PHYSIOCHEMICAL TREATMENT OF TANNERY WASTEWATER
BY ELECTROCOAGULATION
Ernest R. Ramirez, Manager for Environmental Evaluation
Swift Environmental Systems Company
Oak Brook, Illinois 60521
L. K. Barber, Director of Manufacturing
A. C. Lawrence Leather Company'
Winchester, New Hampshire 60521
O. A. Clemens, Director
Swift Environmental Systems Company
Oak Brook, Illinois 60521
INTRODUCTION
Tannery wastewater treated in this paper deals with the A. C. Lawrence Leather Company, Inc. plant situated in Winchester, New Hampshire.   The plant processes approximately 2500 sheepskins per day in a one-shift operation.  Wastewater generated during a
15-hr period amounts to approximately 400,000 gal.  The tannery does not have a beam
house, and the following operations are carried out at the plant:   aqueous cleaning and
degreasing, both chrome and vegetable tanning, drying, buffing and dyeing.
Substantial amounts of salt and surfactant are used in the operation. Also, organic
dyeing of the pelts is carried out.   The tannery obtains  its water from the Ashuelot River.
A small part of its water also comes from the city. The city of Winchester, New Hampshire
has no municipal treatment plant and, therefore, the tannery discharges its effluent waters
directly into the Ashuelot River.
Due to the high usage of surfactants and emulsifiers in the soaking and cleaning operation, the lanolin and suspended materials are extremely well emulsified.   This condition requires that substantial amounts of trivalent metal coagulants be used to break the emulsion
if the primary treatment is to be effective.
PRINCIPLES INVOLVED IN ELECTROCOAGULATION
AND ELECTROFLOTATION
During the summers of 1973 and 1974, pilot studies using a 10-gpm flow rate showed
that best results are obtained when electrocoagulation is carried out in a sequential two-
step operation.   All attempts made to carry out primary wastewater treatment with the
wastewater from Winchester tannery showed that a simple flotation principle was totally
inadequate to satisfactorily treat this type of wastewater.   The high density of the suspended
material (dirt and grit in the skins), together with the low surface tension of the wastewater, strongly favored settling of the metal coagulant and pollutants in the physiochemical
treatment.   It became apparent that if treatment was to be carried out at rates of 400 or
500 gpm in a small flotation basin (20 to 25 min dwell time), that something would have
to be done to lower the specific gravity of the floe prior to the electroflotation step.
Details on the principles involved in electrocoagulation and electroflotation have been
discussed elsewhere [1-8].   It was soon found that an electrocoagulation chamber, having
a dwell time between 1 /2-min and 3 min, would adequately  meet the requirement of reducing the apparent specific gravity of the floe to a value of about 0.8 g/cm3.
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