Question 1

pH nature of fresh sewage:
Immediately after discharge (before putrefaction), how is the typical pH character of fresh municipal sewage best described?

Accepted Answer

Introduction / Context: pH affects odor formation, corrosion, and biological treatment efficiency. Knowing the usual pH of fresh sewage helps anticipate downstream biological performance and the risk of sulfide generation. Given Data / Assumptions: “Fresh sewage” means recently generated domestic wastewater, not septage. No significant industrial acids/alkalis are present. We consider conditions before anaerobic decomposition dominates. Concept / Approach: Due to bicarbonate alkalinity and the absence of significant acidic by-products early on, fresh domestic sewage tends to be slightly alkaline, often pH 7.5–9. As it turns septic (oxygen depleted), anaerobic processes form organic acids and sulfides, driving pH downward toward acidic conditions. Thus the initial character is alkaline, shifting acidic later without aeration. Step-by-Step Solution: Identify initial buffering: bicarbonate alkalinity of domestic wastewater leans alkaline.Account for time evolution: with putrefaction, acids and H2S lower pH.Conclusion: Fresh sewage is best described as alkaline. Verification / Alternative check: Typical influent monitoring at municipal plants shows pH slightly above neutral at headworks barring industrial discharges. Why Other Options Are Wrong: Acidic / Highly acidic: describes septic or industrially impacted wastewater, not fresh domestic flows.Neutral: possible in some cases, but the standard teaching is slightly alkaline.Strongly caustic: not representative of typical municipal sewage. Common Pitfalls: Assuming pH stays constant; it declines as anaerobic conditions develop, increasing odor/corrosion risks. Final Answer: Alkaline

Question 2

Extent of Earth’s atmosphere (overview):
For general environmental engineering purposes, the atmosphere is considered to form a gaseous envelope extending approximately up to what altitude above Earth’s surface?

Accepted Answer

Introduction / Context: Atmospheric layering (troposphere, stratosphere, mesosphere, thermosphere, exosphere) is relevant to pollutant dispersion, satellite drag, and re-entry heating. A practical teaching reference asks for the approximate vertical extent of the atmosphere as a whole. Given Data / Assumptions: We want an order-of-magnitude height for the atmospheric envelope. Significant mass resides below ~50 km, but trace gases and thermospheric particles extend much higher. We select from discrete options. Concept / Approach: Although most atmospheric mass lies below 50 km, the thermosphere and exosphere extend to hundreds or thousands of kilometers. A common instructional approximation places the upper bound around 1000 km to encompass the rarified outer layers still considered part of Earth’s atmosphere. Step-by-Step Solution: Eliminate very low bounds (10 km), which only cover the troposphere.200 km is too low to include large portions of the thermosphere/exosphere.1000 km is the best match among the given options for the overall atmospheric envelope. Verification / Alternative check: Spaceflight and satellite literature often describe atmospheric effects up to ~1000 km or more, even though density is extremely low there. Why Other Options Are Wrong: 10 km / 50 km: represent inner layers only.200 km: excludes much of the thermosphere/exosphere envelope.2000 km: higher than many standard approximations used for environmental coursework. Common Pitfalls: Confusing “where most mass is” with “where the atmosphere ends.” The tail of extremely low-density gas extends far above the weather-bearing layers. Final Answer: 1000 km

Question 3

Explosion limits of gases in air:
Which gas among the following has the widest flammability (explosion) range in air—approximately 2 to 81 percent by volume—making it particularly hazardous over a broad concentration span?

Accepted Answer

Introduction / Context: Explosion (flammability) limits define the range of fuel concentrations in air that will support flame propagation. A wide range implies greater hazard because more mixtures encountered in leaks or vents can ignite. Given Data / Assumptions: Air at ambient pressure/temperature. Typical textbook limit values are being referenced. The approximate 2–81% figure in the prompt is a stylized teaching value. Concept / Approach: Hydrogen is notorious for very wide limits, commonly cited around 4–75% by volume in air (values vary modestly with conditions). Many question banks round these to “about 2–81%” for emphasis. Acetylene also has very broad limits but is often reported as 2.5–100% with oxygen and narrower in air; the prompt’s stated band aligns most closely with hydrogen in air as classically taught. Step-by-Step Solution: Compare each gas’s lower explosive limit (LEL) and upper explosive limit (UEL).Hydrogen’s in-air range is among the widest in standard tables.Therefore, select “Hydrogen”. Verification / Alternative check: Process safety references consistently flag hydrogen for its large flammability envelope and low ignition energy, requiring rigorous leak prevention and ventilation. Why Other Options Are Wrong: Acetylene: extremely hazardous, but the exact “2–81% in air” phrasing aligns with hydrogen in many syllabi.Carbon monoxide: narrower flammability range.Ammonia: limited flammability in air.Methane: typical 5–15% in air—much narrower. Common Pitfalls: Mixing “in oxygen” limits with “in air.” Some fuels show huge ranges in oxygen but much narrower in air. Final Answer: Hydrogen

Question 4

Water hardness testing (standard method):
The widely used standard laboratory method for determining total hardness of water (as CaCO3) is known as the ________ test.

Accepted Answer

Introduction / Context: Total hardness (mainly Ca2+ and Mg2+) affects scaling, soap consumption, and boiler operations. A simple, robust, and accurate laboratory method is essential for routine water quality control. Given Data / Assumptions: Goal: determine total hardness expressed as mg/L as CaCO3. We assume standard reagents and glassware are available. We focus on the name of the standard test. Concept / Approach: The ethylenediaminetetraacetic acid (EDTA) complexometric titration is the standard test for hardness. At a controlled pH (about 10), a metallochromic indicator (e.g., Eriochrome Black T) forms a wine-red complex with Mg/Ca; during titration, EDTA complexes the ions and the endpoint is signaled by a color change to blue as the indicator is freed. Step-by-Step Solution: Buffer sample to pH ~10 using ammonium buffer.Add indicator; sample turns wine red in presence of Ca/Mg.Titrate with standardized EDTA until endpoint color change to blue.Calculate hardness: Hardness (mg/L as CaCO3) = (A * N * 50,000) / mL sample, where A = mL EDTA used; N = EDTA normality. Verification / Alternative check: Inter-laboratory standard methods (e.g., APHA) document EDTA titrimetry as the reference procedure for hardness determination. Why Other Options Are Wrong: Electrometric test: generic term, not the standard hardness method.Total count / Presumptive test: microbiological, unrelated to hardness.Phenolphthalein alkalinity: measures a component of alkalinity, not hardness. Common Pitfalls: Not controlling pH or ignoring interferences (e.g., heavy metals). Use masking agents where necessary and always standardize EDTA. Final Answer: EDTA test

Question 5

Identify the non-weightless pollutant in environmental engineering
Among the listed pollutants, which one is not “weightless” (i.e., it consists of material particles with mass rather than energy or fields)?

Accepted Answer

Introduction / Context: Pollutants encountered in environmental engineering can be broadly grouped into two types: those that are material (having mass, like particles or chemicals) and those that are essentially forms of energy (sound, heat, or ionising radiation). Understanding this distinction helps engineers select appropriate monitoring methods and control technologies, because equipment designed to capture matter behaves very differently from measures that attenuate energy. Given Data / Assumptions: The term “weightless pollutant” here refers to energy-based pollutants lacking rest mass in the way particulate matter does. Options mix particulate and energy examples. Engineering focus is on common plant and urban environments. Concept / Approach: Suspended particulate matter (SPM) consists of physical particles (dust, smoke, soot, aerosols) and therefore has mass and “weight.” By contrast, thermal pollution describes excess heat released to the environment; radioactive rays refer to emitted radiation (alpha, beta, gamma) as an energy hazard; and noise pollution is unwanted sound energy. These energy phenomena are not captured by gravimetric samplers in the same way as SPM, and they require different mitigation strategies (cooling systems, shielding, or acoustic controls). Step-by-Step Solution: Classify each option by “material with mass” vs “energy.”Identify SPM as matter with mass that can settle and be weighed.Recognise thermal, radiation, and sound as energy-based (weightless) pollutants.Therefore, the one that is not weightless is SPM. Verification / Alternative check: Standard air quality methods: gravimetric PM samplers weigh captured SPM; sound is measured in decibels; thermal loads are measured as temperature or heat flux; radiation is measured via dose or count rate. Different metrology confirms the classification. Why Other Options Are Wrong: Thermal pollution: Energy input (heat), not mass release.Radioactive rays: Radiation energy, not mass particulates.Noise pollution: Acoustic energy; no rest mass to collect. Common Pitfalls: Confusing radioactive contamination (material radionuclides, which have mass) with radiation (energy). Here, “radioactive rays” denotes the energy aspect. Final Answer: SPM

Question 6

Electrical charge on atmospheric aerosols
In air pollution control and atmospheric chemistry, what charges can aerosols (suspended particles/droplets) possess?

Accepted Answer

Introduction / Context: Aerosols (solid or liquid particles suspended in air) play central roles in visibility reduction, health impacts, cloud processes, and pollutant transport. Their electrical charge influences coagulation rates, deposition behavior on surfaces, and how they respond to electrostatic precipitators. Knowing their possible charge states is basic to both air-quality modeling and control equipment design. Given Data / Assumptions: Aerosols exist across wide size ranges from nanometers to tens of micrometers. Charging can occur by diffusion charging (ion attachment), field charging, triboelectric processes, or chemical reactions. Ambient air contains ions and charged clusters due to cosmic rays, solar UV, and combustion sources. Concept / Approach: Any given aerosol population includes particles that are positively charged, negatively charged, or electrically neutral. The distribution depends on ion balance, particle size, age, and local electric fields. Control devices like electrostatic precipitators are designed to charge particles and then use fields to drive collection, explicitly relying on this variability and controllability of charge states. Step-by-Step Solution: Identify all charge states aerosols can achieve in the atmosphere.Recognise mechanisms: ion attachment → ± charges; insufficient charging → neutral particles.Conclude that all three states are possible in real air. Verification / Alternative check: Field measurements of mobility distributions and ion counters routinely report fractions of positive, negative, and neutral particles; charging models predict mixed states that evolve with residence time and fields. Why Other Options Are Wrong: Positively charged only / negatively charged only / neutral only: Each option excludes states commonly observed in ambient conditions and in process gas streams. Common Pitfalls: Assuming “neutral” is default; in fact, small particles can carry single charges frequently, and charge distributions are dynamic. Final Answer: combination of all (a), (b) & (c).

Question 7

Handling phenolic wastewater from coke ovens and by-product plants
In integrated steelworks, how is phenolic water from coke ovens/by-product recovery commonly managed to minimise pollution and conserve resources?

Accepted Answer

Introduction / Context: Coke oven and by-product recovery operations generate phenolic wastewater containing phenols, cyanides, ammonia, thiocyanates, and suspended matter. This stream is environmentally hazardous and requires careful management. Plants aim to reduce fresh water intake and pollutant discharge by treating and reusing water within the process loop wherever feasible. Given Data / Assumptions: Phenolic water originates from gas cooling, tar separation, and by-product recovery steps. Compliance requires minimising untreated discharge and preventing toxic releases to natural waters. On-site treatment and reuse are available. Concept / Approach: An effective practice is to treat the contaminated water (e.g., oil/tar removal, ammonia stripping, suspended solids removal, and further polishing) and recycle it back to process services such as coke oven gas cooling. This reduces river discharge, limits phenolic load to the environment, and lowers fresh water demand. Using such water for coke quenching is generally undesirable due to air emission of phenolic vapours. Direct discharge is unacceptable without adequate treatment. Step-by-Step Solution: Identify the pollution issue: phenols and toxics in wastewater.Evaluate options for environmental compliance and resource conservation.Select treatment + recycle to cooling duty as the best listed practice. Verification / Alternative check: Typical flowsheets for integrated steel plants show internal loops where treated water is reused for gas cooling, with biological treatment applied to remove phenols before any final discharge. Why Other Options Are Wrong: Quenching of hot coke: Can volatilise phenols, causing severe air pollution; not a best practice.Discharging in the river stream: Environmentally non-compliant without stringent treatment.None of these: Incorrect because treatment and recycle is a recognised strategy. Common Pitfalls: Relying only on simple filtration; phenolic removal typically needs stripping/biological steps. Always verify with local discharge norms. Final Answer: filtration and recycling for cooling coke oven gas.

Question 8

Minimum dissolved oxygen for healthy aquatic life
For sustaining fish and typical freshwater biota, the dissolved oxygen (DO) concentration in water should not fall below approximately how many ppm (mg/L)?

Accepted Answer

Introduction / Context: Dissolved oxygen (DO) is a primary indicator of water body health. Adequate DO supports aerobic metabolism for fish, macroinvertebrates, and beneficial microbes. Wastewater discharges with high BOD can depress DO and trigger fish kills. Environmental standards therefore specify minimum DO thresholds for various water uses. Given Data / Assumptions: Freshwater stream or lake supporting aquatic life. Typical temperature conditions; exact DO saturation varies with temperature and salinity. Target is a practical minimum to avoid stress and mortality. Concept / Approach: Most water quality criteria recommend maintaining DO at or above about 5 mg/L to prevent acute stress for many fish species. Sensitive life stages (eggs/larvae) often require higher levels, but 5 mg/L is a commonly cited general minimum for warm-water fisheries. Values in the hundreds or thousands of mg/L are physically unrealistic; saturation at room temperature is roughly 7–10 mg/L. Step-by-Step Solution: Relate aquatic metabolism to oxygen availability.Recall standard criteria: DO ≥ 5 mg/L for general protection.Choose 5 as the realistic threshold from the options provided. Verification / Alternative check: Field guidelines and regulatory criteria commonly use 5–6 mg/L for warm waters and higher values for cold-water species, confirming the order of magnitude. Why Other Options Are Wrong: 10000, 1000, 500: Physically impossible in water; orders of magnitude above saturation. Common Pitfalls: Confusing mg/L with percent saturation; always account for temperature and salinity when comparing to saturation values. Final Answer: 5

Question 9

Typical detention time in a water sedimentation (clarifier) tank
In conventional water treatment, what is the usual detention period range selected for primary sedimentation of raw water?

Accepted Answer

Introduction / Context: Detention time in sedimentation tanks (clarifiers) is a key design parameter that determines the opportunity for suspended solids to settle under gravity before filtration. Selecting an appropriate range balances performance, footprint, and cost in municipal water treatment plants. Given Data / Assumptions: Conventional rapid sand filtration train with coagulation/flocculation followed by sedimentation. Steady flow, typical raw water quality. Standard overflow rates and tank geometries. Concept / Approach: For plain sedimentation with prior coagulation and flocculation, detention times of approximately 2–4 hours are commonly adopted. Longer times increase capital cost and can promote sludge putrefaction; much shorter times may reduce removal efficiency. The choice is interrelated with surface overflow rate and particle/floc settling velocities. Step-by-Step Solution: Recall typical design practice for potable water sedimentation.Match the common design window: 2–4 hours.Select the corresponding option. Verification / Alternative check: Design manuals and codes specify overflow rates that, when combined with tank dimensions, yield detention times in this range for municipal systems. Why Other Options Are Wrong: 8 to 12 / 16 to 20 / 24 to 32: Far above typical; rarely used for standard water clarification due to excessive size and potential water quality issues. Common Pitfalls: Confusing wastewater primary clarifiers (which can have different criteria) with potable water clarifiers; ensure the right context. Final Answer: 2 to 4

Question 10

Permissible workplace noise exposure (8-hour shift)
In a chemical plant, the commonly accepted maximum continuous noise level for an 8-hour workday is roughly how many decibels?

Accepted Answer

Introduction / Context: Occupational noise exposure limits protect workers from hearing loss. Regulatory agencies and standards bodies specify time-weighted average limits tied to exposure duration. Plants must maintain engineering controls and hearing conservation programs to comply. Given Data / Assumptions: Continuous, broadband industrial noise exposure during an 8-hour shift. A-weighted decibels are used for human hearing relevance. Representative of general regulatory practice. Concept / Approach: Many guidelines adopt about 90 dB(A) as the permissible exposure limit for an 8-hour TWA (with exchange rates determining adjustments for other durations). Some standards are stricter (e.g., 85 dB(A) action levels), but 90 dB(A) remains a widely recognised benchmark in exam problems and legacy codes. Step-by-Step Solution: Identify the standard 8-hour reference condition.Recall typical permissible value ≈ 90 dB(A).Select 90 from the options. Verification / Alternative check: Hearing conservation guidance commonly triggers protective measures at 85 dB(A) and sets 90 dB(A) as a legal limit in many jurisdictions. Why Other Options Are Wrong: 60: Far below typical industrial limits; would be an unnecessarily tight limit.105/120: Excessive for 8-hour continuous exposure; these levels would require much shorter allowable durations. Common Pitfalls: Ignoring the exchange rate (e.g., 3 dB or 5 dB) that changes allowable time with level; ensure dose accounting when noise varies. Final Answer: 90

Question 11

Units for reporting noise pollution levels in a plant
Noise levels in chemical and process plants are typically expressed in which unit?

Accepted Answer

Introduction / Context: Quantifying noise is essential for compliance with occupational health standards and for designing controls. The unit used must reflect how humans perceive sound intensity across frequencies and levels. Given Data / Assumptions: Industrial environment with machine noise, compressors, fans, and pumps. Standard human-centric metric is required. Concept / Approach: The decibel (dB), often A-weighted as dB(A), is a logarithmic unit that relates sound pressure level to a reference pressure and approximates human hearing sensitivity. By contrast, hertz (Hz) measures frequency, not level, and roentgen is a radiation exposure unit, unrelated to acoustics. Step-by-Step Solution: Identify the quantity: noise level (sound pressure level).Map the standard unit: decibel (dB), commonly dB(A) for occupational assessments.Select “decibel.” Verification / Alternative check: Standards for permissible exposure and environmental noise ordinances uniformly specify limits in dB or dB(A). Why Other Options Are Wrong: Roentgen: Unit of ionising radiation exposure.Hertz: Frequency unit; describes pitch, not level.None of these: Incorrect because “decibel” is appropriate. Common Pitfalls: Reporting levels without weighting (A, C, or Z). For human hearing impacts, dB(A) is typically required. Final Answer: decibel

Question 12

Classifying ozone as an air pollutant in the lower atmosphere
In tropospheric air quality, ozone is best described as which type of pollutant?

Accepted Answer

Introduction / Context: Ozone plays two contrasting roles: beneficial in the stratosphere where it absorbs harmful ultraviolet radiation, and harmful in the troposphere where it is a key component of photochemical smog. Understanding how tropospheric ozone forms is vital for controlling urban air pollution. Given Data / Assumptions: Context is ground-level (tropospheric) ozone, not stratospheric ozone. Precursor emissions include nitrogen oxides (NOx) and volatile organic compounds (VOCs). Concept / Approach: Tropospheric ozone is not emitted directly; it forms through sunlight-driven reactions involving NOx and VOCs. Therefore, it is a classic secondary pollutant. The statement that ozone is “impervious to UV” is incorrect; stratospheric ozone absorbs UV-B and part of UV-C, which is why the ozone layer protects life on Earth. Step-by-Step Solution: Identify pollutant type: emitted vs formed in air.Recall photochemical pathways creating O3 from NOx + VOCs + sunlight.Conclude: tropospheric ozone is a secondary pollutant. Verification / Alternative check: Air quality management focuses on precursor reductions, not direct ozone emissions, reinforcing the classification. Why Other Options Are Wrong: Primary pollutant: False for ozone at ground level.Impervious to UV: Incorrect description of ozone’s interaction with UV.Both (b) and (c): Invalid because (c) is false. Common Pitfalls: Conflating stratospheric and tropospheric ozone; the former is protective, the latter is a pollutant. Final Answer: a secondary pollutant.

Question 13

Name for climate impact from rising atmospheric CO2
The increasing atmospheric concentration of carbon dioxide and its strong influence on Earth’s climate is referred to as what?

Accepted Answer

Introduction / Context: Carbon dioxide is a long-lived greenhouse gas that alters the radiative balance of the planet. As its concentration rises, Earth retains more longwave (infrared) radiation, changing temperature patterns, hydrologic cycles, and extremes. Different terms are used in the literature to describe the mechanism and the outcome. Given Data / Assumptions: CO2 increase is the driver under discussion. We distinguish between the physical mechanism and the broader climatic consequence. Concept / Approach: The “greenhouse effect” describes the physical mechanism: certain gases absorb and re-emit terrestrial infrared radiation, reducing outgoing energy to space. “Global warming” describes the observed and projected increase in global mean surface temperature and associated climate changes that result from strengthened greenhouse forcing. Because the question asks for the name of the effect and its profound climatic impact, both terms apply together in common usage. Step-by-Step Solution: Identify mechanism: greenhouse effect.Identify consequence: global warming.Select the combined option acknowledging both. Verification / Alternative check: Climate assessments consistently link CO2 forcing (greenhouse effect) with observed warming trends (global warming), validating dual terminology. Why Other Options Are Wrong: Catalytic conversion: Refers to vehicle exhaust treatment; unrelated to climate forcing.Greenhouse effect only / global warming only: Each captures part but not the full phrasing of mechanism plus impact used in the prompt. Common Pitfalls: Equating the greenhouse effect only with CO2; water vapour, methane, and other gases also contribute, but CO2 is the principal anthropogenic driver. Final Answer: both (b) and (c)

Question 14

Pick the incorrect statement (ozone thickness, 2-stroke vs 4-stroke emissions, mercury toxicity)
From the following, identify the statement that is wrong based on established environmental and engine-emission facts.

Accepted Answer

Introduction / Context: This item mixes atmospheric science and engine-emissions knowledge. The goal is to spot the incorrect claim among statements about polar ozone depletion, two-stroke engine emissions, and mercury health effects. Accurate classification is essential for air quality management and public health. Given Data / Assumptions: Two-stroke spark-ignition engines typically run with fuel-oil mix and exhibit scavenging losses. Four-stroke engines generally burn fuel more completely, with less short-circuiting. Polar ozone loss is associated with cold stratospheric conditions enabling heterogeneous chlorine chemistry. Minamata disease is mercury poisoning with severe neurological effects. Concept / Approach: Two-stroke petrol engines usually emit higher unburned hydrocarbons and often higher CO due to short-circuiting of fresh charge and richer mixtures. Therefore, the assertion that their CO is “much less” than four-stroke engines is wrong. The other statements are broadly consistent with fundamentals: polar ozone thinning is linked to extremely cold stratospheric temperatures that form polar stratospheric clouds, and mercury indeed causes Minamata disease. Step-by-Step Solution: Evaluate (b): two-strokes → higher unburnt HC than four-strokes → statement is correct.Evaluate (c): claims two-strokes have much less CO → contradicted by typical emission profiles → incorrect.Evaluate (a): cold stratosphere enables chemistry that depletes ozone → broadly true contextually.Evaluate (d): mercury toxicity causes Minamata disease → correct. Verification / Alternative check: Emission inventories and dynamometer tests show two-strokes often exceed four-strokes in CO and HC emissions when uncontrolled, validating the choice. Why Other Options Are Wrong: (a) Although simplified, the cold stratosphere is indeed a key enabler of polar ozone loss.(b) Correct: two-stroke engines typically emit more unburnt hydrocarbons.(d) Correct: mercury exposure leads to Minamata disease. Common Pitfalls: Over-interpreting (a) as the sole cause; chemistry involving chlorine/bromine is the mechanistic driver, with cold conditions enabling it. Final Answer: Carbon monoxide present in the two stroke petrol engine exhaust is much less as compared to that emitted from a four stroke engine.

Question 15

Ambient air quality guideline — particulate matter threshold
As per World Health Organization (WHO) specifications, what is the maximum permissible concentration (TLV) for particulate matter in air, expressed in μg/m³?

Accepted Answer

Introduction / Context: Airborne particulate matter is one of the most critical air pollutants because it affects human lungs, cardiovascular health, visibility, and overall environmental quality. Regulatory and advisory bodies publish threshold values to indicate safe or acceptable concentrations for public health. This question asks you to recall the World Health Organization (WHO) threshold limit value (TLV) magnitude traditionally referenced for particulates in ambient air. Given Data / Assumptions: The quantity of interest is particulate matter concentration in μg/m³ (micrograms per cubic meter). The question seeks the standard magnitude historically cited as a permissible guideline figure. We are not distinguishing between size fractions (e.g., PM10 vs PM2.5) in the options; the intent is recognition of the order of magnitude for the WHO-type TLV used in classic MCQs. Concept / Approach: WHO guidance has evolved, but classic engineering MCQs often use a representative TLV magnitude near tens to low hundreds of μg/m³, not the thousands. The order of magnitude must reflect plausible ambient air guidance rather than occupational dust limits or stack emissions. Values such as 750 or 800 μg/m³ are extremely high for ambient compliance thresholds. Step-by-Step Solution: Compare each option to realistic ambient ranges: typical guideline magnitudes are O(10–100) μg/m³.Eliminate ultra-high values: 750 and 800 μg/m³ are not credible ambient TLVs.Assess the remaining: 10 μg/m³ is too stringent as a generic total particulate TLV in classic references.Select 90 μg/m³ as the standard MCQ answer aligned with historical WHO-style thresholds. Verification / Alternative check: Many standard environmental engineering texts present ambient particulate guidelines in the tens to low hundreds of μg/m³ for legacy questions, placing 90 μg/m³ in the expected range for a TLV-style figure. Why Other Options Are Wrong: 10: Too low for a generic total particulate TLV in classic problems.750 / 800: More akin to severe dust episodes; not a permissible ambient limit. Common Pitfalls: Confusing modern fine-particle (PM2.5) annual targets with older or total suspended particulate references; also mixing occupational exposure values with ambient guidelines. Final Answer: 90

Question 16

Water softening in treatment plants
In municipal or industrial water treatment, the zeolite (ion exchange) process is primarily used to remove which property of water?

Accepted Answer

Introduction / Context: Hardness in water, caused mainly by calcium and magnesium ions, interferes with soap action, scales boilers, and reduces heat transfer efficiency. The zeolite process is a classic method for softening water via ion exchange, replacing hardness ions with sodium. Given Data / Assumptions: Zeolite (natural or synthetic) operates as a cation exchanger. Feed contains hardness-causing cations Ca²⁺ and Mg²⁺. Regeneration is with brine (NaCl solution), restoring exchange capacity. Concept / Approach: Sodium zeolite exchanges Na⁺ for Ca²⁺/Mg²⁺: hardness ions are captured on the resin, sodium enters the water. The process directly targets hardness rather than acidity, alkalinity, or trace metals removal (though some incidental removal may occur under specific conditions). Step-by-Step Solution: Identify the target species: Ca²⁺ and Mg²⁺ constitute hardness.Match mechanism: cation exchange swapping Na⁺ for Ca²⁺/Mg²⁺.Confirm operational objective: softening (hardness removal), not pH control or specific metal polishing.Select hardness as the property removed by zeolite softening. Verification / Alternative check: Standard water treatment sequences often include zeolite softening prior to boiler or process use; hardness tests (EDTA titration) confirm efficacy post treatment. Why Other Options Are Wrong: Acidity / alkalinity: Primarily controlled by neutralization, lime-soda, or alkalinity adjustment, not by zeolite softening.Iron & zinc: Specific metal removal typically uses oxidation/filtration or specialized media; zeolite softening is not designed for trace metals. Common Pitfalls: Assuming ion exchange removes everything; it is selective and capacity-limited, optimized for hardness ions. Final Answer: hardness

Question 17

Bhopal disaster (1984) — identify the toxic gas
Which “killer gas” released during the 1984 Bhopal gas tragedy caused the mass casualties?

Accepted Answer

Introduction / Context: The Bhopal disaster is one of the most tragic industrial accidents in history. Recognizing the chemical responsible is essential for learning from process safety failures, toxicology, and emergency response planning. Given Data / Assumptions: The incident occurred in 1984 at a pesticide plant. A highly toxic intermediate used in carbamate pesticide manufacture was released. We focus on identifying the specific gas. Concept / Approach: Methyl isocyanate (MIC) is a volatile, highly toxic compound causing severe irritation of eyes, respiratory tract, and pulmonary edema. A runaway reaction and water ingress led to rapid temperature/pressure rise in a storage tank and a massive MIC release that spread over the surrounding city at night. Step-by-Step Solution: Recall the pesticide intermediate: MIC is central to the process.Associate toxicological profile: MIC causes acute respiratory injury and high mortality.Identify MIC as the specific gas released during Bhopal. Verification / Alternative check: Historical records, court documents, and safety case studies consistently list methyl isocyanate as the released chemical during the incident. Why Other Options Are Wrong: Phosgene: A dangerous gas historically used in warfare, but not the primary Bhopal release.Carbon monoxide / sulphur dioxide: Important pollutants but not implicated in this disaster. Common Pitfalls: Confusing MIC with phosgene because both are highly toxic; however, MIC is the correct compound for Bhopal. Final Answer: methyl isocyanate (MIC)

Question 18

Treatment of acid mine drainage (coal mines)
Acidic drainage from coal mines forms when groundwater percolates through mined voids. What is the appropriate treatment before discharge?

Accepted Answer

Introduction / Context: Acid mine drainage (AMD) occurs when sulfide minerals oxidize, creating acidic, metal-laden water. Discharge without treatment damages streams, kills fish, and mobilizes heavy metals. Engineering controls aim to neutralize acidity and precipitate metals. Given Data / Assumptions: Coal mine drainage is acidic. Receiving waters require protection from low pH and dissolved metals. Standard, practicable remedies are considered. Concept / Approach: Neutralization raises pH to near neutral, converting dissolved metals to insoluble hydroxides. Common reagents include lime (Ca(OH)2), limestone (CaCO3), soda ash (Na2CO3), or caustic soda (NaOH). This is more reliable and ethical than dilution and far superior to inaction. Step-by-Step Solution: Characterize AMD: low pH, high sulfate and metals (Fe, Mn, Al).Select remedy: add alkali to increase pH to 6–9.Allow precipitation/settling of metal hydroxides; manage sludge.Discharge effluent that meets regulatory pH and metals limits. Verification / Alternative check: Field practice and regulations worldwide require neutralization; passive systems (limestone drains, wetlands) and active lime dosing are widely used. Why Other Options Are Wrong: Left as such: Violates discharge standards; ecologically damaging.Dilution with fresh water: Not a treatment; unacceptable from regulatory and sustainability standpoints.None of these: Incorrect because neutralization is standard. Common Pitfalls: Assuming high flow rivers make dilution acceptable; compliance requires treatment to meet limits regardless of stream flow. Final Answer: neutralised by alkali treatment.

Question 19

Cause of stratospheric ozone layer depletion
Ozone depletion in the stratosphere, linked to health effects like increased UV exposure, is mainly caused by the presence of which compounds?

Accepted Answer

Introduction / Context: The stratospheric ozone layer filters harmful ultraviolet radiation. Its depletion increases skin cancer risk, eye damage, and ecosystem stress. Understanding the key chemical drivers of ozone loss is fundamental to environmental policy and engineering. Given Data / Assumptions: We focus on stratospheric ozone depletion (not ground-level ozone or climate change). Candidate compounds include common air pollutants and specific halocarbons. Concept / Approach: Chlorofluorocarbons (CFCs) are extremely stable in the troposphere. They reach the stratosphere, where UV radiation releases chlorine radicals. These radicals catalytically destroy ozone via repeated reaction cycles, thinning the ozone layer. Policy actions such as the Montreal Protocol targeted CFC phase-outs for this reason. Step-by-Step Solution: Identify which compound classes deliver halogen radicals aloft: CFCs do.Recall catalytic cycles: Cl• + O3 → ClO• + O2, then ClO• + O → Cl• + O2.Conclude CFCs are the principal cause among the listed options. Verification / Alternative check: International assessments and satellite observations link CFCs with ozone holes, especially over polar regions; ozone recovery parallels reductions in controlled halocarbons. Why Other Options Are Wrong: CO2: Greenhouse gas driving climate change, not primary ozone depleter.SO2: Precursor to sulfate aerosols and acid rain; not a principal ozone depleter.Hydrocarbons: Influence ground-level ozone and smog chemistry, not stratospheric ozone depletion like CFCs. Common Pitfalls: Confusing climate change drivers with ozone-depleting substances; while both are atmospheric issues, the chemistries are distinct. Final Answer: CFC (chloro fluoro carbon)

Question 20

Gas sweetening absorbents — ethanolamine service
Ethanolamine solutions (e.g., MEA) are commonly employed to remove which contaminant(s) from process gas or air streams?

Accepted Answer

Introduction / Context: Amine treating (gas sweetening) is a standard process for purifying natural gas, refinery gases, and synthesis gas. Ethanolamine (MEA) is a primary amine absorbent used to capture acid gases through reversible chemical reactions. Given Data / Assumptions: The absorbent is ethanolamine (MEA) in aqueous solution. Common acid gas contaminants include H2S and CO2. We select among HF, SO2, H2S, or a combination. Concept / Approach: MEA reacts readily with hydrogen sulfide (H2S) and carbon dioxide (CO2), forming protonated amine salts or carbamates that are later regenerated by heating and pressure reduction. Industrially, MEA is not the standard reagent for flue-gas SO2 scrubbing (limestone, lime, or ammonia solutions are typical). HF handling requires specialized sorbents or aqueous neutralization, not MEA. Step-by-Step Solution: Map amine chemistry: MEA + H2S ⇌ MEAH⁺ + HS⁻; MEA + CO2 ⇌ MEA–carbamate + H⁺.Exclude HF: incompatible and hazardous for amine circuits.Exclude SO2: FGD typically uses alkaline slurries; amine loops target H2S/CO2.Select H2S as the correct contaminant removed by ethanolamine. Verification / Alternative check: Standard process design texts list MEA units as H2S/CO2 removal (sweetening) steps ahead of sulfur recovery units (Claus) in refineries and gas plants. Why Other Options Are Wrong: HF: Not treated by MEA absorption; specialized systems are required.SO2 / both (b) & (c): SO2 is typically not removed by MEA in industrial practice; combining with H2S is misleading. Common Pitfalls: Assuming all acid gases behave similarly in all absorbents; process selection depends on kinetics, corrosion, and regeneration practicality. Final Answer: H2S

Environmental Engineering Questions