17    IMPROVING STABILITY OF A PAPER MILL SLUDGE
Amalendu Bagchi
Environmental Engineer, Department of Natural Resources
Madison, Wisconsin 53707
INTRODUCTION
The following two major issues are associated with the disposal of paper mill sludges: leachate
containment and stability of the sludge. This paper will discuss the second issue. Stability of the sludge
will dictate the allowable top and side slopes of a paper mill landfill. Stability of a sludge can be
improved by dewatering and by mixing with other material like wood bark, flyash, etc. The case study
cited here deals with improving stability by mixing with flyash. A study was undertaken for improving
stability of the sludge generated by the wastewater treatment plant at Rhinelander Paper Company
(hereafter called Ripco.) The sludge disposed in the landfill is a mixture of approximately 80%
secondary process sludge and 20% primary process sludge (average of 35,000 cubic yd/yr). The paper
mill buys pulp for its use. The major products of the paper mill are: release paper, grease proof paper,
etc. Small quantities of flyash and bottom ash (approximately 4,000 cubic yd/yr), generated by the
mill, are also disposed at the landfill.
Figure 1 shows a plan view of the new landfill which has a 2-foot clay liner and a leachate collection
system. Original approval allowed 13.6 acres of landfill area (subdivided into three phases: phase
1-6.6 acres, phase II-4 acres, phase III-3 acres) for a total air space of 350,100 cubic yards. After the
'slope study', discussed in this paper, Ripco was permitted to increase top slope of the landfill from 8:1
(horizontahvertical) to 6:1 for all three phases. As a result of this increase of top slope the total
available air space in phases I and II increased to almost approved volume for all the three phases. So,
at present, Ripco has decided not to build phase III which will result in substantial savings for disposal
of the sludge.
Around 1984 cell A of the landfill was near capacity and cell B was ready for use. Sludge was piled
along the cell A/cell B boundary to a slope of 5:1 approximately. During spring of that year, the slope
at the interface of cell A and B failed and a significant volume of sludge 'flowed' into cell B. At that
time the overall stability of the top surface of the landfill was also poor. Ripco was asked to take
Figure 1.   Plan view of old and new landfills.
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