Concrete tanks are typically used when installing
package plant oxidation ditches. This results in
lower maintenance costs as concrete tanks do not
require periodic repainting or sand blasting.
Fabricated steel or a combination of steel and
concrete can also be used for construction,
depending on site conditions (Lakeside, 1999).
The volume of the oxidation ditch is determined
based on influent wastewater characteristics,
effluent discharge requirements, HRT, SRT,
temperature, mixed liquor suspended solids
(MLSS), and pH. It may be necessary to include
other site specific parameters to design the
oxidation ditch as well.
Some oxidation ditches do not initially require
clarifiers, but can later be upgraded and expanded
by adding clarifiers, changing the type of process
used, or adding additional ditches (Kruger, 1999).
PERFORMANCE
The performance of package plants in general can
be affected by various operational and design issues
(Metcalf and Eddy, 1991).
? Large and sudden temperature changes
? Removal efficiency of grease and scum from the
primary clarifier (except with oxidation ditches
that do not use primary clarifiers)
? Incredibly small flows that make designing self-
cleansing conduits and channels difficult
? Fluctuations in flow, BOD5 loading, and other
influent parameters
? Hydraulic shock loads, or the large fluctuations
in flow from small communities
? Sufficient control of the air supply rate
Extended aeration plants