DEWATERING OF DISSOLVED AIR FLOTATION SLUDGE
BY CENTRIFUGATION
James Alton Caruthers, Graduate Student
Franklin E. Woodard, Associate Professor
Civil Engineering Department
University of Maine
Orono, Maine 04473
INTRODUCTION
As society demands greater effluent water quality from its industries, the cost of obtaining that quality has greatly increased.   With this increased cost, it has become desirable for industries to decrease waste loads and to reuse or recycle waste products as a
means of minimizing the cost of treatment.
The poultry processing industry in Maine has a market for the sludge that it obtains
from the treatment of its wastewaters.   By increasing the concentration of solids in the
sludge, the cost of transportation of the sludge to the rendering plant and the cost of
energy required in evaporation could be greatly reduced, thereby making the finished
product more marketable.
The objective of the study was to determine the feasibility of dewatering this waste
sludge by centrifugation.   In order to carry out this feasibility study, it was necessary to
determine the centrifuging characteristics of the sludge and the predictability of these
characteristics.
A preliminary study was carried out to determine the sludge characteristics and the
variability of each.   The effects of these variations were then related to centrifuge performance.   A mathematical model was developed to predict the total solids in the pellet
and the volume of the pellet on the basis of retention time, centrifugal force, total solids
in the raw sludge and the grease concentration in the raw sludge.
EXPERIMENTAL SLUDGE
The sludge used in this work was obtained at the Penobscot Poultry Company in Belfast, Maine.   This plant processes 70,000 to 90,000 chickens per day and produces whole
and cut-up chickens for the retail trade.   The waste loads from the plant are shown below
and the plant flow chart in Figure 1.   The waste load figures are per bird and for an average production of 72,000 birds per day.
12 gallons of water
0.0397 #BOD
0.0333 #SS
0.0229 # Grease
From this waste flow most blood, feathers and pieces of chicken larger than a 60-mesh
screen are removed before they reach the treatment plant.   The treatment plant, as shown
in Figure 2, is a dissolved-air flotation system with alum and an anionic polymer being
added to the waste before flotation [ 1 ].   The system produced approximately 4000 gal
of floated sludge per day.   This sludge is highly variable in nature and has the following
characteristics:
Total Solids
9 to 18%
pH
5.0 to 5.8
Grease
30 to 75 g/1
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