United States
Environmental Protection
Agency
Industrial Environmental Research
Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S2-80-210 Jan. 1981
Project Summary
Innovative Destruction of
Complex Industrial Wastes
Auto Oxidation of Tannery
Beamhouse Wastewater
David G. Bailey
This project was intended to obtain
data on the effectiveness of a novel
destruction technique for treating
potentially toxic pollutants from a
wide range of manufacturing sources.
The particular waste used for evalua-
tion was a tannery unhairing effluent.
The novel technique examined was an
auto-oxidation process.
Tannery unhairing waste was
treated in a pilot plant scale auto-
oxidation unit designed and built by
Technical Associates for Industry.
Inc., Red Bank, New Jersey 07701.
This waste is highly alkaline with a pH
generally higher than 11 and has a
COD greater than 50,000 mg/liter,
consisting largely of protein and
sulfide. The auto-oxidation pilot plant
in static tests effectively and rapidly
removed sulfide from the waste.
Removal of COD, nitrogen, and
suspended solids was considerably
less effective. Combining the auto-
oxidation with ultraviolet light and a
hydrogen peroxide addition improved
the COD removals very little.
Introduction
In 1968, the Hides and Leather
Laboratory was approached by
Technical Associates for Industry (TAFI)
with a proposal to test an innovative
process for treatment of tannery lime-
sulfide unhairing wastes. TAFI is a
small, private consulting firm. Their
general interest was in treatment of
industrial and municipal wastes to meet
regulatory limits. Their experience to
date, on treatment of wastes with this
process, was on municipal sludges and
industrial wastes with high carbohy-
drate content. The process is b.ased on a
free-radical, auto-oxidation mechanism
of breakdown of the waste. The free
radicals are produced by passing the
solution under pressure through an
orifice. The basis for free radical produc-
tion was proposed by N. Zaleiko during
treatment. The collapse of gas bubbles
in cavitation can develop very high local
temperatures. Under adiabatic condi-
tions, gas temperatures at the minimum
bubble radium can reach 2,000°F.
There, local high temperatures can be
expected to lead to ionization effects
and the production of hydroxy-free
radicals and peroxides. Extensive cavi-
tation effects on the oxidation of phenol
are described by Chen et al.
The effluent stream from the unhair-
ing process in a tannery is a difficult
waste to treat by conventional methods.
Typical composition of unhairing waste
is: BOD, 20,000 ppm; COD, 40,000 to
60,000 ppm; solids, 50,000 ppm; pH,
12.5; and sulfide, 1,000 to 3,500 ppm.
The beamhouse process starts by
soaking hides in water in order to rehy-
drate them and to remove salt. The
soaked hides are then placed in a 2-4%
calcium hydroxide suspension along
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with approximately 2% by weight of the
hide of sodium sulfide in order to
dissolve the hair. The hides may then be
relimed with additional calcium
hydroxide or simply washed. From this
stage they continue into the actual
tanning process.
Conclusions
The innovative treatment of tannery
wastes, using the oxidative pilot plant
manufactured by TAFI, rapidly removed
sulfide from tannery limesulfide unhair-
ing effluent. Removal of COD,
suspended solids, and nitrogen under
the conditions studied was not effective.
The excessive formation of foam in this
waste might have been responsible. No
estimate of cost effectiveness was
made to determine whether this
process could be used commercially to
treat beamhouse effluent.
Experimental Procedures
The apparatus which is the basis of
this treatment process, the oxidation
pilot plant, is detailed in Figure 1. The
material to be treated was pumped from
a feed tank (250 gal) into a reservoir
which was maintained at a level of
approximately 18 gal. The treated solu-
tion flows out of the system through the
overflow at the same rate that feed was
pumped into the system. Solution from
the reservoir was pumped by a 5 hp
circulation pump through the oxidation
nozzle and back to the reservoir through
a %" ID copper pipe at a rate of 5
gal/min. The oxidation nozzle was
essentially a constriction in the recycle
loop. As the solution flowed out of the
nozzle, the pressure on the solution was
rapidly reduced causing cavitation. At
the same time, air was incorporated into
the loop to prevent the level of dissolved
oxygen from dropping to zero. Two types
of tests were run on the apparatus. The
first, referred to as a static test, consis-
ted of recycling the solution to be
treated from the reservoir, through the
pump and around the loop, through the
oxidation nozzle and back into the
reservoir. No additional feed was added.
In a continuous run, the second type of
run, the reservoir and the overflow from
the treatment was allowed to flow out
into a final tank or into a drain. At a later
stage of the research, an ultraviolet
lamp was added to the system
positioned directly at the end of the
oxidation nozzle. When used in the
experiments, hydrogen peroxide was
pumped into the system as indicated
just before the pump. Metal salts, when
added for catalysis, were added in the
reservoir or dissolved in the feed tank. In
a continuous run, the feed was typically
added at a rate of 0.3-0.5 gal/hr.
Samples were taken for evaluation of
treatment from the overflow. The
analyses were performed according to
standard methods except as indicated.
Analyses reported are:
.Oxidation Nozzle
Pressure
Gauge
Circulation
Pump
Figure 1. Schematic of auto-oxidation pilot plant.
2
Feed Tank
1. Sulfide (s=),
2. Total Kjeldahl nitrogen using a
Technicon autoanalyzer (n),
3. TOC (total organic carbon) using a
Beckman TOC instrument,
4. COD (chemical oxygen demand)
performed by the techniques
developed by Oceanography and
accepted by Standard Methods,
5. Suspended solids (ss), and
6. Volatile suspended solids (vs).
Results
The removal of sulfide by this method
was consistent and rapid in the static
tests. Initial sulfide concentrations in
these runs were between 150 to 500
ppm. In less than 100 min, the sulfide
concentrations were reduced to less
than 2 ppm in each of the trial runs. This
was consistent even when the pH
dropped as low as 8.5. Presumedly, the
sulfide was oxidized to sulfate. The
changes in TKN, TOC, COD, suspended
solids and volatile solids were small and
not consistent.
Continuous waste treatment was
done with a 10:1 dilution of the original
waste. A continuous trial can be started
in two ways. The reservoir and oxidation
loop can be filled with the diluted waste
solution to be treated or with tap water.
Approximately 150 min at 0.5 gal/min
was required to approach a steady state
between the solution being added and
the contents of the reservoir, when the
system starts with water. Sulfide reduc-
tion under these conditions was
between 25 and 50%. Little change in
TOC, suspended solids, and volatile
solids was observed, although there
was a small overall reduction.
Continuous runs were repeated using
a more conventional 2-hr settled waste
as the starting material. The dilution
was again 10:1. In these runs, samples
were taken from the storage or feed tank
as well as from the reservoir overflow.
Only slight reductions were observed in
any of the parameters when compared
to those from the feed-tank solution.
Within the scatter of the values ob-
tained, no trend is apparent.
A preliminary bench-top experiment
was performed to examine the effect of
addition of peroxide, ultraviolet light,
and copper ions to tannery limesulfide
unhairing solutions. The procedure
followed was to place 1 liter of unhair-
ing waste in a beaker with constant
stirring under a Phipps-Bird apparatus.
Samples were then taken at 0, 15, 36
90, and 120 min and at 20 hr. Samples
were analyzed for pH, sulfide, tot
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Kjeldahl nitrogen, TOC, COD, sus-
pended and volatile solilds. The control
samples showed no change. Addition of
ultraviolet light to the solutioin did not
alter values over the 20-hr period.
David G. Bailey is with the U.S. Department of Agriculture, Eastern Regional
Research Center. Philadelphia. PA 19118.
Mark J. Stutsman is the EPA Project Officer (see below).
The complete report, entitled "Innovative Destruction of Complex Industrial
Wastes—Auto Oxidation of Tannery Beamhouse Wastewater," (Order No.
PB 81-129 025; Cost: $6.50. subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Industrial Environmental Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
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•ft U S GOVERNMENT PRINTING OFFICE, 1981 — 757-012/0759
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Environmental Protection
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Center for Environmental Research
Information
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