Q.1 What is the primary purpose of anaerobic digestion in biowaste management?
To produce biogas for energy recovery
To sterilize the waste
To increase the moisture content of waste
To convert waste into compost directly
Explanation - Anaerobic digestion breaks down organic matter without oxygen, producing methane‑rich biogas that can be used for electricity or heat.
Correct answer is: To produce biogas for energy recovery
Q.2 Which sensor is most commonly used to monitor the pH level in a bioreactor during bioconversion?
Thermocouple
Potentiometric pH electrode
Infrared gas sensor
Capacitive moisture sensor
Explanation - Potentiometric pH electrodes provide real‑time measurement of hydrogen ion concentration, critical for microbial activity control.
Correct answer is: Potentiometric pH electrode
Q.3 In a feedstock pre‑treatment system, which electrical component converts AC mains voltage to a lower DC voltage for sensor circuitry?
Transformer
Rectifier
Inverter
Capacitor
Explanation - A rectifier changes alternating current (AC) to direct current (DC), supplying low‑voltage power to electronic sensors.
Correct answer is: Rectifier
Q.4 Which type of motor is preferred for driving the agitator in a large‑scale anaerobic digester?
Stepper motor
DC shunt motor
Induction motor
Servo motor
Explanation - Induction motors provide reliable, high‑torque operation at constant speed, ideal for continuous mixing.
Correct answer is: Induction motor
Q.5 What is the main advantage of using a membrane bioreactor (MBR) over conventional activated sludge for wastewater from food processing?
Higher temperature tolerance
Lower capital cost
Superior effluent quality due to membrane filtration
Faster microbial growth rates
Explanation - MBRs combine biological degradation with a membrane barrier, producing clearer effluent with less suspended solids.
Correct answer is: Superior effluent quality due to membrane filtration
Q.6 Which parameter is most directly affected by the duty cycle of a PWM‑controlled pump in a biowaste slurry handling system?
Pump flow rate
Pump voltage rating
Pump material composition
Pump noise level
Explanation - Pulse‑width modulation (PWM) adjusts the average voltage to the pump motor, controlling its speed and therefore the flow rate.
Correct answer is: Pump flow rate
Q.7 In biowaste-to‑bioethanol conversion, which enzyme class hydrolyzes cellulose into glucose?
Proteases
Lipases
Cellulases
Amylases
Explanation - Cellulases break the β‑1,4‑glycosidic bonds in cellulose, releasing glucose monomers for fermentation.
Correct answer is: Cellulases
Q.8 Which electrical safety device protects a biowaste processing plant from over‑current caused by motor stalls?
Fuse
Thermostat
Varistor
Relay
Explanation - A fuse breaks the circuit when current exceeds its rating, preventing damage from motor stall currents.
Correct answer is: Fuse
Q.9 What does the term ‘biogas upgrading’ refer to?
Increasing the temperature of biogas
Removing CO₂ and impurities to raise methane concentration
Compressing biogas for storage
Mixing biogas with air for combustion
Explanation - Upgrading processes such as water scrubbing or pressure swing adsorption increase the calorific value of biogas by reducing CO₂.
Correct answer is: Removing CO₂ and impurities to raise methane concentration
Q.10 Which type of control algorithm is commonly used for maintaining dissolved oxygen (DO) levels in aerobic composting reactors?
Proportional‑Integral‑Derivative (PID) control
Bang‑bang control
Open‑loop control
Fuzzy logic control
Explanation - PID controllers continuously adjust aeration rates to keep DO at set points, balancing speed and stability.
Correct answer is: Proportional‑Integral‑Derivative (PID) control
Q.11 Which component converts the low‑frequency voltage signal from a current transformer (CT) into a readable digital value for a PLC?
Analog‑to‑Digital Converter (ADC)
Digital‑to‑Analog Converter (DAC)
Optocoupler
Transformer
Explanation - ADC samples the analog voltage from the CT and converts it into a digital number that the PLC can process.
Correct answer is: Analog‑to‑Digital Converter (ADC)
Q.12 Which of the following is a key advantage of using a three‑phase induction motor in biowaste shredders?
Simpler wiring than single‑phase motors
Higher efficiency and smoother torque delivery
Lower starting current
Self‑starting capability without a starter
Explanation - Three‑phase motors provide constant power flow, reducing vibration and improving cutting performance.
Correct answer is: Higher efficiency and smoother torque delivery
Q.13 What is the main function of a gas holder (e.g., a floating‑roof digester) in a biogas plant?
To store solid residues
To regulate temperature
To store biogas safely and accommodate volume changes
To filter impurities from the gas
Explanation - A floating roof moves up and down with gas volume, preventing pressure buildup and maintaining safety.
Correct answer is: To store biogas safely and accommodate volume changes
Q.14 In a biowaste composting facility, what does the term ‘carbon‑to‑nitrogen (C/N) ratio’ indicate?
The amount of electricity generated per kilogram of waste
The balance between carbon and nitrogen in the feedstock, affecting microbial activity
The ratio of moisture to dry matter
The ratio of biogas to methane produced
Explanation - An optimal C/N ratio (~25‑30:1) ensures microbes have sufficient nutrients for efficient decomposition.
Correct answer is: The balance between carbon and nitrogen in the feedstock, affecting microbial activity
Q.15 Which type of renewable energy system can be integrated with a biogas plant to utilize excess heat?
Solar photovoltaic panels
Wind turbines
Combined heat and power (CHP) unit
Geothermal heat pump
Explanation - CHP captures heat from biogas combustion for heating or drying processes, improving overall energy efficiency.
Correct answer is: Combined heat and power (CHP) unit
Q.16 What is the typical methane content (by volume) of raw biogas from agricultural waste?
10‑15%
20‑25%
50‑70%
80‑90%
Explanation - Raw biogas usually contains 50‑70% methane, with the remainder mainly CO₂ and trace gases.
Correct answer is: 50‑70%
Q.17 Which electronic device is used to measure the flow rate of biogas in a pipeline?
Thermocouple
Flow meter (e.g., turbine or ultrasonic)
Pressure transducer
pH probe
Explanation - Flow meters calculate gas volume per unit time, essential for monitoring biogas production.
Correct answer is: Flow meter (e.g., turbine or ultrasonic)
Q.18 What is the most common method for removing hydrogen sulfide (H₂S) from biogas?
Adsorption on activated carbon
Scrubbing with water
Iron oxide (Fe₂O₃) or iron sponge absorption
Cooling the gas to cryogenic temperatures
Explanation - Iron‑based sorbents chemically bind H₂S, efficiently reducing its concentration to safe levels.
Correct answer is: Iron oxide (Fe₂O₃) or iron sponge absorption
Q.19 Which parameter is most directly controlled by a variable‑frequency drive (VFD) in a biowaste pump system?
Pump voltage rating
Pump speed (rpm)
Pump material
Pump lifetime
Explanation - A VFD adjusts the frequency of the supply voltage, thereby controlling motor speed and flow rate.
Correct answer is: Pump speed (rpm)
Q.20 In the context of biowaste valorisation, what does the term ‘hydrothermal liquefaction’ refer to?
A process that converts wet biomass into liquid bio‑oil using high temperature and pressure
A method of drying biomass with microwaves
A chemical pretreatment using acids
A biological fermentation to produce ethanol
Explanation - Hydrothermal liquefaction operates at 200‑350 °C and 10‑25 MPa, breaking down wet organic matter into bio‑oil, gases, and solids.
Correct answer is: A process that converts wet biomass into liquid bio‑oil using high temperature and pressure
Q.21 Which type of battery is most suitable for storing excess electricity generated by a biogas‑fueled micro‑grid?
Lead‑acid battery
Lithium‑ion battery
Nickel‑cadmium battery
Alkaline battery
Explanation - Lithium‑ion batteries offer high energy density, longer cycle life, and efficient charge‑discharge performance for grid storage.
Correct answer is: Lithium‑ion battery
Q.22 What does the term ‘solid‑state fermenter’ imply in biowaste conversion processes?
Fermentation occurs with solid substrates and limited free water
The fermenter is built from solid metal components
Fermentation uses solid metal catalysts
The process occurs at solid temperature ranges
Explanation - Solid‑state fermentation (SSF) uses moist solid feedstock, often yielding higher enzyme concentrations than submerged fermentation.
Correct answer is: Fermentation occurs with solid substrates and limited free water
Q.23 Which instrument measures the concentration of volatile fatty acids (VFAs) in an anaerobic digester?
Gas chromatograph (GC)
pH meter
Conductivity sensor
Thermometer
Explanation - GC separates and quantifies VFAs such as acetate, propionate, and butyrate in the liquid phase.
Correct answer is: Gas chromatograph (GC)
Q.24 In an electrical schematic, what does the symbol of three parallel lines represent?
Ground
Transformer
Three‑phase supply
Resistor
Explanation - Three parallel lines denote a three‑phase electrical system, common in industrial biowaste equipment.
Correct answer is: Three‑phase supply
Q.25 Which of the following best describes the role of an electrostatic precipitator in a biogas plant?
Removes particulate matter from exhaust gases
Increases methane concentration
Regulates pressure in the gas pipeline
Measures biogas flow
Explanation - Electrostatic precipitators charge particles and collect them on plates, cleaning the gas stream before release.
Correct answer is: Removes particulate matter from exhaust gases
Q.26 What is the main environmental benefit of converting food waste into bio‑hydrogen via dark fermentation?
Reduced nitrogen emissions
Lower greenhouse‑gas emissions compared with landfilling
Higher soil fertility
Increased water usage
Explanation - Dark fermentation captures energy as hydrogen and prevents methane formation that would occur in landfills.
Correct answer is: Lower greenhouse‑gas emissions compared with landfilling
Q.27 Which component provides over‑current protection for a PLC controlling a biowaste treatment line?
Circuit breaker
Heat sink
Transformer
Capacitor bank
Explanation - Circuit breakers interrupt current when it exceeds a preset limit, protecting sensitive PLC hardware.
Correct answer is: Circuit breaker
Q.28 In a bio‑electrochemical system (BES), what is the primary function of the anode?
Oxidize organic waste and release electrons
Reduce water to produce oxygen
Store electrical energy
Regulate temperature
Explanation - At the anode, microbes break down organics, transferring electrons to the electrode, which flow to the cathode.
Correct answer is: Oxidize organic waste and release electrons
Q.29 Which of the following is a common by‑product of the thermochemical conversion of biowaste (e.g., pyrolysis)?
Bio‑char
Ethanol
Ammonia
Urea
Explanation - Pyrolysis of organic waste under limited oxygen yields bio‑char, syngas, and bio‑oil.
Correct answer is: Bio‑char
Q.30 What does the term ‘load factor’ describe in the context of an electrical system for a biowaste plant?
Ratio of average load to maximum rated load over a period
Power factor of the system
Voltage drop across cables
Frequency stability of the grid
Explanation - Load factor indicates how efficiently the capacity of the system is utilized over time.
Correct answer is: Ratio of average load to maximum rated load over a period
Q.31 Which analytical technique is most suitable for determining the elemental composition (C, H, N, S) of biowaste feedstock?
X‑ray diffraction (XRD)
Inductively Coupled Plasma (ICP) spectroscopy
Elemental (CHNS) analyzer
Fourier‑transform infrared (FTIR) spectroscopy
Explanation - CHNS analyzers combust a sample and quantify carbon, hydrogen, nitrogen, and sulfur gases.
Correct answer is: Elemental (CHNS) analyzer
Q.32 In a PLC ladder diagram, which symbol represents a normally open (NO) contact?
—| |—
—|/|—
—[ ]—
—( )—
Explanation - The ‘| |’ symbol denotes a normally open contact that closes when its input is true.
Correct answer is: —| |—
Q.33 Which type of sensor is typically used to detect the level of solid waste in a storage hopper?
Ultrasonic level sensor
Thermocouple
pH probe
Hall effect sensor
Explanation - Ultrasonic sensors emit sound waves and measure the time of flight to determine the distance to the material surface.
Correct answer is: Ultrasonic level sensor
Q.34 What is the main purpose of adding lime (Ca(OH)₂) to the digestate after anaerobic digestion?
To increase methane production
To neutralize acidity and improve fertilizer value
To reduce moisture content
To sterilize pathogens
Explanation - Lime raises the pH of the digestate, making it more suitable as a soil amendment.
Correct answer is: To neutralize acidity and improve fertilizer value
Q.35 Which of the following best describes ‘energy recovery efficiency’ in a biowaste-to-energy plant?
Ratio of electrical energy produced to the total chemical energy in the feedstock
Percentage of waste volume reduced
Amount of water reclaimed from the process
Number of microbes present in the digester
Explanation - Energy recovery efficiency compares usable output energy to the theoretical energy content of the waste.
Correct answer is: Ratio of electrical energy produced to the total chemical energy in the feedstock
Q.36 Which device is used to convert the low‑voltage DC output of a solar panel array into AC for feeding the grid in a biowaste plant that uses solar power?
Inverter
Rectifier
Transformer
Converter
Explanation - Inverters change DC to AC, enabling integration with the utility grid.
Correct answer is: Inverter
Q.37 During biowaste composting, why is temperature monitoring critical?
To ensure pathogens are killed and the compost is stable
To control the pH level
To measure methane production
To adjust the electrical supply
Explanation - Thermophilic temperatures (>55 °C) destroy pathogens and accelerate organic matter breakdown.
Correct answer is: To ensure pathogens are killed and the compost is stable
Q.38 Which of the following is NOT a typical feedstock for biowaste bioconversion?
Fruit peels
Plastic bags
Eggshells
Spent coffee grounds
Explanation - Plastics are synthetic polymers and cannot be biologically degraded under normal bioconversion processes.
Correct answer is: Plastic bags
Q.39 What does the term ‘specific methane yield’ (SMY) refer to?
Liters of methane produced per kilogram of volatile solids added
Kilowatt‑hours of electricity generated per hour
Mass of digestate produced per day
Temperature increase per gram of substrate
Explanation - SMY quantifies the efficiency of anaerobic digestion in converting organic matter to methane.
Correct answer is: Liters of methane produced per kilogram of volatile solids added
Q.40 Which of the following control strategies is most suitable for maintaining constant pressure in a biogas storage tank?
On‑off pressure switch
PID pressure controller
Manual valve adjustment
Frequency inverter
Explanation - A PID controller continuously adjusts inlet/outlet valves to keep pressure at the set point.
Correct answer is: PID pressure controller
Q.41 In a biowaste-to-bio‑hydrogen system, which microbe is commonly employed for dark fermentation?
Clostridium spp.
Saccharomyces cerevisiae
Lactobacillus spp.
Nitrosomonas spp.
Explanation - Clostridia are anaerobic bacteria that efficiently convert carbohydrates to hydrogen and organic acids.
Correct answer is: Clostridium spp.
Q.42 Which electrical parameter indicates the phase difference between voltage and current in an AC circuit?
Resistance
Power factor
Capacitance
Inductance
Explanation - Power factor (cos φ) reflects the cosine of the phase angle between voltage and current waveforms.
Correct answer is: Power factor
Q.43 What is the role of a heat exchanger in a combined heat and power (CHP) unit attached to a biogas engine?
To cool the engine only
To transfer waste heat to a secondary process (e.g., drying)
To generate electricity directly
To filter biogas
Explanation - Heat exchangers recover thermal energy from exhaust gases, improving overall plant efficiency.
Correct answer is: To transfer waste heat to a secondary process (e.g., drying)
Q.44 Which type of bioreactor is best suited for the continuous production of bio‑ethanol from sugarcane bagasse hydrolysate?
Batch reactor
Plug‑flow reactor
Stirred‑tank continuous reactor
Packed‑bed reactor
Explanation - Stirred‑tank continuous reactors provide uniform mixing and steady substrate feed, ideal for ethanol fermentation.
Correct answer is: Stirred‑tank continuous reactor
Q.45 Which of the following is a major challenge when scaling up laboratory bioconversion processes to industrial scale?
Finding enough raw material
Maintaining uniform temperature and mixing
Reducing the number of enzymes required
Increasing the pH to neutral levels
Explanation - Large reactors face gradients in temperature, substrate, and oxygen, which can affect microbial performance.
Correct answer is: Maintaining uniform temperature and mixing
Q.46 What does a ‘digital twin’ refer to in the context of modern biowaste treatment plants?
A virtual replica of the plant used for simulation and optimization
A duplicate physical plant located elsewhere
A backup power system
A second bioreactor for redundancy
Explanation - Digital twins model real‑time operations, allowing predictive maintenance and process improvement.
Correct answer is: A virtual replica of the plant used for simulation and optimization
Q.47 Which factor most directly influences the rate of hydrolysis in an anaerobic digester treating food waste?
Ambient light intensity
Particle size of the feedstock
Color of the digester walls
Type of motor used for mixing
Explanation - Smaller particles provide larger surface area, accelerating enzymatic hydrolysis.
Correct answer is: Particle size of the feedstock
Q.48 Which electronic component can be used to smooth the output voltage of a rectifier feeding a sensor circuit?
Inductor
Diode
Capacitor
Resistor
Explanation - Capacitors store charge and reduce ripple voltage, providing a steadier DC supply.
Correct answer is: Capacitor
Q.49 In the context of biowaste management, what does the abbreviation ‘LCA’ stand for?
Linear Control Algorithm
Life Cycle Assessment
Low Carbon Act
Liquid Carbon Analyzer
Explanation - LCA evaluates environmental impacts of a product or process from raw material extraction to disposal.
Correct answer is: Life Cycle Assessment
Q.50 Which material is most commonly used for constructing the inner lining of a biogas storage tank to prevent corrosion?
Stainless steel
Polyethylene (HDPE)
Aluminium
Concrete
Explanation - HDPE provides chemical resistance to H₂S and moisture, extending tank life.
Correct answer is: Polyethylene (HDPE)
Q.51 What is the typical voltage rating for a low‑voltage control circuit in an industrial biowaste plant?
120 V AC
240 V AC
480 V AC
600 V AC
Explanation - 240 V AC is a standard low‑voltage level for motor starters, sensors, and PLCs in many regions.
Correct answer is: 240 V AC
Q.52 Which of the following gases is NOT typically present in raw biogas?
Methane (CH₄)
Carbon dioxide (CO₂)
Nitrogen (N₂)
Hydrogen sulfide (H₂S)
Explanation - Nitrogen is usually minimal in biogas; the main components are CH₄, CO₂, and trace H₂S.
Correct answer is: Nitrogen (N₂)
Q.53 In a PLC program, which function block would you use to calculate the moving average of a temperature sensor reading?
PID
Timer
Filter (Moving Average)
Counter
Explanation - A moving‑average filter smooths sensor noise by averaging recent data points.
Correct answer is: Filter (Moving Average)
Q.54 Which of the following best describes ‘hydrolysis’ in the context of anaerobic digestion?
Conversion of biogas to electricity
Breakdown of complex polymers into soluble monomers
Oxidation of methane to CO₂
Condensation of water vapor
Explanation - Hydrolysis enzymatically cleaves carbohydrates, proteins, and fats into sugars, amino acids, and fatty acids.
Correct answer is: Breakdown of complex polymers into soluble monomers
Q.55 What is the typical range of operating temperature for a mesophilic anaerobic digester?
10‑20 °C
30‑38 °C
45‑55 °C
60‑70 °C
Explanation - Mesophilic digestion occurs optimally around 35 °C, balancing microbial activity and stability.
Correct answer is: 30‑38 °C
Q.56 Which type of transformer is used to step down the voltage for low‑power instrumentation in a biowaste plant?
Power transformer
Isolation transformer
Current transformer
Potential transformer
Explanation - Isolation transformers provide electrical separation and reduce voltage to safe levels for sensors.
Correct answer is: Isolation transformer
Q.57 During the pretreatment of lignocellulosic waste, which chemical is most commonly used for alkaline delignification?
Sulfuric acid
Sodium hydroxide (NaOH)
Hydrochloric acid
Acetic acid
Explanation - Alkaline NaOH breaks lignin bonds, enhancing enzymatic access to cellulose.
Correct answer is: Sodium hydroxide (NaOH)
Q.58 Which type of pump is typically used for transferring viscous slurry from a composting unit?
Centrifugal pump
Gear pump
Diaphragm pump
Peristaltic pump
Explanation - Gear pumps handle high‑viscosity fluids with minimal pulsation, suitable for slurries.
Correct answer is: Gear pump
Q.59 What does the abbreviation ‘SCADA’ stand for in plant automation?
Supervisory Control and Data Acquisition
Standard Control and Diagnostic Analyzer
Signal Conditioning and Data Automation
Systematic Control and Direct Access
Explanation - SCADA systems monitor and control industrial processes, collecting real‑time data for operators.
Correct answer is: Supervisory Control and Data Acquisition
Q.60 Which method is commonly employed to measure the chemical oxygen demand (COD) of biowaste leachate?
Spectrophotometric dichromate method
Titration with NaOH
Gas chromatography
pH meter
Explanation - COD quantifies the amount of oxidizable organic matter using a dichromate reagent and spectrophotometric readout.
Correct answer is: Spectrophotometric dichromate method
Q.61 Which component in a biogas engine’s fuel system helps remove water vapor before combustion?
Water separator (scrubber)
Fuel injector
Turbocharger
Exhaust manifold
Explanation - Water separators prevent moisture from entering the engine, protecting components and ensuring efficient combustion.
Correct answer is: Water separator (scrubber)
Q.62 What is the primary purpose of a ‘flashing valve’ in a biogas pipeline?
To increase gas pressure
To remove liquid water from the gas stream
To add methane to the gas
To regulate temperature
Explanation - Flashing valves depressurize the gas, causing dissolved water to vaporize and be removed.
Correct answer is: To remove liquid water from the gas stream
Q.63 Which parameter is most important for selecting a catalyst for the Fischer‑Tropsch synthesis of bio‑fuels from syngas?
Catalyst color
Specific surface area
Magnetic susceptibility
Melting point
Explanation - Higher surface area provides more active sites, improving conversion efficiency.
Correct answer is: Specific surface area
Q.64 In the context of electrical safety, what does the acronym ‘LOTO’ stand for?
Lock‑Out, Tag‑Out
Low‑Octane Transfer Operation
Linear Overload Thermal Override
Logical Order of Transmission
Explanation - LOTO procedures ensure that equipment is de‑energized and cannot be inadvertently started during maintenance.
Correct answer is: Lock‑Out, Tag‑Out
Q.65 Which of the following is a primary benefit of integrating a bio‑char production line with a biowaste pyrolysis plant?
Increased biogas yield
Production of a valuable soil amendment
Higher electricity generation
Reduced need for water
Explanation - Bio‑char improves soil fertility and carbon sequestration, adding revenue streams to the plant.
Correct answer is: Production of a valuable soil amendment
Q.66 Which type of sensor would you select to continuously monitor the concentration of methane in a biogas stream?
Electrochemical methane sensor
Thermocouple
Capacitive humidity sensor
Photoelectric sensor
Explanation - Electrochemical sensors provide selective, real‑time detection of methane concentrations.
Correct answer is: Electrochemical methane sensor
Q.67 What is the usual pH range for optimal methanogenic activity in an anaerobic digester?
4.0‑5.5
5.5‑6.5
6.8‑7.5
8.0‑9.0
Explanation - Methanogens thrive in near‑neutral conditions; deviations can inhibit methane production.
Correct answer is: 6.8‑7.5
Q.68 Which component is responsible for converting the rotational motion of a motor into linear motion for moving solid waste pallets?
Gearbox
Lead screw (or ball screw)
Cam
Pulley
Explanation - Lead screws transform rotational torque into precise linear displacement, suitable for pallet handling.
Correct answer is: Lead screw (or ball screw)
Q.69 What does the term ‘biomass ash content’ indicate in the context of combustion of biowaste?
The amount of inorganic residue left after burning
The carbon content of the biomass
The moisture level of the feedstock
The energy density of the fuel
Explanation - Ash content reflects the proportion of non‑combustible minerals, affecting furnace operation and ash handling.
Correct answer is: The amount of inorganic residue left after burning
Q.70 Which type of controller would you use to start a motor only after a specific temperature has been reached in a composting unit?
Proportional controller
On‑delay timer
Temperature‑triggered relay
PID controller
Explanation - A temperature‑triggered relay closes its contacts when the setpoint temperature is exceeded, energizing the motor.
Correct answer is: Temperature‑triggered relay
Q.71 In a biowaste-to‑energy plant, which factor most directly influences the overall plant efficiency?
Color of the plant building
Altitude of the site
Heat recovery system design
Number of staff on shift
Explanation - Effective heat recovery maximizes the usable energy from combustion or biogas combustion.
Correct answer is: Heat recovery system design
Q.72 Which of the following is a primary greenhouse gas emitted if biowaste decomposes aerobically in open dumps?
Methane (CH₄)
Nitrous oxide (N₂O)
Carbon dioxide (CO₂)
Sulfur hexafluoride (SF₆)
Explanation - Aerobic decomposition releases CO₂; methane is predominant under anaerobic conditions.
Correct answer is: Carbon dioxide (CO₂)
Q.73 Which measurement unit is commonly used for reporting the specific power output of a biogas engine (kW per cubic meter of biogas per hour)?
kW·m⁻³·h⁻¹
kWh
MW
BTU/h
Explanation - Specific power expresses engine output per unit of fuel flow, useful for comparing engine performance.
Correct answer is: kW·m⁻³·h⁻¹
Q.74 Which type of algorithm is most suitable for predicting biogas production from varying feedstock composition using historical data?
Linear regression
Genetic algorithm
Neural network
Breadth‑first search
Explanation - Neural networks can model complex, non‑linear relationships between feedstock characteristics and biogas yield.
Correct answer is: Neural network
Q.75 Which of the following best describes a ‘closed‑loop’ control system in a biowaste processing plant?
Control actions are based on preset schedules only
The system uses feedback from sensors to adjust actuators continuously
Control is performed manually by operators
The system does not use any sensors
Explanation - Closed‑loop systems continuously compare measured variables to set points and correct deviations.
Correct answer is: The system uses feedback from sensors to adjust actuators continuously
Q.76 What is the main advantage of using a variable‑speed drive (VSD) on the agitator motor of an anaerobic digester?
It eliminates the need for a power supply
It allows precise control of mixing intensity, saving energy
It increases the temperature of the digester
It reduces the size of the digester
Explanation - VSDs adjust motor speed to match mixing requirements, reducing unnecessary power consumption.
Correct answer is: It allows precise control of mixing intensity, saving energy
Q.77 In the context of biowaste pretreatment, which mechanical process reduces particle size by crushing and grinding?
Hydrolysis
Milling
Fermentation
Distillation
Explanation - Milling physically reduces size, improving surface area for subsequent biochemical reactions.
Correct answer is: Milling
Q.78 Which type of electrical protection device detects a ground fault and quickly disconnects the circuit?
Fuse
Circuit breaker
Residual‑Current Device (RCD) or Ground‑Fault Circuit Interrupter (GFCI)
Thermal overload relay
Explanation - RCD/GFCI monitors imbalance between live and neutral currents, tripping within milliseconds on a fault.
Correct answer is: Residual‑Current Device (RCD) or Ground‑Fault Circuit Interrupter (GFCI)
Q.79 Which parameter is directly measured by a turbidity sensor in a biowaste slurry?
Light scattering caused by suspended particles
Electrical conductivity
Temperature
pH
Explanation - Turbidity sensors emit light; the amount of scattered light correlates with particle concentration.
Correct answer is: Light scattering caused by suspended particles
Q.80 What is the purpose of a ‘feed‑forward’ control element in a bioprocess control system?
To react after a disturbance occurs
To anticipate a change based on measured disturbances and act pre‑emptively
To store excess energy
To filter sensor noise
Explanation - Feed‑forward control uses disturbance measurements to adjust the manipulated variable before the process deviates.
Correct answer is: To anticipate a change based on measured disturbances and act pre‑emptively
Q.81 Which of the following gases can be used as a co‑feed in a gasification process to improve syngas quality?
Steam (H₂O vapor)
Helium
Ozone (O₃)
Carbon monoxide (CO₂)
Explanation - Steam gasification adds H₂ to the syngas, improving its heating value and downstream processing.
Correct answer is: Steam (H₂O vapor)
Q.82 Which type of battery storage system is most suitable for short‑term buffering of biogas‑generated electricity on a farm?
Lead‑acid battery bank
Flow battery
Lithium‑ion battery bank
Sodium‑sulfur battery
Explanation - Lithium‑ion offers high power density and rapid charge‑discharge cycles ideal for daily fluctuations.
Correct answer is: Lithium‑ion battery bank
Q.83 Which electrical measurement device would you use to verify the frequency of the grid connection for a biogas generator?
Multimeter
Oscilloscope
Frequency meter (or power quality analyzer)
Clamp meter
Explanation - A frequency meter directly measures the line frequency (e.g., 50 Hz or 60 Hz).
Correct answer is: Frequency meter (or power quality analyzer)
Q.84 What is the most common method for removing ammonia (NH₃) from biogas before combustion?
Water scrubbing
Activated carbon adsorption
Molecular sieve adsorption
Chemical absorption with sulfuric acid
Explanation - Water absorbs ammonia effectively, reducing corrosion and NOₓ formation during combustion.
Correct answer is: Water scrubbing
Q.85 Which of the following best defines ‘circular economy’ in the context of biowaste management?
Using waste as a feedstock for new products and energy, minimizing landfill
Increasing the amount of waste generated each year
Exporting waste to other countries
Burning waste without energy recovery
Explanation - Circular economy emphasizes resource recovery and closed‑loop utilization of waste streams.
Correct answer is: Using waste as a feedstock for new products and energy, minimizing landfill
Q.86 Which sensor technology is best suited for detecting the presence of volatile organic compounds (VOCs) emitted during composting?
Metal‑oxide semiconductor (MOS) sensor
Thermocouple
Hall effect sensor
Ultrasonic sensor
Explanation - MOS sensors change resistance in the presence of VOCs, enabling detection of odorous compounds.
Correct answer is: Metal‑oxide semiconductor (MOS) sensor
Q.87 In a biowaste processing facility, what does the term ‘downtime’ refer to?
The period when the plant is producing maximum output
The time when equipment is not operating due to maintenance or faults
The time taken for waste to decompose
The duration of a power outage in the nearby city
Explanation - Downtime reduces overall plant availability and productivity.
Correct answer is: The time when equipment is not operating due to maintenance or faults
Q.88 Which type of motor is typically used for low‑speed, high‑torque applications such as screw conveyors in biowaste handling?
Synchronous motor
Induction motor
Stepper motor
Servo motor
Explanation - Induction motors are robust, efficient, and provide the necessary torque at low speeds.
Correct answer is: Induction motor
Q.89 What is the purpose of a ‘scrubber’ in a biogas cleaning train?
To cool the gas
To remove acidic gases like H₂S and CO₂
To increase methane concentration
To add oxygen to the gas
Explanation - Scrubbers use liquids or solids to absorb harmful acidic components, protecting downstream equipment.
Correct answer is: To remove acidic gases like H₂S and CO₂
Q.90 Which parameter is most directly influenced by the use of a variable‑frequency drive (VFD) on a pump motor in a biowaste slurry line?
Pump motor voltage rating
Pump flow rate
Pump material composition
Pump shaft diameter
Explanation - VFD adjusts motor speed, thereby controlling the pump’s output flow.
Correct answer is: Pump flow rate
Q.91 Which of the following is a common method for measuring the solids content (TS – total solids) of a biowaste sample?
Gravimetric drying at 105 °C
pH titration
Conductivity measurement
Spectrophotometry
Explanation - Drying removes water; the weight loss corresponds to moisture, and the remaining mass is total solids.
Correct answer is: Gravimetric drying at 105 °C
Q.92 In a digital control system, what does the term ‘latency’ refer to?
The time delay between an input signal and the system’s response
The maximum voltage the system can handle
The amount of memory available
The frequency of the power supply
Explanation - Latency affects how quickly the controller can react to changing process conditions.
Correct answer is: The time delay between an input signal and the system’s response
Q.93 Which of the following best describes the role of ‘catalytic cracking’ in a biowaste pyrolysis plant?
Breaking down large molecules into smaller ones using a catalyst to increase bio‑oil yield
Increasing the temperature of the reactor
Removing ash from the product stream
Compressing the produced gases
Explanation - Catalytic cracking lowers activation energy, improving conversion efficiency and product quality.
Correct answer is: Breaking down large molecules into smaller ones using a catalyst to increase bio‑oil yield
Q.94 What is the main function of a ‘feed pump’ in a continuous anaerobic digester system?
To remove biogas from the digester
To supply fresh substrate continuously into the digester
To regulate temperature
To vent excess pressure
Explanation - The feed pump ensures a steady influx of waste, maintaining stable digestion conditions.
Correct answer is: To supply fresh substrate continuously into the digester
Q.95 Which of the following gases is considered a potent greenhouse gas that can be emitted from improperly managed biowaste?
Methane (CH₄)
Nitrogen (N₂)
Oxygen (O₂)
Argon (Ar)
Explanation - Methane has a global warming potential about 28‑36 times that of CO₂ over 100 years.
Correct answer is: Methane (CH₄)
Q.96 Which PLC instruction is typically used to compare a sensor reading against a setpoint and trigger an output when the reading exceeds the setpoint?
ADD
GT (Greater Than)
MOV
NOP
Explanation - GT evaluates if the first operand is greater than the second and can activate a coil or alarm.
Correct answer is: GT (Greater Than)
Q.97 What is the main advantage of using a ‘floating‑roof’ digester compared to a fixed‑roof design?
Higher temperature stability
Ability to accommodate variable gas volumes without pressure buildup
Lower construction cost
Better resistance to corrosion
Explanation - The floating roof rises with gas production, maintaining safe pressure levels.
Correct answer is: Ability to accommodate variable gas volumes without pressure buildup
Q.98 Which factor most influences the rate of methanogenesis in a thermophilic digester?
pH value
Color of the feedstock
Ambient humidity
Magnetic field strength
Explanation - Thermophilic methanogens require a narrow pH range (≈7.0‑7.5) for optimal activity.
Correct answer is: pH value
Q.99 Which of the following best describes a ‘bio‑refinery’ concept applied to agricultural waste?
A facility that only burns waste for heat
A plant that converts waste into multiple value‑added products (e.g., biogas, bio‑char, chemicals)
A storage area for raw agricultural products
A laboratory for genetic modification of crops
Explanation - Biorefineries integrate several conversion pathways to maximize resource utilization.
Correct answer is: A plant that converts waste into multiple value‑added products (e.g., biogas, bio‑char, chemicals)
Q.100 Which device would you install to protect a PLC input from voltage spikes caused by inductive loads?
Metal‑oxide varistor (MOV)
Fuse
Thermistor
Potentiometer
Explanation - MOVs clamp transient over‑voltages, protecting sensitive electronics from spikes.
Correct answer is: Metal‑oxide varistor (MOV)
Q.101 What does the term ‘hydraulic retention time (HRT)’ signify in a bioreactor?
The time required for a motor to reach full speed
The average time the liquid stays in the reactor
The period of electrical maintenance shutdown
The duration of a batch fermentation
Explanation - HRT is calculated as reactor volume divided by influent flow rate and influences treatment efficiency.
Correct answer is: The average time the liquid stays in the reactor
Q.102 Which of the following is a typical indicator that a biogas engine is operating inefficiently?
Low exhaust temperature
High unburned methane in the exhaust
Steady voltage output
Constant fuel flow
Explanation - Incomplete combustion leads to methane slip, indicating poor engine tuning or air‑fuel imbalance.
Correct answer is: High unburned methane in the exhaust
Q.103 Which of the following is a common by‑product of the anaerobic digestion of food waste that can be used as a fertilizer?
Digestate
Bio‑oil
Syngas
Methanol
Explanation - Digestate contains nutrients (N, P, K) and is often applied to soils as a bio‑fertilizer.
Correct answer is: Digestate
Q.104 In a control panel, what is the purpose of a ‘dead‑front’ design?
To allow easy access to live parts
To prevent accidental contact with energized components
To improve heat dissipation
To reduce noise
Explanation - Dead‑front enclosures hide live parts, enhancing operator safety.
Correct answer is: To prevent accidental contact with energized components
Q.105 Which analytical technique would you use to identify the functional groups present in bio‑oil produced from biowaste pyrolysis?
FTIR (Fourier‑Transform Infrared Spectroscopy)
X‑ray diffraction (XRD)
Scanning electron microscopy (SEM)
Atomic absorption spectroscopy (AAS)
Explanation - FTIR detects characteristic vibrations of chemical bonds, revealing functional groups in liquids.
Correct answer is: FTIR (Fourier‑Transform Infrared Spectroscopy)
Q.106 Which of the following best describes the function of a ‘bio‑filter’ in a waste‑to‑energy plant?
To cool the exhaust gases
To remove particulate matter by mechanical filtration
To biologically oxidize odorous gases (e.g., H₂S) using microorganisms
To compress biogas for storage
Explanation - Bio‑filters use a microbial layer to convert harmful gases into less odorous compounds.
Correct answer is: To biologically oxidize odorous gases (e.g., H₂S) using microorganisms
Q.107 Which voltage level is commonly used for medium‑voltage distribution in an industrial biowaste processing plant?
120 V
480 V
11 kV
33 kV
Explanation - Medium‑voltage ranges from 1 kV to 35 kV; 11 kV is a typical distribution voltage in many facilities.
Correct answer is: 11 kV
Q.108 What is the primary purpose of adding trace nutrients (e.g., nickel, cobalt) to an anaerobic digester?
To increase the pH
To stimulate the activity of methanogenic archaea
To reduce odor
To improve the color of the digestate
Explanation - Trace metals act as co‑factors for enzymes involved in methane production.
Correct answer is: To stimulate the activity of methanogenic archaea
Q.109 Which of the following control strategies is most appropriate for maintaining a constant substrate feed rate despite fluctuations in feedstock supply?
Open‑loop control
Feed‑forward control based on upstream sensor data
Manual adjustment
Time‑based scheduling only
Explanation - Feed‑forward uses real‑time feedstock measurements to adjust pump speed, keeping flow steady.
Correct answer is: Feed‑forward control based on upstream sensor data
Q.110 Which of the following is NOT a typical end‑use of biowaste‑derived biogas?
Electricity generation
Vehicle fuel (CNG)
Direct injection into gasoline engines without upgrading
Heat production for district heating
Explanation - Biogas must be cleaned and possibly upgraded before use in gasoline engines; otherwise it can cause damage.
Correct answer is: Direct injection into gasoline engines without upgrading
Q.111 What does the term ‘thermal desorption’ refer to in biowaste gas cleaning?
Removing moisture by heating
Heating contaminated media to release adsorbed pollutants for capture
Cooling the gas stream to condense organics
Adding heat to increase biogas volume
Explanation - Thermal desorption regenerates adsorbents (e.g., activated carbon) by volatilizing captured contaminants.
Correct answer is: Heating contaminated media to release adsorbed pollutants for capture
Q.112 Which of the following is a common method for measuring the calorific value of biogas?
Bomb calorimetry
pH titration
Viscometry
Conductivity measurement
Explanation - Bomb calorimeters combust a known volume of gas and measure the heat released.
Correct answer is: Bomb calorimetry
Q.113 In a biowaste treatment plant, what is the main role of a ‘SCADA HMI’ (Human‑Machine Interface)?
To physically move waste material
To provide operators with a graphical view of plant status and allow control actions
To store raw biowaste
To generate electricity
Explanation - HMI displays data, alarms, and enables manual overrides for process control.
Correct answer is: To provide operators with a graphical view of plant status and allow control actions
Q.114 Which of the following gases can be produced by dark fermentation of food waste and used as a clean fuel?
Hydrogen (H₂)
Ozone (O₃)
Carbon monoxide (CO)
Sulfur dioxide (SO₂)
Explanation - Dark fermentation converts carbohydrates to hydrogen and organic acids under anaerobic conditions.
Correct answer is: Hydrogen (H₂)
Q.115 Which of the following is a common indicator of over‑loading in an anaerobic digester?
Drop in pH (acidification)
Increase in temperature
Decrease in gas production
Increase in digestate volume
Explanation - Excess substrate leads to acid accumulation faster than methanogens can consume, lowering pH.
Correct answer is: Drop in pH (acidification)
Q.116 Which type of electronic component is commonly used to protect low‑voltage control circuits from electromagnetic interference (EMI) generated by large motors?
Ferrite bead
Zener diode
Photodiode
LED
Explanation - Ferrite beads suppress high‑frequency noise on power and signal lines.
Correct answer is: Ferrite bead
Q.117 What does the term ‘substrate loading rate’ (SLR) refer to in bioreactor design?
The speed at which the reactor rotates
The amount of volatile solids fed per unit volume per day
The temperature increase per hour
The pressure drop across the reactor
Explanation - SLR (kg VS m⁻³ d⁻¹) determines the organic load applied to the microbial community.
Correct answer is: The amount of volatile solids fed per unit volume per day
Q.118 Which of the following best explains why a biogas upgrading unit may use a membrane separation technology?
Membranes selectively allow CO₂ to pass while retaining CH₄, increasing methane purity
Membranes heat the biogas to improve combustion
Membranes add oxygen to the gas mixture
Membranes store biogas for later use
Explanation - Selective permeation separates CO₂, raising the methane concentration in the product stream.
Correct answer is: Membranes selectively allow CO₂ to pass while retaining CH₄, increasing methane purity
Q.119 Which of the following is a key benefit of integrating Internet‑of‑Things (IoT) sensors in biowaste management facilities?
Eliminating the need for human operators
Real‑time remote monitoring and predictive maintenance
Increasing the size of the facility
Reducing the chemical composition of waste
Explanation - IoT devices transmit data for analytics, enabling early fault detection and optimized operation.
Correct answer is: Real‑time remote monitoring and predictive maintenance
Q.120 What is the typical moisture content range of feedstock that is optimal for anaerobic digestion?
5‑10%
30‑50%
70‑85%
90‑95%
Explanation - High moisture facilitates microbial activity; too low moisture hampers hydrolysis, too high may cause dilution.
Correct answer is: 70‑85%
Q.121 Which of the following is a common method for measuring dissolved gases (e.g., methane) in liquid digestate?
Headspace gas chromatography
pH meter
Turbidity sensor
Thermocouple
Explanation - Samples are equilibrated in a sealed vial; the headspace gas is analyzed by GC to quantify dissolved gases.
Correct answer is: Headspace gas chromatography
Q.122 Which electrical device converts a high‑frequency AC signal into a lower‑frequency AC signal suitable for driving large pumps?
Frequency converter (VFD)
Rectifier
Transformer
Inverter
Explanation - A VFD adjusts both voltage and frequency to control motor speed for large pumps.
Correct answer is: Frequency converter (VFD)
Q.123 In a biowaste processing plant, what does the term ‘throughput’ refer to?
The total energy produced per year
The amount of waste processed per unit time (e.g., tonnes per day)
The number of employees working in the plant
The voltage level of the plant’s power supply
Explanation - Throughput quantifies plant capacity and influences design specifications.
Correct answer is: The amount of waste processed per unit time (e.g., tonnes per day)
Q.124 Which of the following gases is typically removed by a ‘scrubber’ using an alkaline solution in a biogas cleaning train?
Carbon dioxide (CO₂)
Methane (CH₄)
Nitrogen (N₂)
Oxygen (O₂)
Explanation - Alkaline scrubbers (e.g., NaOH solution) chemically absorb CO₂, raising methane purity.
Correct answer is: Carbon dioxide (CO₂)
Q.125 Which of the following best describes the purpose of a ‘buffer tank’ in a biogas plant?
To store excess biogas for later use
To temporarily hold digestate before further processing
To regulate temperature of the reactor
To house the control panel
Explanation - Buffer tanks accommodate fluctuations in gas production and demand, ensuring a steady supply.
Correct answer is: To store excess biogas for later use
Q.126 Which parameter is most directly affected by the use of a ‘heat‑integrated’ dryer in a biowaste processing line?
Electrical voltage
Energy consumption
Color of the dried product
Acidity of the waste
Explanation - Heat integration recovers waste heat, reducing overall energy demand for drying.
Correct answer is: Energy consumption
Q.127 Which type of control valve is commonly used for precise modulation of gas flow in a biogas upgrading system?
Globe valve
Butterfly valve
Ball valve
Needle valve
Explanation - Needle valves provide fine flow control due to their tapered plug design.
Correct answer is: Needle valve
Q.128 What is the main reason for installing a pressure relief valve on a biogas storage tank?
To increase biogas production
To prevent over‑pressurization and possible rupture
To improve the quality of the gas
To regulate temperature
Explanation - Pressure relief valves open automatically when pressure exceeds a set limit, ensuring safety.
Correct answer is: To prevent over‑pressurization and possible rupture
Q.129 Which of the following is a typical characteristic of a ‘thermophilic’ anaerobic digester compared to a ‘mesophilic’ one?
Higher operating temperature (≈55‑60 °C)
Lower methane yield
Longer start‑up time
Greater sensitivity to pH fluctuations
Explanation - Thermophilic digesters run at higher temperatures, offering faster reaction rates but higher energy input.
Correct answer is: Higher operating temperature (≈55‑60 °C)
Q.130 Which of the following is an example of a ‘green metric’ used to evaluate biowaste conversion processes?
Specific methane yield
Carbon footprint (kg CO₂‑eq per tonne of waste)
Electrical power factor
Voltage drop across cables
Explanation - Carbon footprint quantifies greenhouse‑gas emissions, a key sustainability indicator.
Correct answer is: Carbon footprint (kg CO₂‑eq per tonne of waste)
Q.131 Which type of pump is most suitable for transferring low‑viscosity liquid (e.g., clarified biogas slurry) at high flow rates?
Centrifugal pump
Peristaltic pump
Gear pump
Piston pump
Explanation - Centrifugal pumps handle large volumes of low‑viscosity fluids efficiently.
Correct answer is: Centrifugal pump
Q.132 Which of the following is a common method for reducing odors emitted from a composting facility?
Covering the compost with a tarp
Increasing the moisture content
Adding more organic waste
Operating at lower temperatures
Explanation - Physical barriers limit the release of volatile odorous compounds.
Correct answer is: Covering the compost with a tarp
Q.133 Which of the following components would you use to convert a 5 V DC sensor output to a 0‑10 V signal for PLC input?
Signal conditioner (amplifier)
Transformer
Rectifier
Fuse
Explanation - Signal conditioners scale and condition sensor outputs to match PLC input ranges.
Correct answer is: Signal conditioner (amplifier)
Q.134 What is the main advantage of using a ‘dual‑stage’ anaerobic digester (e.g., separate hydrolysis/acidogenesis and methanogenesis stages)?
Reduced capital cost
Improved process stability and higher methane yields
Simpler control strategy
Lower temperature requirement
Explanation - Separating stages optimizes conditions for each microbial group, enhancing overall performance.
Correct answer is: Improved process stability and higher methane yields
Q.135 Which of the following is a key factor influencing the choice between a batch and a continuous reactor for biowaste treatment?
Color of the reactor walls
Desired production rate and feedstock variability
Length of the plant’s electrical cables
Number of employees
Explanation - Continuous reactors handle variable flows better and support steady‑state operation, while batch reactors are simpler for small‑scale or intermittent loads.
Correct answer is: Desired production rate and feedstock variability
Q.136 Which of the following is a typical safety interlock used on a biogas engine to prevent operation when oxygen levels are too high?
O₂ sensor linked to engine shutdown logic
Temperature sensor on the exhaust
Flow meter on the fuel line
Vibration sensor on the motor
Explanation - Elevated oxygen can cause unsafe combustion; the sensor triggers a shutdown to protect equipment.
Correct answer is: O₂ sensor linked to engine shutdown logic
Q.137 Which of the following is the most appropriate method for quantifying the nitrogen content in a digestate sample?
Kjeldahl digestion
Gravimetric analysis
UV‑Vis spectroscopy
Gas chromatography
Explanation - Kjeldahl method determines total nitrogen by converting it to ammonium and measuring concentration.
Correct answer is: Kjeldahl digestion
Q.138 What does the acronym ‘PLC’ stand for in industrial automation?
Power Line Converter
Programmable Logic Controller
Pulse Light Converter
Process Light Controller
Explanation - PLCs are rugged computers used to automate electromechanical processes.
Correct answer is: Programmable Logic Controller
Q.139 Which of the following best describes a ‘co‑generation’ (CHP) system in a biowaste plant?
Generating only electricity
Generating only heat
Simultaneously producing electricity and useful heat from the same energy source
Storing biogas in underground caverns
Explanation - Combined heat and power (CHP) improves overall energy efficiency by capturing waste heat.
Correct answer is: Simultaneously producing electricity and useful heat from the same energy source
Q.140 Which of the following is a common indicator of fouling in a heat exchanger used for biogas cleaning?
Increase in pressure drop across the exchanger
Decrease in voltage supply
Higher pH of the outlet stream
Reduced color intensity of the gas
Explanation - Fouling creates resistance to flow, raising the pressure differential.
Correct answer is: Increase in pressure drop across the exchanger
Q.141 Which type of power quality issue is most likely to affect sensitive instrumentation in a biowaste plant?
Voltage sag
Harmonic distortion
Frequency drift
All of the above
Explanation - Voltage sags, harmonics, and frequency variations can all degrade sensor accuracy and controller performance.
Correct answer is: All of the above
Q.142 What is the primary reason for adding a ‘gas‑oil separator’ after a biogas engine?
To separate unburned oil droplets from exhaust gases
To increase the methane content of the gas
To cool the exhaust gases
To add oxygen to the exhaust
Explanation - Oil separators prevent oil carry‑over that could foul downstream equipment or cause emissions.
Correct answer is: To separate unburned oil droplets from exhaust gases
Q.143 Which of the following is a typical range for the specific power output (kW per cubic meter of biogas per hour) of a small biogas engine?
0.1‑0.3 kW·m⁻³·h⁻¹
1‑2 kW·m⁻³·h⁻¹
5‑10 kW·m⁻³·h⁻¹
20‑30 kW·m⁻³·h⁻¹
Explanation - Small internal‑combustion biogas engines typically deliver about 1‑2 kW per cubic meter of biogas per hour.
Correct answer is: 1‑2 kW·m⁻³·h⁻¹
Q.144 Which of the following is a key advantage of using a ‘wet‑type’ biogas purifier over a ‘dry‑type’ system?
Higher removal efficiency for H₂S and CO₂
Lower water consumption
Smaller physical footprint
No need for waste disposal
Explanation - Wet scrubbers can achieve higher absorption rates for acidic gases compared to dry adsorbents.
Correct answer is: Higher removal efficiency for H₂S and CO₂
Q.145 Which of the following best defines ‘bio‑hydrogen’?
Hydrogen produced by water electrolysis using renewable electricity
Hydrogen generated biologically through processes such as dark fermentation
Hydrogen extracted from natural gas
Hydrogen stored in metallic hydrides
Explanation - Bio‑hydrogen is produced by microorganisms converting organic substrates into H₂ under anaerobic conditions.
Correct answer is: Hydrogen generated biologically through processes such as dark fermentation
Q.146 In a biowaste conversion plant, which parameter is most directly monitored by a ‘gas flow meter’?
Biogas composition
Biogas production rate (volume per time)
Biogas temperature
Biogas pressure
Explanation - Flow meters measure the volumetric flow of gas, indicating production performance.
Correct answer is: Biogas production rate (volume per time)
Q.147 Which of the following is the most suitable material for constructing pipelines that transport biogas containing H₂S?
Carbon steel
Stainless steel (e.g., 304L)
Aluminium
PVC
Explanation - Stainless steel resists corrosion caused by H₂S, extending pipeline life.
Correct answer is: Stainless steel (e.g., 304L)
Q.148 Which of the following is a primary factor that determines the design capacity of a biogas storage vessel?
Peak biogas production rate
Color of the biogas
Number of employees in the plant
Ambient humidity
Explanation - Storage must accommodate the maximum gas generation between usage periods.
Correct answer is: Peak biogas production rate
Q.149 What is the typical range of the heating value (HHV) of raw biogas?
15‑20 MJ m⁻³
20‑25 MJ m⁻³
30‑40 MJ m⁻³
50‑60 MJ m⁻³
Explanation - Raw biogas (≈55‑65% CH₄) has an HHV around 20‑25 MJ per cubic meter.
Correct answer is: 20‑25 MJ m⁻³
Q.150 Which of the following is a common method for upgrading biogas to biomethane suitable for injection into the natural gas grid?
Pressure swing adsorption (PSA)
Simple filtration through sand
Cooling to -100 °C
Adding liquid nitrogen
Explanation - PSA selectively adsorbs CO₂ and other impurities, delivering high‑purity methane.
Correct answer is: Pressure swing adsorption (PSA)