Water and Wastewater Treatment

Washing machines work on the principle of centrifugation - spinning the drum at high speed forces water out of wet clothes through the drum holes. This is the same principle as centrifuges used in laboratories. Diffusion, reverse osmosis, and dialysis are not relevant to washing machine operation.

Coagulation is the initial step in water purification where chemicals (like alum) are added to neutralize charges on suspended particles, causing them to clump together into larger particles called floc. This is necessary because the particles are too small to settle on their own. Sedimentation follows coagulation - it's where the heavy floc settles to the bottom. Aeration adds oxygen and distillation is a completely different process involving boiling and condensation.

Permanent hardness of water is caused by dissolved chlorides and sulfates of calcium and magnesium, which cannot be removed by boiling. Washing soda (sodium carbonate decahydrate, Na2CO3·10H2O) removes permanent hardness through a chemical reaction: sodium carbonate reacts with calcium and magnesium salts to form insoluble carbonates that precipitate out, softening the water. Potassium permanganate, chlorine, and bleaching powder are disinfectants/oxidizers, not water softeners.

Water filter is the correct answer because it's not an aquarium filter type. Under Gravel Filter, Hang on Back (HOB) filter, and Sponge filter are all specific types of filtration systems used in fish tanks. A water filter is a general term for filtering drinking water, not designed for aquariums.

Grey water is the term for gently used water from bathroom sinks, showers, and washing machines that can be reused for purposes like landscape irrigation. It's distinct from black water (sewage) and fresh water.

Permanent hardness is caused by dissolved calcium and magnesium sulfates/chlorides that can't be removed by boiling. Washing soda (sodium carbonate) softens water by precipitating these ions as insoluble carbonates. Chlorine and bleaching powder are disinfectants, while potassium permanganate is an oxidizing agent - none remove hardness.

Ultraviolet rays are used to clean water in modern filters. Most ultraviolet purification systems are combined with various forms of filtration, as UV light is only capable of killing microorganisms such as bacteria, viruses, molds, algae and yeast. UV light generally has no impact on chlorine, VOCs and heavy metals.

This is the correct option. WWTP stands for Waste Water Treatment Plant.

This is the correct option. The treatment of sewage at WWTP involves processes like sedimentation, filtration and chlorination. 

This is the correct option as this statement is false. The treatment of sewage consists of three stages - primary treatment, secondary treatment and tertiary treatment.

This is the correct option as this is done in the third stage of sewage treatment. In the third stage of primary treatment, the water is passed through the sedimentation tanks.

Yes, it gets hard and blocks the drain. It reduces the filtering capacity of soil pores.

Yes, it is correct, as germs cannot be removed by physical process only. It is removed by the chemical process, in which chlorination is done.

Yes, it is correct. Chlorination is an excellent way to disinfect drinking water supplies.

Sulphurous acid is the chemical compound with the formula H₂SO₃. It is used as reducing agents and as disinfectants.They are also mild bleaches, and are used for materials which may be damaged by chlorine-containing bleaches.