Q.1 What is the primary purpose of an activated sludge process in wastewater treatment?
To physically remove suspended solids by filtration
To biologically degrade organic matter using microorganisms
To chemically neutralize acidic waste streams
To evaporate water and concentrate contaminants
Explanation - Activated sludge relies on a mixed microbial community that consumes dissolved organic matter, reducing BOD and COD levels.
Correct answer is: To biologically degrade organic matter using microorganisms
Q.2 Which of the following is a typical indicator of effluent quality for a municipal wastewater treatment plant?
Total Dissolved Solids (TDS)
Biochemical Oxygen Demand (BOD5)
Electrical Conductivity (EC)
pH
Explanation - BOD5 measures the amount of dissolved oxygen required by microorganisms to break down organic material in 5 days and is a standard effluent quality parameter.
Correct answer is: Biochemical Oxygen Demand (BOD5)
Q.3 In a wastewater treatment plant, a Hall effect flow meter is most commonly used for:
Measuring dissolved oxygen concentration
Measuring the flow rate of conductive liquids
Measuring pH of the influent
Detecting suspended solids
Explanation - Hall effect flow meters generate a voltage proportional to the flow of conductive fluids, making them ideal for water and wastewater streams.
Correct answer is: Measuring the flow rate of conductive liquids
Q.4 Which of the following best describes the role of an anoxic zone in an activated sludge system?
Promote aerobic oxidation of organic matter
Facilitate nitrogen removal via denitrification
Increase sludge settling velocity
Neutralize acidic wastewater
Explanation - Anoxic zones lack dissolved oxygen but provide nitrate for denitrifying bacteria to convert nitrate to nitrogen gas, reducing total nitrogen.
Correct answer is: Facilitate nitrogen removal via denitrification
Q.5 What is the main advantage of using a membrane bioreactor (MBR) over conventional activated sludge?
Higher energy consumption
Lower sludge production and better effluent quality
Simpler maintenance
Elimination of biological processes
Explanation - MBRs combine biological treatment with membrane filtration, producing high‑quality effluent and reducing the need for secondary clarifiers.
Correct answer is: Lower sludge production and better effluent quality
Q.6 Which of the following sensors is most appropriate for real‑time monitoring of dissolved oxygen in a bioreactor?
pH probe
Galvanic DO sensor
Turbidity meter
Conductivity sensor
Explanation - Galvanic dissolved oxygen sensors produce a current proportional to the oxygen concentration, ideal for continuous monitoring.
Correct answer is: Galvanic DO sensor
Q.7 In the context of wastewater treatment, what does the term ‘hydraulic retention time (HRT)’ refer to?
The time required for sludge to settle
The average time water spends in a treatment unit
The duration of disinfection step
The time needed for microbial growth
Explanation - HRT is calculated as the volume of a reactor divided by the influent flow rate, representing how long water is retained for treatment.
Correct answer is: The average time water spends in a treatment unit
Q.8 Which type of pump is most commonly used for transferring sludge in a wastewater treatment plant?
Centrifugal pump
Peristaltic pump
Positive displacement screw pump
Submersible turbine pump
Explanation - Screw pumps handle high‑viscosity, solids‑laden fluids like sludge without clogging, providing steady flow.
Correct answer is: Positive displacement screw pump
Q.9 What is the main function of a grit chamber in a wastewater treatment plant?
Remove suspended organic matter
Settle fine sand and inorganic particles
Disinfect the wastewater
Aerate the influent
Explanation - Grit chambers allow heavy inorganic particles (sand, gravel) to settle out, protecting downstream equipment.
Correct answer is: Settle fine sand and inorganic particles
Q.10 Which of the following chemical processes is primarily used to remove phosphorus from wastewater?
Chlorination
Flocculation with alum (Al2(SO4)3)
Aeration
Reverse osmosis
Explanation - Alum reacts with phosphate to form insoluble aluminum phosphate flocs that can be settled and removed.
Correct answer is: Flocculation with alum (Al2(SO4)3)
Q.11 In a sequencing batch reactor (SBR), which phase follows the fill phase?
Settle phase
Aeration phase
Decant phase
Idle phase
Explanation - After filling, the mixed liquor is aerated to promote microbial degradation of organics before settling.
Correct answer is: Aeration phase
Q.12 Which parameter is directly measured by a conductivity sensor in wastewater?
Total suspended solids
Ionic strength of the water
Biological oxygen demand
pH level
Explanation - Conductivity reflects the ability of water to conduct electricity, which depends on dissolved ions.
Correct answer is: Ionic strength of the water
Q.13 What is the typical pH range for optimal nitrification in a biological treatment system?
4.0 – 5.5
6.5 – 8.5
8.5 – 10.0
10.0 – 11.5
Explanation - Nitrifying bacteria are most active in neutral to slightly alkaline conditions.
Correct answer is: 6.5 – 8.5
Q.14 Which of the following is a major advantage of using solar energy for powering aeration blowers in wastewater treatment?
Eliminates the need for oxygen transfer
Provides a constant power supply regardless of weather
Reduces operating costs and carbon footprint
Increases sludge production
Explanation - Solar power can offset electricity consumption for aeration, cutting energy costs and greenhouse gas emissions.
Correct answer is: Reduces operating costs and carbon footprint
Q.15 Which of the following best describes a ‘biofilm reactor’?
A tank where microorganisms are suspended in the liquid
A system where microorganisms grow on a solid support surface
A reactor that uses ultraviolet light for disinfection
A chamber that relies solely on chemical oxidation
Explanation - Biofilm reactors (e.g., trickling filters, moving bed biofilm reactors) provide a surface for microbes to attach and treat wastewater.
Correct answer is: A system where microorganisms grow on a solid support surface
Q.16 What is the function of a dissolved air flotation (DAF) unit in wastewater treatment?
To increase the temperature of the influent
To remove fine suspended particles by attaching them to micro‑bubbles
To disinfect the effluent with ozone
To add nutrients for microbial growth
Explanation - DAF injects fine air bubbles that adhere to particles, causing them to float for removal.
Correct answer is: To remove fine suspended particles by attaching them to micro‑bubbles
Q.17 Which of the following statements about ‘energy recovery’ in wastewater treatment is true?
Methane from anaerobic digestion can be used to generate electricity
All wastewater treatment plants are net energy consumers
Energy recovery only refers to solar panels on roofs
Biogas cannot be used for heating
Explanation - Anaerobic digestion produces biogas (mainly methane) that can fuel generators or be upgraded to renewable natural gas.
Correct answer is: Methane from anaerobic digestion can be used to generate electricity
Q.18 In the context of wastewater treatment, what does the acronym “TOC” stand for?
Total Organic Carbon
Thermal Oxidation Coefficient
Turbidity of Clarifier
Temperature of Conductivity
Explanation - TOC measures the amount of carbon found in organic compounds, indicating overall organic pollution.
Correct answer is: Total Organic Carbon
Q.19 Which type of control algorithm is commonly employed for maintaining dissolved oxygen levels in an aeration basin?
Proportional‑Integral‑Derivative (PID) controller
Fuzzy logic controller
Open‑loop control
Dead‑band controller
Explanation - PID controllers adjust blower speed based on the error between measured and setpoint DO, providing stable control.
Correct answer is: Proportional‑Integral‑Derivative (PID) controller
Q.20 Which of the following is NOT a typical by‑product of the chlorination disinfection process?
Trihalomethanes (THMs)
Chlorine dioxide
Chlorite
Bromate
Explanation - Bromate forms during ozonation of bromide‑containing water; it is not a direct chlorination by‑product.
Correct answer is: Bromate
Q.21 What is the primary purpose of a primary clarifier in a wastewater treatment plant?
To biologically degrade organic matter
To remove large solids and settleable organic material
To disinfect the water
To add nutrients for microbial growth
Explanation - Primary clarifiers allow heavy particles to settle, reducing the load on downstream biological units.
Correct answer is: To remove large solids and settleable organic material
Q.22 In an anaerobic digester, which group of microorganisms is responsible for converting volatile fatty acids into methane?
Acidogens
Methanogens
Hydrolytic bacteria
Nitrifiers
Explanation - Methanogenic archaea convert acetate and hydrogen into methane, completing the anaerobic digestion process.
Correct answer is: Methanogens
Q.23 Which of the following best describes the term ‘sludge age’ (or mean cell residence time, MCRT) in activated sludge systems?
The time it takes for sludge to settle in a clarifier
The average time microorganisms remain in the reactor
The age of the equipment used in the plant
The duration of the aeration cycle
Explanation - Sludge age influences the composition of microbial populations and treatment performance.
Correct answer is: The average time microorganisms remain in the reactor
Q.24 Which type of membrane is most commonly used for micro‑filtration (MF) in wastewater treatment?
Polyethersulfone (PES) hollow‑fiber membranes
Cellulose acetate reverse osmosis membranes
Metallic ultrafiltration membranes
Graphene nanofiltration membranes
Explanation - PES hollow‑fiber membranes provide high flux and chemical resistance, suitable for MF applications.
Correct answer is: Polyethersulfone (PES) hollow‑fiber membranes
Q.25 What is the main advantage of using a ‘lift pump’ in a wastewater treatment plant’s sludge handling system?
It can handle high‑pressure gas streams
It can move sludge vertically without priming
It requires no electricity
It filters the sludge while pumping
Explanation - Lift pumps are designed for low‑density, solids‑laden fluids and can lift sludge from lower to higher elevations efficiently.
Correct answer is: It can move sludge vertically without priming
Q.26 Which of the following is a common method for removing ammonia from wastewater after biological nitrification?
Air stripping
Biological denitrification
Chemical precipitation with calcium carbonate
Reverse osmosis
Explanation - Air stripping transfers ammonia from water to the gas phase, where it can be captured or neutralized.
Correct answer is: Air stripping
Q.27 In a wastewater treatment plant, the term ‘effluent’ refers to:
The raw sewage entering the plant
The treated water discharged from the plant
The sludge produced during treatment
The air emissions from the plant
Explanation - Effluent is the final, usually regulated, outflow from the treatment process.
Correct answer is: The treated water discharged from the plant
Q.28 Which of the following devices is most suitable for measuring the turbidity of wastewater?
Spectrophotometer
Turbidity meter (nephelometer)
pH meter
Conductivity probe
Explanation - A nephelometer measures the intensity of scattered light, providing a turbidity reading in NTU.
Correct answer is: Turbidity meter (nephelometer)
Q.29 What is the primary function of an oxidation ditch in wastewater treatment?
To provide an anaerobic environment for sludge digestion
To create extended aeration for organic matter removal
To settle out grit and sand
To disinfect the effluent
Explanation - Oxidation ditches are circular or oval channels where water circulates under aerobic conditions for extended treatment.
Correct answer is: To create extended aeration for organic matter removal
Q.30 Which of the following is a key factor influencing the design flow of a wastewater treatment plant’s pump system?
Biological oxygen demand of influent
Viscosity and density of the liquid
pH of the effluent
Color of the wastewater
Explanation - Pump sizing depends heavily on fluid properties such as viscosity and density, affecting head and power requirements.
Correct answer is: Viscosity and density of the liquid
Q.31 Which type of aeration system provides the highest oxygen transfer efficiency (OTE) in large municipal plants?
Fine bubble diffusers
Surface aerators
Mechanical paddle wheels
Airlift pumps
Explanation - Fine bubbles create a larger gas–liquid interfacial area, improving OTE compared with coarse bubbles.
Correct answer is: Fine bubble diffusers
Q.32 In wastewater treatment, the term ‘slug flow’ is most closely associated with:
Laminar flow of clear water
Intermittent bursts of high‑velocity flow in pipes
Steady-state aeration
Continuous chemical dosing
Explanation - Slug flow occurs when gas pockets form and move through pipelines, often seen in sewer lines.
Correct answer is: Intermittent bursts of high‑velocity flow in pipes
Q.33 What is the purpose of adding sodium bisulfite to a wastewater stream after chlorination?
To increase chlorine residual
To neutralize excess chlorine
To raise the pH
To precipitate heavy metals
Explanation - Sodium bisulfite acts as a dechlorinating agent, converting residual chlorine to chloride ions.
Correct answer is: To neutralize excess chlorine
Q.34 Which of the following best describes the concept of ‘nutrient recovery’ in wastewater treatment?
Removing all nutrients to meet discharge limits
Extracting usable nitrogen and phosphorus for fertilizers
Converting nutrients into biogas
Using nutrients to generate electricity
Explanation - Nutrient recovery processes aim to harvest N and P, reducing environmental impact and creating value‑added products.
Correct answer is: Extracting usable nitrogen and phosphorus for fertilizers
Q.35 Which of the following is a major limitation of using reverse osmosis (RO) for treating municipal wastewater?
High energy consumption and membrane fouling
Inability to remove dissolved salts
Requirement for high temperatures
Generation of excessive sludge
Explanation - RO requires high pressure, leading to high energy use, and membranes are prone to fouling by organics and colloids.
Correct answer is: High energy consumption and membrane fouling
Q.36 What does the term ‘biodegradability index (BI)’ represent in wastewater analysis?
Ratio of BOD5 to COD
Ratio of COD to TDS
Ratio of pH to temperature
Ratio of suspended solids to total solids
Explanation - BI = BOD5/COD; values close to 1 indicate high biodegradability, whereas low values suggest refractory organics.
Correct answer is: Ratio of BOD5 to COD
Q.37 Which of the following is NOT a typical indicator of sludge quality for disposal or reuse?
Volatile solids content
Pathogen count
Sludge color
Heavy metal concentration
Explanation - While color may indicate certain compounds, it is not a standard regulatory parameter for sludge quality assessment.
Correct answer is: Sludge color
Q.38 In a wastewater treatment plant, a “feed pump” is primarily used to:
Move influent from the sewer to the treatment units
Discharge treated effluent to the receiving water body
Recirculate sludge within the digester
Inject chemicals into the process
Explanation - Feed pumps convey raw wastewater into the plant’s primary treatment stage.
Correct answer is: Move influent from the sewer to the treatment units
Q.39 Which of the following technologies can be used to remove emerging contaminants (e.g., pharmaceuticals) from wastewater?
Advanced oxidation processes (AOPs)
Coarse screening
Grit removal
Primary sedimentation
Explanation - AOPs generate highly reactive radicals capable of degrading trace organic pollutants that conventional processes cannot remove.
Correct answer is: Advanced oxidation processes (AOPs)
Q.40 What is the purpose of a ‘dead‑end’ filtration system in wastewater treatment?
To continuously flush the filter media
To allow flow only in one direction until the filter is back‑flushed
To maintain a constant back‑pressure
To provide aeration
Explanation - Dead‑end filters collect solids until they are removed by a back‑wash cycle.
Correct answer is: To allow flow only in one direction until the filter is back‑flushed
Q.41 Which type of sensor would be most appropriate for detecting the presence of hydrogen sulfide (H₂S) gas in an anaerobic digester?
Electrochemical H₂S sensor
Infrared CO₂ sensor
Ultrasonic flow sensor
pH probe
Explanation - Electrochemical sensors are specifically designed to detect low concentrations of H₂S gas.
Correct answer is: Electrochemical H₂S sensor
Q.42 Which of the following best explains why a ‘mixing tank’ is used before anaerobic digestion?
To increase the temperature of the feedstock
To homogenize the feedstock and distribute inoculum evenly
To aerate the mixture
To remove heavy metals
Explanation - Uniform mixing ensures consistent microbial activity and prevents channeling in the digester.
Correct answer is: To homogenize the feedstock and distribute inoculum evenly
Q.43 What is the typical range for the oxygen transfer efficiency (OTE) of fine bubble diffusers in wastewater treatment?
5‑10 %
15‑30 %
35‑55 %
60‑80 %
Explanation - Fine bubble diffusers generally achieve OTE between 35–55 %, depending on water quality and diffuser design.
Correct answer is: 35‑55 %
Q.44 Which of the following is a direct environmental benefit of implementing tertiary filtration in a wastewater plant?
Reduced energy consumption
Lower nitrogen concentrations in receiving waters
Higher sludge production
Increased BOD in effluent
Explanation - Tertiary filtration often includes processes like denitrification, reducing nitrogen loads to ecosystems.
Correct answer is: Lower nitrogen concentrations in receiving waters
Q.45 In wastewater treatment, the term ‘bio‑augmentation’ refers to:
Adding chemicals to boost microbial activity
Introducing specialized microorganisms to improve degradation of specific pollutants
Increasing the hydraulic retention time
Installing additional pumps
Explanation - Bio‑augmentation adds strains with desired metabolic capabilities to enhance treatment performance.
Correct answer is: Introducing specialized microorganisms to improve degradation of specific pollutants
Q.46 Which of the following is the most common method for measuring total suspended solids (TSS) in wastewater?
Gravimetric analysis after filtration
Spectrophotometric analysis
pH titration
Conductivity measurement
Explanation - Samples are filtered, the residue dried and weighed to determine TSS concentration.
Correct answer is: Gravimetric analysis after filtration
Q.47 What is the primary function of a ‘chemical dosing pump’ in a wastewater treatment plant?
To increase hydraulic pressure
To inject precise quantities of chemicals such as coagulants or pH adjusters
To remove sludge
To provide aeration
Explanation - Chemical dosing pumps ensure accurate addition of treatment chemicals for processes like coagulation or pH control.
Correct answer is: To inject precise quantities of chemicals such as coagulants or pH adjusters
Q.48 Which of the following processes can be used to remove pathogens from treated wastewater before discharge?
Ultraviolet (UV) disinfection
Aeration
Coagulation
Flocculation
Explanation - UV light inactivates microorganisms by damaging their DNA, providing a chemical‑free disinfection method.
Correct answer is: Ultraviolet (UV) disinfection
Q.49 In a wastewater plant, what is the role of a ‘scum removal system’?
To extract oil and grease that float on the surface
To remove heavy metals
To filter out fine suspended solids
To aerate the influent
Explanation - Scum removal units skim the floating layer of oils, grease, and foam, protecting downstream equipment.
Correct answer is: To extract oil and grease that float on the surface
Q.50 Which of the following parameters is most directly affected by the temperature of the wastewater in a biological treatment process?
pH
Dissolved oxygen concentration
Microbial activity rate
Color
Explanation - Temperature influences enzymatic reactions and hence the overall metabolic rate of the microbial community.
Correct answer is: Microbial activity rate
Q.51 What is the typical dosage range for alum (Al₂(SO₄)₃) when used for phosphorus removal in a municipal plant?
0.5‑1 mg/L
5‑10 mg/L
10‑30 mg/L
100‑200 mg/L
Explanation - Alum is commonly dosed between 10 and 30 mg/L to precipitate phosphorus as aluminum phosphate.
Correct answer is: 10‑30 mg/L
Q.52 Which type of wastewater treatment process is most effective at removing dissolved inorganic nitrogen (ammonia) without adding external carbon sources?
Nitrification–denitrification with external carbon
Partial nitritation–anammox
Chemical precipitation with lime
Ultrafiltration
Explanation - Anammox converts ammonia and nitrite directly to nitrogen gas, requiring minimal external carbon.
Correct answer is: Partial nitritation–anammox
Q.53 In a wastewater treatment plant, which instrument provides the most reliable measurement of the concentration of total dissolved solids (TDS)?
Conductivity meter
pH meter
Turbidity sensor
Dissolved oxygen probe
Explanation - TDS correlates strongly with electrical conductivity; calibration can convert conductivity to TDS values.
Correct answer is: Conductivity meter
Q.54 What is the main purpose of adding a ‘carbon source’ such as methanol in a denitrification tank?
To increase the pH
To provide electrons for nitrate reduction to nitrogen gas
To raise the temperature
To precipitate phosphates
Explanation - Denitrifying bacteria need an organic carbon source as an electron donor to convert nitrate to nitrogen gas.
Correct answer is: To provide electrons for nitrate reduction to nitrogen gas
Q.55 Which of the following best describes the concept of ‘energy-neutral’ wastewater treatment plants?
Plants that generate as much electricity as they consume
Plants that do not use any electricity
Plants that rely only on solar power
Plants that discharge no effluent
Explanation - Energy‑neutral plants balance energy consumption with generation (e.g., from biogas, hydro‑kinetic turbines).
Correct answer is: Plants that generate as much electricity as they consume
Q.56 Which of the following is the most common method for controlling algal growth in an open wastewater lagoon?
Adding chlorine
Applying herbicides
Increasing hydraulic residence time
Introducing predatory fish
Explanation - Selective algicides (e.g., copper sulfate) are often used to control algal blooms in lagoons.
Correct answer is: Applying herbicides
Q.57 In wastewater treatment, the term ‘COD’ stands for:
Chemical Oxygen Demand
Carbon Oxide Dispersion
Controlled Oxygen Depletion
Cumulative Organic Dilution
Explanation - COD measures the total amount of oxygen required to chemically oxidize both biodegradable and non‑biodegradable organic matter.
Correct answer is: Chemical Oxygen Demand
Q.58 What is the primary reason for installing a ‘backwash’ system in a sand filter used for tertiary treatment?
To increase the flow rate
To remove accumulated solids and restore filter permeability
To add disinfectant chemicals
To raise the temperature of the water
Explanation - Backwashing reverses flow, flushing out trapped particles and preventing clogging.
Correct answer is: To remove accumulated solids and restore filter permeability
Q.59 Which of the following is an advantage of using a ‘moving bed biofilm reactor’ (MBBR) over traditional activated sludge?
Lower sludge production and higher biomass retention
Elimination of aeration
No need for pumps
Higher chemical usage
Explanation - MBBRs retain biofilm carriers, increasing biomass concentration while reducing excess sludge.
Correct answer is: Lower sludge production and higher biomass retention
Q.60 For which purpose is a ‘pH adjustment tank’ most commonly used in a wastewater treatment plant?
To neutralize acidic or alkaline influent before biological treatment
To increase temperature of the wastewater
To remove suspended solids
To aerate the effluent
Explanation - Maintaining optimal pH (6‑8) is critical for microbial activity; pH tanks add acid or base as needed.
Correct answer is: To neutralize acidic or alkaline influent before biological treatment
Q.61 Which of the following best characterizes the term ‘sludge dewatering’?
Increasing the moisture content of sludge
Reducing water content to produce a more solid cake for disposal
Heating sludge to kill pathogens
Adding chemicals to increase sludge volume
Explanation - Dewatering processes (e.g., centrifuges, belt presses) remove water, reducing sludge volume and handling costs.
Correct answer is: Reducing water content to produce a more solid cake for disposal
Q.62 Which of the following statements about ‘hydraulic loading rate’ is correct?
It is the amount of sludge per unit area per day
It is the influent flow per unit area of a treatment basin
It is the concentration of dissolved oxygen
It is the temperature of the wastewater
Explanation - Hydraulic loading rate (m³/m²·day) describes how much water a surface‑based unit (e.g., lagoon) receives.
Correct answer is: It is the influent flow per unit area of a treatment basin
Q.63 In the context of wastewater treatment, what does the acronym ‘EPA’ stand for?
Environmental Protection Agency
Energy Production Association
Effluent Purification Alliance
Electronic Process Automation
Explanation - The EPA sets regulatory standards for water quality and wastewater treatment in the United States.
Correct answer is: Environmental Protection Agency
Q.64 Which of the following is a common indicator for the presence of heavy metals in sludge?
Total Kjeldahl Nitrogen (TKN)
Loss on ignition (LOI)
X‑ray fluorescence (XRF) spectroscopy
Biochemical oxygen demand (BOD5)
Explanation - XRF provides rapid, non‑destructive elemental analysis, ideal for detecting heavy metals.
Correct answer is: X‑ray fluorescence (XRF) spectroscopy
Q.65 What is the main environmental concern associated with the discharge of untreated or partially treated wastewater into natural water bodies?
Increased sunlight penetration
Eutrophication caused by excess nutrients
Higher water temperature only
Reduced salinity
Explanation - Nutrients (nitrogen, phosphorus) promote algal blooms, leading to oxygen depletion and ecosystem damage.
Correct answer is: Eutrophication caused by excess nutrients
Q.66 Which of the following best describes the function of a ‘suction pump’ in a sludge handling system?
To pressurize the influent water
To draw sludge from a lower elevation to a higher elevation
To inject chemicals into the sludge
To measure sludge density
Explanation - Suction pumps create a negative pressure, lifting sludge for transport to thickeners or digesters.
Correct answer is: To draw sludge from a lower elevation to a higher elevation
Q.67 Which of the following processes is most effective for removing ammonia from a high‑strength industrial wastewater?
Air stripping
Biological nitrification‑denitrification
Chemical precipitation with calcium hydroxide
Reverse osmosis
Explanation - Air stripping is efficient for high ammonia concentrations, especially when combined with acid absorption.
Correct answer is: Air stripping
Q.68 Which of the following best explains why ‘suspended growth’ systems require larger reactor volumes than ‘attached growth’ systems for the same loading?
Suspended growth systems have higher oxygen transfer efficiency
Attached growth systems have higher biomass concentration per unit volume
Suspended growth systems operate at lower temperatures
Attached growth systems need more space for equipment
Explanation - Biofilm carriers provide a large surface area, allowing higher microbial density and smaller reactors.
Correct answer is: Attached growth systems have higher biomass concentration per unit volume
Q.69 What is the main purpose of installing a ‘float valve’ in a wastewater pump station?
To regulate the pH of the influent
To prevent the pump from running dry by shutting off at low water levels
To increase the pressure of the water
To add chemicals automatically
Explanation - Float valves detect low water levels and stop the pump, protecting it from damage.
Correct answer is: To prevent the pump from running dry by shutting off at low water levels
Q.70 Which of the following best describes the principle of ‘electrocoagulation’ for wastewater treatment?
Using an electric current to generate coagulant metal ions in situ
Applying high pressure to force water through a membrane
Adding chemical coagulants manually
Using ultraviolet light to break down contaminants
Explanation - Electrocoagulation dissolves sacrificial anodes (e.g., iron, aluminum) to produce metal hydroxides that destabilize particles.
Correct answer is: Using an electric current to generate coagulant metal ions in situ
Q.71 In a wastewater treatment plant, what does the acronym ‘SCADA’ stand for?
Supervisory Control and Data Acquisition
Standard Chemical Analysis Device
Sewage Control and Distribution Automation
Solar Controlled Aeration Device
Explanation - SCADA systems collect real‑time data and allow remote control of plant equipment.
Correct answer is: Supervisory Control and Data Acquisition
Q.72 Which of the following is a typical indicator used to assess the efficiency of a disinfection step?
Residual chlorine concentration
Total suspended solids
Biochemical oxygen demand
Alkalinity
Explanation - Residual chlorine (or other disinfectant) indicates that sufficient disinfectant remains to ensure pathogen inactivation.
Correct answer is: Residual chlorine concentration
Q.73 What is the main reason for using ‘low‑pressure’ aeration diffusers in deep‑well aeration systems?
To reduce energy consumption
To increase the size of bubbles
To prevent corrosion of the diffuser
To generate higher dissolved oxygen concentrations
Explanation - Low‑pressure diffusers operate at lower air pressures, consuming less energy while still providing adequate oxygen transfer.
Correct answer is: To reduce energy consumption
Q.74 Which of the following wastewater treatment technologies can simultaneously remove pathogens, organics, and nutrients in a single step?
Constructed wetlands
Membrane bioreactor (MBR)
Oxidation ditches
Primary sedimentation
Explanation - MBR combines biological degradation, membrane filtration, and can be configured for nutrient removal and pathogen reduction.
Correct answer is: Membrane bioreactor (MBR)
Q.75 What is the primary benefit of using a ‘variable frequency drive (VFD)’ on wastewater pumps?
It eliminates the need for a pump motor
It allows precise control of pump speed, reducing energy use
It increases the pump’s maximum pressure
It automatically cleans the pump impeller
Explanation - VFDs adjust motor speed to match flow demand, improving efficiency and lowering electricity consumption.
Correct answer is: It allows precise control of pump speed, reducing energy use
Q.76 Which of the following is an advantage of using ‘ultraviolet (UV) LEDs’ over traditional mercury‑vapor UV lamps for disinfection?
Higher UV output per watt
Longer lamp life and lower maintenance
Ability to generate ozone
Lower initial cost
Explanation - UV LEDs have solid‑state designs with longer lifespans and no hazardous mercury.
Correct answer is: Longer lamp life and lower maintenance
Q.77 Which of the following best explains the purpose of a ‘flocculator’ in a water treatment train?
To break up large particles
To aggregate fine particles into larger flocs for easier removal
To increase water temperature
To add chlorine
Explanation - Flocculation gently mixes coagulant‑treated water, promoting formation of settleable flocs.
Correct answer is: To aggregate fine particles into larger flocs for easier removal
Q.78 In a wastewater treatment plant, what does the term ‘peak flow’ refer to?
The maximum hydraulic load experienced during a short period
The average daily flow rate
The minimum flow rate in the system
The flow rate during maintenance shutdowns
Explanation - Peak flow events (e.g., storms) require plant components to handle high, transient flow rates.
Correct answer is: The maximum hydraulic load experienced during a short period
Q.79 Which of the following processes is primarily used to remove dissolved gases such as carbon dioxide from wastewater?
Air stripping
Coagulation
Sedimentation
Flocculation
Explanation - Air stripping transfers volatile gases from liquid to air, reducing dissolved CO₂ levels.
Correct answer is: Air stripping
Q.80 Which of the following is a common indicator for the presence of toxic organic compounds (e.g., phenols) in wastewater?
Chemical Oxygen Demand (COD)
Total Kjeldahl Nitrogen (TKN)
Volatile Organic Compounds (VOCs) analysis
Total Suspended Solids (TSS)
Explanation - VOCs testing specifically targets toxic organic substances that may not be reflected in COD alone.
Correct answer is: Volatile Organic Compounds (VOCs) analysis
Q.81 What is the typical purpose of a ‘sand filter’ used as a tertiary treatment step?
To remove dissolved salts
To reduce turbidity by trapping fine particles
To disinfect the water with UV light
To add nutrients for downstream processes
Explanation - Sand filters capture remaining suspended solids, providing a final polishing step.
Correct answer is: To reduce turbidity by trapping fine particles
Q.82 Which of the following statements about ‘bioelectrochemical systems’ (BES) for wastewater treatment is true?
They rely solely on chemical oxidation
They can generate electricity while treating wastewater
They are only used for desalination
They require high temperature to operate
Explanation - BES, such as microbial fuel cells, use microorganisms to oxidize organics and produce an electric current.
Correct answer is: They can generate electricity while treating wastewater
Q.83 In a wastewater treatment plant, the term ‘effluent compliance’ most commonly refers to:
Meeting the required temperature of the discharged water
Meeting regulatory limits for pollutants in the discharged water
Achieving maximum flow rate
Ensuring the effluent is clear
Explanation - Compliance means the effluent meets or is below the concentration limits set by environmental authorities.
Correct answer is: Meeting regulatory limits for pollutants in the discharged water
Q.84 Which of the following is a key advantage of using ‘gravity‑fed’ sewer systems over pressurized systems?
Lower construction and operating costs
Higher flow capacity
Better control of odor
Ability to handle very high pressures
Explanation - Gravity systems rely on natural slope, reducing the need for pumps and energy consumption.
Correct answer is: Lower construction and operating costs
Q.85 Which of the following processes is primarily responsible for the removal of nitrogen through the conversion of nitrate to nitrogen gas?
Nitrification
Denitrification
Ammonification
Anammox
Explanation - Denitrifying bacteria reduce nitrate (NO₃⁻) to nitrogen gas (N₂) under anoxic conditions.
Correct answer is: Denitrification
Q.86 What is the main function of a ‘turbidity sensor’ in a wastewater treatment plant’s control system?
To adjust pH automatically
To trigger backwashing of filters when turbidity exceeds a setpoint
To increase temperature when needed
To measure dissolved oxygen
Explanation - High turbidity indicates filter fouling; the sensor can automatically initiate backwash cycles.
Correct answer is: To trigger backwashing of filters when turbidity exceeds a setpoint
Q.87 Which of the following best describes the purpose of a ‘sludge thickener’?
To increase the water content of sludge
To concentrate sludge by removing a portion of the water
To sterilize the sludge
To add nutrients to the sludge
Explanation - Thickeners reduce sludge volume and prepare it for further treatment or disposal.
Correct answer is: To concentrate sludge by removing a portion of the water
Q.88 Which of the following is the most common method for measuring the concentration of ammonia nitrogen (NH₃‑N) in wastewater?
Nessler’s reagent colorimetric method
Turbidity measurement
Conductivity probe
pH meter
Explanation - The Nessler method forms a colored complex with ammonia, allowing spectrophotometric quantification.
Correct answer is: Nessler’s reagent colorimetric method
Q.89 In wastewater treatment, what is the primary role of a ‘buffer tank’?
To store chemicals for dosing
To smooth out flow and load fluctuations entering downstream processes
To increase temperature of the influent
To remove pathogens
Explanation - Buffer tanks provide hydraulic and organic load buffering, protecting downstream units from shock loads.
Correct answer is: To smooth out flow and load fluctuations entering downstream processes
Q.90 Which of the following processes is commonly used to treat high‑strength industrial wastewater containing refractory organics?
Anaerobic digestion
Advanced oxidation processes (AOPs)
Primary sedimentation
Air stripping
Explanation - AOPs (e.g., ozone‑hydrogen peroxide, UV‑H₂O₂) generate hydroxyl radicals that degrade recalcitrant compounds.
Correct answer is: Advanced oxidation processes (AOPs)
Q.91 Which of the following statements about ‘hydraulic short‑circuiting’ in a clarifier is true?
It improves sludge settling
It leads to uneven flow distribution, reducing clarifier performance
It increases the retention time of water
It eliminates the need for a weir
Explanation - Short‑circuiting causes some water to bypass the intended path, decreasing effective settling time.
Correct answer is: It leads to uneven flow distribution, reducing clarifier performance
Q.92 Which of the following is a typical operating temperature range for mesophilic anaerobic digesters?
10‑15 °C
30‑38 °C
45‑55 °C
60‑70 °C
Explanation - Mesophilic microbes thrive best between 30 and 38 °C, offering stable digestion performance.
Correct answer is: 30‑38 °C
Q.93 What is the primary reason for adding a ‘pH buffer’ (e.g., sodium bicarbonate) to an anaerobic digester?
To increase the temperature
To maintain a stable pH for microbial activity
To accelerate sludge settling
To provide additional carbon source
Explanation - Anaerobic microbes are sensitive to pH; buffers prevent acidification from volatile fatty acid accumulation.
Correct answer is: To maintain a stable pH for microbial activity
Q.94 Which of the following technologies can be used to recover phosphorus from wastewater as a solid product?
Chemical precipitation with struvite (MgNH₄PO₄·6H₂O)
Air stripping
UV disinfection
Membrane ultrafiltration
Explanation - Struvite precipitation recovers phosphorus as a marketable fertilizer crystal.
Correct answer is: Chemical precipitation with struvite (MgNH₄PO₄·6H₂O)
Q.95 Which of the following is a typical symptom of ‘sludge bulking’ in an activated sludge system?
Very rapid sludge settling
Poor sludge settling and high effluent turbidity
Increased biogas production
Lower temperature in the clarifier
Explanation - Bulking occurs when filamentous bacteria dominate, reducing sludge density and causing poor settling.
Correct answer is: Poor sludge settling and high effluent turbidity
Q.96 What does the term ‘biological phosphorus removal (BPR)’ rely on?
Chemical precipitation with aluminum salts
Enhanced growth of polyphosphate accumulating organisms (PAOs) under alternating anaerobic/aerobic conditions
Physical filtration
UV oxidation
Explanation - BPR exploits PAOs that store phosphorus intracellularly when exposed to alternating redox conditions.
Correct answer is: Enhanced growth of polyphosphate accumulating organisms (PAOs) under alternating anaerobic/aerobic conditions
Q.97 Which of the following is the most appropriate method for measuring the concentration of volatile organic compounds (VOCs) in wastewater?
Gas chromatography‑mass spectrometry (GC‑MS)
Gravimetric analysis
pH meter
Turbidity sensor
Explanation - GC‑MS separates and identifies VOCs with high sensitivity, suitable for trace analysis.
Correct answer is: Gas chromatography‑mass spectrometry (GC‑MS)
Q.98 In a wastewater treatment plant, what is the primary purpose of a ‘feed‑forward control loop’?
To adjust setpoints based on measured process variables after they occur
To predict influent conditions and adjust process variables preemptively
To shut down the plant during emergencies
To control temperature only
Explanation - Feed‑forward control uses measured disturbances (e.g., influent flow) to modify control actions before the process is affected.
Correct answer is: To predict influent conditions and adjust process variables preemptively
Q.99 Which of the following best describes the function of a ‘gravity sewer’?
A sewer that relies on pumps to move wastewater
A sewer that uses the natural slope to convey wastewater to a treatment plant
A sewer that treats wastewater on‑site
A sewer that only transports stormwater
Explanation - Gravity sewers move wastewater by gravity, minimizing energy use.
Correct answer is: A sewer that uses the natural slope to convey wastewater to a treatment plant
Q.100 What is the main reason for installing an ‘overflow weir’ in a wastewater treatment plant’s wet well?
To provide a point for chemical dosing
To prevent excess water from flooding the plant by allowing controlled overflow
To increase the temperature of the water
To enhance biological activity
Explanation - Overflow weirs protect infrastructure by safely directing excess flows away.
Correct answer is: To prevent excess water from flooding the plant by allowing controlled overflow
Q.101 Which of the following processes is most effective at removing dissolved iron (Fe²⁺) from wastewater?
Oxidation followed by precipitation as Fe(OH)₃
Air stripping
Membrane ultrafiltration
Biological nitrification
Explanation - Oxidizing Fe²⁺ to Fe³⁺ causes it to precipitate as ferric hydroxide, which can be settled out.
Correct answer is: Oxidation followed by precipitation as Fe(OH)₃
Q.102 Which of the following best explains why ‘hydraulic retention time (HRT)’ is typically longer in a primary clarifier than in an aeration tank?
Primary clarifiers need more time for biological reactions
Aeration tanks operate at higher temperatures
Primary clarifiers are designed to allow solids to settle, requiring longer residence time
Aeration tanks are usually deeper
Explanation - Adequate HRT in clarifiers ensures that settleable particles have time to settle out.
Correct answer is: Primary clarifiers are designed to allow solids to settle, requiring longer residence time
Q.103 Which of the following is a common method for reducing odor emissions from a wastewater treatment plant?
Installing a sand filter
Using biofilters or activated carbon filters
Increasing the temperature of the effluent
Adding more chlorine
Explanation - Biofilters and activated carbon adsorb or biologically degrade odorous compounds like H₂S.
Correct answer is: Using biofilters or activated carbon filters
Q.104 What is the primary purpose of a ‘safety relief valve’ on a high‑pressure wastewater pump?
To increase pump speed
To prevent over‑pressurization by releasing excess pressure
To add chemicals automatically
To measure flow rate
Explanation - Safety relief valves protect equipment from damage caused by pressure spikes.
Correct answer is: To prevent over‑pressurization by releasing excess pressure
Q.105 Which of the following is the most suitable method for determining the presence of coliform bacteria in treated wastewater?
Membrane filtration followed by incubation on selective media
Measuring BOD5
Conductivity test
pH measurement
Explanation - Membrane filtration concentrates bacteria onto a filter that is then cultured to detect coliforms.
Correct answer is: Membrane filtration followed by incubation on selective media
Q.106 Which of the following best describes the concept of ‘hydraulic gradient’ in a wastewater pipeline?
The change in temperature per unit length
The difference in hydraulic head per unit length, driving flow
The variation of pH along the pipe
The change in chemical composition per unit length
Explanation - Hydraulic gradient is the driving force for fluid movement in pipes and channels.
Correct answer is: The difference in hydraulic head per unit length, driving flow
Q.107 What is the main function of a ‘chemical dosing skid’ in a wastewater treatment plant?
To house pumps, tanks, and controls for accurate chemical addition
To filter the influent water
To provide storage for sludge
To generate electricity
Explanation - A dosing skid integrates all components needed for precise chemical injection.
Correct answer is: To house pumps, tanks, and controls for accurate chemical addition
Q.108 Which of the following parameters is most directly affected by the ‘mixing intensity’ in an anaerobic digester?
pH stability
Methane production rate
Turbidity
Color
Explanation - Adequate mixing ensures uniform substrate distribution and prevents stratification, enhancing methane generation.
Correct answer is: Methane production rate
Q.109 Which of the following best explains why ‘temperature control’ is important in a nitrifying biofilter?
Nitrifying bacteria are highly temperature‑sensitive and work best between 15‑30 °C
Temperature has no effect on nitrification
Higher temperatures always reduce nitrification rates
Low temperatures increase dissolved oxygen
Explanation - Nitrifiers have optimal activity in the 15‑30 °C range; temperature extremes inhibit their function.
Correct answer is: Nitrifying bacteria are highly temperature‑sensitive and work best between 15‑30 °C
Q.110 What is the main environmental benefit of implementing ‘constructed wetlands’ for wastewater treatment?
Higher energy consumption
Natural removal of nutrients, organics, and some metals with low operational cost
Elimination of all pathogens
Complete removal of dissolved salts
Explanation - Constructed wetlands use vegetation and microbes to treat wastewater with minimal energy input.
Correct answer is: Natural removal of nutrients, organics, and some metals with low operational cost
Q.111 Which of the following is a common method for measuring the concentration of sulfide (S²⁻) in wastewater?
Methylene blue colorimetric method
Ion-selective electrode specific for sulfide
Turbidity measurement
pH meter
Explanation - Sulfide ion-selective electrodes provide direct, real‑time measurement of sulfide concentrations.
Correct answer is: Ion-selective electrode specific for sulfide
Q.112 In wastewater treatment, which of the following statements about ‘hydraulic overload’ is true?
It improves sludge settling
It reduces the residence time, leading to poorer treatment performance
It increases the temperature of the influent
It eliminates the need for chemical dosing
Explanation - Hydraulic overload shortens HRT, limiting the time available for physical, chemical, and biological processes.
Correct answer is: It reduces the residence time, leading to poorer treatment performance
Q.113 Which of the following best describes the role of ‘bio‑solids’ in a wastewater treatment plant?
They are the organic-rich sludge that can be processed for reuse or disposal
They are the clean water leaving the plant
They are the chemical coagulants added to the process
They are the gases produced during aeration
Explanation - Bio‑solids are the stabilized organic material generated after treatment, often used as fertilizer or disposed of.
Correct answer is: They are the organic-rich sludge that can be processed for reuse or disposal
Q.114 Which of the following is the most appropriate technique for reducing the concentration of dissolved nitrate in drinking water sourced from a treated wastewater plant?
Ion exchange
Sand filtration
Air stripping
UV disinfection
Explanation - Ion exchange resins selectively remove nitrate ions, providing effective reduction for potable water.
Correct answer is: Ion exchange
Q.115 In the context of wastewater treatment, what does the term ‘sludge age’ indicate?
The age of the sludge handling equipment
The average time that the microorganisms remain in the system before being wasted
The time required for sludge to dewater
The duration of the disinfection step
Explanation - Sludge age (or MCRT) influences microbial composition and treatment efficiency.
Correct answer is: The average time that the microorganisms remain in the system before being wasted
Q.116 Which of the following is a typical indicator of successful phosphorus removal in a wastewater plant?
Effluent PO₄³⁻ concentration below 1 mg L⁻¹
Effluent BOD₅ below 5 mg L⁻¹
Effluent pH between 6.5‑7.5
Effluent temperature below 10 °C
Explanation - Regulatory limits for phosphorus often require effluent phosphate concentrations under 1 mg L⁻¹.
Correct answer is: Effluent PO₄³⁻ concentration below 1 mg L⁻¹
Q.117 Which of the following best explains the purpose of a ‘floc‑monitoring sensor’ in a wastewater treatment plant?
To detect the size and concentration of flocs for optimal dosing control
To measure dissolved oxygen only
To adjust temperature automatically
To count the number of bacteria
Explanation - Floc‑monitoring sensors help operators fine‑tune coagulant/flocculant dosing for efficient solid removal.
Correct answer is: To detect the size and concentration of flocs for optimal dosing control
Q.118 What is the typical range of dissolved oxygen (DO) concentration required in an aerobic biological reactor?
0.5‑1.0 mg L⁻¹
2‑4 mg L⁻¹
6‑8 mg L⁻¹
10‑12 mg L⁻¹
Explanation - Maintaining DO at 2‑4 mg L⁻¹ supports aerobic microbial activity without excessive energy use.
Correct answer is: 2‑4 mg L⁻¹
Q.119 Which of the following is a major advantage of using a ‘step‑feed’ configuration in an activated sludge plant?
Reduces the need for aeration
Allows for better control of organic load and prevents overload of the aeration tank
Eliminates the need for secondary clarification
Increases sludge production
Explanation - Step‑feed introduces influent in stages, smoothing load variations and enhancing treatment stability.
Correct answer is: Allows for better control of organic load and prevents overload of the aeration tank
Q.120 Which of the following is the most common method for measuring the concentration of total phosphorus (TP) in wastewater?
Colorimetric ascorbic acid method after digestion
Conductivity measurement
Turbidity sensor
pH meter
Explanation - The ascorbic acid method measures both orthophosphate and total phosphorus after persulfate digestion.
Correct answer is: Colorimetric ascorbic acid method after digestion
Q.121 In wastewater treatment, which of the following processes is primarily responsible for the removal of dissolved organic carbon (DOC) in the absence of oxygen?
Aerobic oxidation
Anaerobic digestion
Chemical precipitation
Filtration
Explanation - Anaerobic digestion degrades DOC under anoxic conditions, producing biogas.
Correct answer is: Anaerobic digestion
Q.122 Which of the following statements best characterizes a ‘closed‑loop’ water reuse system in an industrial wastewater context?
Water is discharged to a river after treatment
Treated water is recycled back into the process, minimizing fresh water intake
Water is evaporated and lost to the atmosphere
Water is stored in open ponds for later use
Explanation - Closed‑loop systems aim for water conservation by reusing treated effluent within the same facility.
Correct answer is: Treated water is recycled back into the process, minimizing fresh water intake
Q.123 Which of the following is the most appropriate approach for controlling excessive foam formation in an activated sludge basin?
Increasing temperature
Adding antifoam chemicals
Reducing aeration
Increasing pH
Explanation - Antifoam agents suppress foam by reducing surface tension and disrupting bubble formation.
Correct answer is: Adding antifoam chemicals
Q.124 What is the primary purpose of a ‘biogas flare’ in a wastewater treatment plant?
To burn off excess methane for safety and emission control
To increase sludge production
To aerate the influent
To add nutrients to the digester
Explanation - Flaring safely combusts surplus biogas, preventing uncontrolled releases.
Correct answer is: To burn off excess methane for safety and emission control
Q.125 Which of the following best describes the function of a ‘headworks’ facility in a municipal wastewater system?
The final polishing step before discharge
The initial treatment area that screens, grit removes, and equalizes influent flow
The chemical dosing station for phosphorus removal
The energy recovery unit
Explanation - Headworks prepares raw wastewater for downstream processes by removing large debris and grit.
Correct answer is: The initial treatment area that screens, grit removes, and equalizes influent flow
Q.126 Which of the following is the most common method for measuring the concentration of total nitrogen (TN) in wastewater?
Kjeldahl digestion followed by distillation and titration
Conductivity measurement
Turbidity sensor
pH meter
Explanation - The Kjeldahl method quantifies organic nitrogen and ammonia, providing total nitrogen content.
Correct answer is: Kjeldahl digestion followed by distillation and titration