Section 16. TANNERY WASTES
IMPROVED COLOR REMOVAL IN
SPENT VEGETABLE TANNING LIQUORS
Janice L. Suddath, Engineer
AWARE, Inc.
Nashville, Tennessee 37204
Edward L. Thackston, Chairman
Department of Civil and Environmental Engineering
Vanderbilt University
Nashville, Tennessee 37235
The need for cost effective treatment methods for vegetable tanning wastes has long been
recognized. Most attention has been focused on wastewaters from chrome tanning processes, the most prevalent type of tanning in the United States. The vegetable process, the
oldest and slowest (and probably the least efficient) of the tanning processes, has declined
in the U.S. in recent years because of its high cost and pollutional problems. There are
probably not more than a dozen significant vegetable tanneries left in the U.S. and most of
them are concentrated in the Northeast. In its development for the leather tanning industry
[ 1 ], the EPA recognized the pollutional problems of highly colored spent vegetable tanning
liquors, but did not set color limits due to insufficient data on color problems throughout
the industry.
Studies conducted at Vanderbilt University between 1968 and 1970 by Koon |2],
Tomlinson and co-workers [3-6], and Thackston [7], explored treatment options for a
small tannery using alum, chrome and vegetable tanning processes. A report summarizing
the conclusions of these studies [7] indicated that the spent vegetable tanning liquors,
representing a small fraction of the tannery's total wastewater flow, were somewhat resistant
to treatment and interfered with biological treatment of the remaining wastewaters. Segregation and separate treatment of these special wastes was therefore recommended. In subsequent studies with a laboratory blend of vegetable tanning extracts [5,6], Tomlinson
developed a new treatment scheme which achieved 95% color reductions by coagulating the
liquors at their approximate isoelectric point (pH 2.3) with cationic polymers. This approach
was not immediately pursued due to questions concerning its cost-effectiveness for general
use in the tanning industry. However, the development of increasingly stringent effluent
guidelines for this and other industries has focused attention on treatment technologies
previously considered economically unfeasible.
PURPOSE OF RESEARCH
This report explores the application of Tomlinson's proposed treatment scheme for
waste vegetable tanning liquors in an attempt to make it economical for general use. It is
hoped that the results of this work will aid in alleviating some of the high costs pollution
control problems of the vegetable tanning industry and give it a chance to survive the competition from other tanning processes and foreign competition. The investigation of complex
physical-chemical mechanisms was beyond the scope of this study, even though such work
could undoubtedly contribute much to the understanding of coagulation phenomena.
After a new literature search was conducted and several chemical companies were contacted for information concerning polymers which could be used as primary coagulants
for tannery wastes, the laboratory investigation was designed to include:
801