DEWATERING OF A BIOLOGICAL SLUDGE FROM A
PAPER MILL WASTEWATER TREATMENT PLANT
Roger O. Dickey, Project Engineer
Roger C. Ward, Project Manager
Howard, Needles, Tammen & Bergendoff
Indianapolis, Indiana 46268
The high disposal cost of aerobically digested waste activated sludge from a paper mill
(Container Corporation of America) secondary wastewater treatment plant prompted a
search for a less costly sludge disposal system. Candidate sludge thickening and dewatering
systems were identified, screened, and evaluated. Bench and pilot scale tests were performed
as an integral part of the cost evaluation and final system design. A belt press sludge dewatering system was constructed, and its full-scale performance has been documented.
The paper mill secondary wastewater treatment plant in Wabash, IN, consists of an activated sludge process which treats paper mill primary effluent and municipal primary effluent
from an adjacent municipal wastewater treatment plant. The municipal wastewater is added
for cooling and nutritive purposes.
Figure 1 is a schematic of the paper mill secondary wastewater treatment plant and the
municipal wastewater treatment plant. Table I lists the typical wastewater treatment plant
influent characteristics.
The paper mill primary sludge is recycled to the paper making process for recovery of
paper fiber. The municipal primary and waste activated sludges are anaerobically digested.
The secondary wastewater treatment plant generates between 1600 and 2300 pounds per
day (dry solids basis) of aerobically digested waste activated sludge. This sludge gravity
thickens to only 1.0 to 1.5% solids, producing a large and costly volume of liquid sludge
for disposal on land application sites.
Mechanical thickening or dewatering was deemed necessary to reduce the volume of
sludge for ultimate disposal to a manageable and less costly amount.
The approach taken for selection of the best sludge thickening and/or dewatering system consisted of three phases: (1) preliminary screening of candidate systems; (2) economic
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Figure 1. Schematic of wastewater treatment plant.
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