Environmental Engineering Reference
In-Depth Information
Corrective actions
(note that corrective actions for filter fly problems
revolve around the need to disrupt the fly's life cycle—about 7 to 10 days
in warm weather)
•
Increase the recirculation rate to obtain a hydraulic loading of at
least 200 gpd/ft
2
. At this rate, filter fly larvae are normally flushed
out of the filter.
•
Clean filter walls and remove weeds, brush, and shrubbery around
the filter. This removes some of the area for fly breeding.
•
Dose the filter periodically with low
chlorine concentrations (less
than 1 mg/L). This normally destroys larvae.
•
Dry the filter media for several hours.
•
Flood the filter for 24 hr.
•
Spray the area around the filter with
insecticide. Do not use insec-
ticide directly on the media because of the chance of carryover and
unknown effects on the slime populations.
7.3.7.5 Freezing
Symptoms
•
Decreased air
temperature results in visible ice formation and
decreased performance.
•
Distributed wastes are in a thin film or spray. This is more likely to
cause ice formation.
Causal factors
•
Recirculation causes increased temperature drops and losses.
•
Strong prevailing winds cause heat losses.
•
Intermittent dosing allows water to stand too long, causing
freezing.
Corrective actions
(all are based on a need to reduce heat loss as the
wastes move through the filter)
•
Reduce recirculation as much as possible to minimize cooling
effects.
•
Operate two-stage filters in parallel to reduce heat loss.
•
Adjust splash plates and orifices to obtain a coarse spray.
•
Construct a windbreak or plant evergreens or shrubs in the direc-
tion of the prevailing wind.
•
If intermittent dosing is used, leave dump gates open.
•
Cover pump wet wells and dose tanks to reduce heat losses.
