Environmental Engineering Reference
In-Depth Information
Corrective actions
(listed in
increasing
impact on the quality of the
plant effluent)
•
Remove all leaves, sticks, and other debris from the media.
•
Increase recirculation of dilute, high-strength wastes to improve
sloughing to keep voids open.
•
Use a high-pressure stream of water to agitate and flush the ponded
area.
•
Rake or fork the ponded area.
•
Dose the filter with
chlorine solution for 2 to 4 hr. The specific
dose of chlorine required will depend on the severity of the pond-
ing problem. When using elemental chlorine, the dose must be suf-
ficient to provide a residual at the orifices of 1 to 50 mg/L. If the
filter is severely clogged, the higher residuals may be required to
unload the majority of the biomass. If the filter cannot be dosed by
elemental chlorine, chlorinated lime or hypochlorite powder may
be used. Dosing should be in the range of 8 to 10 lb of chlorine per
1000 ft
2
of media.
•
If the filter design permits, the filter media can be flooded for a
period of 4 hr. Remember, if the filter is flooded, care must be taken
to prevent hydraulic overloads of the final settling tank. The trick-
ling filter should be drained slowly at low low periods.
•
Dry the media. By stopping the flow to the filter, the
slime will dry
and loosen. When the flow is restarted, the loosened slime will flow
out of the filter. The amount of drying time will be dependent on
the thickness of the slime and the amount of removal desired. Time
may range from a few hours to several days.
Note:
Portions of the media can be dried without taking the filter out of
service by plugging the orifices that normally service the area.
If these corrective actions do not provide the desired improvement,
the media must be carefully inspected. Remove a sample of the media
from the affected area. Carefully clean the sample, inspect it for its solid-
ity, and determine its size uniformity (3 to 5 in.). Media that appear to be
decomposing or are not uniform should be replaced.
7.3.7.2 Odors
Frequent offensive odors usually indicate an operational problem.
These foul odors occur within the filter periodically and are normally
associated with anaerobic conditions. Under normal circumstances,
a slight anaerobic slime layer forms due to the inability of oxygen to
penetrate all the way to the media; however, under normal operation,
the outer slime layers will remain aerobic, and no offensive odors are
produced.
