Treatment of Pulp and
Paper Mill Waste for High Rate
Filtration Using Plastic Filter Media
W. WESLEY ECKENFELDER, JR., Associate Professor of Sanitary Engineering
and
EDWIN L. BARNHART, Research Associate
Department of Civil Engineering
Manhattan College
Riverdale, New York
In recent years plastic filter media has been applied to the treatment of
pulp and paper mill wastes. Hydraulic loadings as high as 4.0 gpm/ft2 and
organic loadings as high as 800 lbs BOD/1000 ft3/day have been employed.
BOD removals as high as 50 per cent have been reported under these conditions.
The performance of these filters has been related to the filter depth, the
contact time between waste flow and filter surface and the quantity of active
slime on the filter media. This paper presents results obtained relating contact time to filter surface and on the BOD removal capacity of two types of
filter media in the treatment of dilute black liquor and a board mill waste.
RESIDENCE TIME RELATIONSHIPS
It has long been recognized that the time of contact of a waste with a
filter surface influences the BOD removal rate. Time of contact is in turn
related to the hydraulic loading and to the presence of filter slime. Typical
results obtained on various filter media relating mean contact time to hydraulic loading are shown in Figure 1. It is apparent from Figure 1 that increasing the hydraulic load will decrease the mean residence time. A general relationship developed by the authors showed that contact time per unit
filter depth is related to the specific surface (ft2/ft3) ofthe filter media and
to the hydraulic loading through the relationship:
t/D . C^ CD
in which t = mean residence time
D = filter depth
C = constant
Ay = specific surface
Q = hydraulic loading
m & n = constants
In Equation (1) m is a constant for any geometrically similar media and
n decreases as Av decreases.
The presence of filter slime influences the residence time-hydraulic
loading relationship. Bloodgood, et al. (1), showed that for flow over an inclined plane, the increase in retention time in the presence of slime employ-
- 105  -