How is static electricity used in the real world?

Answer 1

One example:

To reduce pollution from smoke stacks, or to purify air within households, companies/individuals use a filtration system called an electrostatic precipitator (ESP).

The system works by passing smoke through a grid of electrically charged rods. The particles in the smoke pick up a charge of Q. The smoke then travels through a series of plates that have a charge of -Q. Since opposite charges attract, the particles cling to the plates. The plates are then shaken so that the ash falls into a hopper that can be removed and discarded.

This process can reduce air pollution from a smoke stack by 99%.