Removal of White Water Effluent
Turbidity by Biological
Treatment Processes
WILLIAM L. CARPENTER, Research Associate
National CouncU  of the Paper Industry for Air and Stream Improvement, Inc.
Department of Geography and Environmental Engineering
The John Hopkins University
Baltimore, Maryland
JAMES R. JANIS, Staff Engineer
Consumer Protection and Environmental Health Service
U. S. Public Health Service
Washington, D. C.
INTRODUCTION
This paper is a summary of earlier work conducted by the authors (1). It is the
purpose of this study to discover why turbidity is removed in biologic treatment; to
determine which operating parameters are significant in obtaining high removals; and
to determine which starches contribute most to high effluent turbidities.
Properties of Papermill Whitewater
This study deals with effects of three major contributors to papermUl white-
water turbidity; kaolin, Ti02, and starch. Van Olphen (2) indicates that the paper
industry is the largest single user of kalonite clays; consuming about 50 per cent of the
production. Clays are applied as fillers and coatings in uncoated, coated and fine
papers.
Titanium dioxide, even more than kaolin, contributes to Whitewater turbidity
(3) since it has high optical scattering powers, thereby reducing the light transmitted
in straight lines through a water sample.
Although small amounts of both kaolin and Ti02 will remain in suspension
naturally, the paper industry uses binders such as starch to obtain highly opalescent
(and thus highly turbid) coating waters, commonly called "colors," these are mUky-
white suspensions applied in thin layers during the papermaking process. Starch acts
as a stabUizer in the colloidal system by forming protective colloids, literally coating
small particles and preventing attractive van der Waals forces from destabilizing the
system. Other additives are also used in the paper process: dispersants (polyphosphates), flow modifiers (sodium sUicates), lubricants (sodium stearate) and a myriad
of others. Each mill has its own formula and to describe their effects on turbidity
would require at least another paper. But starch is universally used in conjunction
with these other additives, and its presence provides some of the most difficult wastewater turbidity removal problems. A description of starches used in this study (provided by the National Starch and Chemical Company) is summarized in Table I.
These are 1) pearl starch, a potato derivative; 2) a lightly oxidized starch (LOS)
described by the manufacturer as low chlorination; 3) a highly oxidized starch (HOS)
described as high chlorination; 4) a cationic surface sizing starch (CAT-B); and 5) a
cationic wet-end additive starch (CAT-A). The abbreviations used are the author's.
Pearl and oxidized starches have been used in the paper industry for years, but
cationic starches have gained prominence only recently. The most important attribute
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