All Free Civil Engineering MCQs with Answers

• A. Dissolved oxygen
• B. Total hardness
• C. Electrical conductivity
• D. Alkalinity

Explanation: Dissolved oxygen is the oxygen present in water and is directly available to aquatic organisms.

• A. Dense and rapidly settling
• B. Light and difficult to settle
• C. Completely dissolved in water
• D. Chemically bonded to hardness

Explanation: Dissolved air flotation attaches fine air bubbles to low-density particles, causing them to rise for removal.

• A. Remove coarse floating debris
• B. Provide preliminary grit removal
• C. Improve effluent quality beyond secondary treatment
• D. Transport sewage to the plant

Explanation: Tertiary treatment provides additional polishing after primary and secondary treatment, such as removing residual solids, nutrients or…

• A. Contact the chlorine solution
• B. Stay inside the inlet screen
• C. Remain in the sewer pipe
• D. Remain in the aeration system

Explanation: Sludge age, also called solids retention time, represents the average period microorganisms are retained in the biological treatment…

• A. Long retention under anaerobic conditions
• B. Excessive dissolved oxygen
• C. High water velocity with good ventilation
• D. Short travel time with fresh sewage

Explanation: When sewage remains stagnant or moves slowly for a long period, oxygen is depleted and anaerobic decomposition can produce offensive…

• A. Increase the moisture of waste
• B. Control pests, odour and windblown litter
• C. Replace the leachate collection system
• D. Accelerate uncontrolled burning

Explanation: Daily cover seals the exposed waste surface and helps control insects, rodents, odour, litter and fire hazards.

• A. Strong ammonia odour and high temperature
• B. High content of fresh food scraps
• C. Dark, stable appearance and earthy odour
• D. Rapid production of foul-smelling gases

Explanation: Mature compost is relatively stable, dark and soil-like, with an earthy odour and little further heat generation.

• A. Destroys atmospheric ozone directly
• B. Forms heavy particles in sewer air
• C. Causes permanent water hardness
• D. Combines with haemoglobin and reduces oxygen transport

Explanation: Carbon monoxide binds strongly with haemoglobin to form carboxyhaemoglobin, reducing the blood's oxygen-carrying capacity.

• A. Using cleaner fuel or improving combustion
• B. Increasing the stack height
• C. Diluting the exhaust with outdoor air
• D. Releasing emissions during windy weather

Explanation: Cleaner fuel and improved combustion reduce pollutant formation at the source, which is generally more effective than dispersing…

• A. The settling index
• B. The C times T value
• C. The sludge age
• D. The loading ratio

Explanation: The C times T value represents disinfectant concentration multiplied by the effective contact time and is used to assess disinfection…

• A. Design speed of a rapid sand filter
• B. Required chlorine residual in clear water
• C. Optimum coagulant dose for raw water
• D. Expected sludge age in an aeration tank

Explanation: A jar test simulates coagulation and flocculation at laboratory scale to identify a suitable coagulant dose and mixing condition.

• A. Iron and manganese oxides
• B. Calcium and magnesium chlorides
• C. Sodium and potassium sulfates
• D. Calcium and magnesium bicarbonates

Explanation: Temporary hardness is associated mainly with bicarbonates of calcium and magnesium and can often be reduced by boiling.

• A. Smooth variations in flow and pollutant load
• B. Remove coarse solids from incoming sewage
• C. Disinfect the final treated effluent
• D. Digest excess sludge under anaerobic conditions

Explanation: An equalization basin stores wastewater temporarily and releases it at a more uniform rate and composition.

• A. Nitrifying microorganisms
• B. Filamentous microorganisms
• C. Methane-producing microorganisms
• D. Algae-forming microorganisms

Explanation: Filamentous microorganisms can form open, poorly settling structures in activated sludge, causing bulking and a high sludge volume.

• A. Chemical precipitation of suspended solids
• B. Rapid evaporation of oxygen from the water
• C. Microbial oxidation of biodegradable organic matter
• D. Increased oxygen production by aquatic plants

Explanation: Microorganisms use dissolved oxygen while decomposing biodegradable organic matter, so oxygen levels can fall downstream from a discharge.

• A. Ground-level ozone
• B. Carbon monoxide
• C. Particulate lead
• D. Sulfur dioxide

Explanation: Flue-gas desulfurization removes sulfur dioxide from combustion gases, commonly using alkaline sorbents.

• A. Carbon monoxide, hydrocarbons and nitrogen oxides
• B. Sulfur dioxide, lead and carbon dioxide
• C. Dust, smoke and asbestos fibres
• D. Chlorine, ammonia and hydrogen sulfide

Explanation: A three-way catalytic converter oxidizes carbon monoxide and unburnt hydrocarbons and reduces nitrogen oxides in suitable exhaust…

• A. Biologically stabilize waste into finished compost
• B. Consolidate waste before transport to a distant facility
• C. Produce electricity from landfill methane
• D. Remove dissolved pollutants from landfill leachate

Explanation: A transfer station receives waste from small collection vehicles, consolidates it and loads it into larger vehicles for economical…

• A. Noise near an industrial plant
• B. Dissolved oxygen in water
• C. Suspended particulate matter
• D. Chlorine residual in drinking water

Explanation: A high-volume air sampler draws a large quantity of air through a filter, allowing suspended particulate matter to be collected and…

• A. Most heat-sensitive disease organisms
• B. Bacteria and many viruses
• C. Protozoan cysts and oocysts
• D. Dissolved salts and minerals

Explanation: Boiling provides thermal disinfection and destroys many bacteria, viruses and protozoan forms when applied adequately.