Heat Treatment for Dewatering Waste
Activated Sludge in Pulp Mill Waste Treatment
O. H. MOSS, Engineer
A. E. HABERER, Associate Engineer
C. A. BARTON, Group Leader
Environmental Control Section
The Procter & Gamble Company
Cincinnati, Ohio
INTRODUCTION
In the fall of 1970, the Charmin Paper Products Company, a wholly owned
subsidiary of the Procter & Gamble Company was searching for a better method to
condition waste activated sludge from the secondary treatment facilities at its
Mehoopany, Pennsylvania mill. The waste treatment facilities at this new mill on the
banks of the Susquehanna River provide in excess of 90 percent BOD and suspended
solids removal. The cost of this vast waste treatment complex exceeded $10 million,
with an annual operating cost of approximately $2.5 million. Upon consideration of
all the alternatives, including an existing polyelectrolyte system the Porteous Process
was selected as most probably the best solution to the sludge conditioning problem.
The ability of heat treatment to condition sewage sludges for dewatering has
been known for many years (1, 2, 3, 4). W. K. Porteous is generally credited with
developing the initial concepts of the process in 1934. However, most of the early
batch-type operations were European installations and, consequently, the acceptance
of heat treatment has only come to the forefront in this country in recent years. This
influx of interest was primarily generated by the development of a continuous
process to replace the semi-continuous batch operations of the past.
Therefore, to evaluate the process and the associated vendor hardware, a 3 gpm
pilot plant was rented from BSP Corporation. The unit was installed on site in
Mehoopany and operated during September and October, 1970.
The basic flow diagram for the Porteous Process is shown in Figure 1. After
passing through a grinder, raw sludge is fed by a ram pump through a heat exchanger,
where the sludge is preheated before going to the reactor vessel. As the preheated
sludge enters the vertical reactor standpipe, steam is injected to bring the sludge
temperature and pressure up to desired levels. The sludge then flows up the vertical
standpipe and into the reactor vessel for holding at high temperature and pressure.
Sludge is withdrawn from the bottom of the reactor after some detention time and
proceeds into another heat exchanger, where it gives up heat to water in a
closed-lOOp, counter-current flow pattern. The cooled, heat-treated sludge is then
discharged for subsequent dewatering. The heated water is circulated to the cold side
of the heat exchanger to preheat the incoming sludge as previously described.
636