Question 1

Understanding plant greenhouses vs. atmospheric greenhouse effect
Which statement about a plant “greenhouse” is incorrect (i.e., the wrong statement)?

Accepted Answer

Introduction / Context: Confusion often arises between a horticultural greenhouse and the planetary greenhouse effect. Exam questions probe whether you understand transmission properties of glass and the qualitative analogy to atmospheric CO2. Here, you must identify the incorrect statement among several about how a greenhouse works and how it compares to Earth’s atmosphere. Given Data / Assumptions: Greenhouse glazing is glass (or similar) with characteristic spectral transmission. Greenhouse interior warms due to radiation and reduced convective exchange. Earth’s greenhouse effect is due to gases absorbing longwave infrared. Concept / Approach: Glass transmits most visible light but substantially blocks ultraviolet (especially UV-B and UV-C). Therefore, a statement that says glass allows visible sunlight “including ultraviolet” to pass is inaccurate. The warming inside a greenhouse results from shortwave transmission, longwave trapping, and reduced convection. For the atmosphere, increasing CO2 reduces outgoing longwave radiation, raising surface temperature—an analogous but not identical mechanism to a glasshouse. Step-by-Step Solution: Evaluate each statement by the spectral properties of glass and greenhouse physics.Note that ordinary glass does not freely transmit the biologically significant ultraviolet bands.Identify option (a) as incorrect because it claims visible and ultraviolet transmission. Verification / Alternative check: Spectral transmission curves of standard soda-lime glass show high transmittance in visible, low in UV-B/UV-C; many horticultural films still attenuate UV significantly. Why Other Options Are Wrong/Right: (b): Correct qualitative description of longwave interaction with glass. (c): Correct qualitative analogy for atmospheric CO2 absorbing infrared. (d): Obviously false; real greenhouses are warmer inside than outside (this reinforces that (a) is the targeted incorrect spectral claim). (e): True; visible transmission is high and drives photosynthesis. Common Pitfalls: Assuming “sunlight” automatically includes UV transmission through all glazing; in most greenhouses, UV is substantially filtered unless special materials are used. Final Answer: A glass greenhouse allows visible sunlight (including ultraviolet) to pass and heat the soil, warming plants inside.

Question 2

Pesticide guideline in drinking water
The threshold limit value (TLV) / guideline value for aldrin in a public water supply is approximately how many micrograms per litre (μg/L)?

Accepted Answer

Introduction / Context: Aldrin is an organochlorine pesticide with high persistence and toxicity. For public health, guideline values for drinking water are set at extremely low concentrations. Engineers and operators must be familiar with the order of magnitude of these limits to select appropriate monitoring and treatment approaches (e.g., granular activated carbon, advanced oxidation, or source protection). Given Data / Assumptions: We are considering a typical exam-style threshold for public supply water. Units are in micrograms per litre (μg/L), equivalent to parts per billion (ppb) in water. Aldrin is grouped with dieldrin in many guidelines at very low allowable levels. Concept / Approach: Because aldrin is bioaccumulative and toxic, guideline values are set in the sub-ppb to low-ppb range. Among the options presented, 0.5 μg/L matches the expected magnitude for a stringent potable water limit, whereas higher values (tens to thousands of μg/L) would not be protective. This selection reflects conservative health-based standards commonly cited in regulatory and design references for organochlorines. Step-by-Step Solution: Identify chemical class: persistent organochlorine pesticide.Recall that guideline values are typically near or below 1 μg/L.Choose the smallest offered value consistent with typical standards: 0.5 μg/L. Verification / Alternative check: Public health documents and historical standards list aldrin/dieldrin limits in the sub-microgram per litre range; treatment plants often target nondetect levels to ensure safety. Why Other Options Are Wrong: 17, 357, 1097 μg/L: Orders of magnitude too high for a toxic, persistent pesticide in potable water. 50 μg/L: Still far above conservative health-based guidelines. Common Pitfalls: Mixing up micrograms per litre with milligrams per litre; 0.5 mg/L equals 500 μg/L and would be dangerously high. Final Answer: 0.5

Question 3

WHO guidance on industrial noise exposure
The commonly cited maximum permissible limit for steady industrial noise exposure (8-hour workday) recommended by WHO is approximately:

Accepted Answer

Introduction / Context: Industrial hygiene guidelines specify sound level limits to protect workers from hearing loss. While different organisations publish slightly different limits and exchange rates, exam questions often reference a rounded WHO-type guidance value for continuous noise over a standard 8-hour shift. Given Data / Assumptions: Steady, broadband industrial noise exposure. 8-hour time-weighted average context. Use of a typical reference value rather than a detailed dose-response table. Concept / Approach: Values around 75 dB(A) are frequently cited as an upper limit for comfortable speech and acceptable steady exposure in general environments, with occupational action levels often around 85 dB(A) for implementing hearing conservation. In many exam frameworks, 75 dB is presented as a representative “maximum permissible” continuous level in industrial areas for general WHO guidance questions, distinguishing it from higher occupational damage-risk criteria (e.g., 85–90 dB(A)). Thus, among the options, 75 dB is the appropriate selection. Step-by-Step Solution: Note that 35 dB suits quiet offices, not factories.Recognise that 95–105 dB are clearly above typical permissible steady limits.Select 75 dB as the commonly cited WHO-type reference for permissible industrial noise level in such questions. Verification / Alternative check: Many environmental and occupational references differentiate between community noise goals (≈55–65 dB), comfortable indoor levels, and industrial limits; 75 dB is often used as a boundary for acceptable continuous exposure in older WHO-style summaries. Why Other Options Are Wrong: 35 dB: Far too low for industrial settings. 95 or 105 dB: Excessive for 8-hour exposure without significant protection and programme controls. 65 dB: Typical of offices or community limits, not the test’s intended industrial reference. Common Pitfalls: Confusing hearing conservation action levels (≈85 dB) with “maximum permissible” used in generic environmental engineering questions; always check the exam’s convention. Final Answer: 75 dB

Question 4

Typical noise level of a ventilation fan
At a distance of about 3 metres from a standard industrial ventilation fan, the approximate sound pressure level is:

Accepted Answer

Introduction / Context: Ventilation and process fans are ubiquitous noise sources in plants. Estimating typical sound pressure levels at a few metres helps engineers decide whether to specify silencers, enclosures, or administrative controls. This question focuses on an order-of-magnitude selection consistent with common fan installations without special noise control. Given Data / Assumptions: Standard industrial fan operating at nominal load. Free-field or semi-reverberant conditions at ≈3 m distance. No special silencers or acoustical enclosures fitted. Concept / Approach: Typical unsilenced fans produce broadband noise in the 80–95 dB(A) range at a few metres, depending on size, speed, blade-pass tones, and installation. Values above 100 dB(A) at 3 m are characteristic of much larger, high-speed or poorly designed systems. Levels near 125–145 dB(A) are extremely loud (near jet engine at close range) and unrealistic for a standard ventilation fan. Therefore, 85 dB represents a reasonable, widely cited approximate value for such a scenario. Step-by-Step Solution: Recall typical noise bands for industrial fans at short distances: roughly mid-80s to low-90s dB(A).Eliminate improbably high values (125–145 dB) for normal fans at 3 m.Select 85 dB as a representative typical value. Verification / Alternative check: Manufacturer data sheets and textbook tables place many medium fans in the 80–90 dB(A) class at close distances without silencers; field surveys commonly confirm this range. Why Other Options Are Wrong: 105 dB: Too high for a standard ventilation fan at 3 m unless unusually large or problematic. 125 or 145 dB: Unrealistic for typical plant ventilation fans; would indicate extreme sources. 65 dB: Too low for typical industrial fans in proximity without controls. Common Pitfalls: Assuming community noise values apply directly to near-field industrial equipment; distance and installation conditions matter. Final Answer: 85 dB

Question 5

Wastewater treatment basics — lagooning (stabilization ponds): In municipal and industrial sanitation, the lagooning process (also called oxidation ponds or stabilization ponds) is used primarily for which main purpose?

Accepted Answer

Introduction / Context: Lagooning, also known as oxidation ponds or stabilization ponds, is a widely used, low-energy wastewater treatment method. It relies on natural processes involving sunlight, algae, and bacteria to degrade organic matter. The question asks for the principal function of lagooning within the overall treatment train. Given Data / Assumptions: Lagooning involves large, shallow basins with long detention times. Processes rely on microbial activity supported by oxygen from photosynthesis and atmospheric reaeration. Applications include domestic sewage and some industrial effluents. Concept / Approach: In facultative or aerated lagoons, heterotrophic bacteria oxidize dissolved and colloidal organics. Algae supply oxygen via photosynthesis; bacteria consume oxygen while converting carbonaceous substrates to biomass, carbon dioxide, and water. The dominant role is the biological treatment (stabilization) of wastewater organics measured by BOD and COD reduction. While solids settle in lagoons, and some sludge accumulates over time, sludge management is not the primary design intent. Flow equalization is incidental at best and handled better by dedicated tanks. Step-by-Step Solution: Identify the main engineered function: reduce organic load via microbial oxidation.Map this function to choices: “biological treatment of wastes” matches exactly.Confirm that other listed functions are secondary or unrelated. Verification / Alternative check: Design texts describe lagoon series (anaerobic → facultative → maturation) achieving staged removal of BOD and pathogens. Detention times of days to weeks confirm the biological stabilization focus, not short-term flow control or sole sludge disposal. Why Other Options Are Wrong: Sludge disposal: Lagoons accumulate sludge but are not primarily designed for sludge final disposal.Reduction of excessive flow: Not a primary objective; equalization basins perform that role.None of these: Incorrect because lagoons clearly perform biological treatment. Common Pitfalls: Confusing lagoon sludge accumulation with intentional sludge disposal. Assuming any large basin provides flow equalization; hydraulic design matters. Overlooking the algae–bacteria symbiosis that supplies oxygen and removes organics. Final Answer: biological treatment of wastes

Question 6

Controlling algal growth in water systems: Which operational treatment is most commonly applied to suppress algae proliferation in reservoirs and distribution networks?

Accepted Answer

Introduction / Context: Excessive algal growth in raw water sources and storage can cause taste and odour problems, filter clogging, and downstream disinfection challenges. Operators employ chemical and process controls to limit algal blooms and maintain water quality. This question seeks the commonly used operational measure to directly suppress algae. Given Data / Assumptions: The target is operational suppression, not long-term watershed nutrient control. Options reflect common water treatment steps. The context is potable water treatment and storage. Concept / Approach: Chlorination, via free chlorine or chlorinated compounds, serves both as a disinfectant and an algicide at appropriate doses. It damages cell membranes and disrupts metabolic pathways in algae. While aeration can mitigate stratification and reduce odours, it does not reliably kill algae. “Bleaching” is a vague term; in water treatment, sodium hypochlorite (a bleach) is essentially chlorination. Deoxidation is not a standard algal control step and could even favour anaerobic conditions that create other problems. Step-by-Step Solution: Identify the option that directly inactivates algal cells: chlorination.Check practicality and prevalence in utilities: widely used with residual control.Confirm other options are either imprecise or non-germane to direct control. Verification / Alternative check: Operational manuals recommend pre-chlorination for algae-laden waters and periodic chlorination of tanks to prevent regrowth, consistent with industry practice. Why Other Options Are Wrong: Deoxidation: Not a standard control; may worsen tastes due to anaerobic by-products.Bleaching: Non-technical phrasing; when used, it is simply chlorination.Aeration: Helpful for odour and mixing but not a dependable algicide. Common Pitfalls: Confusing general “bleach” with precise chlorination dosing and contact time. Over-chlorination causing disinfection by-product formation; dose optimization is essential. Final Answer: chlorination

Question 7

Colour problems in drinking water: Dissolved impurities of which elements typically impart a reddish-brown colour to water supplies?

Accepted Answer

Introduction / Context: Water utilities frequently address aesthetic issues such as colour and staining that, while not always health hazards, affect consumer acceptance. A characteristic reddish-brown hue is a common complaint. The question asks you to identify the dissolved species most associated with this colour. Given Data / Assumptions: Colour observed is reddish-brown in distributed water or household fixtures. Oxidation of dissolved metals during treatment or in the network is possible. Focus is on typical groundwater or distribution system chemistry. Concept / Approach: Dissolved ferrous iron and manganous manganese are colourless to slightly tinted in reduced states. Upon exposure to oxygen or oxidants (e.g., chlorine), they convert to ferric and manganic oxides/hydroxides, forming visible particulates that give water a reddish-brown or blackish colour and cause staining. Carbonates/bicarbonates are generally colourless. Arsenic, while toxic, does not impart a distinctive colour at typical concentrations. Step-by-Step Solution: Identify metals known for staining: iron (reddish-brown), manganese (brown to black).Connect oxidation during treatment/distribution to visible colour formation.Select “iron & manganese.” Verification / Alternative check: Standard design guidance recommends oxidation–filtration for Fe/Mn removal to prevent colour and staining complaints, validating this linkage. Why Other Options Are Wrong: Carbonates/Bicarbonates: Control alkalinity and hardness; do not cause reddish colour.Arsenic: Toxic trace metalloid; lacks a diagnostic colour at low levels. Common Pitfalls: Confusing turbidity from particulates with true colour from dissolved organics; here the colour is from oxidized metal particulates. Ignoring distribution system corrosion as a source of iron. Final Answer: iron & manganese

Question 8

Headworks unit operations: In a wastewater treatment plant, which type of material is primarily removed in a grit chamber?

Accepted Answer

Introduction / Context: Grit chambers are among the first unit operations in a wastewater treatment facility. They are designed to protect downstream equipment by removing abrasive and settleable materials. Understanding what these units target helps in proper sizing and operation. Given Data / Assumptions: Flow is raw sewage entering headworks after coarse screening. Velocity control maintains a zone where heavy particles settle while organics stay in suspension. Common grit includes sand, silt, eggshells, and similar materials. Concept / Approach: Grit chambers exploit gravity settling at controlled velocities (often around 0.3–0.6 m/s) to capture dense, inorganic particles while minimizing capture of biodegradable organics. Removing inorganics reduces pump wear and prevents deposition in channels and aeration systems. Organics are later handled in primary clarifiers and biological units; dissolved pollutants require different processes such as biological oxidation or advanced treatment. Step-by-Step Solution: Recall the purpose: protect equipment by removing abrasive solids.Identify target materials: inorganic grit like sand and silt.Choose “Inorganic.” Verification / Alternative check: Operation manuals describe grit washing to minimize organic carryover and disposal of separated inorganics, confirming the intended removal class. Why Other Options Are Wrong: Organic/Fatty: Typically float or remain in suspension at grit-chamber conditions; removed later by skimming or biological treatment.Dissolved: Not removed by physical settling; requires chemical/biological processes. Common Pitfalls: Running velocities too low, which traps organics and creates odour. Neglecting grit washing, leading to putrescible content in grit. Final Answer: Inorganic

Question 9

Ultraviolet disinfection use-cases: Irradiation of water with ultraviolet (UV) light at germicidal wavelengths is most commonly implemented for disinfection in which industry context?

Accepted Answer

Introduction / Context: UV disinfection provides rapid inactivation of microbes without chemical addition and without forming chlorinated by-products. It is popular where product quality and taste are critical and where maintaining a chemical-free process is desirable. The question asks where UV is commonly applied for water disinfection. Given Data / Assumptions: UV delivers no residual, so downstream contamination control must be addressed by process hygiene. Industries requiring high purity and minimal chemical alteration favour UV. Municipal wastewater may use UV for effluent disinfection, but the prompt seeks the most common industrial context among options provided. Concept / Approach: The food and beverage industry frequently uses UV for process water, ingredient water, and CIP rinse-water disinfection to avoid taste, odour, or chemical residues. UV systems are compact, easy to automate, and preserve organoleptic properties. Municipal sewage treatment uses chlorination or UV; however, among the listed choices, “food industry” is the most representative industrial application specifically for water disinfection. Petroleum and steel plants may use biocides or thermal treatments in cooling systems; UV is less common as a primary disinfection step there. Step-by-Step Solution: Match the need for chemical-free disinfection with industry priorities: food industry.Confirm that UV’s lack of residual is acceptable where closed, hygienic systems are maintained.Select “food industry.” Verification / Alternative check: Industry guidance and vendor case studies highlight widespread adoption of UV in dairies, breweries, and bottled-water facilities, supporting this selection. Why Other Options Are Wrong: Municipal sewage treatment: UV is used, but the option list asks for an industrial context; food industry is a clearer, common fit.Petroleum refinery / Iron & steel: Process waters typically require different controls; UV is not the dominant disinfection method. Common Pitfalls: Assuming UV always replaces chlorine; many systems still require a downstream residual for distribution. Ignoring UV transmittance; high colour/turbidity reduce UV efficacy. Final Answer: food industry

Question 10

Natural sources of air pollution: Which option represents an unequivocally natural source of air pollutants (independent of human activity)?

Accepted Answer

Introduction / Context: Air pollution arises from both anthropogenic and natural sources. While some sources may be either human-caused or natural (e.g., wildfires), others are inherently natural geophysical phenomena. This question tests recognition of an unambiguously natural source among the options. Given Data / Assumptions: “Natural source” means it can occur without human initiation. Forest fires can be natural or human-caused; deforestation is anthropogenic. Volcanic eruptions emit gases and particulates from Earth's interior without human cause. Concept / Approach: Volcanic eruptions inject sulphur dioxide, carbon dioxide, hydrogen chloride, ash, and other species directly into the atmosphere. They are classical examples of natural pollution events and have historically impacted climate and air quality. Forest fires do occur naturally via lightning, but the term in regulatory contexts often includes widespread human-caused fires; to avoid ambiguity, the unequivocally natural choice is volcanic eruption. Deforestation is by definition human-driven land-use change. Step-by-Step Solution: Evaluate each source for independence from human action.Forest fire: ambiguous; can be human-caused or natural.Deforestation: anthropogenic.Volcanic eruption: natural geologic source → select. Verification / Alternative check: Air quality inventories list volcanic emissions as natural background sources influencing sulphate aerosol formation and visibility, confirming the selection. Why Other Options Are Wrong: Forest fire: Not unequivocally natural; many are anthropogenic.Deforestation: Human activity; not a natural emission source.None of these: Incorrect because volcanic eruption qualifies. Common Pitfalls: Interpreting “forest fire” as always natural; policies distinguish cause-based categories. Overlooking volcanic gas composition and its strong atmospheric impact. Final Answer: Volcanic eruption

Question 11

Toxic gas categories and TLV ranges: A gas with a permissible safe limit (TLV) in the range of approximately 100–1000 ppm would best be classified as which toxicity category?

Accepted Answer

Introduction / Context: Threshold limit values (TLVs) provide guidance for safe airborne concentrations of chemicals in occupational settings. In many environmental engineering texts, qualitative toxicity categories are loosely related to order-of-magnitude TLV ranges to support risk prioritization. This question asks which category matches a TLV on the order of 100–1000 ppm. Given Data / Assumptions: TLV range considered: about 10^2 to 10^3 ppm for gases. Relative classification scheme: lower TLV implies higher toxicity. Context aligns with typical textbook categories (extremely, highly, moderately, etc.). Concept / Approach: Chemicals with extremely low TLVs (for example, less than 1 ppm) are considered extremely toxic (e.g., methyl isocyanate). As TLV values rise into tens and hundreds of ppm, the relative toxicity category becomes moderate because higher ambient concentrations are tolerated before adverse effects occur. Values above 1000 ppm might be considered low acute toxicity under short exposure for some gases, but 100–1000 ppm generally aligns with moderate toxicity in many tabulations used for quick hazard screening. Step-by-Step Solution: Recognize the inverse relation: lower TLV → higher toxicity.Compare the provided band (100–1000 ppm) with qualitative categories.Map to “moderately” toxic based on common instructional ranges. Verification / Alternative check: Reference tables in industrial hygiene training commonly place very hazardous gases in the sub-ppm to single-digit ppm range, while moderate hazards often occupy the 100+ ppm region for TLVs or short-term exposure limits, supporting the selected category. Why Other Options Are Wrong: Highly / Extremely / Very extremely: These denote much lower permissible concentrations (often sub-ppm to tens of ppm), inconsistent with 100–1000 ppm. Common Pitfalls: Treating TLV categories as absolute; they are heuristic and can vary by source. Ignoring exposure duration differences (TWA vs. STEL). Final Answer: moderately

Question 12

Primary air pollutant prominence: Among the following, which gas is typically the most abundant constituent of urban air pollution from mobile sources by volume?

Accepted Answer

Introduction / Context: Air pollution inventories distinguish pollutants by mass and volume contributions. In urban areas dominated by traffic, certain primary pollutants dramatically outweigh others by concentration, even if their mass impacts differ. This question asks which listed gas is typically the most abundant by volume from mobile sources. Given Data / Assumptions: Context is urban, on-road emissions without advanced controls. Mobile sources produce CO, NOx, hydrocarbons, and some SOx depending on fuel sulphur. Hydrogen sulphide is not a characteristic traffic pollutant. Concept / Approach: Carbon monoxide is produced in large quantities by incomplete combustion in spark-ignition engines. Near-roadway measurements frequently show CO in the parts-per-million range, far exceeding typical ambient NOx or SO2 levels. While oxides of nitrogen are critical for ozone formation, their volumetric concentrations are commonly lower than CO in traffic plumes. Hydrogen sulphide is associated with industrial or natural sources, not general urban traffic. Step-by-Step Solution: Identify the pollutant most directly linked to incomplete combustion in gasoline engines: CO.Compare typical near-road concentrations: CO > NOx by volume.Select “Carbon monoxide.” Verification / Alternative check: Historic EPA and other urban monitoring datasets show CO spikes of several ppm on roadsides, with NO2 commonly lower in ppm terms, affirming the selection, even though NOx may dominate certain impact metrics. Why Other Options Are Wrong: Oxides of sulphur: Dependent on fuel sulphur; generally much lower for transport emissions in many regions.Oxides of nitrogen: Important but typically lower by volume than CO in traffic plumes.Hydrogen sulphide: Not a primary urban traffic pollutant. Common Pitfalls: Confusing concentration dominance with overall harm; NOx and SOx can have outsized environmental effects despite lower volume. Assuming diesel-dominated fleets mirror gasoline fleet CO profiles; diesel emits less CO. Final Answer: Carbon monoxide

Question 13

Material degradation from oxidants: Elevated ozone and smog exposure in air is especially known to cause which specific type of damage to materials?

Accepted Answer

Introduction / Context: Ambient oxidants such as ozone are highly reactive and can attack organic materials, leading to premature aging or failure. Recognizing signature damage patterns helps in diagnosing environmental exposure problems in infrastructure and consumer goods. This question focuses on the best-known effect of ozone-rich smog on materials. Given Data / Assumptions: Consider common ambient ozone levels found in polluted urban air. Exposure occurs over weeks to years, not laboratory extremes. Materials include elastomers, paper, textiles, and electrical components. Concept / Approach: Ozone reacts with unsaturated bonds in elastomers (e.g., natural rubber, some synthetic rubbers), causing chain scission. Under stress, microcracks initiate and propagate, a phenomenon known as ozone cracking. This manifests as characteristic surface cracks on tires, seals, and gaskets. While ozone can also contribute to fading dyes and affecting paper properties, the most diagnostic and severe everyday effect is cracking of rubber goods. High-voltage insulators are more affected by contaminants, moisture, and tracking than by ordinary ambient ozone alone. Step-by-Step Solution: Identify which material class has strong, well-documented susceptibility to ozone: elastomers.Recall the mechanism: attack on double bonds → chain scission → cracks under strain.Select “cracking of rubber products.” Verification / Alternative check: Maintenance guidance for seals and tires recommends ozone-resistant compounds or protective waxes/antiozonants in smog-prone regions, reaffirming this is the hallmark effect. Why Other Options Are Wrong: Paper embrittlement: Primarily due to acid hydrolysis and aging; ozone plays a lesser role.Dye fading: Possible, but sunlight and oxidants both contribute; less specific than rubber cracking.Electrical insulator damage: Typically from tracking/pollution flashover rather than ambient ozone alone. Common Pitfalls: Attributing any material degradation to “smog” generically; mechanisms differ by material. Ignoring mechanical strain, which accelerates ozone cracking in elastomers. Final Answer: cracking of rubber products

Question 14

Particle terminology in air pollution: Carbonaceous airborne particles with diameters smaller than about 1 micrometre are commonly termed what?

Accepted Answer

Introduction / Context: Airborne particulate matter is classified by size and formation mechanism because capture methods, health impacts, and optical effects depend on particle scale. Very fine carbonaceous particles produced by combustion are ubiquitous in urban atmospheres and visibility studies. This question asks for the commonly used term for submicron carbonaceous particles. Given Data / Assumptions: Particle size considered: less than about 1 micrometre (1 µm). Composition: primarily carbonaceous from combustion processes. Context: air pollution and environmental engineering terminology. Concept / Approach: “Smoke” typically refers to fine particulate matter formed by the condensation and nucleation of combustion products, often in the submicron range. It includes soot, tarry droplets, and other ultrafine particles that strongly scatter light and reduce visibility. “Aerosol” is a broader term for any suspension of fine solids or liquids in air; while technically accurate, it is not specific to carbonaceous combustion products. “Grit” denotes coarse particles orders of magnitude larger. “Aggregates” describes morphology (clusters) rather than a pollution class. Step-by-Step Solution: Relate particle origin (combustion) and scale (submicron) to terms used in air pollution.Distinguish general term “aerosol” from specific “smoke.”Choose “smoke.” Verification / Alternative check: Instrumentation for smoke measurements (e.g., light extinction, black carbon analyzers) targets submicron fractions, consistent with the definition adopted here. Why Other Options Are Wrong: Grit: Coarse settleable matter, typically > 75 µm.Aggregates: Describes structure, not a standard pollutant class.Aerosols: Overly broad; includes sea salt, dust, and mists. Common Pitfalls: Using “aerosol” when the intent is specifically combustion smoke. Assuming visibility impairment is dominated by coarse particles; fine smoke drives light scattering. Final Answer: smoke

Question 15

Air pollution and public health:
High concentrations of carcinogenic hydrocarbon pollutants (e.g., polycyclic aromatic hydrocarbons from incomplete combustion) in ambient atmospheric air primarily lead to which outcome in exposed populations?

Accepted Answer

Introduction / Context: Hydrocarbon pollutants in the air include a broad class of compounds, ranging from volatile organics to heavy polycyclic aromatic hydrocarbons. Many of these species, especially polycyclic aromatic hydrocarbons from diesel exhaust, coal tar, and other high-temperature processes, are proven or suspected carcinogens. This question checks whether you can identify the principal long-term health outcome most closely associated with sustained exposure to carcinogenic hydrocarbons in ambient air. Given Data / Assumptions: The term “carcinogenic hydrocarbons” emphasizes compounds with established or probable cancer risk. Population exposure is at elevated concentrations relative to background and occurs over extended durations. Short-term irritant effects may occur, but the question asks for the primary health outcome. Concept / Approach: Carcinogenicity is the defining toxicological endpoint for this pollutant group. While hydrocarbons can also aggravate respiratory symptoms, the hallmark risk from compounds like benzo[a]pyrene is initiation and promotion of malignant transformation after metabolic activation and DNA adduct formation. Therefore, the most accurate selection is cancer, not merely transient respiratory irritation. Step-by-Step Solution: Recognize the keyword “carcinogenic” → focus on malignancy risk rather than acute effects.Identify typical sources (vehicle exhaust, industrial combustion, biomass burning) that emit PAHs.Select the outcome most directly linked in epidemiology and toxicology: cancer. Verification / Alternative check: Occupational and urban epidemiology repeatedly correlates long-term PAH exposure with elevated incidence of lung cancer and certain other cancers, reinforcing that malignancy is the principal concern. Why Other Options Are Wrong: Silicosis: caused by crystalline silica dust, not hydrocarbons.Respiratory disease such as asthma only: hydrocarbons can irritate, but the stem stresses carcinogenic species, pointing to cancer as the primary outcome.Reduced crop yield: more associated with ozone or sulfur dioxide effects on vegetation.Acute metal fume fever: linked to metal oxide fumes (e.g., zinc), not hydrocarbons. Common Pitfalls: Confusing general hydrocarbon irritation with the specific cancer risk from PAHs; ignoring the qualifier “carcinogenic.” Final Answer: Cancer

Question 16

Wastewater metrics in process industries:
In the context of chemical process plants, the term BOD (biochemical oxygen demand) is normally used for which type of stream or sample characterisation?

Accepted Answer

Introduction / Context: BOD, or biochemical oxygen demand, is a cornerstone metric in environmental engineering. It estimates the amount of dissolved oxygen that microorganisms will consume while degrading biodegradable organic matter in water over a specified incubation period and temperature (commonly 5 days at 20°C for BOD5). Given Data / Assumptions: BOD is discussed within the scope of process industry discharges. We compare across solids, gases, and liquid streams. Standard laboratory protocols and regulatory frameworks apply. Concept / Approach: BOD pertains to oxygen consumption potential in aqueous media; therefore it is inherently a liquid-phase wastewater parameter. It is used to gauge pollution load, size biological treatment units, and demonstrate compliance with discharge permits. It does not characterize gases or dry solids and is distinct from chemical oxygen demand (COD), which chemically oxidizes organics. Step-by-Step Solution: Identify the medium: BOD testing requires a water sample with biodegradable organics.Relate to typical applications: influent/effluent monitoring for treatment plants.Select the option that names liquid effluents (wastewater). Verification / Alternative check: Design calculations for aeration tanks and secondary clarifiers often start from BOD load (kg/day), confirming its tight linkage to liquid effluents. Why Other Options Are Wrong: Solid wastes: measured by moisture, volatile solids, calorific value; BOD is not standard.Gaseous effluents: organics measured as VOCs or TOC in air, not BOD.Boiler feed water: characterized by hardness, silica, dissolved oxygen, not BOD.Stack particulates: measured as PM; BOD is irrelevant. Common Pitfalls: Confusing BOD with COD or TOC; assuming any “organic” measure implies BOD irrespective of phase. Final Answer: Characterisation of liquid effluents (wastewater)

Question 17

Drinking water aesthetics and staining:
What is the common consequence in households when iron and manganese are present in distributed water at elevated levels (above aesthetic limits)?

Accepted Answer

Introduction / Context: Iron and manganese frequently occur in groundwater and, when delivered to consumers without adequate treatment, lead to aesthetic and operational issues. While not typically acute toxicants at low concentrations, their presence above secondary standards creates nuisance problems that utilities strive to prevent. Given Data / Assumptions: The question focuses on practical household consequences. “Elevated levels” implies concentrations above aesthetic guidelines (e.g., iron > 0.3 mg/L, manganese > 0.05 mg/L). Water is otherwise potable with routine disinfection. Concept / Approach: When iron and manganese oxidize, they form colored particulates (reddish-brown iron oxides, black manganese oxides) that deposit on porcelain fixtures, tiles, and laundry, causing conspicuous staining. They also impart metallic taste and can promote biofouling, but the most visible symptom is discoloration and staining. Step-by-Step Solution: Identify metal species: Fe2+/Mn2+ oxidize to insoluble oxides/hydroxides.Relate oxidation products to appearance: rust-colored or black deposits.Select the outcome most consistent with household complaints: staining/discoloration. Verification / Alternative check: Customer service records at utilities commonly register “brown water” and staining events tied to iron and manganese breakthrough or distribution system disturbances. Why Other Options Are Wrong: Reduction in dissolved oxygen content: DO is a bulk water parameter, not a direct consumer-visible effect from trace Fe/Mn.Temporary hardness: caused by bicarbonates of calcium and magnesium, not Fe/Mn specifically.Acute microbial contamination: unrelated to Fe/Mn presence per se. Common Pitfalls: Equating any mineral issue with hardness; overlooking the distinct aesthetic signatures of iron (reddish) and manganese (black/gray) deposits. Final Answer: Discoloration and staining of bathroom fixtures and laundry

Question 18

Microbiology of sewage treatment:
The majority of bacteria naturally present in raw domestic sewage belong to which nutritional class, based on how they obtain energy and carbon?

Accepted Answer

Introduction / Context: Sewage treatment exploits the natural ability of microorganisms to degrade organic matter. Understanding which microbial groups dominate in influent sewage helps explain why biological processes like activated sludge and trickling filters are effective. Given Data / Assumptions: Typical domestic sewage composition with high biodegradable organics (BOD). Ambient conditions support mixed microbial consortia. Focus is on broad trophic classification: parasitic vs saprophytic vs strictly anaerobic pathogens. Concept / Approach: Saprophytes feed on dead or decaying organic material, exactly the substrate provided by sewage. While pathogens can be present, they are a small fraction compared with the vast community of saprophytic heterotrophs that drive biochemical oxidation and stabilization of wastes. Step-by-Step Solution: Identify the dominant energy source in sewage: abundant dissolved and particulate organics.Match to microbial lifestyle: saprophytic heterotrophs thrive on these substrates.Select the option that names saprophytic organisms. Verification / Alternative check: Process performance correlations (e.g., sludge yield, oxygen uptake rate) align with active saprophytic biomass that metabolizes organics to CO2, water, and new cells. Why Other Options Are Wrong: Parasitic: require living hosts; not the primary degraders in sewage.Obligate anaerobic pathogens: may exist but are not the majority; sewage contains both aerobic and anaerobic saprophytes.Phototrophic: require light; not dominant in opaque sewage. Common Pitfalls: Overstating pathogen prevalence relative to the robust decomposer community responsible for treatment. Final Answer: Saprophytic (decomposers of organic matter)

Question 19

Domestic sewage composition (typical values):
Approximately what fraction of most domestic sewage is solids by weight, with the remainder being water?

Accepted Answer

Introduction / Context: Design and operation of sewers and treatment plants rely on typical ranges for wastewater composition. A key rule of thumb is that domestic sewage is mostly water with a tiny fraction of solids, which has profound implications for hydraulics, pumping energy, and treatment unit sizing. Given Data / Assumptions: “Most domestic sewage” refers to combined domestic wastewater excluding unusual industrial inputs. Values are approximate and used for preliminary design and education. Solids include dissolve and suspended portions. Concept / Approach: Domestic sewage commonly contains about 0.1 percent solids (1,000 mg/L) and 99.9 percent water by weight. Understanding this helps students appreciate why processes like primary settling and biological treatment handle dilute streams yet must remove contaminants efficiently to protect receiving waters. Step-by-Step Solution: Recall the design heuristic: 99.9% water, ~0.1% solids.Eliminate unrealistic values: 5% or 10% solids would be sludge-like, not typical sewage.Select 0.1 percent as the best estimate. Verification / Alternative check: Measured total solids in municipal wastewater typically range near 700–1200 mg/L, aligning with ~0.1 percent by weight for domestic streams. Why Other Options Are Wrong: 0.001 percent: too low for typical municipal influent.5 or 10 percent: orders of magnitude higher than observed; comparable to concentrated sludge.1 percent: higher than usual for raw sewage; could reflect thickened slurries. Common Pitfalls: Confusing total solids in raw sewage with sludge concentrations or industrial wastewater strengths. Final Answer: 0.1 percent

Question 20

Flue gas desulfurization by sorbent injection:
During pulverized coal firing in boilers, limestone powder is injected primarily to achieve which effect on the flue gases?

Accepted Answer

Introduction / Context: Sorbent injection is a practical approach to control sulfur emissions from coal combustion. Finely divided limestone or lime reacts with sulfur dioxide to form stable calcium sulfite/sulfate solids that can be captured downstream, thereby lowering gaseous SO2 released to the atmosphere. Given Data / Assumptions: Pulverized coal boiler with in-furnace or duct injection of calcium-based sorbent. Goal is emission control, not catalytic promotion of SO3. Particulate capture devices (e.g., ESP or baghouse) are present to remove reaction products. Concept / Approach: Calcium carbonate (CaCO3) calcines to CaO at high temperature; CaO then reacts with SO2 (and O2) to form CaSO3/CaSO4. The overall effect is chemical sequestration of sulfur species from the gas phase, reducing stack SO2. This is the basis of furnace sorbent injection and circulating dry scrubbers. Step-by-Step Solution: Recognize limestone’s role as a sulfur sorbent rather than a catalyst.Recall reaction pathway: CaCO3 → CaO + CO2; CaO + SO2 (+ 1/2 O2) → CaSO3/CaSO4.Choose the option stating “Reduce SO2 content.” Verification / Alternative check: Performance metrics are often expressed as SO2 removal efficiency (%) versus Ca/S molar ratio, confirming the objective is SO2 reduction. Why Other Options Are Wrong: Catalytically convert SO2 to SO3: not desirable; SO3 can cause acid mist and fouling.Increase dew point: not an aim; higher acid dew points can worsen corrosion.Increase NOx formation: the opposite of typical goals; combustion tuning seeks NOx reduction. Common Pitfalls: Assuming limestone acts as a catalyst; it functions as a reactive sorbent forming solid salts. Final Answer: Reduce SO2 content in the flue gas

Environmental Engineering Questions