____________, often known as water cleaning, is the process of eliminating contaminants from wastewater before it may be reused or delivered to water bodies. (knowledge)

The correct answer is: Sewage treatment

• Sewage treatment is the process of waste water treatment 
• Sewage is the waste water that gets collected due to various activities like domestic and industrial work
• The sewage is carried to the treatment plant through a network of pipes called sewerage
• In the treatment plant, the sewage is subjected to suitable treatment methods like biological or chemical or physical methods (based on the nature of waste water), before it can be reused or fed into water bodies