reaeration

Reaeration is the process of reintroducing atmospheric air into a liquid, typically water, to increase dissolved oxygen (DO) levels and to exchange gases such as carbon dioxide and methane. In environmental engineering and limnology, reaeration describes gas transfer across the air–water interface that replenishes oxygen consumed by organisms and oxidation processes.

In natural aquatic systems, reaeration occurs primarily at the water surface through wind-driven turbulence, waves, and mixing. The rate depends on the reaeration coefficient (often denoted k2), which is influenced by surface area, temperature, water depth, wind speed, and the presence of surface films or pollutants. Accurate estimation of k2 is important for modeling DO dynamics and ecosystem health.

In wastewater treatment, reaeration refers to supplying air to biological treatment units to maintain aerobic conditions for microbial degradation of organic matter. It is achieved by diffused-air systems (fine or coarse bubble diffusers), surface aerators, or jet and spray systems. Proper reaeration prevents oxygen depletion, enables nitrification and biological oxidation, and helps volatilize some gases.

Measurement and design tools include oxygen transfer rate, oxygen transfer efficiency, and mass-transfer coefficients (kLa in stirred tanks, k2 in natural waters). Determining DO sag and oxygen uptake rate guides process optimization and environmental impact assessments. Operational factors such as energy consumption, and potential foaming or biofilm formation influence performance.

Reaeration is a key concept in water quality management, contributing to aquatic habitat health, odor control, and treatment plant performance. Related topics include gas transfer, aeration, and dissolved oxygen modeling.