Which of the following is a method by which mud can accumulate in a filter?

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Mud can accumulate in a filter when fine solids bind together into ball-shaped aggregates. These mud balls form from clay and silt fines that get sticky, often with help from microbial activity and organic matter, creating a cohesive mass that behaves like a single particle. As water moves through the filter media, these balls get trapped in the spaces between grains and can grow, reducing pore space, causing clogging and uneven flow. They can also break loose and be carried by backwash if not removed, contributing to persistent buildup inside the filter bed. This specific ball-like accumulation explains how mud can accumulate inside a filter, which isn’t described by a surface crust of sand or by mere changes in temperature or pH.