processing of radioactive ores, medical/research isotopes, and natural sources (radon, cosmic rays). Units: Becquerel/Curie (activity), Gray/rad (absorbed dose), and Sievert/rem (equivalent/biological dose).