Q: Water treatment: For trace concentrations of organic contaminants (e.g., < 200 mg/L COD), which method is generally the most effective for removal?

Introduction / Context: Wastewater often contains small amounts of dissolved organic compounds that are not easily removed by sedimentation or simple biological treatment. Selecting the right polishing step is crucial to meet discharge or reuse standards. Given Data / Assumptions: Organic contaminants present at low (trace) levels, below roughly 200 mg/L. Goal: high-efficiency removal for polishing/tertiary treatment. Methods considered: adsorption, coagulation, biological ponds, lagooning. Concept / Approach: Activated carbon exhibits high surface area and affinity for a wide range of dissolved organics (e.g., phenols, dyes, taste/odor compounds). At low concentrations, adsorption performs better than bulk biological processes or coagulation, which are less selective for dissolved, non-particulate organics. Step-by-Step Solution: 1) Identify target phase: dissolved organics (not suspended solids).2) Match process: adsorption removes dissolved species effectively at low concentrations.3) Consider alternatives: coagulation targets colloids/particulates; ponds/lagooning require long retention and may not reach low residuals.4) Choose activated carbon adsorption as best option. Verification / Alternative check: Design manuals list granular activated carbon (GAC) filters or powdered activated carbon (PAC) dosing as standard polishing for low-level organics, often following biological treatment and clarification. Why Other Options Are Wrong: Chemical coagulation: Limited effect on dissolved, non-ionizable organics.Biological oxidation pond/Lagooning: Space- and time-intensive; variable performance at trace levels. Common Pitfalls: Expecting primary or secondary treatment alone to meet stringent organics limits.Ignoring carbon exhaustion and the need for regeneration/replacement. Final Answer: Activated carbon adsorption

Q: Blast furnace gas cleaning wastewater: Which unit process is typically used to remove suspended solids from BF gas cooling/cleaning effluent?

Introduction / Context: Blast furnace (BF) gas cleaning uses scrubbers and separators that produce wastewater laden with fine solids (flue dust, iron oxides). Effective primary treatment is needed to remove these suspended solids before downstream polishing or reuse. Given Data / Assumptions: Wastewater contains high suspended solids and colloidal fines. Objective: primary solid-liquid separation. Coagulant options available to enhance settling. Concept / Approach: Radial settling tanks (clarifiers) and thickeners provide quiescent zones for particle settling. Lime and ferrous sulphate destabilize colloids, increase floc size, and accelerate sedimentation. The dense underflow can be thickened and handled, while clarified overflow proceeds to further treatment if needed. Step-by-Step Solution: 1) Characterize solids: iron-rich fines with poor natural settling.2) Apply coagulation/flocculation: lime raises pH and aids coagulation; ferrous salts form hydroxide flocs.3) Use radial settlers/thickeners to separate flocculated solids efficiently.4) Produce clarified effluent and concentrated sludge for disposal or recovery. Verification / Alternative check: Steel plant water circuits commonly show BF scrubber effluents routed to thickeners with coagulant dosing before reuse or discharge. Why Other Options Are Wrong: Biological pond: Targets biodegradable organics, not primarily suspended mineral solids.Lagooning: Too slow and land-intensive for heavy solids loads.Filtration only: Rapid blinding and impractical without prior clarification. Common Pitfalls: Skipping coagulation, leading to carryover and poor clarity.Undersized settlers that cannot handle peak turbidities. Final Answer: Radial settling tank (thickener) with coagulant addition (lime and ferrous sulphate)

Q: Public health in water supply: Excess fluoride (fluorine) in drinking water most commonly leads to which condition?

Introduction / Context: Fluoride is a trace element with a narrow beneficial range. Low levels can reduce dental caries, but excessive intake leads to fluorosis. Water treatment decisions rely on understanding this dose-response relationship. Given Data / Assumptions: Drinking water contains fluoride above recommended limits. Exposure is chronic over years. Population-level health effects are of concern. Concept / Approach: Chronic excess fluoride causes dental fluorosis (mottling, enamel hypomineralization) and, at higher exposures, skeletal fluorosis (joint pain, stiffness, bone changes). The mechanism involves altered mineralization processes in developing teeth and bone. Step-by-Step Solution: 1) Identify contaminant: fluoride (F−) at elevated concentration.2) Map to health effect: excess → fluorosis (dental first; skeletal with prolonged high doses).3) Distinguish from cavities: low fluoride reduces caries; excess does not cause cavities.4) Conclude: the principal condition is fluorosis. Verification / Alternative check: Epidemiological studies in endemic regions consistently link high-fluoride groundwater with dental and skeletal fluorosis; defluoridation (e.g., activated alumina, Nalgonda process) reduces incidence. Why Other Options Are Wrong: Dental cavities/tooth decay: Associated with insufficient fluoride, not excess.Respiratory disease: Not a primary outcome of fluoride in water. Common Pitfalls: Assuming “more fluoride is always better.”Ignoring children's heightened susceptibility during enamel formation. Final Answer: Fluorosis

Q: Safety engineering: Which gas among the following has the widest flammability (explosive) limits in air, making it the most hazardous in this respect?

Introduction / Context: Flammability (explosive) limits define the range of fuel-air mixtures that can propagate flame. Wider limits indicate a gas is more easily ignitable over a broader concentration range, increasing handling and storage risk. Given Data / Assumptions: Standard conditions near ambient temperature and pressure. Typical lower and upper flammability limits (LFL/UFL) in air. Gases considered: acetylene, hydrogen, carbon monoxide, gasoline vapor. Concept / Approach: Acetylene has exceptionally wide limits (approx. LFL ~2.5% to UFL ~81% by volume in air). Hydrogen is also wide (~4% to 75%), but narrower than acetylene. Carbon monoxide (~12.5% to 74%) and gasoline vapor (range varies with composition, generally narrower) are less extreme. Step-by-Step Solution: 1) Compare LFL/UFL: determine width = UFL − LFL.2) Acetylene: ~78.5% width; Hydrogen: ~71% width; CO: ~61.5% width; Petrol vapor: narrower and temperature dependent.3) Conclude acetylene exhibits the widest flammability range. Verification / Alternative check: Chemical safety datasheets and fire protection handbooks consistently report acetylene's extremely wide explosive limits, necessitating strict flashback and backfire controls in oxy-acetylene systems. Why Other Options Are Wrong: Hydrogen: Very wide, but still narrower than acetylene.CO: Wide but not the widest among those listed.Petrol vapor: Composition-dependent and generally narrower than acetylene. Common Pitfalls: Assuming hydrogen is always the most hazardous due to low ignition energy; range width also matters.Ignoring the role of temperature and oxygen enrichment on limits. Final Answer: Acetylene

Q: Public health impact of leaded gasoline exhaust exposure: Which health effects are commonly associated with inhalation of lead compounds from vehicle emissions?

Introduction / Context: Before the global phaseout of tetraethyl lead in gasoline, ambient lead exposure from vehicle exhaust was a major public health concern. Understanding lead toxicity remains relevant for legacy contamination and certain industrial exposures. Given Data / Assumptions: Exposure pathway: inhalation of lead compounds in exhaust particulates. Population: urban residents, mechanics, and traffic workers (historically). Lead is a cumulative toxicant with multi-organ effects. Concept / Approach: Lead interferes with heme synthesis, causing anaemia; it is neurotoxic, affecting cognitive function and peripheral nerves; and it produces systemic toxicity known as plumbism (blood poisoning). Children are especially vulnerable to neurodevelopmental impacts at low levels. Step-by-Step Solution: 1) Identify toxicant: inorganic lead compounds in exhaust.2) Haematologic effect: inhibition of delta-ALA dehydratase and ferrochelatase → anaemia.3) Neurological effect: central and peripheral neurotoxicity → nervous system disorders.4) Systemic effect: classical plumbism encompassing GI, renal, and cardiovascular symptoms.5) Therefore, all listed health effects can occur. Verification / Alternative check: Public health literature documents reductions in blood-lead levels following unleaded fuel adoption, confirming the vehicular source-pathway. Why Other Options Are Wrong: Single effects (a), (b), or (c) understate lead’s multi-system toxicity. Common Pitfalls: Assuming only acute high-dose exposure is harmful; chronic low dose is also hazardous.Overlooking pediatric susceptibility and socioeconomic exposure patterns. Final Answer: All of the above (a), (b) & (c)

Q: Automotive emissions behavior: During which operating condition of a spark-ignition engine is the carbon monoxide (CO) concentration in the exhaust typically at its maximum?

Introduction / Context: CO formation in spark-ignition (SI) engines is strongly influenced by air–fuel ratio. Rich mixtures (fuel > stoichiometric) favor incomplete oxidation to CO, while leaner mixtures promote full conversion to CO2. Understanding CO behavior aids engine tuning and emission control strategies. Given Data / Assumptions: Conventional SI engine without transient-perfect controls (conceptual behavior also holds with modern systems though mitigated). Operating modes: idle, acceleration, cruise, and deceleration. CO correlates with rich operation and low excess oxygen. Concept / Approach: During acceleration, throttle opening increases and enrichment strategies (or transient wall-wetting effects) momentarily provide rich mixtures to prevent hesitation/knock and to deliver torque. This rich spike increases CO formation. Idle CO can be elevated if mixture is slightly rich, but generally lower than acceleration spikes. Cruise uses near-stoichiometric or slightly lean mixtures, and deceleration often cuts fuel or runs very lean, minimizing CO. Step-by-Step Solution: 1) Identify CO driver: rich mixtures with insufficient O2.2) Map operating modes: acceleration → richest; cruise → near stoichiometric; idle → moderate; decel → lean/fuel cut.3) Conclude maximum CO occurs during acceleration. Verification / Alternative check: Engine emission maps show transient CO peaks with throttle tip-in. Modern closed-loop systems and catalytic converters reduce the peak magnitude but the relative tendency remains. Why Other Options Are Wrong: Deceleration: Fuel cut/lean → minimal CO.Cruising: Near-stoichiometric/lean burn → low CO.Idle: Can be rich but generally lower CO than under load during acceleration. Common Pitfalls: Confusing hydrocarbon spikes at cold start with CO behavior during warm operation.Ignoring the catalytic converter’s role in post-combustion CO oxidation. Final Answer: Acceleration (rich mixture demand)

Q: Volcanic emissions — which pollutant is generally not released during eruptions? Identify the pollutant that is not typically emitted in significant amounts by volcanic activity.

Introduction / Context: Volcanic eruptions release large volumes of gases and aerosols that influence air quality and climate. Knowing the common constituents helps distinguish natural emissions from anthropogenic pollution sources. Given Data / Assumptions: Eruptive gases largely originate from magmatic volatiles. Major known volcanic gases include H2O, CO2, SO2, H2S, HCl, HF, and smaller amounts of CO. Hydrocarbons are typically associated with biogenic or petrogenic processes, not magmatic degassing. Concept / Approach: Magmas carry dissolved volatile species; upon decompression, these exsolve and vent. The geochemistry of magmatic systems favors simple molecules (H2O, CO2, SO2) rather than complex reduced hydrocarbons. Trace CO may occur from incomplete oxidation or high-temperature equilibria, but complex hydrocarbons are not characteristic products of volcanic degassing. Step-by-Step Solution: List typical volcanic gases: H2O, CO2, SO2, H2S, halogen acids, and trace CO.Compare with options: hydrocarbons are not characteristic of magmatic emissions.Conclude hydrocarbons are the least likely among the options. Verification / Alternative check: Volcanological surveys and gas monitoring consistently report SO2 and CO2 as dominant, with H2S and some CO present; hydrocarbons are rarely reported in significant quantities. Why Other Options Are Wrong: SO2: classic volcanic gas responsible for aerosol formation. H2S: common reduced sulfur gas from geothermal and volcanic vents. CO: detected in smaller amounts relative to CO2 and SO2. Common Pitfalls: Equating smoke-like plumes with hydrocarbon soot; volcanic plumes are dominated by inorganic gases and ash. Final Answer: Hydrocarbons

Q: Toxic metals and cardiovascular risk Exposure to small amounts of which substance is associated with high blood pressure and increased risk of heart disease in humans?

Introduction / Context: Chronic exposure to certain heavy metals can elevate cardiovascular risk by inducing oxidative stress, renal dysfunction, and endocrine disruption. Recognizing the key culprits is essential for occupational and environmental health. Given Data / Assumptions: Low-level, chronic exposure scenario. Outcome: hypertension and heart disease. Common environmental/industrial toxicants considered: cadmium, mercury, asbestos, hydrogen sulfide. Concept / Approach: Cadmium is well documented to cause nephrotoxicity and to be associated with hypertension. Cadmium accumulates in kidneys and blood vessels, promoting sodium retention and vascular dysfunction, which elevates blood pressure and contributes to cardiovascular disease. Mercury is neurotoxic and can affect the cardiovascular system but is less consistently tied to hypertension at low chronic doses compared with cadmium. Asbestos is a fibrous silicate linked to pulmonary disease and cancers, not hypertension. Hydrogen sulfide is an acute toxic gas primarily affecting respiration and the nervous system. Step-by-Step Solution: Identify which agent has the strongest epidemiologic link to hypertension.Cadmium exposure correlates with higher BP and cardiovascular events in population studies.Select cadmium as the correct answer. Verification / Alternative check: Occupational medicine references highlight cadmium-induced renal injury with secondary hypertension; public health advisories flag cadmium in tobacco smoke and certain industrial emissions. Why Other Options Are Wrong: Mercury: cardiovascular effects possible, but neurotoxicity is primary; association with BP is less definitive in low-level exposure. Asbestos: causes asbestosis and mesothelioma; not linked to hypertension. Hydrogen sulfide: acute asphyxiant, not a chronic cardiovascular toxin at small doses. Common Pitfalls: Assuming any toxic metal equally raises BP; mechanisms and dose–response differ. Final Answer: Cadmium

Q: Health effects of carcinogenic chemicals Exposure to chemicals with carcinogenic properties most directly leads to which outcome?

Introduction / Context: Chemicals are classified toxicologically by their principal adverse effects. Carcinogens are agents that increase the incidence of malignant or benign tumors. Understanding this label informs risk assessment, exposure limits, and control strategies. Given Data / Assumptions: Chemical exposure via occupational or environmental routes. Agent is labeled carcinogenic. We seek the primary, defining health outcome. Concept / Approach: By definition, a carcinogen is an agent that can initiate or promote uncontrolled cellular proliferation leading to tumor formation. Other toxic endpoints such as dermatitis, respiratory sensitization (asthma), or asphyxiation may occur with different classes of chemicals, but they do not define carcinogenicity. Step-by-Step Solution: Translate the term “carcinogenic” to its outcome: tumor/cancer formation.Exclude unrelated toxic endpoints (skin irritation, hypoxia, sensitization).Select cancer as the direct consequence. Verification / Alternative check: Regulatory frameworks (IARC, OSHA, REACH) define carcinogens precisely in relation to cancer hazard classifications. Why Other Options Are Wrong: Dermatitis: an irritant effect, not carcinogenicity. Asphyxiation: caused by oxygen displacement or respiratory poisons, unrelated to carcinogenic mechanism. Asthma: immunologic/irritant sensitization, not tumorigenesis. Common Pitfalls: Confusing “toxic” broadly with the specific endpoint “carcinogenic.” Final Answer: Cancer

Q: Environmental engineering basics:\nA shallow basin where municipal sewage is retained for natural biological treatment (sunlight, algae–bacteria symbiosis, long detention time) is called a…

Introduction / Context: Wastewater treatment can be achieved with low-energy, land-intensive systems that rely on sunlight and natural microbial communities. Recognizing unit names and their functions is fundamental for designing cost-effective treatment schemes for small towns and industrial estates. Given Data / Assumptions: Shallow depth, large surface area, and long detention for stabilization. Natural aeration (wind), photosynthetic oxygenation by algae, and bacterial oxidation. Municipal sewage or similar biodegradable wastewater. Concept / Approach: Oxidation ponds (lagoons) are engineered basins where organic matter is degraded biologically under aerobic, facultative, or anaerobic zones depending on depth and loading. They are simple to operate, robust to shock loads, and economical where land is available. The terms “lagoon” and “oxidation pond” are often used interchangeably in practice. Step-by-Step Solution: Match the description “shallow, natural treatment, long detention” with known units.Oxidation pond/lagoon precisely fits these attributes.Therefore, select “Lagoon (oxidation pond)”. Verification / Alternative check: Textbook process flow diagrams list oxidation ponds as low-rate biological systems with hydraulic retention times of days to weeks and depths typically around 1–1.5 m for facultative ponds. Why Other Options Are Wrong: Oxidation ditch: a mechanical aeration system (activated sludge variant), not a shallow passive pond.Imhoff tank: two-story sedimentation with anaerobic digestion below; not an open, shallow, sunlight-driven process.Skimming tank: removes floatables like oil/grease; not for full biological stabilization.Trickling filter: fixed-film aerobic reactor with media and underdrains, not a shallow lagoon. Common Pitfalls: Confusing oxidation ditches (mechanized) with oxidation ponds (passive). The energy footprint and operational complexity differ greatly. Final Answer: Lagoon (oxidation pond)

Question 1

Water treatment: For trace concentrations of organic contaminants (e.g., < 200 mg/L COD), which method is generally the most effective for removal?

Accepted Answer

Introduction / Context: Wastewater often contains small amounts of dissolved organic compounds that are not easily removed by sedimentation or simple biological treatment. Selecting the right polishing step is crucial to meet discharge or reuse standards. Given Data / Assumptions: Organic contaminants present at low (trace) levels, below roughly 200 mg/L. Goal: high-efficiency removal for polishing/tertiary treatment. Methods considered: adsorption, coagulation, biological ponds, lagooning. Concept / Approach: Activated carbon exhibits high surface area and affinity for a wide range of dissolved organics (e.g., phenols, dyes, taste/odor compounds). At low concentrations, adsorption performs better than bulk biological processes or coagulation, which are less selective for dissolved, non-particulate organics. Step-by-Step Solution: 1) Identify target phase: dissolved organics (not suspended solids).2) Match process: adsorption removes dissolved species effectively at low concentrations.3) Consider alternatives: coagulation targets colloids/particulates; ponds/lagooning require long retention and may not reach low residuals.4) Choose activated carbon adsorption as best option. Verification / Alternative check: Design manuals list granular activated carbon (GAC) filters or powdered activated carbon (PAC) dosing as standard polishing for low-level organics, often following biological treatment and clarification. Why Other Options Are Wrong: Chemical coagulation: Limited effect on dissolved, non-ionizable organics.Biological oxidation pond/Lagooning: Space- and time-intensive; variable performance at trace levels. Common Pitfalls: Expecting primary or secondary treatment alone to meet stringent organics limits.Ignoring carbon exhaustion and the need for regeneration/replacement. Final Answer: Activated carbon adsorption

Question 2

Blast furnace gas cleaning wastewater: Which unit process is typically used to remove suspended solids from BF gas cooling/cleaning effluent?

Accepted Answer

Introduction / Context: Blast furnace (BF) gas cleaning uses scrubbers and separators that produce wastewater laden with fine solids (flue dust, iron oxides). Effective primary treatment is needed to remove these suspended solids before downstream polishing or reuse. Given Data / Assumptions: Wastewater contains high suspended solids and colloidal fines. Objective: primary solid-liquid separation. Coagulant options available to enhance settling. Concept / Approach: Radial settling tanks (clarifiers) and thickeners provide quiescent zones for particle settling. Lime and ferrous sulphate destabilize colloids, increase floc size, and accelerate sedimentation. The dense underflow can be thickened and handled, while clarified overflow proceeds to further treatment if needed. Step-by-Step Solution: 1) Characterize solids: iron-rich fines with poor natural settling.2) Apply coagulation/flocculation: lime raises pH and aids coagulation; ferrous salts form hydroxide flocs.3) Use radial settlers/thickeners to separate flocculated solids efficiently.4) Produce clarified effluent and concentrated sludge for disposal or recovery. Verification / Alternative check: Steel plant water circuits commonly show BF scrubber effluents routed to thickeners with coagulant dosing before reuse or discharge. Why Other Options Are Wrong: Biological pond: Targets biodegradable organics, not primarily suspended mineral solids.Lagooning: Too slow and land-intensive for heavy solids loads.Filtration only: Rapid blinding and impractical without prior clarification. Common Pitfalls: Skipping coagulation, leading to carryover and poor clarity.Undersized settlers that cannot handle peak turbidities. Final Answer: Radial settling tank (thickener) with coagulant addition (lime and ferrous sulphate)

Question 3

Public health in water supply: Excess fluoride (fluorine) in drinking water most commonly leads to which condition?

Accepted Answer

Introduction / Context: Fluoride is a trace element with a narrow beneficial range. Low levels can reduce dental caries, but excessive intake leads to fluorosis. Water treatment decisions rely on understanding this dose-response relationship. Given Data / Assumptions: Drinking water contains fluoride above recommended limits. Exposure is chronic over years. Population-level health effects are of concern. Concept / Approach: Chronic excess fluoride causes dental fluorosis (mottling, enamel hypomineralization) and, at higher exposures, skeletal fluorosis (joint pain, stiffness, bone changes). The mechanism involves altered mineralization processes in developing teeth and bone. Step-by-Step Solution: 1) Identify contaminant: fluoride (F−) at elevated concentration.2) Map to health effect: excess → fluorosis (dental first; skeletal with prolonged high doses).3) Distinguish from cavities: low fluoride reduces caries; excess does not cause cavities.4) Conclude: the principal condition is fluorosis. Verification / Alternative check: Epidemiological studies in endemic regions consistently link high-fluoride groundwater with dental and skeletal fluorosis; defluoridation (e.g., activated alumina, Nalgonda process) reduces incidence. Why Other Options Are Wrong: Dental cavities/tooth decay: Associated with insufficient fluoride, not excess.Respiratory disease: Not a primary outcome of fluoride in water. Common Pitfalls: Assuming “more fluoride is always better.”Ignoring children's heightened susceptibility during enamel formation. Final Answer: Fluorosis

Question 4

Safety engineering: Which gas among the following has the widest flammability (explosive) limits in air, making it the most hazardous in this respect?

Accepted Answer

Introduction / Context: Flammability (explosive) limits define the range of fuel-air mixtures that can propagate flame. Wider limits indicate a gas is more easily ignitable over a broader concentration range, increasing handling and storage risk. Given Data / Assumptions: Standard conditions near ambient temperature and pressure. Typical lower and upper flammability limits (LFL/UFL) in air. Gases considered: acetylene, hydrogen, carbon monoxide, gasoline vapor. Concept / Approach: Acetylene has exceptionally wide limits (approx. LFL ~2.5% to UFL ~81% by volume in air). Hydrogen is also wide (~4% to 75%), but narrower than acetylene. Carbon monoxide (~12.5% to 74%) and gasoline vapor (range varies with composition, generally narrower) are less extreme. Step-by-Step Solution: 1) Compare LFL/UFL: determine width = UFL − LFL.2) Acetylene: ~78.5% width; Hydrogen: ~71% width; CO: ~61.5% width; Petrol vapor: narrower and temperature dependent.3) Conclude acetylene exhibits the widest flammability range. Verification / Alternative check: Chemical safety datasheets and fire protection handbooks consistently report acetylene's extremely wide explosive limits, necessitating strict flashback and backfire controls in oxy-acetylene systems. Why Other Options Are Wrong: Hydrogen: Very wide, but still narrower than acetylene.CO: Wide but not the widest among those listed.Petrol vapor: Composition-dependent and generally narrower than acetylene. Common Pitfalls: Assuming hydrogen is always the most hazardous due to low ignition energy; range width also matters.Ignoring the role of temperature and oxygen enrichment on limits. Final Answer: Acetylene

Question 5

Public health impact of leaded gasoline exhaust exposure: Which health effects are commonly associated with inhalation of lead compounds from vehicle emissions?

Accepted Answer

Introduction / Context: Before the global phaseout of tetraethyl lead in gasoline, ambient lead exposure from vehicle exhaust was a major public health concern. Understanding lead toxicity remains relevant for legacy contamination and certain industrial exposures. Given Data / Assumptions: Exposure pathway: inhalation of lead compounds in exhaust particulates. Population: urban residents, mechanics, and traffic workers (historically). Lead is a cumulative toxicant with multi-organ effects. Concept / Approach: Lead interferes with heme synthesis, causing anaemia; it is neurotoxic, affecting cognitive function and peripheral nerves; and it produces systemic toxicity known as plumbism (blood poisoning). Children are especially vulnerable to neurodevelopmental impacts at low levels. Step-by-Step Solution: 1) Identify toxicant: inorganic lead compounds in exhaust.2) Haematologic effect: inhibition of delta-ALA dehydratase and ferrochelatase → anaemia.3) Neurological effect: central and peripheral neurotoxicity → nervous system disorders.4) Systemic effect: classical plumbism encompassing GI, renal, and cardiovascular symptoms.5) Therefore, all listed health effects can occur. Verification / Alternative check: Public health literature documents reductions in blood-lead levels following unleaded fuel adoption, confirming the vehicular source-pathway. Why Other Options Are Wrong: Single effects (a), (b), or (c) understate lead’s multi-system toxicity. Common Pitfalls: Assuming only acute high-dose exposure is harmful; chronic low dose is also hazardous.Overlooking pediatric susceptibility and socioeconomic exposure patterns. Final Answer: All of the above (a), (b) & (c)

Question 6

Automotive emissions behavior: During which operating condition of a spark-ignition engine is the carbon monoxide (CO) concentration in the exhaust typically at its maximum?

Accepted Answer

Introduction / Context: CO formation in spark-ignition (SI) engines is strongly influenced by air–fuel ratio. Rich mixtures (fuel > stoichiometric) favor incomplete oxidation to CO, while leaner mixtures promote full conversion to CO2. Understanding CO behavior aids engine tuning and emission control strategies. Given Data / Assumptions: Conventional SI engine without transient-perfect controls (conceptual behavior also holds with modern systems though mitigated). Operating modes: idle, acceleration, cruise, and deceleration. CO correlates with rich operation and low excess oxygen. Concept / Approach: During acceleration, throttle opening increases and enrichment strategies (or transient wall-wetting effects) momentarily provide rich mixtures to prevent hesitation/knock and to deliver torque. This rich spike increases CO formation. Idle CO can be elevated if mixture is slightly rich, but generally lower than acceleration spikes. Cruise uses near-stoichiometric or slightly lean mixtures, and deceleration often cuts fuel or runs very lean, minimizing CO. Step-by-Step Solution: 1) Identify CO driver: rich mixtures with insufficient O2.2) Map operating modes: acceleration → richest; cruise → near stoichiometric; idle → moderate; decel → lean/fuel cut.3) Conclude maximum CO occurs during acceleration. Verification / Alternative check: Engine emission maps show transient CO peaks with throttle tip-in. Modern closed-loop systems and catalytic converters reduce the peak magnitude but the relative tendency remains. Why Other Options Are Wrong: Deceleration: Fuel cut/lean → minimal CO.Cruising: Near-stoichiometric/lean burn → low CO.Idle: Can be rich but generally lower CO than under load during acceleration. Common Pitfalls: Confusing hydrocarbon spikes at cold start with CO behavior during warm operation.Ignoring the catalytic converter’s role in post-combustion CO oxidation. Final Answer: Acceleration (rich mixture demand)

Question 7

Coke ovens and by-product plants — removal of low-strength phenolic water Phenolic wastewater from coke ovens with phenol concentration less than 100 mg/L is best treated by which method?

Accepted Answer

Introduction / Context: Phenolic water is a common effluent from coke ovens and by-product recovery units in integrated steel plants. When phenol concentrations are relatively low, choosing a cost-effective and reliable treatment process is vital to meet discharge norms while minimizing operating costs. Given Data / Assumptions: Source: coke oven and by-product plant effluent. Phenol concentration: less than 100 mg/L (low-strength phenolic water). Goal: reduce phenol to environmentally acceptable limits with stable operation. Concept / Approach: Biological processes are well suited for low to moderate concentrations of biodegradable organics, including phenols. Oxidation ponds (stabilization ponds) provide long detention time, sunlight exposure, algal–bacterial symbiosis, and natural aeration, enabling biodegradation of phenols at low loadings. Chemical coagulation is generally used for suspended solids and some colloids; it does not reliably destroy dissolved phenolic compounds. Chlorination can oxidize some phenolics but risks forming chlorinated by-products and is inefficient as a sole treatment at these concentrations. Step-by-Step Solution: Classify the wastewater as low-strength phenolic (< 100 mg/L).Match to a biological process that can mineralize phenols: oxidation pond is appropriate and economical.Exclude methods focused on solids removal (coagulation) or with by-product risks (excess chlorination).Select biological oxidation pond as the primary removal step. Verification / Alternative check: Design manuals for steel plant effluents recommend biological treatment (oxidation ponds, trickling filters, or activated sludge) for low phenol concentrations, with polishing if required. Why Other Options Are Wrong: Chlorination: may form chlorophenols and is not efficient as a single-step treatment. Chemical coagulation: targets particulates, not dissolved phenols. None of these: incorrect because an appropriate method (biological oxidation pond) exists. Common Pitfalls: Overdosing oxidants and creating toxic chlorinated by-products. Assuming physico-chemical clarification removes dissolved phenols effectively. Final Answer: Treatment in a biological oxidation pond

Question 8

Volcanic emissions — which pollutant is generally not released during eruptions? Identify the pollutant that is not typically emitted in significant amounts by volcanic activity.

Accepted Answer

Introduction / Context: Volcanic eruptions release large volumes of gases and aerosols that influence air quality and climate. Knowing the common constituents helps distinguish natural emissions from anthropogenic pollution sources. Given Data / Assumptions: Eruptive gases largely originate from magmatic volatiles. Major known volcanic gases include H2O, CO2, SO2, H2S, HCl, HF, and smaller amounts of CO. Hydrocarbons are typically associated with biogenic or petrogenic processes, not magmatic degassing. Concept / Approach: Magmas carry dissolved volatile species; upon decompression, these exsolve and vent. The geochemistry of magmatic systems favors simple molecules (H2O, CO2, SO2) rather than complex reduced hydrocarbons. Trace CO may occur from incomplete oxidation or high-temperature equilibria, but complex hydrocarbons are not characteristic products of volcanic degassing. Step-by-Step Solution: List typical volcanic gases: H2O, CO2, SO2, H2S, halogen acids, and trace CO.Compare with options: hydrocarbons are not characteristic of magmatic emissions.Conclude hydrocarbons are the least likely among the options. Verification / Alternative check: Volcanological surveys and gas monitoring consistently report SO2 and CO2 as dominant, with H2S and some CO present; hydrocarbons are rarely reported in significant quantities. Why Other Options Are Wrong: SO2: classic volcanic gas responsible for aerosol formation. H2S: common reduced sulfur gas from geothermal and volcanic vents. CO: detected in smaller amounts relative to CO2 and SO2. Common Pitfalls: Equating smoke-like plumes with hydrocarbon soot; volcanic plumes are dominated by inorganic gases and ash. Final Answer: Hydrocarbons

Question 9

Toxic metals and cardiovascular risk Exposure to small amounts of which substance is associated with high blood pressure and increased risk of heart disease in humans?

Accepted Answer

Introduction / Context: Chronic exposure to certain heavy metals can elevate cardiovascular risk by inducing oxidative stress, renal dysfunction, and endocrine disruption. Recognizing the key culprits is essential for occupational and environmental health. Given Data / Assumptions: Low-level, chronic exposure scenario. Outcome: hypertension and heart disease. Common environmental/industrial toxicants considered: cadmium, mercury, asbestos, hydrogen sulfide. Concept / Approach: Cadmium is well documented to cause nephrotoxicity and to be associated with hypertension. Cadmium accumulates in kidneys and blood vessels, promoting sodium retention and vascular dysfunction, which elevates blood pressure and contributes to cardiovascular disease. Mercury is neurotoxic and can affect the cardiovascular system but is less consistently tied to hypertension at low chronic doses compared with cadmium. Asbestos is a fibrous silicate linked to pulmonary disease and cancers, not hypertension. Hydrogen sulfide is an acute toxic gas primarily affecting respiration and the nervous system. Step-by-Step Solution: Identify which agent has the strongest epidemiologic link to hypertension.Cadmium exposure correlates with higher BP and cardiovascular events in population studies.Select cadmium as the correct answer. Verification / Alternative check: Occupational medicine references highlight cadmium-induced renal injury with secondary hypertension; public health advisories flag cadmium in tobacco smoke and certain industrial emissions. Why Other Options Are Wrong: Mercury: cardiovascular effects possible, but neurotoxicity is primary; association with BP is less definitive in low-level exposure. Asbestos: causes asbestosis and mesothelioma; not linked to hypertension. Hydrogen sulfide: acute asphyxiant, not a chronic cardiovascular toxin at small doses. Common Pitfalls: Assuming any toxic metal equally raises BP; mechanisms and dose–response differ. Final Answer: Cadmium

Question 10

Health effects of carcinogenic chemicals Exposure to chemicals with carcinogenic properties most directly leads to which outcome?

Accepted Answer

Introduction / Context: Chemicals are classified toxicologically by their principal adverse effects. Carcinogens are agents that increase the incidence of malignant or benign tumors. Understanding this label informs risk assessment, exposure limits, and control strategies. Given Data / Assumptions: Chemical exposure via occupational or environmental routes. Agent is labeled carcinogenic. We seek the primary, defining health outcome. Concept / Approach: By definition, a carcinogen is an agent that can initiate or promote uncontrolled cellular proliferation leading to tumor formation. Other toxic endpoints such as dermatitis, respiratory sensitization (asthma), or asphyxiation may occur with different classes of chemicals, but they do not define carcinogenicity. Step-by-Step Solution: Translate the term “carcinogenic” to its outcome: tumor/cancer formation.Exclude unrelated toxic endpoints (skin irritation, hypoxia, sensitization).Select cancer as the direct consequence. Verification / Alternative check: Regulatory frameworks (IARC, OSHA, REACH) define carcinogens precisely in relation to cancer hazard classifications. Why Other Options Are Wrong: Dermatitis: an irritant effect, not carcinogenicity. Asphyxiation: caused by oxygen displacement or respiratory poisons, unrelated to carcinogenic mechanism. Asthma: immunologic/irritant sensitization, not tumorigenesis. Common Pitfalls: Confusing “toxic” broadly with the specific endpoint “carcinogenic.” Final Answer: Cancer

Question 11

Environmental engineering basics:
A shallow basin where municipal sewage is retained for natural biological treatment (sunlight, algae–bacteria symbiosis, long detention time) is called a…

Accepted Answer

Introduction / Context: Wastewater treatment can be achieved with low-energy, land-intensive systems that rely on sunlight and natural microbial communities. Recognizing unit names and their functions is fundamental for designing cost-effective treatment schemes for small towns and industrial estates. Given Data / Assumptions: Shallow depth, large surface area, and long detention for stabilization. Natural aeration (wind), photosynthetic oxygenation by algae, and bacterial oxidation. Municipal sewage or similar biodegradable wastewater. Concept / Approach: Oxidation ponds (lagoons) are engineered basins where organic matter is degraded biologically under aerobic, facultative, or anaerobic zones depending on depth and loading. They are simple to operate, robust to shock loads, and economical where land is available. The terms “lagoon” and “oxidation pond” are often used interchangeably in practice. Step-by-Step Solution: Match the description “shallow, natural treatment, long detention” with known units.Oxidation pond/lagoon precisely fits these attributes.Therefore, select “Lagoon (oxidation pond)”. Verification / Alternative check: Textbook process flow diagrams list oxidation ponds as low-rate biological systems with hydraulic retention times of days to weeks and depths typically around 1–1.5 m for facultative ponds. Why Other Options Are Wrong: Oxidation ditch: a mechanical aeration system (activated sludge variant), not a shallow passive pond.Imhoff tank: two-story sedimentation with anaerobic digestion below; not an open, shallow, sunlight-driven process.Skimming tank: removes floatables like oil/grease; not for full biological stabilization.Trickling filter: fixed-film aerobic reactor with media and underdrains, not a shallow lagoon. Common Pitfalls: Confusing oxidation ditches (mechanized) with oxidation ponds (passive). The energy footprint and operational complexity differ greatly. Final Answer: Lagoon (oxidation pond)

Question 12

Air pollution focus:
Among the following criteria pollutants, which is generally considered the most severe due to its role in acid rain, respiratory irritation, and corrosion of materials?

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Introduction / Context: Environmental engineers prioritize pollutants based on toxicity, persistence, and population exposure. Sulfur dioxide has historically been a major contributor to acid deposition, visibility impairment, and acute respiratory effects, especially from coal- and oil-fired sources without flue gas desulfurization. Given Data / Assumptions: The comparison is limited to the listed common gaseous pollutants. “Most severe” is interpreted in the classical regulatory/impact sense considering acid rain formation and direct health/material impacts. No special local context that would elevate others beyond typical global prioritization. Concept / Approach: SO2 oxidizes in the atmosphere to sulfates, forming acid aerosols and precipitation that damage ecosystems, buildings, and human health. While NOx, VOCs, CO, and particulates are serious, SO2’s combined roles in acid deposition and direct irritation often place it at the top of legacy severity rankings for combustion sources. Step-by-Step Solution: Evaluate each pollutant’s primary impacts.Hydrocarbons and NOx are key for ozone/smog; CO is toxic but typically localized; PM is critical but not listed as the correct choice in this classic comparison set.SO2 uniquely couples acid rain formation with health/materials harm.Thus, choose “Sulfur dioxide (SO2)”. Verification / Alternative check: Historical air-quality management (e.g., desulfurization programs) targeted SO2 early due to its outsized environmental footprint relative to many sources. Why Other Options Are Wrong: Hydrocarbons/NOx: central to photochemical smog, but here SO2 is traditionally judged more severe per the prompt framing.CO: acutely toxic yet less corrosive and not linked to acid rain.Particulates: highly important but not the keyed answer in this particular comparison; many PM issues also stem from SO2 forming sulfates. Common Pitfalls: Equating ozone/smog severity with overall environmental severity in every context; acid rain and sulfate PM impacts from SO2 remain historically pivotal. Final Answer: Sulfur dioxide (SO2)

Question 13

Water treatment fundamentals:
For removing suspended solids from polluted water in the most practical and economical way (prior to finer polishing), which primary unit operation is used?

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Introduction / Context: Designing a treatment train starts with the cheapest bulk separation steps. Suspended solids are best handled early by gravity clarification before moving on to filtration, biological treatment, or disinfection. Picking the right first step minimizes lifecycle cost and footprint. Given Data / Assumptions: Suspended solids are the primary concern at this stage. We seek a practical, economical process suitable for large flows. Pre-treatment chemicals (coagulants) may be added to enhance settling where needed. Concept / Approach: Sedimentation (clarification) exploits gravity to settle denser-than-water particles in quiescent basins or clarifiers. It is simple, robust, and cost-effective. Skimming targets floatables; chlorination kills pathogens but does not remove solids; biological oxidation degrades dissolved/colloidal organics, not settleable solids; reverse osmosis is too costly for bulk solids removal. Step-by-Step Solution: Match contaminant type (suspended solids) to the most economical separation (settling).Confirm alternatives: skimming is for oils/greases; chlorination is for disinfection; biological oxidation is secondary treatment; RO is polishing.Select “Sedimentation (clarification)”. Verification / Alternative check: Standard water and wastewater flowsheets place primary clarifiers ahead of aeration basins and filters to cut loadings and operating costs. Why Other Options Are Wrong: Skimming: limited to floatables, not general suspended solids.Chlorination: does not remove solids; it disinfects.Biological oxidation: targets dissolved/colloidal organics; not a primary solids removal step.Reverse osmosis: excessive cost/complexity for bulk solids removal. Common Pitfalls: Jumping to advanced membranes when gravity settling provides a cheaper, simpler solution with fewer fouling issues. Final Answer: Sedimentation (clarification)

Question 14

Human sensory detection of gaseous pollutants:
Which of the following common atmospheric pollutants is readily detectable by its characteristic pungent odour at low concentrations?

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Introduction / Context: Basic sensory cues can indicate the presence of certain pollutants. While monitoring instruments are essential for compliance, some contaminants have distinctive smells that alert workers and residents to potential exposure in the absence of meters. Given Data / Assumptions: Ambient or workplace air with potential combustion-related pollutants. Question asks which is detectable by odour to humans. We assume typical sensitivity ranges and common descriptions from safety data references. Concept / Approach: Sulfur dioxide has a sharp, choking, pungent odour that becomes noticeable at relatively low concentrations. By contrast, carbon monoxide and carbon dioxide are odourless; nitrogen dioxide has a harsh acrid smell but is often less immediately recognized by laypersons; ozone has a distinctive sharp smell but is not listed as the keyed answer in classical introductory sets where SO2 is emphasized for odour and irritation from combustion sources. Step-by-Step Solution: Evaluate odour properties: CO and CO2 are odourless; SO2 is pungent; NO2 acrid; O3 sharp.Align with typical teaching focus: SO2 is commonly cited as odour-detectable and irritating from sulfurous fuels.Hence, select “Sulfur dioxide (SO2)”. Verification / Alternative check: Safety datasheets and occupational hygiene texts list SO2 as having a strong, irritating odour at low ppm levels; CO/CO2 are explicitly odourless. Why Other Options Are Wrong: CO: odourless and colorless—particularly dangerous for this reason.NO2: acrid smell but not the canonical introductory answer; many learners misidentify it.CO2: odourless, non-irritating at low levels.O3: characteristic smell, but the question focus typically highlights SO2 in combustion contexts. Common Pitfalls: Assuming “toxic = smelly.” CO is a classic counterexample—highly dangerous yet odourless. Final Answer: Sulfur dioxide (SO2)

Question 15

Coagulation in water treatment: effect of temperature on chemical coagulant dose
In conventional clarification (e.g., alum or ferric salts), how does the required coagulant dosage typically change as the temperature of the polluted/raw water increa…

Accepted Answer

Introduction / Context: Coagulation–flocculation is a fundamental step in water and wastewater treatment. Operators often ask how seasonal temperature changes affect the chemical dose of coagulants (such as alum, ferric chloride, or polyaluminum chloride). Temperature influences viscosity, mixing, collision frequency, and the formation/settling of flocs. Understanding this relationship helps optimize chemical cost and finished water quality. Given Data / Assumptions: Same raw water source and comparable quality except for temperature. Conventional treatment with rapid mix, flocculation, and sedimentation. No dramatic shock loads of organics or turbidity beyond typical seasonal variation. Concept / Approach: As temperature rises, water viscosity decreases, which increases Brownian motion and reduces hydraulic resistance during aggregation. This raises the probability of effective collisions between destabilized particles, improving floc growth at a given coagulant dose. Warmer water also hastens hydrolysis reactions for metal-salt coagulants, reducing the dose needed to reach target zeta potential and floc strength. Step-by-Step Solution: Identify the control variable: raw water temperature increases.Link to mechanisms: lower viscosity and faster hydrolysis → better flocculation kinetics.Operational implication: to achieve the same clarified turbidity/TOC removal, chemical dose can generally be reduced. Verification / Alternative check: Jar tests performed at different temperatures typically show equal or better turbidity removal at a lower coagulant dose as temperature increases. Plant records frequently reflect lower winter performance and higher doses, whereas summer operation often permits dose cuts while maintaining residual criteria. Why Other Options Are Wrong: Increases.: Opposite of typical behavior; colder water usually needs more, not less.Remains constant.: Ignores well-established temperature effects on viscosity and reaction rates.may increase or decrease ; depends on the chemical characteristics of polluted water.: While raw-water chemistry matters, the dominant temperature trend is a decreasing dose with higher temperature for comparable quality targets. Common Pitfalls: Assuming temperature alone dictates dose. Alkalinity, NOM character, and turbidity also drive demand; always confirm with jar tests. Over-reduction of dose can increase filtered-water turbidity or aluminum/iron residuals. Final Answer: decreases.

Question 16

Most hazardous common radionuclide emitter: which one releases α, β, and γ radiation?
Select the radioactive waste that emits all three types of ionising radiation, making it especially hazardous during handling and shielding design.

Accepted Answer

Introduction / Context: Radiation safety in environmental engineering and nuclear waste management hinges on knowing the emission type of radionuclides. Alpha (α), beta (β), and gamma (γ) radiations differ strongly in penetration and shielding requirements. A nuclide (or its decay chain) that presents all three poses broader hazards for storage and transport. Given Data / Assumptions: Compare I-131, Sr-90, Au-198, and Ra-226 with respect to emitted radiation. Consider both the parent and immediate daughters in practical handling scenarios. Concept / Approach: Ra-226 is an alpha emitter whose decay chain rapidly produces gamma-emitting daughters; in practice, the stored material presents α, β, and γ fields. By contrast, Sr-90 is a strong β emitter (with Y-90) and minimal γ; I-131 mainly emits β and γ; Au-198 emits β with notable γ but not α. Step-by-Step Solution: Identify nuclide emissions: Ra-226 → α plus γ from daughters → composite α/β/γ hazard.Contrast with Sr-90: primarily β (and bremsstrahlung if poorly shielded), limited γ.Contrast with I-131 and Au-198: β and γ present, but no α from the parent. Verification / Alternative check: Standard decay scheme charts show Ra-226 (half-life ~1600 years) decays to Rn-222 and further daughters producing penetrating γ; alpha contamination and gamma fields both require attention. Why Other Options Are Wrong: I-131: β + γ, no α.Sr-90: β (with Y-90), essentially no γ photons of concern.Au-198: β + γ, but no α. Common Pitfalls: Overlooking daughter products when planning shielding. With Ra-226, both contamination control (α) and external dose (γ) must be managed. Final Answer: Ra-226

Question 17

Drinking water clarity benchmark: typical desirable turbidity limit
For potable water acceptability in distribution, what is a commonly specified desirable turbidity (expressed in NTU; historically reported as “ppm” in some texts) used by many stan…

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Introduction / Context: Turbidity is a key indicator of particulate content and aesthetic quality in drinking water. Lower turbidity improves disinfection efficacy and reduces the risk of microbial breakthrough. Although turbidity is properly measured in NTU (nephelometric turbidity units), older materials sometimes loosely refer to “ppm”; in practice, specifications are stated in NTU. Given Data / Assumptions: Focus on a commonly cited “desirable” benchmark for finished water (not a relaxed upper emergency limit). Modern distribution systems aim for very low turbidity post-filtration. Concept / Approach: Many guidelines specify a desirable finished water turbidity of about 1 NTU or less at consumers’ taps, with regulatory maxima for conventional treatment typically set at or below 1 NTU in continuous monitoring and occasional short-term limits up to 5 NTU (depending on jurisdiction). Therefore, among the options, 1 is the closest and most appropriate desirable value. Step-by-Step Solution: Clarify units: use NTU as the practical unit.Identify typical desirable target: ≈1 NTU for aesthetic quality and barrier effectiveness.Select the nearest offered value: 1. Verification / Alternative check: Plant performance data for well-operated rapid sand or membrane filtration routinely show < 0.3–1.0 NTU; many utilities set internal goals tighter than regulatory maxima to safeguard disinfection. Why Other Options Are Wrong: 10: Too high for desirable finished water; would be visibly cloudy.250 and 1000: Extremely turbid; represent raw water conditions, not potable water. Common Pitfalls: Confusing “regulatory maximum” with “desirable target.” Always design and operate toward the lower, more protective figure. Final Answer: 1

Question 18

Identify the primary (not secondary) air pollutant in the list
Among the following, which pollutant is not formed in the atmosphere by secondary reactions but is emitted directly from sources?

Accepted Answer

Introduction / Context: Air pollutants are often classified as primary (emitted directly from sources) or secondary (formed in the atmosphere via chemical reactions). Recognizing which is which guides policy and control strategies, because primary pollutants are controlled at the stack/tailpipe, while secondary pollutants require precursor controls and atmospheric chemistry management. Given Data / Assumptions: Ozone and photochemical smog are classic secondary pollutants. Sulphur dioxide (SO₂) is emitted directly by combustion of sulphur-containing fuels and certain industrial processes. Concept / Approach: Tropospheric ozone forms via photochemical reactions involving NOx and VOCs; “photochemical smog” is a composite secondary pollution episode featuring ozone, peroxyacyl nitrates, and oxidants. By contrast, SO₂ emerges primarily from power plants, refineries, smelters, and ships burning sulphur-bearing fuels. Step-by-Step Solution: Classify each option: Ozone → secondary; Photochemical smog → secondary; SO₂ → primary.Select the item that is not secondary: SO₂. Verification / Alternative check: Emission inventories show SO₂ directly measured at sources; atmospheric models treat ozone as a product of precursor chemistry, not as an emitted component. Why Other Options Are Wrong: Ozone: secondary oxidant; not emitted.Photochemical smog: by definition secondary and complex.All (a), (b) & (c): Incorrect because one item (SO₂) is primary. Common Pitfalls: Confusing stratospheric ozone (beneficial) with tropospheric ozone (pollutant). Here we refer to ambient ground-level ozone. Final Answer: Sulphur dioxide

Question 19

Pick the incorrect environmental statement (BOD/COD, engine NOx, stratospheric profile, greenhouse effect)
From the options below, identify the statement that is wrong based on fundamental environmental engineering principles.

Accepted Answer

Introduction / Context: Several staple facts in environmental engineering are tested here: the BOD–COD relationship, NOx propensity of engine cycles, vertical temperature structure of the stratosphere, and the physical basis of the greenhouse effect. One statement is deliberately reversed and must be identified as incorrect. Given Data / Assumptions: BOD measures biodegradable organic load; COD measures total chemically oxidisable matter. Four-stroke spark-ignition engines typically have higher combustion temperatures and can produce more NOx than two-stroke counterparts (which tend to emit more HC and CO). Stratosphere exhibits a temperature inversion; temperature increases with altitude due to ozone absorption of UV. Greenhouse effect involves shortwave solar input and longwave terrestrial re-radiation. Concept / Approach: Check each statement against fundamentals. The greenhouse statement is inverted: the atmosphere (and greenhouses) readily transmit shortwave solar radiation and restrict the escape of longwave infrared radiation emitted by the Earth’s surface. Step-by-Step Solution: (a) BOD < COD: Correct (biodegradable fraction is part of chemically oxidisable load).(b) 4-stroke vs 2-stroke NOx: Plausible/commonly true due to higher in-cylinder temperatures and better scavenging control in 4-strokes.(c) Stratospheric temperature profile: Correct (temperature rises with altitude).(d) Greenhouse statement: Wrong; it should read “allows shortwave solar radiation in and impedes longwave infrared out.” Verification / Alternative check: Textbook radiative balance and atmospheric profiles confirm (c); standard wastewater texts confirm BOD < COD; emission characterization of SI engines aligns with (b). Why Other Options Are Wrong: Only option (d) is incorrect; (a), (b), and (c) are consistent with fundamentals. Common Pitfalls: Mixing up “shortwave in” and “longwave out” in greenhouse descriptions; it is a frequent exam trick. Final Answer: The characteristic of a green house body is that it allows the long wavelength incoming solar radiation to come in but does not allow the short wavelength infra red radiation to escape out of the earth's atmosphere.

Question 20

Noise pollution control: identify the ineffective measure
Which listed measure does not mitigate environmental noise and therefore cannot be considered a control method?

Accepted Answer

Introduction / Context: Noise control relies on source, path, and receiver interventions. Common engineering measures include source quieting (silencers, mufflers), structural strategies (vibration isolation, damping), and path barriers (acoustic walls, vegetation belts). The question probes basic literacy by including an unrelated environmental term. Given Data / Assumptions: Context is environmental acoustics in communities and industry. Options include known noise controls and one unrelated concept. Concept / Approach: Greenhouse gases (CO₂, CH₄, N₂O, etc.) affect climate radiative forcing, not sound propagation or source emission. By contrast, silencers reduce acoustic energy at exhausts/intakes, vibration damping lowers structural-borne noise, and tree belts provide limited but real path attenuation and psychoacoustic benefits. Step-by-Step Solution: Classify options into “noise control” or “not related.”Silencers, damping, and tree plantation → noise controls.Green house gases → unrelated to noise → not a control measure. Verification / Alternative check: Standard acoustics texts describe mufflers and damping; urban planning guidelines endorse green buffers to reduce perceived noise levels. Why Other Options Are Wrong: Use of silencers: Effective source control for engines and blowers.Vibration damping: Reduces structure-borne transmission.Tree plantation: Acts as a path barrier and provides psychological relief; while modest in decibel terms, it is a recognized measure. Common Pitfalls: Overestimating the dB reduction from vegetation alone; dense engineered barriers are typically more effective than trees. Final Answer: Green house gases

Environmental Engineering Questions