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Measurement, Control and Changes in
Foaming Characteristics of Pulping
Wastes during Biological Treatment
WILLIAM L. CARPENTER, Research Associate
ISAIAH GELLMAN, Regional Engineer
National Council for Stream Improvement
Baltimore, Maryland
INTRODUCTION
Foaming problems are frequently encountered during discharge and biological
treatment of pulp and paper mill effluents. Extent of foam formation is contributed
by a number of factors including receiving water effluent content, turbulence,
outfall design, effluent composition, extent of treatment, and foam control measures. Excessive foam can give rise to unsightly receiving water conditions while
process control both in waste treatment and pulp and paper making is made difficult by excessive foam. Where foaming is severe, effective but costly defoaming
treatment is employed. Aside from unsightly plant conditions and hazards to
operating personnel, excessive foam can also impede oxygen transfer during biological treatment of the wastes.
In contrast to the prevelance of these problems, the lack of adequate methods
for characterizing foaminess and of experimental data on the control of, or changes
in, foaminess during biological treatment led to an experimental study at our
laboratory. The study had the following objectives: 1) Development of a standardized procedure for measurement of foaminess; 2) Determination of the degree to
which biological treatment reduces the foaminess of the wastes: 3) Evaluation of
the effectiveness of various foam control formulations during biological treatment
and identification of possible adverse effects on treatment; and 4) Identification
of possible systems and techniques which may be employed to eliminate effluent
foam problems.
SOURCE OF FOAM PRODUCING M/ TERIALS AND RESULTING PROBLEMS
Pulping Operations
Foaming of pulping waste is reportedly (1,2) associated with the type of wood
furnished and recovery practices employed. The basic sources of foams in kraft
pulp mills are the lignin, resin, and fatty acids of the cellulose binding materials
in the wood. Those species characterized by a great deal of pitch, such as southern pines, contribute large quantities of sulfate soaps to the spent cooking liquor
with subsequent appearance of foams. Derivatives of tall oil (a by-product of
kraft pulping) form principal ingredients of most soaps. Sulfonates of lignin formed
during sulfite pulping account for a large portion of the foam produced by these
effluents. In addition, mixing of different effluent streams such as alkaline and
acid bleach plant effluents result in additional foam generation due to evolution of
chlorine from the liquid. Presence of foam in the pulp mill is demonstrated by
interference with pulp washing and screening processes and black liquor evaporator
operation, thus causing excessive chemical losses.
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