Final answer:
The process of reversing water flow to clean a sand filter is known as backwashing. This technique is part of the filtration process in water treatment to maintain the efficiency of the filtration system by flushing out trapped particles.
Step-by-step explanation:
The process of reversing water flow to remove accumulated particles from inside a sand filter is called backwashing. This maintenance technique is commonly used in the filtration process of water treatment plants to clean the filters that have collected solids during the water purification process. After the floc has settled during the sedimentation stage, the clear water on top moves through filters composed of sand, gravel, and sometimes charcoal, which trap particles. Over time, these filters get clogged, and backwashing is performed to flush out the trapped particles and maintain the efficiency of the filtration system. Backwashing can be seen as a form of pressure filtration, where water is forced in the reverse direction through the filter, thereby cleaning it.