Overaeration

Overaeration refers to the introduction of air into a liquid at a rate or extent that drives the dissolved gas concentrations above the equilibrium with the liquid. This results in dissolved gas supersaturation and increased exchange of gases with the atmosphere, often accompanied by surface agitation and foaming. It differs from intentional aeration, which aims to raise dissolved oxygen to a target level without producing supersaturation.

Overaeration can occur in natural or engineered systems when aeration equipment or high mixing energy transfers more air than the liquid can hold. Examples include wastewater treatment processes with aggressive diffusers, aerated stabilization ponds, rapidly mixing tanks, or spillways and turbines that cause intense surface turbulence. It can also occur during rapid depressurization of a saturated liquid, causing release of dissolved gases.

Biological and chemical consequences include gas bubble disease in aquatic organisms caused by supersaturated gases, disruption of normal gas exchange, and pH changes from loss of dissolved carbon dioxide. In wastewater and industrial settings, overaeration increases energy use, promotes foaming, can degrade flocculation and settleability of solids, and may strip volatile compounds such as ammonia, altering nutrient balance and odor emissions.

Prevention and control involve balancing aeration needs with energy use, using appropriate diffuser types and layouts, implementing feedback control on dissolved-oxygen levels, and avoiding excessive surface agitation. De-aeration steps or staged aeration can be used to prevent or reverse unwanted supersaturation where needed.