Wet scrubbers work by contacting the contaminated gas stream with a liquid solution, usually water, to effect removal of the contaminant from the gas stream. This removal occurs in one of two principal ways. If the contaminant is a particulate the removal mechanism is by a physical separation of the particles from the gas stream, i.e., by impaction and diffusion. If the contaminant is a gas, then the removal mechanism is absorption of the gas into the liquid.
In some cases, wet scrubbers can be used to do both simultaneously. For example, in a process gas stream coming from a coal-fired boiler the gas stream contaminants may include both sulfur dioxide (gas) and fly ash particulate (solids) and both can be captured in a single wet scrubbing system.