Civil Engineering Reference
In-Depth Information
Fig. 9-13.
Schematic of a mechanical aeration process
The main advantages of spray aeration are that gas transfer between water drops
and air is rapid, and the system can be aesthetically pleasing. Disadvantages include
potential operating difficulties from icing problems during freezing weather, large
space requirements, high discharge head requirements, and potential clogging of nozzle
orifices, particularly with hard waters.
Spray aeration typically involves spraying water into the open atmosphere, often
into a reservoir or a concrete or earthen basin. Nozzles are often fixed on a pipe grid.
They may also be enclosed in a tower, allowing additional mass transfer as droplets
descend through a countercurrent airflow.
Two common types of spray nozzles are the hollow cone and the full cone. In a
hollow-cone nozzle, a rim of spray is concentrated around the nozzle circumference,
with a ''hollow'' area in the center of the spray jet's cross section. This type of nozzle
produces smaller droplets but requires more pressure for the same amount of flow
through the nozzle. With full-cone nozzles, the water is delivered uniformly, generally
in a round cross-sectional pattern.
Design of Spray Aeration Systems
Typical design values for spray aeration are
shown in Table 9-7. The size, number, and spacing of spray nozzles depend on the
