All Free Civil Engineering MCQs with Answers

• A. Neutralize acidity produced during alum reaction
• B. Increase the dissolved oxygen concentration
• C. Prevent all microbial growth in water
• D. Convert suspended solids into dissolved salts

Explanation: Alum hydrolysis produces acidity, so alkalinity helps maintain a suitable pH and supports formation of aluminium hydroxide flocs.

• A. Coarse grit and large floating debris
• B. Taste, odour and dissolved organic compounds
• C. Water hardness caused by calcium ions
• D. Settleable mineral particles in raw water

Explanation: Activated carbon adsorbs many dissolved organic substances that cause taste, odour and colour.

• A. Domestic sewage from household plumbing fixtures
• B. Stormwater through roof gutters and street inlets
• C. Groundwater through cracks and defective joints
• D. Industrial wastewater discharged through approved connections

Explanation: Infiltration is groundwater entering a sewer through cracks, joints or other defects below the groundwater level.

• A. The concentration of dissolved salts in sludge
• B. The chlorine demand of treated wastewater
• C. The oxygen content of return sludge
• D. The settling characteristics of activated sludge

Explanation: Sludge volume index relates the settled sludge volume to the mass of suspended solids and indicates how well activated sludge settles.

• A. Bacteria and algae under natural conditions
• B. Coarse screens and mechanical compressors
• C. Chlorine and activated carbon particles
• D. Sand grains and pressure-driven membranes

Explanation: Oxidation ponds use bacteria to decompose organic matter, while algae provide oxygen through photosynthesis in the pond system.

• A. Converts all waste into harmless drinking water
• B. Greatly reduces waste volume through controlled combustion
• C. Eliminates the need to control air emissions
• D. Produces compost without requiring biodegradable material

Explanation: Controlled combustion can substantially reduce the volume of municipal solid waste and may also recover energy.

• A. Thermal stratification caused by heated effluent
• B. Desalination and reduced electrical conductivity
• C. Eutrophication and excessive algal growth
• D. Immediate removal of dissolved oxygen by filtration

Explanation: Nitrogen and phosphorus are nutrients that can stimulate excessive algal and aquatic plant growth.

• A. Sulfuric acid aerosol formed in the atmosphere
• B. Ozone formed by reactions in sunlight
• C. Peroxyacetyl nitrate formed in photochemical smog
• D. Sulfur dioxide emitted directly from fuel combustion

Explanation: A primary pollutant is released directly from a source, and sulfur dioxide is emitted during combustion of sulfur containing fuels.

• A. Provides little persistent residual in the distribution system
• B. Cannot inactivate bacteria under any operating condition
• C. Always increases the hardness of treated water
• D. Requires suspended solids to remain in the water

Explanation: Ozone is a strong disinfectant, but it decomposes relatively quickly and therefore provides little lasting protection in distribution…

• A. Dissolved oxygen molecules in the tank water
• B. Suspended microbial solids in the aerated mixture
• C. Settleable grit collected before biological treatment
• D. Chlorine compounds remaining after disinfection

Explanation: Mixed liquor suspended solids are the suspended solids present in the aeration tank, including the microbial flocs responsible for…

• A. Pathogenic microorganisms
• B. Dissolved mineral salts
• C. Large floating and suspended debris
• D. Fine colloidal particles

Explanation: Bar screens physically intercept large materials such as sticks, rags and plastics before later treatment units.

• A. Chlorine comparator
• B. pH meter
• C. BOD incubator
• D. Nephelometer

Explanation: A nephelometer measures turbidity by detecting light scattered by suspended particles in water.

• A. Reverse osmosis
• B. Rapid sand filtration
• C. Microfiltration
• D. Plain sedimentation

Explanation: Reverse osmosis uses pressure to force water through a semipermeable membrane while retaining many dissolved salts.

• A. Storage for treated wastewater
• B. Access for inspection and cleaning
• C. Additional biological treatment
• D. Removal of dissolved oxygen

Explanation: Manholes provide access at changes in sewer direction, slope, size and junctions so that inspection and cleaning can be carried out.

• A. The concentration of dissolved oxygen in rivers
• B. The need for household water meters
• C. Stormwater entering the sewage-treatment plant
• D. The production of water-treatment chemicals

Explanation: Separate systems carry sanitary sewage and stormwater through different pipes, so rainfall produces less hydraulic loading at a…

• A. Dissolved sodium chloride
• B. Large floating objects
• C. Coarse mineral grit
• D. Biodegradable organic matter

Explanation: Secondary treatment uses microorganisms to convert biodegradable organic matter into more stable products, followed by separation of…

• A. Contaminated liquid draining through waste
• B. Methane collected from decomposing waste
• C. Ash remaining after waste combustion
• D. Stormwater flowing over an unused site

Explanation: Leachate forms when water passes through waste and dissolves or carries contaminants with it.

• A. Dissolved salts from wastewater
• B. Particulate matter from gas streams
• C. Nitrogen gas from combustion air
• D. Noise from industrial machinery

Explanation: A baghouse passes polluted gas through fabric bags that trap particulate matter on their surfaces.

• A. Coarse soil particles
• B. Dissolved calcium ions
• C. Volatile organic compounds
• D. Water-treatment alum

Explanation: Sunlight drives reactions between nitrogen oxides and volatile organic compounds, producing ozone and other oxidants associated with…

• A. Plain sedimentation
• B. Coarse screening
• C. Grit removal
• D. Granular activated carbon adsorption

Explanation: Granular activated carbon removes many organic compounds by adsorption onto its highly porous surface, improving taste and odour.