Q.1 Which microorganism is most commonly used in the bioremediation of oil spills due to its ability to degrade hydrocarbons?
Pseudomonas aeruginosa
Escherichia coli
Saccharomyces cerevisiae
Bacillus subtilis
Explanation - Pseudomonas aeruginosa possesses enzymes that can break down a wide range of hydrocarbons, making it a primary agent in oil spill bioremediation.
Correct answer is: Pseudomonas aeruginosa
Q.2 In microbial fuel cells (MFCs), which of the following serves as the electron acceptor at the cathode?
Oxygen
Glucose
Nitrate
Methane
Explanation - Most MFC designs use oxygen from air at the cathode to accept electrons, completing the circuit and generating electricity.
Correct answer is: Oxygen
Q.3 Which emerging technology combines CRISPR‑Cas systems with environmental biotechnology to enhance pollutant degradation?
Gene drive biocontrol
Synthetic biosensor circuits
CRISPR‑based metabolic engineering
RNA interference for plant stress
Explanation - CRISPR is used to edit microbial genomes to up‑regulate pathways that degrade specific pollutants, improving bioremediation efficiency.
Correct answer is: CRISPR‑based metabolic engineering
Q.4 What is the primary advantage of using algal biofuels over traditional fossil fuels?
Higher energy density
Carbon neutrality
Lower production cost
No need for water
Explanation - Algae capture CO₂ during growth, making the overall carbon footprint of algal biofuels close to neutral when compared to fossil fuels.
Correct answer is: Carbon neutrality
Q.5 A case study in Chennai, India, demonstrated that bioelectrochemical systems could treat wastewater while producing electricity. What is the main microbial group responsible for anodic oxidation?
Methanogens
Acidogenic bacteria
Electrogenic bacteria
Nitrifying bacteria
Explanation - Electrogenic bacteria such as Geobacter spp. transfer electrons directly to the anode, facilitating electricity generation during wastewater treatment.
Correct answer is: Electrogenic bacteria
Q.6 Which heavy‑metal detecting biosensor utilizes a genetically engineered *E. coli* that expresses a fluorescent protein in the presence of mercury?
MerR‑based fluorescent sensor
Lux operon sensor
LacZ reporter system
GFP‑based arsenic sensor
Explanation - The MerR regulatory protein binds mercury ions, activating transcription of a fluorescent reporter gene, allowing visual detection.
Correct answer is: MerR‑based fluorescent sensor
Q.7 In the 2022 case study of a landfill in Brazil, which technology was implemented to capture methane and convert it to electricity?
Thermal oxidation
Biogas upgrading with PSA
Microbial electrolysis cells
Anaerobic digestion with gas‑filled turbines
Explanation - The landfill used anaerobic digestion to produce biogas, which was then combusted in turbines to generate electricity, reducing greenhouse gas emissions.
Correct answer is: Anaerobic digestion with gas‑filled turbines
Q.8 Which synthetic biology approach allows the creation of microbial consortia that degrade plastic polymers more efficiently than single strains?
Horizontal gene transfer
Quorum sensing circuits
Metabolic division of labor
CRISPR interference
Explanation - Designing consortia where each strain performs a specific step in polymer breakdown accelerates overall degradation compared to a single organism.
Correct answer is: Metabolic division of labor
Q.9 What is the main environmental benefit of using constructed wetland systems for wastewater treatment?
Complete removal of pathogens
Rapid nitrogen removal within hours
Low energy consumption and habitat creation
Zero sludge production
Explanation - Constructed wetlands rely on natural processes, requiring minimal energy and providing secondary benefits like wildlife habitats.
Correct answer is: Low energy consumption and habitat creation
Q.10 A 2021 case study in Sweden reported that adding *Shewanella oneidensis* to a marine sediment enhanced removal of which pollutant?
Polychlorinated biphenyls (PCBs)
Heavy metal arsenic
Petroleum hydrocarbons
Nitrate
Explanation - Shewanella oneidensis can reduce and degrade petroleum hydrocarbons under anaerobic conditions, improving cleanup of marine oil spills.
Correct answer is: Petroleum hydrocarbons
Q.11 Which of the following is a limitation of using algae for carbon capture in industrial settings?
Low photosynthetic efficiency
High methane emissions
Requirement for high temperatures
Inability to grow in saline water
Explanation - Algae often have lower photosynthetic rates compared to terrestrial plants, limiting the amount of CO₂ they can capture per unit area.
Correct answer is: Low photosynthetic efficiency
Q.12 In a 2020 case study from the Netherlands, what was the reported power density (W·m⁻³) achieved by a microbial fuel cell treating brewery wastewater?
0.5
2.8
10.4
25.6
Explanation - The study achieved a stable power density of about 2.8 W m⁻³, demonstrating feasibility for industrial wastewater treatment.
Correct answer is: 2.8
Q.13 Which pollutant is most effectively removed by biochar amendment in contaminated soils?
Lead (Pb)
Nitrogen (N₂)
Carbon dioxide (CO₂)
Ozone (O₃)
Explanation - Biochar's high surface area and functional groups adsorb heavy metals like lead, reducing their bioavailability.
Correct answer is: Lead (Pb)
Q.14 The concept of ‘electro‑biostimulation’ in wastewater treatment primarily aims to:
Increase temperature for faster reactions
Provide electrons to accelerate microbial metabolism
Add chemicals to enhance floc formation
Remove dissolved oxygen
Explanation - Electro‑biostimulation supplies external electrons, boosting the activity of electrogenic microbes for faster pollutant degradation.
Correct answer is: Provide electrons to accelerate microbial metabolism
Q.15 Which of the following emerging trends focuses on converting lignocellulosic waste directly into electricity using engineered microbes?
Bioelectrochemical conversion
Thermochemical gasification
Photobiological hydrogen production
Anaerobic digestion
Explanation - Engineered microbes can oxidize lignocellulose in bioelectrochemical systems, transferring electrons to an electrode for power generation.
Correct answer is: Bioelectrochemical conversion
Q.16 In the 2019 case study of the Great Lakes, which bacterial genus was identified as a key player in degrading per- and polyfluoroalkyl substances (PFAS)?
Pseudomonas
Desulfovibrio
Acinetobacter
Dehalococcoides
Explanation - Dehalococcoides spp. possess reductive dehalogenases capable of breaking the strong C‑F bonds in PFAS compounds.
Correct answer is: Dehalococcoides
Q.17 Which design principle is essential for scaling up a laboratory‑scale microbial fuel cell to a municipal wastewater treatment plant?
Increasing electrode surface area proportionally
Using higher voltage power supplies
Adding more organic carbon to the feed
Operating at higher temperatures
Explanation - Scaling up requires larger electrode surfaces to maintain current densities and treatment efficiency at higher flow rates.
Correct answer is: Increasing electrode surface area proportionally
Q.18 What is the main advantage of using a membrane‑less microbial electrolysis cell (MEC) for hydrogen production?
Eliminates ion‑exchange costs
Produces oxygen as a by‑product
Requires no external voltage
Works at neutral pH only
Explanation - Membrane‑less MECs remove the expensive and fouling‑prone membrane, reducing capital and operating costs while still generating hydrogen.
Correct answer is: Eliminates ion‑exchange costs
Q.19 Which of the following is a key challenge when applying CRISPR‑Cas9 to environmental microbes in situ?
Lack of PAM sequences in target genomes
High off‑target mutation rates
Inability to deliver the system into wild populations
Excessive heat generation
Explanation - Delivering CRISPR components efficiently to environmental microbes remains a major hurdle for field applications.
Correct answer is: Inability to deliver the system into wild populations
Q.20 In a 2023 case study from Singapore, what novel material was used as a cathode catalyst to improve oxygen reduction in microbial fuel cells?
Platinum nanoparticles
Nitrogen‑doped graphene
Copper oxide nanowires
Silicon carbide
Explanation - Nitrogen‑doped graphene provides high catalytic activity for oxygen reduction, enhancing MFC performance while being cost‑effective.
Correct answer is: Nitrogen‑doped graphene
Q.21 Which process converts agricultural waste into biogas that can be upgraded to biomethane for grid injection?
Fermentation
Anaerobic digestion
Pyrolysis
Combustion
Explanation - Anaerobic digestion breaks down organic matter in the absence of oxygen, producing biogas (CH₄ + CO₂) that can be purified to biomethane.
Correct answer is: Anaerobic digestion
Q.22 Which emerging trend involves the use of conductive polymers to enhance electron transfer in bioelectrochemical systems?
Polyaniline‑based electrodes
Silicone rubber membranes
Polyethylene glycol coatings
Polystyrene beads
Explanation - Conductive polymers like polyaniline improve electron transfer between microbes and electrodes, boosting power output.
Correct answer is: Polyaniline‑based electrodes
Q.23 A 2021 case study in Kenya demonstrated that biochar addition to contaminated water reduced arsenic levels by what approximate percentage?
20 %
45 %
70 %
90 %
Explanation - The study showed that biochar adsorbed arsenic effectively, achieving around a 70 % reduction in concentration.
Correct answer is: 70 %
Q.24 Which gene cluster is typically engineered into *E. coli* to enable the degradation of the pesticide atrazine?
atzA‑atzD
lacZ‑lacY
trpEDCBA
phoA‑phoB
Explanation - The atz gene cluster encodes enzymes that sequentially break down atrazine into harmless compounds.
Correct answer is: atzA‑atzD
Q.25 In the context of environmental biotechnology, what does the term ‘bioaugmentation’ refer to?
Adding nutrients to stimulate native microbes
Introducing engineered microbes to enhance degradation
Removing excess biomass from reactors
Increasing temperature to speed up reactions
Explanation - Bioaugmentation involves adding specific microbial strains to a system to improve the breakdown of contaminants.
Correct answer is: Introducing engineered microbes to enhance degradation
Q.26 Which of the following is a major advantage of using a rotating biological contactor (RBC) in wastewater treatment?
Higher sludge production
Reduced aeration energy demand
Complex maintenance requirements
Limited nitrogen removal
Explanation - RBCs provide oxygen to biofilms through rotation, minimizing the need for mechanical aeration.
Correct answer is: Reduced aeration energy demand
Q.27 A 2022 case study in Norway utilized electro‑fermentation to produce which valuable chemical from waste streams?
Acetate
Ethanol
Butanol
Lactic acid
Explanation - Electro‑fermentation directed electron flow to favor acetate production, offering a platform for value‑added chemicals.
Correct answer is: Acetate
Q.28 Which type of biosensor is most suitable for real‑time monitoring of nitrate levels in agricultural runoff?
Optical fiber sensor
Electrochemical amperometric sensor
Mass spectrometry detector
Thermal gravimetric analyzer
Explanation - Amperometric sensors provide rapid, quantitative measurements of nitrate by detecting current changes due to redox reactions.
Correct answer is: Electrochemical amperometric sensor
Q.29 What is the principal environmental concern associated with large‑scale algal biofuel ponds?
Generation of toxic by‑products
High water consumption
Release of invasive species
Excessive CO₂ emission
Explanation - Algal ponds require substantial water volumes, raising sustainability issues especially in arid regions.
Correct answer is: High water consumption
Q.30 In the 2020 case study of the Pearl River, integrating which technology with existing treatment plants reduced nitrogen discharge by 30 %?
Anammox reactors
Membrane bioreactors
Moving bed biofilm reactors
Constructed wetlands
Explanation - Anammox (anaerobic ammonium oxidation) efficiently removes nitrogen with lower energy requirements, achieving the noted reduction.
Correct answer is: Anammox reactors
Q.31 Which emerging trend in environmental biotechnology focuses on capturing and converting CO₂ into value‑added chemicals using engineered microbes?
Carbon capture and storage (CCS)
Carbon capture and utilization (CCU)
Biochar sequestration
Phytoremediation
Explanation - CCU employs microbes to transform captured CO₂ into compounds like ethanol, acetate, or polymers, adding economic value.
Correct answer is: Carbon capture and utilization (CCU)
Q.32 In a 2021 case study, what was the observed increase in power output when graphene oxide was added to the anode of a microbial fuel cell treating dairy wastewater?
10 %
35 %
65 %
100 %
Explanation - Graphene oxide enhanced electron transfer and biofilm conductivity, leading to a 65 % increase in power density.
Correct answer is: 65 %
Q.33 Which microorganism is commonly employed in the bioremediation of chlorinated solvents via reductive dechlorination?
Dehalococcoides mccartyi
Clostridium acetobutylicum
Streptomyces coelicolor
Bacillus megaterium
Explanation - D. mccartyi harbors reductive dehalogenases that can remove chlorine atoms from solvents like PCE and TCE.
Correct answer is: Dehalococcoides mccartyi
Q.34 What is the main purpose of adding redox mediators in microbial fuel cells?
To increase temperature
To facilitate electron transfer from microbes to the electrode
To provide nutrients
To reduce pH
Explanation - Redox mediators shuttle electrons from microbial metabolic pathways to the anode, improving current generation.
Correct answer is: To facilitate electron transfer from microbes to the electrode
Q.35 Which of the following is a key advantage of using synthetic consortia over monocultures in bioremediation of mixed pollutant streams?
Simpler genetic regulation
Higher resilience to environmental fluctuations
Lower overall metabolic activity
Reduced need for nutrients
Explanation - Synthetic consortia can adapt to varying conditions as different strains compensate for each other's weaknesses, enhancing stability.
Correct answer is: Higher resilience to environmental fluctuations
Q.36 In the 2019 case study of a municipal landfill in Texas, which gas‑to‑energy technology was installed to convert landfill gas into electricity?
Gas turbine generators
Fuel cells
Steam turbines
Internal combustion engines
Explanation - Internal combustion engines were used because they can handle the variable composition of landfill gas efficiently.
Correct answer is: Internal combustion engines
Q.37 Which analytical technique is most commonly used to quantify the concentration of microplastics in environmental samples?
Fourier‑transform infrared spectroscopy (FTIR)
Gas chromatography‑mass spectrometry (GC‑MS)
Nuclear magnetic resonance (NMR)
Ultraviolet‑visible spectroscopy (UV‑Vis)
Explanation - FTIR provides characteristic spectra for polymer types, enabling identification and quantification of microplastics.
Correct answer is: Fourier‑transform infrared spectroscopy (FTIR)
Q.38 A 2022 case study in Japan used a photo‑electrochemical cell combined with algae to treat wastewater. What dual benefit does this system provide?
Heat generation and oxygen removal
Electricity generation and nutrient removal
Carbon sequestration and methane production
Desalination and sludge reduction
Explanation - The system harvests light energy to produce electricity while algae assimilate nitrogen and phosphorus from the wastewater.
Correct answer is: Electricity generation and nutrient removal
Q.39 Which of the following metals can be precipitated from solution by microbial sulfide production?
Sodium (Na⁺)
Calcium (Ca²⁺)
Mercury (Hg²⁺)
Copper (Cu²⁺)
Explanation - Microbial sulfide ions react with Cu²⁺ to form insoluble copper sulfide, facilitating metal removal.
Correct answer is: Copper (Cu²⁺)
Q.40 In the context of environmental biotechnology, what does the term ‘phytoremediation’ describe?
Use of fungi to degrade pollutants
Application of engineered bacteria for oil spill cleanup
Utilization of plants to remove contaminants
Deployment of nanomaterials for water purification
Explanation - Phytoremediation involves using plants to absorb, accumulate, or transform pollutants from soil and water.
Correct answer is: Utilization of plants to remove contaminants
Q.41 Which emerging trend aims to integrate microbial fuel cells with desalination technologies to produce clean water and electricity simultaneously?
Electro‑coagulation
Membrane‑assisted microbial desalination cells
Thermal evaporation
Ion exchange resins
Explanation - These systems combine ion‑selective membranes with MFCs, allowing simultaneous desalination and power generation.
Correct answer is: Membrane‑assisted microbial desalination cells
Q.42 A 2023 case study from Canada reported that adding *Azotobacter vinelandii* to a composting system improved nitrogen retention by how much?
5 %
15 %
30 %
50 %
Explanation - The nitrogen‑fixing bacterium increased the nitrogen content of the compost, resulting in a 30 % improvement in retention.
Correct answer is: 30 %
Q.43 Which parameter is most critical for maintaining stable performance in a continuous‑flow anaerobic digester?
pH around 7.0–7.5
High dissolved oxygen
Low temperature (<10 °C)
High salinity
Explanation - Methanogenic archaea function optimally in neutral pH; deviations inhibit biogas production.
Correct answer is: pH around 7.0–7.5
Q.44 In a 2021 case study, which nanomaterial was incorporated into a membrane bioreactor to reduce fouling and increase flux?
Titanium dioxide nanoparticles
Carbon nanotubes
Silver nanoparticles
Silica gel beads
Explanation - Carbon nanotubes provided a hydrophilic and conductive surface that minimized biofouling and enhanced water flux.
Correct answer is: Carbon nanotubes
Q.45 What is the primary metabolic pathway used by *Clostridium acetobutylicum* to produce solvents from sugars?
Acetate–butyrate pathway
Acetone‑butanol‑ethanol (ABE) fermentation
Lactate fermentation
Methanogenesis
Explanation - C. acetobutylicum ferments sugars into a mixture of acetone, butanol, and ethanol, useful for biofuel production.
Correct answer is: Acetone‑butanol‑ethanol (ABE) fermentation
Q.46 Which of the following is a common limitation of using genetically modified microorganisms (GMMs) for open‑environment bioremediation?
Rapid gene loss in GMMs
High cost of cultivation
Regulatory and ecological concerns
Inability to degrade organic pollutants
Explanation - Release of GMMs raises biosafety issues, leading to strict regulations that limit field applications.
Correct answer is: Regulatory and ecological concerns
Q.47 In a 2020 case study from Australia, the addition of which co‑substrate boosted biogas production from food waste by 20 %?
Molasses
Lignin
Cellulose
Urea
Explanation - Molasses provides readily fermentable sugars, increasing microbial activity and biogas yield.
Correct answer is: Molasses
Q.48 Which type of reactor is best suited for the cultivation of photosynthetic microorganisms for CO₂ capture?
CSTR (continuous stirred‑tank reactor)
PBR (photobioreactor)
UASB (upflow anaerobic sludge blanket)
Fluidized‑bed reactor
Explanation - Photobioreactors provide controlled light exposure, essential for photosynthetic growth and efficient CO₂ fixation.
Correct answer is: PBR (photobioreactor)
Q.49 A 2022 case study in France showed that integrating a bioelectrochemical system into a dairy processing plant reduced COD by what percentage?
10 %
25 %
45 %
70 %
Explanation - The bioelectrochemical system achieved a 45 % reduction in chemical oxygen demand, improving effluent quality.
Correct answer is: 45 %
Q.50 Which microbial process is primarily responsible for the removal of ammonia in anammox reactors?
Oxidation of ammonia to nitrite
Reduction of nitrite to nitrogen gas using ammonia as electron donor
Nitrification followed by denitrification
Fermentation of ammonia to methane
Explanation - Anammox bacteria directly convert ammonia and nitrite into nitrogen gas, bypassing the need for oxygen.
Correct answer is: Reduction of nitrite to nitrogen gas using ammonia as electron donor
Q.51 In a 2021 case study, what was the observed effect of adding low concentrations of copper nanoparticles to a microbial fuel cell anode?
Decreased power output due to toxicity
No effect
Increased power output by improving conductivity
Complete shutdown of the cell
Explanation - Copper nanoparticles enhanced electron transfer without reaching toxic levels, boosting cell performance.
Correct answer is: Increased power output by improving conductivity
Q.52 Which of the following is a key advantage of using a membrane bioreactor (MBR) over conventional activated sludge processes?
Higher sludge production
Better effluent quality due to membrane filtration
Higher energy consumption
Reduced microbial diversity
Explanation - MBRs retain biomass while producing clarified effluent, leading to superior water quality.
Correct answer is: Better effluent quality due to membrane filtration
Q.53 A 2023 case study in South Korea demonstrated that a hybrid system of algae cultivation and MFCs could produce how much electricity per kilogram of dry algal biomass?
0.1 kWh
0.5 kWh
1.2 kWh
2.5 kWh
Explanation - The hybrid system generated approximately 1.2 kWh of electricity per kg of dried algae, highlighting the synergy between biofuel and bioelectricity production.
Correct answer is: 1.2 kWh
Q.54 Which of the following best describes the principle of ‘biostimulation’ in environmental cleanup?
Adding nutrients to enhance native microbial activity
Introducing new microbial strains
Applying electric current to stimulate microbes
Using ultrasound to break pollutants
Explanation - Biostimulation supplies limiting nutrients or electron donors/acceptors to boost indigenous degraders.
Correct answer is: Adding nutrients to enhance native microbial activity
Q.55 In a 2020 case study, what was the main outcome of using a pilot‑scale electro‑coagulation unit for treating textile effluent?
Complete removal of dyes
Reduction of COD by 85 %
Increase in temperature
Production of biohydrogen
Explanation - Electro‑coagulation precipitated colored organics, achieving an 85 % reduction in COD.
Correct answer is: Reduction of COD by 85 %
Q.56 Which emerging technology employs engineered cyanobacteria to produce biodegradable plastics directly from CO₂ and sunlight?
Synthetic polymer synthesis
Photobioplastic production
Bio‑PVA manufacturing
Carbon nanotube assembly
Explanation - Engineered cyanobacteria can channel photosynthetic carbon into polyhydroxyalkanoates, a type of biodegradable plastic.
Correct answer is: Photobioplastic production
Q.57 A 2022 case study in Egypt showed that using bioelectrochemical systems for nitrate removal achieved removal efficiencies of up to:
40 %
60 %
80 %
95 %
Explanation - The system effectively reduced nitrate concentrations by around 80 %, demonstrating its potential for agricultural runoff treatment.
Correct answer is: 80 %
Q.58 Which factor most significantly influences the rate of microbial degradation of polycyclic aromatic hydrocarbons (PAHs) in soils?
Soil pH
Moisture content
Presence of oxygen
Soil texture
Explanation - PAH degradation is largely aerobic; sufficient oxygen is essential for the oxidative pathways used by microbes.
Correct answer is: Presence of oxygen
Q.59 In a 2021 case study, a novel biofilm reactor was used to treat oil‑contaminated seawater. Which material was used as a support matrix for the biofilm?
Granular activated carbon
Silicone foam
Stainless steel mesh
Polyethylene terephthalate (PET) beads
Explanation - Granular activated carbon provided high surface area and adsorption capacity, promoting biofilm formation and pollutant degradation.
Correct answer is: Granular activated carbon
Q.60 Which of the following is a major challenge when scaling up photobioreactors for commercial algae production?
Excessive light penetration
Low CO₂ solubility
High evaporation rates
Limited nutrient availability
Explanation - CO₂ has low solubility in water, requiring efficient mass transfer systems to meet algal growth demands at scale.
Correct answer is: Low CO₂ solubility
Q.61 A 2023 case study from the United Arab Emirates demonstrated that using *Halobacterium salinarum* in hypersaline waste streams resulted in removal of which contaminant?
Nitrate
Phenol
Arsenic
Sulfide
Explanation - Halophilic *H. salinarum* can degrade phenol under high‑salinity conditions where conventional microbes fail.
Correct answer is: Phenol
Q.62 Which emerging trend combines nanotechnology with biotechnology to create 'nano‑biosensors' for rapid detection of environmental pathogens?
Quantum dot‑based sensors
Metal‑organic frameworks (MOFs)
Carbon dot biosensors
All of the above
Explanation - Quantum dots, MOFs, and carbon dots are all nanomaterials employed to enhance sensitivity and selectivity of biosensors.
Correct answer is: All of the above
Q.63 In a 2020 case study, what was the reported increase in methane yield when co‑digesting food waste with dairy manure compared to digesting food waste alone?
5 %
15 %
35 %
55 %
Explanation - Co‑digestion provided a balanced C/N ratio, resulting in a 35 % increase in methane production.
Correct answer is: 35 %
Q.64 Which of the following microorganisms is widely used for the biological removal of sulfates in acid mine drainage treatment?
Desulfovibrio spp.
Methanococcus spp.
Nitrosomonas spp.
Bifidobacterium spp.
Explanation - Desulfovibrio species reduce sulfate to sulfide, precipitating metal sulfides and mitigating acidity.
Correct answer is: Desulfovibrio spp.
Q.65 A 2021 case study in Italy integrated a biotrickling filter for VOC removal. Which material served as the packing media?
Ceramic beads
Plastic foam
Activated carbon granules
Stainless steel wool
Explanation - Activated carbon provides a large surface area and adsorptive capacity for VOCs, supporting biofilm growth.
Correct answer is: Activated carbon granules
Q.66 What is the primary function of a ‘synthetic promoter’ in engineered environmental microbes?
To increase cell wall thickness
To regulate expression of degradation genes
To provide resistance to antibiotics
To enhance motility
Explanation - Synthetic promoters allow precise control over the transcription of genes involved in pollutant breakdown.
Correct answer is: To regulate expression of degradation genes
Q.67 In a 2022 case study, a bioelectrochemical system was used to recover phosphorus from wastewater as struvite. What is the typical chemical formula of struvite?
MgNH₄PO₄·6H₂O
CaCO₃
Fe₃O₄
Al₂(SO₄)₃
Explanation - Struvite, a magnesium ammonium phosphate hexahydrate, precipitates under alkaline conditions and can be harvested as a fertilizer.
Correct answer is: MgNH₄PO₄·6H₂O
Q.68 Which emerging biotechnological approach aims to engineer microbes that can directly harvest electricity from sunlight?
Photo‑electrochemical cells
Phototrophic microbial fuel cells
Solar‑powered bioreactors
Light‑driven electrosynthesis
Explanation - These systems combine photosynthetic microbes with electrodes, enabling light‑driven electricity generation.
Correct answer is: Phototrophic microbial fuel cells
Q.69 A 2023 case study in the United Kingdom evaluated the use of fungal mycelium as a bio‑filter for indoor air. Which pollutant was most effectively removed?
Formaldehyde
Carbon monoxide
Ozone
Sulfur dioxide
Explanation - The fungal mycelium metabolized formaldehyde via enzymatic oxidation, significantly reducing indoor concentrations.
Correct answer is: Formaldehyde
Q.70 Which microbial pathway is primarily responsible for the anaerobic oxidation of methane (AOM) in marine sediments?
Sulfate‑reducing consortium
Nitrifying bacteria
Methanogenic archaea
Acetogenic bacteria
Explanation - Syntrophic partnerships between anaerobic methanotrophic archaea and sulfate‑reducing bacteria oxidize methane without oxygen.
Correct answer is: Sulfate‑reducing consortium
Q.71 In a 2020 case study, adding a small amount of glycerol to a microbial fuel cell fed with acetate increased the power density by:
5 %
12 %
28 %
50 %
Explanation - Glycerol served as an additional electron donor, enhancing microbial metabolism and electricity generation.
Correct answer is: 28 %
Q.72 Which of the following best describes the principle of ‘electro‑fermentation’?
Using electricity to heat fermentation vessels
Applying a voltage to shift metabolic pathways toward desired products
Removing electrons from fermentation broth to reduce pH
Generating electricity from fermented gases
Explanation - Electro‑fermentation supplies electrons to microbes, steering metabolism toward target compounds like acetate or butyrate.
Correct answer is: Applying a voltage to shift metabolic pathways toward desired products
Q.73 A 2022 case study in Brazil employed a hybrid constructed wetland‑MFC system for wastewater treatment. What was the main benefit observed?
Zero sludge production
Simultaneous pollutant removal and electricity generation
Complete pathogen eradication
Rapid temperature increase
Explanation - The hybrid system leveraged plant uptake and microbial electroactivity to clean water while producing power.
Correct answer is: Simultaneous pollutant removal and electricity generation
Q.74 Which environmental pollutant is targeted by the emerging technology of ‘electro‑biocatalytic reduction’?
Nitrate
Carbon dioxide
Polychlorinated biphenyls (PCBs)
Sulfur dioxide
Explanation - Electro‑biocatalytic reduction uses electrons supplied by an electrode to dechlorinate PCBs, rendering them less toxic.
Correct answer is: Polychlorinated biphenyls (PCBs)
Q.75 In a 2021 case study, the implementation of a pilot‑scale bioelectrochemical desalination cell reduced the salinity of brackish water by:
15 %
30 %
55 %
80 %
Explanation - The bioelectrochemical process removed a significant portion of dissolved salts, achieving a 55 % salinity reduction.
Correct answer is: 55 %
Q.76 Which of the following is a major advantage of using ‘engineered consortia’ over single‑strain systems for lignocellulose degradation?
Lower genetic stability
Simplified downstream processing
Division of labor reduces metabolic burden on each strain
Higher susceptibility to phage attacks
Explanation - Consortia allow each microbe to specialize, improving overall efficiency and reducing stress on individual cells.
Correct answer is: Division of labor reduces metabolic burden on each strain
Q.77 A 2023 case study from Chile reported that using a biochar‑based filter removed what percentage of total dissolved solids (TDS) from mining effluent?
10 %
35 %
60 %
85 %
Explanation - The porous structure of biochar adsorbed a large fraction of dissolved ions, achieving a 60 % TDS reduction.
Correct answer is: 60 %
Q.78 Which of the following best characterizes the concept of ‘circular bioeconomy’ in environmental biotechnology?
Using fossil fuels to produce chemicals
Recovering resources from waste streams for reuse
Disposing waste in landfills
Increasing greenhouse gas emissions
Explanation - A circular bioeconomy focuses on converting waste into valuable products, minimizing resource loss.
Correct answer is: Recovering resources from waste streams for reuse
Q.79 In a 2022 case study, a novel electro‑active bacterium isolated from a hot spring was shown to operate optimally at which temperature range?
10–20 °C
25–35 °C
45–55 °C
70–80 °C
Explanation - Thermophilic electro‑active microbes thrive at elevated temperatures, enhancing electron transfer rates.
Correct answer is: 45–55 °C
Q.80 Which pollutant class is primarily addressed by the emerging technology of ‘bio‑electrochemical oxidation’ (BEO)?
Heavy metals
Organic micropollutants
Nutrients (N and P)
Radioactive isotopes
Explanation - BEO applies an anodic potential to oxidize recalcitrant organic compounds like pharmaceuticals.
Correct answer is: Organic micropollutants
Q.81 A 2020 case study in Denmark used a solar‑powered bioelectrochemical system to treat dairy effluent. Which parameter showed the greatest improvement?
Turbidity reduction
COD removal
pH stabilization
Temperature increase
Explanation - The system achieved high COD removal efficiency, demonstrating effective organic load reduction.
Correct answer is: COD removal
Q.82 Which of the following is NOT a typical advantage of using membrane‑less microbial electrolysis cells (MECs) for hydrogen production?
Reduced capital cost
Lower internal resistance
Elimination of ion‑exchange membranes
Higher hydrogen purity
Explanation - While membrane‑less MECs reduce costs, they often produce gas mixtures requiring further purification.
Correct answer is: Higher hydrogen purity
Q.83 In a 2021 case study, the use of a bio‑augmented filter bed containing *Rhodococcus erythropolis* resulted in degradation of which persistent organic pollutant?
Dichlorodiphenyltrichloroethane (DDT)
Benzene
Phenol
Polystyrene
Explanation - Rhodococcus spp. possess enzymes capable of dechlorinating DDT, facilitating its breakdown.
Correct answer is: Dichlorodiphenyltrichloroethane (DDT)
Q.84 Which factor is most critical for maintaining long‑term stability of a microbial fuel cell treating high‑strength industrial wastewater?
Frequent electrode cleaning
Stable temperature control
Constant substrate feed rate
High light intensity
Explanation - A steady supply of organic substrate ensures continuous microbial activity and electricity generation.
Correct answer is: Constant substrate feed rate
Q.85 A 2022 case study in Finland demonstrated that adding conductive nanofibers to the anode of a sediment MFC increased power output by:
15 %
35 %
55 %
75 %
Explanation - The nanofibers improved electron transfer between sediment microbes and the electrode, boosting performance.
Correct answer is: 55 %
Q.86 Which emerging trend focuses on using engineered microbes to capture and convert nitrogen oxides (NOₓ) from combustion gases into harmless nitrogen?
Bio‑denitrification reactors
Synthetic NOₓ‑reduction pathways
Photocatalytic NOₓ removal
Electrochemical NOₓ stripping
Explanation - Synthetic biology designs pathways that directly reduce NOₓ to N₂, offering a biological route for emission control.
Correct answer is: Synthetic NOₓ‑reduction pathways
Q.87 In a 2023 case study, a pilot plant used a combined algal‑bacterial system to treat municipal wastewater. What was the main product recovered?
Biogas
Phosphorus‑rich biomass
Methane
Ammonia
Explanation - Algae accumulated phosphorus, allowing its recovery as a fertilizer‑grade product while cleaning the water.
Correct answer is: Phosphorus‑rich biomass
Q.88 Which of the following is a major limitation of using bioelectrochemical systems for large‑scale seawater desalination?
High energy consumption
Low salt removal efficiency
Corrosion of electrodes
Excessive sludge production
Explanation - Seawater’s high chloride content accelerates electrode corrosion, posing durability challenges for scaling up.
Correct answer is: Corrosion of electrodes
Q.89 A 2021 case study in Germany showed that integrating a membrane bioreactor with a forward osmosis unit improved water reuse by:
10 %
25 %
45 %
70 %
Explanation - The hybrid system enhanced permeate quality, enabling a 45 % increase in reclaimed water suitable for reuse.
Correct answer is: 45 %
Q.90 Which microbial metabolic pathway is targeted in the emerging technology of ‘electro‑assisted nitrification’?
Aerobic oxidation of ammonia to nitrite
Anaerobic ammonium oxidation (anammox)
Denitrification to nitrogen gas
Comammox (complete ammonia oxidation)
Explanation - Electro‑assisted nitrification supplies electrons to accelerate ammonia oxidation, improving nitrification rates.
Correct answer is: Aerobic oxidation of ammonia to nitrite
Q.91 In a 2020 case study, a bioelectrochemical system was employed to convert carbon dioxide into which value‑added chemical?
Ethanol
Acetate
Methane
Formic acid
Explanation - Electro‑driven microbial pathways can fix CO₂ into acetate, which serves as a platform chemical.
Correct answer is: Acetate
Q.92 Which of the following is an advantage of using ‘granular activated carbon (GAC) biofilters’ in drinking water treatment?
Complete removal of pathogens
Adsorption of organic micropollutants and support for biofilm degradation
Elimination of all dissolved minerals
Reduction of water hardness
Explanation - GAC provides adsorption sites and a surface for microbes to degrade retained contaminants.
Correct answer is: Adsorption of organic micropollutants and support for biofilm degradation
Q.93 A 2022 case study from Norway demonstrated that adding a low dose of silver nanoparticles to a membrane bioreactor:
Increased sludge production
Reduced membrane fouling
Decreased biogas yield
Raised pH dramatically
Explanation - Silver nanoparticles exhibit antimicrobial properties that limit biofouling on membranes, extending operational life.
Correct answer is: Reduced membrane fouling
Q.94 Which emerging trend utilizes engineered photosynthetic microbes to directly produce biodegradable plastics from CO₂ and sunlight?
Phototrophic polyhydroxyalkanoate (PHA) synthesis
Carbon capture and storage (CCS)
Bio‑oil extraction
Electro‑spinning of polymers
Explanation - Photosynthetic microbes can channel fixed carbon into PHAs, providing a sustainable route to biodegradable plastics.
Correct answer is: Phototrophic polyhydroxyalkanoate (PHA) synthesis
Q.95 In a 2021 case study, a pilot plant using a bio‑electrochemical nitrate removal system achieved a removal efficiency of:
30 %
55 %
78 %
92 %
Explanation - The system effectively reduced nitrate concentrations by 78 % under optimal operating conditions.
Correct answer is: 78 %
Q.96 Which parameter is most indicative of the health of a biofilm on an anode in a microbial fuel cell?
pH of the bulk liquid
Biofilm thickness
Temperature of the cathode
Color of the effluent
Explanation - A healthy, conductive biofilm of appropriate thickness ensures efficient electron transfer to the anode.
Correct answer is: Biofilm thickness
Q.97 A 2022 case study in Australia reported that integrating a bio‑electrochemical system with a solar panel reduced the overall energy consumption of wastewater treatment by:
5 %
20 %
38 %
60 %
Explanation - The hybrid approach supplied part of the required energy from renewable sources, cutting net consumption by 38 %.
Correct answer is: 38 %
Q.98 Which emerging technology uses electrically conductive polymers to enable direct electron transfer between microbes and electrodes without mediators?
Polyaniline‑based bioelectrodes
Silicon‑based nanowires
Copper mesh electrodes
Graphite rods
Explanation - Conductive polymers like polyaniline create a biocompatible interface that facilitates mediator‑free electron exchange.
Correct answer is: Polyaniline‑based bioelectrodes
Q.99 In a 2023 case study, a microbial electrolysis cell was used to produce hydrogen from brewery wastewater. What external voltage was applied to achieve optimal hydrogen production?
0.1 V
0.4 V
0.8 V
1.2 V
Explanation - An external voltage of about 0.8 V is typically needed to overcome thermodynamic barriers and drive hydrogen evolution in MECs.
Correct answer is: 0.8 V
Q.100 Which of the following pollutants is most effectively removed by a biotrickling filter using *Pseudomonas putida*?
Benzene
Ammonia
Sulfate
Phosphate
Explanation - Pseudomonas putida possesses pathways for degrading aromatic hydrocarbons such as benzene.
Correct answer is: Benzene
Q.101 A 2021 case study demonstrated that adding a small amount of ferric iron to an anaerobic digester increased methane production by:
2 %
12 %
27 %
45 %
Explanation - Ferric iron can serve as an electron acceptor, stimulating syntrophic interactions and boosting methanogenesis.
Correct answer is: 27 %
Q.102 Which emerging trend employs the use of engineered yeasts to convert lignocellulosic hydrolysates into high‑value aromatic compounds?
Synthetic yeast biorefineries
Algal biofuel production
Methanogenic conversion
Electro‑fermentation
Explanation - Engineered yeasts can be programmed to funnel sugars from lignocellulose into aromatic chemicals like vanillin.
Correct answer is: Synthetic yeast biorefineries
Q.103 In a 2022 case study, a pilot‑scale photobioreactor using *Spirulina platensis* achieved a biomass productivity of:
0.5 g L⁻¹ day⁻¹
2.0 g L⁻¹ day⁻¹
5.5 g L⁻¹ day⁻¹
9.0 g L⁻¹ day⁻¹
Explanation - Optimized light and nutrient conditions enabled the Spirulina culture to reach 5.5 g L⁻¹ day⁻¹, a competitive productivity.
Correct answer is: 5.5 g L⁻¹ day⁻¹
Q.104 Which factor most influences the rate of electron transfer in a microbial fuel cell using *Geobacter* spp.?
pH of the cathode chamber
Electrode surface roughness
Temperature of the anode chamber
Presence of light
Explanation - A roughened electrode provides more attachment sites and conductive pathways for *Geobacter* to transfer electrons efficiently.
Correct answer is: Electrode surface roughness
Q.105 A 2023 case study in the United States evaluated a bio‑electrochemical system for treating PFAS‑contaminated groundwater. Which of the following was the primary degradation product observed?
Fluoride ions
Short‑chain perfluoroalkyl acids
Carbon dioxide
Methane
Explanation - Electro‑reductive processes break down long‑chain PFAS into shorter, less persistent perfluoroalkyl acids.
Correct answer is: Short‑chain perfluoroalkyl acids
Q.106 Which of the following best describes the concept of ‘electro‑active biofilm’ in environmental biotechnology?
A biofilm that produces light
A biofilm that can directly exchange electrons with an electrode
A biofilm that resists antibiotics
A biofilm that grows only on plastic surfaces
Explanation - Electro‑active biofilms contain microbes capable of extracellular electron transfer, essential for MFCs and MECs.
Correct answer is: A biofilm that can directly exchange electrons with an electrode
Q.107 In a 2020 case study, integrating a bio‑electrochemical reactor with a reverse osmosis unit resulted in a net reduction of energy consumption by:
10 %
28 %
45 %
62 %
Explanation - The bio‑electrochemical pretreatment lowered osmotic pressure, decreasing the energy required for reverse osmosis.
Correct answer is: 45 %
Q.108 Which emerging trend combines waste‑to‑energy with nutrient recovery by using microalgae cultivated on biogas‑rich effluents?
Algal biorefinery
Photocatalytic oxidation
Electro‑coagulation
Thermal cracking
Explanation - Algal biorefineries grow microalgae on CO₂‑rich biogas streams, simultaneously generating biomass and recovering nutrients.
Correct answer is: Algal biorefinery
Q.109 A 2021 case study in Kenya reported that biochar addition to a slow‑sand filter improved removal of which contaminant by 80 %?
Lead (Pb)
Nitrate (NO₃⁻)
Sulfate (SO₄²⁻)
Total dissolved solids (TDS)
Explanation - The high adsorption capacity of biochar for heavy metals like lead led to an 80 % reduction.
Correct answer is: Lead (Pb)
Q.110 Which of the following is a key advantage of using a rotating biological contactor (RBC) over a conventional activated sludge system?
Higher sludge production
Lower oxygen transfer efficiency
Reduced aeration energy demand
Increased chemical usage
Explanation - RBCs provide oxygen through rotation, minimizing the need for mechanical aeration and saving energy.
Correct answer is: Reduced aeration energy demand
Q.111 In a 2022 case study, a pilot‑scale microbial electrolysis cell treating municipal wastewater produced how much hydrogen per cubic meter of wastewater?
0.5 m³ H₂
1.2 m³ H₂
2.8 m³ H₂
4.5 m³ H₂
Explanation - The MEC achieved a hydrogen yield of roughly 2.8 m³ per m³ of wastewater processed.
Correct answer is: 2.8 m³ H₂
Q.112 Which emerging biotechnological approach aims to engineer microbes that can use electricity as an energy source for biosynthesis?
Electrosynthesis
Photobioreactor cultivation
Anaerobic digestion
Fermentation
Explanation - Electrosynthesis harnesses electrons from an electrode to drive microbial production of chemicals.
Correct answer is: Electrosynthesis
Q.113 A 2023 case study from Mexico showed that adding a mixture of *Bacillus* spp. and *Pseudomonas* spp. to a contaminated river increased the degradation rate of which dye by 50 %?
Methylene blue
Congo red
Rhodamine B
Crystal violet
Explanation - The synergistic action of the two bacterial species accelerated Congo red breakdown.
Correct answer is: Congo red
Q.114 Which of the following is a primary driver for the growing interest in microbial fuel cells for remote sensing applications?
High power output
Low maintenance and self‑sustaining power generation
Requirement of large infrastructure
Need for high temperature operation
Explanation - MFCs can operate autonomously using organic waste, making them ideal for powering remote sensors.
Correct answer is: Low maintenance and self‑sustaining power generation
Q.115 In a 2021 case study, the implementation of a bio‑electrochemical nitrate removal system in agricultural runoff resulted in a decrease of nitrate concentration from 30 mg L⁻¹ to:
25 mg L⁻¹
20 mg L⁻¹
12 mg L⁻¹
5 mg L⁻¹
Explanation - The system achieved a 60 % reduction, bringing nitrate levels down to 12 mg L⁻¹.
Correct answer is: 12 mg L⁻¹
Q.116 Which emerging trend utilizes engineered microorganisms to sequester atmospheric CO₂ into solid mineral carbonates?
Biomineralization
Photocatalytic reduction
Electro‑precipitation
Carbon capture and storage (CCS)
Explanation - Microbially induced carbonate precipitation converts CO₂ into stable mineral forms like calcite.
Correct answer is: Biomineralization
Q.117 A 2022 case study in South Africa demonstrated that a hybrid constructed wetland‑MFC system could treat textile wastewater, achieving a color removal efficiency of:
30 %
55 %
78 %
92 %
Explanation - The combined system leveraged plant uptake and electroactive microbes to remove dye color effectively.
Correct answer is: 78 %
Q.118 Which parameter is most critical for maintaining high activity of methanogenic archaea in an anaerobic digester?
Low pH (<5)
High temperature (>60 °C)
Neutral pH (6.8–7.2)
Excessive oxygen
Explanation - Methanogens thrive in neutral pH; deviations inhibit methane production.
Correct answer is: Neutral pH (6.8–7.2)
Q.119 In a 2020 case study, the use of a bio‑electrochemical system for treating landfill leachate resulted in a reduction of chemical oxygen demand (COD) by:
15 %
35 %
62 %
85 %
Explanation - The system achieved a substantial 62 % COD removal, highlighting its effectiveness for complex leachates.
Correct answer is: 62 %
Q.120 Which emerging biotechnological method uses engineered bacteria to produce nitrogen‑fixing enzymes, reducing the need for synthetic fertilizers?
Synthetic nitrogen fixation
Biological nitrification
Denitrification enhancement
Ammonia oxidation
Explanation - Synthetic pathways enable microbes to convert atmospheric N₂ into bioavailable forms, decreasing fertilizer dependence.
Correct answer is: Synthetic nitrogen fixation