Sanitary and Waste Water Engineering MCQs 2026

Separate sewer system has

1. ASingle pipe for all flows always✓
2. BDistinct sanitary and storm sewers✓
3. CNo storm drainage✓
4. DNo sanitary lines✓

Standard BOD test incubation period at 20°C is

1. A3 days✓
2. B5 days✓
3. C7 days✓
4. D10 days✓

Typical BOD/COD ratio for untreated domestic sewage is approximately

1. A0.4 to 0.6✓
2. B0.9 to 1.0✓
3. C0.1 to 0.2✓
4. D0.8 to 0.9✓

Activated sludge process relies primarily on

1. AAnaerobic bacteria in septic tank✓
2. BPhysical filtration only✓
3. CChemical precipitation alone✓
4. DAerobic microorganisms in mixed liquor✓

Mean cell residence time in activated sludge is controlled by

1. ASludge wasting rate✓
2. BPrimary clarifier depth✓
3. CGrit chamber velocity✓
4. DTrickling filter media size✓

F/M ratio in activated sludge stands for

1. AFlow to Mass ratio✓
2. BFilament to Mixed liquor ratio✓
3. CFood to Microorganism ratio✓
4. DFinal to Initial BOD ratio✓

Typical MLSS concentration in conventional activated sludge is

1. A50 to 100 mg/L✓
2. B2000 to 4000 mg/L✓
3. C10000 to 15000 mg/L✓
4. D100 to 200 mg/L✓

Drying beds for sludge dewatering depend on

1. AEvaporation and drainage✓
2. BReverse osmosis✓
3. CCentrifugal pumps only✓
4. DActivated carbon adsorption✓

Belt filter press is used for

1. AAeration of mixed liquor✓
2. BMechanical sludge dewatering✓
3. CGrit washing✓
4. DInfluent screening✓

Centrifuge dewatering uses

1. ABiological nitrification✓
2. BTrickling filter recirculation✓
3. CSedimentation in oxidation pond only✓
4. DHigh rotational speed to separate solids✓

Composting of sludge requires

1. AAdequate carbon-nitrogen balance and aeration✓
2. BComplete anaerobic sealed conditions always✓
3. CZero moisture✓
4. DSub-zero temperature✓

Industrial wastewater with heavy metals needs

1. ADirect discharge to oxidation pond only✓
2. BNo treatment in Pakistan✓
3. CPretreatment before biological treatment✓
4. DOnly dilution with storm water✓

Equalization tank purpose is

1. ARemove all BOD✓
2. BDampen flow and load variations✓
3. CProvide final disinfection✓
4. DReplace secondary clarifier✓

Grease trap is installed to

1. AIncrease BOD loading✓
2. BProvide nitrification✓
3. CMeasure COD✓
4. DRemove fats oils and grease from kitchen waste✓

Grit chamber removes

1. ADissolved ammonia✓
2. BAll organic matter✓
3. CInorganic settleable particles like sand✓
4. DBiogas methane✓

Horizontal flow grit chamber design uses

1. AControlled velocity near 0.3 m/s✓
2. BVelocity 5 m/s✓
3. CZero velocity always✓
4. DVelocity 10 m/s✓

Aerated grit chamber uses

1. AChlorine gas✓
2. BDiffused air to separate organic matter from grit✓
3. CMembrane filtration✓
4. DTrickling filter media✓

Bar screen with 25 mm spacing is classified as

1. AFine screen✓
2. BMicro screen✓
3. CCoarse screen✓
4. DMembrane screen✓

Comminutors are used to

1. ADigest sludge anaerobically✓
2. BShred coarse solids in sewage✓
3. CMeasure BOD✓
4. DRemove nitrogen✓

Infiltration in sewer systems refers to

1. ASewage leaking to groundwater as standard term✓
2. BRain falling on manholes only✓
3. CIndustrial discharge✓
4. DGroundwater entering sewer pipes✓

Exfiltration from sewers causes

1. AGroundwater and soil contamination✓
2. BReduced treatment cost✓
3. CImproved pipe strength✓
4. DHigher BOD removal in plant✓

I/I stands for in sewerage engineering

1. AInfluent and Inhibition✓
2. BInternal and Intermittent✓
3. CInorganic and Industrial✓
4. DInfiltration and Inflow✓

Self cleansing velocity in sewers prevents

1. APipe corrosion only✓
2. BSediment deposition in pipes✓
3. CBiological treatment failure✓
4. DGrit chamber overflow✓

Manning formula is used in sewer design to relate

1. ABOD and COD✓
2. BSludge age and F/M✓
3. CFlow velocity and pipe slope✓
4. DNitrification rate✓

Peak factor in sewage flow accounts for

1. ADiurnal and seasonal variation✓
2. BOnly pipe material✓
3. COnly manhole spacing✓
4. DOnly sludge density✓

Hazen-Williams formula is also used for

1. AWater and sewage pressure pipe flow✓
2. BSludge digestion rate✓
3. CBOD kinetics only✓
4. DWind rose analysis✓

Force main is required when

1. ASewer is always gravity✓
2. BNo pumping ever needed✓
3. CGravity flow is not feasible✓
4. DTreatment plant is uphill without lift✓

Wet well in pumping station collects

1. ATreated effluent only✓
2. BSewage before pumps activate✓
3. CDrinking water✓
4. DSludge cake✓

Chlorination of treated effluent purpose is

1. APathogen disinfection✓
2. BIncrease BOD✓
3. CPromote nitrification✓
4. DRemove grit✓

Dechlorination may be needed to

1. AIncrease COD✓
2. BPromote algae in aeration tank✓
3. CRemove grit✓
4. DReduce chlorine toxicity to aquatic life✓

Sewer pipe minimum slope is governed by

1. AOnly pavement CBR✓
2. BOnly wind speed✓
3. COnly earthquake zone✓
4. DDiameter and self cleansing velocity✓

Sludge digestion reduces

1. AConcrete strength✓
2. BPipe diameter✓
3. CVolatile solids and pathogens✓
4. DManning n value✓

Oxidation pond treatment depends on

1. AHigh pressure pumps only✓
2. BAnaerobic methanogenesis only✓
3. CAlgae-bacteria symbiosis and sunlight✓
4. DMembrane filtration✓

Detention time in facultative oxidation pond is typically

1. A30 minutes✓
2. B5 to 10 days✓
3. C2 hours✓
4. D1 hour✓

Primary treatment removes mainly

1. ASettleable and floatable solids✓
2. BDissolved nutrients completely✓
3. CAll pathogens✓
4. DHeavy metals completely✓

Secondary treatment target is mainly

1. AOnly grit and oil✓
2. BTotal dissolved solids only✓
3. CRadioactive isotopes✓
4. DBiodegradable organic matter and BOD✓

Tertiary treatment may include

1. AOnly bar screens✓
2. BNutrient removal and filtration✓
3. CGrit channels only✓
4. DRaw sewage pumping✓

Nitrification converts

1. ANitrate to nitrogen gas✓
2. BBOD to methane✓
3. CPhosphate to sludge only✓
4. DAmmonia to nitrate✓

Denitrification requires

1. AAnoxic conditions and organic carbon✓
2. BHigh dissolved oxygen✓
3. CChlorine dosing✓
4. DUltraviolet light only✓

Biological phosphorus removal uses

1. AOnly primary clarifiers✓
2. BOnly chlorination✓
3. CAlternating anaerobic-aerobic zones✓
4. DOnly grit removal✓

Membrane bioreactor combines

1. AActivated sludge with membrane filtration✓
2. BTrickling filter with chlorination✓
3. CSeptic tank with RO only✓
4. DGrit chamber with UV✓

Typical pore size classification for MBR is

1. AGravel filtration✓
2. BRapid sand 1 mm only✓
3. CMicrofiltration or ultrafiltration✓
4. DNo filtration✓

UV disinfection mechanism is

1. ASedimentation of viruses✓
2. BDNA damage to microorganisms✓
3. CChemical oxidation with chlorine✓
4. DFiltration through sand✓

Landfill disposal of dewatered sludge requires

1. ANo regulation✓
2. BDirect dumping in rivers✓
3. CEnvironmental compliance and leachate control✓
4. DOpen burning only✓

Phosphorus removal chemically uses commonly

1. AOnly aeration✓
2. BOnly grit removal✓
3. COnly UV without coagulants✓
4. DLime or alum coagulation✓

Reclaimed wastewater for irrigation requires

1. ANo treatment ever✓
2. BAdequate treatment and pathogen control✓
3. COnly grit removal✓
4. DRaw sewage application✓

Effluent discharge standards in Pakistan are set by

1. ANEQS National Environmental Quality Standards✓
2. BOnly local mason✓
3. COnly WHO exclusively without local law✓
4. DNo standards exist✓

Lagoons in Pakistan rural areas are often

1. AMBR plants✓
2. BLow cost facultative ponds✓
3. CNuclear cooled basins✓
4. DOnly packaged RO units✓

Rotating biological contactor RBC uses

1. AStatic sand filter only✓
2. BOnly chemical coagulation✓
3. COnly grit channel✓
4. DRotating media discs in wastewater✓

Sequencing Batch Reactor SBR operates in

1. AFill react settle decant cycle✓
2. BContinuous flow only always✓
3. CNo aeration ever✓
4. DOnly primary treatment✓

Contact stabilization process uses

1. AOnly oxidation pond✓
2. BOnly septic tank✓
3. CSmall contact tank and larger stabilization tank✓
4. DOnly UASB✓

SRT in activated sludge is

1. ASewer Rise Time✓
2. BSludge Return Temperature✓
3. CSettlement Rate Test✓
4. DSolids Retention Time✓

ThOD theoretically represents

1. AOxygen required for complete oxidation✓
2. BOnly chlorine demand✓
3. COnly nitrogen gas volume✓
4. DOnly sludge volume✓

COD measures

1. AOnly biodegradable fraction✓
2. BOnly nitrogen✓
3. CTotal organic matter oxidizable chemically✓
4. DOnly suspended grit✓

Sludge volume index SVI indicates

1. ABOD of influent✓
2. BCOD of effluent✓
3. CChlorine residual✓
4. DSettleability of activated sludge✓

Sludge bulking is often caused by

1. AExcessive grit removal✓
2. BFilamentous bacteria overgrowth✓
3. CToo much chlorine in influent✓
4. DZero organic loading✓

Primary sludge from municipal WWTP is typically

1. ASterile and inert✓
2. BLiquid with zero solids✓
3. CAlready stabilized completely✓
4. DHigh solids content and putrescible✓

Return activated sludge is recycled to

1. AFinal effluent outlet✓
2. BSludge drying beds only✓
3. CPrimary clarifier underflow exclusively✓
4. DAeration tank inlet✓

Extended aeration activated sludge typically operates at

1. AHigh F/M and short SRT✓
2. BLow F/M and long SRT✓
3. CZero dissolved oxygen✓
4. DNo sludge return✓

Trickling filter media commonly used in Pakistan is

1. ASand only✓
2. BSteel plates✓
3. CRock or plastic media✓
4. DConcrete blocks without voids✓

Hydraulic loading on trickling filter is expressed as

1. Am³/m²/day✓
2. Bkg BOD/ha/day✓
3. Cm/s Manning velocity✓
4. DkN/m² contact pressure✓

Organic loading on trickling filter is expressed as

1. Am³/m²/day✓
2. Bmg/L MLSS✓
3. CkPa head loss✓
4. Dkg BOD/m³/day✓

Anaerobic digestion produces biogas rich in

1. AOxygen✓
2. BChlorine✓
3. CMethane✓
4. DNitrogen gas only✓

Optimum temperature range for mesophilic anaerobic digestion is

1. A30 to 38°C✓
2. B5 to 10°C✓
3. C55 to 65°C✓
4. D80 to 90°C✓

Two-stage anaerobic digestion separates

1. APrimary and secondary settling✓
2. BAcid formation and methane formation✓
3. CNitrification and denitrification✓
4. DScreening and grit removal✓

UASB reactor is primarily used for

1. ADisinfection with chlorine✓
2. BGrit removal✓
3. CAnaerobic treatment of high-strength wastewater✓
4. DStorm water detention✓

Septic tank provides

1. APrimary sedimentation and anaerobic digestion✓
2. BComplete nitrification✓
3. CReverse osmosis✓
4. DActivated sludge aeration✓

Typical detention time in septic tank is

1. A5 minutes✓
2. B7 days minimum✓
3. C30 days✓
4. D24 to 48 hours✓

Imhoff tank combines

1. AAeration and chlorination✓
2. BSedimentation and sludge digestion✓
3. CFiltration and UV✓
4. DFlocculation and adsorption✓