Liquefied air gases find many applications in waste water treatment. Most are non-cryogenic, for example ozone generation for oxidation of persistent pollutants, or oxygen for aerobic wastewater treatment.
Treated water from anaerobic wastewater plants often contains no oxygen. Liquid oxygen can be used to re-oxygenate the water prior to discharge.
The liquid state of the gas is mainly utilized to facilitate its transport and storage. Liquefied gas occupies only a fraction of the volume of gaseous gas, even when the latter is compressed to high pressures.