Trickling requires a 1 to 3 m height gravity fall.
This basic process (photo 2) is used when a gravity fall height of 1 to 2 metres is available and when a high level of effectiveness is not required.
trickling over trays
These aerators have been more or less perfected and use a forced ventilation system.
trickling over contact media
This technique is identical to that of the standard trickling filter (see fundamental biological engineering processes applicable to water treatment).
Both the latter techniques can be used to reach extremely high rates of mass transfer and oxidation.