Sanitary and Waste Water Engineering MCQs 2026

Infiltration in sewer systems refers to

1. A Sewage leaking to groundwater as standard term ✓
2. B Rain falling on manholes only ✓
3. C Industrial discharge ✓
4. D Groundwater entering sewer pipes ✓

Industrial wastewater with heavy metals needs

1. A Direct discharge to oxidation pond only ✓
2. B No treatment in Pakistan ✓
3. C Pretreatment before biological treatment ✓
4. D Only dilution with storm water ✓

Exfiltration from sewers causes

1. A Groundwater and soil contamination ✓
2. B Reduced treatment cost ✓
3. C Improved pipe strength ✓
4. D Higher BOD removal in plant ✓

I/I stands for in sewerage engineering

1. A Influent and Inhibition ✓
2. B Internal and Intermittent ✓
3. C Inorganic and Industrial ✓
4. D Infiltration and Inflow ✓

Self cleansing velocity in sewers prevents

1. A Pipe corrosion only ✓
2. B Sediment deposition in pipes ✓
3. C Biological treatment failure ✓
4. D Grit chamber overflow ✓

Manning formula is used in sewer design to relate

1. A BOD and COD ✓
2. B Sludge age and F/M ✓
3. C Flow velocity and pipe slope ✓
4. D Nitrification rate ✓

Peak factor in sewage flow accounts for

1. A Diurnal and seasonal variation ✓
2. B Only pipe material ✓
3. C Only manhole spacing ✓
4. D Only sludge density ✓

Separate sewer system has

1. A Single pipe for all flows always ✓
2. B Distinct sanitary and storm sewers ✓
3. C No storm drainage ✓
4. D No sanitary lines ✓

Sewer pipe minimum slope is governed by

1. A Only pavement CBR ✓
2. B Only wind speed ✓
3. C Only earthquake zone ✓
4. D Diameter and self cleansing velocity ✓

Hazen-Williams formula is also used for

1. A Water and sewage pressure pipe flow ✓
2. B Sludge digestion rate ✓
3. C BOD kinetics only ✓
4. D Wind rose analysis ✓

Force main is required when

1. A Sewer is always gravity ✓
2. B No pumping ever needed ✓
3. C Gravity flow is not feasible ✓
4. D Treatment plant is uphill without lift ✓

Centrifuge dewatering uses

1. A Biological nitrification ✓
2. B Trickling filter recirculation ✓
3. C Sedimentation in oxidation pond only ✓
4. D High rotational speed to separate solids ✓

Composting of sludge requires

1. A Adequate carbon-nitrogen balance and aeration ✓
2. B Complete anaerobic sealed conditions always ✓
3. C Zero moisture ✓
4. D Sub-zero temperature ✓

Belt filter press is used for

1. A Aeration of mixed liquor ✓
2. B Mechanical sludge dewatering ✓
3. C Grit washing ✓
4. D Influent screening ✓

Drying beds for sludge dewatering depend on

1. A Evaporation and drainage ✓
2. B Reverse osmosis ✓
3. C Centrifugal pumps only ✓
4. D Activated carbon adsorption ✓

Typical MLSS concentration in conventional activated sludge is

1. A 50 to 100 mg/L ✓
2. B 2000 to 4000 mg/L ✓
3. C 10000 to 15000 mg/L ✓
4. D 100 to 200 mg/L ✓

F/M ratio in activated sludge stands for

1. A Flow to Mass ratio ✓
2. B Filament to Mixed liquor ratio ✓
3. C Food to Microorganism ratio ✓
4. D Final to Initial BOD ratio ✓

Activated sludge process relies primarily on

1. A Anaerobic bacteria in septic tank ✓
2. B Physical filtration only ✓
3. C Chemical precipitation alone ✓
4. D Aerobic microorganisms in mixed liquor ✓

Mean cell residence time in activated sludge is controlled by

1. A Sludge wasting rate ✓
2. B Primary clarifier depth ✓
3. C Grit chamber velocity ✓
4. D Trickling filter media size ✓

Standard BOD test incubation period at 20°C is

1. A 3 days ✓
2. B 5 days ✓
3. C 7 days ✓
4. D 10 days ✓

Typical BOD/COD ratio for untreated domestic sewage is approximately

1. A 0.4 to 0.6 ✓
2. B 0.9 to 1.0 ✓
3. C 0.1 to 0.2 ✓
4. D 0.8 to 0.9 ✓

Equalization tank purpose is

1. A Remove all BOD ✓
2. B Dampen flow and load variations ✓
3. C Provide final disinfection ✓
4. D Replace secondary clarifier ✓

Grease trap is installed to

1. A Increase BOD loading ✓
2. B Provide nitrification ✓
3. C Measure COD ✓
4. D Remove fats oils and grease from kitchen waste ✓

Grit chamber removes

1. A Dissolved ammonia ✓
2. B All organic matter ✓
3. C Inorganic settleable particles like sand ✓
4. D Biogas methane ✓

Horizontal flow grit chamber design uses

1. A Controlled velocity near 0.3 m/s ✓
2. B Velocity 5 m/s ✓
3. C Zero velocity always ✓
4. D Velocity 10 m/s ✓

Aerated grit chamber uses

1. A Chlorine gas ✓
2. B Diffused air to separate organic matter from grit ✓
3. C Membrane filtration ✓
4. D Trickling filter media ✓

Bar screen with 25 mm spacing is classified as

1. A Fine screen ✓
2. B Micro screen ✓
3. C Coarse screen ✓
4. D Membrane screen ✓

Comminutors are used to

1. A Digest sludge anaerobically ✓
2. B Shred coarse solids in sewage ✓
3. C Measure BOD ✓
4. D Remove nitrogen ✓

Wet well in pumping station collects

1. A Treated effluent only ✓
2. B Sewage before pumps activate ✓
3. C Drinking water ✓
4. D Sludge cake ✓

Dechlorination may be needed to

1. A Increase COD ✓
2. B Promote algae in aeration tank ✓
3. C Remove grit ✓
4. D Reduce chlorine toxicity to aquatic life ✓

Chlorination of treated effluent purpose is

1. A Pathogen disinfection ✓
2. B Increase BOD ✓
3. C Promote nitrification ✓
4. D Remove grit ✓

Return activated sludge is recycled to

1. A Final effluent outlet ✓
2. B Sludge drying beds only ✓
3. C Primary clarifier underflow exclusively ✓
4. D Aeration tank inlet ✓

Extended aeration activated sludge typically operates at

1. A High F/M and short SRT ✓
2. B Low F/M and long SRT ✓
3. C Zero dissolved oxygen ✓
4. D No sludge return ✓

Trickling filter media commonly used in Pakistan is

1. A Sand only ✓
2. B Steel plates ✓
3. C Rock or plastic media ✓
4. D Concrete blocks without voids ✓

Hydraulic loading on trickling filter is expressed as

1. A m³/m²/day ✓
2. B kg BOD/ha/day ✓
3. C m/s Manning velocity ✓
4. D kN/m² contact pressure ✓

Organic loading on trickling filter is expressed as

1. A m³/m²/day ✓
2. B mg/L MLSS ✓
3. C kPa head loss ✓
4. D kg BOD/m³/day ✓

Anaerobic digestion produces biogas rich in

1. A Oxygen ✓
2. B Chlorine ✓
3. C Methane ✓
4. D Nitrogen gas only ✓

Optimum temperature range for mesophilic anaerobic digestion is

1. A 30 to 38°C ✓
2. B 5 to 10°C ✓
3. C 55 to 65°C ✓
4. D 80 to 90°C ✓

Two-stage anaerobic digestion separates

1. A Primary and secondary settling ✓
2. B Acid formation and methane formation ✓
3. C Nitrification and denitrification ✓
4. D Screening and grit removal ✓

UASB reactor is primarily used for

1. A Disinfection with chlorine ✓
2. B Grit removal ✓
3. C Anaerobic treatment of high-strength wastewater ✓
4. D Storm water detention ✓

Septic tank provides

1. A Primary sedimentation and anaerobic digestion ✓
2. B Complete nitrification ✓
3. C Reverse osmosis ✓
4. D Activated sludge aeration ✓

Typical detention time in septic tank is

1. A 5 minutes ✓
2. B 7 days minimum ✓
3. C 30 days ✓
4. D 24 to 48 hours ✓

Imhoff tank combines

1. A Aeration and chlorination ✓
2. B Sedimentation and sludge digestion ✓
3. C Filtration and UV ✓
4. D Flocculation and adsorption ✓

Oxidation pond treatment depends on

1. A High pressure pumps only ✓
2. B Anaerobic methanogenesis only ✓
3. C Algae-bacteria symbiosis and sunlight ✓
4. D Membrane filtration ✓

Detention time in facultative oxidation pond is typically

1. A 30 minutes ✓
2. B 5 to 10 days ✓
3. C 2 hours ✓
4. D 1 hour ✓

Primary treatment removes mainly

1. A Settleable and floatable solids ✓
2. B Dissolved nutrients completely ✓
3. C All pathogens ✓
4. D Heavy metals completely ✓

Secondary treatment target is mainly

1. A Only grit and oil ✓
2. B Total dissolved solids only ✓
3. C Radioactive isotopes ✓
4. D Biodegradable organic matter and BOD ✓

Tertiary treatment may include

1. A Only bar screens ✓
2. B Nutrient removal and filtration ✓
3. C Grit channels only ✓
4. D Raw sewage pumping ✓

Nitrification converts

1. A Nitrate to nitrogen gas ✓
2. B BOD to methane ✓
3. C Phosphate to sludge only ✓
4. D Ammonia to nitrate ✓

Denitrification requires

1. A Anoxic conditions and organic carbon ✓
2. B High dissolved oxygen ✓
3. C Chlorine dosing ✓
4. D Ultraviolet light only ✓

Biological phosphorus removal uses

1. A Only primary clarifiers ✓
2. B Only chlorination ✓
3. C Alternating anaerobic-aerobic zones ✓
4. D Only grit removal ✓

Membrane bioreactor combines

1. A Activated sludge with membrane filtration ✓
2. B Trickling filter with chlorination ✓
3. C Septic tank with RO only ✓
4. D Grit chamber with UV ✓

Typical pore size classification for MBR is

1. A Gravel filtration ✓
2. B Rapid sand 1 mm only ✓
3. C Microfiltration or ultrafiltration ✓
4. D No filtration ✓

Sludge volume index SVI indicates

1. A BOD of influent ✓
2. B COD of effluent ✓
3. C Chlorine residual ✓
4. D Settleability of activated sludge ✓

Sludge bulking is often caused by

1. A Excessive grit removal ✓
2. B Filamentous bacteria overgrowth ✓
3. C Too much chlorine in influent ✓
4. D Zero organic loading ✓

Primary sludge from municipal WWTP is typically

1. A Sterile and inert ✓
2. B Liquid with zero solids ✓
3. C Already stabilized completely ✓
4. D High solids content and putrescible ✓

Sludge digestion reduces

1. A Concrete strength ✓
2. B Pipe diameter ✓
3. C Volatile solids and pathogens ✓
4. D Manning n value ✓

UV disinfection mechanism is

1. A Sedimentation of viruses ✓
2. B DNA damage to microorganisms ✓
3. C Chemical oxidation with chlorine ✓
4. D Filtration through sand ✓

COD measures

1. A Only biodegradable fraction ✓
2. B Only nitrogen ✓
3. C Total organic matter oxidizable chemically ✓
4. D Only suspended grit ✓

ThOD theoretically represents

1. A Oxygen required for complete oxidation ✓
2. B Only chlorine demand ✓
3. C Only nitrogen gas volume ✓
4. D Only sludge volume ✓

SRT in activated sludge is

1. A Sewer Rise Time ✓
2. B Sludge Return Temperature ✓
3. C Settlement Rate Test ✓
4. D Solids Retention Time ✓

Contact stabilization process uses

1. A Only oxidation pond ✓
2. B Only septic tank ✓
3. C Small contact tank and larger stabilization tank ✓
4. D Only UASB ✓

Sequencing Batch Reactor SBR operates in

1. A Fill react settle decant cycle ✓
2. B Continuous flow only always ✓
3. C No aeration ever ✓
4. D Only primary treatment ✓

Rotating biological contactor RBC uses

1. A Static sand filter only ✓
2. B Only chemical coagulation ✓
3. C Only grit channel ✓
4. D Rotating media discs in wastewater ✓

Lagoons in Pakistan rural areas are often

1. A MBR plants ✓
2. B Low cost facultative ponds ✓
3. C Nuclear cooled basins ✓
4. D Only packaged RO units ✓

Effluent discharge standards in Pakistan are set by

1. A NEQS National Environmental Quality Standards ✓
2. B Only local mason ✓
3. C Only WHO exclusively without local law ✓
4. D No standards exist ✓

Reclaimed wastewater for irrigation requires

1. A No treatment ever ✓
2. B Adequate treatment and pathogen control ✓
3. C Only grit removal ✓
4. D Raw sewage application ✓

Phosphorus removal chemically uses commonly

1. A Only aeration ✓
2. B Only grit removal ✓
3. C Only UV without coagulants ✓
4. D Lime or alum coagulation ✓

Landfill disposal of dewatered sludge requires

1. A No regulation ✓
2. B Direct dumping in rivers ✓
3. C Environmental compliance and leachate control ✓
4. D Open burning only ✓