All Free Civil Engineering MCQs with Answers

• A. Schmutzdecke
• B. Sludge blanket
• C. Filter ripening bed
• D. Oxidation ditch

Explanation: The schmutzdecke is a biologically active layer formed on the surface of a slow sand filter.

• A. To increase water hardness by adding minerals
• B. To add oxygen and strip unwanted gases
• C. To remove settled grit from raw water
• D. To destroy all organisms by heating

Explanation: Aeration brings water into contact with air, adding oxygen and helping remove gases such as hydrogen sulfide and carbon dioxide.

• A. Total hardness
• B. Chloride ions
• C. Total coliform bacteria
• D. Electrical conductivity

Explanation: Coliform bacteria are used as indicator organisms because their presence suggests possible contamination and inadequate sanitary…

• A. Chemical precipitation of water hardness
• B. Primary removal of sewage solids
• C. Biological oxidation of organic waste
• D. Storage after treatment and pressure balancing

Explanation: A clear-water reservoir stores treated water before distribution and helps balance variations between treatment output and consumer…

• A. To remove sand and other heavy inorganic particles
• B. To oxidize dissolved organic matter biologically
• C. To disinfect sewage before discharge
• D. To concentrate dissolved salts by evaporation

Explanation: Grit chambers remove dense inorganic materials such as sand, gravel and eggshells that could damage pumps or accumulate in later units.

• A. Add oxygen to raw sewage
• B. Separate biological solids from treated liquid
• C. Remove dissolved salts by crystallization
• D. Screen large floating refuse

Explanation: The secondary clarifier allows biological flocs to settle, producing a clarified effluent and concentrated sludge.

• A. Sulphate into hydrogen sulfide
• B. Nitrate nitrogen into nitrogen gas
• C. Ammonia nitrogen into nitrate nitrogen
• D. Carbon dioxide into methane

Explanation: Nitrification is an aerobic biological process in which ammonia is oxidized first to nitrite and then to nitrate.

• A. Mechanical screening alone
• B. Open burning
• C. Pyrolysis without oxygen
• D. Composting

Explanation: Composting uses controlled aerobic microbial activity to stabilize biodegradable waste and produce a humus-like material.

• A. Centrifugal force
• B. Ultraviolet radiation
• C. Chemical neutralization
• D. Microbial oxidation

Explanation: A cyclone forces the gas into a spiral motion, causing particles to move outward under centrifugal force and fall into a collection…

• A. Diluting emissions with taller stacks
• B. Using a cleaner fuel
• C. Monitoring ambient temperature
• D. Increasing chimney height

Explanation: Using a cleaner fuel reduces the pollutant generation rate before the exhaust reaches the atmosphere.

• A. To remove suspended solids by gravity
• B. To convert hardness into insoluble carbonates
• C. To satisfy chlorine demand and produce a free residual
• D. To increase dissolved oxygen by mechanical mixing

Explanation: Breakpoint chlorination adds enough chlorine to react with reducing substances and combined chlorine, after which a measurable free…

• A. Primary sedimentation
• B. Preliminary treatment
• C. Screening treatment
• D. Tertiary treatment

Explanation: Tertiary or advanced treatment can remove nutrients that remain after conventional biological treatment.

• A. Settling solids and anaerobic decomposition
• B. Rapid filtration and chlorination
• C. Aerobic oxidation in suspended growth
• D. Chemical precipitation of dissolved salts

Explanation: A septic tank retains settleable solids and allows anaerobic organisms to partially decompose the accumulated sludge.

• A. Excessive chlorine formation
• B. Deposition of solids on the sewer bottom
• C. Infiltration of groundwater through joints
• D. Generation of dissolved oxygen in sewage

Explanation: A self-cleansing velocity keeps suspended solids moving so they do not settle and obstruct the sewer.

• A. Double
• B. Become four times greater
• C. Become half as large
• D. Remain unchanged

Explanation: Theoretical detention time equals tank volume divided by flow rate. With constant volume, doubling the flow rate reduces the detention…

• A. Dissolution of sulphates in groundwater
• B. Direct release of carbon dioxide from deep aquifers
• C. Settling of coarse dust in a storage yard
• D. Photochemical reactions involving nitrogen oxides and hydrocarbons

Explanation: Ground-level ozone forms through sunlight-driven photochemical reactions involving nitrogen oxides and volatile organic compounds.

• A. Prevents vertical mixing of polluted air
• B. Raises the wind speed near the ground
• C. Converts all particulate matter into gases
• D. Increases rainfall over the emission source

Explanation: During an inversion, warmer air overlies cooler air near the surface and suppresses vertical circulation.

• A. Coarse screening
• B. Sludge dewatering
• C. Grit removal
• D. Breakpoint chlorination

Explanation: Dewatering removes a substantial portion of water from sludge, reducing its volume and handling cost.

• A. Increase rainwater infiltration into waste
• B. Convert plastics directly into compost
• C. Capture methane and control gas migration
• D. Remove all dissolved salts from leachate

Explanation: Decomposing organic waste produces methane and carbon dioxide. Gas collection reduces fire and explosion risks, limits migration to nearby…

• A. Methane
• B. Carbon monoxide
• C. Ground-level ozone
• D. Sulphur dioxide

Explanation: Sulphur dioxide is oxidized in the atmosphere to sulphuric acid and related compounds that contribute to acid deposition.