Environmental Engineering Reference
In-Depth Information
Corrective actions:
Use the procedure described below to deter-
mine the appropriate sludge depth:
−
Clean bed and apply smaller depth of sludge (e.g., 6 to 8 in.).
−
Measure the decrease in depth (drawdown) at the end of 3
days of drying.
−
Use a sludge depth equal to twice the 3-day drawdown depth
for future applications.
Allow the sludge to dry to the minimum allowable percent solids
and remove. After the sludge has dried, remove the sludge and
0.5 to 1.0 in. of sand and add clean sand. Use an external water
source (with backflow prevention) to slowly flush underdrains;
repair or replace underdrains as required. Prevent damage to the
underdrains by draining during freezing weather. Use polymer to
increase bed performance, and cover or enclose the beds.
•
symptom 2.
Influent sludge is very thin.
Causal factor:
Coning in the digester
Corrective action:
Reduce rate of sludge withdrawal.
•
symptom 3.
Sludge feed lines plug frequently.
Causal factor:
Solids or grit accumulating in the lines
Corrective actions:
Open lines fully at the start of each with-
drawal cycle; flush lines at the end of each withdrawal cycle.
•
symptom 4.
Flies are breeding in the drying sludge.
Causal factors:
Inadequately digested sludge; natural insect
reproduction
Corrective actions:
Break sludge crust, and apply a larvicide
(borax); use insecticide (if approved) to eliminate adult insects;
remove sludge as soon as possible.
•
symptom 5.
Objectionable odors are detected when sludge is
applied to the bed.
Causal factor:
Raw or partially digested sludge applied to the bed
Corrective actions:
Add lime to the sludge to control odors and
potential insect and rodent problems; remove the sludge as
quickly as possible; identify and correct the digester problem.
10.7.2 rotary vacuum filtration
Rotary vacuum filters have also been used for many years to dewa-
ter sludge. The vacuum filter includes filter media (belt, cloth, or metal
coils), media support (drum), vacuum system, chemical feed equipment,
and conveyor belts to transport the dewatered solids. Chemically treated
solids are pumped to a vat or tank in which a rotating drum is submerged.
As the drum rotates, a vacuum is applied to the drum. Solids collect on
