Water Treatment Plant Units Questions and Answers

Answer: D

The common methods of desalinating water are distillation (the water is evaporated and condensed, leaving the salts behind), reverse osmosis (water is forced through a semi-permeable membrane at a pressure above the osmotic pressure) and electrodialysis (ions are drawn out of the water through ion-selective membranes in an electric field). Filtration, by itself, removes suspended solids but not dissolved salts, so the options that list it are wrong.

Answer: C

The incorrect statement is Screening is to remove objectionable tastes, odours and to remove dissolved gases from the water.

Screening is the first treatment step: bar screens remove large floating and suspended material such as leaves, sticks and debris. Removing tastes, odours and dissolved gases such as carbon dioxide and hydrogen sulphide is the job of aeration.

The other three statements are correct: raw water contains suspended, colloidal and dissolved impurities; disinfection, especially the residual chlorine it leaves, protects water against contamination on its way to consumers; and waterborne diseases are caused by pathogenic organisms.

Answer: D

The process is Filtration.

After coagulation and sedimentation, very fine suspended particles, colloidal matter and many bacteria still remain. Passing the water through a bed of sand in slow or rapid sand filters removes them by straining, sedimentation in the pores, adsorption and biological action.

Screening removes only large floating matter before treatment, sedimentation is the stage these particles have escaped, and disinfection kills pathogens rather than removing fine particles.