Q.1 What is the primary purpose of a microbial fuel cell (MFC)?
To generate electricity from organic waste
To produce biofuels from algae
To desalinate seawater
To synthesize polymers
Explanation - MFCs exploit the metabolic activity of microorganisms to convert chemical energy in organic substrates directly into electrical energy.
Correct answer is: To generate electricity from organic waste
Q.2 Which microorganism is most commonly used in the bioremediation of oil spills?
Pseudomonas aeruginosa
Escherichia coli
Streptococcus pneumoniae
Saccharomyces cerevisiae
Explanation - Pseudomonas species can degrade hydrocarbons efficiently, making them suitable for cleaning oil-contaminated environments.
Correct answer is: Pseudomonas aeruginosa
Q.3 In a bioelectrochemical system, the anode is typically kept under which condition?
Anaerobic
Aerobic
Hypertonic
Alkaline
Explanation - The anode chamber must be anaerobic to allow electroactive microbes to transfer electrons to the electrode without oxygen interference.
Correct answer is: Anaerobic
Q.4 Which of the following is a key advantage of using bioreactors for wastewater treatment?
Lower energy consumption compared to conventional methods
Instant removal of all contaminants
No need for microbial activity
Elimination of sludge production
Explanation - Bioreactors rely on microbial metabolism, which often requires less external energy than physical-chemical treatment processes.
Correct answer is: Lower energy consumption compared to conventional methods
Q.5 What does the term 'bioremediation' refer to?
The use of living organisms to degrade environmental pollutants
The chemical synthesis of biodegradable plastics
The conversion of solar energy into electricity
The mechanical filtration of water
Explanation - Bioremediation harnesses microorganisms or plants to break down hazardous substances into less toxic forms.
Correct answer is: The use of living organisms to degrade environmental pollutants
Q.6 Which component of a microbial fuel cell directly collects electrons from microbes?
Anode
Cathode
Membrane
Pump
Explanation - Microbes oxidize substrates and transfer electrons to the anode, which then moves them through an external circuit.
Correct answer is: Anode
Q.7 What is the main function of a proton exchange membrane (PEM) in a bioelectrochemical system?
To allow protons to pass while blocking oxygen and contaminants
To generate heat
To store electrical charge
To provide structural support
Explanation - PEM separates the anodic and cathodic compartments, permitting selective proton transfer to maintain charge balance.
Correct answer is: To allow protons to pass while blocking oxygen and contaminants
Q.8 Which of the following gases can be produced by electrogenic bacteria in a bioelectrochemical system?
Hydrogen
Methane
Oxygen
Carbon Dioxide
Explanation - Certain electrogenic bacteria can reduce protons at the cathode to produce hydrogen gas.
Correct answer is: Hydrogen
Q.9 Which environmental parameter most directly influences the rate of microbial degradation in a bioreactor?
Temperature
Color
Magnetic field
Sound intensity
Explanation - Microbial metabolic rates increase with temperature up to an optimum, affecting degradation speed.
Correct answer is: Temperature
Q.10 In the context of environmental biotechnology, what does 'phytoremediation' involve?
Using plants to clean up contaminated soils and water
Employing fungi to produce antibiotics
Deploying algae for biofuel production
Applying bacteria to ferment waste
Explanation - Phytoremediation utilizes the natural ability of plants to absorb, accumulate, or degrade pollutants.
Correct answer is: Using plants to clean up contaminated soils and water
Q.11 Which type of electrode material is most commonly used for the anode in a microbial fuel cell due to its high conductivity and biocompatibility?
Carbon cloth
Copper foil
Aluminum sheet
Gold plating
Explanation - Carbon-based materials provide a suitable surface for biofilm formation and have good electrical conductivity.
Correct answer is: Carbon cloth
Q.12 What is the main by‑product when a microbial fuel cell oxidizes glucose at the anode?
Carbon dioxide
Nitrogen gas
Methane
Sulfuric acid
Explanation - Oxidation of organic substrates such as glucose releases CO₂ as a metabolic by‑product.
Correct answer is: Carbon dioxide
Q.13 Which process converts toxic heavy metals into less harmful forms using microorganisms?
Bio‑precipitation
Photosynthesis
Electrolysis
Distillation
Explanation - Microbes can change metal solubility by converting them into insoluble compounds that precipitate out of solution.
Correct answer is: Bio‑precipitation
Q.14 In an aerobic bioreactor, which gas must be continuously supplied to maintain microbial activity?
Oxygen
Helium
Carbon monoxide
Nitrogen
Explanation - Aerobic microbes require oxygen as the terminal electron acceptor for respiration.
Correct answer is: Oxygen
Q.15 Which of the following is a key challenge when scaling up microbial fuel cells for commercial use?
Low power density
Excessive heat generation
Rapid corrosion of electrodes
Inability to handle liquids
Explanation - MFCs currently produce relatively low power per unit area, limiting their large‑scale applicability.
Correct answer is: Low power density
Q.16 What does the term 'electrogenic bacteria' refer to?
Bacteria capable of transferring electrons to an external electrode
Bacteria that produce electric shocks
Bacteria that only survive in electric fields
Bacteria that synthesize batteries
Explanation - Electrogenic bacteria can export electrons generated during metabolism to solid surfaces, enabling electricity generation.
Correct answer is: Bacteria capable of transferring electrons to an external electrode
Q.17 Which of the following pollutants can be degraded by the fungus *Phanerochaete chrysosporium*?
Polyaromatic hydrocarbons (PAHs)
Sodium chloride
Carbon monoxide
Methane
Explanation - The white‑rot fungus produces lignin‑degrading enzymes that break down complex aromatic compounds.
Correct answer is: Polyaromatic hydrocarbons (PAHs)
Q.18 In the context of environmental biotechnology, what does the acronym 'BOD' stand for?
Biochemical Oxygen Demand
Biological Oxidation Device
Bacterial Oxygen Depletion
Bio‑organic Discharge
Explanation - BOD measures the amount of dissolved oxygen needed by microorganisms to decompose organic matter in water.
Correct answer is: Biochemical Oxygen Demand
Q.19 Which type of reactor is designed to keep microbes in suspension, providing high contact between cells and substrate?
Stirred‑tank reactor
Fixed‑bed reactor
Trickle‑bed reactor
Membrane bioreactor
Explanation - A stirred‑tank reactor continuously mixes the contents, keeping cells and nutrients evenly distributed.
Correct answer is: Stirred‑tank reactor
Q.20 Which of the following is NOT a typical product of anaerobic digestion?
Hydrogen sulfide
Methane
Carbon dioxide
Oxygen
Explanation - Anaerobic digestion occurs in the absence of oxygen, so O₂ is not produced.
Correct answer is: Oxygen
Q.21 What is the role of a cathode in a microbial fuel cell?
To accept electrons and complete the electrical circuit
To generate organic substrates
To house the microbial community
To pump nutrients into the system
Explanation - The cathode receives electrons from the external circuit, often reducing oxygen to water.
Correct answer is: To accept electrons and complete the electrical circuit
Q.22 Which environmental factor can cause the most rapid decline in microbial activity in a bioreactor?
pH dropping far below neutral
Light intensity increase
Magnetic field strength
Altitude
Explanation - Extreme pH can denature enzymes and inhibit microbial metabolism, leading to rapid activity loss.
Correct answer is: pH dropping far below neutral
Q.23 What is the primary source of electrons for microbes in a microbial fuel cell?
Organic substrates such as glucose
Sunlight
Atmospheric nitrogen
Metallic ions
Explanation - Microbes oxidize organic compounds, releasing electrons that are transferred to the anode.
Correct answer is: Organic substrates such as glucose
Q.24 Which of the following best describes a 'biofilm' in environmental biotechnology?
A structured community of microorganisms attached to a surface
A single cell floating in water
A layer of soil organic matter
A type of synthetic polymer
Explanation - Biofilms consist of microbial cells embedded in extracellular polymeric substances, adhering to solid substrates.
Correct answer is: A structured community of microorganisms attached to a surface
Q.25 In bioremediation, what does the term 'intrinsic bioremediation' mean?
Utilizing the natural microbial population already present at the contaminated site
Adding genetically engineered microbes to the site
Applying chemical oxidants to degrade pollutants
Using heat to sterilize the soil
Explanation - Intrinsic bioremediation relies on indigenous microbes to degrade contaminants without external augmentation.
Correct answer is: Utilizing the natural microbial population already present at the contaminated site
Q.26 Which of the following is a common electron acceptor used at the cathode of a microbial fuel cell operating in air?
Oxygen
Nitrogen
Carbon monoxide
Methane
Explanation - Oxygen is readily available and serves as an efficient terminal electron acceptor, being reduced to water.
Correct answer is: Oxygen
Q.27 Which environmental biotechnology technique is most suited for treating oil‑contaminated marine water?
Oil‑degrading bacterial consortia in bioreactors
Thermal incineration
Mechanical filtration only
UV radiation
Explanation - Specific bacteria can metabolize hydrocarbons, making them effective for marine oil spill cleanup.
Correct answer is: Oil‑degrading bacterial consortia in bioreactors
Q.28 What does the term 'electroactive' refer to in microbes?
Ability to transfer electrons outside the cell
Ability to generate light
Ability to move using flagella
Ability to withstand high voltage
Explanation - Electroactive microbes can export electrons to external conductors, enabling bio‑electrochemical applications.
Correct answer is: Ability to transfer electrons outside the cell
Q.29 Which of the following is a major limitation of using algae for wastewater treatment?
Requirement of sufficient light intensity
Production of toxic gases
Inability to uptake nitrogen
High metal accumulation
Explanation - Algal growth depends on light; insufficient illumination reduces treatment efficiency.
Correct answer is: Requirement of sufficient light intensity
Q.30 What is the main advantage of a membrane bioreactor (MBR) over conventional activated sludge processes?
Higher effluent quality due to physical separation of biomass
Lower construction cost
No need for aeration
Elimination of microbial activity
Explanation - MBRs use membranes to retain microorganisms, producing clearer effluent with less suspended solids.
Correct answer is: Higher effluent quality due to physical separation of biomass
Q.31 Which of the following gases is commonly produced at the cathode of a microbial electrolysis cell (MEC) for hydrogen generation?
Hydrogen
Methane
Carbon dioxide
Ozone
Explanation - MECs apply a small voltage to drive the reduction of protons to H₂ at the cathode.
Correct answer is: Hydrogen
Q.32 In bioremediation, the term 'bioaugmentation' means:
Adding selected microbial strains to enhance degradation
Increasing temperature to accelerate reactions
Removing all native microorganisms
Adding chemical nutrients only
Explanation - Bioaugmentation introduces specialized microbes to a site to improve contaminant breakdown.
Correct answer is: Adding selected microbial strains to enhance degradation
Q.33 Which of the following metals is most toxic to microbial activity at low concentrations?
Copper
Sodium
Magnesium
Calcium
Explanation - Copper can inhibit enzymes and membrane functions even at trace levels, affecting microbial health.
Correct answer is: Copper
Q.34 Which process is used to remove nitrogen from wastewater by converting ammonia to nitrogen gas?
Anammox (Anaerobic Ammonium Oxidation)
Photosynthesis
Fermentation
Sedimentation
Explanation - Anammox bacteria oxidize ammonium directly to N₂ under anaerobic conditions, reducing nitrogen load.
Correct answer is: Anammox (Anaerobic Ammonium Oxidation)
Q.35 What is the primary function of extracellular polymeric substances (EPS) in a biofilm?
Providing structural matrix and protection for microbial cells
Generating electrical current
Absorbing sunlight
Catalyzing chemical reactions
Explanation - EPS bind cells together, protect them from environmental stress, and facilitate nutrient capture.
Correct answer is: Providing structural matrix and protection for microbial cells
Q.36 Which of the following is an example of a genetically engineered microbe used in environmental biotechnology?
Pseudomonas putida engineered to degrade polychlorinated biphenyls (PCBs)
Bacillus subtilis producing insulin
Saccharomyces cerevisiae used in brewing
Escherichia coli for laboratory cloning
Explanation - Engineered strains can be tailored to break down persistent organic pollutants like PCBs.
Correct answer is: Pseudomonas putida engineered to degrade polychlorinated biphenyls (PCBs)
Q.37 In a microbial fuel cell, the term 'internal resistance' refers to:
The opposition to current flow within the cell components
The resistance of microbes to electricity
The resistance of water to flow
The resistance of the external load
Explanation - Internal resistance arises from electrode materials, membrane, and solution conductivity, reducing overall power output.
Correct answer is: The opposition to current flow within the cell components
Q.38 Which of the following is NOT a typical indicator of successful bioremediation?
Increase in dissolved oxygen
Reduction of contaminant concentration
Rise in soil pH above 12
Growth of pollutant‑degrading microbes
Explanation - Extremely high pH is harmful to most microbes and does not indicate remediation success.
Correct answer is: Rise in soil pH above 12
Q.39 What is the primary electron acceptor for most aerobic microorganisms?
Oxygen
Nitrate
Sulfate
Carbon dioxide
Explanation - Aerobic respiration uses O₂ as the terminal electron acceptor to generate ATP.
Correct answer is: Oxygen
Q.40 Which factor is most critical for maintaining a stable microbial population in a continuous flow bioreactor?
Steady substrate feed rate
Frequent temperature fluctuations
Changing pH every hour
Intermittent light exposure
Explanation - Consistent substrate supply prevents starvation or washout, keeping the microbial community stable.
Correct answer is: Steady substrate feed rate
Q.41 In the context of bioelectrochemical systems, what does the term 'Coulombic efficiency' measure?
The fraction of electrons from substrate oxidation recovered as electrical current
The amount of heat generated per unit time
The speed of water flow through the system
The volume of gas produced per hour
Explanation - Coulombic efficiency indicates how effectively electrons are captured by the external circuit versus other pathways.
Correct answer is: The fraction of electrons from substrate oxidation recovered as electrical current
Q.42 Which of the following is a common method for increasing the surface area of an anode in a microbial fuel cell?
Using carbon felt or mesh
Polishing the metal surface
Coating with oil
Embedding with glass beads
Explanation - Porous carbon structures provide a large area for biofilm attachment and electron transfer.
Correct answer is: Using carbon felt or mesh
Q.43 What is the main environmental benefit of using bioreactors for industrial wastewater treatment?
Reduced chemical usage and lower sludge production
Complete elimination of all pollutants
Zero energy consumption
Instant treatment within seconds
Explanation - Biological processes often need fewer chemicals and generate less solid waste compared to physico‑chemical methods.
Correct answer is: Reduced chemical usage and lower sludge production
Q.44 Which of the following is a typical by‑product of nitrification in wastewater treatment?
Nitrite (NO₂⁻)
Methane (CH₄)
Hydrogen sulfide (H₂S)
Ammonia (NH₃)
Explanation - Nitrification converts ammonia first to nitrite, then to nitrate under aerobic conditions.
Correct answer is: Nitrite (NO₂⁻)
Q.45 In phytoremediation, which plant part is primarily responsible for extracting heavy metals from soil?
Roots
Leaves
Flowers
Stem
Explanation - Roots absorb and accumulate metals, often storing them in root tissues or translocating them to shoots.
Correct answer is: Roots
Q.46 Which of the following statements best describes 'anaerobic digestion'?
A biological process that decomposes organic matter in the absence of oxygen, producing biogas
A chemical process that oxidizes metals using air
A thermal process that burns waste at high temperatures
A mechanical process that filters water through sand
Explanation - Anaerobic digestion yields methane and carbon dioxide while reducing waste volume.
Correct answer is: A biological process that decomposes organic matter in the absence of oxygen, producing biogas
Q.47 Which type of microbial metabolism is most commonly exploited in microbial fuel cells?
Respiratory electron transfer to external electrodes
Photosynthesis
Fermentation producing ethanol
Nitrification
Explanation - Electrogenic microbes transfer electrons outside the cell during respiration, enabling electricity generation.
Correct answer is: Respiratory electron transfer to external electrodes
Q.48 What is the main purpose of adding a buffer solution to a bioreactor?
To maintain a stable pH for microbial activity
To increase temperature
To provide nutrients
To accelerate gas production
Explanation - Buffers resist pH changes caused by metabolic acids or bases, protecting microbial enzymes.
Correct answer is: To maintain a stable pH for microbial activity
Q.49 Which of the following pollutants can be removed by a constructed wetland?
Nutrients (nitrogen and phosphorus)
Radioactive isotopes
Heavy metals only
All of the above
Explanation - Constructed wetlands use plants and microbes to uptake and transform nutrients, reducing eutrophication risk.
Correct answer is: Nutrients (nitrogen and phosphorus)
Q.50 Which enzyme family is primarily responsible for the degradation of chlorinated organic compounds by bacteria?
Dehalogenases
Amylases
Proteases
Lipases
Explanation - Dehalogenases catalyze the removal of halogen atoms, enabling breakdown of chlorinated pollutants.
Correct answer is: Dehalogenases
Q.51 What is the typical voltage range generated by a single-chamber microbial fuel cell?
0.3 – 0.7 V
1.5 – 2.5 V
5 – 10 V
12 – 24 V
Explanation - Individual MFCs produce low voltages; series connections are required for higher power applications.
Correct answer is: 0.3 – 0.7 V
Q.52 Which factor most directly influences the rate of oxygen transfer in an aerobic bioreactor?
Agitation speed (mixing)
Color of the reactor
Magnetic field strength
External humidity
Explanation - Higher agitation increases surface area contact between gas and liquid, improving oxygen dissolution.
Correct answer is: Agitation speed (mixing)
Q.53 Which of the following is a primary goal of 'biofiltration' in air pollution control?
Removal of volatile organic compounds (VOCs) using microbial activity
Cooling of exhaust gases
Increasing humidity of the air stream
Adding fragrance to the air
Explanation - Biofilters contain media colonized by microbes that metabolize VOCs as they pass through.
Correct answer is: Removal of volatile organic compounds (VOCs) using microbial activity
Q.54 In environmental biotechnology, the term 'bioprospecting' refers to:
Searching for novel organisms or enzymes with useful applications
Mining for mineral resources
Planting crops in new regions
Testing water for pathogens
Explanation - Bioprospecting aims to discover new biological tools for remediation, bioenergy, or industry.
Correct answer is: Searching for novel organisms or enzymes with useful applications
Q.55 Which of the following is NOT a typical characteristic of extremophilic microbes used in bioremediation?
Requirement for moderate temperature (20‑30 °C)
Tolerance to high salinity
Ability to survive in acidic pH
Resistance to heavy metals
Explanation - Extremophiles thrive under conditions (high temperature, salinity, pH) that are outside the moderate range.
Correct answer is: Requirement for moderate temperature (20‑30 °C)
Q.56 Which of the following processes converts CO₂ into useful organic compounds using microorganisms?
Carbon fixation (e.g., via cyanobacteria)
Combustion
Electrolysis of water
Photolysis of ozone
Explanation - Photosynthetic microbes capture CO₂ and, using light energy, produce biomass or other organics.
Correct answer is: Carbon fixation (e.g., via cyanobacteria)
Q.57 What is the main reason for adding trace nutrients (e.g., nitrogen, phosphorus) to a landfill leachate treatment system?
To support microbial growth and activity
To increase the pH dramatically
To neutralize heavy metals
To reduce temperature
Explanation - Microbes need essential nutrients to metabolize organic contaminants efficiently.
Correct answer is: To support microbial growth and activity
Q.58 Which of the following is a common indicator that a microbial community is experiencing 'substrate limitation'?
Decreased respiration rate
Sudden pH rise
Increase in turbidity
Rapid temperature rise
Explanation - When substrate runs out, microbial metabolic activity drops, reflected in lower oxygen consumption.
Correct answer is: Decreased respiration rate
Q.59 In a bioelectrochemical system, the term 'overpotential' refers to:
Extra voltage required beyond the thermodynamic potential to drive a reaction
Potential generated by microbes spontaneously
Voltage loss due to external wiring resistance
Potential stored in a capacitor
Explanation - Overpotential accounts for kinetic barriers at the electrode surface, reducing overall efficiency.
Correct answer is: Extra voltage required beyond the thermodynamic potential to drive a reaction
Q.60 Which of the following is a primary mechanism by which algae remove nutrients from wastewater?
Assimilative uptake of nitrogen and phosphorus for growth
Evaporation of water
Chemical precipitation of metals
Filtration through cell walls
Explanation - Algae incorporate nutrients into their biomass, effectively reducing concentrations in the water.
Correct answer is: Assimilative uptake of nitrogen and phosphorus for growth
Q.61 Which of the following best describes the role of a 'cathodic catalyst' in a microbial fuel cell?
Accelerates the reduction of oxygen to water at the cathode
Inhibits microbial growth at the anode
Generates light for photosynthesis
Produces heat to keep the system warm
Explanation - Catalysts (e.g., platinum, carbon‑based) lower the activation energy for oxygen reduction, improving power output.
Correct answer is: Accelerates the reduction of oxygen to water at the cathode
Q.62 Which microbial process is primarily responsible for the formation of sulfide odor in anaerobic sludge digesters?
Sulfate‑reducing bacteria reducing sulfate to hydrogen sulfide
Nitrifying bacteria producing nitrite
Methanogens producing methane
Photosynthetic bacteria producing oxygen
Explanation - SRB use sulfate as an electron acceptor, yielding H₂S, which smells like rotten eggs.
Correct answer is: Sulfate‑reducing bacteria reducing sulfate to hydrogen sulfide
Q.63 Which of the following is a limitation of using genetically modified microorganisms (GMMs) for field bioremediation?
Regulatory and ecological concerns regarding their release
Inability to degrade any pollutants
Excessive cost compared to chemical methods
Lack of metabolic activity
Explanation - GMMs may spread unintended genes and face strict biosafety regulations, limiting field applications.
Correct answer is: Regulatory and ecological concerns regarding their release
Q.64 What is the main advantage of using a 'sequencing batch reactor' (SBR) over continuous flow reactors?
Flexibility to operate in distinct phases (fill, react, settle, draw)
Lower capital cost
No need for microbial inoculation
Higher temperature tolerance
Explanation - SBRs can be programmed for various treatment steps in a single tank, providing operational versatility.
Correct answer is: Flexibility to operate in distinct phases (fill, react, settle, draw)
Q.65 In the context of bioenergy, which term describes the conversion of waste organic matter directly into electricity without combustion?
Microbial fuel cell technology
Incineration
Anaerobic digestion
Thermal cracking
Explanation - MFCs generate electricity via direct electron transfer from microbes to an electrode, bypassing combustion.
Correct answer is: Microbial fuel cell technology
Q.66 Which of the following is a common method for monitoring microbial activity in a bioreactor?
Measuring dissolved oxygen consumption
Counting fish species
Measuring light intensity
Weighing the reactor
Explanation - Oxygen uptake rate reflects aerobic microbial metabolism and is a standard performance indicator.
Correct answer is: Measuring dissolved oxygen consumption
Q.67 What does the term 'bioaugmentation' NOT involve?
Adding nutrients to stimulate existing microbes
Introducing specialized microbial strains
Altering the physical structure of the reactor
Increasing temperature dramatically
Explanation - Bioaugmentation focuses on microbial addition or stimulation, not extreme temperature changes.
Correct answer is: Increasing temperature dramatically
Q.68 Which of the following processes can produce electricity and treat wastewater simultaneously?
Microbial fuel cell operation
Reverse osmosis
Chemical coagulation
Thermal distillation
Explanation - MFCs convert the chemical energy of organic waste into electricity while degrading pollutants.
Correct answer is: Microbial fuel cell operation
Q.69 Which of these is a typical indicator that a microbial community has entered the stationary phase in batch culture?
Constant cell concentration despite nutrient availability
Rapid increase in cell density
Sudden drop in pH
Immediate cessation of gas production
Explanation - In stationary phase, growth rate equals death rate; cell numbers plateau.
Correct answer is: Constant cell concentration despite nutrient availability
Q.70 What is the primary environmental concern associated with the accumulation of sludge from conventional wastewater treatment?
Landfill space consumption and potential contaminant release
Excessive oxygen generation
Increase in water temperature
Generation of pure hydrogen
Explanation - Sludge requires disposal; if not treated properly, it can leach pollutants into the environment.
Correct answer is: Landfill space consumption and potential contaminant release
Q.71 Which of the following is a commonly used electron donor for denitrifying bacteria in a wastewater treatment system?
Methanol
Chlorine
Helium
Nitrogen gas
Explanation - Methanol serves as a carbon source and electron donor, facilitating the reduction of nitrate to nitrogen gas.
Correct answer is: Methanol
Q.72 In a microbial electrolysis cell (MEC), why is an external voltage applied?
To overcome thermodynamic barriers and drive hydrogen production
To heat the reactor
To sterilize the system
To generate light for photosynthesis
Explanation - MECs require a small additional voltage to make the reduction of protons to H₂ energetically favorable.
Correct answer is: To overcome thermodynamic barriers and drive hydrogen production
Q.73 Which type of microbe is typically responsible for the final step of converting acetate to methane in anaerobic digestion?
Methanogenic archaea
Lactobacilli
Cyanobacteria
Nitrobacter
Explanation - Methanogens convert acetate and hydrogen/CO₂ into methane during the methanogenesis phase.
Correct answer is: Methanogenic archaea
Q.74 Which of the following is an example of a 'bioindicator' used to assess environmental health?
Lichens indicating air quality
Thermometers measuring temperature
pH strips for acidity
Rain gauges measuring precipitation
Explanation - Lichens are sensitive to pollutants like sulfur dioxide; their presence/absence reflects air quality.
Correct answer is: Lichens indicating air quality
Q.75 What is the main advantage of using a 'two‑chamber' microbial fuel cell over a single‑chamber design?
Separation of aerobic and anaerobic zones, improving electron flow
Lower cost of construction
Higher temperature tolerance
Elimination of the need for a membrane
Explanation - Two‑chamber MFCs keep the anode anaerobic and the cathode aerobic, enhancing overall performance.
Correct answer is: Separation of aerobic and anaerobic zones, improving electron flow
Q.76 Which of the following chemicals is commonly added to wastewater to precipitate phosphates as insoluble salts?
Aluminum sulfate (alum)
Sodium chloride
Hydrochloric acid
Ammonium nitrate
Explanation - Alum reacts with phosphate to form aluminum phosphate, which settles out of solution.
Correct answer is: Aluminum sulfate (alum)
Q.77 Which parameter is most directly used to calculate the hydraulic retention time (HRT) of a reactor?
Volume of the reactor divided by influent flow rate
pH of the influent
Temperature of the reactor
Concentration of dissolved oxygen
Explanation - HRT = Reactor volume / Flow rate; it indicates the average time the liquid stays in the system.
Correct answer is: Volume of the reactor divided by influent flow rate
Q.78 In the context of environmental biotechnology, which term describes the process of converting waste biomass into valuable chemicals using microbes?
Bioconversion
Electrolysis
Distillation
Pyrolysis
Explanation - Bioconversion utilizes microbial metabolism to transform organic waste into fuels, acids, or other useful products.
Correct answer is: Bioconversion
Q.79 Which of the following is a major factor limiting the widespread commercial adoption of microbial fuel cells?
Low power density and high cost of electrode materials
Excessive heat generation
Requirement for high radiation levels
Inability to treat any type of waste
Explanation - Current MFCs produce limited power per unit area, and expensive materials like carbon composites raise costs.
Correct answer is: Low power density and high cost of electrode materials
Q.80 Which of the following is NOT a typical use of bioelectrochemical systems (BES) in environmental applications?
Generation of electricity from wastewater
Desalination of seawater by reverse osmosis
Production of hydrogen gas
Recovery of nutrients as fertilizers
Explanation - BES are used for energy recovery and nutrient recycling, not for pressure‑driven desalination processes.
Correct answer is: Desalination of seawater by reverse osmosis
Q.81 Which microbial process is responsible for the conversion of nitrite to nitrate in a nitrifying biofilter?
Nitrite‑oxidizing bacteria (e.g., Nitrobacter)
Denitrifying bacteria
Methanogenic archaea
Sulfur‑oxidizing bacteria
Explanation - Nitrobacter oxidizes NO₂⁻ to NO₃⁻ under aerobic conditions, completing nitrification.
Correct answer is: Nitrite‑oxidizing bacteria (e.g., Nitrobacter)
Q.82 What is the main purpose of adding a 'sacrificial anode' in a corrosion protection system for pipelines?
To preferentially corrode instead of the protected metal
To increase the temperature of the pipeline
To generate electricity for the pipeline
To filter contaminants from the fluid
Explanation - A more reactive metal (e.g., zinc) corrodes first, protecting the less reactive pipeline steel.
Correct answer is: To preferentially corrode instead of the protected metal
Q.83 Which of the following is a key advantage of using constructed wetlands for wastewater treatment?
Low energy requirements and natural aesthetic value
Instant removal of all pathogens
High chemical usage
Requirement for complex machinery
Explanation - Constructed wetlands rely on natural processes, needing minimal energy and offering habitat benefits.
Correct answer is: Low energy requirements and natural aesthetic value
Q.84 In bioelectrochemical systems, what does the term 'reverse electrodialysis' refer to?
Generating electricity from the salinity gradient between seawater and fresh water
Reversing the direction of electron flow in a fuel cell
Converting electricity into chemical energy
Using electrodes to filter particles
Explanation - Reverse electrodialysis exploits ion concentration differences to produce voltage across selective membranes.
Correct answer is: Generating electricity from the salinity gradient between seawater and fresh water
Q.85 Which of the following is a common method for measuring the power output of a microbial fuel cell in the laboratory?
Connecting a variable resistor and recording voltage and current
Weighing the anode before and after operation
Measuring the temperature of the electrolyte
Counting the number of microbes on the electrode
Explanation - Power (P = V × I) is determined by measuring voltage across and current through a known load.
Correct answer is: Connecting a variable resistor and recording voltage and current
Q.86 Which of the following enzymes is primarily responsible for the breakdown of cellulose in composting processes?
Cellulase
Amylase
Protease
Lipase
Explanation - Cellulases hydrolyze β‑1,4‑glycosidic bonds in cellulose, releasing glucose units.
Correct answer is: Cellulase
Q.87 In a bioelectrochemical system designed for nitrate removal, what is typically used as the electron acceptor at the cathode?
Nitrate (NO₃⁻)
Oxygen (O₂)
Carbon dioxide (CO₂)
Hydrogen sulfide (H₂S)
Explanation - The cathode can reduce nitrate to nitrogen gas, facilitating denitrification without external chemicals.
Correct answer is: Nitrate (NO₃⁻)
Q.88 Which of the following is a key characteristic of a 'hyperthermophilic' microbe used in industrial bioprocesses?
Optimal growth temperature above 80 °C
Requirement for complete darkness
Sensitivity to high salt concentrations
Dependence on oxygen for metabolism
Explanation - Hyperthermophiles thrive at very high temperatures, useful for processes that benefit from heat stability.
Correct answer is: Optimal growth temperature above 80 °C
Q.89 What is the primary reason for using a 'packed‑bed' reactor in certain bioremediation applications?
Provides a large surface area for biofilm attachment
Ensures complete mixing of the liquid
Eliminates the need for nutrients
Prevents any microbial growth
Explanation - Packed media (e.g., gravel, plastic beads) give microbes a substrate to colonize, enhancing degradation rates.
Correct answer is: Provides a large surface area for biofilm attachment
Q.90 Which of the following processes is most appropriate for removing dissolved gases (e.g., CO₂) from wastewater before discharge?
Degassing via air stripping
Filtration through sand
Chemical precipitation
Biological nitrification
Explanation - Air stripping transfers volatile gases from liquid to gas phase, allowing their removal.
Correct answer is: Degassing via air stripping
Q.91 In the context of environmental biotechnology, what does 'bioleaching' involve?
Using microorganisms to extract metals from ores or waste materials
Leaching chemicals using strong acids
Physical grinding of rocks
Applying high pressure to dissolve metals
Explanation - Bioleaching employs microbes that oxidize sulfides, liberating metal ions for recovery.
Correct answer is: Using microorganisms to extract metals from ores or waste materials
Q.92 Which of the following is a typical indicator that a biofilm in a reactor is becoming too thick and may impede performance?
Reduced substrate conversion efficiency
Increased light transmission
Higher temperature in the reactor
Decreased pH
Explanation - Thick biofilms can limit mass transfer of nutrients and waste, lowering overall reactor efficiency.
Correct answer is: Reduced substrate conversion efficiency
Q.93 Which of the following is a key advantage of using 'electroactive biofilms' over suspended microbial cultures in MFCs?
Improved electron transfer due to close contact with the electrode
Lower cost of media preparation
Elimination of the need for a cathode
Ability to operate at high temperatures
Explanation - Electroactive biofilms form directly on the electrode, reducing resistance and enhancing current density.
Correct answer is: Improved electron transfer due to close contact with the electrode
Q.94 What is the most common method for quantifying the concentration of a specific pollutant (e.g., benzene) in water samples in a laboratory?
Gas chromatography (GC)
Visual inspection
pH meter reading
Thermal conductivity measurement
Explanation - GC separates and detects volatile organic compounds like benzene with high sensitivity.
Correct answer is: Gas chromatography (GC)
Q.95 Which of the following statements about 'syntrophic' relationships in anaerobic digestion is correct?
Two microbial species cooperate by transferring metabolites that one cannot process alone
Microbes compete fiercely for the same substrate
All microbes act independently without interaction
Only one species is present in the reactor
Explanation - Syntrophy involves cross‑feeding, e.g., fermenters produce hydrogen that methanogens consume, keeping reactions thermodynamically favorable.
Correct answer is: Two microbial species cooperate by transferring metabolites that one cannot process alone
Q.96 Which type of reactor is best suited for treating high‑strength industrial wastewater with a short hydraulic retention time?
Plug‑flow reactor (PFR)
Batch reactor
Upflow anaerobic sludge blanket (UASB)
Lagoons
Explanation - UASB reactors handle high organic loads with short HRTs due to dense microbial granules and efficient contact.
Correct answer is: Upflow anaerobic sludge blanket (UASB)
Q.97 In a bioelectrochemical system designed for CO₂ reduction, which product is most commonly targeted?
Formate (HCOO⁻)
Methane (CH₄)
Oxygen (O₂)
Nitrogen (N₂)
Explanation - Electrochemical reduction of CO₂ at the cathode often yields formate as a primary, easily detectable product.
Correct answer is: Formate (HCOO⁻)
Q.98 Which of the following is a potential environmental risk associated with the release of engineered microbes into natural ecosystems?
Horizontal gene transfer to native organisms
Immediate increase in water temperature
Reduction of atmospheric CO₂ to zero
Complete sterilization of soil
Explanation - Engineered genes may spread to wild microbes, potentially creating unforeseen ecological impacts.
Correct answer is: Horizontal gene transfer to native organisms
Q.99 What is the primary function of a 'cathodic chamber' in a microbial electrolysis cell used for hydrogen production?
To provide a site for proton reduction to hydrogen gas
To store excess microbes
To generate oxygen for the anode
To heat the electrolyte
Explanation - The cathodic chamber supplies electrons and protons that combine to form H₂ under applied voltage.
Correct answer is: To provide a site for proton reduction to hydrogen gas
Q.100 Which of the following is an advantage of using 'electrokinetic remediation' for soil contamination?
Ability to mobilize and extract heavy metals from low‑permeability soils
Complete sterilization of all soil microbes
Requirement of high temperatures
Production of large amounts of methane
Explanation - Electric fields drive charged contaminants towards electrodes, enabling collection from otherwise inaccessible zones.
Correct answer is: Ability to mobilize and extract heavy metals from low‑permeability soils
Q.101 Which of the following terms best describes the conversion of nitrogen gas (N₂) into ammonia (NH₃) by certain microorganisms?
Biological nitrogen fixation
Denitrification
Nitrification
Ammonification
Explanation - Diazotrophic bacteria possess nitrogenase enzymes that reduce atmospheric N₂ to NH₃.
Correct answer is: Biological nitrogen fixation
Q.102 In an MFC, which factor most directly influences the 'Coulombic efficiency'?
Proportion of electrons from substrate oxidation that reach the anode
Color of the electrode
Volume of the reactor
Ambient sound level
Explanation - Coulombic efficiency quantifies how effectively electrons are captured for electricity versus being lost to side reactions.
Correct answer is: Proportion of electrons from substrate oxidation that reach the anode
Q.103 Which of the following is a common method for enhancing mass transfer in a packed‑bed bioreactor?
Increasing flow velocity
Adding more packing material
Reducing temperature
Covering the reactor with a dark cloth
Explanation - Higher flow rates improve substrate diffusion to the biofilm, boosting reaction rates.
Correct answer is: Increasing flow velocity
Q.104 What does the acronym 'MFC' stand for in environmental biotechnology?
Microbial Fuel Cell
Molecular Filtration Chamber
Metallic Fuel Converter
Methane Fermentation Column
Explanation - MFCs are devices that generate electricity directly from the metabolic activity of microbes.
Correct answer is: Microbial Fuel Cell
Q.105 Which of the following is an example of a 'green' technology that integrates electrical engineering and environmental biotechnology?
Microbial electrolysis cells for hydrogen production
Coal‑fired power plants
Chemical chlorine disinfection
Incineration of municipal waste
Explanation - MECs combine bio‑catalysis and electrochemistry to generate clean hydrogen from waste streams.
Correct answer is: Microbial electrolysis cells for hydrogen production
Q.106 Which of the following is a typical indicator that a microbial fuel cell is experiencing 'substrate limitation'?
Drop in voltage output over time
Sudden increase in temperature
Rapid formation of bubbles
Change in electrode color
Explanation - When substrate is scarce, electron generation decreases, leading to lower voltage and power.
Correct answer is: Drop in voltage output over time
Q.107 Which of the following is a common electron donor used in denitrification processes for wastewater treatment?
Methanol
Ozone
Helium
Nitrogen gas
Explanation - Methanol supplies carbon and electrons needed for microbes to reduce nitrate to nitrogen gas.
Correct answer is: Methanol
Q.108 What is the main purpose of using a 'catalyst layer' on the cathode of a microbial fuel cell?
To accelerate the reduction reaction (e.g., O₂ → H₂O)
To increase the weight of the cell
To block electron flow
To generate heat
Explanation - Catalysts lower activation energy for cathodic reactions, improving overall cell performance.
Correct answer is: To accelerate the reduction reaction (e.g., O₂ → H₂O)
Q.109 Which of the following best describes 'bioenergy'?
Energy derived from biological sources such as biomass, biogas, or biofuels
Energy generated exclusively from fossil fuels
Energy obtained by burning coal
Energy produced by nuclear fission
Explanation - Bioenergy utilizes organic materials or microbial processes to generate usable energy forms.
Correct answer is: Energy derived from biological sources such as biomass, biogas, or biofuels
Q.110 Which parameter is most directly affected by the presence of a high concentration of sulfide ions in an anaerobic digester?
Methane production rate
Temperature stability
Color of the effluent
pH increase
Explanation - Sulfide can inhibit methanogenic archaea, reducing methane yield.
Correct answer is: Methane production rate
Q.111 In environmental biotechnology, the term 'biomass' typically refers to:
The total mass of living microbial cells in a system
The amount of plastic waste in a landfill
The volume of water in a river
The energy content of coal
Explanation - Biomass quantifies the concentration of microorganisms, often expressed as mg/L or g/L.
Correct answer is: The total mass of living microbial cells in a system
Q.112 Which of the following is a primary advantage of using a 'membrane bioreactor' (MBR) for tertiary wastewater treatment?
High-quality effluent with low turbidity
Zero electricity consumption
Removal of all dissolved gases
Complete elimination of all pathogens
Explanation - The membrane physically separates biomass, resulting in clear water suitable for reuse.
Correct answer is: High-quality effluent with low turbidity