Test: Problems In Filter Operation - Civil Engineering (CE) MCQ

Explanation: When cleaned bed is put into operation, the loss of head through it is 15-30cm and it goes on increasing as impurities are arrested in filter media.

Explanation: As the thickness of suspended matter on top of the sand bed increases, the head loss is increased. So, it is directly proportional to head loss.

Explanation: The head becomes negative when the loss of the head through the bed depth exceeds the static head.The negative head is the fall of liquid level in the piezometric tube below the center line of under drainage system.

Explanation: The permissible negative head loss of a rapid sand filter is 0.8-1.2m. When the permissible limits are reached, the filter run is terminated and the filter is back washed.

Explanation: Clogging of bed is caused due to accumulation of solids on the top surface of filter media, which results in the formation of mud balls and cracking of the bed.

Explanation: Mud balls are formed in filters due to insufficient washing of sand grains. Mud accumulates on the sand surface and form a dense mat.

Explanation:The cracking of bed is more prominent near the wall junction which allows dirty matter to penetrate into filter media which decreases the efficiency of filtration.

Explanation: During Sand leakage, layers of gravel are displaced during back-washing. This can be minimized by proper proportioning of sand and gravel layers.

Explanation: The tendency of jetting can be minimized by surface washing. It can also be minimized by the use of an 8cm layer of coarse garnet between fine media and gravel.

Explanation: Air binding is caused by the released of dissolved air and gases from water to form bubbles which occupy void space of the filter media and the drainage system.