In a filtration system, adding an anthracite coal layer over greensand primarily improves which performance aspect?

In a filtration system, adding an anthracite coal layer over greensand primarily improves which performance aspect?

• A. greater iron-holding capacity
• B. longer filter run times
• C. higher degree of coal and greensand mixing, aiding adsorption
• D. less floc penetration into the greensand

Answer: (B)

Adding an anthracite top layer changes how the bed handles particulates and how quickly it becomes clogged, which mainly extends how long you can run the filter before backwashing. The coal layer provides a more porous, coarse surface that catches larger particles early and protects the deeper greensand from rapid clogging. That keeps the headloss from rising as quickly, so you can operate longer between cleanings. Greensand still handles oxidation and removal of metals like iron, but the coal top’s benefit is primarily the longer run time due to improved filtration performance and reduced clogging.

Adding an anthracite top layer changes how the bed handles particulates and how quickly it becomes clogged, which mainly extends how long you can run the filter before backwashing. The coal layer provides a more porous, coarse surface that catches larger particles early and protects the deeper greensand from rapid clogging. That keeps the headloss from rising as quickly, so you can operate longer between cleanings. Greensand still handles oxidation and removal of metals like iron, but the coal top’s benefit is primarily the longer run time due to improved filtration performance and reduced clogging.