Mycelium helps plants absorb ...

Mycelium helps plants absorb water and nutrients, as well as build up the immunity of the trees and plants. This is called the mycorrhizal network.   Since mycelium is a type of mold, it spreads very quickly.  In Minecraft version 1.13 and below, getting rid of mycelium was quite easy. Letting water flow over the blocks would decay the mold and destroy it. However, after version 1.13 was released, this feature was removed. Getting rid of mycelium in versions 1.14+ is hard, but still possible

Fungus absorbs nutrients from its environment (substrate, log, etc) through its mycelium in a two-stage process. First, the hyphae secrete enzymes into the decaying wood or other substrate. These enzymes break down biological polymers into smaller units such as monomers.  Water Distillers are another way to remove nitrates from water. It easily removes nitrates and other sediments, including complex elements, by the distillation process. It is a process where the unwanted chemicals and substances are removed from water by evaporation on the water’s surface.