Methanogens are bacteria that are most active in which stage?
- Anaerobic sludge digestion
- Primary sedimentation
- Sequential filtration
- Aeration tanks
Explanation: Methanogens are anaerobic bacteria that thrive in the oxygen-free environment of the sludge digester.
In sewage treatment, 'Sludge Bulking' is a common problem caused by the overgrowth of:
- Nitrifying bacteria
- Filamentous bacteria
- Methanogens
- Viral pathogens
Explanation: Filamentous bacteria prevent the sludge from compacting tightly, leading to poor settling and high solids in the effluent.
The sedimented bacterial flocs in the settling tank are referred to as:
- Anaerobic sludge
- Activated sludge
- Primary sludge
- Digested sludge
Explanation: Once the BOD is reduced, the effluent is passed into a settling tank where the bacterial flocs are allowed to sediment as activated sludge.
Which disinfectant provides a 'residual' effect, protecting water during distribution?
- Boiling
- Chlorine
- UV radiation
- Ozone
Explanation: Unlike UV or Ozone, chlorine maintains a residual concentration that continues to kill pathogens even after the initial treatment.
The 'Chemical Oxygen Demand' (COD) test differs from the BOD test by measuring:
- Biodegradable organic matter
- Total organic matter
- Dissolved oxygen only
- Non-biodegradable matter
Explanation: COD uses a strong chemical oxidant to measure nearly all organic compounds, including those that are not biologically degradable.
Which of the following describes 'Oxidation Ponds' used for sewage treatment?
- High energy usage
- Shallow lagoons
- Chemical reactors
- Deep tanks
Explanation: Oxidation ponds are low-cost, shallow lagoons where sunlight, algae, and bacteria work together to treat sewage.
A 'Membrane Bioreactor' (MBR) combines biological treatment with:
- Microfiltration
- Activated carbon
- Chlorine gas
- Ultraviolet light
Explanation: MBR uses membranes instead of secondary clarifiers to separate the biomass, resulting in much higher effluent quality.
In a septic tank, the treatment of sewage is primarily:
- Anaerobic
- Aerobic
- Electrolytic
- Physicochemical
Explanation: Septic tanks are localized treatment systems where anaerobic bacteria digest organic solids in the absence of air.
Secondary treatment of sewage is alternatively known as:
- Chemical treatment
- Physical treatment
- Mechanical treatment
- Biological treatment
Explanation: It is called biological treatment because it utilizes the metabolic activities of aerobic and anaerobic microbes to decompose organic matter.
What is the recommended maximum BOD for treated sewage discharged into inland surface waters in India?
- 30 mg/L
- 10 mg/L
- 100 mg/L
- 500 mg/L
Explanation: According to CPCB standards, the BOD of the treated effluent should typically not exceed 30 mg/L for river discharge.
The primary treatment of sewage is fundamentally characterized as a:
- Mechanical process
- Physical process
- Biological process
- Chemical process
Explanation: Primary treatment involves the physical removal of particles from sewage through sequential filtration and sedimentation.
In the primary treatment stage, floating debris is removed by:
- Sedimentation
- Chlorination
- Sequential filtration
- Microbial action
Explanation: According to NCERT, floating debris is filtered out in stages (sequentially) to ensure larger objects do not interfere with downstream machinery.
Which gas produced in the anaerobic digester is the most significant contributor to its fuel value?
- Hydrogen
- Hydrogen sulfide
- Methane
- Carbon dioxide
Explanation: Biogas contains approximately 50-75% methane ($CH_4$), which is the primary combustible component.
The 'UASB' reactor is a popular modern technology for treating industrial sewage. What does 'U' stand for?
- Upflow
- Ultraviolet
- Underground
- Uniform
Explanation: UASB stands for Upflow Anaerobic Sludge Blanket, a high-rate anaerobic system used for high-strength organic wastewater.
The discharge of untreated sewage into water bodies leads to a 'Fish Kill' because of:
- Oxygen depletion
- Water toxicity
- Increased salinity
- Temperature rise
Explanation: Microbes consume the available dissolved oxygen to break down the sewage, leaving none for the fish to breathe.
Which chemical is most commonly used for the disinfection of treated effluent?
- Potassium
- Chlorine
- Sodium chloride
- Nitrogen
Explanation: Chlorination is a standard step to kill remaining pathogens before the water is released or reused.
Which of the following is a common symptom of 'Blue Baby Syndrome' caused by nitrate-rich water?
- Loss of hearing
- Chronic diarrhea
- High fever
- Methemoglobinemia
Explanation: Nitrates in drinking water can interfere with the blood's ability to carry oxygen, specifically affecting infants.
The Ganga Action Plan was initiated by which government body?
- Ministry of Environment
- Ministry of Power
- Ministry of Agriculture
- NITI Aayog
Explanation: The Ministry of Environment and Forests initiated plans like the Ganga and Yamuna Action Plans to protect major rivers from sewage pollution.
The process of 'Sludge Stabilization' primarily aims to:
- Increase volume
- Add nutrients
- Reduce odors
- Increase moisture
Explanation: Stabilization makes the sludge less biodegradable and reduces volatile solids, which minimizes foul odors and pathogen levels.
The solid material that settles down during primary treatment is called:
- Primary sludge
- Tertiary sludge
- Activated sludge
- Secondary effluent
Explanation: All solids that settle during the primary sedimentation process form the primary sludge, while the supernatant forms the effluent.
The primary effluent is passed into large aeration tanks specifically to:
- Remove chemicals
- Agitate microbes
- Kill bacteria
- Filter grit
Explanation: Constant mechanical agitation and air pumping allow vigorous growth of useful aerobic microbes into flocs.
A small part of the activated sludge is pumped back into the aeration tank to serve as:
- Inoculum
- Fertilizer
- Catalyst
- Disinfectant
Explanation: A portion of the activated sludge acts as a 'starter' or inoculum to initiate the biological process in the next batch of primary effluent.
The anaerobic digestion of sludge also produces which gas along with methane and H2S?
- Carbon dioxide
- Neon
- Oxygen
- Argon
Explanation: Biogas is a mixture of methane ($CH_4$), carbon dioxide ($CO_2$), and hydrogen sulfide ($H_2S$).
Which specific bacteria are primarily responsible for the 'Nitrification' process in sewage?
- Rhizobium and Azotobacter
- Lactobacillus
- Nitrosomonas and Nitrobacter
- Methanobacterium
Explanation: Nitrification is a two-step aerobic process where ammonia is converted to nitrite and then to nitrate by these specific nitrifying bacteria.
Which of the following gases makes biogas highly flammable?
- Hydrogen sulfide
- Carbon dioxide
- Nitrogen
- Methane
Explanation: Methane ($CH_4$) is the primary combustible component of biogas.
In the context of STPs, what does 'MLSS' stand for?
- Mixed Liquor Suspended Solids
- Maximum Load Sewage
- Minimum Liquid Salt
- Microbial Liquid Sludge
Explanation: MLSS (Mixed Liquor Suspended Solids) is the concentration of suspended solids, mostly microbes, in the aeration tank.
A higher BOD value in a sewage sample indicates that the water is:
- Safe for drinking
- Highly polluted
- Relatively clean
- Rich in oxygen
Explanation: The greater the BOD of waste water, the more organic matter is present, indicating a higher level of polluting potential.
The 'Sludge Volume Index' (SVI) is a standard parameter used to monitor:
- Sludge settleability
- Dissolved salts
- Chemical toxicity
- Pathogen count
Explanation: SVI indicates the volume in milliliters occupied by 1 gram of activated sludge after settling for 30 minutes; it is crucial for clarifier efficiency.
The 'Detention Time' in a sedimentation tank is the average time taken by:
- Bacteria to die
- Water to pass
- Solids to settle
- Gas to escape
Explanation: Detention time is the theoretical time that a unit volume of water spends in a treatment tank to allow processes like settling.
Secondary treatment is continued until which of the following is significantly reduced?
- Total volume
- BOD level
- Floating debris
- Salt concentration
Explanation: The treatment process aims to reduce the BOD of the sewage until it is low enough to be safely discharged into natural water bodies.
The Water (Prevention and Control of Pollution) Act was enacted in India in:
Explanation: The 1974 Act provided the legal framework for the establishment of the Central and State Pollution Control Boards to monitor water quality.
Biochemical Oxygen Demand (BOD) is a direct measure of the:
- Pathogen count
- Organic matter
- Dissolved oxygen
- Inorganic salts
Explanation: BOD measures the amount of oxygen consumed if all the organic matter in one liter of water were oxidized by bacteria.
The term 'Greywater' refers to domestic wastewater excluding that from:
- Toilets
- Sinks
- Showers
- Washing machines
Explanation: Greywater is wastewater from kitchens, baths, and laundries. Wastewater containing human excreta from toilets is known as 'Blackwater'.
The biological treatment of sewage using plants like Water Hyacinth is called:
- Bio-augmentation
- Biomagnification
- Phytoremediation
- Eutrophication
Explanation: Phytoremediation uses plants to absorb, concentrate, or stabilize contaminants in wastewater and soil.
In the secondary treatment, aerobic microbes consume the major part of the:
- Floating plastics
- Toxic metals
- Organic matter
- Inorganic salts
Explanation: The microbes use the organic matter in the effluent as food, thereby reducing the biochemical oxygen demand.
What happens when the organic waste in a river increases?
- BOD increases
- BOD decreases
- DO stays constant
- DO increases
Explanation: High organic load requires more oxygen for microbial decomposition, leading to an increase in BOD.
The primary objective of building STPs (Sewage Treatment Plants) is to:
- Generate electricity
- Produce fertilizer
- Reduce water pollution
- Control floods
Explanation: STPs ensure that sewage is treated to be less polluting before it is discharged into natural water bodies like rivers.
Tertiary treatment of sewage is primarily intended to remove:
- Large debris
- Floating oil
- Organic matter
- Nutrients and chemicals
Explanation: Tertiary treatment uses physicochemical processes to remove nitrates, phosphates, and toxic chemicals that secondary treatment misses.
Effluent from the primary settling tank is subsequently transferred to:
- River bodies
- Aeration tanks
- Sludge digesters
- Chlorination chambers
Explanation: The liquid portion (effluent) moves to the secondary treatment stage, which begins in large aeration tanks.
The conversion of nitrates back into nitrogen gas is termed:
- Nitrogen fixation
- Nitrification
- Denitrification
- Ammonification
Explanation: Denitrification is an anaerobic process carried out by bacteria like Pseudomonas to remove nitrogen from the effluent.
Which phase of treatment is most effective at removing suspended plastic and solid waste?
- Secondary
- Primary
- Tertiary
- Quaternary
Explanation: Physical screening and sedimentation in the primary phase remove the majority of the large suspended solids and debris.
During anaerobic digestion, bacteria produce a mixture of gases primarily consisting of:
- Helium and Methane
- Oxygen and Methane
- Methane, CO2, and H2S
- Nitrogen and CO2
Explanation: Anaerobic digesters produce biogas, which is a mixture of methane, carbon dioxide (CO2), and hydrogen sulfide (H2S).
What is the relationship between dissolved oxygen and BOD in sewage?
- Inversely proportional
- No relationship
- Logarithmic relationship
- Directly proportional
Explanation: As the BOD increases (due to high organic waste), the dissolved oxygen decreases as it is consumed by microbes.
Sustainable sewage management prioritizes which '3R' strategy?
- Refine, Relate, Restore
- Read, React, Resolve
- Reduce, Reuse, Recycle
- Release, Run, Recycle
Explanation: The focus is on reducing water waste, reusing treated effluent for irrigation/industry, and recycling nutrients from sludge.
The removal of 'Grit' (soil and small pebbles) in primary treatment is done by:
- Filtration
- Evaporation
- Sedimentation
- Centrifugation
Explanation: Grit is heavy and is removed through the process of sedimentation where it settles at the bottom of the tank.
What is the primary role of the 'Secondary Clarifier' in an activated sludge plant?
- Grit removal
- Biomass separation
- Chemical addition
- Oxygen transfer
Explanation: It allows the microbial flocs to settle so that clear effluent can be discharged and sludge can be recycled or wasted.
In sewage treatment, 'Skimming' is a process used to remove:
- Bacterial flocs
- Oil and grease
- Dissolved salts
- Heavy grit
Explanation: Skimming tanks allow lighter materials like fats, oils, and grease to float to the surface where they are mechanically removed.
In the context of sewage treatment, 'Flocs' are mesh-like masses of:
- Algae and Fungi
- Viruses and Bacteria
- Bacteria and Fungi
- Protozoa and Algae
Explanation: Flocs consist of aerobic bacteria associated with fungal filaments to form mesh-like structures that consume organic matter.
The liquid that flows out after the solid waste has settled in a tank is the:
- Sludge
- Inoculum
- Grit
- Effluent
Explanation: Effluent refers to the liquid waste or sewage discharged into a river or the next stage of treatment.
Heavy metals in industrial sewage are particularly dangerous because they are:
- Non-biodegradable
- Very volatile
- Highly flammable
- Readily evaporated
Explanation: Heavy metals like Mercury and Lead do not break down and can accumulate in the food chain (biomagnification).
Which of the following is a 'Physicochemical' process typical of tertiary treatment?
- Sequential filtration
- Reverse osmosis
- Anaerobic digestion
- Aeration
Explanation: Tertiary treatment utilizes advanced technologies like reverse osmosis, carbon filtration, or ion exchange to remove dissolved solids and nutrients.
The 'Trickling Filter' system is an example of which biological treatment process?
- Anaerobic digestion
- Physical screening
- Suspended growth
- Attached growth
Explanation: In trickling filters, microbes grow as a biofilm attached to a fixed medium (like stones or plastic) over which sewage is sprayed.
The removal of nitrogen and phosphorus from sewage is essential to prevent:
- Global warming
- Acid rain
- Eutrophication
- Ozone depletion
Explanation: Excess nutrients lead to algal blooms (eutrophication), which deplete dissolved oxygen and kill aquatic life.
Which parameter is most critical for the survival of aerobic bacteria in the aeration tank?
- Total salinity
- Total alkalinity
- Dissolved oxygen
- High temperature
Explanation: Aerobic bacteria require a minimum dissolved oxygen (DO) level (usually >2 mg/L) to maintain metabolic activity and oxidize organic matter.
Which organism is commonly used as an 'indicator' of fecal contamination in treated sewage?
- Escherichia coli
- Streptococcus
- Salmonella typhi
- Vibrio cholerae
Explanation: The presence of E. coli indicates that the water has been contaminated with feces and may contain other dangerous pathogens.
The majority of the activated sludge is pumped into large tanks called:
- Settling tanks
- Aeration tanks
- Anaerobic sludge digesters
- Filtration units
Explanation: The bulk of the sludge is digested by anaerobic bacteria which break down the aerobic bacteria and fungi in the flocs.
The secondary treatment process is essentially a way to:
- Evaporate water
- Mimic natural purification
- Filter plastics
- Neutralize acids
Explanation: It uses natural microbial processes in a controlled environment to purify water, similar to how rivers self-purify.
Which of the following is NOT a physical step in sewage treatment?
- Screening
- Sedimentation
- Filtration
- Microbial digestion
Explanation: Microbial digestion is a biological process, whereas filtration and sedimentation are physical processes.
Primary sludge is typically disposed of or used for:
- Disinfection
- Landfills or composting
- Aeration tanks
- Drinking water
Explanation: Primary sludge contains heavy solids and is often used in landfills or treated further for compost.
Biogas produced in sewage treatment plants is commonly used as a source of:
- Organic fertilizer
- Drinking water
- Energy
- Chemical solvent
Explanation: Methane is highly flammable, making biogas an excellent renewable energy source for heating or electricity in the plant.