EPA R2-73-209
_ Environmental Protection Technology Series
APRIL 1973
Secondary Waste Treatment
for A Small Diversified Tannery
Office of Research and Monitoring
U.S. Environmental Protection Agency
Washington, D.C. 20460
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and
Monitoring, Environmental Protection Agency, have
been grouped into five series. These five broad
categories were established to facilitate furt1 er
development and application of environmental
technology. Elimination of traditional grouping
was consciously planned to foster technology
transfer and a maximum interface in related
fields. The five series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
This report has been assigned to the ENVIRONMENTAL
PROTECTION TECHNOLOGY series. This series
describes research performed to develop and
demonstrate instrumentation, equipment and
methodology to repair or prevent environmental
degradation from point and non—point sources of
pollutidn. This work provides the new or improved
technology required for the control and treatment
of pollution sources to meet environmental quality
standards.
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EPA-R2-73-209
April 1973
SECONDARY WASTE TREATMENT FOR A
SMALL DIVERSIFIED TANNERY
by
Edward L. Thackston
Grant No. WPRD 25-01
Project 12120EFM
Project Officers
James J. Westrick
James Kreissl
U.S. Environmental Protection Agency
National Environmental Research Center
Cincinnati, Ohio 45268
Prepared for
OFFICE OF RESEARCH AND MONITORING
U.S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402
Price $1.25 domestic postpaid or SI GPO Bookstore
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EPA REViEW NOTICE
This report has been reviewed by the Environmental
Protection Agency and approved for publication.
Approval does not signify that the contents necessarily
reflect the views and policies of the Environmental
Protection Agency, nor does mention of trade names
or commercial products constitute endorsement or
recommendation for use.
II
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ABSTRACT
The CoIdwell Lace Leather Co. of Auburn, Kentucky, a small
tannery using primarily alum tanning but some chrome and vegetable
tanning, received a demonstration grant in 1967 from the FWPCA to
investigate and demonstrate methods of treating tannery wastes for
discharge to a small stream. research contract with Vanderbilt Uni-
versity produced findings which have previously been reported and are
reviewed herein.
A modified completely—mixed activated sludge plant was constructed,
along with facilities to handle specific problem wastes. After operating
for a year, an EPA survey team conducted a study which showed that the
plant was performing as predicted by the research phase, except for solids
carryover from the secondary clarifier due to mechanical problems. After
the problems were corrected, the plant began producing an effluent which
more than met expectations, removing 97% of the suspended solids and
95% of the BOD. Due to conservation measures inside the tannery,
however, the load on the plant is somewhat less than the design load, so
the plant is operating as an extended aeration plant.
II I
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TABLE OF CONTENTS
Page
A BSTRA CT . . . . . . . . . . . . . . .
TABLE OFCONTENTS v
LIST cDF FIGURES. ix
LIST OF TABLES . . . . . . . . . . . . . . . . x i
CON.JCLUSIONS 1
INTRODUCTION 3
BRIEF LITERATUREREVIEW . . . . . . . . 5
THEMANUFACTURING PROCESS...... 7
Wastewater Characteristics 9
Alum Tanning Process Waste Characteristics 9
Chrome Tanning Liquor Characteristics 12
Spent Vegetable Tanning Liquor 12
Alum Tanning Process Composite Characteristics 13
POLLUTIONAL LOAD 15
TREATMENT PROCESSES INVESTIGATED 17
Pretreatment 17
Sedimentation Studies 17
Spent Chrome Tanning Liquor Treatment 20
Spent Vegetable Tanning Liquor 22
Color Removal from Dye Wastes 27
Biological Treatment 29
Organic Content Reduction by Activated Sludge 31
Oxygen Requirements of Biological Unit 35
PROPOSED WASTE TREATMENT SYSTEM 37
V
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TABLE OF CONTENTS (continued)
Page
PROCESS DESIGN RECOMMENDATIONS . . . . . . . . . . . . . 39
TREATMENT PLANTDESIGN •. . . . . •......... . . • 41
General Description of Waste Treatment Plant 41
Detailed Description of Plant Treatment Units and
Design Criteria 42
Chrome Tanning Solution 42
Vegetable Tanning Liquor 42
Spent Dye Solutions 42
Screening and Equalization 43
Equalization Basin 43
Primary Clarifier 44
Aeration Basin 44
Final Clarifier 45
Sludge Concentration and Storage Tank 45
Lime Waste Storage 45
Nutrient Requirements 45
Laboratory Building 46
CONSTRUCTION AND STARTUP . . . . . . . . . . . . . . . . . 47
EVALUATION OF PLANT PERFORMANCE . . . . . . . . . . . . . 49
Water Flow 49
Summary of Plant Performance 50
BOD and COD Load 52
Organic Matter Removal 57
Solids 58
Ntrogen 60
Water Temperature 61
pH 61
Sulfides 62
Phosphorus 62
Dissolved Oxygen 62
Heavy Metals 63
Coliform Bacteda 64
vi
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TABLE OF CONTENTS (conflnued)
Page
TREATMENT PLANTOPERATION . •....... . . . . •.... 65
PLANT PERFORMANCE SINCE EPA SURVEY . . . . . . . . • • • 67
ACKNOWLEDGEMENTS. . . . . . . . . . . • • • 71
REFERENCES . . . . . . . . . . . . . . . . . . . . 73
v i i
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LIST OF FIGURES
No. Page
1 ALUM TANNING PROCESS AT CALDWELL LACE LEATHER
COMPANY 8
2 COD AND TURBIDITY OF SUPERNATANT AFTER LABORATORY
SEDIMENTATION AS A FUNCTiON OF pH 18
3 ZETA POTENTIAL OF SUPERNATANT AS A FUNCTION OF pH 18
4 SLUDGE INTERFACE SETTLING CURVE FOR ALUM TANNING
PROCESS COMPOSITE WASTE 20
5 TOTAL CHROMIUM IN SUPERNATANT AS A FUNCTION
OFpH 21
6 COLOR REMOVAL FROM SPENT DYE SOLUTION BY
ACTIVATED CARBON 28
7 TWO FILL-AND-DRAW UNITS 29
8 CONTINUOUSLY FED ACTIVATED SLUDGE UNITS 30
9 OXYGEN UPTAKE OF UNACCLIMATED ACTIVATED SLUDGE
FED TANNERY WASTES 31
10 COD REMOVED AS A FUNCTION OF LOADING 32
11 COD REMAINING AS A FUNCTION OF AERATION TIME 34
12 BOD OF INFLUENT AND EFFLUENT OF CONTINUOUS
FLOW SYSTEM 34
13 OVERALL TREATMENT SCHEME PROPOSED FOR THE
CALDWELL LACE LEATHER COMPANY 38
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LIST OF TABLES
No. Page
1 CHEMICAL CHARACTERISTICS OF ALUM TANNING PROCESS
WASTES AT THE CALDWELL LACE LEATHER COMPANY 10-11
2 CHARACTERISTICS OF SPENT VEGETABLE TANNING LIQUOR 12
3 CHARACTERISTICS OF ALUM TANNING PROCESS COMPOSITE
WASTES AT THE CALDWELL LACE LEATHER COMPANY 14
4 WEEKLY POLLUTIONAL LOAD FROM TANNING OPERATION 15
5 TOTAL DAILY WATER USAGE FEBRUARY THROUGH AUGUST
1967 16
6 EFFECT OF pH ON COLOR INTENSITY OF SPENT VEGETABLE
TANNING LIQUOR 23
7 EFFECTS OF ACETONE TREATMENT OF SPENT VEGETABLE
TANNING LIQUOR 23
8 TREATMENT OF SPENT VEGETABLE TANNING LIQUOR
WITH ALUM TANNING SOLUTION 24
9 ANALYSIS OF VEGETABLE TANNING LIQUOR TREATED
WITH ALUM TANNiNG LIQUOR 25
10 QUALITATIVE RESULTS OF SELECTED COMPOUNDS FOR
COLOR REMOVAL FROM SYNTHETiC DYE MIXTURE 26
11 REMOVAL OF COLOR BY TWO ACTIVATED CARBON
COLUMNS IN SERIES--RUN NO. 2 27
12 COMPARISON OF COD AND BOD VALUES 33
13 WATER FLOW DURING SURVEY 50
14 MEAN VALUES OF PARAMETERS DURING EPA SURVEY 51
x i
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LIST OF TABLES (continued)
No. Page
15 BOD LOAD DURING SURVEY 52
16 COD LOAD DURING SURVEY 53
17 BOD LOADING RATES DURING SURVEY
18 COD LOADING RATES DURING SURVEY 55
19 ORGANIC MATTER REMOVALS DURING EPA SURVEY 58
20 SUSPENDED SOLIDS DURING EPA SURVEY
21 MEAN VALUES OF NITROGEN FORMS DURING EPA SURVEY 59
22 MEAN VALUES OF HEAVY METALS DURING EPA SURVEY 63
23 COLIFORM COUNTS DURING EPA SURVEY 64
24 PLANT PERFORMANCE IN 1972 67
X I I
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CONCLUSIONS
This project showed that wastes from a small tannery using the alum tanning
method principally, with small amounts of chrome and vegefable tanning,
can be treated effectively, by adjustments of convenflonal methods, for
discharge into a small stream without damage. The design of the completely
mixed activated sludge plant was based on a laboratory pilot plant study,
and the operating results of the full—scale plant closely duplicated the
results of the laboratory study.
Results of a survey of the operation of the full—scale plant showed BOD
removals of 93% and COD removals of 88 /c. Both would have been higher
had not a problem with the sludge return system caused excessive solids
carryover from the secondary clarifier during the survey.
Implementation of the recommendations of the EPA survey team and con-
sultants resulted in improved operation during 1972. By mid—1972, SS
reductions of 97% and BOD removals of 96% were being achieved.
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INTRODUCTION
In 1967, the CaIdwell Lace Leather Company, of Auburn, Kentucky, was
awarded research and demonstration grant No. WPRD 25-01, by the Federal
Water Pollution Control Administration, now part of the Environmental Pro-
tect ion Agency (EPA) to develop and demonstrate methods for the treatment
of tannery wastes.
This tannery is unusual, and possibly unique, in that all three major tanning
processes——chrome fanning, alum tanning, and vegetable tanning——are carried
out at the same location. Thus, there was an opportunity to work with a wide
variety of waste streams, and to determine the effect each would have on the
waste treatment process. In addition to the actual tanning processes, the waste
treatment plant would also be required to handle the wastes from the leather
finishing operations, such as fat liquoring and dyeing.
Tannery wastes ore not a large part of the overall pollution problem in the
United States, but they can cause severe localized problems. Typically, tan-
nery wastes are highly concentrated, both in terms of organic matter and
inorganic ions; and the batch nature of the tanning process results in a waste
stream which varies radically with time. These characteristics have made com-
plete biological treatment of tannery wastes rare in the past.
It was anticipated that design parameters developed through this study would
be applicable to the tanning industry in general. While previous work had been
concentrated on pretreatment schemes, this study was to investigate and de-
velop a treatment method for the tannery wastewaters so that they could be
discharged directly into a small receiving stream.
The tannery is located on the bank of Black Lick Creek, a small stream which
rises about 0.5 miles south of the town of Auburn. The stream then flows north-
ward through the town and adjacent farmland for about three miles until it
disappears in a series of sinkholes and enters the underground water streams
which flow through the cavernous limestone which underlies most of central
Kentucky.
The waste treatment plant of the City of Auburn is located directly across the
creek from the tannery. When the municipal treatment plant was built, if was
intended to serve the entire city, including the tannery. However, the design
failed to take into account the particular characteristics and high strength of
tannery wastes and was never able to operate satisfactorily. In an effort to
eliminate the impact of the tannery on the treatment plant, the city began by-
passing the tannery wastes directly into the creek.
3
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When the impact of the tannery wastes on the stream was brought to the
attention of the tannery officials by the Kentucky Health Department, they
agreed to construct and operate their own waste treatment plant and applied
to FWPCA for techrikal assistance because of the absence of available infor—
mation on methods of complete treatment of tannery wastes. The research and
development grant was the result of this appeal.
In the first phase of this project, the Caldwell Lace Leather Company awarded
a contract to Vanderbilt University, of Nashville, Tennessee, to investigate
the characteristks of the different waste streams and to develop treatment
methods. This “research phase” of the project was completed in September,
1967, and the results were reported by Tomlinson, Thackston, et al. (1)(2).
The consulting firm of Howard K. Bell and Associates, of Lexington, Kentucky,
was retained to design a treatment plant embodying the concepts and features
recommended by the research team. The treatment plant design was approved
by the Kentucky Department of Health and bids For construction were called
for. Because of difficulties in construction unrelated to the treatment process
or the plant design, completion of construction was delayed until December,
1970.
Difficulties in start—up were also encountered, and it was May, 1971, before
the treatment plant began functioning smoothly. In November, 1971, a team
from the EPA conducted a survey of operation of the treatment plant to deter-
mine the effectiveness of the treatment being provided.
This report will review the characteristics of the wastes generated by the tan-
nery and associated operations, describe the research which led to the design
of the treatment process, describe the process and treatment plant design, and
report onhe results being achieved by the treatment plant. It will serve as the
final report to EPA on the demonstration grant. It will borrow heavily on the
already published reports mentioned earlier for the research and design phases,
on the design report of Howard K. Bell and Associates, and on the report of
the EPA industrial waste survey team for the section on results being achieved.
4
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BRIEF LITERATURE REViEW
The brief survey of the literature presented here was originally conducted in
1967. Since then, several significant articles and reports have been published.
However, these have not been included in this literature survey because they
were not available to the researchers at the time the work was being done. Thus,
this survey briefly outlines the state—of—the—art of tannery waste treatment at the
time of conception of the treatment plant which is the subject of this report.
The effects of tannery wastewaters on receiving streams and treatment facilities
have been of concern to the tanning industry and to sanitary engineers for many
years, although significant progress in devising suitable treatment techniques
has been minimal. There have been a number of review and summary type articles
on tannery process description, wastewater characterization,and suggested treat-
ment techniques (3) (4) (5) (6) (7) (8) (9) (10) (11). The data indicate that the
wastes are highly variable in composition because of the nature of the tanning
process. The most extensive description is possibly that of Mosselli, Masselli,
and Burford (6).
There are several types of tanning processes, and the use of any of the processes
is considered an art, with each individual tanner developing his own procedure
and processing solutions. The types of treatment used for tannery waste gener-
ally have been limited to screening, flow equalization, and plain sedimenta-
tion or chemical precipitation, followed by treatment combined with municipal
wastewaters. The success of biological treatment processes has been limited
because of the high BOD concentration of the wastes, the extreme variability
with time, and the presence of toxic components in the wastes. In spite of an
extensive literature search, little was found in the way of laboratory or design
data for complete treatment schemes. However, the information uncovered is
valuable as background and for defining the problem.
In addition to the general review type of article, the literature contains a
large number of articles describing the treatment of tannery wastes in combina-
tion with municipal wasfewaters. Typical published reports (12) (13) (14) (15)
(16) (17) (18) (19) (20) (21) (22) indicate that the tannery wastewaters are
amenable to combined treatment with municipal wastewater if the ratio of
tannery waste flow to total flow does not exceed approximately 25 percent.
Also, it has been emphasized that pretreatment of the tannery wastes, including
hair and fleshings removal, neutralizaHon, and/or equalization, is important
for satisfactory operation of the combined plant. The disposal of sludge produced
from the treatment of tannery washes is reported as being one of the major prob-
lems of tannery waste treatment. It does not dewater well and tends to clog
vacuum filters. The high concentrations of inorganic ions tends to hamper
5
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separate anaerobic digesfion. Since the purpose of this study was to develop
methods for treating tannery wastes alone, this portion of the literature was
not pursued extensively.
Parker (23) reported on the use of spray irrigation for the disposal of the
wastewaters from a large tannery which used the vegetable tanning process.
Once operating problems were overcome, the process apparently was successful
in disposing of the wastes without nuisance. However, large amounts of land
are required for this method.
Studies also have been conducted on possible methods of treatment of selected
waste streams from a tannery. For example, Berg et al. (24) investigated the
use of manganese for the precipitation of sulfides from beam-house wastes.
Also, other physical and chemical methods have been investigated for suspended
solids and biochemical oxygen demand removal from tannery wastewaters em-
ploying the chrome tanning process. Sproul e l al. (25) (26) reported good
reductions in BOD and suspended solids by using the spent chrome liquors as
coagulants. The use of organic polyelectolytes also was invesHgated.
The references mentioned in this brief literature survey are only a portion of
the total articles published in the worldwide literature. Eye and Graef (27)
published a bibliography of 245-articles relating to tannery effluents. If is
interesting to note that many of the articles first were published in European
journals, thus indicating the geographical extent of the interest in treatment of
wastewaters from tanneries.
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THE MANUFACTURiNG PROCESS
The leather production facilities at Caidwell Lace Leather Company generally
could be described as typical of a small tannery. The manufacturing processes
are conducted by use of conventional lime pits, Fleshing and unh&ring machines,
rotary drums, and rocker vats (for vegetable tanning). Approximately 85 per-
cent of the leather production at this plant at the time of the study was by the
alum tanning process, with chrome—fanned leather and vegetable—tanned leather
accounting for approximately equal fractions of the remaining 15 percent.
The green salted hides first are soaked in three separate changes of water for
a total of 24 hours to wash off the extraneous dirt, salt, and manure. They
then are placed in a Ume solution For seven days to loosen the hair and swell
the hides. Small quantities of sulfides also are added to aid in this process.
Each lime pit is used twice before discharge.
On removal from the lime pits, the hides are passed through successive machines
for removal of hair and flesh particles. The hides then are washed in a continu-
ous stream of water for about 30 minutes to remove the excess lime. To remove
the remaining lime and the soluble proteinaceous material, the hides are placed
in a rotating drum containing ammonium chloride and an enzymatic compound
containing trypsin. After two hours in this ‘ bating” solution, the hides are
rinsed again.
Up to this point, the hides have all recved essentially the same treatment.
Afterwards, the treatment varies with the type of tanning.
The hides slated to undergo alum tanning are pickled in an acid and sodium
chloride solution in a rotating drum and the alum solution then is added directly
to the drum. After tanning, the hides are split and shaved to uniform thickness,
and sent to the dyeing plant. Since the alum tan is not water resistant, the dye-
ing must take place in an alum tan solution. Oils and fats then are added and
the hides taken out and allowed to dry. Figure 1 is a schematic of the alum
tanning process.
The chrome tanning process is similar to the alum tanning process except the
pickling solution is slightly different. Chromium sulfate is used as a tanning
agent instead of alum, and a re—tan is not necessary during dyeing.
In the vegetable tanning process, the hides are soaked in vats containing solu-
tions of bark extracts and synthetic tanning agents for about five weeks before
washing and dyeing. The waste discharge from this process is relatively small,
but quite troublesome because of very high solids content, color, and COD.
7
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Soaking and Washing
Batch
.1 Discharqe
Lime
Sodium Sulfide
-J Liming
Unhairing and Hair Washing
4
LF1e ing J
1
Lime Washout
Batch
Discharge
1 Intermittent
I Wash Water
Internii ttent
Wash Water
J 30 Mins.
@ 90°F
OroDon XX
Triton Xll4
Na Cl
Al urn
H 2 S0 4
L
f
Bate and Delirne
1
Bate and Delime Washout
Pickle and Alum Tan
3
1 Batch
J Discharge
J Batch
Discharge
Drying
Acid
Al tim
NaC1
Sodium Acetat 1.
Oils
Dyes
air —I Retan
I Coloring and Fatliquoring
I Finishing Department I
1 Batch
J Discharge
FIGURE 1 - ALUM TANNING PROCESS AT CALDWELL LACE
LEATHER COMPANY
8
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Studies of water—use records for a two—month period revealed that the average
total water use was 520 gal/i 00 lb (2,200 1/100 kg) of hides processed. The
processes contributing the most wastewater were the de—lime and bate wash, the
lime wash, and the soak. The processes contributing the greatest pollution load,
in terms of COD, were the lime pits discharge, the de—lime and bate wash, the
spent dye solution, and the spent vegetable tanning liquor.
Wastewater Characteristics
Considerable effort was expended during the project to analyze the different
types of wastewater emanating from the tannery.
The samples collected included grab samples from each major process step, com-
posite samples of total alum tanning process wastes, and a weekly composite from
the effluent of the existing holding tank. Other samples were collected at
selected times and locations to aid in the overall evaluation of the wastewater
problem. The alum tanning process composite wastewater samples were prepared
by collecting spent liquors from the various operations and combining the different
wastes on the basis of the quantity of the flow discharged from each process.
Alum Tanning Process Waste Characteristics
The average pollutional characteristics of the waste streams from the individual
operations in the alum tanning process (Table 1) differ widely.
The wastewater from the lime pit is basically a lime—saturated solution contain-
ing undissolved lime, hair, and dissolved proteinaceous material, and represents
the waste with the highest COD. The high neutralizing capacity of this waste
can be used to good advantage in the overall treatment scheme. Although the
pH of the composite sample from the lime washout operation was high (11 .2),
chemical analysis and the e(ectrometrk titration curves indicated that the caustic
alkalinity and buffering capacity of this waste stream was limited.
The wastewater from the pickling—alum tanning solution can be described best
as an acidic salty solution of aluminum sulfate containing considerable quantities
of dissolved organic material. The electrometric titration curve for the spent
pickling—alum tanning solution suggested that the high mineral acidity of this
waste stream could be used to reduce the alkalinity of the wastes from the previous
processes by combining the waste streams.
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TABLE 1 - CHEMICAL CHARACTERISTICS OF ALUM TANNING PROCESS
WASTES AT THE CALDWELL LACE LEATHER COMPANY *
Parameter
Washing
and
Soaking
Lime
Pit
Discharge
Lime
Washout
Bate
and
Delime
Washout_ -
Spent
Alum
Tanning
Liquor
Spent
Dye
Solution
Conductivity, 13,800 27,000 2,600 4,400 60,000
mcromhos/cm - - - -
pH 7.2 12.1 11.1 8.8 3.3 3.4
6.8—7.4 11.9—12.3 10.9—11.3 8.7—8.9 3.2—3.6 —
Phenolphthalein
Alkalinity, 4,980 180 160
mg/I as Ca CO 3 3,810—6,150 130—225 130—190
Total Alkalinity, 215 6,240 380 460
mg/I as CaCO 3 140-295 4,970—7,500 335-430 430480
Mineral Acidity, 13,400 9,600
mg/I as CaCO 3 9,000-20, 200 -
Total Acidity, 25 22,100 17,200
mg/I as CaCO 3 0-40 20,000-27,400 -
Chlorides, mg/I 5,100 11,980 580 940 33,160 25,480
osCl 2,590-8,250 8,350—15,600 530-630 710-1180 24300-38700 25250-25700
Total Hardness, 210 6,480 280 540
mg/I as CaCO 3 - -
*Values tabulated are averages with range underneath
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TABLE 1 - CONTINUED
Parameter
Washing
and
Soaking
Lime
Pit
Discharge
.
Lime
Washout
Bate
and
Delime
Washout
SDerit
Alum
Tanning
Liquor
Soent
bye
Solution
Total Solids,mg/I 109,800
Fixed Solids,mg/I 54,630
Suspended Solids, 1,720
mg/I -
COD, mg/I 1,190 11,720 800 1,620 5,400 5,330
925-1670 9760-13,800 780-830 1600-1640 2750-7300 5050-5610
BOD, mg/I - 2,750 5,000
Ammonia Nitrogen, 26 169 15 358 456
mg/I
Organic Nitrogen,
mg/I 12 168 12 26 15
Total Phosphate,
mg/I 8 3 7 4 6
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The spent dye solution for the alum fanning operations is basically the same
as the alum tanning solution, with the addition of dyes and oils. The only
other difference is that somewhat smaller quantities of salt and acidic com-
pounds are used in the preparation of alum tanning dye solution.
Chrome Tanning Liquor Characteristics
The spent chrome liquor contained between 400 and 600 mg/I of chromium,
had a COD of 4,300 mg/I, and had a chloride content of 72,000 mg/I. The
pH of the spent chrome tanning liquor ranged between 3.5 and 4.5, and had
a characteristic light blue color. The characteristics of the wastes from the
coloring operation following chrome tanning were essentkzlly the same as those
from the coloring operation following alum tanning, except for the lack of
alum. The ratio of pounds of chrome tanned hides to gallons of spent chrome
liquor was about lOto 1.
Spent Vegetable Tanning Liquor
A sample of the spent vegetable tanning liquor was obtained as it was discharged
from the last vat (No. 5) to the plant sewer. Chemical analyses of this dis-
charge (Table 2) show that the solution is essentially a colloidal suspension of
the bark extracts, which are largely tonnins.
TABLE 2 — CHARACTERISTICS OF SPENT VEGETABLE TANNING LIQUOR
Characteristic
Concen—
tration
Suspended solids, mg/I
1,840
Total solids, mg/I
76,600
Total volatile solids, mg/I
24,000
Total fixed solids, mg/I
52,600
Chemical oxygen demand,
mg/I
51,600
5-Day BOD, mg/I
2,500
Ultimate BOD, mg/I
7,500
pH
Color, Caldwell color units
5.0
95
12
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The color of the spent vegetable tanning liquor is different in hue and tint
from the commonly—used platinum—cobalt standards, making comparison with
the standards difficult. Therefore, the optical density of the solution was
measured with a spectrophotometer at a wavelength of 420 mu and converted
to “Caidwell Color Units” by use of a standard curve. Twenty Caldwell color
units have an optical density of 0.56.
Alum Tanning Process Composite Characteristics
Since this tanning process results in a series of batch discharges throughout
the operating day, it was decided to collect samples of wastewater From each
operation and prepare composite process samples, based on the daily volume
of waste discharged from each operation. One disadvantage of the method of
compositing employed was that wastewater resulting from floor washings was
not included in the final composite. The overall net effect of this method of
sampUng was to obt&n composite samples in which the concentration ofpollu—
tants would be somewhat higher than if they had been collected from the total
plant effluent, since comparison with the process wastes showed that the floor
washings were relatively free of pollutants. However, the weight of pollutants
discharged could be assumed to be approximately the same as would be obtained
from the plant effluent.
Later laboratory studies indicated that color removal by biological treatment
was not effective. Therefore, composite samples were prepared with and
without the spent dye solutions. Characterisfics of the composite samples are
presented in Table 3.
The different composite samples prepared varied during the course of the study
because they were prepared from different batch discharges. The mayor dif-
ferences among the composite samples were in the variables pH, alkalinity,
and acidity because of the highly variable characteristics of the lime pit dis-
charges. The organic content as measured by chemical oxygen demand was
relatively unchanged at approximately 3,000 mg/I, and the biochemical oxy-
gen demand of the composite samples w’ s relatively stable at from 22 to 35
per cent of the chemical oxygen demand.
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TABLE 3.--CHARACTERI STI Cs OF ALUM TANNI NG PROCESS
COMPOSI TE WASTES AT THE CALDWELL LACE LEATHER COMPANY
ConducHvity, mkromhos/cm
pH
Phenolphthalein Alkalinity
mg/I as CaCO 3
Total Alkalinity, mg/I as CaCO 3
Mineral Acidity, mg/I as CaCO 3
Total Acidity, mg/I as CaCO3
Chlorides, mg/I as Cl
Total Hardness, mg/I as CaCO3
Chemical Oxygen Demand, mg/I
Total Solids, mg/I
Total Fixed Solids, mg/I
Ammonia Nitrogen, mg/I
Organic Nitrogen, mg/i
Iota P0 4 , mg
Biochemical Oxygen Demand
5-day, 20°C, mg/I
11,000
5.5—8.5
605
1,080
none
none
3,600
1,630
2,950
10,430
7,760
145
47
5.2
650-950
Parameter
Sample
Alum
Composite
Including
Spent Dye
Alum
Composite
Excluding
Spent Dye
4.9-8.0
none
300—400
4,700
3,050
196
43
750-1050
14
-------
POLLUTIONAL LOAD
The pollufional load from the tanning operation s highly variable throughout
the operating day. Since both the wastewater characteristics and the flow
vary with individual steps in the operation, the pollutional load discharged per
unit of time throughout the day will not characterize the waste. Also, some
units are discharged only two or three times weekly. These factors make pollu—
tional load expressed on a daily basis unrealistic. The shortest time interval in
which the tanning operations are normally repetitive is one week. Although the
tannery works a five—day week, the flow must be fed to the biological treatment
units over a seven-day week. This fact, plus the need to reduce the impact of
batch discharges, will make equalization necessary. Therefore, the pollutional
load from each operation is expressed in Table 4 on a weekly basis.
TABLE 4--WEEKLY POLLUTIONAL LOAD FROM TANNING OPERATIONS
Chemical
Alka-
Total
Process
Flow
(gal/week)
Oxygen
Demand
(lbs/week)
unity
as CaCO 3
(lbs/week)
Acidity
as CaCQ3
(lbs/week)
Chlo—
rides
(lbs/week)
Soak
2 4,000
190
45
7
1020
Lime Pit
7,500
725
390
None
750
Discharge
Lime Wash
30,000
200
95
None
-
Delime &
40,000
540
150
None
313
Bate Wash
Spent Alum
3,000
135
-
550
830
Solution
Spent Dye
6,000
265
-
860
1275
Solution
Spent Vege-
600
258
None
-
-
table
Liquor
Spent Chrom
600
20
None
85
360
Liquor
TOTAL
111,700
2333
680
1502
4548
15
-------
The volumes of wastewater discharged from the tannery were determined by
daily records of total water used at the plant. Records of total daily flows
and hourly water usage that were kept from February through August of 1967
were reviewed and were used for this project. Water used for tanning opera-
tions was obtained from Black Lick Creek and was coagulated and settled
prior to use.
The mean, median, minimum,and maximum doily water usages are presented
in Table 5. It iS of interest to note that the variation of daily mean flows
during the week is less than 5,000 gallons. This is significant when determin-
ing the economical size for the equalization basin. The ratio of maximum
flow to the mean flow for a particular day of the week varied from 1 .38
(Thursday) to 1 .57 (Wednesday), and the ratio of the maximum day to the
minimum day was 2.45 Although the extreme variation was from 20,155 to
49,900 gallons per day, 80 percent of the flows were between 25,000 and
40,000 gallons per day. Over the period of record, the plant averaged 520
gallons of water for each 100 pounds of hides processed 0
TABLE 5-—TOTAL DAILY WATER USAGE
FEBRUARY THROUGH AUGUST, 1967
Day
of
Week
No. of
Obser—
vations
Flow in Gallons per Day
Mean
Median
Minimum
Maximum
Monday
Tuesday
Wednesday
Thursday
Friday
28
29
29
29
21
34,300
32,100
31,300
33,000
29,500
32,900
30,225
29,155
32,700
28,240
26,100
24,085
23,900
25,900
20,155
49,360
49,900
47,720
45,610
41,100
16
-------
TREATMENT PROCESSES INVESTIGATED
Based on the literature review, water—use records, and wastewater character-
istics, tannery waste treatment plants should include certain units or processes.
The following operations were considered during this study:
1. Screening.
2. Flow equalization.
3. pH adjustment.
4. Primary sedimentation.
5 Biological treatment and secondary sedimentation.
In addition to the major elements listed above, it was determined that certain
waste streams should receive special treatment before being discharged to the
equalization basin 0 These were:
1. Spent chrome tanning solution 0
2. Spent vegetable tanning solution.
3. Spent dye solutions 0
Pretreatment
Field studies showed that 80—mesh vibrating screens effectively screened hair,
fleshings, and leather bits from the tannery’s wastewater. However, clog-
ging was evident and a self—cleaning arrangement would be necessary.
Clogging was less severe when a 200—mesh screen was used.
Sedimentation Studies
For the sedimentation studies, a composite sample of wastes from the alum
tanning process was adlusted to various pH values with either lime or sul-
furic add. The p11—adjusted samples were flash mixed and allowed to settle
for one hour. The resulting supernatants then were analyzed for turbidity
and COD (Figure 2). Optimum pH for coagulation and sedimentation was
found to be 6.7. One hour of sedimentation removed about 71 percent of
the COD at pH 6.7 and about 64 percent at the original ph.
17
-------
5.0 6.0 7.0 8.0
pH
FIGURE 2--COD AND TURBIDITY OF SUPERNATANT
AFTER LABORATORY SEDIMENTATION AS A FUNCTION OF pH
20 - I
(1)
1-
-J
0
? 10-
-IS-
w
N 2 O
pH
FIGURE 3--ZETA POTENTIAL OF SUPERNATANT AS A FUNCTION OF pH
18
5.0
6.0
7.0
8.0
9.0
U-
0
a
U- i
zz
LIJ<
>-
xz
UJ
-Jo-
0 ( J)
UJ
0
1,050 -
000-
950-
0
CuD
0
I I I I
COD OF RAW WASTE, 3,230 mg/I
TURBIDITY
0
0
I —
z(J)
3Oo )-
20
>-u
I0
—-J
I I — I
I I
0
0
-------
The large amount of alum remaining in the spent alum tanning solution, com-
bined with the lime from the lime pit discharge, resulted in a noticeable floc
being formed in the alum tanning process wastewater composite. Ferric chlo—
ride and alum were added in increasing dosages but neither produced any
obvious improvement in the floc characteristics. The addition of cationic
polyelectrolytes was found to be even less effective than additional alum or
ferric chloride.
The zeta potential of the particles in the various supernatants also was deter-
mined. A plot of these data (Figure 3) suggests that the optimum turbidity
removal at pH 6.7 is due primarily to charge neutralization.
Floc formation was evident when the pH of the alum tanning process waste—
water composite sample was adjusted to 6.7. However, the floc formed was
light and fluffy, and might be resuspended by sludge removal facilities within
the sedimentation basin.
Anionic polyelectrolytes were found to be effective coagulant aids, which
agreed with the findings of Eye and Graef (29). Six mg/I of Nalco—675, an
anionic polyelectrolyte, were added to the raw waste and, after 30 minutes
of settling, the supernatant had a COD of 800 mg/I, approximately 15 per-
cent less than that obtained without polyelectrolyte. Even more important,
the hoc was dense and tough, and resettled rapidly when disturbed, If was
further determined that increasing the dosages of polyelectrolyte did not signi—
ficantly improve the floc properties. The anionic polyelectrolyte, DOW-A—22,
was found to have about the same effect as Nalco—675 and at approximately
the same dosage.
Surface loading rates were determined for a sedimentation basin receiving
the wastewater, which had been adjusted to a p t - 1 of 6.7, using the method
outlined by Rich (28). A one—liter graduated cylinder was filled with the pH—
adjusted waste and the location of the supernatant—sludge interface was deter-
mined at various times (Figure 4). The suspended solids concentration in the
settled sludge was 7,300 mg/I. The surface loading rate was calculated to
be 750 gal/day—sq ft with a detention time of 1 .5 hr. The resulting superna—
tant had a COD of about 925 mg/I and a total suspended solids concentration
of about 150 mg/I.
At a pH of 6.7 and a dosage of 6 mg/I of Nalco-675, the surface loading
rate was calculated to be 860 gal/day—sq ft 0 Therefore, the use of the anionic
polyelectrolyte increased the permissible sedimentation basin surface loading
rate,
19
-------
4
E
U
I
LU
I
LU
U
L&
LU
z
LU
0
C l )
ELAPSED TIME, MINUTES
FIGURE 4 - SLUDGE INTERFACE SETTLING CURVE
FOR ALUM TANNING PROCESS COMPOSITE WASTE
Spent Chrome Tanning Liquor Treatment
The spent chrome tanning liquor is a concentrated, acidic solution containing
a high concentration of chromium, chlorides, and other contaminants. Its
characteristics make it desirable to pre-treat this relatively small quantity of
waste prior to dischorge into the total waste stream. One commonly used method
of chromium removal is conversion of all chromium to the trivalent form and then
precipitation of the trivalent ions as chromium hydroxide. As the chromium ions
in the spent chrome tanning solution ore already in the trivalent form, removal of
the chrome can be accomplished by pH adjustment and sedimentation.
The results of the lab tests (Figure 5) show that optimum removal of chromium
from the spent chrome liquor was attained at a pH of 11 5, in this study, although
o pH of 9 5 produced results almost as good.
30
0
00 10 20 30 40 50 60 70
20
-------
I I I
11.0 13.0
FIGURE 5 - TOTAL CHROMIUM IN SUPERNATANT
AS A FUNCTION OF pH
Observations also were made on the settleability of precipitated chrome
sludge. A surface loading rate of approxmately 200 gal/day-sq ft was cal-
culated using the procedure outlined by Rich (28). The detention time under
the conditions of the test should be at least four hours. Suspended solids
concentrations were 1 ,530 mg/I and 22,000 mg/I in the pH adjusted waste
and in the sludge, respectively. After approximately 4 hours of sedimenta-
tion, the supematant had a total chrome content of 25 mg/I and a COD of
about 3,000 mg/I. After 21 hr of sedimentation, the chrome content was
6 mg/I. The chrome content of the final waste dilscharge will be much less
00-
0
0
E
0
I
U
-J
I-
0
F —
600-
5
400-
300-
200—
100-
0
0
0
05.0
7.0
9.0
pH
21
-------
after it is diluted with the other plant wastes, and the concentration in the
receiving stream will be negligible.
Spent Vegetable Tanning Liquor
Although the volume of this waste is not large, even at a vegetable tannery
(about ten percent of total flow), it represents a large fraction of the pollu—
tional load because of its strong concentration. The BOD and COD are not
removed easily by biological waste treatment because of the nature of the
tannin molecules, and there is some toxic effect. Also, the color, which is
intense, is not removed by biological waste treatment. This suggests that
this waste should be treated separately to remove the tannin colloids which
cause the high COD and color before it is discharged to the equalization
basin.
The effect of pH on the color intensity of the spent vegetable tanning liquor
was established by color observations at various pH levels (Table 6). pH has
a pronounced effect on the color of this waste, especially in the alkaline
range. Also, it was found that the color intensity declined with the addition
of acid, but that the color returned to the same level with readjustment of
pH. Dosages of granular activated carbon up to 5,000 mg/I were used in
the preliminary color removal tests with no detectable reduction in the color,
even with contact times up to 20 hr. From a qualitative standpoint,
dosages of carbon wilt reduce the color somewhat. However, this possibility
of treatment for color removal from spent vegetable tanning liquor was not
investigated further because of the excessive dosages required for very
limited color removal.
The method of removal of lignin from pulp mill black liquor as developed by
Woodward and Etzel (30) was investigated as a means of treatment of the
spent vegetable tanning liquor. Briefly stated, the method requires equal
addtions of waste and solvent, pH adjustment, slow mix, and sedimentation.
The supernatant is decanted, vacuum distilled for removal of solvent, and
treated with 35—percent hydrogen peroxide in a waste—to—peroxide volume
ratio of 10—to—i. Etzel reported that the best results were obtained by using
acetone as the solvent.
Samples of the spent liquor and acetone were mixed in ratios of 9—to—i,
2—to—i, and i—to—i, adlusted to pH 12 with sodium hydroxide, and slowly
mixed for 15 mm.
22
-------
TABLE 6 EFFECT OF pH ON COLOR INTENSITY
OF SPENT VEGETABLE TANNING LIQUOR
H
p
Color Intensify
(CaIdwell color units)
5.0*
6.0
7.0
8.0
9.0
10.0
12.0
95
127
187
380
490
1,000
1,960
*Original pH of sample
TABLE 7 - EFFECTS OF ACETONE TREATMENT OF
SPENT VEGETABLE TANNING LiQUOR
Ratio of Vege-
table Tan Uquor Appearance after 6—hr
to Acetone Contact Time
9:1
NoFloc
3:1
Both settleoble and
floating solids
1:1
Approximately 25 percent
of total volume s settled
sludge; good separation
23
-------
The most promising results were obtained with a one—to—one ratio of waste
to acetone (Table 7). However, from an operating standpoint, recovery of
the acetone would be necessary for the process to be economical. Other
treatment techniques which would be more applicable to tannery wastes
then were investigated.
The spent alum tanning solution also was evaluated for treatment of the
spent vegetable tanning liquor. Tests using spent alum as the coagulant
were conducted with some observations on sludge settling rates and total
sludge production (Table 8).
Results of selected chemical analyses of the supernatant from the alum treat-
ment are presented in Table 9. The parameters of particular significance——
color and suspended solids——are reduced markedly although the COD
reduction primarily is because of dilution and the reduction in color is
partially due to the reduction in the pH. The reduction in the other para-
meters was not as significant.
TABLE 8 — TREATMENT OF SPENT VEGETABLE TANNING LIQUOR
WITH ALUM TANNING SOLUTION*
Settling Time
(mm)
Ratio of Vegetable Tan
to spent Alum Solul Ion
4:1
2:1
1:1
0
10
20
45
60
1,080
200t
150
90
60
55
30
200t
180
160
130
120
50
200t
200
180
160
145
70
*Results tabulated as height of supemotant—sludge interface in ml.
tlotal volume of waste plus alum.
24
-------
TABLE 9 - ANALYSIS OF VEGETABLE TANNING LIQUOR
TREATED WITH ALUM TANNING LIQUOR
Parameter
Ratio of Vegetable to
Alum Tanning Liquor
4:1
1:1
Raw Waste
pH
Total solids, mg/I
Total vol. solids, mg/I
Suspended solids, mg/I
COD, mg/I
Color, CaIdwell color
units
SS in sludge, mg/I
3.5
73,760
31,400
1,260
41,800
90
23,820
3.35
71,510
31,560
30
27,900
38
12,800
5.0
76,600
24,000
1,840
51,600
120
Further reductions in color content should be produced by adjustment of the
pH to approximately seven. This would enhance greatly the production of
an insoluble aluminum hydrous oxide floc, adding the effects of orthokinetic
flocculation to the perikinetic coagulation.
It should be noted that the sludge in the four—to—one vegetable to alum
tanning liquor solution settled much faster than that resulting from the equal
volumes of vegetable to alum tanning liquor. A settling period of 16 to 18
hr would be required to produce the above sludge densities if a ratio of
1—to—i were used; while only 2 to 4 hr are needed for the 4-to—i ratio.
However, the quality of the effluent resulting from the longer settling time
would justify the use of a one—to—one ratio for this particular installation
where the volume of vegetable tanning liquor s small.
Studies of the use of NaOCI as an oxident showed that massive doses were
required to reduce the color of the spent vegetable tanning liquors appreci-
ably. Doses of free available chlorine of 8000 mg/I, and detention times
of 2 to 4 hours were necessary to effect color removal. This treatment was
not considered economical.
25
-------
Some investigators have found that lime is an effective coagulant for spent
vegetable tanning liquors, but repeated trials with the liquors used in this
study produced no beneficial results. The result of lime addition was only
to produce a very turbid, muddy—looking solution and no settleable sludge.
Filtration of this solution did not remove the color. Because all vegetable
tanning solutions are different, however, lime coagulation may be success-
ful in some instances, and this process should be investigated in every case.
TABLE 10 - QUALITATIVE RESULTS OF SELECTED COMPOUNDS FOR
COLOR REMOVAL FROM SYNTHETIC DYE MIXTURE
Compound
Test
Condition
Results*
Comment
1
2
3
Stannous Basic solution X Colored
chloride (NaOH) ppt formed
Stannous Acid medium X
chloride (HCI)
Sodium mefa— Aqueous dye X
bisulfite solution
Sodium meta— Acidic X
bisulfite
Sodium meta— Basic X
bisulfite
Zinc—dust pH 9.0 1—hr X Small
contact time amount ppt
Hydrazine Basic media X
chloride
Hydrazine Acidic media X
chloride
Sodium Aqueous dye X High dos-
hypochlorite solution ages
Sodium sulfite Acidic media X
Potassium per— Acidic media X pH 3, and
manganate sodium meta—
bisulfite to
reduce ex-
cess KMnO
*Resul1 by Appearance: 1 - Color removal completely; 2 — Color
intensity decreased; 3 — No obvious change.
26
-------
After the completion of the research phase of this project, a later project
developed an effective method of removing the color from spent vegetable
tanning liquors, but this method was not available when the treatment plant
described in this report was designed. Briefly, the process involves the
addition of acid to lower the pH of the solution to the isoelectric point of
2.0 to 2.5, and the addition of a high molecular weight cafionic poly—
electrolyte to coagulate the colloidal solution.
Color Removal from Dye Wastes
The color in the spent dye wastes was not removed or diminished by bio-
logical waste treatment. Selected chemicals were investigated as pretreat-
ment processes for the dye wastes prior to biological treatment (Table 10).
Because of the large dosages necessary to effect color removal, this route
was not pursued extensively.
Considerable work then was done using adsorption on activated carbon to
remove the color. This approach generally was successful, although large
quantities of carbon and low application rates were necessary. Regenera-
tion of the carbon by elution with acid and alkali were unsucessful.
TABLE 11 - REMOVAL OF COLOR BY TWO ACTIVATED CARBON
COLUMNS IN SERIES--RUN NO. 2
Cumulative Ratio of Effluent
Flow Color to Spent
( ml) Dye Color
110 0
320 0
530 0
740 0
1,060 0.015
1,370 0.022
1,630 0.033
1,955 0.042
2,215 0.055
2,640 0.082
2,850 0.134
3,160 0.178
3,345 0.254
Note: Flow rate = 0.5 gpm/sq ft; color in dye composite 60
Caidwell color units.
27
-------
Breakthrough of color was quite rapid, even at an application rate of 0.5
gpm/sq ft. Consequently, columns in series were tried with considerably
better results. The results of a test using two columns in series are presented
in Table 11. Each column contained 3.5 g of flne carbon and 2.0 g of coarse
carbon (as a filtering material to prevent clogging of fine carbon).
Since clogging of the fine might be a problem, a test was run to evaluate
the relative effectiveness of fine and coarse carbon. The color removal
capacity of the fine carbon was approximately five times that of the coarse
carbon (Figure 6 .
The results show that dye adsorption is relatively slow, and that columns
in series or a deep bed should be used.
I - 1 1
0.4 RATE’O. gpm/sqtt i
CC P IN S ENT DYE
COMPOSITE 24 ‘A ELL UNITS
0.3- -
“I
/
0 7 GRAMSOF / I
0.2 — CO. RSE CARBON / / -
CO . .uMN DIA.= un. /21 GRAMS OF
/ FINE CARBON
0.1 — 4’ /COLUMN DlA.:O.68in _
Y0
0 - o_ _______
0 1.0 2.0 3.0 4.0 5.0 6.0 7.0
VOLUME OF EFFLUENT-LITERS
FIGURE 6 - COLOR REMOVAL FROM SPENT DYE
SOLUTION BY ACTIVATED CARBON
28
-------
Biological Treatment
Both trickflng filters and stabilization ponds have been tested or recom-
mended in the past for the treatment of tannery wastes. However, trickling
filters tend to become coated with grease and/or precipitated calcium
carbonate from the beamhouse wastes. Also, ponds require large land
areas——not available in this instance nor in many tanneries. Consequently,
biological treatment studies were conducted utilizing the activated sludge
process.
A completely mixed system was used in the lab studies and was recommended
for the treatment plant. Completely mixed systems are more stable, easier
to operate, and help to dilute and alleviate shock or load variations on the
biological system. Preliminary work indicated that a convenflonally loaded
system would be satisfactory.
Four laboratory scale biological units (Figures 7 and 8) were employed in
the studies. Two were continuous—flow units using settled alum tanning
process composite wastes as feed (including spent dye) and two were fill-
and—draw units, with 23 hr of aeration and 1 hr of sedimentation. One
fill-and—draw unit used alum tanning process composite waste with dye
solution, and the other unit employed alum tanning process composite wastes,
FIGURE 7 - TWO FILL-AND-DRAW UNITS
29
-------
FIGURE 8 - CONTINUOUSLY FED ACTIVATED SLUDGE UNITS
without the spent dye solution. After it became apparent that the dye
color was not being removed by biological treatment, feed without the dye
was used. The waste was screened, adjusted to pH 6.7, and settled for
2 hr before being fed to the biological treatment units.
As a preliminary step, the oxygen uptake rate of sludge from the Franklin,
Tennessee, municipal plant was measured, after the addition of several
tannery waste concenfrations, to determine the general toxic effects of
the tannery wastes to unaccUmated sludge. The results (Figure 9) indicate
no toxk effects in the concentrations studied. As the total plant corn—
posite was used, all of the waste streams were represented, including the
vegetable tan liquor, the chrome tan liquor, and the dye wastes.
30
-------
E
w
zZ
a-
z
w
>-
><
0
TIME - HOURS
FIGURE 9 - OXYGEN UPTAKE OF UNACCLIMATED ACTiVATED
SLUDGE FED TANNERY WASTES
Organic Content Reduction by Activated Sludge
The effluent from all laboratory activated sludge units was collected and
analyzed, and the organic content reduction in terms of COD was calcu-
lated. The effluent COD was run on an unfiltered sample, since this
represents the total organic load discharged to a receiving stream (Figure 10).
Approximately 65 percent of the COD was removed up to a loading rate
of 0.9 lb COD/day-lb of MLVSS. At higher loading rates, the efficiency
declines somewhat. This loading rate is approximately equal to 0.55 lb/day—
lb on a BOD basis.
The COD of the effluent was generally 400 to 500 mg/I with few exceptions
even though the applied load varied. While this is quite high, it includes
much non—biodegradable organic matter. Table 12 presents the results of
simultaneous BOD and COD tests on the waste at various stages and shows
5 ID 15 20 25 30
31
-------
U)
L U
>
0
LU
I—
z
LiJ
F-
0
(-)
0
z
0
c
0
lb COD/day
ORGANIC CONTENT APPLIED - lb MLVSS
FIGURE 10 - COD REMOVED AS A FUNCTION OF LOADING
that the BOD/COD ratio is much lower on the effluent than it is on the
influent to the biological units. These data, along with Figure 11, indicate
a BOD reduction of approximately 90 percent in the biological units.
Coupled with the reduction in the primary clarifier, an overall reduction
of better than 90 percent is indicated.
It s important to note that the first two lines of Table 12 represent the re-
moval prior to the addition of supplemental phosphorus to the system. After
phosphorus addition at BaD/P ratio of 100/I was started, the removal
efficiency was improved significantly.
The activated sludge settled well with concentration factors in the range
of 3.5 to 6. A test also was run on the kinetics of the COD removal pro-
cess (Figure 11).
00 0.2 0.4 0.6 0.8 1.0 1.2 1.4
32
-------
TABLE 12 - COMPARISON OF COD AND BOD VALUES
.
Sample Description
No.
COD
(mg/I)
BOD
(mg/I)
RatioofBOD
to COD
Effluent from continuous—flow
act. sludge. (Alum corn—
positewith dye)
1
2
3
407
400
675
125
140
110
0.31
0.35
0.16
Effluent from batch treat—
ment unit. (Alum corn-
posite with dye)
1
2
3
4
740
340
540
414
77
56
35
48
0. 10
0.16
0.06
0.12
Effluent from batch treat—
ment unit. (Alum corn-
posite without dye)
1
2
3
4
5
440
545
510
246
655
13
16
23
17
27
0.030
0.029
0.045
0.068
0.041
Alum process composite
waste after primary
treatment
1
2
3
4
1,485
1,240
1,310
1,470
1,010
760
780
800
0.68
0.61
0.60
0.54
All COD removal which occurs fakes place with 10 to 15 hr. This agrees
with the results of the oxygen uptake curves plotted in Figure 9, even
though the sources of activated sludge were different.
The BOD exerted for a 14—day period by the pretreated alum process com-
posite (with dye) and of the effluent from the continuous flow system is
presented in Fgure 12. For comporatve purposes, BOO on the pre—treated
samples was determined using settled wasfewafer and the settled effluent
from the biological unit as seed. There was no significant difference in the
rate of oxygen utilization nor in the total oxygen required for stabilization.
33
-------
FIGURE 11 - COD REMAINING AS A FUNCTION OF AERATION TIME
01 234567891011 121314
TIME - DAYS
FIGURE 12 — BOD OF INFLUENT AND EFFLUENT
OF CONTINUOUS FLOW SYSTEM
1250
1000
.7
500
E
0
z
w
0
z
L U
(9
>-
x
0
-J
0
uJ
I
0
AERATION TIME - HOURS
900
800
700
600
500
FEED WITH SETTLED
SEWAGE AS SEED __ . ——°—
0
E
0
0
400
FEED WITH NO. I
EFFLUENT AS SEED
300
NOTE FEED WAS PRETREATED
COMPOSITE ALUM TANNING WASTES
EFFLUENT OF UNIT NO.1 (NO SEED)
34
-------
Oxygen Requirements of Biological Unit
The oxygen uptake of the mixed liquor in the activated sludge units was
measured using a dissolved oxygen meter. During the short period of obser—
vation the air supply and waste feed to the unit were turned off. The
MLVSS was 2,300 mg/I and the loading rate was 0.56 lb COD/day/lb of
M LVSS.
Based on the data from these observations, the dissolved oxygen require-
ment for the activated sludge unit was found to be approximately 17 mg/I—hr,
or 7.4 rng/I—hr—1,000 mg/I of MLVSS. This is esSentially the same as the
value of 7.5 commonly used for the terminal section of activated sludge
units. A completely mixed system is comparable in loading to the terminus
of a conventional system, since the COD of the effluent is equal to the COD
at any point in a completely mixed system. Similar tests were made on the
other continuously operating aeration unit, and essentially the same
dissolved oxygen requirements were observed.
35
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PROPOSED WASTE TREATMENT SYSTEM
Based on the results of the laboratory studies, it was concluded that the
tannery wastes could be treated effectively, after equaUzation, by the
standard operations of coagulation, sedimentation, and act ivateci sludge—
type biological treatment. It was recommended that a completely mixed
activated sludge system be installed. No problems with toxicfty were
anticipated, and use of a completely mixed system with provision for flow
equalization prior to the biologkal system was believed to be adequate to
eliminate problems caused by the shock loads so common to tanneries.
The laboratory studies also showed that the common practice of combining
all waste flows from tanneries prior to treatment is unwise. Certain waste
streams, such as waste chrome tanning liquor and waste vegetable tanning
liquor have different characteristics which make them more amenable to
separate treatment, It was recommended that these waste streams be
separated and given special treatment prior to introduction to the equali—
zat ion basin.
The overall treatment scheme recommended for the Caldwell Lace Leather
Company is shown in Figure 13. It is believed that this system can be
used, with appropriate local modifications, to treat the waste from most
tanneries for discharge to a receiving stream or to a municipal treatment
plant. For tanneries not practicing all three types of tanning, the
appropriate treament process(es) can be omitted.
37
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Main Waste tiater Flow Vibratinq Screen
Treatment ___________
Eciualizatjon Basin
Spent Dye for _____ (Continuously Mixed)
Color
Solution ______________________
Removal
_____________ Pump
onstart I umping Rate
Precipita-
Spent Chrome tion with
Lime
Tanning Liquor
pH Adiustnent
______ H ________
Addition of An
Spent Lime ‘ Lime Hold- _______
________ Polyel ectrol yte
Solution 1 ing Tank
Spent Alum {Alum Hold- _______
Tanning ing Tank ______
Liquor
Sedimentation Basin
Adjust-
Spent Vegetable ment of oH ______
and Coaqu- ___________ __________
Tanninq lation
Solution
with Alum __________
— — Aeration
Settling
Thickener ___________ _________
Sludge to Final sc
ha roe
Disposal
FIGURE 13 — OVERALL TREATMENT SCHEME PROPOSED FOR
THE CALDWELL LACE LEATHER COMPANY
33
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PROCESS DESIGN RECOMMENDATIONS
In the report of the laboratory studies (1), the following recommendations
were made as to the process design of the biological system. Based on the
results plotted in Figure 10, a maximum loading rate of 0.7 pounds of
COD per day per pound of MLVSS was recommended. This is safely below
the rate at which the efficiency of removal begins to be a function of load-
ing rate. Based on a value of 65 percent for the BOD/COD ratio (Table 12),
this corresponds to a loading rate of 0.45 on a BOD basis. This was con-
sidered to be a reasonable value for completely mixed systems.
Based on the data from Table 4, the total COD load from the process units
is 2333 pounds per week. The load from the total plant might be as great
as 3000 pounds per week. Assuming a conservative figure of 50 percent
removal of COD in the primary sedimentation tank, the load on the biologi-
cal system iS 1500 pounds per week, or 300 pounds per day based on a five—
day week. This would require 425 pounds of biological solids in the
aeration unit.
The air required by the biological unit could be supplied by either diffused
air or mechanical surface aerators. The oxygen requirements for 425
pounds of biological solids would be 122 pounds per day based on a conser-
vative figure of 12 mg/I—hr—gram of biological solids.
The volume of excess sludge from the aeration unit was estimated to be
1000 gallons per day, based on 55 percent synthesis, an endogenous de—
struction rate of 5 percent per day and a solids concentration of 10,000
mg/i. Provision must be made for the disposal of this sludge, along with
the solids from the primary clarifier. The volume to be handled could be
considerably reduced by a gravity thickener.
Sufficient return sludge capacity should be provided to assure maintenance
of an adequate solids level in the aeration unit. For a concentration
factor of 3, a return sludge rate of 50 percent would be necessary. The
pumping rate should be adjustable over a wide range to accomodate varia—
tions in the process.
It was predicted that the effluent from the proposed plant should have a
5—day BOD of 25 to 75 mg/I, a COD of 400 to 600 mg/I, and a suspended
solids content of 25 to 100 mg/I. It was also stated that, in normal opera-
tion, the BOD of the effluent should be closer to 25 than 75 mg/I, while
39
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the suspended so’ids content of the effluent would depend primarily on the
efficiency of removal of micro—organisms in the secondary clarifier
following the activated sludge unit. This is a function of several design
variables, primarily inlet and outlet conditkns, and the quality of the
sludge in the process, which can be controlled by proper operation.
40
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TREATMENT PLANT DESIGN
The tannery waste treatment plant was designed by Howard K. Belt,
Consulting Engineers, Inc., of Lexington, Kentucky. The following
description of the waste treatment plant is based largely on the engineering
report submitted by the firm to the Kentucky Department of Health in
June of 1968.
General Description of Waste Treatment Plant
The main waste flow is collected in the present wet well from which point
it is pumped to the screen and equolizaHon basin utilizing the old pump and
a new one of the same capacity.
From the equalization basin the waste is pumped to a primary clarifier from
which it flows by gravity through the aeration basin and final clarifier and
thence to the receiving stream. A solution containing an anionic polymer
can be added to the suction side of the pump delivering the waste to the
primary tank.
Sludge is collected in the hopper of the primary clarifier and will be
pumped to the sludge storage tank.
Aeration of the mixed liquor is provided by a mechanical aerator.
The settled activated sludge is returned from the final clarifier to the aera-
tion basin by continuous pumping. Sludge is wasted as necessary by pump-
ing sludge to the sludge holding tank or to the primary tank for settling
with the primary sludge.
Chlorination facilities have not been installed at this time, but a chlorine
contact basin and chlorination equipment can be installed at a later date
if it is found to be necessary.
A lime solution holding tank was provided to store the lime solution pumped
from the vats on a schedule of two days one week and three days the follow-
ing week. The Unie solution is allowed to drain from the holding tank into
the raw waste wet well over the time perod between fillings instead of
slugging the equalization tank when the lime pits are emptied.
Sludge from the sludge thickening tank is hauled by tank truck to a land fill
on a farm of the plant owner. Equipment is provided for covering the sludge
in the fill as needed.
4,
-------
In view of the high ground water condition at the site and the resulting high
expense for dewatering extensive excavaflons and the expense of protecting
structures in the ground against uplift, steel basins and tanks located above
ground level were used.
Detailed Description of Plant Treatment Units and Design Criteria
Chrome Tanning Solution — The chrome tanning solution is discharged in
batches of about 200 gallons each at intervals of three times per week. A
tank of 250 gallons capacity would have been sufficient to batch treat this
waste but, in order for it to also be used for treating the vegetable tan
liquor, a capacity of 450 gallons was provided. This tank is of wood stave
construction and is located adjacent to the old alum solution tank.
Chrome waste is pumped to this tank from the tanning wheels with a porta-
ble pump. Hydrated lime is added in the amount of about six pounds to
200 gallons of waste to adjust the pH of the solution to 11.0 to 11 .5 for
precipitation of the chrome. Mixing of the lime info the solution is
accomplished with a wooden paddle.
Vegetable Tanning Liquor — At the time the laboratory studies were made
the plant was discharging about 200 gallons per day of spent vegetable tan-
ning liquor. Since that time some of the vegetable tanning production has
been transferred to another tannery and only 200 gallons per week is now
being discharged to the waste stream.
Batch treatment of the vegetable tanning solution by mixing it with equal
volumes of waste alum tanning solution was recommended by the laboratory
studies report. However, since the vegetable tanning production was
reduced to the point where only 200 gallons per week of tanning liquor is
wasted, it did not appear that any pretreatment of this waste is necessary.
A dilution ratio of about 800 to 115 provided in the total waste flow and
this dilution has resulted in no dscernable increase in color in the total
stream.
Spent Dye Solutions — Attempts to fortify and reuse dye solutions were
recommended by the Vanderbilt report, and efforts in this direction were
made by the tannery in order to decrease the amount of dye waste in the
total stream flow. Eventually, they were able to achieve this, and each
batch is now being used two or three times. This has resulted in a signifi-
cant reduction in the dye waste flow and in the color of the mixed waste.
42
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For 90 percent color removal from 800 gallons of dye waste per day,27
pounds of carbon would have been required,and for 70 percent removal,
22 pounds would have been required. At a carbon cost of 26 cents per
pound,the resulting daily costs would be $7.03 and $5.72 per day,.respec—
tively. This would have resulted in a monthly operation cost of approxi-
mately $150.
Because of the difficulty of determining the final quantity or the precise
effect of the dye waste on the treated final effluent, an agreement was
reached with the state pollution control authorities whereby color removal
facilities would not be initially installed so long as they can be added
later if found to be necessary. This has not been found necessary.
Screening and Equalization — Screening of the waste is mandatory to remove
hair, flesh particles, and bits of leather from the waste stream. Prelimin-
ary studies were conducted using a vibrating screen, but during construction,
a sloping slotted screen was substituted. This type of screen had just
appeared on the market and was especially recommended for applications
such as this.
Equalization Basin — Because of the variations in waste flow and character-
istics and the necessity of operating the biological process on weekends
when the plant is not in operation, some type of equalization basin was
necessary.
For an average weekly flow of approximately 160,000 gallons it was pro-
posed to feed the waste to the treatment plant as follows:
Weekdays — 1500 gallons per hour from 7am to 5 pm
750 gallons per hour from 5pm to 7 am
Weekends — 750 gallons per hour
This pumping schedule results in a daily design flow of 25,500 gallons per
day for weekdays and a weekly flow of 163,500 gallons. Design of sedi-
mentation basins and other facilities with short detention times was based on
the daytime flowrate of 1500 gallons per hour or 25 gallons per minute.
The average weekday flowrate of 25,500 gallons per day is 17.7 gallons per
minute.
43
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If an equalization basin of 50,000 gallons or less had been constructed, it
would have been necessary to schedule the pumping rates to the treatment
units so that the basin was essentially empty on Monday morning. This
would have resulted in unequalized, undiluted waste being pumped
directly to the treatment units on Monday morning. To prevent this, a
basin of 62,500 gallons capacity was provided so that a buffer volume of
12,000 to 15,000 gallons of waste remains in the tank at the start of
operations on Monday morning.
A 10—hp mechanical mixer is mounted on beams above the tank, and has
turbine blades located near the bottom of the tank. An air compressor pro-
vides about 10 cfm of air, released below the turbine blades, to prevent
anaerobic conditions.
Primary Clarifier - A surface loading of 635 gal!ons per day per square foot
and a detention of 1 .5 hours was provided for the primary clarifier at the
design flow of 1500 gallons per hour. A conical hopper bottom with a
60—degree slope provides for storage and some compaction of sludge.
A chamber was provided on the outside of the tank to provide a two—minute
reaction time with the coagulant aid prior to entering the settling basin.
Aeration Basin — The report recommended a loading of about 0.70 pounds
COD per day per pound of mixed liquor volatile suspended solids. A basin
with capacity of one day’s average flow of 25,500 gallons was provided.
The design toad is 3,000 pounds of COD per week, and 50% of this load
was assumed to be removed in the primary clarifier, thus leaving 1,500
pounds of COD to reach the biological process. At the proposed treatment
rates the plant wilt handle 25,500 gallons per day for five days, or a
daily flow of 15.6% of the weekly flow. Thus, the design daily COD load
to the biological process was 234 pounds and the maximum day of 36,000
gallons would provide 330 pounds of COD.
The design for the maximum day COD required 330/. 70 = 472 pounds of
MLVSS. At the average day flow, the loading would be 0.50 pounds of
COD per day per pound of MLVSS. In a basin of 25,500 gallons capacity
this would result in a MLVSS concentration of 2,220 mg/I and a total
MLSS concentration of 3,470 mg/i, which is the approximate concentra-
tion at which the pilot tests were run.
Oxygenation is provded by a 5—hp mechanical surface aerator. Calcula-
tions indicated that a 3—hp unit would have been sufficient, but a 5—hp
unit was provided to give a slight margin of safety.
44
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Final Clarifier — A circular center—feed clarifier with a 4 5—degree conical
bottom was provided Following the aeration basin. The surface loading at
the design flow of 1500 gallons per hour is 653 gal/day—sq ft , and the
detention time is two hours. Settled sludge is pumped continuously from
the point of the cone.
Sludge Concentration and Storage Tank — The laboratory data showed that
after one hour of settling the sludge volume is about 25 percent of the
original and that after 14 hours of settling the volume of sludge is reduced
to about one—half of the one-hour volume. On the basis of 25,500 gallons
flow per day, this would result in a 3,190 gallons of primary sludge per day.
Waste activated sludge was projected at about 1,000 gallons per day at
1 percent solids concentration. Thus, the expected solids volume was
4,190 gallons per day. A circular tank with a conical bottom was con-
structed to provide 12,570 gallons of sludge storage, or about three days
production.
This capacity was considered to be conservative, since this sludge volume
was based on the total flow from the plant, whereas the sludge volume
measurements were made on the composite alum tanning process waste
alone. Additional storage time in the sludge storage basin was expected
to result in an increase in the solids concentration and, thus, in a lesser
quantity of sludge to be hauled away.
Piping was provided from the sludge storage tank to the suction of the raw
waste pumps and an alternate pump discharge line was provided for filling
the tank truck.
Lime Waste Storage — Lime waste is discharged from the beam house vats
every other work day, making four days one week and three days the next
week. The volume of the solution added to the vats is approximately
2,200 gallons. If is desirable to distribute this flow somewhat evenly into
the equalization basin, so a new 2500-.gallon storage tank for this purpose
was provided.
Nutrient Requirements — The laboratory studies found that the industrial
waste does not contain sufficient phosphorus to support the biological life
in the system. The phosphorus required is one pound per 100 pounds of
BOD applied to the sev- ondary system. The average weekly BOD load is
916 pounds, so 9.16 pounds of phosphorus per week would be required.
45
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The most economical source of phosphorus is Triple Super Phosphate ferti-
lizer which contains 42 percent P 2 0 5 and costs approximately $5.00 per
100 pounds. About 50 pounds of Triple Super Phosphate is required per
week so, ten pounds of the fertilizer was originally added to the qualiza-
tion basin each working day of the week.
Laboratory Building — A small prefabricated steel building housing a
laboratory, the pumps, electrical gear, air compressor, polyelectrolyte
dissolving tank and feeder, and pH recorder was provided adjacent to
the waste treatment plant.
46
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CONSTRUCTION AND STARTUP
The waste treatment plant was constructed, essentially as described in the
preliminary report, during 1970. Considerable delay was experienced in
beginning construction because of the difficulty of securing an experienced
contractor to build a small plant in a small town. Further delay was
experienced later in the construction phase because of faulty instructions
which accompanied the paint selected for the interior of the treatment unit
tanks. Because of some omitted steps in the instructions, the paint all
peeled off when the tanks were filled. This difficulty too was rectified
and construction was finally completed in June, 1970.
Initially, attempts were made to start the biological process without re-
sorting to seeding with sludge from another plant, but these attempts were
unsuccessful. Sufficient biological growth would not take place. Even-
tually, two tank trucks of activated sludge from a nearby plant were added
to the aerator, and the plant began functioning. The reasons for the lack
of spontaneous biological growth were not determined, but possibilities
include the extremely high salt content of the waste, the presence of
inhbiting substances, or the presence of a heavy foam blanket.
Foaming has been an operational problem at the plant from the beginning.
Foaming occurs both in the equalization basin and in the aerator. Anti—
foaming agents currently keep the problem under control, but the cost has
led the tannery to also consider the use of sprays using final effluent to
knock down the foam in the basins. The source of the foam is probably
the detergents used in the tanning process.
The initial performance of the plant could be described as fair. Many
problems were caused by lack of a trained operator and by continued
problems with the pumps. It is an accepted fact that it is difficult to find
reliable heavy—duty pumps in small sizes, and this fact has been confirmed
again in this case. In addition, the organic load on the treatment plant
was significantly higher than expected. The BOD of the influent averaged
2500 mg/I, almost double the value of 1300 mg/I found during the
laboratory studies.
Initially, the effluent BOD, predicted by the laboratory study report to be
in the range of 25 to 75 mg/I, varied between 50 and 200 mg/I. Then, in
the November, 1970, to February, 1971, period, it rose to over 300 mg/I,
obviously much too high. However, most of the effluent BOD was caused
by carryover of suspended solids from the final clarifier.
47
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The loss of suspended solids was caused by several factors, but primarily by
a MLSS concentration in the aerator which was too high, and by unstable
operation of the pumps. Unstable pump operation led to many hydraulic
surges, which stirred up the ugh floccu lent solids in the final clarifier.
Also, the return sludge line frequently clogged, either partially or com-
pletely, and the sludge layer in the clarifier built up to the level of the
bottom of the skirt around the center influent well. The water Flowing out
through the narrow space between the bottom of the skirt and the sludge
layer was therefore increased in velocity and scoured up considerable
sludge which rose to the surface where it was swept over the weir. The
MLSS concentration, originally planned for the level of 3000—3500 mg/I,
averaged over 5000 mg/I. This increased the solids loading on the clari-
fier, creating density currents and contributing to the problem of rising
clouds of sludge and the resulting solids loss, The effluent suspended solids
averaged between 300 and 600 mg/I, and values as high as 1200 mg/I were
obtained.
By March, 1971, a capable operator had been secured and partially trained,
and the author had visited the plant as a consultant and identified some of
the reasons for the plant’s poor performance. The MLSS in the aerator was
lowered from 13,400 mg/I to the range of 4000-5000 mg/i, and the effluent
suspended solids dropped to the -range of 50-150 mg/I.
Further improvement in average plant performance occurred during the
summer of 1971. Arrangements were made with the Environmental Protec-
tion Agency, through its Office of Operations, Radiological and Industrial
Waste Evaluation Section, in Cincinnati, Ohio, to perform an industrial
waste survey of the tannery’s waste treatment system. The objective of the
survey was to collect comprehensive data from which the efficiency of the
treatment system could be evaluated. The evaluation of the performance
of the plant was necessary to confirm or refute the findings of the laboratory
studies and complete this final report of the project. A secondary objec-
tive of the study was to obtain data to aid in the establishment of effluent
guidelines for the tannery industry.
48
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EVALUATION OF PLANT PERFORMANCE
The industrial waste survey was conducted by EPA personnel during the
period October 28, 1971, through November 10, 1971. During the 14—day
survey, 24—hour composite samples (beginning at 8:00 a.m.) were collected
of the primary clarifier influent, the primary clarifier effluent, and the
final effluent. On several occasions, the automatic samplers failed, and
grab samples were taken as subsfltutes. Additional grab samples were
collected from the aerator, the sludge recirculation stream, and the final
effluent for determination of suspended solids, pH, sulfides, nitrites,
dissolved oxygen (DO), and sludge volume index (SVI).
All analyses, except where specifically mentioned, were conducted in
accordance with “standard methods.” Total organic carbon (TOC) was
determined with a Beckman Carbon Analyzer. Dissolved Oxygen was de-
termined with a Weston and Stack oxygen analyzer. Atomic absorption
methods were used for analyses of iron, total chromium, and aluminum.
Flow rates were determined by “spill and fill” methods.
Water Flow
The flow through the treatment plant during the survey is in question.
Records were kept of both plant water use (from the plant water meter) and
of waste flow. The two groups of data do not agree. The apparent waste
flow averaged 11.5 gpm during the survey, while the apparent average
plant water use was 14.5 gpm. It has been assumed during the entire project
that the waste flow would be approximately the same as the plant water use.
Some small loss is expected, but not the apparent loss of 3.0 gpm, or
21 percent. It is not known which, if either, group of data is in error, or if
some other factor caused the two records of flow to be so different.
The flow data obtained during the survey are shown in Table 13. The
presence of the equalization tank means that the daily values of flow will
not agree. The waste flow will be more constant than the water use. How-
ever, the totals and averages over the two—week period should agree closely.
The water use during the survey was less than that found during the labora-
tory study three—and—a—half years earlier. The average weekday flow of
26,860 gal/day compares with the value of 32,000 found earlier, and the
weekly flow of 145,500 gal/week compares with the value of 160,000 gal/
week found earlier.
49
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TABLE 13 - WATER FLOW DURING SURVEY
Date
Day
Water Use
Waste Flow
(gal/day)
(gal/mm)
(gal/day)
(gal/mm)
Oct. 28
Oct. 29
Oct. 30
Oct. 31
Nov. 1
Nov. 2
Nov. 3
Nov. 4
Nov. 5
Nov. 6
Nov. 7
Nov. 8
Nov. 9
Nov. 10
Thur.
Fri.
Sat.
Sun.
Mon.
Tues.
Wed.
Thur.
Fri.
Sat.
Sun.
Mon.
Tues.
Wed.
31,850
27,365
15 2
23,040
26,995
30,455
28,590
26,865
7,405
10,245
35,055
28,180
22.1
19.0
5 3
.
16.0
18.8
21.2
19.8
18.7
2.6
7.1
24.4
19.5
18,400
21,000
21,000
10,100
19,450
17,700
12,250
11,250
18,000
14,000
19,700
20,000
12,950
12.8
14.6
14.6
7.0
13.5
12.3
8.5
7.8
12.5
9.7
13.7
13.9
9.0
TOTAL
AVE.
AVE WEEKDAY
291,310
20,800
26,860
14.5
18.7
215,800+
16,600
17,100
11.5
11.9
The average flowrate of waste through the treatment plant during a period
must be known in order to calculate the loading of various waste constitu-
ents on the plant or on the stream. For this report, the values of flow used
to calculate loading were those reported by the survey team for waste flow,
not water use. Since the waste F low will not match the variation of water
use with time because of the equalization basin, the water use records
could not be used even if it were certain that they were accurate.
Summary of Plant Performance
The overall performance of the waste treatment plant during the EPA survey
is tabulated in Table 14. An overall assessment of the performance, simply
stated, could be that efficiency is good, but that there are still several
areas that need further investigation and mprovement. The prInciple area
5fl
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TABLE 14 - MEAN VALUES OF PARAMETERS DURING EPA SURVEY
Sample
Parameter Location
.
Primary
Influent
.
Primary
Effluent
Secondary
Effluent
BOD5,mg/l
1437
619
96
COD ,mg/l
4016
1149
481
CODF, mg/I
987
975
254
TOC 1 ,mg/l
1191
388
150
TOC , mg/I
TKN, mg/I
354
490
356
-
76
322
Org. N, mg/I
328
-
175
NH 3 -N, mg/I
N -N, mg/I
162
0.1
-
-
147
34*
N0 3 -N, mg/I
SS, mg/I
0.1
3135
-
110
0.4
223
pH, units
7.6
7.5
7.3
Temp.,°F
—
—
56.8
Sulfide, mg/I
7.9
8.6
0
Alkalinity, mg/I
516
—
141
Acidity, mg/i
181
-
46.5
Sulfates, mg/I
2743
-
3071
Chlorides, mg/I
5174
—
5127
Phosphorus, mg/I
22.8
—
13.4
DO, mg/l**
5•7
TDS, mg/I
12,795
13,242
13,016
*Mean value of grab samples only
**Mean value of readings from DO probe only
of concern is solids carryover in the secondary clarifier, leading to high
BOD 5 in the final effluent. Specific variables will be discussed in more
detail later in this section.
51
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TABLE 15 - BOD LOAD DURING SURVEY
Date
Flow
(gal/
day)
BOD to
Primary
BOD to
Secondary
BOD to
Stream
(mg/I)
lb
( 7)
(mg/I)
lb
( i i
mg/I
lb
Thur Oct 28
18,400
1567
240
540
83
39
6
Fri 29
21,000
1450
254
670
107
37
6
Sat 30
21,000
2133
374
960
168
D
-
Sun 31
10,100
1250
105
800
67
D
Mon Nov 1
19,450
1400
227
590
96
D
-
Tues 2
17,700
2100
309
700
103
D
-
Wed 3
12,250
1533
160
590
62
D
-
Thur 4
11,250
1583
148
530
50
D
—
Fri 5
18,000
1650
248
740
111
144
22
Sat 6
14,000
1166
136
470
55
115
13
Sun 7
——
——
——
——
——
127
Mon 8
19,700
850
139
420
69
180
30
Tues 9
20,000
883
147
540
90
82
14
Wed 10
12,950
1117
121
500
54
45
5
Average
16,600
1437
199
619
86
96
14
Design
25,500
1320
280
660
140
50
10
D = Dissolved Oxygen Depleted
BOD and COD Load
Tables 15 and 16 present the daily average values of BOD and COD,
respectively, which were measured during the survey. The average values
and the values used for design purposes are also presented, and all con-
centration values are converted to pounds per day, using the measured
daily average waste flow.
The BOD concentrations in the raw waste and in the primary effluent,
1437 mg/I and 619 mg/I, are close to those assumed for design, 1320 mg/I
and 660 mg/I, but the actual effluent BOD was higher, 96 mg/I vs. 50 mg/I.
The measured load to both the primary and secondary systems is less than
52
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TABLE 16 - COD LOAD DURING SURVEY
Date
Flow
(gal/
day)
COD to
Primary
COD to
Secondary -
COD
to Stream
(mg/I)
lb
( )
(mg/I)
lb
(mg/I)
lb
Oct 28
18,400
5670
870
1200
184
315
48
29
21,000
3810
666
1280
224
291
51
30
21,000
3860
675
1310
229
716
125
31
1Q. 000
3110
262
1160
98
428
36
1
19,450
4080
662
1060
172
413
67
2
17,700
6000
885
1340
198
673
99
3
12,250
4080
416
1180
120
661
68
4
11,250
3840
360
1070
100
553
52
5
18,000
3840
576
1090
164
453
68
6
14,000
4140
482
1030
120
532
62
7
--
--
--
--
--
480
-
8
19,700
3250
533
1390
228
629
103
9
20,000
2500
416
950
158
442
74
10
12,950
4030
435
874
94
154
17
Average
16,600
4016
575
1149
159
481
66
Design
25,500
2200
468
1100
234
500
106
that assumed for design, however, because of the lower flow. The BOD
removal efficiency of the primary clarifier was 57%, compared to an
assumed 50%; the efficiency of the secondary system was 84.5%, compared
to an assumed 92%; and the overall efficiency was 93%, compared to the
assumed 96%. The failure of the plant to achieve the design efficiency
was primarily due to excess solids carryover from the secondary clarifier,
as will be shown later.
The COD concentration in the raw waste was almost double the assumed
value of 2200 mg/I, but the measured concentrations in the prmary and
secondary effluents were very close toihe assumed values of 1100 mg/I and
500 mg/I. The COD load on the primary system was only slightly higher
53
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TABLE 17 - BOD LOADING RATES DURING SURVEY
Date
BOD
(tb/day)
MLSS
(mg/I)
MLVSS
(mg/I)
MISS
Loading
(1/day)
MLVSS
Loadng
(1/day)
Oct28
83
3584
2108
0.09
0.15
29
107
3380
2536
0.12
0.16
30
168
--
--
--
--
31
67
-—
--
Nov 1
96
3528
-—
0.10
--
2
103
3585.
——
0.11
-—
3
62
3813
——
0.06
——
4
50
3352
-—
0.06
--
5
111
3476
--
0.12
--
6
55
--
--
--
--
7
--
-—
--
--
--
8
69
3638
2624
0.07
0.10
9
90
4263
--
0.08
--
10
54
4145
2860
0.05
0.07
Average
86
3676
2532
0.09
0.13
Design
140
3470
2220
0.15
0.24
than that assumed for design, however, because of the lower flow, and the
COD load in the secondary influent and effluent were significantly less
than the assumed values, because of the reduced flow and the increased
efficiency of the primary clarifier. The actual efficiency of 71% is signifi-
cantly greater than the 5O’/ assumed for design. The COD removal
efficency found durng laboratory studies was but a value of only
50 Yo was assumed for design to allow for the normal reduction in efficiency
due to turbulence and density currents not present in the laboratory column.
The COD reduction in the secondary system was 58%, compared to the
assumed 55%, and the overall efficiency was 88%, compared to the assumed
efficiency of 77%.
54
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TABLE 18 - COD LOADING RATES DURING SURVEY
- Date
COD
(lb/day)
MLSS
(mg/I)
MLVSS
(mg/I)
MLSS
Loading
(1/day)
MLVSS
Loading
(1/day)
Oct. 28
184
3584
2108
0.20
0.32
29
224
3380
2536
0.25
0.34
30
229
-—
--
——
31
98
-—
--
—-
-—
Nov. 1
172
3528
-—
0.19
—-
2
198
3585
-—
0.21
—-
3
120
3813
--
0.12
-—
4
100
3352
—-
0.11
——
5
164
3476
--
0.18
--
6
120
--
--
--
--
7
--
--
--
--
--
8
228
3638
2624
0.24
0.34
9
158
4263
-—
0.15
—-
10
94
4145
2860
0.09
0.13
Average
159
3676
2532
0.17
0.24
Design
234
3470
2220
0.26
0.39
The BOD and COD loading rates during the survey, based on both MLSS
and MLVSS, are presented ; Tables 17 and 18. The values of MLSS are
taken both from the EPA survey and from plant records. Most of the EPA
survey records were rejected as being much too low because of an inappropri-
ate sampler. When grab samples were used, the EPA survey results and the
plant records agreed closely, and an average value was used.
Values of MLVSS were only from the EPA survey results. Values which
were obtained using inappropriate sampling methods were not used. The
55
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inappropriate sampler consisted of a cup which was lowered periodically on
a timed signal into a perforated pipe extending down into the aeration basin.
However, values obtained using this sampler were only about 60% of those
obtained when grab samples were analyzed. The perforated pipe created a
semi—quiescent environment inside the pipe and the lack of turbulence
caused the sludge to settle somewhat. The sludge concentration was thus
lower inside the pipe, especially near the surface where the sample cup was
primarily flied, than the sludge concentration outside the pipe. The cup
sampler was discarded on November 7, when the discrepancy in concentra-
tions using the two sampling methods was discovered.
In calculating the loading rates, the estimated solids in the secondary clari-
fier were added to the solids in the aerator to obtain the total solids in the
system. The clarifier was assumed to contain solids at a concentration of
15,000 mg/I too level two feet above the conical section. This produced
a total solids content of 175 lb in the clarifier and volatile solids content of
120 lb. Under normal operating conditions, with the return sludge pumps
working well and the sludge lines clear, the solids content of the clarifier
would be much less than this.
The BOD loading rate found during the EPA survey was only about 60% of
the design loading rote, both because of the lower BOD load and the
slightly higher solids concentrations. The BOD loading, based on volatile
solids, was only 0.13/day, compared to the design value of 0.24. (The
design value would be 0.30/day if the solids content of the clarifier were
ignored, and the overage survey value would be 0.16/day.) The value of
0.13/day places the plant in the category of an extended aeration plant,
whereas a standard loading was assumed.
The laboratory study report recommended a COD loading rate of 0.70/day,
based on volatile solids. The design report adopted a COD loading rate of
0.70/day for the maximum day’s flow of 36,000 gal, equivalent too load-
ing rate of 0.50/day for the normal day’s flow of 25,500 gal. This rate be-
comes 0.39/day when the approximately 120 lb of volatile solids in the
clarifier during the study is consdered. The actual average COD loading
rate found during the EPA survey was only 0.24/day, about one-half the
intended design value.
The BOD/COD ratio found during the laboratory study was 0.60. The
average SOD/COD ratio for the primary effluent found during the EPA
56
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survey was 0.54. The ratio found for the raw waste was only 0.36. Thus,
much of the increase in the raw waste COD from the values found during
the earlier survey consisted of non—biodegradable material which was re-
moved by the primary clarifier.
The results of the EPA survey show that the treatment plant was definitely
underloaded during the survey. Based on these results, the MLSS in the
aerator should probably be lowered to the range of 2500 mg/I in order to
reduce the solids load on the secondary clarifier and, hopefully, reduce the
solids carryover. If this were done, and the volatile solids content of the
clarifier could be kept to 50 lb, the COD loading rate would still be only
0.38/day and the BOD loading rate only 0.21/day if the load did not in-
crease, well within safe limits.
Organic Matter Removal
The performance of the treatment plant in removing organic material during
the EPA survey was generally good. The organic content of the waste was
measured in terms of BOD5, COD, and TOC during the survey, with the
COD and TOC tests run on both total and filtered samples. The results, in
terms of maximum, mean, and minimum, are presented in Table 19.
Table 19 contains no real surprises or anomaUes. The results of the daily
samples are relatively consistent, with the low values almost always occur—
ting on November 8 or 9, as illustrated in Tables 14—17. As expected,
there is less variation from day to day as the sampling point advances through
the treatment plant.
The most striking result of the data in Table 18 is the difference in values
between filtered and total COD and TOC of the final effluent. This result
was expected because of the obvious loss of solids from the secondary clari-
fier. The data shows that the total COD and TOC is approximately double
the filtered values. This result illustrates the importance of final clarifier
performance in producing a good effluent, and the importance of improving
performance in this particular case. In this case, where half the final
effluent COD is due to solids loss, a reduction in effluent COD of approxi-
mately 30 to 40% should result if the efficiency of the final clarifier im-
proved to the point where it could be considered average.
57
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TABLE 19 - ORGANIC MATTER REMOVALS DURING EPA SURVEY
Parameter
Sample
Lccat Ton
Primary
I nfluent
Primary
Effluent
Secondary
Effluent
BOD 51 mg/l
Maximum
Mean
Minimum
2133
1437
850
960
619
420
180
96
37
COD 11 mg/l
Maximum
Mean
Minimum
6000
4016
2500
1
1390
149
874
716
481
154
CODF,mg/l
Maximum
Mean
Minimum
1250
987
787
1130
975
768
346
254
139
TOCT,mg/l
Maximum
Mean
Minimum
2000
1191
740
455
388
295
212
150
79
TOC ,mg/I
Maximum
Mean
Minimum
500
354
260
480
356
295
97
76
62
Solids
The solids content of the waste is shown in Table 20. The high dissolved
solids content (about 4(Wo of that of seawater) results from the initial rinse
to remove the salt used to preserve the hides. Although much higher than
most wastes, the concentration does not appear to inhibit the biological system.
The data shows that the primary clarifier did an excellent job of removing
suspended solids, with an average removal of slTghtly over 96%. Only a few
high values prevented the average removal from being even greater. The
median value of suspended soUds in the primary effluent was 56 mg/I.
58
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TABLE 20 - SUSPENDED SOLIDS DURING EPA SURVEY
Sample
Parameter Location
Raw
Waste
Primary
Effluent
S
econdary
Effluent
Dissolved Solids,
mg/I
Maximum
14,754
14,863
13,942
Mean
12,795
13
,242
13
,016
Minimum
9,451
11,134
12,251
Suspended Solids,
mg/
Maximum
546
400
Mean
3,135
110
223
Minimum
12
56
The secondary clarifier, however, did not perform well at all, as already
noted. The average effluent suspended solids of 223 mg/I is much too high,
and should be about what the minimum actually was——56 mg/I.
TABLE 21 - MEAN VALUES OF NITROGEN FORMS DURING EPA SURVEY
Sample
Parameter Location
Primary
Influent
Primary
Effluent
Secondary
Effluent
TKN, mg/I
Org.-N, mg/I
NH 3 -N, mg/I
NO -N, mg/I
NO -N, mg/I
435
250
185
0.1
0.1
308
132
176
0.1
0.1
274
117
158
31
0.2
59
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Nitrogen
The wastewater is high in nitrogen. There are three major sources of nitrogen,
organic solids from the hides, dimethyl amine used in the lime soaking pits as
an alternative to sodium sulfide, and ammonium sulfate used in the alum pro-
cess. Table 21 contains the mean values of Total Kjeldahl Nitrogen (1K N),
Organic Nitrogen, Ammonia Nitrogen (NH 3 —N), Nitrate Nitrogen (NO —N),
and Nitrate Nitrogen (NO —N) in the primary influent, primary effluent,
and secondary effluent for the last four days of the survey, which were the
only days for which data is available fromall threesampling locations.
The removal of TKN is only fair for a plant of this type — 37%. Examination
of the data in Table 21 shows that 47% of the organic nitrogen is removed in
the primary clarifier, but very little is removed in the secondary system. Of
the 117 mg/I of organic nitrogen in the final effluent, approximately 15 mg/i
can be attributed to the activated sludge solids carryover. Of the organic
nitrogen tlremovedtl by the primary clarifier, some undoubtedly was in the
solid form and settled with the sludge, but some was probably also hydrolyzed
to the ammonia form.
The ammonia nitrogen content of the waste decreased only 5% through the
primary clarifier, but it must be kept in mind that both removal (via sedi-
mentation) and addition (via conversion from the organic form) was probably
taking place. However, since most of the ammonia nitrogen is expected to
be in the dissolved form, little sedimentation was expected.
The amount of ammonia nitrogen removed in the secondary system is low,
considering the low actual loading rate, but not lower than expected, since
the planned loading rate did not provide for complete nitrification. Part of
the removal of ammonia nitrogen can be attributed to stripping of the rela-
tively volatile dimethyl amine and part to biological oxidation to nitrite.
The nitrification step is obviously being inhibited by some mechanism, since
nitrite concentrations in the effluent are extremely high and nitrate concen-
trations almost negligible. Almost the entire 33—mg/I drop in TKN through
the secondary system shows up as an accumulation of nitrite (31 mg/I). Even
allowing for the fact that some of the TKN in the secondary effluent is es-
sentially added by solids carryover rather than the residual of what entered
the system, the low nitrate concentration shows that very little conversion of
nitrite to nitrate took place. Usually this phenomenon is due to low oxygen
60
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levels, but the oxygen content of the aerator during the survey averaged
8.5 mg/I, so this could not be the cause in this case. if is likely, in this
case, that the problem can be attributed to some inhibiting substance,
possibly a detergent used in the leather finishing process. It is also possible
that the high nitrite bufldup was partially responsible for the lack of greater
conversion of ammonia to nitrite.
The nitrogen concentration of the effluent could be reduced indirectly by
reducing the amount of dimethyl amine used in the soaking process, and re-
turning to a greater use of sodium sulflde. The survey showed that the rela-
tively low level of sulfides present in the waste was completely oxidized by
the secondary system. However, there is no evidence at’ present that the
nitrogen discharged to the stream significantly affects either the oxygen level
or the productivity of the water. This is an area which would merit further
investigation.
Water Temperature
The temperature of the aerator contents at the beginning of the survey was
70°F, but declined to the mid—forties by the end of the survey because of
the onset of cold weather. The above—ground steel tanks and the long de-
tention times makes the temperature of the aerator closely follow trends in
average daily temperature. However, no significant effect of temperature
on treatment efficiency can be noted——possibly because of the long detention
times and low loading rate during the survey.
pH
The pH of the raw waste varies greatly, but the equalization basin is very
effective in moderating extreme changes in pH. Discharges from the lime
pits are pumped to a storage tank and bled into the equalization tank
gradually. However, the acid alum fanning solutions and dyeing solutions
are dumped directly.
Close attention by the production supervisor of the tannery and the waste
treatment plant operator is necessary to monitor the pH of the equalization
basin and pump lime solution from the storage tank into the equalization
basin whenever a discharge of tanning or dyeing solution depresses the pH
below 7.0. This attention was satisfactorily provided during the EPA survey
by the regular plant operator. The daily average pH of the aeration basin
61
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never varied outside the range of 6.7 to 7.7. When the lime solution storage
is depleted, lime in 50—pound bags is used to raise the pH, if necessary.
Su If ides
The concentration of sulfide in the waste is not high, because much of the
sodium sulfide formerly used in the lime soaking pits as an aid to unhairing
has been replaced by dimethyl amine. The low concenfration of about 8 mg/I
is completely removed by the secondary system.
Phosphorus
During the laboratory studies, the waste was shown to be phosphorus deficient,
so the design report recommended that triple superphosphate be added to the
equalization tank as a nutrient. Later, the point of addition was moved
directly to the aerator, since the high pH values sometimes experienced in
the equalization basin were precipitating it as calcium and aluminum phosphates.
Values of phosphorus determined during the EPA survey showed the waste not
to be phosphorus deficient. The average of 22.8 mg/I in the primary influent
is almost four times the 6.2 mg/I needed for biological growth, asSuming a
1:100 P:BOD ratio. Actually, less than that is probably needed because the
currently low loading rate causes lttIe net cell growth and much biological
phosphorus is recycled. Thus, the average effluent concentration was a
high 13.4mg/I.
There are two known sources of phosphorus——the organic phosphorus in the
organic waste from the hides, and sodium hexametaphosphate used in the
vegetable tanning process. Some of the organic phosphorus was probably re-
moved in the primary clarifier. How much is unknown, because phosphorus
was not run on the primary effluent.
During the survey, the regular operator obtained a Hach kit for determination
of phosphorus on the secondary influent and effluent, and now hopes to add
triple superphosphate when the concentration drops too low.
Dissolved Oxygen
The accurate measurement ofdissolved oxygen concentrations in the aeration
basin and in the final effluent by the Winkler method proved to be impossible
because of the high nitrite levels. Therefore, the Winkler method was dis-
carded and a dissolved oxygen probe substituted about halfway through the
62
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survey. Dissolved oxygen in the aeration basin averaged 8.5 mg/I, and DO
in the final effluent averaged 5.7 mg/I, with a low of 2.2 mg/I and a high
of 8.5 mg/I. Concentrations in both locations are easily satisfactory and
show that the aerator is more than large enough for sufficient aeration.
Heavy Metals
Heavy metals measured in the primary influent and secondary effluent were
calcium, total chromium, hexavalent chromium, iron, aluminum, sodium,
and boron. The boron and hexavalent chromium concentrations were deter-
mined only one time, on a composite sample of all samples taken during the
entire survey. The mean values of the concentrations determined are shown
in Table 22. All metal concentrations were relatively consistent from sample
to sample except influent total chromium, which varied from 1.3 mg/I to 13. 5
mg/I, and effluent aluminum, which varied from 1.0mg/Ito 18.2 mg/I.
TABLE 22 - MEAN VALUES OF HEAVY METALS DURING EPA SURVEY
Metal
Primary
Influent
Secondary
Effluent
Calcium, mg/I
478
485
Total Chromium, mg/I
6.5
0.4
Hexavalent Chromium,
mg/f
0.03
0.01
Iron, mg/I
13.3
<1.0
Aluminum, mg/I
298
8.3
Sodium, mg/I
3798
3851
Boron, mg/I
0.83
0.96
As expected, calcium, sodium, and boron were essentially unaffected by
treatment. However, since the hydroxides (or other complex precipitates)
of iron, aluminum, and trivalent chromium are relatively insoluble at pH
7.5 and above, it is assumed that the removal of the metals occurred, at
least partially, by precipitation in the primary clarifier. This cannot be
shown definitely, however, because heavy metals were not run on the
primary effluent.
63
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Coliforrn Bacteria
Only a few coliform bacteria tests were conducted, because the samples had
to be iced and sent to the Cincinnati laboratory for analysis. The results,
shown in Table 23, are highly variable, and averages would be meaningless.
The data do show, however, that the great majority of coliform bacteria in
the final effluent are of non—fecal origin. Given the fact that the municipal
waste treatment plant discharges into the stream at the same location and
that there is no use of the stream by humans for drinking purposes or recrea—
F ion, chlorination of the effluent does not seem justified on the basis of the
present data.
TABLE 23 - COLIFORM COUNTS DURING EPA SURVEY*
Location of
Sample and
Col i form Type
Date
9/23/71
10/3/71
10/7/71
11/12/71
Primary lnfluent
Total
170,000
--
——
--
Fecal
73,000
11,000
6,000
5,000
Primary Effluent
Total
—-
——
—-
16,300,000
Fecal
-—
2,600
1,800
3,000
Secondary Effluent
Total
590,000
—-
--
8,600,000
Fecal
29,000
1,300
2,400
430
*All counts expressed as colform bacteria per lOOm l.
64
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TREATMENT PLANT OPERATION*
The success of treating this particular tannery waste is determined largely
upon the conscientiousness and training of the operator. Fortunately, the
operator at Caldwell has both qualities which resulted in acceptable treat-
ment of CaIdwell’s wastewater. Nevertheless, problems were encountered
with pump failure, lines plugging, and pH monitoring equipment. On one
occasion (11/7—8), the transfer line from the equalization basin to the Moyno
pump became clogged which resulted in dry operation of the Moyno pump.
The dry operation coupled with grit resulted in stator disintegration and scor-
ing of the rotor which contributed to no—flow conditions to the system for
about 12 hours. A stand—by Moyno pump was put into operation after the
clogged line was blown with air. The efficiency of treatment was not af-
fected after the shut—down period. The fact that the soluble TOC on the
following day (longer operation time) was not significantly different than
the mean value for the study suggests that the remaining soluble organics in
the final effluent were highly refractory substances. Relatively nonbiode—
gradable detergents probably contribute significantly to the refractory load
to the stream. The detergents also presented an aerator foam problem severe
enough to warrant the use of an antifoaming agent. CaIdwell may well in-
vestigate the use of spray nozzles to minimize foam in the aerator, possibly
using final effluent as a source of water.
Another problem area is the sludge recirculatiori pump and associated trans-
fer lines. Oberdorfer pump flow rates ranged from zero when clogged to
6.1 gal/mm after cleaning. These flow rates were measured by the “spill
and fill method” as opposed to reading flow rates from manometer—orifice
measuring devices installed by the consulting engineer. It was recommended
that all orifice plates be removed from transfer lines in an effort to minimize
clogging in the relatively small openings and use “spill and fill” techniques
for daily measurement of flow.
*These comments on plant operation are taken verbatum from the EPA
survey report written by Ed Berg.
65
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PLANT PERFORMANCE SINCE EPA SURVEY
In the months since the EPA survey, tannery personnel have worked to in-
crease the efficiency of the waste treatment system by taking actions both
inside the tannery and at the waste treatment plant. On the basis of records
kept by the tannery for submission to the Kentucky Water Pollution Control
Commsson, the results have been excellent. Table 24 summarizes the data
gathered from January, 1972, through June, 1972.
TABLE 24 — PLIANT PERFORMANCE IN 1972
Month
Water
Flow
(gal/day)
SS(mg/l)
0
/o
Reduc.
BOD(rng/l)
0
/0
Reduc.
In
Out
In
Out
Jan
Feb
Mar
Apr
May
June
EPA Ave.
22,300
23,300
24,100
22,300
23,700
24,000
20,800
1406
1690
1358
2400
2098
3032
3135
55
47
66
61
34
52
223
96
97
95
97
97
98
93
510
229
201
416
666
664
1437
39
17
19
20
27
21
96
92
91
90
95
96
96
94
The effluent of the plant in 1972 is a marked improvement over that found
during the EPA survey. This is due to two influences. First, the strength
of the incomingwaste is consderably lower in both SS and BOD. Secondly,
the percentage removal of both SS and BOD has improved.
The final effluent SS content is almost totally a function of the efficiency
of the secondary clarifier. During the EPA survey, it will be recalled that
the secondary effluent had twice the SS content of the primary effluent.
The much better performance of the secondary clarifier has reduced the SS
toss to less than 25% of that during the EPA survey.
67
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The reduction in SS loss also causes a reduction in final effluent BOD almost
as great——to only 25% of that found during the EPA survey. The current per-
formance of the waste treatment plant is equal to or better than the upper
limits of performance estimated by the laboratory study and would be difficult
to improve upon significantly.
The plant is loaded even lighter now than it was during the EPA survey, when
it was definitely underloaded. The reduction in overall plant loading is not
quite as great as the reduction in SS and BOD, because the flow, as measured
by water use (7—day per week average of water meter reading) increased l5%
over that during the EPA survey. True average loadings cannot be computed
from available data because BOD and SS tests are not run every day and no
tests are run on the primary effluent, but if is certain that the secondary
system is operating in the extended aeration range. Mixed liquor suspended
solids content of the aerator has averaged about 6000 mg/I during 1972, but
sludge is withdrawn somewhat more regularly than before, so fluctuations are
not as great.
Several reasons have been advanced by the tannery management for the
drop in waste loading. There has been some small reduction in production,
but not enough to cause the large drop in loading. Two changes inside the
tannery probably account for the major drop.
Much less water is now being used in the cowhide fleshing operation, and
the great bulk of the fleshings are now collected from the floor and hauled
to landfill rather than being flushed down the drain to the treatment plant.
In addition, a screen has been installed inside the buflding to trap large
solids before they leave the plant. This action probably did not have as
much effect as the first one mentioned, however, because the treatment plant
was preceded by a slotted screen anyway.
Chrome tanning liquor and vegetable tanning liquor are now being hauled
directly to the landfill rather than discharged to the treatment plant. The
chromium is precipitated by lime in the tank truck before discharge.
Whether or not the reasons outlined above completely or adequately account
for the decrease in waste load to the plant is problematical, but is the best
explanation which plant personnel can advance. A definite answer could be
obtained only by another complete waste survey.
68
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Operation of the treatment plant tself has also improved. Operator experi-
ence and competence has increased. Most pumps have been replaced and
the new ones run much more smoothly and reliably, eliminating most of the
clogging problems, and the surges associated with the previous off—on
operation. The secondary clarifier efficiency s the primary beneficiary of
this program. This was the major problem identified during the EPA survey.
It cannot be stated with certainty, but t is probable that the waste treatment
plant could now accept a much greater organic load, approaching the design
load, without a great decrease in performance efficiency. These results
again demonstrate that satisfactory waste treatment for an alum tannery is
possible, if due care s taken in process and plant design, and if competent
and conscienfous operation is provided.
69
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ACKNOWLEDGEMENTS
The material in this report is based on a variety of sources, but three deserve
special mention. The section on the original laboratory studies is based on
a report by H. D. Tomflnson, E. L. Thackston, V. W. McCoy, and P. A.
Krenkel. The design material is based on the preliminary design report by
J. Wiley Finney of Howard K. Bell, Consulting Engineers, Inc. The
material on the EPA survey comes largely from a preliminary report by Ed
Berg, who was in charge of the EPA industrial waste survey team. The
contributions of all are gratefully acknowledged.
The author would also like to acknowledge the outstanding cooperation and
patience, over the entire five years of this project, of the officials of the
Caidwell Lace Leather Co., particularly J. Richard Howlett, President, and
Jim Moore, Vice—President.
This project was supported by the U. S. Environmental Protection Agency,
and its agency predecessors, through research and demonstration grant No.
WPRD 25—01. The support, encouragement, advice, and patience of the
project officers, James Kreissl and James Westrick, is gratefully
acknowledged.
The aid of Mrs. Betty Fans in the preparation of the manuscript of the final
report is also gratefully acknowledged.
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REFERENCES
1. Tomlinson, H. D., E.. L. Thackston, P. A. Krenkel, and V. W. McCoy,
“Complete Treatment of Tannery Wastes,” Tech. Report No. 15,
Sanitary and Water Resources Engineering, Vanderbilt University,
Nashville, Tennessee, 1968.
2. Tomlinson, H. D., E. L. Thackston, P. A. Krenket, and V. W. McCoy,
“Laboratory Studies of Tannery Waste Treatment,” Journal , Water
Pollution Control Federation , 41, 4, 660, April, 1969.
3. Spiers, C. H., “The Wastes of the Leather Industry,” National Leather—
sellers College, London, England, SEI.
4. Sutherland, R., “Industrial Wastes——Tanning Industry,” md. and Eng.
Chem. , 39, 628, 1947.
5. Harnly, J. W., “Liquid Industrial Wastes——Tanneries,” md. and Eng.
Chem. , 44, 520, 1952.
6. Industrial Waste Guide, Supplement D, Ohio River Pollution Survey,
U. S. Public Health Service, Washington, D. C.., 1944.
7. MosselU, J. W., N. W. MasselU, and M. G. Burford, “Tannery
Wastes——Pollution Sources and Methods of Treatment,” New England
Interstate Water Pollution Control Commission, Boston, Mass., 1958.
8. O’Flaherty, F., “Leather.” Rept. and Papers of the Res. Lab. of the
Tanners’ Council of ,America, Inc., IX, 485, 1965
9. Eye, J. D., “The Treatment and Disposal of Tannery Wastes,” Rept.
and Papers of the Res. Lab. of the Tanners’ Council of America, Inc.,
IX, 438, 1965.
10. Southgate, B. A., “Symposium on Liquid Industrial Wastes——Waste Dis-
posal in Britain,” lnd. and Eng. Chem. , 44, 524, 1952.
11. Vflla, L., “Waste—Water in the Tanning Industry and its Purification,”
Jour. Amer. Leather Chemists Assn. , 61, 414, 1966.
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12. Hczseltine, T. R., “Tannery Wastes Treatment with Sewage at Williams-
port, Pennsylvania,” Sewage and Industrial Wastes , 30, 1, 65,
Jan 1958.
13. Warrick, L. F., and E. J. Beatly, “Treatment of Tannery Wastes with
Domestic Sewage,” Sew. Works Jour. , 8, 122, 1936.
14. Porter, W., “Operating Problems from Tannery Wastes at Bal Iston Spa.,
N. Y.,” Sew. Works Jour. , 21, 7, 738, July, 1949.
15. Power, R. M., “The Treatment of Tannery Wastes With Sanitary Sewage
at Ayer, ” SanUalk , 5, 4, 19, 1957.
16. Rosenthal, B. L., “Treatment of Tannery Waste——Sewage Mixture on
Trickling Filters,” Sanitalk , 5,4, 21, 1957.
17. Rosenthal, B. 1., “Treatment of Tannery Wastes by Activated Sludge,”
Sanitalk , 6, 1, 7, 1957.
18. Taylor, W. H., “Disposal of Tannery Wastes,” Sanitalk , 1,4, 24, 1953.
19. Nemerow, N. L., and R. S. Armstrong, “Proto—type Studies of Com-
bined Treatment of Wastes from 22 Tanneries and Two Municipalities,”
Proc. 22nd md. Waste Conf. , Purdue Univ., Lafayette, indiana, 1967.
20. Nemerow, N. 1., and R. S. Armstrong, “Combined Tannery and
Municipal Waste Treatment, Gloversville——Johnstown, N. Y.,”
Proc. 21st md. Waste Conf. , Purdue Univ., Ext. Ser. 121, 447, 1966.
21. Wims, F. J., “Treatment of Chrome Tanning Wastes for Acceptance by
an Activated Sludge Plant,” Proc. 18th md. Waste Conf. , Purdue
Univ. Ext. Ser. 115, 534, 1963.
22. Filbert, J. W., and R. E. Pailthorp, “Biological Waste Treatment in
the Chrome Tannery,” Leather and Shoes , 14, Dec, 1967.
23. Parker, R. R., “Disposal of Tannery Wastes,” Proc. 22nd md. Waste
Conf., Purdue Univ., Lafayette, Indiana, 1967.
24. Berg, N., T. H. Miller, A. P. Pearce S. G. Shuttleworth, and
D. A. Williams—Wynn, “Studies on Elimination of Sulfide from
Tannery Beambouse Effluents by Manganese Catalyzed Oxidation,”
Jour. Amer. Leather Chemists Assn. , 62, 684, 1967.
74
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25. Sproul, 0. J., P. F. Atkins, and F. E. Woodard, “Investigations on
Physkal and Chemkal Treatment Methods for Cattle Skin Tannery
Wastes,” Journal WPCF , 38, 4, 508, April, 1966.
26. Sprout, 0. J., K. Keshavan, and R. E. Hunter, “Extreme Removals
of Suspended Solids and BOD in Tannery Wastes by CoagulaHon
with Chrome Tan Dump Liquors,u Proc. 2 1st md. Waste_Conf., Purdue
Univ. Ext. Ser. 121, 600, 1966.
27. Eye, J. D.,and S. P. Graef, “Literature Survey on Tannery Effluents,”
Jour. Amer. Leather Chemists Assn. , 62, 194, 1967.
28. Rich, L. G., Unit Operations of Sanitary Engineering , John Wiley and
Sons, New York, N. Y., 1961.
29. Eye, J. D., and S. P. Graef, “Pilot Plant Studies on the Treatment of
Tannery Wastes,” unpublished manuscript.
30. Woodard, F. E.,and J. E. Etzel, “Coacervatlon and Chemical Coagula—
tion of Lignin from Pulp Mill Black Liquor,” Journal WPCF , 37,
7, 990, July, 1965.
S. c;ov N:1fN \rrcc FFICL 19735L4155/294
75
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I SELECTED WATER • R jortNo. 2. 3.AccessionNo.
RESOURCES ABSTRACTS
INPUT TRANSACTION FORM
4. Title S. port& e
Secondary Waste Treatment for a Small
Diversif led Tannery
8. ‘formT Orgt. . .atioz
2 epoUNo.
Aurhor(s)
Thackston,. E. L. 10. ProJect No.
12120 EFM
9. Orp,anrz stioz,
Caldwell Lace Leather Company 11. Contr .wtlGrantNo.
Auburn, Kentucky WPRD 25-01
1: Typc . Repo and
PerioaCcvored
‘2. S isorir ()rgar tion
15. Surp)crnon s Not s
Environmental Protection Agency report
number, EPA—R2—73—209, April 1973.
26. .Ahctr;4Ct
The Caidwell Lace Leather Co. of Auburn, Kentucky, a small tannery using
primarily alum tanning but some chrome and vegetable tanning, received a demon-
stration grant in 1967 from the FWPCA to investigate and demonstrate methods
of treating tannery wastes for discharge to a small stream. A research contract
with Vanderbilt University produced findings which have previously been reported
and are reviewed herein.
A modified completely—mixed activated sludge plant was constructed, along
with facilities to handle specific problem wastes. After operating for a year,
an EPA survey team conducted a study which showed that the plant was perform-
ing as predicted by the research phase, except for solids carryover from the
secondary clarifier due to mechanical problems. After the problems were correct-
ed, the plant began producing an effluent which more than met expectations,
removing 97% of the suspended solids and 95% of the BOD. Due to conservation
measures inside the tannery, however, the load on the plant is somewhat less
than the design load, so the plant is operating as an extended aeration plant.
17a. Descriptors
Wastewater treatment, activated sludge, industrial wastes, testing, research and
development, evaluation, laboratory tests, sampling, acceptance testing, settling
basins, chemical oxygen demand, biochemical oxygen demand
.27b, Identifiers
Tannery wastes, leather production
17c, COWRRFi ld & Group 05 D
1! . A i /s 9 1 1/tv 29. Security Class. 2!. No. “ Send To:
‘Repo. ‘ages
WATER RESOURCES SCIENTIFIC INFORMATION CENTER
J. Sc . U.S. DEPARTMENT OF THE INTERIOR
(F e) WASHINGTON, D. C. 20240
Ah.rs . tcr Edward L. Thackaton Iritrttjon
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