Question 1

Identify the incorrect statement about air pollutants and sources
Evaluate the following statements and choose the one that is wrong.

Accepted Answer

Introduction / Context: This question blends toxicology, atmospheric chemistry, and combustion science. Correctly spotting the incorrect statement requires recognising typical emission profiles and natural sources of organic vapours. Given Data / Assumptions: Normal combustion systems can operate in regions that are oxidising or locally reducing. Biogenic volatile organic compounds (VOCs) are well-documented. Nitrogen dioxide (NO2) has distinct optical absorption features. Concept / Approach: (a) Benzo[a]pyrene (a polycyclic aromatic hydrocarbon) is indeed found in tobacco smoke, char/soot, and exhaust—true. (b) NO2 absorbs in the visible (brown color) and UV; it resides in the troposphere—true. (c) Certain trees emit isoprene/terpenes (hydrocarbons), supporting this statement—true. (d) Claiming H2S is never produced is false: reducing zones, incomplete combustion, or fuel-bound sulfur chemistry can yield H2S alongside SO2. Step-by-Step Solution: Assess (a): Known carcinogenic PAH in smoke and exhaust → correct.Assess (b): NO2 has strong visible/UV absorption; tropospheric presence is routine → correct.Assess (c): Biogenic emissions from certain trees (isoprene/monoterpenes) → hydrocarbon pollutants → correct.Assess (d): Absolute statement “not at all” contradicts reducing flame chemistry → incorrect. Verification / Alternative check: Combustion literature notes H2S and COS formation under fuel-rich conditions; flue gas desulfurisation systems also measure reduced sulfur species. Why Other Options Are Wrong: (a), (b), (c) align with established observations and are not wrong. Common Pitfalls: Treating combustion as perfectly oxidising everywhere; in real furnaces, mixing and local equivalence ratios vary spatially. Final Answer: H2S is not at all produced during combustion of sulphur bearing fuels as all the sulphur is oxidised to SO2.

Question 2

What does aeration remove from water?
In water treatment, aeration primarily accomplishes the removal of which constituent class?

Accepted Answer

Introduction / Context: Aeration involves intimate contact between water and air, typically by spraying, diffused aeration, or cascade towers. It is an important pretreatment step for taste and odour control, corrosion mitigation, and removal of undesirable gases. Given Data / Assumptions: Typical raw groundwater or surface water with dissolved gases (e.g., CO2, H2S) present. Standard municipal-scale aeration equipment. Concept / Approach: Aeration strips volatile dissolved gases by mass transfer to the air phase and can also oxidise certain species (e.g., Fe2+ to Fe3+). It is not a primary method for removing suspended solids (settling/filtration are used) or dissolved solids (which require ion exchange, RO, or precipitation). Step-by-Step Solution: Identify principal mechanism: gas–liquid mass transfer and oxidation.Map to target contaminants: CO2, H2S, some VOCs → removed by stripping.Conclude dissolved gases are the main class removed by aeration. Verification / Alternative check: Design guides state aeration effectiveness for degassing and oxidation; turbidity removal relies on settling/filtration, not aeration alone. Why Other Options Are Wrong: Suspended solids: Require sedimentation/flocculation/filtration.Dissolved solids: Need softening, membranes, or chemical precipitation.None of these: Incorrect because dissolved gases are targeted. Common Pitfalls: Assuming aeration meaningfully lowers TDS; it does not, except for removal of volatile components that contribute little to TDS. Final Answer: dissolved gases

Question 3

Which of the following is not considered an air pollutant category?
Select the option that does not represent a specific class of substances typically listed as ambient air pollutants.

Accepted Answer

Introduction / Context: Ambient air quality frameworks generally list pollutants as specific chemicals or classes of substances (e.g., ozone, particulate matter, nitrogen dioxide). Some terms describe hazards (health effects) rather than the pollutants themselves. Distinguishing these helps clarify monitoring and control strategies. Given Data / Assumptions: The question asks for an item that is not a “specific air pollutant category.” Every other option can exist in the air as identifiable substances or particulate classes. Concept / Approach: Ozone (O3) is a regulated ambient air pollutant. Pesticides can volatilise and become airborne or attach to dust; many jurisdictions monitor pesticide drift as air contaminants. Metallic powders are particulate pollutants (e.g., aluminum, iron fines) contributing to PM. “Carcinogens,” however, is a hazard classification based on health effect; it is not a single substance or chemical class used in ambient pollutant lists. Specific carcinogenic pollutants (e.g., benzene, benzo[a]pyrene) are regulated by name, not by the category “carcinogens.” Step-by-Step Solution: List options that are concrete pollutants in air: O3, pesticides, metallic dust → all concrete.Recognise “carcinogens” describes health property, not a specific pollutant grouping for ambient standards.Choose “Carcinogens” as the item that is not a distinct pollutant category. Verification / Alternative check: Ambient air standards enumerate pollutant names or PM metrics (PM10, PM2.5) rather than effect-based groupings. Why Other Options Are Wrong: Ozone: Clearly defined pollutant with standards.Pesticides: Airborne residues and drift are monitored contaminants.Metallic powders: Particulate pollutants by composition/size. Common Pitfalls: Assuming pesticides are solely water/soil pollutants; many are semi-volatile and can be transported by air. Final Answer: Carcinogens

Question 4

Primary health impact of carbon monoxide (CO) exposure
Which effect best describes the hazard of carbon monoxide to humans at elevated concentrations?

Accepted Answer

Introduction / Context: Carbon monoxide (CO) is a colorless, odorless gas produced by incomplete combustion. It is a common indoor and outdoor pollutant, especially from engines, heaters, and poorly vented combustion appliances. Understanding its primary health mechanism is essential for prevention and emergency response. Given Data / Assumptions: Exposure scenarios include enclosed or poorly ventilated spaces with combustion sources. Acute health impact is of interest. Concept / Approach: CO binds preferentially to hemoglobin to form carboxyhemoglobin, reducing blood’s oxygen-carrying capacity and impairing oxygen delivery to tissues. This leads to hypoxia and can cause headache, dizziness, loss of consciousness, and death. CO does not primarily damage building materials, nor is it a plant growth regulator at ambient levels; asthma exacerbation is more associated with other pollutants (e.g., ozone, particulate allergens). Step-by-Step Solution: Identify CO’s toxic action: strong binding to hemoglobin.Link reduced oxygen delivery to systemic hypoxia.Recognise the clinical endpoint: asphyxiation and potentially fatal outcomes. Verification / Alternative check: Medical guidance emphasizes rapid removal from exposure and oxygen therapy to displace CO from hemoglobin—consistent with an asphyxiant mechanism. Why Other Options Are Wrong: Asthma: CO is not a typical asthmagen; irritant gases and particles are more implicated.Crop growth: CO is not a primary phytotoxic agent at environmental concentrations.Building materials: Acid gases (SO2, NOx) and particulates cause material damage, not CO. Common Pitfalls: Underestimating risk in garages and enclosed spaces; even brief exposures at high CO levels can be lethal. Final Answer: asphyxiation (suffocation) leading to death.

Question 5

Standard tropospheric lapse rate relation
In the troposphere (the weather-dominant layer), the air temperature t at a height h (in metres) above mean sea level follows which relation, given sea-level temperature is 15°C and t is in °C?

Accepted Answer

Introduction / Context: Weather, clouds, and most air pollution dispersion occur in the troposphere. A widely used engineering approximation for temperature variation with altitude is the standard tropospheric lapse rate. This question checks your ability to recall the canonical linear relationship between temperature and height in the lower atmosphere. Given Data / Assumptions: Layer: Troposphere (surface up to roughly 8–18 km). Sea-level temperature: 15°C. Height h is in metres; temperature t is in °C. Use the International Standard Atmosphere (ISA) average lapse rate. Concept / Approach: The standard environmental lapse rate for the troposphere is about 6.5°C per 1000 m (i.e., 0.0065°C per metre). Temperature decreases approximately linearly with altitude: t(h) = t0 - L*h, where t0 is sea-level temperature and L is the lapse rate. Step-by-Step Solution: Identify lapse rate L = 0.0065 °C/m (equivalently, 6.5 °C/km).Set sea-level temperature t0 = 15 °C.Write linear relation: t = 15 - 0.0065 h.Compare with the options and select the matching expression. Verification / Alternative check: For h = 1000 m, t = 15 - 6.5 = 8.5 °C, which is within typical tropospheric profiles and aligns with standard atmosphere tables. Why Other Options Are Wrong: t = 15 + 0.0065h: Implies temperature increases with height, which contradicts tropospheric behavior.t = 0.0035h - 15 / t = 15 - 0.0035h: Use an incorrect magnitude (3.5 °C/km), not the standard 6.5 °C/km rate. Common Pitfalls: Mixing up units (metres vs. kilometres) or confusing troposphere with stratosphere, where temperature can increase with height due to ozone absorption. Final Answer: t = 15 - 0.0065h

Question 6

Lime–soda softening in water treatment
Which constituent is primarily removed from water using the lime–soda process during conventional softening?

Accepted Answer

Introduction / Context: Water softening protects boilers, heat exchangers, and distribution systems from scale caused by hardness ions. The lime–soda process is a classic chemical softening method in municipal and industrial water treatment. Given Data / Assumptions: Lime–soda uses lime (Ca(OH)2) and soda ash (Na2CO3). Hardness arises mainly from Ca2+ and Mg2+ salts. We must identify which type of hardness is the principal target. Concept / Approach: Lime alone removes temporary (carbonate) hardness by precipitating CaCO3 and Mg(OH)2. Adding soda ash (the soda in lime–soda) enables removal of non-carbonate (permanent) hardness by converting Ca2+ to CaCO3 via carbonate addition. Thus the hallmark of the lime–soda process is its ability to remove permanent hardness efficiently in addition to reducing temporary hardness. Step-by-Step Solution: Temporary hardness: removed by lime; Mg2+ also precipitated as Mg(OH)2 with sufficient pH.Permanent hardness: requires carbonate addition (soda ash) to precipitate CaCO3 from CaSO4/CaCl2, etc.Key distinction: the “soda” component specifically targets permanent hardness.Hence, the primary removal associated with lime–soda is permanent hardness. Verification / Alternative check: Standard design texts show stoichiometric soda dosing proportional to non-carbonate hardness; jar tests and residual hardness calculations confirm effectiveness. Why Other Options Are Wrong: Foul smell and taste: Addressed by aeration, activated carbon, or oxidation—not by lime–soda chemistry.Iron and manganese: Typically removed via oxidation and filtration; softening may incidentally remove some but is not the primary method.Temporary hardness: Reduced by lime, but the question emphasizes the lime–soda process, whose distinguishing feature is permanent hardness removal. Common Pitfalls: Assuming softening targets only carbonate hardness; the soda step is specifically for non-carbonate (permanent) hardness. Final Answer: Permanent hardness

Question 7

SO₂ odor threshold in ambient air
At approximately what concentration of sulphur dioxide (SO₂) in air does a distinctly pungent smell become noticeable?

Accepted Answer

Introduction / Context: Sulphur dioxide (SO₂) is a key air pollutant from combustion of sulfur-bearing fuels. Recognizing odor thresholds helps in field diagnosis of emissions and potential health impacts. Given Data / Assumptions: The question asks for the approximate concentration at which SO₂ odor is distinctly pungent. Units are parts per million (ppm) in air. We seek an order-of-magnitude threshold used in conventional environmental MCQs. Concept / Approach: Human odor detection thresholds for SO₂ are often cited near sub-ppm to around 1 ppm, with a distinctly irritating/pungent sensation in the vicinity of 1 ppm and above. Lower values (0.01–0.1 ppm) may be detectable to very sensitive individuals but are not the commonly cited “pungent” threshold in basic references. Step-by-Step Solution: Establish typical odor threshold range: roughly 0.3–1 ppm.Select the conservative, classroom-typical “pungent” level: 1 ppm.Cross-check that higher values (e.g., 4 ppm) imply strong irritancy beyond first detection. Verification / Alternative check: Occupational hygiene sources describe eye and respiratory irritation escalating from low single-digit ppm upward; therefore, 1 ppm as a pungent threshold aligns with didactic values. Why Other Options Are Wrong: 0.01 / 0.1 ppm: Too low for a typical “pungent” descriptor in standard MCQs.4 ppm: Noticeably irritating, but the standard first pungent detection is already achieved closer to 1 ppm. Common Pitfalls: Confusing minimal detection by highly sensitive individuals with a broadly accepted educational threshold for pungency. Final Answer: 1

Question 8

Use of alum in conventional water treatment
Aluminium sulphate, Al₂(SO₄)₃ (alum), is primarily used for which unit process?

Accepted Answer

Introduction / Context: Clarification of raw water requires aggregation of fine colloids that do not settle on their own. Coagulants like alum are central to producing potable water and protecting downstream filters from fouling. Given Data / Assumptions: Chemical: Aluminium sulphate (alum), Al₂(SO₄)₃. Goal: Identify its main purpose in a conventional treatment train. Concept / Approach: Alum hydrolyzes to form aluminium hydroxide floc and releases acidity, destabilizing negatively charged colloids. This promotes floc formation, which can then be removed by sedimentation and subsequent filtration. Alum is therefore associated with coagulation (and flocculation as a follow-on step). Step-by-Step Solution: Add alum to rapid mix → hydrolysis forms Al(OH)₃ floc.Charge neutralization and sweep floc mechanism capture colloids.Settle in clarifier; polish via filters.Therefore, the unit process is coagulation. Verification / Alternative check: Standard treatment trains comprise coagulation–flocculation–sedimentation–filtration–disinfection; alum belongs to the first step. Why Other Options Are Wrong: Sedimentation / filtration: Physical removal processes following coagulation; alum is not dosed at these steps for their primary function.Disinfection: Achieved by chlorine, ozone, UV, etc., not alum. Common Pitfalls: Confusing the chemical addition step (coagulation) with the subsequent physical removal steps. Final Answer: coagulation

Question 9

Sound level of a person shouting at full voice
A typical shout at full voice corresponds to approximately which sound level in decibels (dB)?

Accepted Answer

Introduction / Context: Sound levels are measured on a logarithmic decibel scale, important for environmental noise control and occupational hygiene. Everyday reference points help estimate exposure severity. Given Data / Assumptions: “Shouting at full voice” is a near-field vocalization, typically at 1 m reference distance. We seek an order-of-magnitude decibel value. Concept / Approach: Typical human voice levels: whisper ~30 dB, normal conversation ~60 dB, loud speech ~70 dB, shout ~80–90 dB, and rock concerts/ sirens can exceed 100 dB. Therefore, 80 dB is a representative single-number answer for a shout, suitable for MCQ contexts. Step-by-Step Solution: Align daily references: conversation ~60 dB.Increase for shouting by ~20 dB → around 80 dB.Check options and select the plausible typical value: 80 dB. Verification / Alternative check: Occupational noise charts commonly place loud human vocal effort in the 80–90 dB range at close distance. Why Other Options Are Wrong: 25 / 50 dB: Too quiet; 50 dB corresponds to a quiet office or subdued conversation.120 dB: Extremely loud; near aircraft engine/PA systems—far beyond normal shouting. Common Pitfalls: Forgetting that the decibel scale is logarithmic: a 10 dB increase represents a tenfold increase in intensity and is perceived as roughly twice as loud. Final Answer: 80

Question 10

Lethal sulphur dioxide (SO₂) concentrations in air
At about what SO₂ concentration (ppm) can death occur after short exposure in severely polluted air scenarios?

Accepted Answer

Introduction / Context: Sulphur dioxide is a strong respiratory irritant. Acute exposure to very high concentrations can be life-threatening. Engineers should understand approximate fatality thresholds to evaluate hazard scenarios like accidental releases. Given Data / Assumptions: Units are ppm in air. “Death may occur” refers to short-term, high-level exposure in the absence of rapid evacuation. Concept / Approach: SO₂ causes bronchoconstriction, airway inflammation, and pulmonary edema at high concentrations. Historical toxicology references cite lethality risk in the several-hundred ppm range for short exposure. Therefore, 400 ppm is the representative single-choice value used in many environmental engineering MCQs. Step-by-Step Solution: Recognize that single- to double-digit ppm (20–100 ppm) produce severe irritation but are generally below typical acute lethality thresholds.Identify several-hundred ppm as the critical zone for life-threatening outcomes.Select 400 ppm to represent the lethal short-term exposure level. Verification / Alternative check: Emergency response guides and classical toxicology tables indicate rapidly increasing danger moving from 200 to 500+ ppm; 400 ppm is a standard “danger of death” benchmark for didactic purposes. Why Other Options Are Wrong: 20 / 100 / 200 ppm: Hazardous and damaging but generally cited below commonly referenced lethal short-term values in basic MCQ frameworks. Common Pitfalls: Confusing occupational short-term exposure limits (STELs) with acute lethality thresholds; the latter are much higher. Final Answer: 400

Question 11

Identify the non-coagulant in water treatment chemicals
Which of the following is not used as a chemical coagulant in conventional clarification?

Accepted Answer

Introduction / Context: Clarification requires coagulants to destabilize colloids. Knowing which chemicals serve as coagulants vs. disinfectants or pH adjusters is vital in designing and operating treatment trains. Given Data / Assumptions: Candidates include common water treatment chemicals. We must identify the one that is not a coagulant. Concept / Approach: Alum (Al₂(SO₄)₃) and iron salts (e.g., ferrous sulphate) are classic coagulants. Hydrated lime can enhance coagulation via pH adjustment and, in softening, precipitate hardness—often grouped within the coagulation/softening toolkit. Chloramine (formed from chlorine and ammonia), however, is a secondary disinfectant used for residual maintenance in distribution systems, not for coagulation. Step-by-Step Solution: Classify each chemical by primary use.Recognize chloramine as a disinfectant, not a coagulant.Select “Chloramine” as the non-coagulant. Verification / Alternative check: AWWA and standard methods list chloramination under disinfection, not coagulation. Why Other Options Are Wrong: Aluminium sulphate / Ferrous sulphate: Direct coagulants forming insoluble hydroxide flocs.Hydrated lime: Facilitates coagulation/softening through alkalinity and precipitation; widely used in clarification processes. Common Pitfalls: Assuming all chemical additions prior to sedimentation are “coagulants.” Some, like lime, primarily adjust pH/alkalinity but are integral to coagulation performance. Final Answer: Chloramine

Question 12

Typical pollutants from petroleum refineries
Which combination best represents the principal air pollutants commonly emitted from petroleum refinery operations?

Accepted Answer

Introduction / Context: Refineries process sulfur-containing crude and operate numerous combustion units and process vents. Understanding typical pollutant profiles informs monitoring, permitting, and control technology selection. Given Data / Assumptions: We focus on common, impactful pollutants. Emissions arise from heaters, boilers, FCC units, flares, and sour gas handling. Concept / Approach: Carbon monoxide (CO) is produced by incomplete combustion. Sulphur dioxide (SO₂) forms when sulfur in fuels or off-gases is oxidized. Hydrogen sulfide (H₂S) occurs in sour refinery streams and may be released if not fully captured/converted (e.g., via amine treating and Claus units). While CO₂ is ubiquitous, it is not typically grouped with “criteria pollutants” in classic MCQs; nitrogen oxide speciation as NO vs NO₂ varies, and SO₃ is a minor fraction compared to SO₂. Step-by-Step Solution: Identify incomplete combustion → CO emissions.Link sulfur to SO₂; sour streams to H₂S.Select the triplet that best matches refinery pollutant fingerprints: CO, SO₂, H₂S. Verification / Alternative check: Emission inventories show significant SO₂ from sulfur-bearing fuels and CO from heaters/flares; H₂S is a key hazard in sour gas systems. Why Other Options Are Wrong: CO₂, NO, SO₃ / CO₂, H₂S, NO₂ / SO₃, NO₂, CO₂: Either overemphasize CO₂ (a greenhouse gas rather than a classical “pollutant set” here) or include SO₃ as a primary, which is typically a much smaller fraction than SO₂. Common Pitfalls: Assuming NO or NO₂ dominate over sulfur species in sour operations; sulfur control is a central refinery environmental challenge. Final Answer: CO, SO₂ & H₂S.

Question 13

Health and performance impacts of excessive workplace heat
Thermal stress in hot work environments most commonly leads to which outcomes?

Accepted Answer

Introduction / Context: Heat stress is a key occupational hazard in foundries, refineries, and process plants. It affects worker safety, productivity, and error rates. Understanding combined effects helps justify ventilation, cooling, and administrative controls. Given Data / Assumptions: “Excessive heat & temperature” implies high radiant and convective loads. We consider typical physiological and performance outcomes. Concept / Approach: The human thermoregulatory system responds to heat by increasing skin blood flow and sweating. This often causes fatigue, dehydration, and changes in respiration and heart rate. Cognitive and manual performance decline as thermal strain increases, reducing efficiency and elevating accident risk. Step-by-Step Solution: Map common symptoms: fatigue from sustained thermoregulation and dehydration.Physiological response: elevated breathing and heart rate to dissipate heat and supply oxygen.Performance effect: declines in alertness and precision → reduced efficiency.All listed outcomes occur; choose “all (a), (b) & (c).” Verification / Alternative check: Occupational guidelines (e.g., WBGT-based) tie work-rest cycles and hydration plans to mitigate these effects, confirming their prevalence. Why Other Options Are Wrong: Each single item (a), (b), or (c) is true; the comprehensive choice is the combination of all three. Common Pitfalls: Underestimating respiratory changes; workers often hyperventilate subtly in hot conditions, especially with physical exertion. Final Answer: all (a), (b) & (c).

Question 14

Drivers that accentuate the greenhouse effect
Which of the following human activities intensify the greenhouse effect and thereby contribute to global warming?

Accepted Answer

Introduction / Context: The greenhouse effect is a natural phenomenon, but human activities have strengthened it by increasing atmospheric greenhouse gases. Recognizing the broad categories of contributing actions is fundamental to environmental engineering and policy. Given Data / Assumptions: We evaluate three activity classes: land-use change, industrialization, and transportation. We seek the combination that intensifies greenhouse forcing. Concept / Approach: Deforestation reduces carbon sinks and often emits CO₂ via biomass burning and decay. Rapid industrialization generally increases fossil fuel consumption, emitting CO₂ and other greenhouse gases. Transportation growth raises fuel combustion emissions (CO₂, N₂O), and methane can rise from associated supply chains. Together, they elevate atmospheric greenhouse gas concentrations and radiative forcing. Step-by-Step Solution: Link deforestation → reduced CO₂ uptake + emissions from land clearing.Link industrialization → increased energy demand → fossil fuel combustion → CO₂.Link transportation → mobile-source CO₂ and other GHGs.All three intensify the greenhouse effect; select the combined option. Verification / Alternative check: Emission inventories attribute large shares of global CO₂ to power/industry and transport; land use change is also a major contributor historically and regionally. Why Other Options Are Wrong: Each individual option is a contributor, but the comprehensive effect arises from all activities together. Common Pitfalls: Confusing ozone layer issues with greenhouse forcing; while both are atmospheric topics, their mechanisms and key gases differ. Final Answer: all (a), (b) and (c).

Question 15

Removal of radionuclides from contaminated water
Radioactive substances present in a polluted water stream can most effectively be removed by which treatment method?

Accepted Answer

Introduction / Context: Water streams contaminated with radionuclides require specialised treatment because radioactive ions pose long-term health and environmental risks even at very low concentrations. Environmental engineers choose processes that selectively remove ionic species with high efficiency, allow safe handling, and minimise secondary waste volume. Understanding which unit operation is best suited for dissolved radioactive ions is essential for plant design and emergency response. Given Data / Assumptions: Dissolved radioactive species are primarily in ionic form (e.g., Cs+, Sr2+, Co2− complexes). Target is polished removal to very low residual levels. Normal water temperatures and pH within treatable ranges. Concept / Approach: Ion exchange uses solid media with fixed functional groups that swap harmless counter-ions for target radionuclides. Resins or inorganic exchangers (e.g., zeolitic media) provide high selectivity, allowing very low effluent concentrations. The process is compact, controllable, and widely proven at nuclear facilities, research labs, and hospitals. In contrast, conventional coagulation/filtration removes particulates and some colloids but is far less selective for dissolved ions. Biological oxygen treatment is designed for biodegradable organics, not for ionic species. Air stripping works for volatile compounds, not for nonvolatile metal/radionuclide ions. Step-by-Step Solution: Identify contaminant category: dissolved radioactive ions.Match process to mechanism: selective removal via ion exchange sites.Confirm practicality: well-established media, regenerable or disposable, with shielded handling.Select the best option: adsorption using ion exchange materials. Verification / Alternative check: Decontamination factors achieved by properly selected ion exchange media are significantly higher than those from generic physical separation methods; many nuclear effluent standards rely on this step for compliance. Why Other Options Are Wrong: Biological oxygen treatment: Targets BOD and nutrients; ineffective for radionuclide ions. Coagulation and filtration: Limited for dissolved ions unless converted to insoluble forms first. Air stripping: Works on volatile organics/ammonia; not applicable to nonvolatile radionuclides. None of these: Incorrect because ion exchange is suitable and standard. Common Pitfalls: Assuming that any “advanced” unit (membranes, coagulation aids) will equal ion exchange selectivity; overlooking resin fouling by iron or organics without pretreatment; forgetting to plan for spent resin disposal per radiation safety rules. Final Answer: Adsorption using ion exchange materials

Question 16

Hydrodynamic noise from flowing liquids
The major root cause of high hydrodynamic noise (noise generated by liquid flow in pipes, valves, and pumps) is:

Accepted Answer

Introduction / Context: Hydrodynamic noise arises when liquid flow creates pressure fluctuations that couple into structures and air, producing audible or ultrasonic noise. This phenomenon is common in throttling valves, high-head pumps, and restrictive fittings. Recognising the dominant mechanisms allows engineers to mitigate noise through design and operating changes before resorting to heavy acoustic treatments. Given Data / Assumptions: Incompressible liquid flow with possible local pressure drops. Presence of valves, orifices, elbows, or impellers that may induce strong pressure gradients. Standard industrial piping systems (metals, typical diameters). Concept / Approach: Cavitation occurs when local static pressure falls below the liquid’s vapour pressure, forming vapour bubbles that subsequently collapse in regions of higher pressure. This collapse is highly energetic and generates intense, broadband pressure pulses. These pulses translate to structural vibration and radiated noise, and they can cause erosion and pitting. While boundary layer turbulence and general flow fluctuations contribute to noise, cavitation dominates when present because its bubble collapses emit far stronger impulses over a wide frequency range. Step-by-Step Solution: Evaluate likely noise sources in liquid systems (turbulence, separation, cavitation).Assess intensity: collapsing vapour bubbles produce the highest impulse magnitudes.Identify most probable major cause under high differential pressure or poor NPSH: cavitation. Verification / Alternative check: Field evidence: reducing valve pressure drop, increasing NPSH available, or using anti-cavitation trims typically yields pronounced noise reductions, confirming cavitation as the primary driver when present. Why Other Options Are Wrong: Pipe wall vibrations due to external impacts: Not the root fluid-mechanics cause; often a consequence of flow excitation. Boundary layer separation only: Can generate noise, but typically less severe than cavitation-induced pulses. Random flow fluctuations only: Background noise contributor; rarely dominant versus cavitation. Poor acoustic insulation: A transmission issue, not the source mechanism. Common Pitfalls: Attempting to fix cavitation noise solely with lagging; the correct approach is hydraulic: reduce pressure drop per stage, raise suction pressure, or use multi-hole/anti-cavitation valve trims. Final Answer: Cavitation

Question 17

Strategies for industrial noise control
In a chemical plant with high noise levels, which combination is recognised as the comprehensive control strategy?

Accepted Answer

Introduction / Context: Industrial noise management follows a hierarchy of controls to ensure regulatory compliance and worker safety. Because plant noise often arises from multiple equipment items and pathways, an effective programme rarely relies on a single measure. Instead, source controls, path (transmission) controls, and receiver protection act together to deliver sustained reductions. Given Data / Assumptions: Multiple rotating machines (fans, compressors), process valves, and piping contribute to noise. Occupational exposure limits apply over an 8-hour shift. Objective: practical, maintainable noise reduction. Concept / Approach: The “three-pronged” strategy includes: (1) source control (quieter equipment selection, balance/alignment, anti-cavitation trims, vibration isolation, silencers on intakes/exhausts); (2) path control (enclosures, acoustic barriers, duct liners, lagging, break-out noise reduction, room acoustic treatment); and (3) receiver protection (hearing protection devices, exposure time management, quiet zones). Applying all three provides robust reductions and accommodates operational constraints. Step-by-Step Solution: Identify dominant sources using surveys and octave-band measurements.Engineer source solutions first (silencers, trims, isolation) to lower emissions.Interrupt transmission paths via enclosures and barriers.Protect personnel with PPE and administrative controls where residual levels remain. Verification / Alternative check: Case studies show that combining a modest source reduction with a modest transmission reduction often outperforms either alone and can avoid costly over-design at a single point. Why Other Options Are Wrong: Any “only” option ignores the complementary nature of controls and typically fails to achieve targets across all work areas. Administrative controls only: Helpful but insufficient without engineering measures. Common Pitfalls: Overreliance on hearing protection without addressing sources; neglecting maintenance-induced noise increases (bearing wear, misalignment) after initial success. Final Answer: All (a), (b) & (c)

Question 18

Role of atmospheric CO2 in the greenhouse effect
Which statements correctly describe how increased atmospheric CO2 influences Earth’s energy balance?

Accepted Answer

Introduction / Context: Greenhouse gases such as carbon dioxide change the way Earth absorbs and emits radiation. A clear understanding of shortwave versus longwave interactions explains why adding CO2 warms the surface and lower atmosphere. This question tests core radiative concepts used in climate and environmental engineering analyses. Given Data / Assumptions: Sunlight reaching Earth spans mainly visible and near-infrared wavelengths (shortwave) at the top of the atmosphere. Earth’s surface and atmosphere emit primarily in the thermal infrared (longwave). CO2 has absorption bands in the infrared region. Concept / Approach: Shortwave solar radiation passes largely through the atmosphere to the surface, where it is absorbed and converted to heat. The warmed surface emits longwave infrared radiation upward. CO2 and other greenhouse gases interact with portions of this longwave radiation, absorbing and re-emitting it in all directions, including back toward the surface. The result is a reduction in the net rate of heat loss to space, leading to a higher equilibrium surface temperature compared with a CO2-free atmosphere. Step-by-Step Solution: Associate incoming solar energy with mostly shortwave that transmits relatively well through the atmosphere.Recognise that CO2 absorbs specific longwave bands, partly reflecting/absorbing infrared emissions.Conclude that reduced longwave escape raises surface-air temperatures (heat-trap effect). Verification / Alternative check: Radiative transfer models and spectral measurements show strong CO2 absorption near 15 micrometres; increases in concentration raise effective radiating height and reduce outgoing longwave radiation until temperatures adjust. Why Other Options Are Wrong: Each single statement (a, b, or c) captures only part of the mechanism; the complete description requires all three. None of these: Incorrect because all statements collectively are consistent with greenhouse theory. Common Pitfalls: Confusing “visible” and “ultraviolet”; in common usage shortwave includes visible and some near-UV. The key idea is that shortwave largely passes, while longwave is partially trapped by CO2. Final Answer: All (a), (b) and (c)

Question 19

Photochemical formation of eye-irritating pollutants
Direct reactions of unsaturated hydrocarbons with nitrogen oxides (NO or NO2) in sunlight commonly form which eye-irritant compound in photochemical smog?

Accepted Answer

Introduction / Context: Urban air pollution episodes under sunny, stagnant conditions often involve reactions between volatile organic compounds (VOCs) and nitrogen oxides. The resulting oxidants and secondary pollutants cause eye irritation and respiratory stress. Environmental engineers must recognise key products to design control strategies targeting VOC and NOx precursors. Given Data / Assumptions: Unsaturated hydrocarbons (alkenes, aromatics) are present from traffic and solvents. NO and NO2 are available from combustion sources. Sunlight drives radical chemistry forming secondary oxidants. Concept / Approach: Peroxyacetyl nitrate (PAN) forms via photochemical oxidation of hydrocarbons producing peroxyacetyl radicals, which then react with NO2. PAN is a potent eye irritant and a plant toxin, acting as a marker of photochemical smog severity. While “photochemical smog” is the name of the overall phenomenon, the specific eye-irritant compound commonly identified is PAN. Compounds like benzopyrene are carcinogenic polycyclic aromatics from incomplete combustion, not primary photochemical products of VOC + NOx reactions. Polymers like polyacrylonitrile are unrelated to atmospheric photochemistry. Step-by-Step Solution: Identify the chemical class: secondary pollutant formed from VOC + NOx under sunlight.Recall the hallmark product associated with eye irritation in smog: PAN.Select “Peroxyacetyl nitrate (PAN).” Verification / Alternative check: Field measurements in photochemical smog events consistently show PAN alongside ozone and aldehydes; PAN tracks with oxidant levels and eye irritation complaints. Why Other Options Are Wrong: Photochemical smog: Describes the overall mixture, not a specific compound. Benzopyrene: Soot-phase carcinogen, not the main photochemical eye irritant. Polyacrylonitrile: A synthetic polymer; irrelevant to atmospheric formation. Formaldehyde only: An irritant and intermediate, but PAN is the classic eye-stinging oxidant cited in smog chemistry. Common Pitfalls: Equating general smog with a single compound; multiple species (ozone, PAN, aldehydes) co-occur, but PAN is especially noted for ocular irritation. Final Answer: Peroxyacetyl nitrate (PAN)

Question 20

Biological treatment in trickling filters
During biological treatment of sewage in a trickling filter, the predominant microorganisms are:

Accepted Answer

Introduction / Context: Trickling filters are attached-growth biological reactors where wastewater is distributed over a medium (stones or plastic media) supporting a biofilm. Oxygen transfer occurs by natural or forced ventilation. Knowing whether the process is primarily aerobic or anaerobic guides expectations for BOD removal, odour formation, and nitrification potential. Given Data / Assumptions: Wastewater is distributed intermittently or continuously over the medium. Air flows through voids, supplying oxygen to the biofilm. Normal domestic or municipal sewage loadings. Concept / Approach: Trickling filters are designed to maintain aerobic conditions in the active biofilm, enabling aerobic heterotrophs and nitrifiers to remove organic matter and oxidise ammonia when design allows. While micro-zones deeper in the slime layer can be anoxic, the bulk mechanism relies on oxygen diffusion and is classified as aerobic treatment. “Saprophytic” simply means decomposer, which could be aerobic or anaerobic; the more precise and correct classification here is aerobic bacteria. Anaerobic systems, such as digesters or septic tanks, operate without oxygen and are not representative of trickling filters. Step-by-Step Solution: Identify reactor type: attached-film trickling filter with ventilation.Relate oxygen supply to microbial ecology: aerobic biofilm dominates pollutant removal.Choose the most accurate description: aerobic bacteria. Verification / Alternative check: Design texts specify air requirements and ventilation for trickling filters to ensure aerobic operation and prevent odour generation typical of anaerobic processes. Why Other Options Are Wrong: Anaerobic bacteria: Not predominant in well-aerated trickling filters. Saprophytic bacteria: Too general; does not specify oxygen requirement. Parasitic bacteria: Not relevant to wastewater treatment performance. Photoautotrophic cyanobacteria: Require light and are not the principal degraders in trickling filters. Common Pitfalls: Assuming any biofilm reactor is mixed redox; while micro-gradients exist, the process is fundamentally aerobic in design and operation. Final Answer: Aerobic bacteria

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