Environmental Engineering Reference
In-Depth Information
method for dewatering sludge. Moreover, no special training or expertise
is required. The downside, however, is that drying beds require a great
deal of manpower to clean them, they can create odor and insect prob-
lems, and they can cause sludge buildup during inclement weather.
10.7.1.1 Performance Factors
In sludge drying beds, various factors affect the length of time
required to achieve the desired solids concentrations. The major factors
and their impact on drying bed performance include the following:
•
Climate—
Drying beds in cold or moist climates will require signifi-
cantly longer drying times to achieve an adequate level of percent
solids concentrations in the dewatered sludge.
•
depth of applied sludge—
The depth of the sludge drawn onto the bed
has a major impact on the required drying time. Deeper sludge layers
require longer drying times. Under ideal conditions, a well-digested
sludge drawn to a depth of approximately 8 inches will require
approximately 3 weeks to reach the desired 40 to 60% solids.
•
Type of sludge applied—
The quality and solids concentration of the
drying media will affect the time requirements.
•
Covered drying beds prevent rewetting of the sludge
during storm events. In most cases, this reduces the average drying
time required to reach the desired solids levels.
Bed cover—
10.7.1.2 Operational Considerations
Although drying beds involve two natural processes—drainage and
evaporation—that normally work well enough on their own, a certain
amount of preparation and operator attention are still required to main-
tain optimum drying performance. In the preparation stage, for exam-
ple, all debris is removed from the raked and leveled media surface, then
all openings to the bed are sealed. After the bed is prepared properly, the
sludge lines are opened, and sludge is allowed to flow slowly onto the
media. The bed is filled to the desired operating level (8 to 12 inches).
The sludge line is closed and flushed, and the bed drain is opened. Water
begins to drain. The sludge remains on the media until the desired per-
cent solids (40 to 60%) is achieved. Later, the sludge is removed. In most
operations, manual removal is required to prevent damage to the underd-
rain system. The sludge is disposed of in an approved landfill or by land
application as a soil conditioner. In the operation of a sludge drying
bed, the operator observes the operations, looks for various indicators
of operational problems, and makes process adjustments as required.
Following are some examples:
•
symptom 1.
Sludge takes a long time to dewater.
Causal factors:
Sludge applied too deep; sludge applied to a dirty
bed; plugged or broken drain system; insufficient design capacity;
inclement weather; poor drying conditions
